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Outdoor Free Flight Forum => Towline Gliders => Topic started by: TheLurker on January 01, 2019, 03:36:28 PM



Title: Horsa-ing around
Post by: TheLurker on January 01, 2019, 03:36:28 PM
Airspeed Horsa.

I like work-horse aircraft and the Airspeed Horsa is one I particularly like.  However, leaving aside 6' plus span RC behemoths, I could find only one plan for a model at the sort of size that I have house-room for, R.V. Base's design for the Dec '43 Aero Modeller with a span of about 22". You can find a copy on outerzone (ID 3798).

The original plan was drawn at half size and having looked it over I thought it would benefit from some simplifications as well as rescaling to a span of about 32" (bungee launching; for the use of) so after a great deal of faffing around with Inkscape, bits of card and likewise pestering of Abl & Jack Plane I now have an untested plan for a 32 1/8" (projected) span approximation to an Airspeed Horsa which (fingers crossed) should be big enough to fly OK (if it flies at all) and well within the 36" limit.

Approximation?  Aye.  This is will very definitely be a scale-ish model. It's more about getting something that flies and looks the part when it's aloft than a concours d'elegance winner.

Untested?  Oh dearie me yes. The plan is quite definitely a work in progress.  There are all sorts of niggles and unknowns to be worked out with this one as we go along.  In fact that's where anything, if there is anything, of interest with this build will lie.  For instance; at the moment I'm not even sure whether or not it will have any sort of undercarriage as my wet finger guesstimate of wing loading for the 22" span indicated it was borderline for a glider without the UC.

One decision has been made and will be adhered to.  In the spirit of kit scale (and to keep weight down) the model will be finished in Al. tissue as MK II (AS. 58) TL472 which was, for a very short period in 1946, silver doped overall.

So ladies and gentlemen you are invited to pull up a seat, grab a snack, pour yourself a drink and watch a disaster unfold, very, very slowly, before your very eyes!

Lurk


Title: Re: Horsa-ing around
Post by: Balsa Ace on January 01, 2019, 03:57:57 PM
That's a great choice for a very interesting project,Lurk.

Scott


Title: Re: Horsa-ing around
Post by: Jasco on January 08, 2019, 07:16:19 PM
I want to throw my encouragement your way!  Watch a disaster unfold very slowly? Hilarious! My last project stalled just before the final steps in readying for test flights. Alas, she looks good just sitting there.
Dont forget to post plenty of in progress pics. I love seeing other techniques. (Or even the same ones)


Title: Re: Horsa-ing around
Post by: vtdiy on January 08, 2019, 08:12:06 PM
That would be really cool!


Title: Re: Horsa-ing around
Post by: TheLurker on January 09, 2019, 01:21:12 AM
Well so far I've managed to cut some of the pieces for the keel, real life, hey ho, and as exciting as I find them I can't believe anyone else would.  Even MrsLurker, who is pretty good at feigning interest in things aeromodelling, was struggling to display anything other than a blank look when presented with these masterpieces as in,  "Hmmm. Yes Dear.  Several bits of oddly shaped balsa.  How very interesting, do tell me more."  However, both progress and disaster will be published as and when.


Title: Re: Horsa-ing around
Post by: vtdiy on January 09, 2019, 10:22:42 AM
Mighty oaks from little acorns......!


Title: Re: Horsa-ing around
Post by: TheLurker on January 13, 2019, 11:35:50 AM
Now have the beginnings of a fuselage.  Keel, port frames and side-keel in place. 

Keels are hard balsa. Frames medium.  Longerons are going to be medium.  And that's the next task; cut some 1/16" strip for the longerons and after that set up a jig for bending / steaming them to cope with the after part of the fuselage.

Fairly pleased with the accuracy of the part profiles so far. They do need a bit of fettling, the long one piece side keel in particular, but allowing for my cheap and nasty ink-jet printer's iffy image reproduction and the inevitable blade wobbles when cutting the parts they'll do.

Remember I said it'd be slow?  Not logging hours, but this is about two evening sessions and as well as two long-ish weekend sessions. If you've got something more interesting to do I wouldn't hang around here expecting hourly updates. :)

Pics.  Cut parts, test fitting and glued fuselage waiting longerons.


Title: Re: Horsa-ing around
Post by: TheLurker on January 14, 2019, 04:16:44 PM
Cut some strip this evening and just carried out a test fit.  Unusually for stuff I cut the longerons drop nicely into place, but have turned up the first snag.  One of the lower slots at frame 6 is misaligned, see the attachments.  I thought, for all of 3 femtoseconds,  about cutting new F6s, then about widening the slot and then finally I thought, "Stuff it. It's a test build.  I'll update the plan and part profile and that'll do." :) 

It's not quite a disaster as was promised, but at least summat has gone wrong, so you won't be getting your ticket money back. :)

Sorry about the soft focus image of the afterpart of the fuselage; the camera lied. It told me it was correctly focused.


Title: Re: Horsa-ing around
Post by: vtdiy on January 14, 2019, 04:22:48 PM
Looks like it's coming along nicely, to me.


Title: Re: Horsa-ing around
Post by: bobson on January 14, 2019, 04:33:17 PM
Looks great, nice progress! Maybe you've seen this -- Tom Nallen II built a Horsa a few years ago that is an incredible scale model and flyer. Not sure if it was from the same plans.

https://www.youtube.com/watch?v=S5vZcZ0HUos


Title: Re: Horsa-ing around
Post by: TheLurker on January 15, 2019, 12:59:09 AM
Looks great, nice progress! Maybe you've seen this -- Tom Nallen II built a Horsa a few years ago that is an incredible scale model and flyer. Not sure if it was from the same plans.
Oh dear. That sets rather a high bar to clear doesn't it? :)  That's a lovely piece of work and thanks very much for the link; it shows that I probably won't have to sacrifice the undercarriage to save weight.

I'm probably wrong but I don't think Mr. Nallen's model is from the R.V. Base plan.  The stabilizer seen in the clip has correct square-ish tips, the Base original has very rounded, almost semi-circular, stabilizer tips.  Squaring off the stab. tips was one of a number of minor changes I made when redrawing and resizing it.


Title: Re: Horsa-ing around
Post by: TheLurker on January 16, 2019, 03:29:22 PM
Couldn't live with the misaligned longeron at F6 so widened the slot, first one down from the side keel, and packed the gap as per pic and made note (a proper one in the log, in black ink) to go back and revise the part profiles for the F6 pair.

Port half built, lifted it off the board this evening.  Sternpost pulled a tiny pit port, but otherwise all seems OK. With luck stbd side keel will correct that.  


Title: Re: Horsa-ing around
Post by: DavidJP on January 18, 2019, 11:56:07 AM
Nice and neat Lurky. 

I have always fancied doing one of these ranging from slope soarer to a big radio model and now to the little FF job.

As a matter of interest over the years I have concluded that stringers in notches are not essential and so simply laying them on the former can work a little more easily? But I see you are using stringers that are rectangular in section rather than square. 

The other thing I learnt building the KK flying scale models was that it was better to put the stringers on "in the air" to reduce the bus. going out of shape.  But they did not have keels!

I did know a couple of chaps by the way who were in the Glider Pilot Regiment (one built built models too).  Bit daunting when you think they were   disposable - often used only once!!  Pegasus Bridge (as it became known) for example.


Title: Re: Horsa-ing around
Post by: TheLurker on January 18, 2019, 04:01:39 PM
Quote from: DavidJP
Nice and neat Lurky. 
So far!  Many a slip twixt cup and lip.

Quote from: DavidJP
...I see you are using stringers that are rectangular in section rather than square. 
Ah. Yes.  That would be because they're, "orl me own work" and I'm not that good with the old balsa stripper. I rather like using notched frames because the strip is held securely on 3 sides rather than butted to it. I expect there's probably no difference in robustness between the two methods, but it's my comfort blanket and I'm not giving it up without a fight. :)

Quote from: DavidJP
I did know a couple of chaps by the way who were in the Glider Pilot Regiment...
I'm always extremely impressed by the nerve and bravery of such people.  FWIW this area is stiff with aerodromes that were involved in glider (and other) ops.  Brize was a GCU, Down Ampney, Fairford and a couple of others were all operational fields for glider units.


Quote from: DavidJP
The other thing I learnt building the KK flying scale models was that it was better to put the stringers on "in the air" to reduce the bus. going out of shape.  But they did not have keels!
Yeah, when I was discussing the plan and the build notes I've put together with Abl a month or two back he made much the same point and I expect for skilful builders it's a method that works well, but I'm a ham-handed bodger and would probably break two longerons for every three I fitted.  Hence my use of the half shell and jig approach.  And that gives me a nice excuse to post a couple of pics of the fuselage mounted in its cradle ready for the stbd side which I'll be starting on tomorrow.

Still puzzling / waiting for inspiration to strike about the most robust / lightest way to provide fuselage mounting points for the UC so have deferred that little task for now.


Title: Re: Horsa-ing around
Post by: abl on January 18, 2019, 04:59:52 PM
If you're still looking for an undercarriage solution, my bid would be:
1. Leave off the skid as it doesn't usually appear in photos and its simpler without one
2. Use two bits of wire per side, the ends of which plug into aluminium or brass tubes that are the full width of the fuselage (possibly with 1/8" square cross-members and some gussets):
   a) A V-shaped bit for the bottom two members that plugs into the bottom two tubes, and
   b) A long bit that plugs into the top tube and has the axle on the other end, bound with thin fusewire and soldered where it intersects the apex of the V of part A, using Lurker Industries Large Equipment Division's biggest soldering iron.

You can put a slight bend on the plug-in bits to make an interference fit but it'll still be disassemble-able for transport and should knock-off in the event of a mishap.


Title: Re: Horsa-ing around
Post by: DavidJP on January 19, 2019, 09:38:17 AM
Looking at your pictures - particularly of the jig set up - I think you are jolly well entitled to keep your security blanket.  Any prospect of an even slightly untrue fuselage is surely eliminated. And it is far simpler than the old bit of 1/4inch spruce I stick down the fuselage so I may well adopt your method next time.  Take it that there is no fee?


Title: Re: Horsa-ing around
Post by: TheLurker on January 19, 2019, 02:52:35 PM
War & Peace alert.  Cup of tea and biscuit required for this one.  :)

If you're still looking for an undercarriage solution, my bid would be:
1. Leave off the skid as it doesn't usually appear in photos and its simpler without one
2. Use two bits...
Thanks Abl, my mind (no comments please) was/is running along those lines for the UC, but I'm swithering about putting a length of hard 1/16" above the Al. through tubes or inserting a small patch of infill between the longerons to support said tubes in the manner of a motor peg.  The Parish Idiot, despite noting in the draught build guide that the longeron supporting the through tubes should be hard strip, has used medium.  This is unlikely to survive many landings.  The hard strip approach has the edge at the moment purely on the grounds of simplicity.   The attached explanatory images page shows the Mr. Base's original scheme for the UC wirework. The through wires (which will become tubes) are fixed to the lower longerons.

Fuse wire? Who has fuse wire in the house these days?  May have to unbraid some fine wire. :)

As for fitting the skid, that's not really a problem and it shouldn't interfere with the UC. See the attached exp. images page and "cutting" from the plan.  The single central ram variant (MK I, AS.51s) is a piece of cake to deal with and I think I have a fix for the double ram type (MK II AS.58s).   Now, if you were modelling a GCU airframe then you could legitimately lose the skid and have a really natty scheme into the bargain.  By happy coincidence p23 of the Feb. AeroModeller has an example of a GCU scheme for a G.A. Hotspur which is shown as part of Colin Baxter's article on 2-D CAD.  If you haven't got a copy yet your favourite search engine should turn up good examples.  There are some colour publicity photographs showing paratroopers disembarking from GCU machine at Brize Norton somewhere out there.

What might be an issue with the skid is fouling or snagging the tow on launch as my estimated position for the tow hook is quite close to the front of the skid.  Some non-scale remedy may be called for to deal with this, but we'll cross that bridge when (if) it gets as far as flying.

Quote from: DavidJP
... Any prospect of an even slightly untrue fuselage is surely eliminated.   
Ermm, let's not say that until we're done, eh? :)

Quote from: DavidJP
I may well adopt your method next time.  Take it that there is no fee?

Fee?  *chortle* Well if you're offering, mine's a pint. The cradle (if it's not obvious) is dead easy.  Some 2" x 1" (or metric equiv.) pine batten from the local DIY barn. Pretty cheap. but choose carefully; some of it can be pretty bendy and we don't want that.  "Lolly" sticks from a "craft" type shop (in the U.K. "The Works" or "HobbyCraft" carry them, but again pick and choose because they too can be bendy.  Bendy is not good.  And finally some map pins from your favourite stationery supplier.  Glue some lolly sticks on the base and ends of two lengths of batten to keep everything aligned.  I drill a couple of holes in the base sticks. It lets me pin the frame to the board so it doesn't skate around.  I likewise drill holes for the map pins in the clamping sticks that hold the keel in place.  Pine is soft enough (just) to take the map pins so it means you can reposition the clamping sticks if needs be as you're working and all component parts can be re-used for subsequent keel builds.


A little more progress today.  Ballast chamber fitted in line with Mr. Base's original design.  This is a contingency measure. I'm hoping that I'll be able to use some sort of ballast tray between the two horizontal nose formers (NF1 & NF2) so that AUW can be kept a smidgen lower.  Remainder of starboard frames being fitted this evening but you know what that looks like so I won't bore you with pictures of that.


Title: Re: Horsa-ing around
Post by: TheLurker on January 20, 2019, 03:50:47 PM
I'm pleased to report that the Dept. of Aviation Archaeology at the Lurker Industries Aeroplane Company has made an interesting discovery about the Horsa plan as it is at the moment.

Observant types will have noticed the absence of keel over a significant part of the fuselage top.  I certainly did, but I thought that the wing platform bridging this gap combined with suitably placed gussets would reinstate/provide the necessary vertical stiffness in the centre of the fuselage. Errr.. no.  There are number of possible reasons for this any one or all of which might be contributory factors.

- The plan has been scaled up by just under 50%.  The Longeron count was increased (+2 each side) to allow for this, but 1/16" strip was retained rather than specifying thicker strip.  Various reasons for this not the least being the tight bends required from F5 to the stern post.

- There's a wide gap between F3,F4 and F4, F5.  These gaps are proportionally wider than those drawn on the original because the original plan had them drawn too small for the root / central section ribs.  

- I've used medium rather than hard strip for the longerons.  Still think this was the right thing to do but...

For this build I've introduced some diagonal bracing in the F3/4 and F4/5 bays and it seems to do the trick.  I'm debating whether or not to do the same for bays F5/6 and F3/2 so the remaining longerons are yet to be fitted while I sleep on the problem.

I'll probably revise the plan so that a saddle keel is used, but that will have to wait until I've test flown (oh, you incurable optimist you!) this build to check that the wing incidence is OK because if a top / saddle keel is introduced I intend to rest the wing platform on it. There's not much extra length/weight in the diagonal bracing compared to the proposed additional section of keel and it does mean you can tinker with the built in incidence of the main 'plane, but a full keel is likely to make it an easier airframe to build.

I may increase the bulkhead count as well to reduce the width of the bays.  Bit of a trade of for weight there.  Another problem to ponder in slow time I think. Revisit it when I've got a realistic idea of AUW / wing loading for this one.

The last pic is for fun.  It's my homebrewed "Is the wing platform level and not bowed" tool for testing in temporarily inaccessible locations.

I don't know about you but I think it's rather fun resurrecting sketchy 75 year old plans.  :)


Title: Re: Horsa-ing around
Post by: DavidJP on January 20, 2019, 05:44:00 PM
Still looking neat! 


Title: Re: Horsa-ing around
Post by: TheLurker on January 21, 2019, 02:36:58 PM
There'll be no building work for a few days, but progress of a sort today.  

Abl (he being a grate brane and my topp secrit weapon for this projject) and I have been swapping e-mails on the UC issue.  Now if I were at the start of the build I'd nick his ideas unreservedly and without modification*, but what with my various gaffes so far this build is going to be a bit of a mule.  So the nice bits of what follows are Abl's, the less umm appealing bits are some other fellow's and we won't talk about him.

The first pic was an idea I had this morning to provide a reasonably robust way of mounting the tubes and the second pic Abl's ideas.  

The hinge idea will be nicked without hesitation for this build. I was going to use a simple pop-fit but I was tactfully reminded that this would probably end in tears, see what I did there?  no I'm not sorry :), as the UC strut dragged its way across the underside of the wing.

He also suggested replacing the keel mountings with half formers and attaching the tube to those as well as remarking on the flimsiness of 1/32" sheet that I was thinking of using between the longerons and I would have happily nicked that idea as well, but for where I am in the build.
 
As I type this I think that the plan is :

+ Use 1/16" hard sheet as the inter-longeron mount for the axle through tubes in place of the 1/32", but retain the keel mounted post for ease/practicality of construction at this stage in the build.  The diagonal braces and ready fitted longerons making inserting additional half formers a tad awkward.  I may also extend the mounting plates back to the bulkheads. It oughtn't add too much weight for some useful support against the drag of the UC being pulled out of the tubes as well as reducing the risk of broken longerons.

+ Update the plan to use Abl's half-former approach.  It'll address both the axle tube problem and the vertical flexing issues I found yesterday.  I was thinking about reducing bulkhead separation anyway, i.e. more bulkheads, but hanging fire on the idea because of the increased weight.  However I think this tips the balance in their favour.

The final pic. is a rough sketch of how I'll deal with the twin ram skid mounting.  It needs a bit of refinement, but you get the idea.

And one last thing. Will use additional gussets in bays F2/3 and F5/6 rather than add diagonal bracing.

Lurk.


*And pretend they were mine. :)


Title: Re: Horsa-ing around
Post by: TheLurker on January 22, 2019, 03:24:25 PM
Nose formers.  I had intended to use the original part profiles for the (plan view) nose profiles, but I was looking at them a day or so ago and decided they were too approximate even for my determinedly low-fidelity approach to scale modelling.  And as I had a little unexpected build time this evening I've redrawn the part profiles and cut them.  Not a hugely exciting step, quite hum-drum in fact, but satisfying.


Title: Re: Horsa-ing around
Post by: OZPAF on January 22, 2019, 07:38:50 PM
The horse is getting close to escaping from the stable Lurk. Your undercarriage design considerations made interesting reading. I think I would like to see some sort of a diagonal strut from your outboard axle support back to the keel to avoid damage from a wheel digging in, I'm not sure if the stringers will be able to take an impact load of this type.

However this is only a suggestion for the engineering staff of Lurker Industries.

John


Title: Re: Horsa-ing around
Post by: TheLurker on January 23, 2019, 12:48:15 PM
Quote from: OZPAF
> The horse is getting close to escaping from the stable Lurk.
Weeks yet.  Nigh on a fortnight in and the fuselage isn't yet done.

Quote from: OZPAF
I think I would like to see some sort of a diagonal strut from your outboard axle support back to the keel to avoid damage from a wheel digging in, I'm not sure if the stringers will be able to take an impact load of this type.

Did you miss this, "... I may also extend the mounting plates back to the bulkheads. It oughtn't add too much weight for some useful support against the drag of the UC being pulled out of the tubes as well as reducing the risk of broken longerons...." in an earlier post?

I scribbled a little pic this morning at work (I was waiting for a long test run to complete - honest) based on what I thought I remembered of your suggestion.  It shows what I have planned and what my (faulty) memory thought you'd suggested.  I don't think bracing to the keel as you suggest will be possible given the position of the through tubes relative to the keel.  Never mind, this build was expected to uncover problems with the plan and if the finished article is a tad fragile so be it because any subsequent versions won't suffer from the same problem(s).


Quote from: OZPAF
However this is only a suggestion for the engineering staff of Lurker Industries.
Keep 'em coming.  Any and all contributions welcome. 

Lurk


Title: Re: Horsa-ing around
Post by: OZPAF on January 23, 2019, 04:36:06 PM
Actually I was just thinking of a bracing strut rather than a gusset arrangement, however what you have shown would be definitely stronger. The strut would need to be something like 2.5 square at a guess and running to the bulkhead similar to your gusset, if it is difficult to run to the keel.

Good to see that the Engineers are checking the suggestion box. :)

John


Title: Re: Horsa-ing around
Post by: TheLurker on January 25, 2019, 01:52:24 PM
Quote from: OZPAF
Good to see that the Engineers are checking the suggestion box. :)
Hoh yes!  That's the thing about "engineers"* they're not bumptious enough to think they know it all.  Well most of them aren't anyway. :)

To business!  Yes! We have no bananas, we have no bananas today! (https://www.youtube.com/watch?v=PDd8shcLvHI) 

OK DavidJP you can relax, you didn't jinx it.  :)

Fuselage is out of the frame and looking true to my tired old peepers.  Still got to finish off the UC mounting points and the stbd mounting point for the stab. struts, but it's looking more Horsa than "ish" to me now.  Without the noseblock and missing some of the UC mountings it tips the scales at 19g so current wet-finger guess for uncovered fuselage weight, sans UC, is north of 30g, probably well north.

Couple of glitches.
 - The ballast chamber is off-centre by about 1mm.  I am more annoyed by this than I should be.
 - There's a bit of wasp-waisted-ness about bulkhead 6 at L3.  It's not too bad, but I need to revisit that part profile, again.  It has to be said that frame 6 has been a pain from the off.  I've lost count of the number of times it got redrawn even before I started on the build.

While I'm here. UK bods.  Anyone know a cheap bricks and mortar source of bamboo?  Bamboo skewers would do.  I want some for the stab struts and I don't need enough replacement stock at the moment to make it worth the cost of postage to place an order with SLEC/Balsa Cabin/whoever.


*Meaning anyone who builds anything.


Title: Re: Horsa-ing around
Post by: Mefot on January 25, 2019, 02:36:45 PM
That's looking like a really nice build of a rarely modelled subject.

Sources of bamboo skewers are far and wide, supermarkets and pound shops being two of the cheapest and, just as important, convenient sources. For bigger diameters, but considerably more expensive, knitting needles in accurate diameters available from many craft shops. For smaller diameters I use incense sticks. Once the smelly stuff is scraped off it leaves you with a 1.3mm diameter stick. I've managed to "machine" these down to 20 thou diameter with no problems.


Title: Re: Horsa-ing around
Post by: TheLurker on January 26, 2019, 06:07:29 AM
...a rarely modelled subject.

It is.  I suspect that it's because there are very many good scale models of single/twin seat soarers that fly really well whereas the Horsa was never really much more than a 25 man parachute that could be towed to its dropzone* so it may be that the best one can hope for with a model, at least at this scale, is a stable glide to landing from the release point.   And if I get that from this model I shall be very well pleased.

The other reason may be that very few people have the space for the RC behemoths and that plans for models in the sub 4' wing span range seem to be difficult to find.

Thanks for the bamboo "pointers".

Lurk.


*That sounds like a terribly dismissive comment. It's not meant to be.  The Horsa was designed for a job, which wasn't soaring, and it did it very well.


Title: Re: Horsa-ing around
Post by: DavidJP on January 26, 2019, 09:18:02 AM
OK DavidJP you can relax, you didn't jinx it.  Smiley

I simply had confidence, old boy.

You know given the circumstances when these gliders were built I would not be surprised if more than a few showed a bit of being out of true!!  There as a war on, re marketing them after they had served their purpose was not a serious concern. 


Title: Re: Horsa-ing around
Post by: TheLurker on January 27, 2019, 03:49:41 PM
Quote from: DavidJP
...re marketing them after they had served their purpose was not a serious concern.
You probably already know, but a good number of the "left-over" fuselages got converted into "houses" because of the desperate housing shortage.

Progress, but glacially slow. Mainly because I'm working out stuff as I go along.

Made a start on a revisions to the plan to deal with the vertical flex issues and to incorporate Abl's suggestion for mounting the UC through tubes.

Another little part profile adjustment found to be necessary.  The skid has to be slightly shorter than is proper to allow for reasonable positioning of the tow-hook.  Not a major disappointment as I was expecting to have have to adopt some non-scale fudges because of the tow-hook anyway.

Have more or less got the test build's UC through tube mountings in place.  One piece of infill yet to fit and then it's just a case to cutting and expoxying the brass tube in place.  Why brass?  None of the Al tube I have has the combination of suitable internal diameter and small outer diameter of the brass.

Pics.  A cutting from the plan, you may need to use the "make it bigger" button in the top RH corner of the thumbnail viewer, and a view of the rear through tube in place with the mounting block for the skid's port ram.


Title: Re: Horsa-ing around
Post by: Mefot on January 27, 2019, 04:10:37 PM
Quote from: DavidJP
...re marketing them after they had served their purpose was not a serious concern.

 The skid has to be slightly shorter than is proper to allow for reasonable positioning of the tow-hook.


Just a thought ( so feel free to ignore it ) !!!

Would it be possible to fit a tow hook either side of a true scale skid ? This would give the option of using either or both hooks for towing.

Keep up the good work  ;D


Title: Re: Horsa-ing around
Post by: TheLurker on January 27, 2019, 04:18:39 PM
Would it be possible to fit a tow hook either side of a true scale skid ? This would give the option of using either or both hooks for towing.
Hadn't thought of that. Will ponder.

Was considering fitting the hook to the skid itself if it needs to be moved aft.  It'll be basswood so will be sufficiently robust.  I have to admit that I'm not too worried about exact scale fidelity for this one.  If it looks "about right" aloft that'll be good enough. The important thing to me is that it flies.


Title: Re: Horsa-ing around
Post by: OZPAF on January 27, 2019, 06:50:07 PM
The undercarriage looks slid in the "flesh". Good work by the Lurker Industries Engineers.

John


Title: Re: Horsa-ing around
Post by: TheLurker on January 30, 2019, 03:43:54 PM
A couple of short evening sessions and I have two roughed out noseblock halves and some firmed up thoughts on alternative ballasting arrangements.  See the attachments.  You'll probably need to use the "make it bigger" button on the thumbnail viewer.

The alternative may not be used, we'll see how we're doing for weight.  At the moment the fuselage, NF2 and roughed out nose "shells" are hovering between 28g & 29g (kitchen scales).  Which is lower than I was fearing, but it's still pushing it given that it's only got a 32" span wing and that with a markedly swept LE into the bargain so there's not that much wing area and there's a UC and skid to add.  This is the point where I start wishing I'd followed my first thoughts and taken the centres out of the frames rather than going with solid ones.  Never mind, that's why we test build, to find out these things.  If push comes to shove I'll have to go with my original idea of flying it without a UC.

Considering hollowing out the nose block shells a bit more, but it's a bit of guess as to how thick to leave the walls for decent crash resilience, and also taking a couple of panels out of the centre of the wing platform by way of weight mitigation measures.


Title: Re: Horsa-ing around
Post by: abl on January 31, 2019, 04:16:07 AM
I think you could probably reduce the wall thickness of the noseblock shells a little, but - given the position of the wing, and the sweepback - I'm wondering whether much nose ballast will be required? It's a very long nose.

So, if I was in your shoes, I'd be tempted to repeat to myself "Remain calm, all is well" and steam ahead...  :)


Title: Re: Horsa-ing around
Post by: TheLurker on January 31, 2019, 02:13:47 PM
Quote from: abl
It's a very long nose.
Aye it is, isn't it?  Takes several deep breaths and attempts to remain calm*.  :)

No building tonight, a bit more thinking things through and scribbling, attached (use the "make it bigger button").

Now pretty confident** about how to deal with the twin ram variant of the skid. The only decisions to be made are whether to go with 18SWG or 20SWG for the load bearing part of the ram and which of the many grass stems I collected in the summer will be used for the outer shells. I am very tempted to go with 20SWG because the stems are really rather strong in compression over the sort of length that will be needed.  We shall see.



*Fails miserably so nips into the Boardroom of The Lurker Industries Aeroplane Co. Ltd. and has a small sherry from the Director's special reserve.

**What goeth before a fall?  Yes.  Got it in one. :)


Title: Re: Horsa-ing around
Post by: TheLurker on February 02, 2019, 04:11:43 PM
The pen-pushers at the Ministry of Supply have been sticking their beaks in again demanding to know why Lurker Industries is falling behind schedule with the current programme of works.  If we've had one querulous letter from them demanding to know why we're behind-hand, we've had a dozen, with a carbon-copy sent to everyone from the Head of the Board of Trade to the Under Gardener's Second Assistant Trowel Polisher at Balmoral.

That's the trouble with these Civil Service wallahs, absolutely no idea of what can go wrong with aeroplane development.  Never mind, onward and upwards eh?


Or...  

After some cock-ups and the odd rethink, of which more in a moment, the Co. has, at last, completed the nose and small sherries were enjoyed by a jubilant group of Directors in the boardroom to mark the fact.


Right let's start with the foul-ups, nothing like a bit of Saturday Night Schadenfreude, which wasn't a John Travolta film, but should have been, to cheer everyone up.

NF2, upper nose former.  The profile for this needs to be redrawn.  No idea how I got it so badly wrong, but the front of the stbd side was cut nearly flat rather than with a gentle curve, see the pic, and as it was cut against the drawn profile using a French curve it must be the drawing that's dud.  Cue a bit of a scurry around on the shopfloor using the port half of the duff NF2 as a template for a new one.  Even then it wasn't as symmetrical as it should have been and required further fettling before it could be fixed in place.

Minor niggle with K1b.  It's not quite deep enough where it runs into the lower keel so a small packing shim about 1" long is required to get a smooth finish to the nose near bulkhead No. 1, see pic.

The ballast chamber "lid" got rethought to make it simpler to build, a lot of time on this build has been spent picking up half finished bits and bobs, looking at them, deciding they don't work and starting over. I had intended it to be a "push through" from either side of the nose, but it struck me as tricky to do well so now it's pushed in/pulled out from the port side.  This means there's no need to build a complicated drawer and get perfect alignment from one side of the fuselage to the other, but the cost is a v. small non-scale wire handle. I can live with this, especially as the shape of the handle is such that it looks like one of the random grab handles that clutter the fuselages of aeroplanes of that generation, but I can see that others might baulk at this.

The simplified lid is little more than a sheet of 1/32" basswood, with one small block of soft balsa forming the fuselage wall and a small wedge on the opposite side which uses NF2 to hold the stbd side of the sheet down when it's in position.  

Of course this means that the ballast chamber affixed to the rear of bulkhead No. 1 is now surplus to requirements and can be deleted from the plan if it turns out the nose chamber is sufficiently large.

Current weight (no UC or skid) is 28g so could be worse.

Tomorrow I'll make a start on the skid.  It'll be interesting to see whether or not the result bears any resemblance to the sketch. :)


Edit to add.  Found some bamboo in my local Poundland - thanks for the nod Mefot -  long cocktail sticks, took a punt thinking, "They look too short for what I want."  They are, by about 1/4"  grrrr.  :)



Title: Re: Horsa-ing around
Post by: dohrmc on February 02, 2019, 06:16:47 PM
Really good stuff, and the pictures are looking good. Well done!


Title: Re: Horsa-ing around
Post by: TheLurker on February 03, 2019, 12:28:32 PM
I did start on the skid, honest, but as the main part is still clamped into the bending frame and will be until tomorrow evening at the earliest I thought I'd have a go at a template for the cockpit glazing.  

I know that plunge moulding or vacuum forming will definitely get you a nicer looking greenhouse, but I couldn't fight the kitchen table builder in me. Anyway it turns out it is possible and the result will certainly be good enough for this "kit-scale" take on the Horsa.  I am considering going for a printed paper canopy - for the fun of it - so I still need to tinker with the template a bit as noted in the pictures to get the glazing bar alignments sorted and I want to move a couple of cut-lines to make it suitable for acetate in case I decide to go that way instead.  

One thing the test canopy does throw into sharp relief is that the cockpit shape is quite a way "off" scale.  However I think I'm going to leave it as is or there'll be nothing left of the original design and given the circumstances the original was produced in I'd feel a bit "off" doing that.  FWIW MrsLurker reckons that with the test glazing in place it looks like it should be on the Grand Union Canal rather than flying.

The picture sequence is a very short summary of the prototyping "process".  I expect none of it is new to anyone here, but everything's better with pictures isn't it? Ask any Management Drone in love with Powerpoint. :)


Title: Re: Horsa-ing around
Post by: abl on February 03, 2019, 02:45:51 PM
Looking good, Lurk.

(BTW, couldn't help noticing that a certain amount of Sherry is consumed at Lurker Industries...?)

A.


Title: Re: Horsa-ing around
Post by: dohrmc on February 03, 2019, 03:58:19 PM
Question:  “Please, when is the best time of day to drink sherry”?

Answer:    “Anytime you can get it”!


Title: Re: Horsa-ing around
Post by: TheLurker on February 04, 2019, 02:25:39 PM
Quote from: abl
...couldn't help noticing that a certain amount of Sherry is consumed at Lurker Industries...
Well, of course.  One really can't offer the Directors' guests whisky or brandy during office hours. Honestly!  We're not sots you know.  However it is good to see that young Mr. Dohrmc has been properly brought up.  Should he find his current employment no longer satisfactory I'm sure we can find a suitable vacancy at Lurker Industries for him.

Unfortunately The Board will be having a meeting over lunch, with a very fine claret, to discuss whether or not to place the four ale bar of The Dog and Duck out of bounds for staff on shift after the latest setback in production which requires the re-bending of the skid blank.  We really don't want any more of those sniffy letters from the Ministry of Supply.

Or...

I am a chump.  When setting up the clamp for the skid blank I grabbed a handful of bits of wood that were about the right size without looking at them particularly closely.  This was a mistake.  Two of those bits were very soft pine.  Can you spell,  "corrugated"?  So the skid blank is back in the rejigged jig, which now has smooth hardwood clamping pieces, for a further 24 hours and I'm going to play safe this evening and catch up with some project documentation and part profile updates.

Today's aeromodelling trivia.  Basswood can be made soft enough to bend easily by placing it in a shallow dish of cold water and cooking it for three minutes on high power in a μwave.  This also turns out to be a very simple way to remove the bend from a piece of wood.

Pics are of the MK-I jig, the corrugated result and a stunningly obvious "how to suck eggs" note.


Title: Re: Horsa-ing around
Post by: OZPAF on February 08, 2019, 07:50:02 AM
I take it - the sharp end punctures the egg and the chisel end is to scrape out the remnants after sucking the contents out via the hole? My grandfather used to eat? drink eggs like this. Hmm!

I can't see the approval and checked stamps on this piece of info from Lurker industries.

John


Title: Re: Horsa-ing around
Post by: TheLurker on February 08, 2019, 08:35:45 AM
Quote from: OZPAF
I take it - the sharp end punctures the egg and the chisel end...
:D.  Ahem, both ends are chisel shaped.

Quote from: OZPAF
I can't see the approval and checked stamps on this piece of info from Lurker industries.
R&D are very, very behind on their paperwork at the moment and the tool-room aren't helping matters by using backs of cigarette packets envelopes for their documentation.

How very interesting. The built in Dr. Bowdler doesn't like a quite common (in every sense of the word) Commonwealth word for cigarettes; he insists on substituting "happy guy".  It'd have the most awful trouble with the text of Tom Brown's Schooldays.


Title: Re: Horsa-ing around
Post by: TheLurker on February 08, 2019, 04:04:51 PM
Finally got the twin ram skid done, pushes the undecorated fuselage weight up to 30g.  Have gone for a more scale like fixing at the nose of the skid.  This may prove a mistake.  I think you'd get away with it for the single ram variant as the fixing for that can be made very much more robust than that for the twin ram for little or no weight penalty, but not sure about this one.  We'll find out, eh?

Despite thinking I'd leave it as it is I think I've worked out what needs to be done to make the canopy more scale like.  Former NF2 needs to move up so that it more nearly half way up the fuselage.  Am in two minds about whether or not to revise the plan.  Tempted to leave well alone because I don't want to throw away too much of the original.


Title: Re: Horsa-ing around
Post by: abl on February 09, 2019, 02:45:04 AM
You could leave the former where it is and just paint/tissue up to the line?

A.

P.S.
Does SWMBO know that you're taking pictures on her kitchen worktop?...  :)


Title: Re: Horsa-ing around
Post by: flydean1 on February 09, 2019, 10:35:51 AM
In addition, you could put in a card or paper "floor" across the side stringers right where they are to give something to mount the pilot, who is not looking forward to joining the infantry upon landing.


Title: Re: Horsa-ing around
Post by: TheLurker on February 09, 2019, 12:21:31 PM
You could leave the former where it is and just paint/tissue up to the line?
Great minds or fools eh?  :)

A good idea and that little bit of trompe l'oeil is already on my list of experiments to try because the current NF2 isn't coming out now that the nose infill and ballast chamber are in place.  I'm going to muck about with the paper canopy template as being the quickest  test; 2 minutes in Inkscape to add a 3 or 4 mm lower border and if it looks right then I'll go with it for this test build.  However the more I think about the more I think I am going to have to update the plan as noted in the earlier post. Before I do that though I need to cut a revised NF2 for test fitting while the fuselage is in its current state.

Quote from: abl
Does SWMBO know that you're taking pictures on her kitchen worktop?...  :)
Shhhh!  The light over the workbench dining room table is too yellow to give a decent photo. and light levels in daylight lately haven't been much to write home about.

Quote from: flydean1
...you could put in a card or paper "floor" across the side...
A nice idea, but it's highly unlikely anything but the bare minimum by way of decoration will be added as this bus barge is already a wee bit on the porky side.

No building today cos I spent most of the morning freezing my backside off at the garage waiting for the car to be put through the MOT & annual service and most of the afternoon trudging around boring* shops, but I did manage to get the build notes brought up to date.  Like the plan they're a bit of a moving target at the moment.  Copies are available and can be sent in plain covers to discerning patrons on receipt of a postal order for 5/-  sent to the usual address.  No refunds.

Current programme of works is:
 - Quick jog around the art gallery with the canopy template as outlined above to see if the eye can be fooled acceptably enough for this build.
 - Another (the 3rd!) NF2 for test purposes as outlined above.
 - Tinker with the glazing template if the revised NF2 position looks good.
 - On to rib cutting and the wing outer sections.

I hope no one here is in any hurry to see this one done.

Cheers,
Lurk.

*Trivial stuff like food; no aeromodelling or other interesting stuff at all. :)


Title: Re: Horsa-ing around
Post by: dohrmc on February 09, 2019, 01:17:25 PM
Well if you are looking for trumpe l’oeil, I am your man.
I am ready to provide a suggestion. It will stun them at the flying field, and may eventually lead to a peerage....or something.

You do not have these critters in England, but a scale Opposum, pronounced “possum” for Brits, clinging to the top of the tail would instantly solve your problem by simple distraction. And they are light! If tail weight is needed, due to the long nose, (the glider nose, not the possum), just have it peering out of a garbage can made from a beer can. Realism too, at almost no cost!

Instant success, fame and glory!


Title: Re: Horsa-ing around
Post by: TheLurker on February 09, 2019, 03:46:52 PM
Quote from: dohrmc
...and may eventually lead to a peerage....or something.
Hmmm, Lord Lurker of Brabagoon1?  Yes I rather like it.

Quote from: dohrmc
...a scale Opposum, pronounced “possum” for Brits, clinging to the top of the tail would instantly solve your problem by simple distraction. And they are light! If tail weight is needed, due to the long nose, (the glider nose, not the possum), just have it peering out of a garbage can made from a beer can. Realism too, at almost no cost!
A devilish cunning plan and if only I were modelling it as a U.S. machine (e.g. LJ161 see here (http://www.americanairmuseum.com/aircraft/18224)) I could have got away with it!

Quote from: dohrmc
Instant success, fame and glory!
Notoriety perhaps. :)

To business.  The 3mm margin on the canopy will be used, sorry no pics, but seen one canopy seen 'em all.  NF2 has been redrawn and, following checks with the good old cardboard cut-out, moved up about 3mm on the plan.  All being well will start on the wing tomorrow.

1 - One for older listeners there.


Title: Re: Horsa-ing around
Post by: TheLurker on February 12, 2019, 04:04:17 PM
Jings! Crivvens! Help ma Boab!    Heaven help us, but this is going to be a fat old bus.  Dumped the, not quite complete*, stbd wing section on the kitchen scales. Five (5) grammes!

Estimating wildly I think I'm looking at an uncovered weight in the mid 50g region.  That's assuming about 15g for the complete wing framework and desperately hoping for no more than 10g for stab and fin and the known 30g for the fuselage and skid.  However, in the very best traditions of MoD (and IT) projects, we shall continue to honour the sunk cost fallacy and pursue it to the end come what may.

At least I have a name for it now, "Fat Boab" :)  

*L.E. to be sanded to profile and a couple of gussets to behind the LE.

ETA - And who knows how many grammes for the UC, so lets just call it 60g shall we?  If anyone's looking for me I'll be in the four ale bar of the Dog and Duck having a consolatory pint or five.


Title: Re: Horsa-ing around
Post by: dohrmc on February 12, 2019, 04:33:59 PM
I bet it flies just fine once you sort out the cg and trim.  These brutes lead a short and nasty life.  No need for fragility!  I like it!!


Title: Re: Horsa-ing around
Post by: dohrmc on February 12, 2019, 08:42:42 PM
Fear not, just weighed the Slingsby. Uncovered wings, no ballast, 65 grams. Not going to worry about it until I see it fly.


Title: Re: Horsa-ing around
Post by: TheLurker on February 17, 2019, 04:28:26 PM
Finally got the port outer wing section built, which made me go back and cut out and reset the LE on the stbd side, and made a start on the centre section. Now here's the thing; if you're going to be lazy and use pre-shaped TE make sure you've got enough for all three sections and not just the outer sections or you're going to have to shape some anyway.





Title: Re: Horsa-ing around
Post by: TheLurker on February 19, 2019, 04:14:29 PM
The fully assembled wing is now sitting on the board while the glue sets.  For those interested the dihedral angle is 36/- and thanks to AvroVulcan for the coins idea.  This is a cock-up on my part when drawing the dihedral guide profile; it should have been about 8 or 10 bob cheaper.  I'll see how (if) it flies before "fxing" the drawing.

If I wasn't pushed for building time I'd be very tempted to scrap this wing and start again. I think I can make the construction a bit simpler, especially the L.E. and I could certainly make a better choice of wood.  The central section before sheeting weighed 4g so I'm expecting the wing to be 15g. Any less and I shall be extremely grateful.

Have been pondering on undercarriages again and had one of those delightful little lightbulb moments today on how to deal with the main leg. It's a variation of the idea Abl outlined earlier in this thread. The Horsa main leg had a shock absorbing strut (rubber in compression according to AP 2097A*, Revised Sept. 1942 ) about half way up this, rather conveniently, is noticably wider than the rest of the strut and would serve as a good place to hide a push fit join. The scribble shows what I'm thinking.  All I've got to do now is find the bits and bobs to make it work.


*Pilot's Notes for Horsa I.


Title: Re: Horsa-ing around
Post by: OZPAF on February 19, 2019, 07:46:07 PM
The 2 bob on top of your dihedral pile is almost as old as the original Horsa :)

Well this is the prototype so Lurker Industries could still use it for stability assessment and crash worthiness testing :)

John


Title: Re: Horsa-ing around
Post by: abl on February 20, 2019, 03:40:28 AM
I like the idea of a sliding fit tube (brass, presumably) if you can make it work nicely - 20 swg is still quite thin, flexible wire. However, I would worry that the landing shock could still be transmitted to the top part of the undercarriage and could easily break the spar at the attachment point unless you back it with a bit of spruce or similar (tapered in thickness, obviously).


Title: Re: Horsa-ing around
Post by: OZPAF on February 20, 2019, 05:06:43 AM
If the bottom section of the UC is taking all the landing shock loads, then why not use something flexible for the top section of the strut? A length of the appropriate size heat shrink or similar?

John


Title: Re: Horsa-ing around
Post by: TheLurker on February 20, 2019, 01:14:32 PM
Quote from: OZPAF
... prototype ... use it for stability assessment and crash worthiness testing
Joking aside that is pretty much the point of this build; to shake the nits out of the plan and to find out whether or not it will fly and if it won't what changes are needed to sort it out.

Quote from: ABL, OZPAF
... I would worry that the landing shock could still be transmitted...
...why not use something flexible for the top section of the strut...
Landing shock? But, but... this is a freeflight glider and they they all come to ground like thistledown on balmy late summer's eve.  OK, OK when you've all finished laughing... back to earth and with a hefty bump into the bargain I expect.

The plan is/was to have a fairly tight push fit leaving a gap between with the lower section of the main leg and the upper section within the "damper" shroud.  A gap of about 1/4" should be enough for the wheels to be pushed up (huzzah for friction) leaving the skid to take the rest of the impact when the leg reaches the limit of its travel.  An alternative may be to put something springy or easily crushable in the gap.  Of course were one building a GCU variant then there would be no skid sooo....

There will also be some spring in the legs attached to the fuselage.

As expected the wing is somewhere between 14 and 15g.  The kitchen scales don't settle on one value so probably 14.5g

I also find I have enough hard 1/8" sheet to cover the hull of a First Rate Line of Battle ship but have I any soft? Hah! Have I cocoa.  So the stab. which was slated for a soft sheet TE will have to make do with some medium if I'm to stand a chance of getting this one done before the spring gardening tasks are allocated and I'll have 'phone those nice people at SLEC PDQ.

And just for the hell of it a picture or two of what it looks like so far.


Title: Re: Horsa-ing around
Post by: cvasecuk on February 20, 2019, 01:57:09 PM
I have just spotted what must be a serious mistake with that plan. The gap from wing TE to tail LE is well under the wing chord. Any measurement of a 3 view of the full size shows it is at least 125% of wing chord, if not more. I am surprised that no-one else has mentioned it.
Ron


Title: Re: Horsa-ing around
Post by: TheLurker on February 20, 2019, 03:59:08 PM
Thanks Ron, that makes things very interesting indeed.  I did mention the possibility of disaster in the opening post of the thread so gawpers hoping for a calamity may yet be rewarded for their patience.   Thank goodness it's only a few bits of balsa eh?

I think I'll press on, but I'll put the undercarriage work to one side so that I can get it out for a test flight PDQ to see whether or this turns it all pear shaped. If it flies OK I can live with the out of scale aspect of it as 100% fidelity to the original was never my aim with this one given the starting point.  

The fun you can have with old plans eh? That'll teach me not to assume that the basic proportions are right.  :)

Edit to Add.
Ah. I have it.  My excuse is that this is now a semi-scale model.  :D


Title: Re: Horsa-ing around
Post by: dohrmc on February 20, 2019, 04:22:54 PM
It may develop that it’s a little twitchy in adjusting it, but I bet it flies fine. Maybe not as well.in turbulent conditions.

Would a torsion bar type landing gear not work well?  At least I think that’s what it is called. I’ll have to check on that.


Title: Re: Horsa-ing around
Post by: dohrmc on February 20, 2019, 05:09:24 PM
Paul McIlrath comes through with this one: "Dear Joe....After reading about George White's ingenious magnetic breakaway landing gear, I had to write about another shock absorber which has worked well for me for a dozen years or more. Description appeared in Bill Warner's column in American Modeler September 1990 and some time later in English Aeromodeller. Conventional wire gears absorb shock by bending. This one works in torsion. In the sketches, the internal horizontal sections absorb most of the shock by twisting. The exposed strut. bends much less. The wheels track better in take-offs and landings and the gear can deflect an amazing amount without taking a permanent set. The horizontal section must be secured to a spar or bulkhead so it will not move but is able to twist. I have bound or sandwiched them using acetate glue, and they break free (to twist) with the first landing shock. The internal vertical legs must be securely fastened to a rugged structural member...
 

Well, I can’t figure out how to post the picture/drawing as is on a pdf. If you go to the Volare web site, George Bredehoft has posted some 850 short articles that were on the now defunct Pensacola Ff club. Scroll down to landing gear attaching, and you will see the above words with a drawing that explains all. An option, anyway.
 


Title: Re: Horsa-ing around
Post by: Indoorflyer on February 20, 2019, 07:35:25 PM
Here we go


Title: Re: Horsa-ing around
Post by: abl on February 21, 2019, 03:35:47 AM
Paul McIlrath comes through with this one: "Dear Joe....After reading about George White's ingenious magnetic breakaway landing gear, I had to write about another shock absorber which has worked well for me for a dozen years or more. Description appeared in Bill Warner's column in American Modeler September 1990 and some time later in English Aeromodeller. Conventional wire gears absorb shock by bending. This one works in torsion. In the sketches, the internal horizontal sections absorb most of the shock by twisting. The exposed strut. bends much less. The wheels track better in take-offs and landings and the gear can deflect an amazing amount without taking a permanent set. The horizontal section must be secured to a spar or bulkhead so it will not move but is able to twist. I have bound or sandwiched them using acetate glue, and they break free (to twist) with the first landing shock. The internal vertical legs must be securely fastened to a rugged structural member...
 

Well, I can’t figure out how to post the picture/drawing as is on a pdf. If you go to the Volare web site, George Bredehoft has posted some 850 short articles that were on the now defunct Pensacola Ff club. Scroll down to landing gear attaching, and you will see the above words with a drawing that explains all. An option, anyway.
 

I think that might work quite well. Let's see what the Chief Designer thinks - he's probably busy at the the moment having his morning sherry.

I have just spotted what must be a serious mistake with that plan. The gap from wing TE to tail LE is well under the wing chord. Any measurement of a 3 view of the full size shows it is at least 125% of wing chord, if not more. I am surprised that no-one else has mentioned it.
Ron


Well spotted, that man. I didn't notice it either, until you pointed it out. Extraordinary.  :)

BTW, Lurk - have you left space for a ballast box in the tail...?


Title: Re: Horsa-ing around
Post by: cvasecuk on February 21, 2019, 10:07:44 AM
It is too late now, but I've been doing some careful measurements and it looks as though the distance between F6 and F7 should be 4".
A quick calculation on your model shows that CG should be about 1.5" from centre section LE but with a tail volume coefficient of only about 0.25 I suspect you will have stability problems!!!
Ron


Title: Re: Horsa-ing around
Post by: Indoorflyer on February 21, 2019, 10:45:33 AM
The plan is also here @ HPA Plan Gallery. There is a comment attached to the plan description that may be of interest...

http://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=4842&mode=search


Title: Re: Horsa-ing around
Post by: TheLurker on February 21, 2019, 02:28:05 PM
Quote from: dohrmc, Indoorflyer
...torsion...
It looks like a nice trick for a single leg arrangement with stub axle, but the Horsa has what amounts to a tripod arrangement of UC legs so I can't see how I can make that work.  The current interference fit arrangement of the lower legs will provide a degree of "controlled disassembly" on hard landing so I think, other more pressing problems presenting themselves, the UC will be left as is assuming the build progresses.

Quote from: abl
...having his morning sherry.
No sherry here today, a most unfriendly telegram or two from the Air Ministry and the Ministry of Supply, but no sherry.  The Board of Directors is also considering offering the Chief Designer the use of the Company Webley.

Quote from: abl
... have you left space for a ballast box in the tail...
I daresay I could make room for one, but it would only add to the air of gloom in the board room if it comes to it.  I was pondering how nose heavy Fat Boab would be on the ride to work this morning and it came to me that's probably how/why the original plan got away with such a heavy tail assembly.

Quote from: cvasecuk
I suspect you will have stability problems!!!
Oh Bother!  Other words beginning with "B" are also available, many very less polite than "bother".

I've gone back and checked and the undersized TE/LE gap is present on the original plan, for round numbers the ratio is about 0.8 rather than 1.25, it's slightly under 0.8 on my rescaled build because I shunted F5 back a touch when I found that the rib profiles as given were too long for the gap given on the original.  In retrospect it would have been a better move to split the difference between F3 & F5 or even shrink the ribs slightly.  Even better, the 3 views I have to hand give a ratio varying between 1.35 and 1.41.

I'm not quite sure what to do now. The comment on the gallery copy of the original plan indicates it flew well with the 80% gap so do I press on or redo* the plan and start on a fresh fuselage?  If I were a faster builder and the spring task allocation were not looming it would be a simple decision.  Opinions invited.

Lurk.

*ETA.  The plan will be re-done, it's a case of whether or not I build a fresh fuselage now or carry on with current one to work any remaining nits** out.

**I would consider it a great courtesy were other members of the congregation able to refrain from identifying the greatest and most obvious nit involved in this project. :)


Title: Re: Horsa-ing around
Post by: abl on February 21, 2019, 05:26:10 PM
> I'm not quite sure what to do now. The comment on the gallery copy of the original plan
> indicates it flew well with the 80% gap so do I press on or redo* the plan and start on a
> fresh fuselage?  If I were a faster builder and the spring task allocation were not looming
> it would be a simple decision.  Opinions invited.

Well. If it was me I'd find it very difficult to live with a fuselage that was too long at the front and too short at the back (I'm on the spectrum). However, I doubt that you're similarly afflicted so unless you can somehow bodge adjust the wing position, I'd recommend going with it as it is. However, if you're going to change the plan and then make it available, it'd be best to make a new fuselage. IMO, anyway.

A.


Title: Re: Horsa-ing around
Post by: dohrmc on February 21, 2019, 06:20:42 PM
Go with what you got.


Title: Re: Horsa-ing around
Post by: OZPAF on February 21, 2019, 06:56:53 PM
My humble advice would be to build a quick profile test glider - even half size, to see what the stability will be like, before operating on the fuselage.

This could also be used if necessary to see how far the wing needs to be moved.

John


Title: Re: Horsa-ing around
Post by: TheLurker on February 22, 2019, 01:44:47 AM
Quote from: abl, dohrmc, OZPAF
...it'd be best to make a new fuselage. IMO, anyway.
...Go with what you got.
...a quick profile test glider

Thanks for those thoughts.  Having had a kip and bearing in mind both other calls on my time and current stocks of suitable sheet I think the plan is to

- Finish off what I've got sans UC and lipstick and see how it flies.

    I have what appears to be a feasible solution for the UC and putting lipstick on this one would be silly given that it is so far off scale but it's still worth building up the empennage to make sure that goes together well and fits correctly.

  Can't see any practical way of adjusting the wing position on the current fuselage.

- Re-do the plan and then build a new fuselage.  

   Given some luck I'll be able to re-use the wing and empennage.

Quote from: abl
I'd find it very difficult to live with ... I doubt that you're similarly afflicted ...
I'm less particular than yourself about detail as my stuff isn't built for scale competition, where detail is important, but leaving aside probable stability issues this is going to look out and out wrong in the air which does not sort well with me at all.


Ructions at The Lurker Industries Aeroplane Company Ltd..
The shop floor staff have just informed the Chief Designer that there is no way on God's Green Earth that anything that wrong is leaving the factory with their name on it. 

or...
I've re-checked sheet stock.  No need to re-order.  There will be a short hiatus while the plan is redrawn and and new parts cut for a new fuselage.


Title: Re: Horsa-ing around
Post by: TheLurker on February 22, 2019, 01:45:12 PM
Some stones are best left unturned.  I should just have built from the original plan and maintained my state of blissful ignorance.  That'll teach me eh?

A couple or three hours mucking about in Inkscape and I have a revised fuselage plan and some updated part profiles. Still got to go back and revise my build notes and some other bits and bobs of admin but thinking that I may not lose too much time over this little hiccup.  So I think to myself, "I wonder how well this lot tallies with (what appears to be) the better of two three views I've got?"  Well...  

The fuselage proportions are now much closer to the prototype,  certainly good enough for me and I knew the stab was oversized but I expect that in freeflight models, but the wing. Hmm, that is a bit iffy.  Not so iffy that the one I've got won't fly, but ...  and as for the UC.  Have a look at the pic.  You'll see what I mean.  Best viewed after you've clicked the "make it bigger" button on the thumbnail viewer

Also attached is the revised fuselage plan.  I've rejigged the lower UC leg mount points yet again and there's a good chance they'll get moved a bit when I can find another 3 view to cross check UC positioning.  

I'm not going to worry about the stab. struts.  The positioning of those is determined by available hard points on the stab so they will remain as they are.  

I will modify the wing plan but mine will keep the one I've built as it's (just about) close enough.

I shouldn't be surprised that the original plan is a bit hit and miss.  It was drawn up in the middle of a war, probably from ropey newspaper photographs and memory because the type was in active service so accurate plans or three views would very definitely not have been available. Viewed in that light I think it's a pretty good representation.

Right I'm off to resharpen my pencils and make a few more changes...  


Title: Re: Horsa-ing around
Post by: TheLurker on March 03, 2019, 07:07:10 AM
A degree of cautious optimism  in the Boardroom at The Lurker Industries Aeroplane Co. Ltd..  Sufficient to allow small glasses of the second best Amontillado all round; apart that is from the Chief Designer who will be very lucky if he gets a bottle of fizzy pop and packet of crisps from the staff canteen.

Fat Boab's fuselage has been moved out of the build shed and will be broken for parts.  Construction of the new fuselage, which the wags on the shop floor have already dubbed, "Wee Eck", is under way and with luck will be done a se'nnight hence. Keep that under your hat though. The Co. doesn't want the Air Ministry hoofing around in their dirty great size nines causing trouble.

Or...

I owe Ron (cvasecuk) a pint at the very least for spotting the problem with No. 1.  Apart from the loss of time and a little bit of balsa it's turned out, so far, pretty well.  I've been able to put the various suggestions and changes found to be required into No. 2 and it seems to be going together much more easily.

Attached are a couple of pictures showing the marked difference between the two.

The delay has proved useful in another way because it's allowed Rich Moore to solve the push fit damper problem for the undercarriage main leg for me. The relevant bit from here (http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=23182.msg238697#msg238697) is,  "I have an idea to slow the movement down, which is essentially a small dash-pot (dampener device) made from a small plastic tube.." I oodles of plastic tube in various diameters salvaged from pump action soap dispensers.


Title: Re: Horsa-ing around
Post by: abl on March 06, 2019, 09:56:21 AM
That looks much better, Lurk...


Title: Re: Horsa-ing around
Post by: TheLurker on March 07, 2019, 03:38:17 PM
That looks much better, Lurk...
Aye, it does and we'll have no more of this ballast chamber in the tail nonsense eh? :)

Jogging along.  Another two or three days at least before the fuselage is back to where it was.  Not too many snags with the revised parts.  Frame 8 as currently drawn is about 1/16" too deep and there's still a measure of wasp-waisted-ness about frames 8 and 9. Not so pronounced as on No. 1, but it's there.  See the pictures.

And just for the fun of it a picture of Wee Eck as it is at the moment and a side by side view of the two fuselages for comparison.


Title: Re: Horsa-ing around
Post by: OZPAF on March 07, 2019, 06:32:22 PM
Well that is looking a lot better - definitely worth the redo.

Perhaps the Lurker Industries Management will now let the Chief designer out of solitary confinement where he was sent - complete with drawing board to redo the fuselage dwgs. :)

John


Title: Re: Horsa-ing around
Post by: TheLurker on March 11, 2019, 04:57:01 PM
There's a John Mayall song, "Crawling up a hill." (https://www.youtube.com/watch?v=W3BK8-Mmn1s)  Sort of sums it up.  Noseblock finally shaped and it only cost two broken longerons and all weekend. 

On the plus side fuselage No. 2 is shaping up to be no heavier than fuselage No. 1 and there's the ghost of a suspicion of a rumour of a chance it may even be slightly lighter despite all the splints on the broken bits.  With the lower UC mounting tubes and wing platform to fit the fuselage sans skid is 20.5g and 21.1g with.  Thirty grammes or under for the larger fuselage will be reckoned an encouraging result.

Quote from: OZPAF
...let the Chief designer out of solitary confinement...
He'll be lucky.  He'll be in purdah a good while yet.  Apart from anything else our head stores wallah has had to chase around suppliers to replace the wasted materiel and you have no absolutely no idea the hoops the Ministries make you jump through these days.  The poor fellow has been buried under an absolute mountain of bumf and you really wouldn't want to hear his opinion of the Chief Designer. The language would make a matelot blush.


Title: Re: Horsa-ing around
Post by: dohrmc on March 12, 2019, 10:09:57 AM
Put him on a diet of bully beef and biscuit for a week.  That will mend his ways for good.


Title: Re: Horsa-ing around
Post by: abl on March 13, 2019, 05:11:49 PM

I think we might get better results by taking away his keys1 to the Sherry cabinet.  :)

Andy

1Temporarily, of course; I'm not a complete monster...


Title: Re: Horsa-ing around
Post by: TheLurker on March 14, 2019, 05:08:55 PM
Sherries all round.  Even the Chief Designer; although he only got a very small glass of Bristol Cream left over from the staff Christmas party and he can count himself jolly lucky he got that.

Right.  Where are we?  Ah yes.  Fuselage No. 2 is now slightly ahead of where I'd got to with No. 1. So heading in the right direction again.

No. 1.  Weight including skid and pegs for rubber bands.  28.8g
No. 2.  Ditto  26.1g

Over 2.5 grammes lighter and a larger fuselage? Aye, I'll take that thank you very much.

No. 2 fuselage is currently balancing about 1.5" back from L.E. which is encouraging.


Pictures show revised wing platform, lower undercarriage leg mounting points and a closer to scale nose profile.  I was never very happy with the wing platform on No. 1.  The dirty great slab of sheet seemed like overkill.


Title: Re: Horsa-ing around
Post by: TimWescott on March 14, 2019, 08:46:30 PM
So, did you leave room to stick a 1/32 scale Jeep in there for balance?


Title: Re: Horsa-ing around
Post by: TheLurker on March 17, 2019, 08:23:15 AM
So, did you leave room to stick a 1/32 scale Jeep in there for balance?
Damn and blast. I knew there was something else I'd forgotten. :)

A morning of coffee and arithmetic working out wire lengths and angles for the UC wires and making minor mods to the plan to accommodate same.  Also learning yet another useful lesson viz:  If you have a copy of the Pilot's Notes read them all the way to the end and not just the leading particulars.  You might find things that save you some grief. See attachments.

Never mind. It made correcting the UC strut angles and positioning a fairly straight-forward task.


Title: Re: Horsa-ing around
Post by: OZPAF on March 17, 2019, 08:02:00 PM
Amazing amount of info on those rigging sheets that you have appropriated from the offices of Airspeed.
I hope the arithmetic suitably improved the flavour of your coffee!

John


Title: Re: Horsa-ing around
Post by: TheLurker on March 18, 2019, 04:00:23 PM
Quote from: OZPAF
I hope the arithmetic suitably improved the flavour of your coffee..
Umm. No.  I'm not very good at arith. :)

Right. I think I've finally got a solution for the vertical UC strut that I'm happy with.

This is a bungee launched glider so no ROG and a very short landing run which means all that's necessary is enough resistance to hold the fuselage off the ground for any posing felt to be necessary before launching and enough give to collapse gracefully and reusably on landing.

So what have we?

+ Spar mounted eye as noted upthread.

+ Tissue covered drinking straw.  

+ Two short sections of tissue covered dowel made to push fit very, snugly into each end of the straw.

+ A hook mounted in each piece of dowel.  

+An eye for the lower hook fitted to the lower UC wires.

+ Part way down the straw, possibly disguised / hidden within a damper shroud a series of lamp style vertical slits.

The dowels take up the initial landing shock by travelling within the straw and if/when the limit of the dowel travel is reached the slits allow the straw to deform and absorb the rest of the impact.  For this incarnation the dowel travel should be enough to allow the skid to absorb really hard landings, but I think this solution allows a skid free (GCU) model to be built with some confidence that the important bits will survive a hard landing.

Being push fit the dowels should also allow the vertical strut to come away if the undercarriage is dragged on landing.

I did try using the flexible section of the straw as the fallback shock absorbing element of the strut, but some very rough and ready testing with the kitchen scales indicates that the slit straw starts to deform somewhere between 50 and 75g whereas the flexible section didn't start collapsing the load was well in excess of 100g.   Mucking about with the prototype also suggests that a prudent modeller will force the slit version through at least one collapse to condition it before fitting it to the model.

And as drinking straws are cheap and easy to prepare replacement in the event of destruction or loss on landing is no great effort and spares can be carried in the field kit.

Pictures show the prototype strut and some deformation tests using 1/8" and 1/16" strip as substitute spars.  These are plastic straws but paper straws should do just as well.  

Edit to add.  The straw is slightly over scale diameter, but I'm not going to worry about it.


Title: Re: Horsa-ing around
Post by: vtdiy on March 18, 2019, 09:42:54 PM
I like your shock absorbers, Lurker!


Title: Re: Horsa-ing around
Post by: OZPAF on March 19, 2019, 06:03:05 AM
Nifty idea there from Lurker Industries. Give that suffering Senior Engineer a raise :)

John


Title: Re: Horsa-ing around
Post by: TheLurker on March 19, 2019, 04:29:28 PM
Revisited the canopy this evening. 

Hadn't yet worked out a reasonably simple way of making an acetate version from cut flat sheet as, unlike a paper version, the joins can't overlap and I also wanted to check that it worked with the more scale canopy depth. 

Think I've got it sorted now.  Trick is to use a 1/16" strip of balsa along the joins where the glazing bars for the forward corners are and not to use the ratty old stuff I used for my experiment which was in no hurry to "take" to the CA.  You can get away with square strip, but it'll be possible to get a better curve if you were to use a flattened isoceles triangle and the strip will be more or less hidden by the tissue or painted glazing bars on the finished article.

The template still needs a bit of fine tuning and a greenhouse made this way will never look as good as a vac. or plunge moulded item, but it does mean that the whole model can be built at the kitchen table and still look right.

Can crack on with the tail surfaces now that I've got undercarriage and canopy assembly more or less sorted out.

Picture shows the slightly messy and incomplete result of this evening's experimentation. 


Title: Re: Horsa-ing around
Post by: TimWescott on March 19, 2019, 08:51:21 PM
... never look as good as a vac. or plunge moulded item, but it does mean that the whole model can be built at the kitchen table ...

You are right next to an oven and probably one room away from a vacuum, and you're not going to vacuum form?


Title: Re: Horsa-ing around
Post by: TimWescott on March 19, 2019, 08:52:57 PM
I just finished Steven Ambrose's "D Day" (for the upteenth time).  You are remembering that a typical scale maneuver for that beast is to land on rough ground and break up, yes?


Title: Re: Horsa-ing around
Post by: TheLurker on March 20, 2019, 02:48:29 AM
Quote from: TimWescott
You are right next to a gas oven with rubbish temperature control and probably one room away from an even dodgier Dyson* vacuum with pitiful suction on the extension hose , and you're not going to vacuum form?
I trust the highlighted amendments clarify the situation?

*We won't be buying another Dyson that's for sure.

I may try plunge moulding as I have a hot air paint stripper, but the point of the acetate template is, should this thing actually fly to be able to present a plan that can be built solely with hand tools and still give an acceptable scale result. 

As I've said elsewhere I remember all too well when I was a kid looking at wonderful plans and realising I couldn't build the model because I didn't have the tools to complete it.  It was quite disheartening.  It also seems to me that if we want to encourage people with no previous exposure to or connection with aeromodelling to take up the hobby that we should provide interesting models, not just anonymous slab sided gliders, that can be built using only hand tools.  I also know of at least one very active member of this forum who lives in a flat and hasn't got the space to store stuff like vac. forming apparatus and, in the UK at least, modern houses are put to shame by even quite modest rabbit hutches when it comes to space.

Here endeth the lesson. :)

Quote from: TimWescott
You are remembering that a typical scale maneuver for that beast is to land on rough ground and break up, yes?
Oh yes. :)


Title: Re: Horsa-ing around
Post by: vtdiy on March 21, 2019, 09:25:13 AM
I liked that!


Title: Re: Horsa-ing around
Post by: TheLurker on March 22, 2019, 04:08:55 PM
Am now in a reasonable position to offer a reasonable initial guess at uncovered weight and wild guess for covered.

At the moment looking at somewhere around 44.5g-45g for uncovered sans UC.

Confirmed weights to nearest tenth of a gramme.
Fuselage, skid and pegs   26.1
Wing                              14.3
Fin/rudder                        0.5

Estimates:
Stab inc bamboo struts    3.8g from weight of uncut wood.

As for covered weight.

Reasonable Guesses

Canopy                          1.5g - 2.0g  worst case. 
                                     Test canopy above made with ratty old thick sheet is 1.8g will be using thinner acetate for "production" version.
Two sheets of Al/Ag tissue (14g)
                                     
Unknowns:
Undercarriage
Dope

So minimum, sans UC, covered weight is going to be somewhere about 60g.  With undercarriage and dope could be looking at a covered weight of 70g+.  If not wildly wrong that's quite encouraging as my West Wings Swallow flies pretty well at 80g+ with a 35" span compared to the 32" span of this one.


Title: Re: Horsa-ing around
Post by: TheLurker on March 23, 2019, 03:59:05 PM
A degree of cheeriness in the board room at Lurker Industries today and it wasn't just due to the sherry.

Now have something that looks like an aeroplane.  I know we all know what they look like, but I couldn't resist tacking it together with a bit of blu-tack and as I'm feeling immoderately chuffed with it (at the moment) you get to see the pics as well.  :)

Interestingly I'm still finding little bits and bobs that need adjusting on the plan even for structures as simple as the fin and stab. Shuffling positions of ribs and so.  Even little things like the note on the fuselage for fitting the stab.

What's left?
 - Shape LE & TE on stab.
 - Recalculate CG for the new fuselage.
 - Work out (new) candidate location for tow.
 - Cut and size the struts for the stabilizer.
 - Build the undercarriage.
 - Covering, decorating and doping.
 - Wrap up the guidance notes.

Knowing what's planned in real life I think (hope) that a fortnight will see it ready for flight trials.  Fingers crossed.

Edit to Add.
 - Work up more accurate wing plan. Which will take me a day or three.


Title: Re: Horsa-ing around
Post by: dohrmc on March 23, 2019, 05:31:41 PM
Fine work! Should be a good Flier.


Title: Re: Horsa-ing around
Post by: abl on March 23, 2019, 07:38:50 PM
Looks good, Lurk.

A.


Title: Re: Horsa-ing around
Post by: TheLurker on March 24, 2019, 03:35:17 PM
Bending up the lower UC wires, which went surprisingly well, and experimenting with various ways of providing the lower eye for the vertical strut hook.  See the pic.  I'm going to go with the 3rd option, single bent wire, because it needs no special tools and adds the minimum amount of weight.  I'm also hoping that the more flexible 22 SWG wire will provide an additional measure of shock absorption on hard landings.

Still puzzling over the lightest, simplest way of providing the AS.58's twin nose wheel UC leg.  Various half-formed thoughts.  None of the satisfactory. More thought needed on this one.

Made up the wheel blanks, laminated balsa discs with grass stem axles, but I won't bother finishing them off until I've got all the other UC parts ready.

Did a bit of build "admin." as well.  Spent an hour or two tidying up the WIP box and the build scrap box sorting out the usable offcuts of strip and sheet from the dross; mainly to clear my head for the final stages but they had both got unusably cluttered and were starting to impede progress.  Don't usually have to do this part way through a build, but what with the reworked fuselage and other experiments there's been a lot of 'scrap' generated.


Title: Re: Horsa-ing around
Post by: vtdiy on March 27, 2019, 10:31:44 PM
Beautiful job you're doing there on that plane, Lurker.


Title: Re: Horsa-ing around
Post by: TheLurker on March 28, 2019, 04:26:52 PM
Quote from: vtdiy
Beautiful job you're doing there on that plane, Lurker.
Too kind, but perhaps best reserve judgement until it's flown, eh? :)

A little more progress and a bit closer to a solid idea of weight.

It looks like the main UC is going to be about 2.0g each side.  The undecorated stbd side with the rough old blank test wheel is tipping the scales at 1.86g and if I allow 2.0g for the nosewheel that pushes the "known" covered weight figure up to around about 66g. 

Still no idea how much weight the EzeDope is going to add (one coat 5%, one coat 30%).  It's a big (by my standards) aeroplane so it's likely to be be several grammes.  Even so a 70g+ unballasted weight is looking like it might be a realistic possibility. 


Title: Re: Horsa-ing around
Post by: TheLurker on March 29, 2019, 04:39:32 PM
Ho hum.  Not an earthly of having the Horsa ready for flight trials a week from now.  I reckon I'll have an absolute max. of 6 hours bench time between now and Friday next.

Still working on the UC and have decided that the solution for the vertical strut, although practical, is just too far off scale even for me as the straw will be at least twice scale diameter.  Bother.  Am starting to think in terms of a grass stem with a strategic cut and push fit joint using a piece of soft 1/16" or 3/32" strip as a joining dowel and expecting to replace these dowels on every flight.  A fairly cheap price to pay for simple construction, decent shock absorbtion and a moderately good match to scale diameter. Not only that but scale landing behaviour! Can't be bad eh? :)

Not all doom and gloom; the main UC legs and all wheels are built and the main gear angles all look about right. Might need a bit of tweaking to reduce/remove some toe-in but that's about it.  Going to leave the main wheels with a flattish top rather than rounding them out properly for the sake of robustness.  For those that are interested the axles are grass stems.  Tried it for the Lacey M-10 and was pleased with both the low weight and how well they worked.

Think that nosewheel strut will be fitted in a similar manner to the main uc legs, but glued into a short section of Al. tube rather than a push fit.

I daresay it's stale buns to the rest of you, but I've finally sorted out a way of getting decently round wheel blanks by hand without recourse to a dremel "lathe". See pics. Next time I'll use slightly heavier card, but the idea works.  Just need to work out a way of reliably keeping the wheels round when sanding to profile.


Title: Re: Horsa-ing around
Post by: strat-o on March 29, 2019, 05:44:24 PM
Thanks for that wheel idea, which I will steal.  One possibility for maintaining the round profile while contouring is to draw a line like a center tread and make sure you don't sand the mark away, like as is done when sanding a solid balsa wing where you mark the high point or max thickness.

Strat-o


Title: Re: Horsa-ing around
Post by: TheLurker on March 30, 2019, 02:08:18 AM
... draw a line like a center tread and make sure you don't sand the mark away...
Fair exchange is no robbery.  I'll have that idea. :)

I had considered a variation on the card masking I use as a guide/precaution against tool wander when grinding out the hub, see pic., and cutting a disc slightly undersized to give the me the limit of the curve on the tyre's sidewall.  I think combined with your centre tread idea that might work quite nicely.  Be a right fiddle for small wheels, but should still be do-able. 


Title: Re: Horsa-ing around
Post by: OZPAF on March 30, 2019, 04:13:44 AM
Fascinating attention to detail there Mr Lurk. I hear that the chief Engineer almost went mad drawing circles on the wall during his solitary confinement :)

John


Title: Re: Horsa-ing around
Post by: TheLurker on March 31, 2019, 09:04:51 AM
Quote from: OZPAF
...chief Engineer almost went mad...
Almost? :)

Yet more undercarriage tweaks.

Hadn't thought to check that I'd got the angles and ground clearances right for the skid.  I have.  Phew. :)

A, dim, lightbulb moment gave me a solution for a single piece push fit damper that looks sufficiently like the prototype to satisfy me, simplifies construction and will look better on the finished article and, rather amusingly, brings us right back to square one as far as vertical strut assembly goes.

In brief; a trapezoidal piece of 80gsm paper narrowing from about 1 1/16" to about 15/16" and about 3 1/2" long. Starting with the broad end wrap it tightly about the strut.  A 1/8" bamboo skewer will do as it's about scale diameter.  Glue the outer seam, remove the strut and harden off the end "cones" with a thin smear of CA. A thin smear of CA on the inside of the tube serves to make the fit a bit more snug if needs be.

If you look at the attached picture you'll see the double-hooked arrangement doesn't look too bad with the wheel in place but if you take the wheel away it's utterly, irredeemably, horrid.  This is to be corrected. The hook and grass stem will be removed from the upper part of the stub axle on the main gear, it'll then be bent to the correct angle and a replacement lower strut leg drilled out to take the stub axle and epoxied permanently in place. The upper part of the strut will still be held in place with a hook and eye at the main spar which will allow a little bit of play if angles aren't absolutely bang on.  The hardest part of this will be drilling out the lower strut as my drill bits jump from hair thin to well over 1mm so I'm having to use a bit of sharpened 22 SWG clamped in mini Mole grips and bamboo isn't the softest of woods. :)

Of course the upper and lower parts of the vertical strut are cut short so that there's a gap between them inside the damper to allow the damper to do just that.

By the by.  If you need small, neat hooks try using a paper clip rather than 22 SWG piano wire.  It's about the same diameter and sufficiently robust but far, far easier to form into a small, neat hook without any great difficulty.  It also makes a jolly handy temporary eye for mounting on the main spar when test fitting the strut.  Strikes me that this might also be a way to go for wire formed tail-wheels on kit scale tail draggers.  I find that even with a vice mounted mandrel I can waste a lot of piano wire getting a reasonably circular result.


Title: Re: Horsa-ing around
Post by: TheLurker on March 31, 2019, 03:14:46 PM
Right this is more like it.

Have a solution for the front gear so with luck tomorrow evening's session will be airframe complete.


Title: Re: Horsa-ing around
Post by: OZPAF on March 31, 2019, 08:03:29 PM
Nice work Mr Lurk - however(yes there is always a however :)) I hope you intend to add a diagonal from the UC attachment on the lower spar up and back to the wing root area? That poor spar may call help when the strut vertical impacts it.
You may banish me to the woodheap for the steam boilers if you have already covered this problem :)

John


Title: Re: Horsa-ing around
Post by: TheLurker on April 01, 2019, 03:39:22 PM
You may banish me to the woodheap for the steam boilers if you have already covered this problem :)
You! Boy!  Stop talking at the back there!  Yes you Ozpaf.   Take 500 lines, "I must pay attention in class." :)

Aye, it's the main reason the main gear has taken so flaming long.  Trying to find a workable and cosmetically acceptable solution for just that problem.  The basic idea of a friction fit of strut sections in a damper sleeve with a gap between the sections to allow friction to take up the landing impact was established weeks ago, but I couldn't work out how to make a decent damper sleeve so there were various fruitless detours.

As built there's between 1/4" and 1/3" of available travel in the damper sleeves, but there's only 1/16" to 1/8" of clearance between the ground and the skid when the wheels are fitted - hey that's almost scale! - so the  skid (with the nosewheels) is likely (I hope) to bear the brunt of most landings. 

I'll need to tweak the fit of the strut parts in the sleeves as they're a bit on the tight side, but that's better than too slack and you don't need too much friction in the sleeve because the lower main gear takes the weight when parked and if they are too tight then they're unlikely to slide in the damper sleeve.  Looking at it assembled I think the lower wires in the main gear might take up quite a bit of any impact as well so it may be posible to let the struts slide quite freely.


Title: Re: Horsa-ing around
Post by: OZPAF on April 01, 2019, 08:36:10 PM
Ah yes! I do seem to remember a few discussions on this now you mention it. :-[ Slits in straws etc.

I should stop snoozing in class :)

John


Title: Re: Horsa-ing around
Post by: TheLurker on April 02, 2019, 04:14:54 PM
The Board of Directors of The Lurker Industries Aeroplane Co. Ltd. are pleased to announce that talmost done has been reached.  To mark the occasion the shop floor staff have repaired to the four ale bar of The Dog And Duck and the Directors are enjoying some rather fine sherry.

Or...
All components now built just got to cover it and decorate it so well and truly on the asymptote.

Definitely not going to need any tail ballast for this go around.  Without the stab. bracing struts in place it only just "floats" on the nosewheels and turns into a tail-sitter at a moment's notice.  The nose up attitude on the ground is right, but it may be slightly high. I'm fairly sure that's a mistake in setting the angles on the wires for the main gear lower legs but I can live with it.  

The tail is held to together with blu-tack hence the wonky alignment.


Title: Re: Horsa-ing around
Post by: OZPAF on April 02, 2019, 05:56:21 PM
Not bad - very Horsarish!  :) 

John


Title: Re: Horsa-ing around
Post by: Pete Fardell on April 02, 2019, 06:04:32 PM
Looking very good, Lurks. I'd certainly trust it to carry my army over the Channel.


Title: Re: Horsa-ing around
Post by: DavidJP on April 03, 2019, 08:36:21 AM
A jolly fine filly you have there old boy.  I recall the chap I worked with who was in the Regiment saying loading was an art because of the balance!


Title: Re: Horsa-ing around
Post by: TheLurker on April 03, 2019, 01:01:02 PM
Quote from: OZPAF
...Horsarish!  :) 
Ta.  Room for improvement, but it's not too bad.  At least it is recognisably a "Horsa" and not, say, a Reliant Robin.

Quote from: Pete Fardell
...I'd certainly trust it to carry my army over the Channel.
Ta, but I'm not sure I would. :)

Quote from: DavidJP
I recall the chap I worked with who was in the Regiment saying loading was an art because of the balance!
Doesn't surprise me at all.  There are quite a few pages, 10 or thereabouts, given over to loading in the Pilots' Notes with quite a few long and involved worked examples.  See the pics. of the first two or three pages.

And never let it be said that H.M. Forces do not care for the welfare of serving personnel.  See item No. 24 - pic. and key - in the cockpit. :)


Title: Re: Horsa-ing around
Post by: Mark Braunlich on April 03, 2019, 02:26:32 PM
Pilot:  Where am I?

Nurse:  You’re in a forward dressing station.  Now just rest easy- like.



Pilot:  What happened?

Nurse:  It appears you were knocked unconscious by you thermos of soup.


Title: Re: Horsa-ing around
Post by: TheLurker on April 12, 2019, 03:37:39 PM
Plodding away covering bits as time allows.  Stab & fin done, wing part done.  In between times having another bash at the canopy.  Am now satisified that I've got the template is as good as it'll get and the construction method likewise. Taken me a few goes to work out a way of gluing it together that doesn't leave one with a glue smeared mess and doesn't need a "heavy" balsa frame .  The current incarnation of the greenhouse is the one that will be fitted. Remaining glazing bars / frame will be painted as per K5083 once it's in place.

For those that are interested. Construction is :

+ Use thin, flexible acetate. About 5 thou seems to work well.
+ Tape to board so that join is as flat as possible with cut edges abutting.
+ Mask off.  It'd probably be easier to mask off before you start, but I didn't think of that until I'd got well into the job.
+ Glue a thin strip of 80gsm paper over the join.  Use the thinnest of smears. Glue a short section first and the "roll" the paper down the join gluing as you go.  Let the CA go off before starting on the second join.
+ Repeat for second join.

Glue a thin strip of appropriately coloured tissue on the outside of each join.

That should give you a canopy weighing 1g or a twiddle over before trimming to fit.

The pics show construction, resulting canopy and some of the prototypes.

Edit to Add.
Having no end of fun trying to establish the CG.  Abl has suggested a practical alternative to Whitehead's heuristic, which gives a CG nigh on 50% of root chord. Which, even with a noticeably swept wing, strikes one as... iffy.


Title: Re: Horsa-ing around
Post by: abl on April 14, 2019, 09:10:18 AM

> Having no end of fun trying to establish the CG.  Abl has suggested a practical
> alternative to Whitehead's heuristic, which gives a CG nigh on 50% of root chord.
> Which, even with a noticeably swept wing, strikes one as... iffy.

So, you made a little chuckie, complete with the rather excessive wing incidence that your larger version has, and it flew OK at 50% root chord? In that case I put it to m'learned colleague that it'll probably be OK...


Title: Re: Horsa-ing around
Post by: TheLurker on April 20, 2019, 04:55:27 PM
Next time I mention that I'm considering using aluminium tissue for a build someone do me a favour and tell me not be such a BF eh?  Thanks.

All parts now covered and fuselage shrunk.  Some wrinkles and cobbles, but I can't afford the time to strip it and re-cover so I'm going to have to live with it. It's not ghastly, but it's nowhere near as good as I wanted it to be.  Shrink the covering on the wings, fin and stab tomorrow. That'll be "fun".  

It is possible to cover the fusage with only four panels - fairly neatly at that - and with something more forgiving than domestic aluminium tissue you should get a very good result.

Because of lack of time I'm going to have to abandon the idea of trying for tissue roundels and fin flashes and cheat by printing them.

I'll sort out some pics tomorrow.


Title: Re: Horsa-ing around
Post by: DavidJP on April 21, 2019, 05:40:27 AM
Good - await pics, but meanwhile are you sure the real thing had no blemishes or wrinkles etc.  Bet you a glass of real ale it did.  But also silver of course exaggerates any blemish or defect.  Have you considered just replacing the panel where it is wrinkled?  I have found it can work well.  You see my covering is often wrinkled too so have lots of practice.


Title: Re: Horsa-ing around
Post by: TheLurker on April 21, 2019, 04:11:19 PM
Quote from: DavidJP
... are you sure the real thing had no blemishes or wrinkles etc. 
Aye, but a couple of feet of scuffed dope on in service air frame isn't noticeable,  a few thousands of an inch wrong on a model is obvious from 5 miles out. The MKI eyeball is not easily deceived in such things.

Quote from: DavidJP
Have you considered just replacing the panel where it is wrinkled? 
I think the fuselage will do as it is.  Some of the problems are starved Horsa, I should have scalloped the frames; schoolboy error on my part so will bear the justified opprobrium of the critics and the nastiest cobble is on the underside so "invisible idiot" applies. :)

The only panel that may get replaced is the port wing LE although as I type this I'm minded to leave well enough alone.  Of course by this time tomorrow I will be so irritated by it that I will replace it. Fortunately lessons learnt on the Swallow build mean that it is a relatively small panel from L.E. to forward spar so if I do decide to fix the d*****d thing it won't be a hugely expensive operation.

Quote from: DavidJP
my covering is often wrinkled too .
Aye mine too, but I've found showering rather than taking long baths helps a bit, but not as much as it used to. :)

Right where are we?  After discussion with the Senior Partner on the usual evening stroll around the Lurker Industries aerdrome peri. track it has been decided that effort will now be concentrated on establishing whether or not the Co. has a viable aeroplane.  Roundels, fin flashes, serial etc. will be applied only if it flies.  It's also likely that the fuselage fairings for the wings will be omitted until the wing's angle of incidence has been confirmed. I'm expecting to have to tinker with this.

Photos on this post.  Various views of the fuselage with a couple showing the cobbles.
A few more photos on the next post inc.  shots showing the messed up port LE panel..


Title: Re: Horsa-ing around
Post by: TheLurker on April 21, 2019, 04:15:20 PM
OK. A few more photos.  Give you an idea what she might look like if she ever makes it to the aerodrome and to show the cobble on the wing.

The canopy hasn't been trimmed to fit yet and, like the stab., is just resting in place so looks a little ... odd.


Title: Re: Horsa-ing around
Post by: TheLurker on April 22, 2019, 10:31:55 AM
The R&D Dept. has been evaluating the Abl patent method* for determining CG in aeroplanes with variable chord wings.  In short the experimentally determined value is at 63% of root chord.  Which has surprised everyone. The R&D Dept. is corresponding with Abl to confirm that that the correct experimental procedure has been adhered to.   The shop floor wouldn't be at all surprised to hear that the boffins have made a bit of a bish of things.  Again.

The test-bed does glide fairly well onto the sofa despite the astonishingly far back CG so I'm now a bit more hopeful that its bigger sister will do so in the big blue room.  Glide angle of the test-bed isn't great, averaging around about 1:6/1:7 with the odd one about 1:9, so I don't think OOS is likely to be a worry with it. 

Some pictures just for the fun of it.  Observant readers will note the continued use of AvroVulcan's patented dihedral jig.

*In summary.
Build a small profile version, minimum 6" span, of the craft and chuck it around until you're happy that it's gliding well. Get it to balance on sharp points, press home to mark the CG.  The point where the line between the points cuts root chord is your CG.


Title: Re: Horsa-ing around
Post by: OZPAF on April 22, 2019, 09:29:04 PM
Perhaps the Horsa could take a shower as well or at least be in the room with the steam?  :D

John



Title: Re: Horsa-ing around
Post by: flydean1 on April 22, 2019, 10:24:52 PM
Remember, your swept leading edges will cause the 63% of root chord to probably be just fine.  The "real" location should be referenced to the average chord which accounts for sweepback.  However, you can ditch the calculations with the Abl method.


Title: Re: Horsa-ing around
Post by: abl on April 23, 2019, 02:57:58 AM
I've just noticed an important variation in the procedure which may account for several apparent inconsistencies - it looks as though the last picture shows that someone in the R&D Dept is about to launch the thing backwards...

 :)

A.