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Author Topic: Horsa-ing around  (Read 5680 times)
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Mefot
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« Reply #25 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.
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TheLurker
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« Reply #26 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.
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DavidJP
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« Reply #27 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. 
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TheLurker
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« Reply #28 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.
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Mefot
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« Reply #29 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  Grin
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TheLurker
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« Reply #30 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.
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OZPAF
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« Reply #31 on: January 27, 2019, 06:50:07 PM »

The undercarriage looks slid in the "flesh". Good work by the Lurker Industries Engineers.

John
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TheLurker
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« Reply #32 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.
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abl
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« Reply #33 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...  Smiley
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TheLurker
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« Reply #34 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*.  Smiley

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. Smiley
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TheLurker
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« Reply #35 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. Smiley


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.  Smiley

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dohrmc
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« Reply #36 on: February 02, 2019, 06:16:47 PM »

Really good stuff, and the pictures are looking good. Well done!
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TheLurker
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« Reply #37 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. Smiley
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abl
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« Reply #38 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.
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dohrmc
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« Reply #39 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”!
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TheLurker
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« Reply #40 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.
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OZPAF
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« Reply #41 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
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TheLurker
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« Reply #42 on: February 08, 2019, 08:35:45 AM »

Quote from: OZPAF
I take it - the sharp end punctures the egg and the chisel end...
Cheesy.  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.
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TheLurker
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« Reply #43 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.
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abl
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« Reply #44 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?...  Smiley
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« Reply #45 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.
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TheLurker
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« Reply #46 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?  Smiley

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?...  Smiley
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. Smiley
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« Reply #47 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!
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TheLurker
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« Reply #48 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) I could have got away with it!

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

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.
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TheLurker
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« Reply #49 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" Smiley  

*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.
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