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Author Topic: Horsa-ing around  (Read 5749 times)
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dohrmc
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« Reply #50 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!!
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dohrmc
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« Reply #51 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.
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TheLurker
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« Reply #52 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.



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TheLurker
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« Reply #53 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.
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OZPAF
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« Reply #54 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 Smiley

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

John
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abl
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« Reply #55 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).
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OZPAF
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« Reply #56 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
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TheLurker
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« Reply #57 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.
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cvasecuk
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« Reply #58 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
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TheLurker
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« Reply #59 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.  Smiley

Edit to Add.
Ah. I have it.  My excuse is that this is now a semi-scale model.  Cheesy
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dohrmc
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« Reply #60 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.
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dohrmc
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« Reply #61 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.
 
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Indoorflyer
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« Reply #62 on: February 20, 2019, 07:35:25 PM »

Here we go
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abl
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« Reply #63 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.  Smiley

BTW, Lurk - have you left space for a ballast box in the tail...?
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cvasecuk
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« Reply #64 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
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Indoorflyer
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« Reply #65 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
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TheLurker
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« Reply #66 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. Smiley
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abl
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« Reply #67 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.
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dohrmc
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« Reply #68 on: February 21, 2019, 06:20:42 PM »

Go with what you got.
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OZPAF
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« Reply #69 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
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TheLurker
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« Reply #70 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.
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TheLurker
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« Reply #71 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...  
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TheLurker
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« Reply #72 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 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.
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abl
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« Reply #73 on: March 06, 2019, 09:56:21 AM »

That looks much better, Lurk...
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TheLurker
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« Reply #74 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? Smiley

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.
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