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Author Topic: Horsa-ing around  (Read 5523 times)
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TheLurker
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« Reply #100 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. Smiley

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. 
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OZPAF
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« Reply #101 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 Smiley

John
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TheLurker
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« Reply #102 on: March 31, 2019, 09:04:51 AM »

Quote from: OZPAF
...chief Engineer almost went mad...
Almost? Smiley

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. Smiley

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. Smiley

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.
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TheLurker
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« Reply #103 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.
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OZPAF
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« Reply #104 on: March 31, 2019, 08:03:29 PM »

Nice work Mr Lurk - however(yes there is always a however Smiley) 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 Smiley

John
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TheLurker
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« Reply #105 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 Smiley
You! Boy!  Stop talking at the back there!  Yes you Ozpaf.   Take 500 lines, "I must pay attention in class." Smiley

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.
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OZPAF
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« Reply #106 on: April 01, 2019, 08:36:10 PM »

Ah yes! I do seem to remember a few discussions on this now you mention it. Embarrassed Slits in straws etc.

I should stop snoozing in class Smiley

John
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TheLurker
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« Reply #107 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.
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OZPAF
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« Reply #108 on: April 02, 2019, 05:56:21 PM »

Not bad - very Horsarish!  Smiley 

John
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Pete Fardell
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« Reply #109 on: April 02, 2019, 06:04:32 PM »

Looking very good, Lurks. I'd certainly trust it to carry my army over the Channel.
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DavidJP
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« Reply #110 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!
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TheLurker
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« Reply #111 on: April 03, 2019, 01:01:02 PM »

Quote from: OZPAF
...Horsarish!  Smiley 
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. Smiley

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. Smiley
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Mark Braunlich
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« Reply #112 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.
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Mark
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« Reply #113 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.
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abl
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Andy Blackburn



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« Reply #114 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...
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TheLurker
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« Reply #115 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.
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DavidJP
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« Reply #116 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.
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TheLurker
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« Reply #117 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. Smiley

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. Smiley

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..
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TheLurker
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« Reply #118 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.
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TheLurker
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« Reply #119 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.
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OZPAF
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« Reply #120 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?  Cheesy

John

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« Reply #121 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.
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Andy Blackburn



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« Reply #122 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...

 Smiley

A.
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TheLurker
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« Reply #123 on: April 23, 2019, 02:23:36 PM »

Quote from: OZPAF
...steam?
Unfortunately that wing panel has already been steamed a couple of times.  It really is a case of me biting the bullet and replacing the duff panel.

Quote from: abl
... it looks as though the last picture shows that someone in the R&D Dept is about to launch the thing backwards...
Yes, there's always one who thinks a canard layout is better.  Shame really as his work's pretty good otherwise. Smiley
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TheLurker
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« Reply #124 on: April 27, 2019, 08:46:25 AM »

Quote from: TheLurker
... a case of me biting the bullet and replacing the duff panel.
I couldn't bear to look at it anymore.  The wing has been completely stripped.  Re-covering scheduled for later today. Am also very tempted to re-do the fuselage, but I'm running out of Al. tissue and getting the wing right is more important.
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