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Author Topic: Bungee Launch 36" Gliders  (Read 31788 times)
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glidermaster
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« Reply #375 on: July 18, 2018, 07:21:39 PM »

Spar-less wings were quite common, and are certainly prone to the warping trouble your describe - i.e. the dihedral/polyhedral tends to increase. Back then I believe they were better off for dope like substances generally, and could possibly control shrinkage a little more adeptly than we can by using banana oil or low shrink dope. Some stub spars, gussets and/or sheeting in the middle bays would certainly be a wise modification, assuming you are not fanatically following the plan.
When I was young my Dad gave me some old rubber and Jetex models that were of the spar-less wing type, and my memory is that they used harder material than we might choose today, for the leading and trailing edges.


John
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TheLurker
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« Reply #376 on: July 19, 2018, 12:35:43 PM »

Thanks for those thoughts John.

...assuming you are not fanatically following the plan.

I had hoped to build it according to the plan as published, but there's no point being dogmatic about it if the result is unflyable; that'd just be a waste of wood, time and tissue.  So it looks like it's going to be the world's first Walthew MK IIa.  After all we must never let it be said that The Lurker Industries Aviation Company isn't at the cutting edge, even if the design is 70 years old. Smiley
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TheLurker
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« Reply #377 on: July 21, 2018, 04:08:46 PM »

As discussed one part finished Walthew MKIIA wing.  

I'm going to try cutting the spar at R4/R13, so that the centre section spar'll extend to R5/R12, and the panels R4/5 and R12/13 will be spar-less.

If you're even vaguely interested; wing build images starting here

Haven't had a chance to muck around with the tow hook on the Swallow yet, too busy sitting in a pub garden today.
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LASTWOODSMAN
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« Reply #378 on: July 21, 2018, 05:51:06 PM »

Nice pics of your model Lurker.   Smiley   Looks like you have a nice and neat building area    Cool  - what type of building board do you use and what are the dimensions ?

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Richard
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« Reply #379 on: July 21, 2018, 08:46:51 PM »

Like your little notes as well Lurk. Shouldn't they have the Lurker Industries Logo on them? Smiley Something like a hat with wings? Smiley
It looks like you are running the spar from tip to tip but you mention in your post that you will be leaving 2 panels spar less? I would leave it as you have shown - that is a delicate wing!
Clean work - Lurker Industries must employ more sweepers than actually builders Smiley

John
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TheLurker
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« Reply #380 on: July 22, 2018, 04:12:48 AM »

Quote from: OZPAF
I would leave it as you have shown - that is a delicate wing!
Aye, it is delicate and I think I'd advise fitting a spar to this wing regardless of potental warping issues, ditto not butt-jointing the ribs to the L.E & T.E.

Unfortunately it can't be left as is.  The wing has to be cut outboard of Rs 5/12 to set the dihedral, see the sketch.   I built it as it is so that I'd get a good alignment on the spar.

I haven't worked out a neat way of covering the gap over panels R4/5 & R12/13.  There's no a lot of wood to play with in the ribs and I fear that taking any more out of them would weaken them a bit too much.  Had the ribs been meatier I'd have moved the spars on the outboard sections forward/back by the width of the spar, doubled the spar slot width on Rs 4/12 and overlapped the central spar and outboard spars at Rs 4/12.   As it is I'm hoping that the fairly beefy ply dihedral braces on the L.E. & T.E. that extend into panels R4/5 & R12/13 will counteract any tendency to increase in dihedral caused by tissue tension.  We'll shall see.

Quote from: LASTWOODSMAN

... a nice and neat building area

Quote from: OZPAF

....employ more sweepers than actual builders.

Neat work space? Oh that's dreadfully easy.  Work on the dining room table and set it up and tear it down at the beginning and end of each session.  Rules, tools etc. packed into a couple of boxes.   On the other hand my study, which is where I do paid work, is a little *ahem* cluttered.  It doubles, quintuples?, as my office, library, wood store, cycling kit store and hangar.

Quote from: LASTWOODSMAN

...what type of building board..

The building board is 36" x 20".  Half inch cork over 3/4" pine.  Pine from my local DIY warehouse.  Cork from Cantrill, details here.
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OZPAF
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« Reply #381 on: July 22, 2018, 08:39:15 PM »

Quote
As it is I'm hoping that the fairly beefy ply dihedral braces on the L.E. & T.E. that extend into panels R4/5 & R12/13 will counteract any tendency to increase in dihedral caused by tissue tension.  We'll shall see.

I don't think I would trust the braces at the LE and TE to do that. There may be a stress riser at the inboard end of the tip panel spar as well. How about leaving the tip panel spar continuing to the dihedral break rib and adding gussets between the spar and the dihedral rib on the tip and centre panel joins, much he same as the centre spar carry through on the KK ELF. Together with the braces this should be reasonable, without much extra weight.

Anyway happy building.

John
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TheLurker
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« Reply #382 on: July 23, 2018, 04:14:02 AM »

Quote from: OZPAF
How about leaving the tip panel spar continuing to the dihedral break rib...
Hmmm.  That sounds like a much better idea.  I shall nick it and pass it off as my own.  Smiley

I can see it being a bit of a fiddle to cut the spar without breaking it and losing too much wood at the cut, but got to be worth a try.   If it comes to it I can resort to one of the bodges I'd considered, but discounted on grounds of weight and general ugliness, of putting in a short "stand-alone" spar supported by gussets either end or a strip of 1/16" x 1/8" as an "I" beam.
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OZPAF
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« Reply #383 on: July 23, 2018, 05:47:52 AM »

Glad it helps, Lurk. You shouldn't have much trouble getting the spar length correct. Bevel the LE and TE to suit the dihedral angle before adding the tip spar. Then bevel it separately using a gauge and add it to the wing.

Again I had to do something similar on my still unfinished KK Elf - apologies Andrew D, who sent me a clean accurate plan.

Happy building.

John
 
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TheLurker
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« Reply #384 on: July 24, 2018, 12:55:12 PM »

Well that went better than I had any right to expect.  Tip dihedral set.  Now for the really difficult bit, getting a decent L.E. profile. Smiley

If you're considering building a Walthew MKIIA wing, i.e. with a spar, I'd suggest that the wing is built in three parts*.  The central section and the two outer sections. This will require 18 ribs rather than 16.  Set the dihedral on the inmost ribs of the outer sections and glue the sections together at the rib faces.  This will mean you don't need the ply dihedral braces, but you may want to add bracing gussets at L.E. and T.E.  A 3 section wing will be very much quicker to build than the approach I've used.

For those morbidly fascinated by people doing things the hard way the dihedral set up for this build begins here.

After I've got the build out of the way I'll draw up a 3 section wing plan and stick it in the gallery together with any notes of archaeological  interest uncovered on this "dig".

*ABL.  You were right.  It would have been easier.
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applehoney
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« Reply #385 on: July 24, 2018, 02:25:35 PM »

>Set the dihedral on the inmost ribs of the outer sections and glue the sections together at the rib faces

May I suggest you set the end ribs of the center section, and the inner end ribs of the tip panels, at 50% apiece of the overall dihedral angle?   I've built many glider and gas models wings in this manner with no in-flight failures.  In the event of an unfortunate impact with terra firma a broken-off tip is usually a clean separation without spar, LE and TE damage
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OZPAF
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« Reply #386 on: July 24, 2018, 08:45:45 PM »

I'm glad it worked for you. It's all very old hat but I only realised how it well it works when building the ELF.

AH raises a good point from his long experience but perhaps the gussets may help in your case as you only have a sliced rib of very shallow depth for this model.

I would prefer taking AH's approach with double ribs butt jointed together in future builds for the easier repair.

John
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TheLurker
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« Reply #387 on: July 25, 2018, 02:25:16 AM »

AH > ...at 50% apiece of the overall dihedral angle...
A good idea, if you're a better builder than me. I have enough trouble getting one piece of wood sanded to the right angle never mind two. Smiley

OZPAF > ...double ribs butt jointed together...
That's what I thought I'd described, or were you querying the suggestion of gussets with butt-jointed ribs?  Note to self: Mustt lern to rite betterer inglish. Smiley

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OZPAF
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« Reply #388 on: July 25, 2018, 05:03:16 AM »

My apologies - I just didn't read your description of the MK 11A wing! Nothing wong wit wot yu rote!

However as doing this relies on the area of the butted ribs to transfer the load it may nor be strong enough for this model.

Quote
Insert Quote

AH > ...at 50% apiece of the overall dihedral angle...
A good idea, if you're a better builder than me. I have enough trouble getting one piece of wood sanded to the right angle never mind two. Smiley

Use a dihedral gauges to guide your sanding block and it will be ok.

John
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TheLurker
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« Reply #389 on: July 25, 2018, 03:37:49 PM »

OZPAF > However as doing this relies on the area of the butted ribs to transfer the load it may nor be strong enough for this model.

Aye, a possibility, but as I wasn't able to get near my building board today I scratched out plan for the B (3 section) wing as outlined above anyway, rather than the A "cut and shut with a spar" variant that I've built.  It's especially for those reckless souls who fancy their chances with a completely untested "design".   Paging Mr. Fardell, paging Mr. Fardell. Will Mr. Fardell please go to the green courtesy telephone by the elephant trap. Smiley 

The B construction variant'll turn up in the gallery in due course.

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TheLurker
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« Reply #390 on: August 28, 2018, 04:21:47 PM »

Well, the Walthew MK II (A) flies.  Lovely and calm this evening so grabbed an hour this evening to see how it'd go off a bungee. The first couple of launches were low power affairs.  There's quite a bit of room for improvement; current endurance is no better than 15s and I need to undo some of my trim *ahem* improvements that I made and tinker with the forward hook because on higher power launches it's hanging on to the hook and losing some height as a result.


Second, short stretch, launch :  linky
Hanging on to the hook:  linky
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billdennis747
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« Reply #391 on: August 29, 2018, 02:14:40 AM »

Just bend the hook down till it comes off easily
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TheLurker
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« Reply #392 on: August 29, 2018, 02:23:43 PM »

Quote from: billdennis747
Just bend the hook down till it comes off easily
That's the plan, such as it is, but the parish idiot didn't take any pliers with him last night did he?  Really, what kind of an unthinking clot, knowing minor tow-hook fettling is likely to be necessary, doesn't take a couple or pairs of pliers with him for the first launches?  That last Q. was rhetorical, in case it's not obvious. Smiley
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billdennis747
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« Reply #393 on: August 29, 2018, 02:39:04 PM »

Quote from: billdennis747
Just bend the hook down till it comes off easily
That's the plan, such as it is, but the parish idiot didn't take any pliers with him last night did he?  Really, what kind of an unthinking clot, knowing minor tow-hook fettling is likely to be necessary, doesn't take a couple or pairs of pliers with him for the first launches?  That last Q. was rhetorical, in case it's not obvious. Smiley
Well nor did I but fingers and brute force work too, unless the hook is 14swg!
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Indoorflyer
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« Reply #394 on: August 29, 2018, 03:12:28 PM »

Always use precision tools around aeroplanes large and small. An automobile door jamb and a tire changing iron will provide the necessary bending forces required...
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Pete Fardell
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« Reply #395 on: September 10, 2018, 06:36:52 AM »

I'm really enjoying following your adventures with the Walthew, Lurks.

I made some pleasing progress with my Frog Petrel at Peterborough yesterday. To start with it was sometimes going up well, but then either not coming off the line or else coming off but flying poorly. Eventually though, some slight change to nose weight and a shim (actually a grass stalk) under the tailplane suddenly sorted it out. What really helped too was that after getting fed up with messing with fiddly bits of thread, and suspecting the wind was lifting the tail from the fuselage, I simply abandoned the AR and DT and just made sure the tail was banded down properly and the rudder fixed straight. It then got very high on the line which was very exciting for me to watch (in a completely different way to watching a rubber scale model's flight).
Anyway, best flight was 26 seconds which is hardly world beating I know, but it looked pretty good in the air and with its other two contest flights that was enough for second place on the very blustery day. The event was won by one C Costa from Portugal, who was here as a guest of JĂșlio Isidro (long time regular Peterborough vistor and TV star). From what was said at the prize giving I understand Mr Costa, now in his eighties, is some kind of freeflight champion so I was very honoured to be beaten by him!

I not only got one of Russ's nice certificates but, after the prizes proper had finished, Hi-Start instigator Dave Rumball sidled up in the manner of Private Walker and quietly handed me this framed AM cover poster to encourage me further in Hi-Start and, he said, just because he'd really enjoyed watching the Petrel's flights. What a gent!
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TheLurker
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« Reply #396 on: September 10, 2018, 01:52:43 PM »

Quote from: Pete Fardell
...the Walthew...
[JoeWalker]
Psst, wanna plan?  Cheap.  No rubbish; honest.
[/JoeWalker]

Quote from: Pete Fardell
...best flight was 26 seconds...
Sounds like a very respectable time to me given how windy it was yesterday.  Seeing how blustery it was here yesterday I'm surprised that anyone got any flying in at all.

Quote from: Pete Fardell
...handed me this framed AM cover poster...
I'm rather jealous of that. Smiley
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LASTWOODSMAN
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« Reply #397 on: September 10, 2018, 10:22:37 PM »

 Congratulations Pete !    Cool
     Regarding Pete's nice framed AM cover poster prize,  in reply  #395 above, for 2nd place in the Bungee Launch 36"  glider category - are there any old time glider modeller experts who would be able to identify the two gliders on the cover, what size they were, were they kitted, and what plans ?   Those look like two perfect "old time" gliders, that I would like to build one thereof, this winter.  Thanks for any help.

LASTWOODSMAN
Richard
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« Reply #398 on: September 11, 2018, 09:40:35 AM »

Just a generic painting, Richard.
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