Jig Builds straight wings - My A$$ !!

[Wynn Robins]

Currently I'm building the Brodak spitfire and using the wing jig with the arrow shaft rods - so I have done one panel - had it on the jig the whole time - everything is straight and true - looks good......

So last night I take it off the jig and set the TE on my glass benchtop - and lo and behold - it has bow in it.....how the HECK did that happen!!!!!

I thought for once I would have a totally straight wing - but doesnt look that way now - might have to get the kettle out and steam it....

Anyone have an idea as to why it might be bowed even when it was all straight during the build?

[Randy Powell]

Well, a lot depends on the structure used and the wood selection. Is it bowed vertically or horizontally?

One of the reason I personally don't like the arrow shaft jigs is I can never get everything lined up. With laser cut ribs and jig holes, I'm told it's much, much better. But I like a jig that locks up the leading and trailing edge and keeps them dead parallel to each other. That's why I use the modified Millennium sort of jig. But that's just me. Al Rabe uses this sort of jig and it obviously works for him. Pat Johnston (who designed the Brodak Spitfire) is also partial to it and he doesn't seem to have any problems. Hey, we all approach things differently, I guess. I'm happy with my method.

[Dick Fowler]

Well, a lot depends on the structure used and the wood selection. Is it bowed vertically or horizontally?

One of the reason I personally don't like the arrow shaft jigs is I can never get everything lined up. With laser cut ribs and jig holes, I'm told it's much, much better. But I like a jig that locks up the leading and trailing edge and keeps them dead parallel to each other. That's why I use the modified Millennium sort of jig. But that's just me. Al Rabe uses this sort of jig and it obviously works for him. Pat Johnston (who designed the Brodak Spitfire) is also partial to it and he doesn't seem to have any problems. Hey, we all approach things differently, I guess. I'm happy with my method.

Ditto! I've never been happy with wings built on rods. The Tom Morris Lincoln Log method is the best as described above by Randy.

[Allan Perret]

Its the combination of jig and straight wood.  Jig gets everything in alignment,  but if you force a curved spar or leading/trailing edge sheeting into the jigs alignment, you are building in components with stress.  When you take it out of the jig, the stress curve back to the natural state.  If your jigging is straight and you use straight wood the wing will come out straight.  I also like the jigs that support the le and te parrallel off the table.  The rods work also, but they are more hassel for me, 

[Matt Colan]

It could be the worktable you were building on.  Also the rods could be warped.  If it isn't even, the jig would set up to how the you table sits.  We spent a whole afternoon to get our worktable straight before even starting construction on the Ares.  I still have a warp in the outboard wing and am tweaking the flaps to get the wing level upright and inverted.

[Wynn Robins]

my build table is dead flat - believe me.....it is a 3' x 6' pice of 1/2" glass over MDF - shimmed where appropriate

I thought it may have been the wood, I guess that is what it is......I will get it figured.

I have built probably 100 planes - but never using this method - should have stuck to the tried and true I guess...

[john e. holliday]

I too have used the Tom Morris method, the CLC Jig, and my own jig using steel rods.  The only way I can get the trailing edge straight is by using straight aluminum angle material.  Of course I use white glue which is bad for warping wood until it dries.  Aluminum angle with aluminum rule on top has kept my trailing edges straight.  I use spring clamps to hold the alum.

I have never had the spars or leading edge bow on me as the spars are tied together with either vertical webs or the cross braces like Tom show.  DOC Holliday

[Jim Treace]

I, too am building the Brodak Spitfire and had trouble with a little wing warp. I used the Brodak rod jig. The wing is built in halves, then joined to get the dihedral. That's when the warp showed. I don't know what caused it, jig, wood, me?? (my table is flat and level). Regardless, a real hassle to get warp out of wing (both panels had warp), with dihedral, at least for me. Took both my wife and myself using lots of hot water and towels to finally get it out. It's now OK, but I am not sure about using the jig again.
Jim

[Jerry Tarnofsky]

If anyone is interested, I will be bringing this wing jig to Brodak's to sell.

Jerry

[Tom Niebuhr]

I have used all 3 methods.. Lost Foam, Lincoln Log, and 3/8" Rods. The area that will cause warps is attaching the leading edge sheeting. My kit construction manuals tell you NOT to force the aft edge of the sheeting to align with the aft edge of the spars.

Instead leave appro. 1/16" of the aft edge of the spars exposed when gluing the leading edge sheeting. Don't force the aft edge of the sheeting into being totally straight. This will prevent stresses from building up that cause warps.  This also has the additional benefit of leaving a little bit of the spar available for the forward edge of the cap strips to adhere to.

[Martin Quartim]

After having the same problem and looking at many wing jigs I put my thoughts towards designing a wing jig so I could do the top and bottom sheeting on the jig

The sliding ruler can be reversed to use a rectangular or a 45o square stick.

It will not work with wings that have a curved LE, though. But I guess the same concept could be used making  blocks.

Martin

[Larry Cunningham]

I'm beginning to believe wing jigs are not so important. One of my best
friends actually builds his stunter wings over a Lamborghini engine!

L.

"Life's Tragedy is that we get old to soon and wise too late." -Benjamin Franklin

[Serge_Krauss]

John Miller shows an interesting and perhaps original (is anything original in CL design and building technique?) jigging method in his Pathfinder L.E. article in the current FM. 'really well done, informative article!

SK

[john e. holliday]

Just got that mag yesterday and read the article last night.  Great pictures and a lot of info.  Also I received the previous FLying Models less than two weeks ago.  Does that mean the June issue will come next week?   By the way most of my profile Goldberg, Sterling and Sig kits were built in my lap.  That was the only way I could get them straight.  DOC Holliday

[John Miller]

John Miller shows an interesting and perhaps original (is anything original in CL design and building technique?) jigging method in his Pathfinder L.E. article in the current FM. 'really well done, informative article!

SK     

Thanks to all for their kind comments on the Pathfinder L.E. article. Gordan felt I was too long winded, but i felt that there should be a lot of information so that there would be few questions when a slightly different method was introduced.

Regarding the jigging method, I can't take credit for coming up with it. This method came about when Gordan and I were trying to come up with a method for building the Tony wing with dihydral. Gordan asked if something like this could be used. It was a good idea, and we worked it out as a collaburation from there.
I like the ability to construct abbout 90% of the wing while still jigged up, but it does require a flat work surface.

[Gordan Delaney]

Sometimes its not just the jig,or wood. Iv`e found that using alfatic or white glues will cause the bow in the trailing edge.
So now I use something differant. like Ambriod. I believe that the white glues have a water type base which will cause the wood to bow. Food for thought.

Gordy

[john e. holliday]

That is the reason I clamp my trailing edges between two peices of aluminum angle.  DOC Holliday

[Dallas Hanna]

Thought this may add another angle to approaching a wing jig.  It's only on the idea of the old "Adjusto Jig" from way back.  I had a supply of small pot magnets so I added a small V-block on top via a stud with lock nuts.  This way, the height of the "v"s can be adjusted to all be at the same height.    The only draw back is that the building board must be of a magnet attracting steel or cast iron.   One of my "boards" is two milling machine tables (new not used) end to end to make the jig 240mm x 2000mm.  It can also be cranked to dihedral if necessary. The T-slots come in handy for clamping.  The method could be used if strips of bright mild steel is placed on top of a normal timber board for the magnets to stay put.  Double side tape is great for the purpose of sticking the M.S strips to the board in the required stations.     I use a good straight edge or other suitable means to give zero across the surface for our straight winged stunters if I've used it for anything with dihedral.

Just out of curiosity, how do modellers check their building boards for flatness??

HH

[Larry Cunningham]

John Miller shows an interesting and perhaps original (is anything original in CL design and building technique?) jigging method in his Pathfinder L.E. article in the current FM. 'really well done, informative article!

SK

Just read that myself last night. Great article! Looks like the weight compares with a typical open bay wing, and finish should be light as well. I've seen the CF tow strands applied to some model fiberglass parts for RC models, and I also believe that Bob Geiske used something similar to stiffen a fuselage. (Seems like I saw that in a Bob Hunt video?)

You notice that Al Rabe uses fully planked wings and always seem to build pretty light models. The "secret" seems to be monocoque structures, which distribute loads smoothly over large surface areas. And I see Dee's wing structure as exploiting this feature as well.

Anyway, it's always interesting to me to see what the masters are doing and how they do it.

L.

"The sacred cows have come home to roost with a vengeance." -Student Bloopers

[jim gilmore]

Just a curious question here....
When you cover a wing with sheeting, do you attempt to make the sheeting curved and then glue it down or do you just start at the leading edge and glue it without an attempt to make it curved first ?
the first way will glue the sheeting to the ribs ad structure with very little preload. The second can create lot of preload and when you remove the rods it's hard to say what it will do....

[Leester]

I usually wet the wood first so it will bend and not crack and works pretty good since using C/A it's not effected by the wet wood.

[Russell Shaffer]

You are right, Jim.  I once built a Nobler wing on a jig and forced the LE sheeting into place.  Everything was great until I took it out of the jig.  I never could get that wing completely straight.

[Air Ministry .]

You can get big problems with temperature / humidity .

If your workshop is siberian , and the ' to use ' timber is on the widowsill in the sun , things get uneven .

In a house that leaked like a sieve , arctic conditions , log fire , wings framed and set on the wall
went crescent along the span , overnight . Strightened out mid afternon , if the weather improved .

So one thinks the best ' ready wood ' storage is adjacent the building board , so any linear / temperature
THING is kept even . Green 9 unseasoned ) timber is likely more prone to it . We all store our wood
a few years before use , Eh . 

Timber stored in the sun , or in the rafters of a tin roof , for ten years , hardens up nicely .

Pre Block sanding the wing sheeting , a few coats of dope , flat off again , dampen inside ( undoped side )

and taped overnight to a 6 in. pvc. tube , was precurved - so opened the curve to fit L.E. . Seemed to work o.k. .

 

[tom_weedman]

If anyone is interested, I will be bringing this wing jig to Brodak's to sell.

Jerry

Pm sent Tom Weedman

[Steve Helmick]

Might possibly have been sold, Thomas. Look at the date of Jerry's post. One of the hazards of the ol' Interweb!  Steve

[RknRusty]

I fully respect that a lot of y'all are way over my current building experience level, but I still have observations that seem undeniable... one is, balsa moves around like a barometer. I don't have much environmental control in my shop, and my wing skeletons remain uncovered through seasonal changes. I've jigged, and I've built loose on the flat table top. Not only does humidity cause shape changes, but so does sanding. Especially the radical sanding of a square half inch LE dowel. Fibers holding its original shape get released, so even with the jig forcing it to remain straight, removing the jig allows everything to sproing into its comfortable new form, and that leaves you with some twists and turns.

I think the best thing to do is to spray it with ammonia Windex while it's still jigged. It's my understanding from reading many build articles and threads that the ammonia weakens the lignin connective tissue allowing the wood to relax into the forced shape from the jig. Upon drying, the lignin regains its strength holding the wood into it's jigged shape... or at least close to it.

Before installation, I always place a pair of 36 or 48" CF tubes between the spar and TE, then step back 15' and eyeball them to confirm they're parallel. Any deviation is small and can usually be forced out with another shot of Windex and some over-twisting, taping it into that shape overnight till the ammonia dries, and so far Mine always come out straight. I do the CF rod test in different areas. First between each halve's tip rib and root rib, them finally one rod on each tip for a final check. That ensures that if only one of the two sides is out of shape, you don't go twisting both panels to straighten it. It's always a happy feeling when both rods finally lay parallel. If it's a non-sheeted LE, you can also place the rods between the spar and LE for an even more accurate assessment.

This always works for me, and I rarely have to try and force out a slight twist with the covering... yes, I'm still a Monokote hack.

I have pictures, but my alarm rings in 130 minutes, Yaaaawn. In case my description is unclear, I'll find the pics tomorrow afternoon.
Rusty

[FLOYD CARTER]

Many responses suggesting many more causes for built-in warps.  Allan Perrot was first to identify the major cause;  forcing parts together will guarantee a warp!

I always use 1/4" steel rods for building wings, and without any problems.  If you find any parts not fitting together easily together before gluing, you must relieve the interference.

If a spar is straight before assembly, it is unlikely to later bend all by itself.