By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by CML

Warped wings

Advice welcomed

All Topics | Latest Posts

Search for:  in Thread Title in  
Tim Saddler26/02/2019 13:09:48
3 forum posts

Hi all,
Just needing some advice on old school balsa and tissue construction method.
I'm building rubber powered 24-36 inch span models.
I've been doing this hobby for 45 years (did have a break for 30 years!) but i've never really managed to guarantee getting built up wings in line at the covering stage.
Before covering they seem in line but after applying 50/50 thinned dope i seem to end up with warping sometimes insignificant, sometimes horrendous.
Do people pin the wing down when applying the dope?
I've tried this and it helps on the top surface of a flat wing chord.
Not sure how you would do this for the bottom surface.

kc26/02/2019 19:13:00
5883 forum posts
168 photos

Hello Tim. Nobody seems to have answered your question yet! Very strange that the forum experts have not replied yet.....

I don't use tissue and dope on small built up wings so I cannot give a useful answer, but I think people do pin them down with spacers whilst the dope dries. No doubt someone else will help a bit more.

Most of us use iron on film for moderate size wings - the film from HobbyKing is a favourite now that Solarfilm is no longer made.

GrahamWh26/02/2019 20:19:36
avatar
355 forum posts
53 photos

Hi Tim,

If I remember rightly I have held the wing off the desk on balsa blocks and placed suitable weights on top at sensible positions above spars etc while the dope dries. I think I must have stopped the blocks sticking by having sellotape on them and moving them a little half way through. It's been a while though. Still have a lot of dope left in the workshop which I may never use again!

My last tissue covered model was an SE5a at 26" wingspan for electric power, before that an Aerographics Sopwith Camel adapted for RC.

Bert26/02/2019 20:46:46
511 forum posts
7 photos

The method I use is to dope both sides of the wing and then pin it down using scraps of 3mm balsa sheet to keep it all clear of the board. You can use scraps of polythene bags to stop the wing from sticking to the packing pieces.

I also do this when water shrinking the tissue, I always use Esaki lite from Balsa Cabin or FF Supplies which I put on damp using dope as the adhesive. I dope the bare framework first.

I hope this helps, it always works for me and many other free flight people.

Bert

Test Pilot26/02/2019 21:41:50
1 forum posts

Tim

I've had the same problem with lightweight structures on rubber models.

I solved it by shrinking the tissue in the normal way with a mist of water, then using non shrinking dope thinned 50/50. Never found it necessary to pin down anything but the smallest wings, but it's good advice and woldd give you even more chance of it coming out straight and true.

Since using this method I've had no problems.

Hope this helps.

TP

Tim Saddler27/02/2019 08:27:02
3 forum posts

Thanks for the advice guys - much appreciated...

I am recovering a rubber P30 model wings and tail that i found in the loft.

I will try Bert's method to avoid warps.

I did do an experiment with solarfilm for another model and found I still got a warp.

I suspect that the demise of "old style" gas fires where you could shrink and twist if you had any issues and only being able to use the iron to final shrink these days was the reason.

Thanks again guys

Engine Doctor27/02/2019 10:48:24
avatar
2207 forum posts
20 photos
Posted by kc on 26/02/2019 19:13:00:

Hello Tim. Nobody seems to have answered your question yet! Very strange that the forum experts have not replied yet.....

 

Possibly not that many of us who used dope and tissue left to answer ! smiley

I haven't used dope and tissue for years now as prefer Lightspan or Airspan .

Here is what I used to do. Pin or glue 1/4 inch balsa scrap on a board to support the wing edges and keep the wing or panel off of the board. Apply thinned dope 50/50 to bottom of panel and pin to the blocks. Now apply dope to the top of the panel and leave to dry thoroughly .

If panel is very light structure then but spray with water first to shrink the tissue and pin to blocks and allow to dry . If this shrinks it sufficiently tight then apply a thinned coat of non shrinking dope to seal the tissue . If you apply shrinking dope on a very light structure and its too strong then it will distort the frame and get a "Starved horse look" Again pin down until thoroughly dry . Panel should then remain straight.

Depending on what dope you use you may have to thin it more or less as it seems to vary wildly these days as does the quality of tissue .

It might pay to make some test frames to test your tissue shrinkage and dope strength.

Hope this helps

 

.

 

 

Edited By Engine Doctor on 27/02/2019 10:49:43

Stearman6527/02/2019 22:46:02
avatar
769 forum posts
893 photos

I've just been surfing for a small clipped wing cub builders kit & had another look at Sig, the kit & manual. In the manual, is a long spiel about what to do with a warped wing, which didn't fill me with enthusiasm for the kit, but may help Tim

"If the wing develops warps during covering and painting, it should be straightened. One good method is to spray on a thin
coat of clear dope on the warped half and allow to dry until it can be handled - but wait no longer than this. Block the wing
up on a flat surface in a twist that has approximately the same amount of warp in the opposite direction from the original
warp. For example, if the trailing edge is warped 1/4" down at the tip, block it up so that it is twisted into a position with 1/4"
up warp at the same spot. The covering will be somewhat stretchy at this point, with the dope not completely dried out.
The twisting can be done without much trouble and is started in the hands to begin the distortion required before fastening
down on a flat surface. Weights will be necessary to hold the wing in this position for about 24 hours. Don't put the wing on
wax paper or use it between the weights and the wing if you think the dope might be soft enough yet to stick. Use plastic
wrap for this purpose. Wax paper will hinder the dope drying process and may leave a residue that will make it
permanently sticky. When you first remove the wing from the twist it will remain for a while with the new oposite warp.
However, the dope is still not completely cured and the internal stresses of the first warp still remain in the structure. In
about a day, part of the first warp will twist back in the original direction. Hopefully. it will end up zero-zero when the dope
has completely cured, which will take at least a week. If not, a futher adjustment may be required, using the results of the
first attempt as a guide. It is a matter of guess work but the rule of thumb about twisting equally in the opposite direction
seems to work out well in practice."

crying

Edited By Stearman65 on 27/02/2019 22:49:22

Edited By Stearman65 on 27/02/2019 22:51:44

Bert28/02/2019 09:08:41
511 forum posts
7 photos

You can avoid all of that long-drawn out process by pinning the surfaces down after shrinking and doping.

if you do decide to go the twist it out route you will be doing it a lot because the warps will always come back.

Bert

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E! 

Latest Forum Posts
Support Our Partners
Motion RC
Slec
CML
Gliders Distribution
Wings & Wheels 2019
electricwingman 2017
Pepe Aircraft
Revoc
Sarik
Advertise With Us
Latest "For Sale" Ads
Does your club have a safety officer?
Q: Does your club have a safety officer, or is the emphasis on individual members to each be their own safety officer?

 Yes we have a SO
 No, it's down to everyone

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us