Washout

[Basil]

I have to build a wing with 'Washout' according to the article. Question one, how do you do this?

Second ; How do I measure 2Degs of washout, or put another way how do I build in 2 degs of W/O for a wing thats 31" in length (each wing)attatched to wing stubs already present?

What about the ailerons, as they cover half the wing length, surely they must show the same characteristics.!!!!! Build wing first then make to fit?

Bas

[Ernie]

Hi Basil, Probably the easiest way is to make a wedge with an angle of 2°,( you can use a school potractor to do this) and a long side equal to the tip chord of your wing. Make it nice and thick, say 1/8

You can use this to pack up the trailing edge of your wing

ernie

[Basil]

Thanks Ernie, so the measure of 2 degs is along the wing tip, not the wing length?? Makes sense, thanks.

What do you do about the Ailerons, I had presumed that they would still be in line with the rear wing edge as normal.

bas

Edited May 5 by Basil

[Simon Chaddock]

Basil

You are correct. In theory the aileron should have the same washout effect. If you built is flat then each end would not line up exactly with the wing. Obviously the longer the aileron the more it will show. The significance of the difference will also depend on the chord of the aileron. A narrow strip aileron it would hardly show but with a broad one it would.

A "technical" solution is to use a building board with a 2 degree washout. If you build the aileron at the same time as the wing it will exactly follow the wing washout.

On the other hand If you choose to build a flat aileron it would be advisable to set it so its outer tip is inline with the wing. That will at least preserve the desired wash out at the wing tip where its beneficial effect is greatest.

Setting up differential aileron movement (more up than down) will reduce the chance of a control input triggers a tip stall.

Be aware that the wing section, its build accuracy and torsional rigidity will effect the benefit that washout can provide to reduce the effect of a tip stall and thus the progress towards a spin. 
Pilot skill is also significant. Avoid a low slow flat final turn on the landing approach. 😉 

I hope this helps. 

 

[Ernie]

Yes Basil   The aim is to have the angle of the wing at the tip  different  to that at the chord. this helps to prevent the dreaded tip stall. Too slow a turn,,tip of wing which is moving slower than the remainder stops working...splat

ernie

 

[Engine Doctor]

Why not just measure a 2 degree angle on the bottom edge of plan and extend the base and angle line to the span of your wing then measure the gap. Pack the tip of the wing trailing edge up by this ammount and pin in position when building and by progressivly smaller ammounts pwcked and pinned towards the root where it should sit flat on the board as should all of the leading edge. Very simple method to set the chord at the root at a different angle to the chord at the tip. Often ailerons are built into the wing at this stage and cut out when wing has set and have the same twist as the wing . Strip ailerons should be easy and line up at both ends as they usually extend the full length of the  trailing edge wich should be staight just set at the two degrees from base to tip with no actual twist  . Problems can  occur with ailetons lining up when the w/o is twisted into a wing after construction . 

If wing is of a flexible construction make sure that the washout is the same on both wings after covering. 

[shepeiro]

One thing I would like to ask related to topic is how to preserve a built in washout during the covering process. 
 

my recent twin model had 2 deg washout built in (similar fashion to what Engine doc outlines above) unfortunately when I popped the left wing off build board I noticed it had slightly less than right wing (not sure how tbh).  
I fixed this in the covering stage as when I shrunk the tissue with water I repinned the wings and after it looked perfect. Unfortunately when I doped the extra shrink added a slight twist again. 
 

I think I can re-wet and pin it again to fix but how do you prevent it from twisting when doping? Was afraid to pin it to stuff as it would potentially stick and spoil the finish

[Engine Doctor]

The only way to hold desired washout when doping is to pin down securely while its drying.

A decent wing design Usually on slightly larger models will usually have "D" box construction to make wing more rigid and hold in any washout. Light structure tend to be more flimsy and rely on the covering for their rigidity so they need to be held securely while drying. 

[Ernie]

Yes, you have to pin it down. I think to  best option is to build in the twist, rather than to try to distort a flat wing, but It still needs pinning. Bet you wish you never asked

ernie

[shepeiro]

I think I can recover it as I use thinned dope so it’s still permeable. 
 

how do you avoid the dope sticking the wing to what your pinning down to?

Edited May 7 by shepeiro

[J D 8 - Moderator]

Use balsa packing bits and cover them with polythene to prevent sticking.

[Piers Bowlan]

If you really want to prevent sticking use cellophane (as used in florists shops) available on eBay.

[Engine Doctor]

Any of the above. One other thing about drying. Dry isnt just touch dry. Wing should stay pinned down for 24 hrs possibly longer to allow dope to fully dry as shrinkage contiues after dope is touch dry . A too powerful dope mix can seriously deform a wing. I used to water shrink tissue then if happy with result apply a very thinned coat of dope .  Now non shrinking dope is often used now fill the weave of tissue without distortion of the frame.

One thing forgot to ask did you prime all the wing and tissue contact areas with full strength dope and allow to dry before applying and water shrinking the tissue? This is needed as once water shrinkage is complete and a thinned dope or thinners is applied it melts the full strength dope previously applied and fixes the tissue to the structure making it rigid. Very necessary for light flimsy structures.

[shepeiro]

8 hours ago, Engine Doctor said:

Any of the above. One other thing about drying. Dry isnt just touch dry. Wing should stay pinned down for 24 hrs possibly longer to allow dope to fully dry as shrinkage contiues after dope is touch dry . A too powerful dope mix can seriously deform a wing. I used to water shrink tissue then if happy with result apply a very thinned coat of dope .  Now non shrinking dope is often used now fill the weave of tissue without distortion of the frame.

One thing forgot to ask did you prime all the wing and tissue contact areas with full strength dope and allow to dry before applying and water shrinking the tissue? This is needed as once water shrinkage is complete and a thinned dope or thinners is applied it melts the full strength dope previously applied and fixes the tissue to the structure making it rigid. Very necessary for light flimsy structures.

no I have heard of this technique but I dry fix my tissue with purple glue stick then very light mist with water after. So it should already be affixed and rigid once dried.  This last wing is the first I have had an issue with using this technique but is also my lightest built around 3g per wing. 

[Basil]

Hi again, I now understand what wash out is. Usually If every item is a good tight fit on dry asy , I can  go round with the Cyno. So if thats the case with the wings in question, I can  pin to board raising the rear of the wing tip , in my case by 1/4", then add cyno. The wing  edge is only pinned on the LE and inner TE.  Assuming that its flexible enough to get the twist  that is!!!!!.Bas

 

[Engine Doctor]

On 08/05/2025 at 18:55, shepeiro said:

no I have heard of this technique but I dry fix my tissue with purple glue stick then very light mist with water after. So it should already be affixed and rigid once dried.  This last wing is the first I have had an issue with using this technique butH8  is also my lightest built around 3g per wing. 

Hi shepeiro. The technique you use doesnt allow the tissue to shrink as a whole over the wing locking it in place. Using dope yo fix it in place then allows the tissue to move while the solvent softens the bond then when dry holds all of the desired twist / washout to lock in place. Using purple glue? Will not allow tissue to move and shriink as one and each section might be slightly tighter before shrinking. 

[shepeiro]

1 hour ago, Engine Doctor said:

Hi shepeiro. The technique you use doesnt allow the tissue to shrink as a whole over the wing locking it in place. Using dope yo fix it in place then allows the tissue to move while the solvent softens the bond then when dry holds all of the desired twist / washout to lock in place. Using purple glue? Will not allow tissue to move and shriink as one and each section might be slightly tighter before shrinking. 

thank you for that explanation. The next stick and tissue model I will try that with as I’m definitely thinking I could get a better finish than I am currently and if it allows the wing to set better in place then it’s worth the extra hassle.