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Warped Wing Recovery


Andy J
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Have a one piece wing which has a foam core, hardwood skin covered with cloth and epoxy belonging to a 6ft wingspan warbird. Unfortunately the model flies with a significant deflection on one wing aileron due to an alignment issue when the wing was originally built resulting in one half of the wing having a different incidence angle at the tip in relation to the other.  Don't think this situation can be recovered unless anyone has any novel ideas I can try.

 

Did think I could build another wing but that is a lot of work given the wing has retracts and flaps so open to any suggestions I could try.

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  I have come across before and the only way I could think of was to saw through the centre section and sand away as much of the original joint bandage/glue before joining back in the correct position. This was on a high wing trainer, very probably a simpler job than on your warbird.

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 It may or may not have a brace but most wings of this type rely on the fibre bandage and its epoxy to bind the obechi skins together, there is little actual strength in the foam its self.  Should there be a brace perhaps a carbon strip could be inserted.

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Presumably it is obvious that that the two halves are misaligned at the root Andy? If the two wing panels are aligned at the root but there is twist in one of the wing halves at the tip (warped) then obviously there is not a lot you can do about that, apart from build another wing, like you say. It could also be worth checking the lateral balance point of the wing, for if one wings is significantly heavier than the other (not uncommon with epoxy/glass wings) this will also affect the lateral trim. In addition! A twist in the fuselage can cause roll (further effect of yaw is roll) requiring aileron trim to correct. I just thought I would add my two penny worth to be clear on what is causing your problem before you saw your lovely wing in half! ? If you can’t live with it the way it is, then there is nothing for it but to saw away, through the spar and all. (if there is one).
I have made several foam wings over the years and usually I make a vertical slot in the wing roots and then cut a full-depth ply web (1mm thick) as a dihedral brace, which I securely epoxy into the foam. A layer of glass cloth and epoxy across the joint should render the wing pretty indestructible.?

I hope you get it sorted Andy and good luck. 

Edited by Piers Bowlan
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If it flies ok then why bother , aileron deflection cant be seen when flying. what is the  significant Aileron trim ?  I have seen some real  horors fly really well with a bit of trimming. They wont win any prizes for accurate aerobatics but fly ok. I'm not saying building like that is OK, far from it . 1, If the joint at the root is aligned ok then the fault/ twist was built in when the veneer was applied to the foam cores . No going back i'm afaraid  and no way of twisting a glassed foam wing succesfully that I am aware of   . 2, If the root is misalligned then cutting and resetting could cure the problem .   If the former  then making a new wing panel is probably the only solution and thats a  lot of work and probably expence to look right in the pits when you could just pull aileron into line while its in the pits ?

 

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Looked again at the wing today and could observe little in terms of the wing tip TE & LE heights in relation to a reference bench line being significantly different. So decided to investigate further as an inbuilt warp does not appear to be the cause of the out of trim condition.

 

Model has not been flown for well over a year so powered up the radio to see what trim setting had been used in the past.

 

Port aileron was sitting a good 3/16" up in relation to the  stb aileron which was at neutral. Tx had full left trim applied which indicates the model has an inbuilt turn to Stb requiring drag on the Port side to achieve straight and level flight.

 

Checked the balanced of the wing and found the Port side heavier which would have helped the inbuilt Stb turn, so don't think that is the cause of the problem.

 

Having refitted the wing noted there appeared some minor misalignment in relation to the tail. Viewing the model from the rear the Port wing seat was high thus forcing the tail to sit as if the model was banked to the right.  Not 100% sure if this is the cause of the out of trim condition but never the less I sanded back the wing seat to achieve a more aligned reference of the tail to the wing.

 

Will now refit the motor and give it another flight to see what happens.

 

 

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12 x8 or 13 x 7 ? Did you balance the wing ? Are ailerons on separate channels or on a "y" lead ? Seems strange that just the port aileron is up and starbd at neutral ? Could it be just a porly set up model ?  If you  say that the wing isn't badly warped then set port aileron to neutral and fly it , making any correction on the sticks. You can then adjust accordingly and make any changes needed.

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 Perhaps worth a look at the aileron itself, is it flat ? Had one once that had warped into a curve for up becoming its own mini aerofoil.

   Read about a Lancaster in squadron service that pilots found to be something of a pig to fly until someone noticed the elevators were upside down and on the wrong side.:classic_ohmy:

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8 hours ago, Engine Doctor said:

12 x8 or 13 x 7 

Installed a 13x6 as could not find anything more suitable, so not far from your recommendations ED.

 

Will try removing some of the adverse yaw trim before I fly as possibly the misaligned wing was the issue but not totally convinced.

 

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Foam wings are usually quite resistant to warps, so if there is no obvious or large misalignment, as someone else said, perhaps the ailerons themselves are warped/mis-shaped? That would at least be a reasonably easy fix. 

 

Also look at fin/rudder alignment. A yaw trim issue could be showing up a roll couple, so it might not necessarily be wing that is the cause. 

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Flew the model yesterday and whilst the amount of left trim required has reduced some aileron deflection is still present.

Unfortunatly an underacariage retract failure prevented further test flights as the leg kept collapsing.

Will get someone else to look at the model as for me there appears nothing obvious as to the reason of the inbuilt left turn.

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Hi Andy . Did you balance the wing ? Were both ailerons set to neutral ? Is fuselage true and is the tail fin set true? Is engine alignment OK ie correct amount of offset ?  As Matt says in earlier post ,check the rudder fin alignment.  An offset or incorrectly set fin and rudder usually make a model yaw but some designs will react with a roll while pitching down and need opposite aileron to correct it. If anything needs adjusting only adjust one thing g  at a time and retest.  Hope you get it sorted.

Edited by Engine Doctor
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Looking again at the wing I have now convinced myself that the wing is indeed twisted with one TE lower than the other so think I will have to live with it.

Further test flights where aborted yesterday as the retracts continue to play up with one leg refusing to extend.

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   I have a model of a Citabria pro, an aerobatic prototype from the 60's. Fly's well but like your model has to have one aileron up a tad to maintain straight flight, putting in some rudder to do the same upsets other aspects of the flight.   Having checked everything I can think of have decided to just live with it.

parasol 3.JPG

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As I have a spektrum AR9350 three axis gyro Rx in the model wondering if that system could compensate for the out of trim settings. At the moment I think all three gyros are set to zero gain so have started reading how to re-programme the Rx but recall last time I did that some 4 years ago it was a nightmare with SW crashes and a blue tooth link on the Rx failing to link to the Phone App.  Did reload the app on my Samsung Tablet last night and at least it seems to run OK so will also download it to my Samsung Phone.  Have long since lost the original model setting on the App as think I changed the phone so its back to square 1 with the set up of each gyro gain.

 

Also think I have cured the undercarriage retract issue today but no doubt that issue will return as the wiring to each retract is not the best with several in-line solder joints.

 

 

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