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Dec 08, 2019, 09:55 AM
Bad Dog Smokes
doublestroken's Avatar
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Discussion

Warped film covered control surfaces. How to correct?


Setting up model and just noticed how warped my elevators are. Before I make things worse, I wanted to make sure my proposed correction technique is correct.

Option #1- Apply over corrected force to the surface to the surface and then apply heat with heat gun to both sides of surface then let cool before removing corrective force? Or option #2- Apply localized heat to the worst area in an attempt that once heat is removed and allowed to cool, the heated area will have more tightening effect? See my exaggerated photo below. Meaning apply heat to the bottom side only near the center (blue taped area) in an attempt to shrink to a flat surface?

On this model done with monkcote, the orange covering required much more heat to shrink out wrinkles than blue, red or white. I also have a heat gun with accurate heat readout to within +/- 10 degrees
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Dec 08, 2019, 10:11 AM
Bad Dog Smokes
doublestroken's Avatar
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Or to word differently... twist against the warp and then heat one or both sides retaining corrective force till cool?
Dec 08, 2019, 10:14 AM
Build a scale plane already!!!
scale_only's Avatar
Yes,, heat might work,, That is how we adjust washout on glider wings,,

Just over twist it in the opposite direction while warming and tightening with the heat gun, let cool,, you might have to repeat the process several times

Just had the same issue on a aileron on my 59" slick, came that way out of the box,,, managed to get it pretty straight
Dec 09, 2019, 03:23 PM
Registered User
As Scale Only said, your option to adding more heat to one side may work.

But typically plastic (and fiber) covering have a "terminal" shrink beyond which applying more heat just causes burn..... you may have already shrunk the covering to this terminal point.
In which case removing the covering, confirming the wood member is flat and recovering is your option.

Also, I note you mention that you can control the temperature of your heat gun.... but likely you are inconsistent to some extent at the distance maintained to the covering. A covering iron in use is more consistent in the temperature applied to covering.

Michael in Ontario, Canada
Dec 09, 2019, 08:07 PM
AMA 537620
ChillPhatCat's Avatar
I have found that if the surface was straight before applying covering, then heating the covering works to correct a warp. But if the structure was built warped, there’s little that can be done to correct it post-covering; you might get it to be straight for a few hours but it eventually settles back into its original state. You may need to rip the covering off, wet the wood structure, unwarp it and fix it in place to dry.
Dec 10, 2019, 07:29 PM
Registered User
My bet is, when you take the warp/twist out and then remove the resulting wrinkles on one side, you'll end up doing the other side as well. That would be my plan anyway.
Dec 10, 2019, 07:36 PM
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exf3bguy's Avatar
I would build some sort of jig that would hold it to the correct alignment while shrinking the covering of both sides at the same time. Shrinking one side at a time is most likely what created the warp in the first place.
Dec 10, 2019, 07:36 PM
Build a scale plane already!!!
scale_only's Avatar
Yes, you for sure have to work both sides at the same time,,, I figured that goes without saying
Dec 10, 2019, 07:39 PM
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exf3bguy's Avatar
Me too but I wanted to throw it out there just in case it wasn't clear.
Dec 19, 2019, 10:36 AM
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I'd make a new one.
Edwin
Dec 19, 2019, 10:51 AM
Registered User
Good grief. It looks like the elevator is twisted. The way you take that out is to twist it the other way and apply heat to take the wrinkles out. Be sure to keep it twisted while it cools so it will hold the new shape.

It's been 10 days, are you still thinking about it?
Dec 19, 2019, 12:39 PM
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E-Challenged's Avatar
Some ARF models use carbon fiber rods as spars in wings and tail parts. Trying to twist and correct warps with heat gun won't work, my Maxford Gee Bee Model E for example.
Dec 19, 2019, 07:18 PM
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exf3bguy's Avatar
All of these ARF models should be jig built in such a manner that warps during the build don't happen. I can see however warps being introduced during covering.
Jan 18, 2020, 12:55 AM
Registered User
Quote:
Originally Posted by doublestroken
Setting up model and just noticed how warped my elevators are. Before I make things worse, I wanted to make sure my proposed correction technique is correct.

Option #1- Apply over corrected force to the surface to the surface and then apply heat with heat gun to both sides of surface then let cool before removing corrective force? Or option #2- Apply localized heat to the crossword solver sip calculator epfo worst area in an attempt that once heat is removed and allowed to cool, the heated area will have more tightening effect? See my exaggerated photo below. Meaning apply heat to the bottom side only near the center (blue taped area) in an attempt to shrink to a flat surface?

On this model done with monkcote, the orange covering required much more heat to shrink out wrinkles than blue, red or white. I also have a heat gun with accurate heat readout to within +/- 10 degrees
it eventually settles back into its original state. You may need to rip the covering off, wet the wood structure, unwarp it and fix it in place to dry.
Last edited by diondrelemarcus; Jan 19, 2020 at 01:12 AM.
Jan 18, 2020, 09:16 AM
Bad Dog Smokes
doublestroken's Avatar
Thread OP
Thanks for the replies guys. I should have updated earlier, but I was able to heat and twist out the warps pretty good. There is a small hump where the monkcote is 3 layers thick at the stripes but much better now. No pics as I'm away from home for a few days.

Now I'm contemplating recovering the whole model as there are bubbles all over the whole model. I can work them out but after a few days they reappear. I'm thinking that there is dust or something under the covering.

I am seriously looking at this covering for another build thats current on the bench. Haven't seen any YouTube videos on Profi Cover II. So maybe I will just strip this thing down and give it a shot. At least then I can swap out the generic pin hinges and install Robarts's. Covering available from Vogelsang Aeroscale. Apparently no sealing on balsa structure is needed with this Profi Cover.
https://www.aeroscale.shop/collections/covering


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