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All Forums >> RC Airplanes >> RC Jets >> What causes gear doors and thin parts to warp weeks after they are dry?
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What causes gear doors and thin parts to warp weeks aft... - 7/14/2012 10:24 PM   
FenderBean



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Status: offline 		Anyone? seems like my gear doors never fit good after the fact and my once flat spoilers are now warped?


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RE: What causes gear doors and thin parts to warp weeks... - 7/14/2012 10:46 PM   
AmishWarlord



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Status: offline 		Wild guess with no info to go on.

You paint the fiberglass gear doors with a paint that softens the gel coat on the part then when it rehardens with the paint it warps.

Painting a motorcycle helmet voids the warranty because some paint affects the shell of the helmet.

Use a plastic safe primer for your base coat.


Oh and if you come back with this comment here is your answer,

"But my doors are made of wood"

You didn't say anything about wooden doors. Wood is lively stuff!




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RE: What causes gear doors and thin parts to warp weeks... - 7/14/2012 10:49 PM   
SPLIT S



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Status: offline 		Need some more info there FB. Weeks after they are dry? What does that mean?

Dan


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RE: What causes gear doors and thin parts to warp weeks... - 7/14/2012 11:57 PM   
FenderBean



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Status: offline 		Well I am talking after its painted and on the jet, I have noticed on my 3 jets so far that this ha happened. My F-14 is just sitting up in my hobby room and the spoilers have warped some, they were fine when I received the jet weeks ago. My F-16 did the same thing on the gear doors, they were fine when it arrived but weeks later they changed.
quote:

ORIGINAL: SPLIT S

Need some more info there FB. Weeks after they are dry? What does that mean?

Dan





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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 12:07 AM   
AmishWarlord



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Status: offline 		What temperature is this "Hobby Room" during the day in the summer?

You said "Up" so I thinking an converted but un-cooled attic space that's 120° in the summer rather than an un-used cooled upstairs bedroom.

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 12:20 AM   
David Searles


 

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Status: online 		Fender,

You probably don't want to hear this, but here it is: The problem is with the quality of the epoxy used at FEJ as well as the fact that they tend to pull these parts from the mold too soon, before they are completely cured. I have owned six FEJ aircraft and every single one has shown this defect. Also the problem tends to only get worse with time. Eventually you will begin to see warps and bubbles in the control surfaces and perhaps even in the fuse body as well.

David S

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 1:30 AM   
FenderBean



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Status: offline 		The hobby room is the bonus room which is cooled, so not a temp thing. The only parts I have seen are the thin non honeycomb parts do this
My surfaces have been fine.


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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 3:09 AM   
invertmast


 

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Status: online 		Its a resin thing, some dont fully cure for months unless they go through a post cure cycle.

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 3:22 AM   
FenderBean



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Status: offline 		Any way to fix this now? maybe close everything up and put some weight on it
quote:

ORIGINAL: invertmast

Its a resin thing, some dont fully cure for months unless they go through a post cure cycle.




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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 5:25 AM   
rpm303


 

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Status: offline 		I had this issue with my FEJ F-16. My gear doors were warped. I used a monocoat heat gun to heat up the doors and used blue tape to tape them down to correct the warp.
Worked very well for me. I always keep the doors taped down when hangered and they havent warped again.

Regards
Bob

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 10:09 AM   
Pondus


 

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Status: offline 		Close everything up and post cure the plane at 60-70 degrees C over night

Problem is just as Invertmast says, on slower curing epoxy resins it's often recommended to do a post cure, usually something like 8-12 hours at a controlled elevated temp. to fully cure the resin. Costly and time consuming so no wonder this is not done by most model airplane manufacturers, downside is just as you have found out that the parts can warp, especially if subjected to high temps.

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 4:27 PM   
FenderBean



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Status: offline 		Im talking weeks/months later this happen, everything is dry by the time it shows up.
quote:

ORIGINAL: Pondus

Close everything up and post cure the plane at 60-70 degrees C over night

Problem is just as Invertmast says, on slower curing epoxy resins it's often recommended to do a post cure, usually something like 8-12 hours at a controlled elevated temp. to fully cure the resin. Costly and time consuming so no wonder this is not done by most model airplane manufacturers, downside is just as you have found out that the parts can warp, especially if subjected to high temps.




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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 5:44 PM   
essyou35


 

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Status: offline 		Fender just curious, are you talking about your FEJ f-16? My 1/8 scale has the same issue. The gear dorrs warp. I hit then with heat and then they are good, but after a few days they warp back.

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 6:23 PM   
DavidR



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Status: offline 		Just the nature of epoxy resin. It continues to shrink/cure. I still build my models, paint black, and let cure in the sun, then, putty/heat up and reposition hatches etc... Before painting. Don't know how I'd approach an ARF since I don't "build" many of them.

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 6:59 PM   
FenderBean



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Status: offline 		Yeah the F-16 did it a little, but my f-14 spoilers are the worse so far. The entire corner has a 1/8in plus gap. not a huge deal since both sides have warped the same, but I like things to be perfecto I figured this would be the norm with material like this that has no wood or carbon to help keep its shape.
quote:

ORIGINAL: essyou35

Fender just curious, are you talking about your FEJ f-16? My 1/8 scale has the same issue. The gear dorrs warp. I hit then with heat and then they are good, but after a few days they warp back.




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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 8:15 PM   
RCNCMAN


 

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Status: offline 		I cannot tell if wood is involved here but if it is the construction should be balanced, same on front as on back. Use a 3, 5 or 7 ply construction just like quality plywood and the form whether flat or shaped should stay as you need it. This can be done with other materials or combinations of materials as well. Just balance it. If 3 ply, the front and back grain direction can be the same with the middle piece rotated 90 degrees.

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 9:55 PM   
FenderBean



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Status: offline 		The doors I am referring to have no wood in them.
quote:

ORIGINAL: RCNCMAN

I cannot tell if wood is involved here but if it is the construction should be balanced, same on front as on back. Use a 3, 5 or 7 ply construction just like quality plywood and the form whether flat or shaped should stay as you need it. This can be done with other materials or combinations of materials as well. Just balance it. If 3 ply, the front and back grain direction can be the same with the middle piece rotated 90 degrees.




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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 10:05 PM   
invertmast


 

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Typically the thinner the parts, the worse the warp becomes without the use of post-curing the parts. Epoxy resin's can continue to cure for months after they are mixed and appear to be cured (IE dry to the touch).

The only recommendation i can tell you, is to put the parts on a flat surface (glass table top) weight then down, then elevator the temperature and leave them in this state for a couple hours (its hard to say exactly how hot and how long since we don't know what resin is used), but 120-130*f at 8 to 12 hours should suffice. only down side, is since they are already painted, you could cause the paint to bubble on the parts. But this is really your only chance in getting them back flat, except for making a secondary structure using G-10 to correct the warp.

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 10:49 PM   
FenderBean



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Status: offline 		Thanks, well I will probably just let it go since there is no easy way to remove them. I will just keep them closed add a little weight to the slat to keep it flat maybe throw a heat gun at it to warm it up just a bit, not enough to damage anything. Thanks
quote:

ORIGINAL: invertmast

Fender,
Typically the thinner the parts, the worse the warp becomes without the use of post-curing the parts. Epoxy resin's can continue to cure for months after they are mixed and appear to be cured (IE dry to the touch).

The only recommendation i can tell you, is to put the parts on a flat surface (glass table top) weight then down, then elevator the temperature and leave them in this state for a couple hours (its hard to say exactly how hot and how long since we don't know what resin is used), but 120-130*f at 8 to 12 hours should suffice. only down side, is since they are already painted, you could cause the paint to bubble on the parts. But this is really your only chance in getting them back flat, except for making a secondary structure using G-10 to correct the warp.




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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 10:58 PM   
rcand


 

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quote:

ORIGINAL: David Searles

Fender,

You probably don't want to hear this, but here it is: The problem is with the quality of the epoxy used at FEJ as well as the fact that they tend to pull these parts from the mold too soon, before they are completely cured. I have owned six FEJ aircraft and every single one has shown this defect. Also the problem tends to only get worse with time. Eventually you will begin to see warps and bubbles in the control surfaces and perhaps even in the fuse body as well.

David S



I tend to believe what you summized is true. I have had dozens of jets from BVM, Airworld, SM, Extreme and never had this problem.

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RE: What causes gear doors and thin parts to warp weeks... - 7/15/2012 11:56 PM   
CraigG



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quote:

ORIGINAL: FenderBean

Thanks, well I will probably just let it go since there is no easy way to remove them. I will just keep them closed add a little weight to the slat to keep it flat maybe throw a heat gun at it to warm it up just a bit, not enough to damage anything. Thanks



If there's room, you could glue some small wood "ribs" to the back side of the doors. Just tape the doors shut while the glue dries.

That's what I did to stiffen this door I cut out of the fuselage.

Craig


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RE: What causes gear doors and thin parts to warp weeks... - 7/16/2012 1:38 AM   
FenderBean



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Status: offline 		I thought about the as well, thanks


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RE: What causes gear doors and thin parts to warp weeks... - 7/16/2012 3:37 AM   
flycatch


 

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Status: offline 		It is called lack of moisture. You most seal the surface of the wood prior to covering or painting.

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RE: What causes gear doors and thin parts to warp weeks... - 7/16/2012 4:15 AM   
David Searles


 

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quote:

ORIGINAL: flycatch

It is called lack of moisture. You most seal the surface of the wood prior to covering or painting.


Read the description. The parts spoken off do not contain any wood. They are cloth and epoxy layups.

David S

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RE: What causes gear doors and thin parts to warp weeks... - 7/16/2012 4:32 AM   
SCALECRAFT



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This issue is common with most inferior epoxy and polyester resins. I have models (old) made out of West System resin and none of the surfaces warp or degrade. I have a few Chinese composite fuses, most of which go soft in the sun (gummy bear soft), hatches and covers shink and warp. Not unheard of with the resins used out there.

Copy the part with epoxy. Or...

Tape down surface and gently use a heat gun. Practice on scrap first.

Steve

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