Need advice re: warp in stab  
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All Forums >> RC Airplanes >> Giant Scale Aircraft - 3D & Aerobatic >> Carden Aircraft >> Need advice re: warp in stab
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Need advice re: warp in stab - 12/11/2007 3:13:11 AM   
luv2flyrc



Posts: 338
Joined: 1/7/2002
From: Mississauga, ON, CANADA
Status: offline 		Hello Gentlemen,

On my fourth Carden build, a 35% extra 260, I've decided to try vacuum bagging the foam parts with epoxy rather than the Probond and weight method I've always used in the past.

I was thrilled with the results of all the fuse pieces but I just did my stabs and I have a warp in the trailing edge. One is worse than the other. The worst one deviates about 1/4" off centre on the trailing edge.

I'm trying to avoid sanding the skins off and redoing them, I've thought of wetting them with Windex and clamping between two straight bars to see if that will straighten them.

Anyone have experiance in straightening foam parts? Also, I'd like to avoid this happening again with the vacuum method, any idea where I went wrong. I've always had perfectly straight results with the weight and probond.

TIA

Mike
       Post #: 1

RE: Need advice re: warp in stab - 12/12/2007 1:26:26 AM   
BBW Walt



Posts: 928
Joined: 1/13/2002
From: NWest, IN, USA
Status: offline 		The windex thing won't do it, it'll come back. Your best bet for trying to fix this is with some hard balsa for the leading and trailing edge on the elevator after you cut it out. Clamp the elevator between 2 parallel bars to hold it flat toward's the trailing edge, glue on the leading and trailing edges with it clamped this way. The edge material will hold some of it out if your edging is stiff but, if you've got a 1/4 inch set in the stab your probably best off getting a new stab and doing another lay up. The method mentioned will hold maybe 3/32 like in an aileron but a 1/4 is a lot especially in a short span like a elevator TE..Walt

(in reply to luv2flyrc)
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RE: Need advice re: warp in stab - 12/12/2007 4:22:18 AM   
DMichael


 

Posts: 747
Joined: 11/1/2002
From: Laurel, MD, USA
Status: offline 		Mike,

I have been wanting to try vacuum bagging myself and would like to avoid the issues you're seeing- would you mind giving us some info on your technique- Did you put the bagged wing back in the shuck with some weight to hold it all in place while it was drying? Not a lot of weight- just enough to hold it straight.

Thanks-

Dave

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RE: Need advice re: warp in stab - 12/12/2007 12:08:45 PM   
luv2flyrc



Posts: 338
Joined: 1/7/2002
From: Mississauga, ON, CANADA
Status: offline 		Up-date

I have been able to remove the warp by spraying with windex and clamping between two straight bars. Both stabs are now perfectly straight however; as Walt suggested the warp may return so, I have used stiff balsa on the trailing edge and will do so on the leading edge as well once I cut the elevator's free. As added insurance, i think I'll epoxy a 5mm carbon fiber rod through the foam at the trailing edge as well, This will add very little weight and be very stff.

Not sure what I did wrong with the vacuum, I placed the stabs in the shucks with some weight, not enough i guess. I want to get it right before I do the wings.

Mike

(in reply to DMichael)
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RE: Need advice re: warp in stab - 12/12/2007 5:31:43 PM   
zzw26n



Posts: 704
Joined: 5/18/2004
From: Shelby Twp., MI, USA
Status: offline

Mike,

Is there a way to guage how much vacume you were using? almost sounds like to much maybe? Very glad you were able to salvage the work you did.

Ward

(in reply to luv2flyrc)
       Post #: 5

RE: Need advice re: warp in stab - 12/12/2007 10:14:43 PM   
as722


 

Posts: 962
Joined: 12/26/2002
From: MT Pocono, PA, ANGOLA
Status: offline 		I have bagged six set of 40% wings in the last two years with very good results. It sounds to me like the surface used to place the foam chucks might not be straight. I always do a dry run first and once vaccum is pulled I place a level along the trailing edge and leading edge to make sure they are good. Once you cut the elevators out they will get better and like walt said if there's any warp left it can usually be fixed with the trailing and leading edges.

Albert

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RE: Need advice re: warp in stab - 12/12/2007 11:31:51 PM   
luv2flyrc



Posts: 338
Joined: 1/7/2002
From: Mississauga, ON, CANADA
Status: offline 		Hi Ward, I don't have a gauge but, I use the little ACP unit that is pre-set to 6"mg for white foam

I'll take your advice Albert and do a dry run on the wings. U may be correct that the surface wasn't true, I wasn't concerned about it because I thought that by vacuum bagging it wasn't necessary as i used very little weight on top.

How much weight do you use when you bag? The idea of vacuum bagging for me was so that I didn't have to hoist all those heavy cement blocks around I'll do the wings on a true surface.

Thanks

Mike

(in reply to as722)
       Post #: 7

RE: Need advice re: warp in stab - 12/13/2007 6:54:41 PM   
as722


 

Posts: 962
Joined: 12/26/2002
From: MT Pocono, PA, ANGOLA
Status: offline 		I like to put some sand in ziplock bags and place a few bags over the piece being vaccumed. Once the vaccum is pulled it isn't nesesary to keep the weight on. Make sure the building table is straight.

Albert

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Carden Aircraft

(in reply to luv2flyrc)
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RE: Need advice re: warp in stab - 12/23/2007 1:17:31 PM   
luv2flyrc



Posts: 338
Joined: 1/7/2002
From: Mississauga, ON, CANADA
Status: offline 		Update,

Well i decided I wasn't happy with the 'straightened" cores after all. I called Carden to order replacements, I had a great conversatiion with Dennis and he told me what I was doing wrong. My advice is, if you're in need of help call Dennis, the man has a wealth of knowlege.

I didn't realize this but, he told me that Carden cuts the cores under weight therefore, if you don't bag under weight you will not get a straight core. That's the reason he marks one side of the cores "DOWN" Also, he said it was absolutely necessary to bag with the shucks on ie: shucks in the bag. This is contrary to 99% of what I read about bagging on RCU before I tried it.

Again, this goes back to the cores being cut under weight.

I hope this info saves someone else a set of cores, I have received my new ones and am about to try it again the right way

Mike

(in reply to as722)
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RE: Need advice re: warp in stab - 12/23/2007 1:35:37 PM   
zzw26n



Posts: 704
Joined: 5/18/2004
From: Shelby Twp., MI, USA
Status: offline

Thanks Mike for posting that and please let us know how thenew ones turn out.


Ward

(in reply to luv2flyrc)
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RE: Need advice re: warp in stab - 1/1/2008 8:38:43 PM   
luv2flyrc



Posts: 338
Joined: 1/7/2002
From: Mississauga, ON, CANADA
Status: offline 		Well, I've skinned the new cores according to Dennis's instructions and VOILA , perfectly straight cores!

Here's the secret, place the cores with schucks in the vacuum bag, weight the cores ( I used about 80lbs) then pull the vacuum. Make sure there are no wrinkles in the bags on the bottom of the schucks.

The cores are dead straight, I'm off to do the wings

Mike

(in reply to zzw26n)
       Post #: 11

RE: Need advice re: warp in stab - 1/1/2008 10:18:59 PM   
zzw26n



Posts: 704
Joined: 5/18/2004
From: Shelby Twp., MI, USA
Status: offline
quote:

ORIGINAL: luv2flyrc

Well, I've skinned the new cores according to Dennis's instructions and VOILA , perfectly straight cores!

Here's the secret, place the cores with schucks in the vacuum bag, weight the cores ( I used about 80lbs) then pull the vacuum. Make sure there are no wrinkles in the bags on the bottom of the schucks.

The cores are dead straight, I'm off to do the wings

Mike


Mike,

Great to hear that everything worked out! I can see the stabs schucks fitting in the bag, but the WINGS are hudge, will they fit in the bag too? Post any picutres if you have them.

regards, Ward


(in reply to luv2flyrc)
       Post #: 12

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