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Wing Sheeting???

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Wing Sheeting???

Old 07-29-2002, 02:37 PM
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Default Wing Sheeting???

I've only done a few... and never vacum bagged, which is supposed to be better.... But you've waited a while with no response at all.

1) make sure you have a FLAT work surface.

2) make up the wing sheeting into a one piece to cover one side size. (usually some sanding to make the edges of the sheets mate up) Depending on technique... glue them and tape into alighnment, or just tape together if using Pro-Bond or other polyurethant foaming glue. I avoid CA at this step, as the CA wicks in and makes the sheet stiff, possibly preventing it bending correctly...

3) If honeycombing the foam... do it now. Prepare the core by sanding ff any core cutting fuzz and then cleaning off all sanding residue. (damp rag gets it very well. Let dry completely if you're using other than polyurethane glue.)

It helps to insert retract mounting blocks or landing gear rails before sheting... smoother result, than putting them in after sheeting, and patching the surface.

4) set the first "shuck" on the work surface. lay in a separator material such as backing from Monokote, or waxed paper. Lay in the sheeting.

5) apply glue of choice. Just enough glue to do the job! (and that takes practice to tell...) You MUST get full bond on the forward 1/3, and the aft 1 inch (and within 1 inch of any cut-out edge for retracts....) The rest of the aft 2/3 can get away with less than "perfect" bonding. (but try for perfect... its stronger.)
Most glues... apply to the foam. Less wicking into the sheeting, and thus less exces glue and less excess weight.

6) Set foam core on the sheet, and cover with (again... use a separator layer...) opposite half of "shuck." Verify alignment and weight down with 1 inch plywood sheet that covers the entire panel. Recheck alignment.

8) Pile on the weight, evenly. Its doubtful you can come up with too much weight. You can apply 20 lbs per sq inch. 5 lbs per sq inch is needed as a minimum.

Drying time depends on adhesive... I advise against trying less than 2 hour epoxy. If you use a contact cement... you don't get a chance to correct a misaligned sheet. Pro-Bond gives at least 30 min working time, even if you spray the wood lightly with water... then it takes overnight to cure enough to remove the weights.

You can do the sheeting on both sides of a core at once... its a bit harder to maintain alignment. If vacuum bagging... prep is the same. In any case... it helps to have someone who's done a wing sheeting job help with the first one. Preferably... someone who's used the same adhesive as you plan on using.
Old 08-17-2002, 07:15 PM
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Default Wing Sheeting???

Vacuum bagging is using a vacuum pump and large bag to apply the pressure to the wing skins, rather than using a board and weights.

assuming the base surface used is true, the vacuum bagging SHOULD come out better, as the applied pressure is more easilly controlled, and more even. If you draw 10 inches vacuum, you have appx 4 lbs/sq inch (which would be a very large stack of books on a typical wing using the board and books as the weights. It takes 144 lbs/sq ft to give 1 psi. 10 College dictionaries in one stack is still short. )

I obviously used a LOT of lead when I sheeted a core that HAD to be straght... and that's one reason why I don't do many. You can get away with less pressure for a sport plane... 10 lb/sq ft is adequate for most of those.

A common shop-vac can usually draw more than 10 inches... but you'd overheat the motor holding that much vacuum for long enough for the vacuum bagging process. (normally uses slow setting epoxy or other glue needing several hours cure time, to gain full benefit of the system.)

Appx 30 inches is a "complete" vacuum, or -14.7 psi at STP (Standard Temp of 70 deg F, and sea level "normal" Pressure.)

You may note some car magazines stating you need to get close to 29 inch vacuum at idle... Its not hard to do with the volume of air a V-8 draws through the intake. (but its not useful to try using the car's vacum system to go the vacuum bagging...)

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