IMAC Wing Sheeting

[MarkDennis]

I'm considering building a new Dalton 300ML but have a couple of questions concerning sheeting the wings and other parts. I would like to use a vacuum bag system, does this need to be done in conjunction with a perfectly flat surface? Or will bagging the wings inside the foam shucks be enough to keep them straight?

 

[Terryscustom]

I've done a number of planes by simply putting them in the shucks, taping them together and bagging them. The bagging pressure is even on all sides then. The important thing is to have an odd number of layers (wing, two sheets balsa, two foam shucks = 5 layers). If you have an even number of layers the stack will always warp. Next time your at the box store look at the plywood sheets, they always have odd number of plys for this same reason.

 

[jtec/radiowave]

Terry,

Interesting, Once you have it in the bag and the vacuum going do you just lay it on a surface ( presume fairly flat ) and let it cure. I wouldn't suspect you use any sort of weight while its curing. Of course I would of said you need the flat surface but you come up with some great ideas!! The odd number of layers blows my mind but your are correct on the ply. Are you using any special procedure?

Al

 

[Terryscustom]

Terry,

Interesting, Once you have it in the bag and the vacuum going do you just lay it on a surface ( presume fairly flat ) and let it cure. I wouldn't suspect you use any sort of weight while its curing. Of course I would of said you need the flat surface but you come up with some great ideas!! The odd number of layers blows my mind but your are correct on the ply. Are you using any special procedure?

Al

Edit: reread your post.... I've even put wings in a bag and layed them loose standing on end against a table. no issues. I am vacuuming at 7-9hg and .7lb density foam.

I did do some destructive testing samples once with one part in a bag with weight on top, one part with two shucks and nothing in a bag and one part shucks and two CNC plywood cauls. They all came out laser straight so I guess the lesson is all these methods work.

 

[jtec/radiowave]

Terry,

obviously we have some foam around here so some testing is in our future. I would have never even thought of trying that or given it a try. Always think you need a dedicated flat surface. That could free up a fair amount of space let alone simplify sheeting

Going to give it a try

Thanks for the idea

Al

 

[jtec/radiowave]

Follow up

I am bagging at about 5hg. 7 to 9 is really sucking it down. Do you think that makes a difference? What about the thickness of the shuck? If we are making a 35% / 40% wing, typically our shuck would be about 4" max thickness.

 

[Fibertech]

I stopped using ply cauls some time ago. I just stick foam and shucks in bag a pull them to 6hg. Thickness has been as thin as 1.5" on shucks with all great results.

 

[Terryscustom]

Shuck thickness is a good question, as would be type of glue. Since I use resin it does not expand or move around like poly and its very easy to get the same volume on each piece of sheeting.

Worst case a flat surface or plywood cauls never hurt.

 

[jtec/radiowave]

Rick,

Is that thickness on a stab? just wondering on Length. We use a fair amount of poly so I think we will give that a try and let you know.

Terry,

I can see your concern about how poly expands and possible issue, with weight and a flat surface would not be a concern. I have a wing for a pattern plane. we get some time maybe I will test that.

Thanks

 

[Fibertech]

Stabs on 33%. I use epoxy only. Not much for poly on sheeting as to heavy and moves around to much.
As always its best to do your own tests.