GJM

I'm getting ready to lay-up a 70" long jet fuse. I will be using 5.8 oz S-2 Glass with .125" flexible cell nomex honeycomb in the flatter sections. Can anyone give me a good starting point for number of layers and orientation. Thank you!

inlinetwin

Make sure the ribbon direction of the core is along the direction of least curvature and place an equal number of layers on both sides of the core. You could lay it up 0-45-core-45-0, just make sure it's balanced.
What kind of curing cycle do you plan on?

GJM

Thanks for that suggestion. Do you think the 5.8 is an ideal weight or do you suggest something different. As far as the curing cycle goes.... I planned on using a room temp epoxy. Thanks again.

Ps. I'm originally from Longmont - How's the weather?

inlinetwin

I didn't address this directly in my post because with the information you provided it would have been a guess. Tell me, what is the jet? Are you building from a kit or plans? Hopefully with this information someone may have some experience with your particular situation.

If you are not running it through an oven then balancing the core is not as critical; how are you laying it up? PFP tool or shaped foam masters?



It was about 72 today with 10 miles vis and there is just a hint of snow on a few distant peaks.[8D]

Darrinc

My Feedback: (5)

That is some pretty heavy glass you are using, so I would do one layer on a 45. The shape of your jet will give you the rigidity that your looking for.

Just remember to do the skins first, then put in the nomex, otherwise it will pull resin out of your cloth and you will have dry spots.

One method is to wet out your outer skin in your mold, and your inner skin on wax paper at the same time. Let the resin get almost to B-Stage. (really tacky) Then lay in your nomex, and inner skin and vaccum bag.

That method works, but it is tricky to get the nomex in properly.

Another method is to lay up your outer skin in the mold and cure it under vaccuum, use peel-ply if you have it. When cured, pull off peel ply or sand really well, then lay in your nomex and CA one edge into place, it will still move some, but it is more controllable. Then wet out under your nomex and innerlayer as above and finish out the layup.

You will need to be careful with the vaccum bag crushing the edge of the nomex. You can place a plywood edge around the mould (kind of like a parting board that over hangs into the mould) to prevent this crushing. If it does get crushed, you can cut out the crushed area and contact cement in the repair.

The proper way to use nomex is to cure your outer skin first, then lay in film adhesive, take a heat gun and install your nomex, (it will stay in place) then cure under vaccum and with heat.

gluedoc

Three questions:

1. What thickness is your honeycomb core?
2. What density is it (pcf)?
3. Why are you using it (do you really need the stiffness of a sandwich construction)?

In most cases, there simply isn't enough thickness involved to get any good benefit out of a sandwich in a small model. Since you are using 1/8 cell sized core, it is likely that your core shear strength is far more than you need for your application, to say nothing of the compression strength. As such, it is likely that your skins will be the weak link in the design. As Darrin pointed out, you likely only need one ply facesheets to handle the stresses, which is a horribly damage intollerant design. You might be better off with solid laminate skins with some bonded carbon planks or blades for added stiffness.

Since you are building a 70" jet fuse, the change in weight of these designs is not likely a factor.

Just out of curiosity, have you done any analysis to ballpark the loads and moments on this section of the aircraft?

Matt