Thread: Discussion Fuse layups and tests
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Old Dec 05, 2012, 01:37 PM
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G_T
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My lightest with hardpoints and screws, with hatch, and a tailboom perhaps 2.5" too long, was around 41.5g (from memory). This is without a tail mount. Trimmed to the length I'd use it, with tail mount added, it would be less than this. I can make lighter but not while keeping it very beefy, not without fabric changes (such as spread tow carbon which you are already using - coming in next batch).

Assuming somewhere around 1g for a horizontal stab mount would be about right. Some are lighter, some are probably heavier, but that sounds about right. I like my mount which is lighter and easy to make, but it requires testing to refine the layup. The usual sort of mounts don't need the testing and aren't so finicky of layup.

Places I shaved weight as I made more fuselages were (1) lighter screws - an easy savings (2) a fair bit less epoxy, but this did require adding a little fabric as less epoxy -> thinner layup -> less stiff (3) minor refinements of what materials I added where.

Getting less epoxy in the final product didn't require a change in how I processed, except for not closing the mold tightly for the first 15 minutes. My mold seals too well around the parting plane and it wouldn't let epoxy out!

If you are not using a very low viscosity epoxy such as MGS, you owe it to yourself to give it a try. It will make a difference as as wetout is easier so less epoxy goes in to start with, and the excess epoxy evacuates easier.

When I lay my fuselages up, I wet the mold, add fabric (dry), try to wet it out from the bottom, then add more on top to finish the job and for the next layer. This minimizes trapped air in the layup so it is stronger - but it is also a touch heavier. Air is lighter than epoxy.

I think I've published my tailboom strength test a few times. Wearing leather gloves, hold the fuselage in the saddle area, on its side (most DLG fuselages are designed to be stiffer and stronger horizontally). Hang a freeweight off the end of the boom. If it holds 5# without complaint (no creaking, cracking noises) then it might be usable. If it holds 7 1/2#, then it is probably just fine. I don't think it needs to hold more than 10# and probably not even that much. If it will, then reduce the fabric! Freeweights are available in 2 1/2# increments as small plates. That makes a convenient test - they even have a hole in the middle.

Gerald
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