ORIGINAL: f3a05

Hi Chris, this is the way I do it, to mount the rear of an out runner to a firewall:

1/ Attach the spinner backplate to the motor’s prop driver.
2/With 1/161/8th spacers between the backplate and the fus.nose, tape the backplate and motor securely in place.
3/ Cut a small square of liteply, just big enough to carry whatever fixings (eg bolts) you will be using to fix the motor to the firewall, and fix it to the back of the motor.
4/ cyano multiple 1/8 or so balsa sticks to the liteply square, with each stick radiating out to touch the fus sides.

You’ll end up with something like this:


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5/Remove the porcupine,draw round the edge,and produce a liteply firewall template., to check the fit to the fus, fixing points, &c.

For the actual firewall, I use two layers of 1/8 liteply, with the outer ply grains at 90 degrees to each other, skinned with 200 gram/sq.metre carbon or glass cloth front and back, all fixed under pressure(I use g-clamps, melamine-faced chipboard, with black polythene bin-liner separating film),using wing-skinning epoxy.
I glue the firewall in,bolted up to the back of the motor, with 24-hour araldite, reinforced with beads of 30-minute epoxy/micro balloons around the margins,front and back faces.

Here(shades of Blue Peter) is one I made earlier:



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