Ok, this cowl is getting the best of me. I have all the openings cut and sanded smooth. The 4 holes are drilled for mounting to plane. The bottom two of four screws go into thick balsa and are nice and tight. The top two have nothing to screw into, but the sheeting balsa.

What can I do to secure?

[&o]

Did you drill the holes in the cowl?? What plane is it?

Place and glue plywood squares under sheet balsa; drill and tap. I like securing my cowls with 6/32 or 8/32 nylon screws. You can also get the nylon nuts if you happen to over-size your tapped holes.

Plywood all the way. Replace that balsa with plywood blocks. Add plywood where necessary. The screws won't hold in balsa.

Dr.1

great, I have to take the prop, cowl, gas tank out of the plane....

Thanks all.

[X(]

Hold on.

What plane is it?. Usually all you have to do is cut small 1/16 or 3/32 thick plywood squares about 1/4" -3/8" square and CA them to the backside of the balsa. Then you put the canopy in place, screw in the screws. Once you get the canopy installed completely remove all of the screws and then place a drop of CA in the holes. The CA will dry and harden the threads in the plywood. This will last forever. Another thing I like to do that will really help is to cut a piece of fuel tubing about 1/16" or a smidge thicker and place a washer and then the fuel tubing over the screw before you screw it in. This acts as a vibration damper and prevents the screw from wallowing out the cowl. Sometimes you can get away without doing this but it is a VERY effective way to ensure that vibration doe not ruin your cowl by wallowing out the holes until the screw heads are smaller than the holes.

Another option to the plywood squares, and a very good one is blind nuts. You install the blind nuts backwards with a drop of epoxy on the inside of the cowl after you drill the holes. Then its just a matter of using a socket head or button head bolt with a lockwasher, washer and piece of fuel tubing. Looks sortof like this. .

http://www.microfasteners.com/catalo...cts/SSCSBA.cfm
http://www.microfasteners.com/catalo...cts/SSCSCA.cfm
http://www.microfasteners.com/catalo...cts/WASFWK.cfm
http://www.microfasteners.com/catalo...ucts/NUTBN.cfm


By the way... EVERYONE should know about Microfasteners. You can order nuts bolts and washers 100 at a time for the cost of a few from "other" places. For instance, 4/40 socket head cap screws are $2 for about 6 from the typical LHS, from MF you can get 100 for <$5.

These screws are also very handy for many things.

http://www.microfasteners.com/catalo...ategory=SHWHMS

Oh yeah[8D], I hava tons of those too.. They are great servo screws and would work perfectly in this application if you wanted to go the screw route since they basically have a built in washer. WAY easier to deal with than philips head. And you can get 100 of them for <$5 ??????

IMHO, the best way to mount a cowl is to epoxy small hardwood blocks to the front of the firewall, then use nylon bolts with nylon washers on teh backside into blind nuts. A little more involved, yes, but I have yet to have one of those nylon bolts come loose, and the nylon washers don't eat into your cowl like metal washers. Yes, I know about using fuel tubing under the washer but this is is simpler. Alternatively, you could just tap the hardwood block and screw the bolts directly in.

Andy

That is a good way to mount a cowl to the firewall. I like the nylon bolt idea. I had not thought of that. The nylon washers I tried with steel bolts and they did not work, it still wallowed out the holes. Sounds like with nylon bolts the problem is solved.