mounting cowlings
 

Hey, I heard from someone about using small pieces of fuel tubing when mounting cowlings to fuse with screws, they said to drill screw mounting holes the diameter of the tubing and then stick your screws through tubing to mount, my question is what size outside diameter fuel tubing to use? I am using hex head servo screws to mount cowling and the hex head is 3/16th in diameter that acts as a built in washer!!!! thanks

Mounting Cowls
 

I don't know about using fuel tubing but I have used the inner nyrod for this. Screws will hold and you and glue it in. I think that fuel tubing would be to flexible and would tend to twist out as you put ascre in it.

mounting cowlings
 

I observed what the big bird pilots were using on those huge cowls because I always had trouble with metal screws auguring out the screw hole from vibration. Many of them were using nylon bolts. On a fiberglass cowling, the vibration wear would be on the bolt and not on the hole in the fiberglass. I started using the nylon bolts and haven't had a problem since. I get 6x32 nylon bolts from hardware stores such as Home Depot or Lowe's.

mounting cowlings
 

Maybe you heard it from me, maybe not!
But this is how I do it:

1) First epoxy hardwood blocks to the firewall, at least 1/4 inch thick and about 1/2 inch square in shape, you'd be glueing to the firewall the 1/4 inch side, do not glue them flush with the side line of the fuselage, but about 1/16 of an inch + or - toward the inside. It is on these blocks where you are going to secure the cowling to. Use at least 4 such pieces, 2 on each side and it wouldn't hurt anything to have another one right at the top. Spread them evenly and just as far apart one from the other as the straight line of the side of the cowling permits.

2) You want to drill through the cowling (it must be in position and held securely with masking tape so as not to move) and the wood blocks, start with a smaller drill bit first, like a 1/16. then start enlarging the holes to the size that would allow you to insert a blind nut (tee nut) on the inside of the wood block, I like to use 4/40 size socket head bolts.

3) After this is done, you must enlarge the holes in the cowling to accept a medium size fuel tubing (silicone), you'll cut the tubing to about 1/8 of an inch in length, now insert first a flat washer through the bolt, then insert the tubing into it and drive the bolt all the way into the blind nut, as you tighten it the tubing will go into the hole and passed that 1/16 of an inch space and then compress and create enough pressure to keep everything in place, regardless of vibration.

4) I like to (after everything is done) cover the hole of the blind nut with a little piece of masking tape (only the side where the bolt comes out from), and then cover the entire nut and the wood with Goop rubber glue, this will keep the nut from backing out and will also make a very good prisoner for the bolt when inserted, you must drive a hole with a 1/16 bit so the bolt can drive through the glue, wait 24 hours to do this, so the glue is fully cured and hardened.

Hope this helps, it is a little more work than screwing the cowling directly to wood blocks, but your cowling will never crack and can be taken off very easily.

mounting cowlings
 

I use 4-40 brass inserts, screwed and glued into the fuselage.

Then the thread never wears out.

-DC

mounting cowlings
 

I know the Lowes here (Dallas area) carries 4-40 nylon screws in their special hardware bins. I have used them by drilling the cowl and mount blocks, and then tapping the blocks with a 4-40 tap. You could probably do the fuel tubing trick along with it to really isolate vibrations.

If you're really into tedious work, you can make silicon "washers" by putting a drop of silicon between two sheets of wax paper and weighting it down to flatten the drops out. After it dries, use some brass tubing to punch screw holes in the "washers" and use them on both sides of the cowl.

PSP Cowl Binders
 

http://www.pspmfg.com/OnlineCatalogPage1.html

Has anyone tried these? Scroll down to "Cowl binders".