*Using Rubber O-Rings On Cowling*
 

The cowling on my Edge 540 is showing signs of wear and its only had a dozen flights. The four screws that hold the cowling on has metal washers, I was told to use rubber O-Rings and it would help stop the cracking and excessive wear. I intially smeared epoxy on the inside of all the holes I made in the cowl. My question is, If I use the rubber O-Rings, would you put the metal washer on top of the O-Ring or not use the metal washer at all?

RE: *Using Rubber O-Rings On Cowling*
 

You can use o-rings, or even a small piece of fuel tubing will accomplish the same thing. They isolate the cowl from vibrations which help protect the cowl. See the attached diagram.

Hope this helps

Ken

RE: *Using Rubber O-Rings On Cowling*
 

The best thing I've found are round servo grommets and servo screws or screws & metal washers - works great.

RE: *Using Rubber O-Rings On Cowling*
 

Thanks for the info guys. This is for a 120 application and seems a little big as far as drilling a big enough hole to put fuel tubing or a round servo grommet. Have any pics of an actual installation?

RE: *Using Rubber O-Rings On Cowling*
 

With fuel tubing over a servo screw the hole only needs to be .090 to .100” diameter and would work fine on a 40-size airplane.

Bill

RE: *Using Rubber O-Rings On Cowling*
 

I punched out some small circles from a punctured inner tube. Then punched a small hole in the middle of each. Put your hold down screw through the cowl and then through one of the rubber circles. If the screw hole in the rubber is tight on the screw the rubber will stay with the screw when it's unscrewed and it holds the screw in the cowl and that helps you keep up with them and has them ready to go when you replace the cowl.

You can also use two rubber circles per cowl hole, one inside the cowl and one outside.

A small set of punches isn't too expensive and you'd be surprised how often you use them around the house much less with this hobby.

RE: *Using Rubber O-Rings On Cowling*
 

Thanks Bills, I just measured the standard fuel tubing that I use and the OD is .250. I found some that was smaller that came with an old kit and it was a little smaller at .187 OD. Thats why I was saying that I thought it might be a pretty good size hole. Just what kind of fuel tubing are you talking about that will fit into a .090 to .100 hole?

RE: *Using Rubber O-Rings On Cowling*
 

Here are some commercially available cowl binders -- seem to be based on the same idea as O-rings or fuel tubing. I purchased these but have yet to use them.


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

RE: *Using Rubber O-Rings On Cowling*
 

Mimhoff,
I have the cowl binders on my UCD 60 with Saito 100.
About 6 gallons now and no problem.
They really hold up great!
I will use them in the future whenever I can.
JLK

RE: *Using Rubber O-Rings On Cowling*
 

That's what I'm talking about. Nice find mimhoff.

RE: *Using Rubber O-Rings On Cowling*
 

RCKen's method is a good fix.

Try this: before you do anything else, glue a CA hinge over each of the holes, on the inside of the cowl, with medium CA. Ensure that the entire hinge is saturated and adheres to the cowl. When dry, open up the screw hole to the same i.d. as your pieces of tubing o.d. Use a washer under the screw head, and you've got a quick, easy vibration isolator.

RE: *Using Rubber O-Rings On Cowling*
 

Steve, yours looks like a good idea also. With RCKen's idea it looks like the fuel tubing gets smashed out at the bottom so do you think there is a need for the CA hinge to be glued to the inside of the cowl?

RE: *Using Rubber O-Rings On Cowling*
 

What I do on all my 25% and larger planes is to use #10 nylon screws/bolts. I tap the wooden blocks, harden with CA, retap and voila! The holes in the composite never enlarge and the cowl never loosens. IMHO using metal screws/bolts and blind nuts - is nuts. I use nylon screws/bolts to hold the canopy frame as well. Never lost a bolt this way. I have done this ever since I lost a canopy frame off a 42% Giles during a snap roll. The flight & landing was a real adrenaline pumper!

Safe Flying!

RE: *Using Rubber O-Rings On Cowling*
 

That's cool to. Where can a guy buy these nylon bolts or screws? I don't think I've ever saw nylon bolts or screws at the LHS except wing hold down bolts.

RE: *Using Rubber O-Rings On Cowling*
 

Slips. I misread the dial caliper by .100”. No wonder my builds turn out so poor. The smallest fuel tubing that I have is .170” OD and I believe it is the tubing that Stihl uses for the clunk line in a saw. The smallest tubing (not fuel) that I have is .125” OD and it came from an oxygen nosepiece used in the hospital. Fuel tubing that fits over the servo screw is approximately .215” OD and would require a hole of .190” to .200”.

Please accept my apologies.

Nylon bolts are available in a variety of sizes below 1/4” from Lowes.

Bill

RE: *Using Rubber O-Rings On Cowling*
 

Lowes has these nylon screws??? Cool, I'm on my way. What dept. would they be in ???

RE: *Using Rubber O-Rings On Cowling*
 

I like servo grommets. Just drill the correct size hole, work the grommet in and it stays with the cowl. Use some of those servo screws that have the "built-in" washer.

RE: *Using Rubber O-Rings On Cowling*
 

I have used RCKen's fuel tubing solution as well as the rubber grommets. I like them both. If the cowl is a tight fitting cowl, the rubber grommets become an issue, and the fuel tubing is the best answer. But since using these methods, I have yet to suffer a cracked cowl.

RE: *Using Rubber O-Rings On Cowling*
 

I guess I just put RTV on the back side of the dowl and use orings around the screws and I don't seem to have the problem. I presently have a 33% Cap with BME 100. I did this on my GP PW with a Brison 3.2 without any wear.

RE: *Using Rubber O-Rings On Cowling*
 

Zippi,

The purpose of the CA hinge is to strengthen the area around the screw hole to prevent any "wallowing out" (enlarging). Might be needed; might not. Its cheap insurance, IMO.

You can find various size nylon nuts and bolts at any hardware store that carries those "tray units" of goodies. You know; where the boxes are on stacked trays that slide out for your perusal. Most of the Ace Hardware stores around here have that, as well as Lowe's and Home Depot. If all else fails, check out www.microfasteners.com

Huge selection, good folks to trade with.

RE: *Using Rubber O-Rings On Cowling*
 

Thanks Steve, I just smear 30 min. epoxy around all the holes that I make in the cowl on the inside. I'll take a look at Lowe's the next time I'm there.

RE: *Using Rubber O-Rings On Cowling*
 

I have used Steve's CA hinge idea for years. The hinge material toughens up the area around the screw hole much better than just smearing epoxy on the area. I'm not sure why, but the combination of CA with that material is super strong. I have used this method on fiber glass as well as ABS plastic with good results. I have not (yet) used the grommet in the hole. I use the socket head servo screws with a nylon washer. It is small and effective.