Bob Chilcoat wrote:
We have been having trouble getting decent replacements for the above,
which pop into the holes in the top of the wing to allow the main gear
struts to be pressurized.

Some ideas... Caplugs http://www.caplugs.com/ has plugs in a variety of
materials. The places I've used them don't get exposed to your kinds of
airspeeds, but I have found that the tapered kind stay in a little better.

We've lost two over the past couple of years.

Is there any good way to "leash" them to the plane, or would this be a
bad idea? I'm thinking something like drilling a hole in the center of
the plug, using a self-locking nut and bolt to bolt a wire, bead chain,
or similar to the plug, and then securing the other end down inside the
wing someplace. On the other hand, the way it is now, if the plug comes
out it's just gone, while with a leashed plug, it's free to dance on the
surface of the wing and beat up the paint and the metal.

I found some better quality plastic (Nylon) from Heyco, and got some
black samples (the minimum order for the white "standard" color ones
was 26,000!).

Mouser http://www.mouser.com/ carries a few Heyco plastic plugs and will
sell in small quantities; a plug for a 1.5" hole (Heyco 2763/DP-1500) is
25 cents quantity one. This is probably black nylon.

These seemed promising, but are just a bit too deep to lock in securely.

Does the bottom of the plug stick down too far and hit something inside
the wing, or is there too much room between the locking tabs and the top
flange of the plug? For the former, maybe some sandpaper or notching
the plug to fit over the obstruction would help. For the latter, maybe
a thin rubber gasket around the plug would take up enough of the slack
to make it grip in better. The hardware store may be able to help, or
ask your dentist for a sheet of rubber you can cut to size. Another
thing I have seen done with these type of plugs is to use a bushing
(hollow plug) in the hole first, and then put a smaller plug in the hole
in the bushing. Sometimes the bushings are made a bit stiffer than the
plugs and stay in the hole a little better.

I don't know the official name of this part, but there is a thing that
is meant to temporarily plug pipes and is also sometimes used on boats.
Basically it's a thick rubber washer between two steel washers with a
bolt running through the middle. You tighten a nut on the bolt (or turn
a cam handle on the bolt), which squeezes the steel washers together and
expands the rubber washer. This would leave more stuff sticking out in
the air stream, though.

_If_ you can get to the hole from somewhere else, how about this: at the
hardware store, buy a PVC pipe reducer - the kind with a flange, big OD
(possibly threaded), and small threaded ID. Also get a PVC pipe plug to
fit the internal threads of the reducer. From the bottom, put the
reducer through the hole so the flange is against the wing, and glue it
down. (Alternatively, get a reducer with a threaded OD, and from the
top, screw down a "nut" cut from another fitting over the threads. Use
PVC solvent to make sure the nut stays put.) From the top, install the
plug. You can use the tapered threads to secure the plug, or maybe use
a cotter pin, Loctite, etc. This also assumes that you can tolerate the
reduction in hole diameter that the pipe reducer will give you.

I am less sure about this one, but I _think_ I've seen some nice flat,
threaded covers on the tops of motorcycle fork struts. They usually
have a flat top with holes for a pin spanner and I _think_ they have an
O-ring on the underside. Again, you might have to to be able to get to
the underside of the hole to attach the part it screws into (which you
may have to cut off of the top of a junk fork), but once you have a
threaded plug, tricks like Loctite can be used.

Further afield (and possibly showing that living in Oklahoma is rubbing
off on me), an older-style outdoor electrical outlet cover has a couple
of nice hinged, gasketed covers on it that are spring-loaded closed.
You'd probably have to cut most of the plate itself off and figure out
a way to attach the rest of it to the wing.

Matt Roberds