The Mother of Invention

wrote:
There's some jumpers somewhere in my kit but I don't want to go dig
them out. Hand them my flashlight. Then have to show them how it
works. Unwrap the wires from around the flashlight, unclip the
alligator clips and you've got a continuity tester about ten feet
long.


I once had a fuel seep somewhere in a 150. Could smell it in the
cockpit, but couldn't find it. Checked all the lines from the tanks,
through the valve, to the firewall, and all the primer lines. Even in a
simple airplane there are a lot of connections.
Air out the airplane. Close the doors. Come back in the
morning, cockpit stinks of avgas. Look all over the systems again;
still nothing.
We have stethoscopes to find funny clicks and knocks and whines.
We have signal tracers and continuity testers and ohmmeters to find bad
electrical connections. We can get ultrasonic air leak detectors to
find microscopic pressure leaks. I have (or had) nothing to find that
tiny fuel seep.
I took some old pitot-static tubing, which is just translucent
polyethylene tubing. Old tubing is better because it has no odor
anymore. I took a bit of 1/16" rubber diaphragm material (a chunk of
old inner tube would work) and formed a funnel, the small end being
tight around the poly tube and the other having about 1 1/4" diameter.
The funnel was about 2 1/2" long. Stapled the diaphragm material
together at the overlap; don't have to get fussy. Duct tape held the
funnel to the tubing. With a pair of scissors, I cut the end of the
funnel so that it fit around my nose with a good seal so that when I
sucked in, the air had to come through the tube.
Now maybe I can nail that tiny seep. Sniffed all the same
fittings I had looked at before, and when I got to the primer inlet
line fitting at the firewall, I had no doubt as to the source of my
leak. IIRC it was the line cracked at the base of the flare, just
enough to allow the gravity head to force a tiny bit of fuel through.
There was never any stain; the fuel was blue and so was the anodized
aluminum fitting, and the leak was never big enough to drip. If it had
broken right off in flight we'd have had a big problem.
I've since used that sniffer to find other leaks. If the cockpit
of a Cessna single smells, the leak could be in either wing or at any
one of about 25 connections, drain points or valve gaskets. Cessnas
aren't known for their airtight cockpits.
I've even found bad electrical crimp connections with it.
Sniffing an almost-inaccessible heat-darkened crimp connector will
tell you if the burn is recent or old. Sticking the tube into an
alternator could identify burned windings.
If you're a smoker, this tool might not work for you..

Dan



You've invented the "Smellescope" from Futurama a thousand years early!

If you need both hands free do you staple the rubber funnel to your nose
or use the duct tape?

Nyuk nyuk nyuk...

VERY clever actually.

John