Message-ID: <19980916191830.11057.qmail@www09.netaddress.usa.net>
Date: Wed, 16 Sep 1998 19:18:30
From: Dan Schaefer <dfschaefer@usa.net>
To: lancair.list@olsusa.com
Subject: aluminum, engine mount welding, canopies
Mime-Version: 1.0

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Marv, you're correct regarding the relative strength of 6061 vs 2024
however, for the application they both are quite strong enough. The
ultimate tensile strength (minimum) for common 6061 T6 is around 
42,000 PSI and for 2024 T3 or T351 is approx. 60,000 PSI. These 
numbers probably mean that either would serve well in most places
you are considering. What might be more important is that 6061 is 
generally a more corrosion resistant alloy (in the nude, that is), 
but if you're anodizing all your aluminum parts, as I did, this is 
less of a consideration. Price may be a better guide, as long as the
other factors wash out - as the thickness of sheet stock goes up, 
say to 0.250 inches, 2024 is about 2 1/2 times more expensive then
6061. By the dway, painting anodized parts is sort of like gilding 
the lily - proper anodizing is hard, looks good, and under normal 
circumstances, won't chip or flake like a painted part might. Also,
if the parts are riveted or bolted to other components, you don't 
want a paint film on there anyway.

On the subject of welding up motor mounts, one (or maybe more) of 
Tony Bingeles' books really treats the task with a lot of insight. I
don't remember which of his three books goes into it, I think it was
the one named "Firewall Forward" but perhaps someone else can say for
sure. In it, he talks about all the things you need to consider, such
as the tendency of oxy-acetylene welding to create very high residual
bending stresses in a welded up assembly and how to remove them so 
the final product doesn't distort to the point that it won't fit when
removed from the jig. I don't weld but a good friend on the airport 
does and watching him tells me that it takes some practice, first to
produce sound welds and then, treating the finished prodect so it 
doesn't twist up like a pretzel (so to speak). Something like a motor
mount, not properly stress relieved, can have mounting points move as
much as 0.125 to 0.250 inch, depending on the geometry of the mount.
But, as this is supposed to be a "learning experience" type activity,
I'd go for it, if it was my project, recognizing that there's more to
it than first meets the eye.

Concerning canopies and their latches, I unfortunately, had mine 90%
done when Don Goetz come up with the forward swing mount. So, I have
the old style parallelogram opening, but at times, I wished I had
the swinger. Those times were everytime I taxied out (or in) in the
summer time! Sure don't need a sauna when all I have to do is go sit
in my cocpit with the canopy down. One thing I couldn't abide, though
was those four little mickey-mouse latches, especially after flying
in a friend's plane and fumbling with them. Both latching and un-
latching, is a royal pain. I also didn't like the fact that the front
latch, in order to be able to get at it, is positioned too far from 
the front corners (it's aft of the instrument panel so you can reach
it). As a result, I designed a mechanism that latches each side with
a single over-center lever (one on each side) that's easy to reach
and places the front latch mechanism right at the front corners of
the canopy. The parts are easy to make out of 1/8th flat stock
aluminum and I'd be happy to send a sketch to Marv for posting if any-
body is interested. Incidentally, with an extra little tool, the 
levers can be pulled closed from the outside letting you lock your 
airplane. The tool is removed and goes with you so it provides some
security for the planes with the old style canopy.

Later,

Dan Schaefer


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