Bill Freeman wrote:
Mike,
Thanks for the clarification. I had no idea that the mount was so
integrated,
and was assuming that there were mounting points on the firewall for the
truss structure, like most homebuilts and most factory jobs, too. So
much for
ASSUME. ( ASS out of U and ME ) :-)
Actually the engine/gear mount do bolt to the firewall in a conventional
fashion. My only point was that you cant buy the mount without the gearlegs
too.
In that case, I still think that the truss-type subframe is likely to be
lighter and
safer overall than the thick-plate bolted aluminum system.
You guys have convinced me.
How about cutting the main eng mount tubes about 2" from the firewall
(assuming
this leaves the gear mount OK, otherwise 2" fwd of the gear mount).
Slip a 3" long piece of the correct ID 4130 tube over the existing stub,
and bolt it in place with two AN4 bolts at 90 deg to each other. Now
insert
NEW pieces of 4130 into these sockets and bolt them into place, also with
two AN4 bolts. Now bend, weld etc as req'd to mount the Mazda. If you
need to revert, unbolt the NEW section of the mount, slip the old factory
part(s) that you cut off (and saved!) and drill thru the two existing 1/4"
holes (previously used for the new fwd mount) in the socket and bolt the
original mount back together. Your reconnected mount will weight perhaps
1/2 lb more than stock and will be plenty strong enough.
But, if you don't want to do this . . . and really NEED to make an
adapter.
Apparently the primary problem is your lack of welding skills. This may be
over blown. If you can cut up the tubing, slot it for end attach
brackets and
make the gussets, my guess is that you can find a local welder that
will come
out and weld it all up for a reasonable fee. Also, basic gas welding
skills
are
not difficult to pick up, our EAA chapt has regular welding courses
over the
last 20 yrs, maybe a nearby chapter does this too. Many JR colleges also
have welding courses. Gas welding gear is <$250 and 4130 gas welds very
well and is structurally sound when gas welded.
Of course, it might not be so easy where you live, and I have not built
such an adapter, so can't be absolutely sure how hard it would be, but
1/2" thick slabs of aluminum just don't turn me on much from a light,
strong and reliable aircraft structure point of view.
No the real problem isnt welding skills. I can tack the thing together and
have a friend who can weld it for the price of a couple of beers. The real
problem is coming up with an idea, selling yourself on it, and then having
to give it up. That and I really did like the idea of an adapter and the
space it allowed for cooling components under the engine. Its kind of
difficult to pass a tube through a radiator core and not have a problem
with leaks. :-)
Mike I have the RV4 drawings. You can mount the rad under all
the necessary tubes. If you mount the hat section under the last rotor
housing (the one nearest the front of the engine in the airplane) you
are not limited by the motor mount. The ring gear and end housing
will limit how far up you can get and tilt the rad.
There are eight or nine other tubes in the stock
mount that can be done away with. You need to add the two side
triangles, a cross tube from rubber mount to rubber mount
just under the pan/hat section and a diagonal parallel with and just
above the rad from one rubber mount point down to the opposite corner
on the firewall. The stock steel pan can be truncated just short
of the front rotor housing and a flat piece of metal used from there
forward as the oil pick up is now towards the rear of the engine. Or
make a new simple and short rectangular alloy pan to fit. PL
Im gonna spend a couple of days playing around with some PVC and see if I
can come up with something that will do the job and clear my radiator.
Pauls design is growing on me. If I need to go to Lyc power at a later date
I'll install a new mount and gearlegs and still be bucks ahead on resale value.
BTW. I'm a MSME, structural engineer, so I see this sort of stuff all
the time.
I gathered that. Evaluation by someone with an engineering background is
the reason I wanted this to go out on the list in the first place. Thanks
for your input. And thanks to you also Paul.
Mike Wills
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