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mike McGee and I were just talking about
my setup, I.e. going from a left turning mount to a right. he pointed out
that this is exactly what Tracy just did with his -4. we guessed that he
didn't change the engine mount geometry, but perhaps offset the vert stab
instead. perhaps I could mount my engine "best fit" and compensate with
the stab as well. if I attempt to put 1 1/2 degrees in the engine,
the left rear rubber mount is too close to the block. I could possibly
offset that one mount point, or, make it tight, and offset the stab more than
normal. I can't even think about what changes a higher cruise speed might
make(hopefully that will be true, right rusty?)
thanks for the measurement, it helps to
hear from several sources. there are always many solutions, despite freed
Breese's fixed answer of "buy a new mount" and "it's way too complicated
to explain to you".
I would like to hear what you guys say
about this geometry. does the vert stab offset create drag? is one
way better than another? will higher cruise speeds affect the alignment, I
know it affects rudder trim?
----- Original Message -----
Sent: Saturday, May 22, 2004 4:26
PM
Subject: [FlyRotary] Re: engine mount
geometry
I am fabricating the bed mount plate for my 20B in an
rv-8. my understanding, from Tracy's advice, is to offset the engine
about 1 1/2 degrees to the right if I use his 2.85 drive.
Hi
Kevin,
Sorry I didn't think
of this before, but last weekend, I measured the offset of my friends RV-8
prop, but never did the math to see what it came out to be. Basically, I
put the prop horizontal, and measured from the tail, to each tip. The
difference was 2 inches, on a 74" prop, which works out to 1.55 degrees right
offset.
The reason I measured
this was to see what his offset was, because he says he doesn't need any
rudder in cruise. My RV-8 also required no rudder in cruise, and neither
of out planes had any offset in the vert stab. Curiously, the same
measurement shows that my RV-3 (-B drive) has 1.25 degrees of left offset, and
I need a buttload of left rudder in cruise. The only thing I can
concluded is that there is right offset somewhere in the in the
tail. I can't tell if the vert stab is offset, but it might be.
There could also just be something crooked that I can't spot. I
didn't build the tail, and fuselage, or I'd know if offset was put
in.
Since I'm
going to the -C drive later this Summer, I'm more than a little
interested to see how the offset works out. Since there already
seems to be some other right offset force at work, I'll probably try flying
the -C drive with the left offset still in the mount. If I'm
careful, it shouldn't be dangerous, and then I can decide if I
need to remove the current offset. If I have to remove it,
I'll shim the mount a half inch on the left to do it. I'll also
reposition the cowl to keep everything lined up. The prop won't
quite be centered, but I defy anyone to
notice.
Cheers,
Rusty
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