First of all, Kevin, when you contacted me you stated that you wanted me to supply the offset information so you could take your mount to someone else "who is an excellent welder" to try to get your mount fixed the way you wanted it. I told you that for me to explain the proceedure would take more time than I was going to put into it because you wanted to take the mount somewhere else instead of sending it back for proper modification. For obvious reasons, both legal and otherwise, I wasn't going to do that. I never ever said you couldn't figure out how to do the proceedure. As far as everyone wanting to change drives, I would love it if there was an easy fix, but because of interferance problems, unfortunately there's not, so a different mount seems to be the only solution if you want to do it safely. It's unfortunate, Kevin, that you have chosen to try to hurt my buisness on this forum because I couldn't give you what you wanted. I could care less about having to build everyone a new mount, I have enough to do, I'm not trying to drum up buisness by insisting you have to have a new mount, but my insistance that everyone consider the safety aspect in all this paramount to their decision in doing anything. Again, I apologize for having to use this forum for things unrelated to building and flying rotaries, this is no place for things like this, but there are two sides to every story. Fred
















At 12:02 AM 5/23/2004, you wrote:

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?
Kevin Lane  Portland, OR
e-mail-> n3773@comcast.net
web-> http://home.comcast.net/~n3773
(browse w/ internet explorer)

----- Original Message -----

From: Russell Duffy

To: Rotary motors in aircraft

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