In a message dated 5/23/2011 2:18:02 P.M. Paraguay Standard Time, echristley@att.net writes:

Thomas Giddings wrote:
>  Thought you guys might like to see my engine compartment. My plan is to mount the Rotary on this mount with a 1/2 " 6061 T6
>  plate. The original design for the Questair Venture used a IO550 Continental bolted directly(via the oil pan) to this engine mount. Since I have no room below this mount because of the nose wheel retracting into it. I am using the mounting plate as a dry sump plate as well. Soooo. the reason I am asking about  raising the Center of thrust is when mounting the Rotary to the original motor mount shown in the Photo and using Marcotte PSRU which rises it another 1.5 in . It actually works out to be around 3 " after I factor in the height of the mount plate PSRU offset and the natural higher point of thrust with the 20B. I seemed to have missed this with all my backyard engineering. The reason i thought this would work better then LS1 I originally planned to install is how neatly the rotary bolted to the original mount without modification to the motor mount and nose wheel retract system. However if you guys think this a none factor . I will proceed . One positive about this I
will have a Bigger prop then Normal and it will give about standard ground clearance. Any other thoughts or observations would be welcome.
>

The line of thrust affects handling when moved in relation to the center of weight. 

 

Probably not a major change. Perhaps a washer or two under the mount to get the trim right. Imagine the pusher sea planes when power is added. Nothing can be that bad. The Venture's moments are short and horizontal tail plane is very small, so it will be a factor, but no worse than both of the crew reaching for a sectional at the same time. 

Most thrust lines are well above ideal just to get the prop off the ground.

Just a guess.......

 

Lynn E. Hanover