>Ken Welter wrote:
>
>> The coot and any pylon pusher plane has a very narrow CG range,
>>the wing has a wider margin that it can be operated in but with
>>this type of plane in the event of a engine failure the prop drag
>>will pull the nose up and with the engine mounted high it will
>>shift the weight aft when the nose comes up. For this reason you
>>need to operate on the forward edge of the CG window of the wings
>>specs. To complicate this the passenger weight is forward and
>>changes the CG drastically and for this I have a 2.5 gallon fuel
>>tank in the nose and a one gallon tank in the tail cone to shift
>>the weight and keep the CG dead on 25 percent of the cord. Jim did
>>not build his coot he just installed the rotary on a coot that he
>>bought and there was two seven gallon tanks in the forward floor
>>boards that I told him needed to be full to fly solo to keep it in
>>CG and he did not believe me but I don't know if they were full at
>>the time. The lake also has this problem and they have weights that
>>they slide in and out of compartments in the front and rear.
>> Ken Welter
>
>Very interesting Ken. Awhile ago I thought a configuration like this might
>lower the position of the CG. Given what you are saying above a pitch up
>would not move the CG aft as it does now with a high mounted engine. Since
>you are already using a belt drive all you would need is a longer belt.
>
>BTW how is Don Moncrieff coming along?
>
>Paul Lamar
From Ken Welter
When I went from the Ross gearbox to the cog belt redrive it made
a big difference in aft CG shifting, the redrive that I am now
running has a 11 inch offset and I can make a redrive with up to a 18
inch offset but to go any farther you would have to have a jack shaft
and run two belts. I did consider running a longer belt but it
brought up a host of other problems so I felt that the 11 inch offset
was the best compromise. As for Don Moncrieff is he still on the list
as I do not remember hearing the name in the coot world and would
like to get in contact with him.
Ken
Ken, I have been thinking about your jack shaft idea. I like it.
Easier than two engines on the same shaft :-)
One advantage is you can do away with the really big and expensive
12 inch cog belt pulley.
Double reduction means you will get 3:1 with a two stage
drive using four inch and seven inch pulleys giving about 3:1 overall.
An 18 inch off set for each reduction gives a 36 inch lowering of the engine.
Advantages are less blockage around the root of the prop and less drag on the
airplane as the motor is down in the back of the cabin and all you have
sticking up is a eight inch wide streamlined pylon. Less drag more MPG!
Not to mention the lower CG advantages. The rads can still go
in the pylon side ways.
Paul Lamar
I actually ran a 3 to 1 ratio jack shaft redrive for about 150 hrs
but the prop was in line with the crank as I ran the first belt up to
the shaft and the one second down to the drive hub, this unit could
be flipped to raise the prop if one wanted to and if anyone is
interested I would sell this redrive for $1000 if you wanted to try
it, however I think the host of problems would not be worth it such
as the fire and heat shield that would be needed and the fire danger
of having the engine burried down in the hull and the weight gain of
the whole package.
Ken Welter
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