Guys,
I installed a external tail bearing on my profile Excitation and found it makes a significant improvement to the stability of the ship in general. One big thing that it did was stabilize the yaw in both pitch up and down maneuvers. Prior to installing the tail bearing I had gone to a pusher prop setup and found that I really liked the additional security on the outside maneuvers that the pusher gave, the insides were a little softer but very manageable. With the tail bearing in place the inside maneuvers are now as stable as the outsides and the question is can we use the pusher vs puller to better advantage in controlling the vertical CG moment due to the battery location?

What I mean is on my profile I have the battery mounted above the wing, the motor is also above the wing in the normal location for an inverted IC engine. This puts a lot of weight up above the leadouts which will want to roll the ship out when upright and in when inverted. This is the same kind of trim problem that the pipe ships have with the pipe below the leadouts producing roll in when upright and out inverted. Now it seems that since we can use either pusher or puller prop rotation we could use the torque reaction to trim some of this out. In my cast I'm thinking that with the motor now very solid, since my ship has the weight above the leadouts using a conventional puller counterclockwise rotation should produce a torque reaction that will act to roll the ship in canceling some of the outward roll of the high vertical CG. If you have the low battery location then the pusher clockwise rotation should work. I think this will work if the motor has the second stabilizing bear or is an in-runner, without the additional support the motor seems to move a lot more then you would think. Anyone try this?

Best,              DennisT

Hi Dennis,
The tail-bearing is simply preventing gyroscopic forces from wiggling your thrustline in the corners and transitions. Great!

As far as vertical CG is concerned ... there is no substitute for getting the plane to hang off the leadouts with the wing vertical as viewed from the nose or tail.
At least we have an advantage with E-power, either the battery or the leadouts can be moved, and the vertical CG will not move during the flight.
That may not be true as a fuel tank empties.

later,
 Dean

Historically there have been a LOT of great flying airplanes built with Tractor style props - but you will have to pry my pushers out of my cold dead fingers...

From your pix it looks like your front mount system was pretty robust to begin with, I am impressed that the rear support added noticable improvement.

In most cases the battery represents roughly 20% of the total weight of the airplane.  I am striving for a location centered on the wing or sometimes slightly higher or lower than that depending on the wing's location relative to the thrust line.  Of course lowering the battery would be the preferred solution, but the torque effect would be curious too - just not sure I would ever switch back to the tractor...

Hi Dennis   This is a topic I have some input on. I have converted two of my SV-22 models to electric in the past two years with the lead outs 1/8 inch lower in wing per. normal piped ship. Both planes flew vary well with lots of line tension and a great hourglass with both tractor and pusher props but I like the tractor better. This is with the battery pack on the moter  mounts above the wing and the plane does not hang strait on the lead outs .  This year I built a purpose electric SVE-22 with battery centered and lead outs centered in the wing. The plane is vary light on the lines and has no hourglass at all. Moving the battery to the top of the compartment helped but may move lead outs down to get the feel I am after.   

Dennis     This plane had a front mounted plett 25-14 but the mount was not strong enough and the motor vibrated at 7200 rpm during ramp up.e I then installed a rear bearing and still had the vibration. Greatly stiffening the front mount was the only cure but then had a hot motor. Did not try the pusher yet, have cut front mount out and am installing a rear mount. This will increase cooling and alleviate the vibration. I will continue to trim the plane Thursday. Frank McMillen wrote a piece for pampa, 9 or 10 years ago on vertical  cg that might be worth a look.

Dennis   Did you have any vibration on ramp up, my plane ate the nose 1/8 of an inch back by the spinner. At one point I smelled burning balsa from the center of the circle. Finished the back mount last night and ramp up is completely vibration free. The plane is now fitted with the 13/4.5 pusher from the 13/4 tractor APC copy from hobby king. It will speed lap times  .2 sec and cut battery Mah. 100.  We will see what it dose for the hourglass.

Guys,
Flew the pusher vs tractor props on my profile for the past two weeks and with the rear external bearing installed on the motor I have been surprised. Prior to installing the rear external bearing there was significant difference on the outsides with the pusher and the insides were soft. With the external bearing there is nothing great with the pusher, the insides and outsides feel the same with the outside banging a bit with the pusher. With the tractor it seems because the battery is above the leadouts it has a moment that rolls the ship out when upright, this is added to by the pusher torque doing the same thing. With the tractor on this ship the torque fights the battery roll and there is almost no bang. Seems the motor mount was allowing some movement of the motor (in and out) that caused the big difference, once the external rear bearing stopped that movement you now get back to just torque reactions and vertical CG. I need to do some additional testing to come to a firm conclusion but for this ship the tractor prop may work better. One thing I did notice that was significant was on takeoff with the tractor it wants to get off the deck much quicker than with the pusher. This is likely because of the prop swirl pushing down on the stab/elevator with the tractor, the pusher holds the ground longer. This in nothing that can't be handled once in the air its not a problem. If you fly in deeper grass you might kept it in mind if you have trouble on takeoff.

Best,             DennisT