Balsa USA Force One conversion
 

Hi Folks,
I have a Balsa USA Force One delta wing that I would like to convert to electric. I use it for aerial video and it works great except that I get a lot of vibration from the OS46FX and tuned pipe config. It weighs about 5lbs 8oz and will do 1000ft climbs at about 125mph which makes some great video but I get a little vibration in the transmitter which causes slight jitter in the video picture.
The Force One is a mid-engine delta with 36" wingspan and the pusher prop goes through a slot in the wing which is 10.5 inches wide so I'm limited to a 10 inch prop. On the OS46SF I use a 10x6 APC pusher prop that turns about 14k rpm. I think that a direct drive brushless motor and nicad pack is the way to go on this as a gearbox might introduce a small amount of vibration, and a brushed motor might have some EMI that might show up on the video output. I don't need a long flight time, about 4-5 minutes would do just fine.
What motor/battery/prop/ESC would I use to get similar performance?
If I can't find an electric 10" diameter pusher prop can I run a brushed motor backwards with a tractor prop?
-Tom

RE: Balsa USA Force One conversion
 

To answer your last question first, you don't use pusher props. Instead you run the motor backwards and use a standard prop. her's a question for you, what is the biggist prop you can run in your model?

John

RE: Balsa USA Force One conversion
 

Looks to be 10 inches to me.

Using a standard tractor prop and reversing the motor is advantageous, as it opens up an entire world of propeller availability. You don't have to special order anymore, and you can try different props. It really doesn't matter where the prop is as long as it's spinning in the right direction. Brushless motors are equally efficient in either direction, so that's not a concern either.

Let's figure 6 pounds electrified. Normally 600 Watts would do it (100 W/lb), but you want "125MPH," 14K with a 10x6 prop or equivalent. Prop pitch is linear, so we could shoot for a 10x8 at 10,500 RPM to get the same pitch speed, which by the way is only about 80MPH ;)

I was going to say that my usual AXi recommendation wouldn't cut the mustard this time, but I might be wrong... It appears that the AXi 2826/10 on 14 cells with a 10.5x7 will spin over 11000 RPM. 10x8 should be comparable in prop load. Watts input is something like 540 Watts, which will easily cover a 5-1/2lb airplane with 100 Watts per pound.

My recommendation would be to use a 4S?P pack of LiPolys instead of 14 NiCd cells. You'll save about 14 ounces of weight if you use a 4S2P Kokam 2000 (15C) pack instead of 14 CP2400 NiCds. In both cases, weight is about 2.1 ounces per cell, but there are about half as many Kokam cells (8) than NiCds (14). You can save even more weight by going to the 20C Kokam 2100 cells because you only need a 4S1P pack. The only difference is that flight times will be half as long.

RE: Balsa USA Force One conversion
 

John the opening is 10.25 inches but I could run a three-blade prop. I have a 10x6 Grish 3-bladed prop which is pretty broad with rounded tips, more than the APC 10x6. Are there any 3-blade 10" electric props? APC makes a 3-blade 10x7 glow prop too.
Matt my weight estimate was off by a bit, the scale says it's 4 3/4 lbs. Does that change the final recommendation?
14 ounces is a lot of weight to save, and I'd probably want to save 21oz and $ and go with a 4S1P if I can still get 4 minutes on the 2100 pack. When it comes to making video, 4 minutes of aerial video is about 3 minutes too much at one particular field. How long would a 2100mah LiPo last at 4S1P?
It sure seems like it's flying faster than 80mph, but not 125mph, that would be 22k rpm wouldn't it!
If the current motor is about 18 oz with the header, pipe, and servo, plus 10oz of glow fuel, then with a 6oz electric motor and an 8oz battery pack this plane could be a pound lighter at takeoff? I might have overall higher performance...
What's the best place to order the Axi motor, Hobby-Lobby?
-Tom

RE: Balsa USA Force One conversion
 

I've been converting a Sig Kougar to electric.

http://www.rcgroups.com/forums/showthread.php?t=277849

I've switched over to a Mega 22/30/4 direct drive on a 4s pack. I'm turning an APC 11x7 eprop at 9200rpm using 45 amps and 624 watts input to the prop. This might be an idea for your plane.

John

RE: Balsa USA Force One conversion
 

I looked a motorcalc and if you push the volts up to lets say 6s (21 volts under load), you can approach 110 mph prop speed. The Mega can run a 50 amps max. It looks as if a 10x8 would run arround this figure.

John

RE: Balsa USA Force One conversion
 

John that's some nice documentation on your Kougar conversion. The Mega 22/30/4 is recommended for much larger planes though, why did you decide to use that instead of the Mega 22/30/3?
What's the difference between the Mega 22/30/3 and the Mega 22/30/4 ? Does the 3 and 4 designate the number of windings or the thickness of the winding copper?