I'm in the process of putting together an electric Vector Arf. It's gonna have a Turnigy 3548-1100 motor in the nose. In researching a prop to spin it looks like the majority of fliers use a 12x6ep running at 8500-8700 rpm. I have a fuelie Vector Arf with a Tower .40 spinning an 11x5 at 9700 rpm. Would I be going wrong trying to dial my electric motor in with the same prop at the same rpm? Why do larger diameter props with high pitch seem to be the way the majority of the setups are going?
         Bob

Are you flying with 3 cells or 4?  The 1100 kv will require 6" pitch on 3 cells, on 4 cells it will be happier spinning up a little faster with a 5.5 or even the 4.5" pitch.
Castle recommends the throttle setting is at least 70% to 85% for best governing performance:

* for the 12x6 pusher on 4 cells with the 1100 kv motor the 8200 RPM represents a 50% throttle setting. Even with 3S you are only at 67% throttle.

* 11x5.5 Pusher turning about 9700-9800 RPM on 4S is around 60% throttle, on 3S it is an 80% throttle setting

* 11/4.5 Pusher turning about 11,200 on 4S is about 69% throttle; on 3S it would require almost 92% throttle (too much!)

Of these choices either the 12x6P on 3S or the 11x4.5P on 4S (my choice) look like the best options...

Hi Bob,
The Tower .40 is a great engine for sport stunt. I've used plenty of them with 11 x 5 props. Just remember that when you say you're turning 9700 rpm, that this is on the ground. The engine can unload another 1000 to even 1500 rpm in the air. I've measured this with an audio tach some years ago when I was making diesels out of Tower .40's. Just by the way, the diesel only picks up 500 rpm in the air. Now with electric stunt, you need to run a governor system, so the rpm will stay the same in the air. Therefore you will need more pitch to run at 9700.

Dennis mentioned the 1100 kv already, and as he says, this is more suited to a 3-cell Lipo. My standard replacement for the .40 size engines is a motor with a kv of 850 to around 900 with an APC 11 x 5.5 prop, either the pusher or the standard tractor prop. The rpm is set between 9600 to 9800 depending on the conditions and your personal flying preferences. I have had plenty of success with the E-Max/Arrowind 2820 motors for this size of model powered by a 4-cell 2200 mAh Lipo. The motor hardly gets warm when you get the right airflow through it, and I've even run 12 x 6 props on it as well.

The CC specs from Dennis are spot on, and this is why the majority of us would recommend a motor with a lower kv and a 4-cell setup. The current will be lower and a 40 amp esc will work perfectly.

Keith R

Lots of good info! Thanks guys. Dennis, Ill be starting with a 3300mah 4s battery. I will need to get the 11/5.5 and 11/4.5 prop to see which one the Vector flies best with.At least now I have some target rpm to start with. Keith, I didn't realize the electric motor held the rpm, I thought it unloaded like the IC engine( I'm gonna like the Hi gov mode).I like what the Castle Ice Lite 50A ESC offers in data log files. I ran the 1100kv motor for 6 min. in my garage(no earplugs!)at 8700 rpm on a 12/6 ep. I averaged 27 amps on 14.5 volts avg. This is about 390 watts,not much. I had about 600 mah left in battery.  I need to make changes if I expect the battery last(used a bit more than 80%) and the plane to pull through manuevers,it felt like it needed more more thrust. I read about a million old posts and still counting before I hit the go button on the timer. Gonna read some more before I let it fly. When I get it right I'll put info in "list your setup".
Bob

Dean,
 The Vector weighs 40.96 oz. This is with the cowl,all electronics but no battery. The 3300mah Power Wing lipo weighs 12.4 oz. making the plane weigh 53.36 oz. I removed the cowl(.96 oz.)to balance the plane bringing the airplane weight to 52.4 oz. with the battery. I need a battery that weighs about a ounce less so I can install the cowling on the plane. I didn't want to cut the wing leading edge to move the battery back more. I have the ESC and timer installed as far back as the wires on them would allow.The ICE Lite 50A ESC is between the landing gear and the Hubin FM 9V timer controls are mounted behind the flaps. The plane balances right where I like the nitro powered Vector(2 7/8" behind L.E.). I would like to end up with a plane that can fly the whole pattern and only use 80% of the battery capacity.
 I hope this is enough information
Bob

And a few more pics.

Looks nice and neat, Bob.
At 52 ounces you might expect about 2.3 Amp-hours of battery consumption per flight with a 4s battery.
A 3.3 A-h battery will yield 70% depth of charge use, which is ideal, to my battery coddling way of thinking.
At 52 ounces, though, I'll bet you'll be happier with a 12-inch doameter prop.
In additon to Dennis fine suggestions, I'd lay in a supply of the 13-4.5P's and start by clipping one to 12".

More diameter hardly touches the average power consumption,
but it dramatically raises the current on the ground and in climbs to the top of the circle; while further reducing the current during dives and during wind-driven whip-up.

The corner-killing effect of prop diameter is less with electric: probably because our actual in-air RPM is less, so there is no reason to fear diameter unless ground clearance is an issue.

let us know how it goes,
  Dean P.
 

I took the Vector out for a few test flights today.Flew 4.7 sec laps and used 2726 mah in 5:30 min.
 I was at the Toledo show and scored a Thunder Power 2700mah battery that weighs 8.7 oz. Thats 3.8 oz. less than what I'm currently using,but I need to get the battery usage down. I'm going to try lowering the rpm's from 10100rpm  to whatever it likes for 5.1 sec. lap times. I may need a different motor to achieve my goal.
 I have the Turnigy SK3548-900 to try if I don't hit my mark with the Turnigy SK3548-1100. I was tickled silly with the maiden flight. Flying electric is like cheating on steroids.
                                                Welcome to the Future,
                                                          Bob