[Gelcoat]

Friends,

I have and RFB Fan Trainer equipped with an OS 45 turning a 10 x 7 prop in pusher mode.
It requires 1lb 8 oz of lead weight up the nose for balance and a total weight of over 9 1/2 pounds. The plane is a rear mounted engine with a large3 shroud around the prop so I cannot encrease the prop size.

I would like to convert to electric using a motor that could turn over 17,000 rpm with a 10 in. 3 blade prop. I could then use the batteries as ballast up front and thus remove dead weight.

What motor would be best with corresponding ESC and batteries. I think that this plane would be much more fun being electric.

Jean B.

[Guest]

Jean, I don't think that a normal .45 would be turning that RPM without needing massive amounts of tweaking or nitro or both.

I think that something like 11K or maybe 13K tops would be a more reasonable number for a 3-blade 10-inch prop (based upon realworld testing of the newest OS MAX 45 -- http://www.masportaviator.com/pdfs/46AXEngineReview.pdf).

To figure out the general size of the motor that you'd need, decide on the battery size (number of cells in series) and divide the desired rpm by the voltage. For a 4s pack and 13000RPM, you'd be looking for a KV of about 900.

Based on my experience with the AXI 2826 series, you'd probably be looking at the 2826/10 or 2826/12 (probably the 12 since its the more powerful motor ), combined with a 60-amp speed control and soemthing like the 3300 mah 4s 20C packs. The Thurnigy42-40B is rated at 900KV which puts it right in the ball-apark that you're looking for.

Flight times would be about 5-10 minutes depending upon the amount of throttling-back you do. Taking off from grass will defintiely suck the amps from your pack.

Oh yes, you're also probably looking at disabling the battery-elimination-circuit (BEC) and using a regular receiver pack as many ESC's can't handle 4 cells driving the receiver.

Weight diference between an OS MAX .45 and the AXI motors is about 19 ounces, so the batteries may not need to go all the way forward in the nose.

[SpaceCowboy]

Hi Jean ; Is that an General Dynamics kit RFB ?

I had one and it barely got off a grass runway. It needed the engine tuned perfectly.

It was powered by a WEBRA Speed 52 heli engine turning a 9x7 3 bladed pusher prop. Not enough pitch to give good thrust and no other pusher prop available.

A guy in my club had the same kit but he powered his with a .60 that you could reverse the rotation by rotating the cylinder; so he could use a normal 3 bladed tractor prop. He also had more prop selection available.

A .45 would only be good for taking off of a paved runway.

I would go electric so you get enough thrust to fly the model and use a tractor prop.

Mike

[Gelcoat]

Greetings,

I want to thank you Byrocat and Spacecowboy for you input to my problem. I wanted to get away from glow fuel and convert to electric. Infor provided will start the process to the solution anùd the trimming away of 1 1/2 pounds of dead weight up front for balance.

I kinf a like the Turnigy motors and will pick up one with Esc and 4 to 5 cell lipo batteries when I'm in Toledo in a few months. One question still remains....will I need pusher props or can the motor proposed be made to turn in the other direction?

Toledo her I come.

I'll be tending the AMR-RC.com booth.

John

[wparsons]

Brushless motors can easily change direction, just change any two of three wires going to it.

[Gelcoat]

Thank you Mr. Parsons; now, I know I'm on the right track.

The RFB Fan Trainer at about 9 1/2 pounds was a very heary bird for a .40 to .50 engine and this made it difficult to take off from grass thus, not very popular at fields. It needed almost 1 1/2 pounds of lead in the nose to balance. Now take off over one pound and fit a more efficient motor and this may change considerably the performance of this plane. One thing for sure, it will be easier to balance. I look forward to the maiden flight....and this plane really stands out in the sky.

John

[bbbair]

Good Day John;

An Electric RFB!! What an idea!

I had a glow RFB 10 years ago and powered it with an ASP 52 - it flew (just) it was a dog in the air and a nightmare to land - too heavy and wire landing gear made it bounce back in the air...

Bottom line - the design was too heavy. Glow or electric try to keep the weight down or you will be disappointed.

As to the electric conversion - good luck! at least you won't have to deal with a shifting CG - the location of the fuel tank was a pain in that plane.

I look forward to hearing how it works!

[skypupnut]

salut Jean
mine will be electric soon also
too much trouble getting the engine started
the tuned pipe made it a lot better 1600 rpm more on webra 50
but was ugly and made it heavier yet

[Gelcoat]

Hello JC, good to hear from you at the start of the year. I still look forward to that coffee when you come up my way.

Let's compare notes as we go along.

I agree with you that the engine would have been digfficult to start weith the pull cord.....aqnd a little dangerous.

Electric will be much more trouble free and a lot cleaner and a good pound lighter. It's a win-win approach....I think.

Jean

[skypupnut]

I will be trying this motor
KD 600XL 1100kv Brushless heli Outrunner / 1600W