reblacklaf

Good day. My friend and I are starting a year long project to build an old Cleveland Models B-17G. It has a 77+ws and we were wondering what the electric motor sizing should be for this model. It was classed as using 2 C engines with 2 dummy for freeflight but are converting to RC and electric power in all 4 nacelles. The kit doesn't show it being sheeted with 1/16" balsa just SilkSpan, though we plan on sheeting the fuselage and sheet the front and back sections of the main wings with cap strips on the ribs. The plan is to have flaps, ailerons, retracts, rudder, elevator and bomb bay door control. This is the first conversion either of us have done, all other builds have been more modern and have included the motor requirements. It is also the first multimotor we have decided to do.

Any input would be greatly appreciated.

Thank You
Randy Black

aeajr

My Feedback: (2)

Are you looking for motor selection input or building input? What sort of help are you looking for?

reblacklaf

Really wanting help selecting motor/battery options as a further check shows powering it with four .19 motors (a lot of power) and using 9x5 - 10-7 props. Plan on 2 motors per battery and separate battery for servos. Thinking on using 3 bladed 9x5 or twin bladed 9x4.7 as I have many in hand from an auction. We are planning on sheeting the plane for strength and using a split fowler flap setup which we are currently laying out.

Randy

aeajr

My Feedback: (2)

Take a look at this book - take particular note of the chapter on sizing your power system.

EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
http://www.rcuniverse.com/forum/m_7100376/tm.htm

You can do some first cut approximations using these calculators:
http://www.electrifly.com/powersyste...tem-index.html

Most are based on single motors. you will need an estimate of the all up finished flying weight. If you are going to have 4 motors then you will take that weight and divide by 4 to get how much each motor is supporting in a power to weight or watts/pound ratio.

Typically you will want to be in the 75 to 125 watts per pound range depending on what kind of performance you expect.


Take a look and then ask some questions.

reblacklaf

Thank you for the input. Will contact you again later. One thing is we would like to keep to a scale 10" three bladed prop.

Randy

reblacklaf

AstroFlight is custom building 4 motors for us. Each will produce 300watts on a 2cell lipo when turning the 8.5"x6 3 bladed props we are using. This should give us good scale performance with a bit of emergency power in reserve. You articles were helpful.

Randy

zeroback

What size mhA 2cell are you going with? On 2S the motors will be pulling 37.5A ruffly 8V X 37.5A = 300W . I'm curious to reason for the 2S? Less amps means smaller Amp ratings for the ESC's and batteries although more cells to contend with. Do you have a link or any specs on the motors Astro is making?

reblacklaf

5000mhA 70c. We are looking for scale handling and flight characteristics. Weight is a big issue as the plane will be sheeted with 1/20" balsa and Flite Metal. The motor was designed to meet our required output. They said a 2 cell battery with 50c discharge was all that would be needed. Airflow for cooling is somewhat limited by the design we are working with and all controls and batteries will be under a removable cabin area which will have the pilot side windows open and the rear single 50cal plexi window removed. They didn't supply the data yet. Another constraint was the size of the motor package and length of the drive shaft on the motor extending far enough that we could use the formed plastic dummy motors from a different kit.

Randy