Converting Rubber to Electric

[bff]

I'm in the middle of converting a Guillow Spitfire from rubber band powered to R/C electric. It's been a fun project! The wing is done - I added an extra rib both sides to increase length and added the Guillow suggested dyhedral. I've mounted the receiver and scr in the cockpit - servos for stab and rudder are just behind the cockpit. The battery is nested above the wing and movable fore and aft for cg adjustment. I'm at the point of mounting the speed 400 and I'm not sure whether to use it direct or geared - what prop size? Plane should weight around 23-25 ozs when done. Any adivice?
thanks, bff. (build'em/fly'em/fix'em)

[Dave Robelen]

Hello BFF,
At the weight and size you describe a geared 400 would be the best option. I have had good results with a 6V sp400 mated to a Mini Olympus gearbox from Hobby Lobby driving a 9-5 grapner slim prop. It is very likely that you will need an 8-cell battery to fly that weight. The 500AR cells from Batteries America work very well for me.
Regards, Dave Robelen

[Rotten Robbie]

What is the wing span and wing area of the Spitfire?

23oz. seems awful heavey for a RB conversion.

Robbie

[bff]

Thanks for the great advice! I know 23 oz is on the heavy side...in the future I will do alot of things differently. However, I like to fly in "scale" and while this plane might "mush" around the sky at moderate throttle, I'll sacrifice run time. By the way, I'm looking for the difinitive chart that relates motors to engines and motors to motors. I have a hard time figuring out what is similar to what. Thanks again for the help. BFF (build'em/fly'em/fix'em)

[Rotten Robbie]

I assume this is the 24" Spitfire.

This airplane has less than 1sqft of wing area. At 24oz it will GLIDE LIKE A BRICK.

I have a P-40 the same size. It weighs 12oz RTF. Power is a 6V S400 with 6 600AE cells. It turns a 6X4 prop by direct drive.

If you try gearing a S400 you will need to go to a 9" prop.

Don't expect this airplane to fly slow.

Get MotoCalc and learn how to check out flyability.

Robbie

[Twmaster]

23 Oz??? Oh my. Are you soldering the balsa together? That sounds way overweight man. Gonna fly like a chunk of concrete. Better call Jenny Craig to fix that overweight bird.

Mike N
Twmaster

[bff]

Thanks for the responses from Rotten Robbie and TWMaster. Sorry it took so long for me to get back. Here's an update.
Final weight RTF will be close to 18 oz. TWMaster, I added an extra F3 rib and associated wing length to each side. This is the broadest chord before the dyhedral. Wing length comes out to about 29". Nevertheless, I'm sure your right, it won't have the best glide ratio. I'm having fun with it anyway. BFF

[Rotten Robbie]

My P-40 has a 23" wing. It looks like it will weigh about 12oz RTF. It has a S400 direct drive with a 6X4 prop.

Get yourself the FREE copy of MotoCalc. Learn how to use it. It will tell you alot about your airplane.

Robbie