Two Speed 280s
 

I just finished a twin 280 tlar (that looks about right) design and have a few questions.

1. I am running two "graupner speed 280 race" motors on a 15 amp speed controler and was wondering what type batterys to use to power them. Voltage/amps ?

2. The plane weighs 14.5 ounces without any batteries and a span of 32 inches and about 225 square inches of wing area. Are the 280s enough to pull this plane?

3. It has a symetrical airfoil that is about 1 inch thick at the spar and an average cord if about 7 inches. Someone told me it would be too thick for this type of plane ( sport ) I guess?

4. What size prop should I use? Oh they are direct drive. I have gws 5 X 3 's on right now.

Haven't atempted to fly it yet.

I will atempt to upload a photo.

RE: Two Speed 280s
 

Go to the Hobby Lobby website and look for the Twin Racer. They use a similar motor set up and you can see what they use.

RE: Two Speed 280s
 

The 280BB race motors are similar in performance characteristics to the venerable Speed 300 motor, IIRC. You should be okay treating them as if they were Speed 300s.

There aren't too many direct drive 300 designs on the market. The 300 is too hot of a motor to spin a useful-size prop direct drive in most applications; it would draw too many Amps. One design where it's used quite successfully comes to mind, though: The Graupner Mini Piper from Hobby Lobby.

I don't know if HL still carries the Mini Piper, but IIRC, it used a Gunther Zagi prop on 6 or 7 cells, and weighed about 10 ounces RTF. Either 6 or 7 NiMH cells like KAN1100s, or a 2S ThunderPower 2100 LiPoly would make a good power source.