What prop for the lawn dart?

[old man emu]

Since I'm building the Lawn Dart from scrounged materials, I am going to use the motor out of the Easystar 1 that I used to have. The Easystar weighed 24 oz (680 gms) with a 6V NiXX battery pack. I don't know what the Lawn Dart will weigh as yet, but it is pretty light.The motor is a Multiplex Permax 400. The only performance data I can find is for when it is getting 7 volts or better.

 

The prop was a 5x4, but in pusher configuration, but the Lawn Dart will need a tractor prop. I haven't made the landing gear yet, so it could be long to get the tips off the ground, as long as the AoA when sitting is less than 15 degrees.

 

Any suggestions?

[M61A1]

Since I'm building the Lawn Dart from scrounged materials, I am going to use the motor out of the Easystar 1 that I used to have. The Easystar weighed 24 oz (680 gms) with a 6V NiXX battery pack. I don't know what the Lawn Dart will weigh as yet, but it is pretty light.The motor is a Multiplex Permax 400. The only performance data I can find is for when it is getting 7 volts or better.

 

The prop was a 5x4, but in pusher configuration, but the Lawn Dart will need a tractor prop. I haven't made the landing gear yet, so it could be long to get the tips off the ground, as long as the AoA when sitting is less than 15 degrees.

 

Any suggestions?

Turn the prop around and reverse the motor to use the existing prop.

[old man emu]

Can't. It has a cone molded on the hub.

[Litespeed]

A 6x4 might do the trick, depends on what speed you want?.

 

If it's for a slowish fun time maybe a 7x4 even, which will drop the revs and trade trade bigger thrust to current drain. You could even go a 7x4.5. The old nicad system can do it but a cheap lipo will last for longer flights and more power headroom.

 

Either way props are cheap, grab a few to find it's happy spot.

 

Happy darting.

[Marty_d]

Props for electric are a different shape and lighter than the IC ones aren't they? I've got a few Bolly props lying around for motors from 0.25ci to 0.90ci, but the postage would be more than you'd spend on a new one.

[old man emu]

According to the specs of my motor

Voltage (V) = 6 volts

Voltage constant (Kv) = 3026

Then

V x Kv = RPM

6 x 3026 = 18,156 RPM

 

The torque Constant (Kt) = 1355/Kv = 1355/3026 = 0.44

 

And now I'm lost. It's bedtime so I'll go looking for answers tomorrow.