RCU Forums - View Single Post - Contra Rotating Propeller Drive for f3a 2m Pattern Planes
Old 07-09-2010, 09:55 AM
  #47  
Brenner
 
Join Date: Jul 2007
Location: Bridgman, MI
Posts: 793
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Jim,

The plane that I'm taking to the Nats is going to have the weight comparision shown in the attached graphic.

However, one thing I need to mention is that this is our first prototype, so it's not what we consider to be our final design. Our design target is to get the total system weight to something below 28 ounces. How successful we are will depend on what we can do to replace CNCed parts with tooled parts.

The CG that I currently fly at is 6.5 mm behind the leading edge of the wing tube. I currently have two battery trays. the one show in the pictures, and another tray that is fitted over the landing gear plate. The one in the picture allows me to move the battery pack all the way back to the front of the wing tube so that I can try different CG positions.

Another reason for me experimenting with the plate shown in the picture is that the Contra Drive moves a lot of it's weight further forward. The actual motor is pushed forward by about 20 mm or so, (note that you can't actually see the back of the motor in these pictures...) and the gearbox is actually integrated into the spinner. Also, the second prop hangs way out front on the tip of the spinner assembly.

Currently my system balances the way I want it with the plate shown in the pictures, and with the batteries pushed to the front of this plate. One side benefit is that the batteries are now much easier to install and remove from the plane. Also, I can get easy access to the wing bolts by undoing a wing nut on the front of the plate and hinging it back.

Brenner ...
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