If you'd like to know more about "variable pitch propellors" try going to the VPP forum. There is lots more info.

Most of the VPP mechanisms in use now consist of a "rotor" head that is just like the tail rotor mechanism on a helicopter. When this technology first came out, many guys were using converted tailrotor set-ups by converting a Trex or Shogun heli rotor.

Here is the basics on how it works.

A servo is placed in the front of the airplane and connected to the mechanism by a pushrod that goes through a hollow shaft on the brushless motor, or is attached to a "swashplate". There are quite a few ready made VPP systems out right now. One is from Ikarus you can find it at www.shockflyer.com and the other that I am familiar with is the Shulman Aviation VPP system designed by Jason Shulman.

Reversing the pitch is done in two different ways. One is by programming "collective" into the radio, and the other way is by using a switch on the radio to reverse the pitch.

Collective is the best route, as it allows you to variate the pitch in both + and - .
The simple switch method either gives you full + or full - pitch.

If you want to see what a VPP system can do, click on this link.
http://67.18.81.100/rcuvideos/magazi...cottfoster.wmv