By Greg Harvey and MARCEE et al

I wish I could take credit for this, but it is a product of a number of people in the MARCEE club.  I'm just the one with some time to write it up.  Over the last two years I have probably broken 50+ orange GWS props of various sizes on various planes.  The final staw was when I build a pointy wingy thingy.  I loved the plane, but swinging a 9 inch prop with no landing gear I was breaking a prop about every 4th flight.  The props a relatively cheap, but still.  After putting this prop saver on I have not broken a prop since (at the time of this writing).  

What you will need

A spare mico servo control arm (like HS 81)
2 very small rubber bands or O-rings (I used two 1/2" outside diameter O-Rings that I got from a regional hardware chain Mendards that came in a pack of 4 for .79)
Any GWS IPS (Indoor Power System) with gearbox
Any size 2 blade GWS prop with the hex nut molding in one end

First remove the outer hex nut, washers and prop leaving the rearward hex nut.  Place the control arm on the shaft with the flat edge facing forward.  The put the washers on followed by the outer nut.  Now tighten the outer nut.  This will for the rear nut into the back of the control arm.  Once it have bottomed out position the whole assebly so that about 1/16" of the prop shaft is protruding.

Now slide a O-ring over each end of the prop.  Place the prop on the tip of the shaft and loop the O-rings over the control arm.  It is a good idea to cross them so that the left O-Ring is looped over the right side of the control arm.  This prevents the O-rings from slipping off the control arms in flight.  

If you have done it right the O-rings will hold the prop on, but if you hit the end of the prop it will pop off the shaft.

If you have any questions you can contact me at gjharvey@mindspring.com