Ok guys, I spent some time today testing with a thermalcouple attached to one of the motors and a temperature monitor mounted to the battery platform (see attached). Here are the results:

No Motor Protectors after 1 min flight (average of 3):
- 11 F deg rise at end of 1 min
- 17 F deg rise (peak) aprox 1 min later after motor shutoff

With Motor Protectors after 1 min flight (average of 3):
- 14 F deg rise at end of 1 min
- 21 F deg rise (peak) aprox 1 min later after motor shutoff

After looking more closely at the the motor design, I can see that the real cooling comes from the air passing thru the motor. Heatsinking the motor case does very little to cool down the temperature of the motor windings and magnets since there is a high thermal resistance between those components and the case. The protectors do not restrict the air flow thru the motor which is why there is only a 3 to 4 degree increase of motor temperature. Notice that there the temperature rise after stopping the motors is about twice the increase from adding the protectors. If you really want to reduce the maximum temperature levels for the motors just spray some compressed air into the top of each motor after landing. I tried this and it immediately stopped the post flight temperature rise.

By the way, I was able to fly inside my 8' x 8' test area for a continuous 5 mins with the motor protectors. I could only do a little over 1 minute without the protectors due to higher instability (I need to understand if this is due to the added weight at each motor or if there is some aerodynamic effect of the tubes that increase the stability). Anyway the temperature rise peak after the 5 min flight was 44 degrees. I believe that 140 degrees is the approximate point at which motor life begins to suffer so flying in the upper 90's might become a problem. Again, you can help things a lot by just spraying compressed air in the tops of the motors after landing.

Finally, I think that a small funnel expansion at the top of the protectors might actually provide increased cooling compared to no protectors. Not sure how it could be fabricated. But for the time being, I'm sticking with this simple approach to protecting the DF during the hard landings along with gaining that additional stability.

Mike