I got this from the sales manager at Hitec. Karbonite gear train servos should NOT be used in aircraft weighing over 12lbs. The longer screw helps but it is not a complete fix. Since turbine jets put even more stress on servos due to the high speeds I would not use them in ANY jet. I recently had a customer lose both aileron servos on takeoff of the maiden flight on a 27% Extra with the longer screws. These were the 6985 servos. The aircraft was thankfully recovered with minimal damage. Hitec replaced the servos with the 5985MG.

I talked with one of my customers who is an engineer dealing with plastics for a local printer manufacturer. He said they have experimented with this type of material and could never achieve consistent strength. It appears that Hitec is experiencing the same problem.

Please don't risk your airplane or injury to those around you. The 5645 servos are a metal gear train and customer feedback has been very positive at my store. If others have had a different experience with this servo I'm sure they'll explain.

This is not a slam on Hitec. About 90% of the servos my store sells are Hitec. They just whiffed on the Karbonite stuff at higher power levels. It seems to be a great material for the smaller servos like the HS-65.