I have 3 Corona 120's all set up the same way, but one corona in particular is giving me a rather odd problem! all 3 Corona's are set up with the same Mega brushless motor, same lipo, same speed control. the only differeance is that the 2 good working coronas both have JR G410T Gyros and the Corona giving me problems is operating on a Futaba GY240 Gyro (I used the GY240 only because JR G410T is out of production)

But anyway, here's the problem;

When I fly the helicopter It has great stability and excellent control responses for the first 4 - 6 minutes, after that the tail rotor control slowly fades away till I have complete lack of tail control. I have almost no tail response anymore, all other cyclic & throttle controls work fine but no more tail response, it gets sluggish in the turns, then disapears all together and the heli is left spinning in circles. Then I unplug the helicopter, let it sit for 10-15 minutes, it works fine again for about 5-6 minutes, then no more tail rotor control again.
I know gyros can be sensitive to temperature change and my heli is going from my aircontioned workshop to a hot vegas outside air temp, but my other 2 good coronas can deal with the heat with no problem or change of behavior.
What Gives here ????????????????????
P.S. I've been flying it with no canopy, so extra in flight cooling dont help!
If the Gyro is at fault, I'll gladly Throw it out although its new, but I was just wondering if it could be something else causing this problem...