Hirobo KV107II is a sucessful twin rotor helicopter commonly known as the Vertol, I have had from new in 1992 it still has the original engine an OS32SX-H which is a little marginal on power during the warmer months of summer. If flown nicely however it is adequate and I have not been tempted to upgade to the .39 or .46, everthing on it is original including the wooden rotor blades. All mixing to the swashplates is a facinating collection of mechanical mixers with some 60 ball links involved so eliminating slop from the system is not going to happen. The mixing system also provides for interesting control during flight and can prove difficult as I believe the full size aircraft also presents a difficult piloting process. It can and I have flown it without a gyro but it is nearly impossible to prevent the nose climbing out in forward flight and the faster it goes the more difficult it becomes. There is a need for at least one Gyro for elevator control, I have three fitted in elevator, aileron, and yaw, the later two at only about 20% control.
August 2017 the engine has had a refit so new bearings, piston, ring, and liner, the mechanics have been disasembled, checked and lubrcated, NimH flight pack replaced with a 2 cell Lipo and BEC set to 5V, servos checked and gear train lubricated.