I have about 150 hours in various Schweizer 269/300 models. I have flown enough in the Schweizers to recognize when something is not "normal".
I am looking to buy a UH12B, but I have zero experience with Hillers, and with 2 bladed teetering rotor systems. Unfortunately, I do not have any point of reference to determine if a particular Hiller is exhibiting a problem or is just exhibiting the uniqueness of that particular model / rotor configuration.
I had an opportunity to fly the Hiller UH12B that I am considering to purchase. I noticed that during engine warm up at 2000 RPM (engine) 200 RPM (rotor) there was a noticeable oscillation in the cyclic that also translated to movement of the fuselage that corresponded with the main rotor, not unlike what I have encountered in a Schweizer, but maybe a little more prominent.
At operating RPM, the oscillation increased accordingly, and would be more accurately described as a vibration, also felt in the cyclic as well as the fuselage. Again, not unlike what I have encountered in the Schweizer, but just more prominent. The vibration isn't uncomfortable, but noticeable.
The mechanics who have been working on the Hiller have accomplished a track and balance, and said that it is running "smooth". The pilot I flew with also said it was running smooth and downplayed the vibration as normal. Since I have no experience in Hillers, it could be exhibiting a major problem, and I have no way to dispute it.
For comparison: Hiller operating RPM = 3100 engine/350 rotor; two blade, teetering.
Schweizer 300C operating RPM = 3300 engine/475 rotor; three blade, fully articulated.
(The 300 CB and CBi operates at lower engine RPM, but still produces 475 rotor RPM)
Does anyone have any insight into what would be "normal" rotor vibration in a Hiller?