This piece originally ran in Vic’s Checkpoints column in the September 2023 issue of EAA Sport Aviation magazine.
This month I’ll get back to the flight testing of the Hummingbird. Yes, the 40 hours required by the Phase I operating limitations have been completed, but I am learning that properly flight testing a helicopter is a whole different ballgame than flight testing an airplane.
Most of the flight testing of other aircraft I have built has been uneventful, except for the Prescott Pusher. After completion of Phase I, it was off to the races, going places, and having fun. Helicopters are much more complicated with lots of moving parts that need to be measured, tweaked, and adjusted to play nice with each other.
It’s still a lot of fun, and I remind myself that I built one to learn something new, and it is doing that quite well. Support from Vertical Aviation has been stellar and made it enjoyable as well.
The only things required on a fixed-wing aircraft propeller are to use the proper torque on the mounting bolts and check the blade track at the tips. Balancing the propeller is a nice touch and usually makes for a substantially smoother ride but is optional.
Helicopter blades are at the opposite end of the spectrum. While propeller blades stay in a fixed-pitch position throughout a revolution (yes, even constant-speed ones), helicopter blades are continually changing in pitch. In forward flight, for example, the retreating blade needs to create more lift across itself as the relative wind has decreased. It does this by assuming a higher angle of attack.
Then, as it continues its arc and becomes the forward-moving blade, the angle of attack needs to be decreased. This is all accomplished at the hub through many moving parts — which all require adjustments. At the same time, all the blades need to be tracking in the same plane.
Initial adjustments for proper blade tracking are done by adjusting the…