Digital "Barstool" Heli Thrust Dyno
The idea is to develop and build a Helicopter Thrust Dynomometer that will accurately and with great repeatability, read the thrust of the main rotor output of R/C helicopters. This will allow the testing and comparison of different rotor blades. Mostly this dyno is for finding the fastest blades for drag racing. But much can be learned from throttle/pitch curve experiments and engine/pipe tuning tests also.
The construction of this dyno follows the philosophy of using off the shelf parts. Two pieces of 2 ft X 2 ft plywood, one 29 inch tall wooden barstool, .75 inch square wood stock and some wood screws finish the parts list. Keeping the heli 33 inches off the ground should help eliminate any ground effect. The digital electronics are adapted from an HP medical project that I was on. The unit was a medical scale using four load cells, a digital display and a microprocessor.
Dyno Tests and Updates
June 3, 2000: The first test of the dyno was with the Shuttle. It was about 72 degrees @ 100 feet above sea level. The heli was clamped down to the top of the barstool. The digital readout was placed 25 feet away for safety via an RJ-45 cable. The first thing I noticed was that when the heli was first spooled up, it shook much harder than usual as the main rotor blades found their centers of gravity. As the main rotor RPM increased, the digital scale was showing an increase in thrust. At maximum thrust, it was reading about 22.5 lbs with the stock wooden Shuttle semi-symetrical blades. The carbon NHP 550mm symetrical blades pulled about 23.5 lbs of thrust. Watching the blades arching upward heavily under load was kind of frightening. Rotor RPM was about 1800 RPM at 15 degrees of pitch at full throttle. This test confirmed my feeling that the NHP blades, although symetrical, do actually make more thrust than
the stock semi-symetrical wood blades. I have always been impressed with the quality and durability of the stock blades however. They have been great for testing over the years. As I decreased the RPM the heli shook again very violently. Later flight tests proved that the heli was fine. I suspect that the shaking has to do with the heli being so firmly anchored to another solid object. An isolation scheme needs to be developed to reduce the shaking because it nearly caused a boom strike. The heli almost fell off of the stand because the anchor had vibrated loose. For proving the basic concept that a heli thrust dyno can be easily made, the test was a success. In future testing I will look into how the various brands and shapes of blades compare to each other. It has been said untold times that 15 degrees is stalling the blades. This dyno will also help find out where blade stall actually occurs.
Blade Test Results
|Hirobo, ZXX, stock wood||semi||550 mm||47 mm||90 grams||22.5 lbs||15||1800
|NHP, carbon, 550s||sym||550 mm||47 mm||98 grams||23.5 lbs.||15||1800