By Geno Mancini, EAA 1287680
About 30 years ago, I decided that if I were going to continue to fly my first RotorWay helicopter, I needed more power. So, back then I designed and built an all-aluminum Chevy V-6 engine with a planetary transmission. It produced more than 300 hp, and I flew it for about 50 hours and then sold it.
One big difference between now and 30 years ago is that there was no internet back then and no one to talk helicopters with, so what I learned came from books or talking on the telephone.
Fast-forward to 2016 and I am retired and need another project. I decided to build another RotorWay, but this time I went with the Allison 250-C20B turbine. Pulled straight out of a Bell Jet Ranger, this turbine puts out 420 hp.
It took approximately two years to complete the build, working on it almost every day — some short hours, some long hours. After looking at hundreds of different paint schemes, I decided to go with a white and blue tear-off look. I just wanted a different look that would catch your eye.
One of the challenges I had was the tail rotor input shaft, the long one that goes down the tail boom. On a Jet Ranger, the input shaft runs at 6000 rpm, so I tried to do the same. After 120 different tests (chromoly shafts, aluminum shafts, rubber-mounted bearings, solid-mounted bearings, vibration dampeners, high-speed U-joints, Thomas couplings, three-segmented shafts, five-segmented shafts, three bulkheads, five bulkheads — you name it, I’d tried it), I finally got the vibration down to 0.1 inches per second at idle and thought that would work. Then I revved it up to 6000 rpm, and that 0.1 went to a 0.5, the bearings were more than 200 degrees, and the tailrotor gearbox was more than 220 degrees.
I said, “That’s it. I’m slowing this shaft down,” and designed and built an all-aluminum 3-to-1 transmission. Now the bearings are less than 100 degrees, and the tailrotor gearbox runs at 120 degrees. I’m sure Bell and all its engineers had many hours developing that input shaft, but I had to move on.
The avionics consist of an MGL glass cockpit, GPS, compass, and comm radio, along with a Sandia STX 165R transponder. There are chip detectors for the engine, transmission, and tail rotor gearbox, and all bearings have sensors and alarms back to the cockpit. Engine and transmission oil flow are also metered and sent back to the cockpit. All alarms show up visually on the 8.5-inch display and audibly through the headset. My goal with the computer system is to let the computer monitor the helicopter; my eyes need to be looking outside.
There are two engine oil coolers and one transmission oil cooler. The helicopter has a 42-gallon fuel capacity and burns 16 gph of either Jet A or diesel, and VNE is 115 mph. The empty weight is 1,100 pounds, max gross is 1,900 pounds, and maximum seat load for pilot and passenger is 500 pounds. I really like the way it flies — so smooth with the turbine engine, especially compared to a piston engine.
I did all of this work out of my own shop in Mountain Iron, Minnesota. To take on a project like this, you need to have access to a lathe, vertical mill, and a TIG welding machine. I also draw all my components on AutoCAD and couldn’t do it without it. This was quite a project, but quite satisfying after it was completed. I never have been afraid to start something new. What I didn’t know, I learned along the way.
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