Subaru powered scorpion kit helicopter modification page 3
Notes from Ron Froeburg: The Subaru engine was modified with a custom built flywheel made from 6061 T6 aluminium, the ring gear was from an automatic flywheel. The drive pulley was machined to fit the all aluminium flywheel. The drive pulley was also 6061 T6 aluminium with a one inch stub shaft out of the top for the upper support bearing.
The oil system was modified by building an oil pan with a lower sump and building the oil pump pick up tube to go to the bottom of the new sump. For the oil to drain to the new sump, two holes were drilled next to the front pulley on the engine (now at the bottom) also valve cover drains were welded ineach cover to the oil pan.
The rotation on the engine was backwards compared to the original boat engine installation so the rotor system had to be reversed with new blade straps being made for the change. The tail rotor was reversed by undoing the pitch links and rotating the blades 180° (degrees).
To sum it up, the ship did fly but power wasn't so good. The engine was advertised as putting out 80hp but was probablyy closer to a more realistic 60hp. We ran it at 4500rpm then tried it at 5000rpm with little improvement. I then ported the engine and raised the compression and finally got it to fly with only marginal power reserves.
|Rear 3/4 view of the completed ship. The engine installation is neat and clean and eliminates several belts and pulleys that are used in the stock Evinrude engine installation|
Editors note: In the early 90's the EA81's power potential hadn't yet been realised. Through further experimentation over the next few years it was discovered that significant horsepower gains could be improved and that was without even considering turbo charging which Doug Schwochert later discovered as a solution to the lack of power issue.
|Subaru powered Scorpion 1 helicopter hover testing|
Ron said that after replacing the Hughes blades with the stock Rotorway blades the stability problems went away and he appeared to have more power (hp). The Huges blades have a built-in twist which were apparently flexing and causing the instability problems.
Froeburg has flown the ship through transitional into forward flight up to about 40 mph. At the time of his latest report no major problems had been encountered.
Apparently he sold the Scorpion to allow time to take on a Rotorway Exec project recently. The new owner had reported that for some unknown reason, the engine had blown while hovering and inquired if he had a possible solution?
It could just be a "fluke" and Ron recommend that he install another engine and give it a go. Unfortunately persisting with research and development is the only way to get these answers! Only time will tell if the little EA81 will be a reliable powerplant for light homebuilt helicopters.
|Subaru EA81 powered Rotorway Scorpion 1 helicopter taxiing|