Thursday, August 10, 2017
Home » Product Reviews » O.S. 91HZ-R 3D Helicopter Engine With Regulator

O.S. 91HZ-R 3D Helicopter Engine With Regulator

Step Up Performance With This Upgrade

We had a chance to review the OS HZ-91 engine with the Align T-Rex 700 last issue and found that this best of breed engine had plenty of power and ran smoothly and powerfully even when the needles were set rich. Its overall performance was more than adequate for a 90-size helicopter. Right after that review the regulated engine upgrade was released. The new on demand regulator system was designed specifically for the O.S. 91HZ and offers a steady fuel supply from the beginning of the tank to the end. This is delivered through a oneway check valve and crankcase pressure coupled with a fuel regulator that provides a measured fuel supply to the carburetor.  

UPGRADING THE O.S. 91HZ
An upgrade option became available for those already flying the O.S. HZ-91. This upgrade was a simple drop-in replacement. We loosened the carb collar pinch point, dropped in the new carb, aligned the notches on both the engine and the carb, and tightened it back up. After that we unscrewed the back plate, added the new back plate that has the pressure nipple; and we were upgraded. The engine performance was noticeably improved. Engine recovery after loading the rotor disc was close to instant and the needle adjustments were much different than expected. We consulted Bert Kammerer who has been testing the engine since

IRCHA 2009 and he told us our midrange is going to end at about a 1/2 turn of the needle and that the high needle is going to end up about 1 1/2 to 1 3/4 turns. We are not used to seeing the needles that lean so the regulator appears to be delivering the fuel very efficiently. If you go with the carb upgrade as opposed to a new engine, and you have run the break-in process already, there is no need to richen up and go through the break-in process again. You are ready to just lean out and jam!
LinksO.S. Engines, distributed exclusively by Great Planes Model Distributors, www.osengines.com, (800) 682-8948