Above & Beyond: Jump Ship
- By E. Stuart Gregg
- Air & Space magazine, March 2001
Courtesy E. Stuart Gregg
In 1942 the U.S. Army Air Forces held a competition for development of an autogiro that could take off and land vertically with little or no roll, unlike the typical autogiros of the day, which required a short takeoff roll. The AAF wanted an aircraft that could be operated in close confines. Prototypes of the Kellett XO-60 and the Pitcairn XO-61 “jump giros” were evaluated, and Kellett won a contract for six YO-60s. (The XO-61 had run into cooling and power problems due to its pusher propeller configuration.)
The following year, my outfit, the 445th Test Squadron of the 50th Fighter Group, stationed at the Air Forces School of Applied Tactics at Orlando, Florida, was tasked with determining how these aircraft could best be used in combat operations. Lieutenant Bob Miller and I, both primarily fighter pilots with no prior experience with such strange aircraft, were ordered to pick up two at the factory in Lansdowne, Pennsylvania, and fly them to Orlando.
In the course of some 20 hours of training under Kellett chief test pilot Dave Driskill, we learned that taking off vertically in the YO-60 was a complicated process, and dangerous if mishandled. Driskill had been in a near-fatal accident in the prototype, and he delighted in showing the resulting scars to us novice giro pilots to drive home the importance of proper technique.
An autogiro uses a standard propeller to pull it through the air, and the airflow over the rotor blades turns its freewheeling lifting rotor. A jump giro has an auxiliary drive shaft from the engine to the rotor, which allows the rotor to build up speed in flat pitch while on the ground, storing kinetic energy like a flywheel. The stored energy allows the aircraft to rise vertically when the pilot abruptly increases rotor blade pitch to lift off. A clutch then disengages the drive shaft to prevent rotor torque from spinning the jump giro like a top.
The YO-60 had a conventional throttle for the 300-horsepower Jacobs engine, a constant-speed propeller on the nose, and traditional stick and rudder controls. However, because of excessive feedback from its mechanical connection to the rotor that caused the stick to thrash about at low rpm, the control stick was secured in a lock on the instrument panel unless rotor speed was above 200 rpm. Only then could it be disengaged. During takeoff, the pilot held it firmly forward and right, to counter rotor feedback and engine torque.
Power was taken off a drive shaft from the rear of the engine to the rotor head and was engaged by a T-handle clutch on the left side of the instrument panel. There was also a rotor pitch-angle lever that the pilot pulled back and locked for flat rotor pitch during rotor rev-up. On top of this lever was a red quick-release button that caused a spring-loaded nine degrees of pitch to be suddenly applied to the rotor blades to facilitate a jump takeoff. All these exotic controls were very confusing to the student pilot, and if not used in proper sequence, the results could be disastrous.
Lightly loaded and in cool weather, the YO-60 could make a spectacular vertical takeoff. It could jump five to 15 feet straight up before accelerating forward in a climbout. In hot weather, with a full load of fuel and a passenger, it would merely lurch into the air, where its straining engine and propeller could eventually make it climb rather handily.
Landing gave us fits. It required one to glide down final approach at only 40 mph, flare at an exaggerated angle 10 feet off the ground, and in this absurd nose-high attitude, allow the aircraft to settle on its tail wheel, then pitch forward onto the nose gear.