RotorWay Scorpion Too / Scorpion 133
Designed by B.J.Schramm, in 1972, the Scorpion II was introduced with an OMC 125 horsepower, 2 cycle engine which provided the added power to fly two lightweight people in cool, low density altitude environments with a gross weight of 1125 pounds. But despite all the improvements, overhaul times on the major components were still not up to the desired levels.
In 1973 the new Scorpion Too made its first flight at Oshkosh with designer B. J. Schramm piloting. In 1975, RotorWay developed its own four-cylinder engine to better meet the helicopter’s requirements for a two-person load and an empty vehicle weight of less than 700 pounds.
In 1974, the company embarked on a major redesign of the helicopter once more with the end goal of reducing the amount of maintenance time required per every hour of flight. The first, and most important, item to be addressed was the elimination of the inefficient 2 cycle engine. The company realized that there would never be a way to sufficiently dampen the excessive vibration and low torque associated with this type of engine. The vibration was found to cause rapid wear in various parts and had a tendency to cause cracks in airframe and drive systems.
Unable to find an engine manufacturer to make their 4-cycle engine suitable for the helicopter, RotorWay set forth on producing their own engine. Called the RotorWay RW 133, this 4 cycle, 4-stroke engine now had the added power and torque the company was looking for. The RW 133 had a cruise speed of 80 mph with a range of 120 miles and a useful load of 420 pounds.
In 1975 a 4-cycle engine, the RW 133, went from design to prototype, to production. In 1976, RotorWay changed the model designation from the Scorpion Too to the Scorpion 133 to indicate the new RW 133 power plant. This new Scorpion has a new asymmetrical airfoil rotor system.
B.J. Schramm wanted to give the world a low-cost personal helicopter, but it wasn't until the summer of 1976 that he finally raised the flag. As of October 1, 1976, RotorWay Corporation sold Scorpion 133 kits for $13,500 including a completely new water-cooled 133 hp (derated from 140) engine designed and produced by RotorWay. Schramm owns his own foundry.
The engine has a single ignition system, the airframe is steel tubing that comes to the builder tack-welded into the proper alignment. The builder with no welding experience is encouraged to get expert help to finish the welds; any experienced aircraft welder could do the job handily. The airframe is designed for very low initial cost. It is also designed to be easy to repair and overhaul, taking only eight hours to disassemble to a bare ship, 16 hours to rebuild the subassemblies and 20 hours to reassemble. The frame is based on several intersecting circles and triangles that offer excellent rigidity, a pylon over the cabin for rollover protection and a notice-able lack of busy little clusters of tubing in favor of simple single-tube structures.
The rotor system is a clockwise-rotating two-blade teeter system (to avoid the cost of designing out ground resonance in the landing gear) with a clever system that separates the collective and cyclic functions so that blade pitch changes only when the pilot moves the collective control. A cable runs up the rotor shaft and curves back down to connect to a scissor that regulates the blade pitch. An otherwise conventional swash plate operates the cyclic control of the rotors. The airfoils are asymmetrical, which Schramm says avoids pressure-center shifts and produces lift at lower angles of attack. The controls are all push-pull cables.
The primary drive uses belts, which have good power-pulse-damping characteristics and perform well in low-torque applications. The secondary uses a chain drive because of the higher torque; the chain produces a loss of only 1.5 percent of power, which is much better than gears would have achieved. Three belts from the secondary run a relay race to the tail rotor, and they're happy transmitting as much as 25 hp, though the Scorpion's tail rotor could never draw more than 15.
The cabin enclosure is all fiberglass and can be removed in 10 or 15 minutes; if it's damaged, it can be repaired with conventional glass-repair kits. It can be equipped with dual controls, which take about 10 minutes to install. The throttle is five percent coordinated with collective. Pedals are conventional, although it takes awhile to get used to kicking the right rudder for hover torque instead of the left, since the rotors turn opposite of normal.
Engine: 105kW Evinrude marine.
Engine: RW 133, water-cooled, four-stroke, 133 hp
Length: 22 ft
Height: 7.5 ft
Width (cab): 4 ft
Rotor dia: 24 ft
Gross weight: 1,235 lb
Empty weight: 805 lb
Accessories: 15 lb
Equipped useful load: 415 lb
Payload max std fuel: 355 lb
Fuel capacity, standard: 10 USG/60 lb
Fuel capacity, optional: 15 USG/90 lb
Disc loading: 2.5 lb/sq.ft
Power loading: 9.3 lb/hp
Rate of climb: 800 fpm
Service ceiling: 10,000 ft
Max cruise: 70 knots
Hover I.G.E. 6500 ft
Range (max fuel, optimum cruise power, one person): 130 nm/2 hr
Range (max fuel, optimum cruise power, two persons): 79 nm/1.3 hr
Fuel flow at maximum cruise 45 lb/hr
Fuel flow at maximum range cruise 40 lb/hr