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The Army Preliminary Evaluation (APE) of the Bell Model 211 prototype helicopter (Hueytug) was conducted at the Bell Helicopter Test Facility, Arlington, Texas, Edwards AFB, California, and Bishop, California, from 19 October through 7 November 1968. Flying qualities, performance, and mission suitability were evaluated to determine aircraft capabilities to carry six thousand pound sling loads at a takeoff gross weight of 14,000 pounds. Primary emphasis was directed toward the artillery mission of displacing a 105mm Howitzer M101A1 with 10 rounds of ammunition and 3 cannoneers. The helicopter had eight deficiencies which require mandatory corrections. Two of these are major design deficiencies that may require extensive engineering redesign. They are the directional oscillations in the 30 to 60 KIAS airspeed range, especially prevalent during heavy sling load missions; lack of sufficient directional control margin during high gross weight (14,000 pounds) and high density altitude (above 4000 feet) conditions. The remaining six deficiencies are ineffective force trim feature at high airspeeds, excessive forward position of longitudinal control at high airspeeds, poor static engine droop compensation, tail rotor drive train torque limitations, lack of an engine power torque limiter and lack of a standby generator for IFR flight. There are seven shortcomings the corrections of which are desirable and should be accomplished as soon as possible. The prototype model 211 could marginally perform the 14,000 pound gross weight mission at sea level. At 4000 feet density altitude the marginal tail rotor control and transmission and drive train torque limitations prevented the helicopter from satisfactorily accomplishing the mission. Correction of the deficiencies discovered during this APE coupled with the 200 horsepower increase in drive train torque limits of the design proposal should result in a superior performing helicopter. Correction of the deficiencies should be accomplished prior to a production contract.

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