Modified Helicopter Icing Spray System Evaluation.

All tests required 55 flight hours 41 flights. During the first testing period, structural and dynamic tests were conducted throughout the CH-47C flight envelope and the physical properties of the spray cloud generated by the modified icing spray system were measured. Two deficiencies were found boom stresses greater than the materials endurance limit which severely restricted the maximum airspeed at which the system could be operated 110 knots true airspeed, and an inadequate and unsafe boom extensionretraction system. Additional modification was made to the system and envelope expansion tests were repeated. During the second testing period, the two deficiencies were eliminated. However, flight with the boom retracted except at very low airspeeds and flight at a rotor speed of 235 rpm continued to produce excessive boom stresses. These excessive stresses constituted a shortcoming. Additional modification to the HISS was made to correct this shortcoming. The modified HISS with this additional change is airworthy within the unrestricted CH-47C flight envelope.