Rotorcraft Pitch-Roll Decoupling Requirements from a Roll Tracking Maneuver

A research investigation has been conducted on the effects of pitch-due-to-roll and roll-due-to-pitch cross coupling on helicopter handling qualities while performing a forward flight (60 knots) roll-axis tracking task. Conducted under the US/German Memorandum of Understanding (MOU) for Cooperative Research in Helicopter Aeromechanics, this study involved complementary use of a NASA-Ames ground-based simulation and two inflight simulations using DLR’s variable-stability BO 105. The results show that for a roll tracking task, the current time-domain pitch-roll cross coupling criteria does discriminate against unacceptable coupling from basic control, rate, and combined control-rate coupling. However, this criteria format does not discriminate against washed-out coupling which can occur in helicopters with feedback control systems. In addition, the data suggest a tightening in the Level 1-2 boundary, and the four-second window specified for obtaining compliance data may not be suited for highly agile helicopters. A newly proposed frequency-domain criteria offers more comprehensive coverage that shows consistency for all types of coupling investigated. An additional benefit is that the required frequency-domain data can be obtained from the bandwidth tests and analysis, thus eliminating the need for additional compliance test data.