Rotorcraft Pitch-Roll Decoupling Requirements from a Roll Tracking Maneuver

Abstract

A research investigation has been conducted on the sects of pitchdue-lo-mll and roll-due-to-pitch cmss coupling on helicopter handling qualities while performing a forward flight (60 knots) mll axis tracking task. Conducted under the USlGerman Memorandum of Understanding (MOU) for Cooperative Research in Helicopter Aeromechanics, this study involved complementary use of a NASA-Ames ground-based simulation and two in-flight simulations using DLR's variable-stability HO 105. The results show that for a roll tracking task, the c u m n t timedomain pitch-mll cross coupling criteria d w s discriminate against unacceptable coupling from basic control, rate, and combined control-rate coupling. However, this criteria format does not discriminate against w a s h e d a~t coupling which can occur in helicopters with feedback contml systems. In addition, the data suggests tightening in the ADS33 Level 1-2 boundary, and the four-second window specified for obtaining compliance data may not be suited for highly agile helicopters. A newly pmposed frequency-domain criteria offers more comprehensive coverage Ulat shows conqistency 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 d u c i n g compliance flight time by eliminating specific pitch-roll coupling tests.