Fixed-base simulation evaluation of various low-visibility landing systems for helicopters

Koziol, Jr. Electronics Research Center SUMMARY A fixed-base simulation evaluation of various low-visibility landing systems for helicopters has been made. The low-visibility mission consisted of a straight-in glide slope and localizer approach with a flare and deceleration maneuver at the end. The landing systems consisted of a fully automatic system and six manual systems. The manual systems consisted of three flight control modes each being flown with a flight director indicator and then with raw data displays. The three flight control modes were an attitude command mode with an unaugmented vertical axis, an attitude command mode with rate of descent command in the vertical axis, and a three-axis velocity command mode. The landing systems and the helicopter were simulated on a hybrid computer. The landing systems were all digital. A series of six subjects consisting of two engineers and four instrument-rated pilots flew each of the modes for the ianding mission. Per- formance data was recorded by the digital computer and analog recorders. “he relative performance of the modes are presented. The results indicate that all modes are acceptable for the mission prior to flare and deceleration. When flare and decel- eration are considered, the simplest attitude command mode becomes unacceptable both with a flight director indicator and with raw data displayed. This is due primarily to the fact that this mode had no augmentation in the vertical axis and the coupled dynamics between pitch and power became difficult to control through the flare and deceleration maneuver. When augmentation in the vertical axis was added to provide a rate of descent command system with altitude hold capability, the system became acceptable both with the flight director indicator and with raw data displays. INTRODUCTION The majority of helicopters flying today do so with no electronic controls or, at most, with limited authority attitude rate stabilizing systems. Although these vehicles demand a high pilot workload they have been very successfully used under VFR conditions and under IFR conditions in cruise flight. Low-speed flight under IFR has been carried out by the military to some degree but it is generally agreed that advanced systems in con-