Decision-Height Windows for Decelerating Approaches in Helicopters: Pilot/Vehicle

摘要

A combined analysis and flight test program was conducted to investigate thecharacteristics of the decision height (DH) window for helicopter decelerating instrument approaches. The concept of an effective flight path angle has been employed to define the DH window in terms of basic rotorcraft performance data. Exploratory flight tests were conducted to validate this approach and to define the approximate dimensions of the DH window 50 feet above ground level. The flight test experiment included an instrument meteorological conditions (IMC) decelerating instrument approach with errors built into the flight director to cause the helicopter to arrive at the decision-height with some glideslope and groundspeed errors. The pilots were required to visually maneuver the rotorcraft from decision-height. The results indicate that the high speed boundary of the DH window is a function of the minimum usable torque, and related to maximum acceptable pitch altitude during deceleration. Some margin is required to account for pilot delay or control misapplication after breakout. The upper glideslope error boundary is based on the maximum negative aerodynamic flight path angle that can be flown at low airspeeds. Poor visual cuing after breakout tends to emphasize the need for margins from the helicopter performance. The low speed boundary of the DH window is based on rotorcraft handling qualities at very low airspeeds. The low glideslope boundary is dependent on obstruction avoidance and ability to see the heliport environment upon breakout at decision-height.