Analysis of low-speed height-velocity diagram of a variable-speed-rotor helicopter in one-engine-failure

This work analyzes the effects of variable operating rotor speed on the helicopter low-speed Height-Velocity (H-V) diagram in one engine inoperative (OEI) situation. Using the UH-60A helicopter as baseline helicopter, a flight dynamics model and the applied optimal control method were validated against the corresponding flight test data. Both low-speed H-V diagram in OEI and landing procedures at corresponding key points (Low hover, Knee and High hover) were investigated. Results indicate that the reduction of operating rotor speed will cause the unsafe area of H-V diagram to shrink gradually at first, and then expand rapidly when the operating rotor speed reduces below a certain value. It is observed that the lower constraint of rotor speed during OEI landing has a significant impact on the H-V diagram. Finally, results also show that a reasonable rotor speed not only effectively reduces the helicopter required power during steady level flight, but also improves the landing performance in the event of OEI. (C) 2019 Elsevier Masson SAS. All rights reserved.