Reducing Helicopter Main Rotor Power Requirements Using Multiple Trailing Edge Flaps And Extendable Chord Sections

Open Access
Author:
Leon, Olivier
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Dr Farhan Gandhi, Thesis Advisor
  • Farhan Gandhi, Thesis Advisor
Keywords:
  • stall alleviation
  • helicopter power reduction
  • TEFs
  • trailing edge flaps
  • extendable chord
  • SETE
  • flight envelope expansion
  • rotor lift redistribution
Abstract:
Reducing helicopter rotor power requirements is of much interest in terms of payload, ceiling altitude, maximum speed and maximum range. Rotorcraft power reduction can be tackled using a large variety of design solutions, ranging from passive blade twist design to active on-blade devices. The present study examines power reductions achievable using two different on-blade active methods. A rotorcraft model was developed in order to realistically assess the performance improvements. A propulsive trim analysis is performed on a UH-60 type helicopter model featuring advanced rotor and fuselage geometry, rigid blades free to flap and a rigid prescribed wake. The first concept, referred to as Static Extended Trailing Edge (SETE), aims at expanding the flight envelope by quasi-statically increasing the chord through the extension of a flat plate through a slit trailing edge over a section of the blade. This device used on the flight envelope boundaries for stall alleviation appears to be a better high-lift device than trailing-edge flaps or even Gurney flaps in that it results in higher lift-to-drag coefficients at high CL. Simulation results indicate that in stall-dominant conditions (high gross-weigh, altitude, sufficient available power) increases of up to 3,000 ft in the maximum altitude, 2,400 lbs in the maximum gross-weight, 26 knots in the maximum speed, and reductions up to 33.4% in the rotor power can be obtained. The blade section with the SETE mechanism was fabricated and appeared to operate well. The second concept aims at reducing the rotor power requirements for a range of advance ratios – from 0 to 0.4 – using multiple spanwise-segmented Trailing Edge Flaps (TEFs). 4 TEFs located from 50% to 90% span actuated up to 2/rev with a maximum amplitude of 5 degrees are optimally deflected to reduce the total average torque. Power reductions ranging from 1.61% to 5.65% depending on airspeed and thrust levels were observed with the UH-60 non-linear twist distribution. Using a -8 degrees linear twist blade, power reductions ranging from 2.74% to 7.98% were observed. Such reductions are obtained by redistributing the lift inboard and reducing the trim controls, globally off-loading the tip of the rotor blade and reducing its drag.