Active Control of Performance and Vibratory Loads using Trailing-Edge Flaps and Leading-Edge Slats

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The objective of this research work is to develop a comprehensive analysis

version of UMARC (University of Maryland Advanced Rotor Code) to study

the capabilities of trailing-edge flaps (TEFs)and leading-edge slats (LESs)

for helicopter vibration reduction and performance improvement and rec-

ommend flap and slat configurations for a typical helicopter rotor such as

UH-60A rotor, which maximize these benefits. This study uses propulsive

free-flight trim except in hover. Using TEFs , the rotor performance in hover

was improved with a combination of torsionally softer blades and positive

TEF deflections. For the vibration reduction studies, a multicyclic control

algorithm was used to determine the actuation schedule . Suitable combi-

nations of lower harmonic TEF inputs were shown capable of reducing the

rotor power requirement by about 4-5 % at an advance ratio of μ = 0.4.

The TEF was shown to be capable of suppressing the vibratory loads at a

range of forward speeds, using half peak-to-peak deflections of about 5 °-10 ° .

Softening the blades in torsion resulted in larger flap actuation requirements

for vibration reduction. Parametric sweeps of TEF actuations were carried

out to determine suitable combinations of steady and various frequencies of

actuation of flaps , which yield overall power reductions and it is observed

that a combination of 1, 2, 3, 4 and 5/rev TEF inputs resulted in a power

reduction of 1.5% , while also reducing certain vibratory loads by more than

50% in high speed-forward flight.

To explore the advantages of leading-edge slats, the slatted airfoils with

configurations S0, S1 and S6 (used by Sikorsky) were used. The slatted blade

sections had the SC2110 baseline/slatted airfoils in place of the baseline UH-

60A airfoils. Dynamic actuations are chosen to retain the high-lift benefits of

the slats while seeking to minimize profile drag penalties over regions of the

rotor disk operating at lower angles of attack, i.e., the advancing side. The

effects of leading-edge slats extending over 20%, 30% and 40% of the blade

span on rotor performance and vibratory hub loads were examined. The

study uses propulsive free flight trim. In moderate to high-speed forward

flight,leading-edge slats were shown to enhance the maximum rotor thrust by 15-30% at advance ratios larger than 0.2 and reduce power requirements

by 10-20% at high thrust levels. 20% span slats offered a good compromise

between power reductions and adverse effect on vibratory hub loads. The rotor

with leading-edge slats could be trimmed at a maximum forward speed that

was about 20 knots greater than for the baseline rotor with no slats.

This study also shows that additional power reduction is achievable by

suitable TEF deployments superimposed on certain slat actuations in

high-speed forward flight.