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The second wind-tunnel test of DLR’s multiple swashplate system

IBC on a five-bladed rotor with fuselage-mounted (fixed frame) actuators

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Abstract

After proving its individual blade control (IBC) capabilities on a four-bladed rotor system in the wind tunnel, the DLR’s multiple swashplate system and its control software were developed further to allow IBC operation on a five-bladed rotor system. After preliminary tests in hover conditions, a second wind-tunnel test was performed in the DNW-LLF wind tunnel in late 2016. The goal of this test on a Mach-scaled model rotor was to reduce vibration, noise, and required rotor power in different flight conditions using proven IBC strategies as well as localized pitch control (LPC) on five blades. In descent flight condition, significant reductions of blade–vortex interaction noise relative to the baseline case were achieved on both sides of the rotor disk through the application of 2/rev higher harmonic control as well as using an LPC schedule. Through the application of 3/rev IBC as well as a vibration controller using a 4–6/rev multi-harmonic IBC signal, 5/rev hub loads were reduced significantly and the 5/rev vertical vibrations were nearly eliminated. In addition, during simulated high-speed-level flight with a wind speed of 76 m/s, the required rotor power was successfully reduced using a 2/rev input with an amplitude of 1\(^\circ\).

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Abbreviations

\(C_\mathrm{{T}}\) :

Thrust coefficient

\(F_{x,y,z}\) :

Hub forces (non-rotating frame) (N)

\(I_\mathrm{{BM},5}\) :

Index for blade-bending moments with influence on 5/rev hub loads

\(M_{x,y,z}\) :

Hub moments (non-rotating frame) (Nm)

\(N_\mathrm{{b}}\) :

Number of blades

p :

Pressure (kPa)

r :

Radial coordinate (m)

R :

Rotor radius (m)

\(VI_{5}\) :

Weighted 5/rev vibration intrusion index

\(V_{\infty }\) :

Wind speed (m/s)

\(y_\mathrm{{tip,el}}\) :

Elastic lag displacement at the blade tip

\(z_\mathrm{{tip,el}}\) :

Elastic flap displacement at the blade tip

\(\alpha _\mathrm{{S}}\) :

Rotor shaft angle (\(^\circ\))

\(\beta _\mathrm{{PC}}\) :

Pre-cone angle (\(^\circ\))

\(\gamma\) :

Flight path angle of the model (\(^\circ\))

\(\Theta _{0,\mathrm{{C,S}}}\) :

Collective and cyclic control angles (\(^\circ\))

\(\Theta _\mathrm{{dip}}\) :

LPC amplitude (\(^\circ\))

\(\Theta _{n}\) :

n/rev HHC Amplitude (\(^\circ\))

\(\sigma\) :

Solidity

\(\Phi _{1,2,H}\) :

Width of LPC slopes and plateau (\(^\circ\))

\(\phi _{n}\) :

Phase of elastic n/rev blade torsion (\(^\circ\))

\(\varphi _\mathrm{{dip}}\) :

LPC Phase (\(^\circ\))

\(\varphi _{n}\) :

n/rev HHC Phase (\(^\circ\))

\(\vartheta\) :

Individual blade-pitch angle (\(^\circ\))

\(\mu\) :

Advance ratio

\(\psi\) :

Azimuth angle (\(^\circ\))

\(\psi _{1,2,a,b}\) :

Additional LPC parameters (\(^\circ\))

\(\Omega _\mathrm{{ref}}\) :

Rotor rotational frequency, (rad/s, Hz)

BL:

Baseline

DLR:

Deutsches Zentrum für Luft- und Raum-fahrt e.V. (German Aerospace Center)

DNW:

Deutsch-Niederländische Windkänale (German-Dutch Wind Tunnels)

FTK:

Fortschrittliche Taumelscheibenkonzepte (advanced swashplate-concepts)

HART:

HHC aeroacoustics rotor test

HHC:

Higher harmonic control

h.p.:

High-pass filtered

IBC:

Individual blade control

LLF:

Large low-speed facility

LPC:

Localized pitch control

META:

MEhrfach-TAumelscheibe (multiple swashplate rotor control system)

MN, MV:

Minimum noise, minimum vibration

SKAT:

Skalierung und Risikominimierung von Technologie bei innovativem Design (Scaling and risk-minimization of technology with innovative design)

SPL:

Sound-pressure level

SPL.rel:

Sound-pressure level relative to max. level of the respective frequency range

SPR:

Stereo pattern recognition

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Acknowledgements

The tests in the DNW wind tunnel were conducted within the framework of the national research project SKAT (Scaling and risk-minimization of technology with innovative design) funded by the German Federal Ministry of Economic Affairs and Energy. The authors would like to express their gratitude towards everyone involved at DLR and DNW during the planning, preparation, and execution of the SKAT wind-tunnel test and the subsequent data analysis.

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Authors and Affiliations

  1. Institute of Flight Systems, German Aerospace Center (DLR), Lilienthalplatz 7, Braunschweig, 38108, Germany

    P. M. Küfmann, R. Bartels, B. G. van der Wall & O. Schneider

  2. German-Dutch Wind Tunnels (DNW), Voorsterweg 31, Marknesse, 8316 PR, The Netherlands

    H. Holthusen & J. Postma

Authors
  1. P. M. Küfmann
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  2. R. Bartels
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  3. B. G. van der Wall
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  4. O. Schneider
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  5. H. Holthusen
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  6. J. Postma
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Correspondence to R. Bartels.

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Küfmann, P.M., Bartels, R., van der Wall, B.G. et al. The second wind-tunnel test of DLR’s multiple swashplate system. CEAS Aeronaut J 10, 385–402 (2019). https://doi.org/10.1007/s13272-018-0323-2

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