Design of a Cruise-Efficient Compound Helicopter

A slowed-rotor compound helicopter is conceptually designed using a multifidelity approach, showing the potential for significant efficiency improvements above conventional helicopters. The cruise tip speed and bilinear twist distribution are optimized using the Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics (CAMRAD II). System-level metrics are computed using the NASA Design and Analysis of RotorCraft (NDARC) program to show top-level payoffs. An aeroperformance map is generated using comprehensive analysis for the optimum twist distribution, providing calibration data for the main rotor model within NDARC. Effects of disk loading and wing loading on the size of the slowed-rotor compound helicopter are analyzed, and off-design performance is computed. Rotor–wing interference effects are analyzed using CAMRAD II for several wing vertical locations.

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Coupled and Trimmed Aerodynamic and Aeroacoustic Simulations for Airbus Helicopters' Compound Helicopter RACER

Journal of the American Helicopter Society ◽

10.4050/jahs.64.032003 ◽

2019 ◽

Vol 64 (3) ◽

pp. 1-14 ◽

Cited By ~ 2

Author(s):

Constantin Öhrle ◽

Felix Frey ◽

Jakob Thiemeier ◽

Manuel Keßler ◽

Ewald Kräamer

Keyword(s):

High Speed ◽

Flight Mechanics ◽

Main Rotor ◽

Noise Emission ◽

Tool Chain ◽

Aeroacoustic Noise ◽

Rotor Wing ◽

Compound Helicopter ◽

Cost Efficient ◽

Cruise Flight

In recent years, various helicopter manufacturers increasingly have been focusing on the development of new high-speed rotorcraft configurations, one of them being the compound helicopter RACER (rapid and cost-efficient rotorcraft) of Airbus Helicopters (AH). However, these new configurations encounter new aeromechanic challenges, in terms of aerodynamic interactions, flight mechanics stability, rotor dynamics, or aeroacoustic noise emission, to name only a few. To support AH at the minimization of risk of RACER's first flight, the Institute of Aerodynamics and Gas Dynamics provides high-fidelity coupled and trimmed aerodynamic and aeroacoustic simulations of the complete helicopter by the application of a multidisciplinary tool chain. In its first part, the work focuses on the description of this advanced tool chain and on important features for the analysis of this new configuration. In the second part, exemplary simulation results for a hover and a high-speed cruise flight condition are shown, and the main aerodynamic interactions between the different components are identified. As expected for this configuration, numerous interactions are found for both flight cases, e.g., main rotor–propeller interaction in hover or main rotor–wing interaction in high-speed flight. Finally, aeroacoustic results are shown for hover with a close look at the propellers' contribution.

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Configuration Study of Electric Helicopters for Urban Air Mobility

Aerospace ◽

10.3390/aerospace8020054 ◽

2021 ◽

Vol 8 (2) ◽

pp. 54

Author(s):

Julia A. Cole ◽

Lauren Rajauski ◽

Andrew Loughran ◽

Alexander Karpowicz ◽

Stefanie Salinger

Keyword(s):

Conceptual Design ◽

Urban Areas ◽

Design Space ◽

Design Method ◽

Urban Air ◽

Main Rotor ◽

Potential Benefits ◽

Compound Helicopter ◽

Configuration Changes

There is currently interest in the design of small electric vertical take-off and landing aircraft to alleviate ground traffic and congestion in major urban areas. To support progress in this area, a conceptual design method for single-main-rotor and lift-augmented compound electric helicopters has been developed. The design method was used to investigate the feasible design space for electric helicopters based on varying mission profiles and technology assumptions. Within the feasible design space, it was found that a crossover boundary exists as a function of cruise distance and hover time where the most efficient configuration changes from a single-main-rotor helicopter to a lift-augmented compound helicopter. In general, for longer cruise distances and shorter hover times, the lift-augmented compound helicopter is the more efficient configuration. An additional study was conducted to investigate the potential benefits of decoupling the main rotor from the tail rotor. This study showed that decoupling the main rotor and tail rotor has the potential to reduce the total mission energy required in all cases, allowing for increases in mission distances and hover times on the order of 5% for a given battery size.

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Refined Performance Results on a Slowed Mach-Scaled Rotor at High Advance Ratios

Journal of the American Helicopter Society ◽

10.4050/jahs.65.012003 ◽

2020 ◽

Vol 65 (1) ◽

pp. 1-13

Author(s):

Xing Wang ◽

Lauren Trollinger ◽

Inderjit Chopra

Keyword(s):

Wind Tunnel ◽

High Speed ◽

Reverse Flow ◽

Flow Region ◽

Comprehensive Analysis ◽

Compressibility Effect ◽

Inflow Condition ◽

Advance Ratio ◽

Slowed Rotor ◽

Performance Results

Owing to its ability to alleviate the compressibility effect on the advancing side, the slowed rotor operating at high advance ratios is a key feature in high-speed compound rotorcraft. A series of wind tunnel tests were conducted in the Glenn L. Martin Wind Tunnel with a four-bladed Mach-scaled articulated rotor. The objective of the tests was to gain a basic understanding of unique features of high-advance-ratio aerodynamic phenomena, such as thrust reversal and dynamic stall in the reverse flow region. In this study, high-advance-ratio tests were carried out with highly similar, noninstrumented blades and on-hub control angle measurements, to minimize possible error due to blade structural dissimilarity and pitch angle discrepancy. The tests were conducted at 900 and 1200 RPM, advance ratios of 0.3–0.9, and a shaft tilt study was conducted at±4°. Pitch and flap motion at the blade roots, rotor performance, and vibratory hub loads were investigated during the test. The test data were then compared with those of previous tests and with predictions from comprehensive analysis. The airload results were investigated using comprehensive analysis to gain insights into the influences of advance ratio and shaft tilt angle on rotor performance and hub vibratory loads. Results indicate that the thrust benefit from backward shaft tilt is dependent on the change in the inflow condition and the induced angle of attack increment, and the reverse flow region at high advance ratios is the major contributor to changes in shaft torque and horizontal force.

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Stability and Control Analysis of the Slowed-Rotor Compound Helicopter Configuration

Journal of the American Helicopter Society ◽

10.4050/jahs.52.239 ◽

2007 ◽

Vol 52 (3) ◽

pp. 239-253 ◽

Cited By ~ 8

Author(s):

Matthew W. Floros ◽

Wayne Johnson

Keyword(s):

Control Analysis ◽

Stability And Control ◽

Compound Helicopter ◽

Slowed Rotor ◽

And Control

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Aerodynamic Interactions on Airbus Helicopters' Compound Helicopter RACER in Cruise Flight

Journal of the American Helicopter Society ◽

10.4050/jahs.65.042001 ◽

2020 ◽

Vol 65 (4) ◽

pp. 1-14

Author(s):

Felix Frey ◽

Jakob Thiemeier ◽

Constantin Öhrle ◽

Manuel Keßler ◽

Ewald Krämer

Keyword(s):

Mutual Influence ◽

Aerodynamic Characteristics ◽

Individual Performance ◽

Aerodynamic Performance ◽

High Fidelity ◽

Main Rotor ◽

Compound Helicopter ◽

Cost Efficient ◽

Cruise Flight

With the pursuit of extending the flight envelopes of helicopters toward higher cruise speed, helicopter manufacturers increasingly have come up with nonconventional configurations in recent years. Among these, Airbus Helicopters' RACER (Rapid And Cost-Efficient Rotorcraft) is a compound helicopter equipped with a boxwing and lateral pusher rotors. In combination with the main rotor, these additional components determine the aerodynamic characteristics of the helicopter. Thereby, depending on the flight conditions, their individual performance is influenced by a variety of interactions. As the understanding of these interactions is vital for the evaluation of the overall system, the respective mutual influence of main rotor, wings, and lateral rotors is analyzed in this paper for cruise flight. For this reason, high-fidelity coupled aerodynamic simulations are conducted not only for the full RACER configuration but also for reduced setups omitting individual components to isolate the effect of these components on the helicopter's aerodynamic performance.

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