Wind‐Tunnel Studies of Helicopter Rotational Noise in Forward Flight

1973 ◽  
Vol 53 (1) ◽  
pp. 331-331 ◽  
Author(s):  
Shelia Widnall
Keyword(s):  
Wind Tunnel ◽  
Forward Flight

On the vortex wake of an animal flying in a confined volume

1991 ◽  
Vol 334 (1269) ◽  
pp. 107-117 ◽  
Keyword(s):  
Wind Tunnel ◽  
Vortex Ring ◽  
Large Diameter ◽  
Ground Effect ◽  
Boundary Effects ◽  
Performance Measurements ◽  
Forward Flight ◽  
Tunnel Wall ◽  
Recirculating Flow ◽  
Air Speed

When an animal flies near a boundary, the airflows it generates interact with that boundary. These interactions may have a significant effect on flight performance, as measured by quantities such as the energy rate to sustain flight, or the circulation of the vortices bound on the wing or shed in the wake (or, equivalently, by the lift and induced drag coefficients). The problem of hovering and slow flight within a confined volume is considered by a theoretical model based on helicopter practice, and by flow visualization experiments. The wake takes the form of a strong recirculating flow within the volume, and because of this recirculation the boundaries appear to cause a large reduction in the induced power required for sustained flight, even when their distance from the animal is several times greater than the wingspan. The correction factor relative to ideal momentum jet theory is greater than for the hovering ground effect, forward flight ground effect, or wind tunnel wall interference problems at comparable distances. The flow pattern that develops in the presence of floor and wall interactions in hovering or slow flight includes a large-diameter vortex ring trapped underneath the animal; this vortex ring is conjectured to be analogous to that below a helicopter in slow descending flight in the 'vortex ring state’. Performance measurements for animals in hovering flight within a confined volume may underestimate power for free hovering by a significant margin. Comparable boundary effects may also be important in confined forward flight. Because of speed-related changes in the wake, and the rise in induced power at lower speeds, the appropriate correction to total mechanical power is dependent on air speed, becoming progressively greater as speed reduces. Some wind tunnel measurements of total metabolic power have produced the apparently anomalous result that power is independent of flight speed within measurement error. These observations may be explained - at least in part - by boundary effects caused by interaction between the wake and the walls of the wind tunnel.

The ABC Helicopter

1969 ◽  
Vol 14 (4) ◽  
pp. 10-19 ◽  
Author(s):  
M. C. Cheney
Keyword(s):  
Wind Tunnel ◽  
Rotor Blades ◽  
Small Scale ◽  
Wind Tunnel Experiments ◽  
Forward Flight ◽  
Basic Principles ◽  
Stability And Control ◽  
Analytical Research ◽  
And Control

Presented is an introduction to the basic principles of the Advancing Blade Concept (ABC) rotor and a review of the related experimental and analytical research conducted in support of the Sikorsky ABC helicopter program. The ABC helicopter is comprised of two coaxial, counter‐rotating rotors having blades rigidly attached to the hub except for feathering freedom. The blades are significantly stiffer than conventional rotor Blades and are capable of supporting large moments without excessive tip deflections. Improved forward flight efficiency and the elimination of retreating blade stall results from the ability of the ABC rotor to utilize to a large extent the lifting potential of the advancing blades—a capability not present in conventional single rotors. Results of various small‐scale wind tunnel experiments are presented along with summaries of several analytical investigations which were conducted to provide information concerning rotor performance, blade dynamics, vibration, and stability and control

Blade Displacement Measurements of a Rotor in Forward Flight in the Langley 14- by 22-Ft Wind Tunnel

2021 ◽  
Author(s):  
Edward T. Schairer ◽  
James T. Heineck ◽  
Hannah R. Spooner ◽  
Austin D. Overmeyer
Keyword(s):  
Wind Tunnel ◽  
Forward Flight ◽  
Displacement Measurements

scholarly journals Wind Tunnel Studies on Hover and Forward Flight Performances of a Coaxial Rigid Rotor

Aerospace ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 205
Author(s):  
Chang Wang ◽  
Minqi Huang ◽  
Xianmin Peng ◽  
Guichuan Zhang ◽  
Min Tang ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Tilt Angle ◽  
Lift Coefficient ◽  
Rotor System ◽  
Rigid Rotor ◽  
Forward Flight ◽  
Coaxial Rotor ◽  
Advance Ratio ◽  
Hover Flight ◽  
Development Center

The aerodynamic performance of a reduced-scale coaxial rigid rotor system in hover and steady forward flights was experimentally investigated to gain insights into the effect of interference between upper and lower rotors and the influences of the advance ratio, shaft tilt angle and lift offset. The rotor system featured by 2 m-diameter, four-bladed upper and lower hingeless rotors and was installed in a coaxial rotor test rig. Experiments were conducted in the Φ3.2 m wind tunnel at China Aerodynamics Research and Development Center (CARDC). The rotor system was tested in hover states at collective pitches ranging from 0° to 13° and it was also tested in forward flights at advance ratios up to 0.6, with specific focus on the shaft tilt angle and lift offset sweeps. To ensure that the coaxial rotor was operating in a similar manner to that of the real flight, the torque difference was trimmed to zero in hover flight, whilst the constant lift coefficient was maintained in forward flight. An isolated single-rotor configuration test was also conducted with the same pitch angle setting in the coaxial rotor. The hover test results demonstrate that the figure of merit (FM) value of the lower rotor is lower than that of the upper rotor, and both are lower than that of the isolated single rotor. Moreover, the coaxial rotor configuration can contribute to better hover efficiency under the same blade loading coefficient (CT/σ). In forward flight, the effective lift-to-drag (L/De) ratio of the coaxial rigid rotor does not monotonously change as the advance ratio increases. Increases in the required power and drag in the case with a high advance ratio of 0.6 leads to the decreasing L/De ratio of the rotor. Meanwhile, the L/De ratio of the rotor is relatively high when the rotor shaft is tilted backward. The increasing lift offset tends to result in reduced required rotor power and an increase in the rotor drag. When the effect of the reduced rotor power is greater than that of the increased rotor drag, the L/De ratio increases as the lift offset increases. The L/De ratio can benefit significantly from lift offset at a high advance ratio, but it is much less influenced by lift offset at a low advance ratio. The forward performance efficiency of the upper rotor is poorer than that of the lower rotor, which is significantly different from the case in the hover flight.

Performance and Loads of a Lift Offset Rotor: Hover and Wind Tunnel Testing

2019 ◽  
Vol 64 (2) ◽  
pp. 1-12 ◽  
Author(s):  
Christopher G. Cameron ◽  
Jayant Sirohi
Keyword(s):  
Wind Tunnel ◽  
Scale Model ◽  
Wind Tunnel Testing ◽  
Forward Flight ◽  
Maximum Increase ◽  
Bladed Rotor ◽  
Advance Ratio ◽  
Thrust And Torque ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The results of hover and wind tunnel tests of a reduced-scale, model rotor operating with lift offset are presented. The two-bladed rotor had a diameter of 2.03 m and constant cross section untwisted blades. Measurements include steady and vibratory hub loads, as well as control angles and pushrod loads. The rotor system was tested in hover and at advance ratios between 0.21 and 0.53, at collective pitches ranging from 3° to 10°, achieving blade loadings in excess of 0.10. At each forward flight operating condition, sweeps of lift offset up to 15% were performed. In forward flight, the rotor effective lift-to-drag ratio was found to increase with increasing advance ratio and lift offset, with a maximum increase of 40% compared to the zero lift offset case. Vibratory loads increased with advance ratio, with the largest loads in the two- and four-per-revolution harmonics. Lift offset is shown to modify vibratory hub forces and moments transmitted to the fixed frame, increasing vibratory rolling and pitching moments while decreasing vibratory thrust and torque.

Rotational Stabilization of Cargo Container Slung Loads

2015 ◽  
Vol 60 (4) ◽  
pp. 1-13 ◽  
Author(s):  
Luigi Cicolani ◽  
Christina Ivler ◽  
Carl Ott ◽  
Reuben Raz ◽  
Aviv Rosen
Keyword(s):  
Wind Tunnel ◽  
Single Point ◽  
Feedback Regulation ◽  
Forward Flight ◽  
Design Data ◽  
Yaw Rate ◽  
Shaft Angle ◽  
Wind Tunnel Data ◽  
The 1960S ◽  
Yaw Moment

The stabilization of “difficult” loads that become aerodynamically unstable at airspeeds well below the power-limited speed of the helicopter-load configuration has been studied since the 1960s. This paper looks at the possibility of stabilizing slung loads in forward flight by imposing a slow steady rotation in yaw (spin stabilization). Slow rotations of 100–150 deg/s suffice to suppress the pendulum motions of the load. A swivel is required at the hook, and only a few foot-pounds of yaw moment are needed to overcome swivel friction and impose the desired yaw rate. The approach is limited to single-point suspensions. A stabilizer design consisting of a one-shaft anemometer-like device with hemispherical cups at the ends was developed in wind tunnel tests. The shaft angle can be controlled to vary the applied yaw moment and allow feedback regulation of the load yaw rate. Flight tests with two cargo containers demonstrated that a simple linear control law with fixed gains was effective in maintaining the desired yaw rate in forward flight over the range of configurations of the test loads. Wind tunnel data were obtained at all stages of the development and testing and proved to be an accurate source of design data and an accurate predictor of performance in flight.

scholarly journals Transient Thrust Analysis of Rigid Rotors in Forward Flight

Aerospace ◽  
2022 ◽  
Vol 9 (1) ◽  
pp. 28
Author(s):  
Travis Krebs ◽  
Goetz Bramesfeld ◽  
Julia Cole
Keyword(s):  
Wind Tunnel ◽  
Theoretical Analysis ◽  
Potential Flow ◽  
Rotor Blade ◽  
Cfd Analysis ◽  
Forward Flight ◽  
Flow Method ◽  
Asymmetric Rotor ◽  
The Mean ◽  
Rigid Rotors

The purpose of this study was to investigate and quantify the transient thrust response of two small rigid rotors in forward flight. This was accomplished using a distributed doublet-based potential flow method, which was validated against wind-tunnel experimentation and a transient CFD analysis. The investigation showed that for both rotors, advancing and retreating blade effects were predicted to contribute to transient thrust amplitudes of 5–30% of the mean rotor thrust. The thrust output amplitudes of individual rotors blades were observed to be 15–45% of the mean rotor thrust, indicating that it is not uncommon for the thrust output variation of an individual rotor blade to approach the same value as the mean thrust output of the rotor itself. In addition to this, the theoretical analysis also illustrated that higher blade thrust oscillations resulted in pronounced asymmetric rotor wake structures.

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