2. December 2022
DLR flight test with CH-53G helicopter

'Danc­ing' he­li­copter helps re­duce noise

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Aeronautics
Dancing above the tarmac
Danc­ing above the tar­mac
Image 1/4, Credit: DLR

Dancing above the tarmac

Dur­ing the tests, the CH-53G he­li­copter of the Ger­man Armed Forces flew at a height of 2 to 12 me­tres above the tar­mac. Five cam­eras record­ed the he­li­copter and the air vor­tices on the ro­tors.
Hovering in front of a hangar with a dot pattern
Hov­er­ing in front of a hangar with a dot pat­tern
Image 2/4, Credit: DLR

Hovering in front of a hangar with a dot pattern

The CH-53G he­li­copter of the Ger­man Armed Forces car­ried out the flight tests in front of a dot pat­tern at­tached to 100 square me­tres of the hangar wall of DLR Braun­schweig.
CH-53G in front of dot pattern
CH-53G in front of dot pat­tern
Image 3/4, Credit: DLR

CH-53G in front of dot pattern

The dot pat­tern on the hangar door helps to make the air vor­tices on the ro­tor blades vis­i­ble
CH-53G with Bo 105 in the background
CH-53G with Bo 105 in the back­ground
Image 4/4, Credit: DLR

CH-53G with Bo 105 in the background

The CH-53G he­li­copter pro­vid­ed by the Ger­man Armed Forces was cho­sen for the tests be­cause its 14-tonne take-off weight makes it one of the heav­ier trans­port he­li­copters. The DLR re­search he­li­copter Bo 105 in the back­ground is a lightweight in com­par­i­son, with a take-off weight of over 2 tonnes.
  • DLR conducts flight test with a CH-53G helicopter.
  • The findings could help reduce noise and vibrations.
  • Focus: Aeronautics

Researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) in Göttingen have visualised the main cause of noise from a heavyweight helicopter in flight. To do this, they conducted flight tests with a CH-53G of the German Armed Forces by letting the helicopter 'dance' close to the ground.

The Sikorsky CH-53G is a large transport helicopter and can carry an internal payload of up to 5500 kilograms. The helicopter had a take-off weight of 14 tonnes for the tests at DLR's Braunschweig site. The helicopter flew at a height of two to twelve metres above the ground in hovering flight. Three high-speed cameras recorded the resulting air vortices on the six rotor blades from different angles, while two additional cameras determined the position of the CH-53G with high precision.

Video: DLR Institute of Aerodynamics and Flow Technology - 'Dancing' helicopter helps reduce noise
Researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) in Göttingen have visualised the main cause of noise from a heavyweight helicopter in flight. To do this, they conducted flight tests with a CH-53G of the German Armed Forces by letting the helicopter 'dance'...

Blade tip vortices cause noise

A helicopter is able to take off and land vertically thanks to its rotor. However, this is also responsible for the noise and vibrations in flight. "Almost all the noise from a helicopter is aerodynamic noise. A large part of it is caused by the blade tip vortices," says Markus Raffel, Head of the Helicopters Department at the DLR Institute of Aerodynamics and Flow Technology in Göttingen.

Blade tip vortices occur at the outer end of a rotor blade, caused by the negative pressure on the upper side and positive pressure on the lower side. This accelerates the air and generates a concentrated vortex behind the rotor blade tip. The noise is caused when the vortex of one rotor blade collides with another rotor blade. These vortices not only cause the typical 'carpet beater' noise, but also lead to vibrations in the helicopter and decrease the comfort of the passengers.

Special measuring technique makes air turbulence visible

The helicopter researchers at DLR in Göttingen are already pioneers in the field of visualising helicopter noise. In 2013, they succeeded in visualising the responsible air vortices in flight for the first time. The visualisation uses a special optical measurement technique.

The Background Oriented Schlieren Method (BOS) was developed at DLR in Göttingen in 2000. Light is refracted in the air by variations in density. Everyone is familiar with this phenomenon from the shimmering over some road surfaces on a hot summer's day. To investigate the blade tip vortices during hovering flight, a large-scale artificial dot pattern was installed at the DLR Braunschweig hangar, and the movement of the dots due to light refraction was observed.

Near the ground, blade tip vortices play a special role because air turbulence can stir up ground material in sandy areas or in snow, which can obstruct the pilot’s view. In this test, the DLR researchers in Göttingen investigated 'scale effects' and were able to show that the vortices are not the same on a large helicopter such as the CH-53G as they are on a smaller model. The findings open up new possibilities for making future helicopters quieter and more comfortable. "We want the vortices on the rotor blades to be as weak as possible and to dissipate quickly," Raffel says. This could be achieved, for example, by giving the rotor blades a curved shape, as is already the case in smaller helicopter models such as the Airbus Helicopters H160. This shape is also based on DLR research.

The tests took place as part of the DLR Urban Rescue project. The CH-53G was provided by the Bundeswehr Technical and Airworthiness Center for Aircraft (Wehrtechnische Dienststelle für Luftfahrzeuge und Luftfahrtgerät).

Contact
  • Jens Wucherpfennig
    Cor­po­rate Com­mu­ni­ca­tions, Göt­tin­gen and Hanover
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 551 709-2108
    Fax: +49 551 709-12108
    Bunsenstraße 10
    37073 Göttingen
    Contact
  • Prof. Dr.-Ing. habil. Markus Raffel
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Aero­dy­nam­ics and Flow Tech­nol­o­gy
    He­li­copters
    Telephone: +49 551 709-2817

    Contact

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