Resource Page : Rotorcraft Downwash/Outwash
When a rotorcraft is operated at low enough height above the ground, the aerodynamic interaction with the surface below causes the flow from its rotors to expand out across the ground as a layer of rapidly-moving airflow, called its outwash. If this outwash is strong enough, it can cause significant upset to bystanders and nearby infrastructure.
Dr Brown's work has shown that the shape and strength of the outwash that any multi-rotor eVTOL aircraft will generate is strongly dependent on the layout of its rotors, amongst other factors.
Indeed, several aspects of the behaviour of the outwash that is created by eVTOL aircraft may come as a surprise to the rotorcraft community - where intuition is largely based on experience with conventional helicopters.
The page below contains a set of resources that you might find useful in helping you to understand
- the physical processes that govern the flow in the outwash below a rotorcraft,
- how and when the outwash below a rotorcraft might become a hazard,
- how the design and operation of eVTOL aircraft influences the outwash that they produce, and
- how the outwash from eVTOL aircraft might influence the design and layout of vertiports.
We would be very happy to discuss our work with you. If you would like to talk to us about our research, please feel free either to contact us directly or to access our contact form through the tab below.
Click on the button below to download a copy of Dr Brown's paper, delivered on 6 September 2023 at
the 49th European Rotorcraft Forum in Bückeburg, Germany.
Extensive worldwide interest in the rotorcraft industry currently exists in developing small, lightweight, electrically-propelled multi-rotor craft, typically capable of carrying four to six passengers on short-range intra-urban missions, for instance as part of a passenger ferry service between an airport and a downtown commuter hub. The potential for the flows generated by helicopter rotors to create significant upset in the vehicle’s surroundings has long been appreciated by the rotorcraft community, yet very little has been written, until recently, about the structure of the downwash field that these new eVTOL aircraft will create, and how this field might interact with the ground during landing and take-off.
A new numerical study suggests that the interactions between the multiple wakes of the rotors of some of these vehicles could amplify and modify key features of the field, especially when it interacts with the ground and turns to outwash. Indeed, the study suggests that the flow out across the ground that is generated by these vehicles could potentially be very different in character and strength to that which is produced by conventional helicopters.
We discuss some of the potential implications of these findings for the developers and operators of these new aircraft, as well as for the designers of the vertiports at which they will begin and end their journeys.
Extensive worldwide interest in the rotorcraft industry currently exists in developing small, lightweight, electrically-propelled multi-rotor craft, typically capable of carrying four to six passengers on short-range intra-urban missions, for instance as part of a passenger ferry service between an airport and a downtown commuter hub. The potential for the flows generated by helicopter rotors to create significant upset in the vehicle’s surroundings has long been appreciated by the rotorcraft community, yet very little has been written, until recently, about the structure of the downwash field that these new eVTOL aircraft will create, and how this field might interact with the ground during landing and take-off.
A new numerical study suggests that the interactions between the multiple wakes of the rotors of some of these vehicles could amplify and modify key features of the field, especially when it interacts with the ground and turns to outwash. Indeed, the study suggests that the flow out across the ground that is generated by these vehicles could potentially be very different in character and strength to that which is produced by conventional helicopters.
We discuss some of the potential implications of these findings for the developers and operators of these new aircraft, as well as for the designers of the vertiports at which they will begin and end their journeys.
Click on the button below to download a copy of the UK Civil Aviation Authority Publication 2576:
'Understanding the downwash/outwash characteristics of eVTOL aircraft'.
This publication summarises Dr Brown's recent work, funded by the UK Civil Aviation Authority, to understand the properties of the outwash that might be created by eVTOL aircraft when they are operated close to the ground.
This publication summarises Dr Brown's recent work, funded by the UK Civil Aviation Authority, to understand the properties of the outwash that might be created by eVTOL aircraft when they are operated close to the ground.
The following presentations of Dr Brown's work on eVTOL outwash are available to watch:
- A recording of the presentation Dr Brown gave in February 2024 to the Vertical Flight Society's eVTOL Flight Test Council, providing an overview of the work contained in CAP2576 (56 minutes long, including questions and discussion).
© Sophrodyne Ltd 2024
