Calculating Helicopter Downwash Force on a House Roof at 700ft?

In summary, the conversation discusses the question of how to calculate the downwards force exerted by a hovering helicopter on the roof of a house at a height of 700ft. It is determined that there are many variables that need to be considered, such as the type of helicopter, its weight, and the altitude. The use of momentum theory and Bernoulli's principle is suggested as a starting point for the calculation. However, it is also noted that this theory does not take into account the induced velocity at points between the rotor disc and infinite distance. The conversation concludes by mentioning that this type of calculation is often done using fluid dynamics or through actual measurements in the field due to the many factors that can affect the outcome.
  • #1
richwigmore
1
0
Does anyone know how to calculate how much downwards force a helicopter would exert on the roof of a house if it hovered over it at 700ft?

Thanks
 
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  • #2
Depends, depends, depends.

There are way too many variables that need to be nailed down. Helicopter type. Gross weight. Altitude. Temperature.
 
  • #3
assume that we have all the parameters, which theory will be used for the calculation?
 
  • #4
Basic momentum theory in a hover which ties into Bernoulli would be the place to start. Essentially it is calculating the change in momentum of a column of air equivalent in area to the rotor disk.

http://www.public.iastate.edu/~aero442/unit2.pdf
 
  • #5
apply bernoulli.
basically its the same problem as the old trick. would your truck go light if all the birds inside it took flight at the same time.
and 700 ft a lot of distance
 
  • #6
Momentum theory is very good to calculate the induced velocity at rotor dics as well as at distance very below the rotor. Unforturnately, it does not have any information for determining the induced velocity at these points which are between the rotor dics and infinite distance, for example at 3 or 4 radiaus below the rotor.
 
  • #7
Hoangthien said:
Momentum theory is very good to calculate the induced velocity at rotor dics as well as at distance very below the rotor. Unforturnately, it does not have any information for determining the induced velocity at these points which are between the rotor dics and infinite distance, for example at 3 or 4 radiaus below the rotor.
That is very true. Usually something along these lines would be calculated via fluid dynamics package or simply measured in the field. There are so many things that could have an effect on the outcome.
 

What is helicopter downwash force?

Helicopter downwash force is the downward flow of air created by the rotating blades of a helicopter. This force is generated as the blades push air downwards in order to generate lift and keep the helicopter in the air.

How is helicopter downwash force calculated?

Helicopter downwash force is calculated using the principles of fluid mechanics, specifically Bernoulli's principle and Newton's laws of motion. The formula for calculating downwash force takes into account factors such as the size and shape of the blades, the speed of the helicopter, and the density of the air.

What are the effects of helicopter downwash force?

The effects of helicopter downwash force can be felt by objects and people in the vicinity of the helicopter. The force can cause objects to be blown away or knocked over, and can create strong winds and turbulence. This can be particularly dangerous for people and objects on the ground near a helicopter.

How does helicopter downwash force affect the helicopter itself?

Helicopter downwash force has a significant impact on the stability and control of the helicopter. As the blades push air downwards, a reaction force is created that pushes the helicopter in the opposite direction. This force can be used to control the direction and altitude of the helicopter, but it must be carefully managed by the pilot.

What measures are taken to minimize the effects of helicopter downwash force?

To minimize the effects of helicopter downwash force, pilots must carefully manage their flight paths and avoid flying too close to the ground or other objects. Some helicopters also have features such as shrouded tail rotors or directional vanes to help control the direction and intensity of the downwash force. Additionally, pilots must be trained to anticipate and compensate for downwash force in order to safely operate a helicopter.

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