Where Can I Find Resources for Calculating Rotor Forces During Auto-Rotation?

[rm446]

Hello,

Out of curiosity I've been trying to mathematically model the forces on a rotor during auto-rotation starting with the basic lift/drag equations used for analyzing basic fixed wing flight (i.e. our beloved L = 0.5*Cl*rho*A*v^2). At first I thought this shouldn't be too hard since it's essentially the same as a fixed wing traveling over an airflow that increased linearly as you go from one end of the wing to the other. However as soon as you add a vertical component to the wind velocity angle of attack begins to vary with distance from the center of the rotor as well as velocity. This basically boils down to a very ugly integration problem and I'm just not that great at this type of mathematics and I figure someone must have done this before in a textbook somewhere.

So I just wanted to ask if anyone knows a good textbook or internet resources that does the calculation I'm trying to do. This doesn't need to specifically be auto-rotation, but any calculation that uses the basic lift/drag calculation to determine the overall forces produced by a rotor which has some vertical speed component.

(Also I have a master's in Mech. Engineering, so I can understand high level math but I have almost no exposure to aeronautical engineering beyond basic fluid dynamics.)

Thanks in advance :)

 

[Cyrus]

Hello,

Out of curiosity I've been trying to mathematically model the forces on a rotor during auto-rotation starting with the basic lift/drag equations used for analyzing basic fixed wing flight (i.e. our beloved L = 0.5*Cl*rho*A*v^2). At first I thought this shouldn't be too hard since it's essentially the same as a fixed wing traveling over an airflow that increased linearly as you go from one end of the wing to the other. However as soon as you add a vertical component to the wind velocity angle of attack begins to vary with distance from the center of the rotor as well as velocity. This basically boils down to a very ugly integration problem and I'm just not that great at this type of mathematics and I figure someone must have done this before in a textbook somewhere.

So I just wanted to ask if anyone knows a good textbook or internet resources that does the calculation I'm trying to do. This doesn't need to specifically be auto-rotation, but any calculation that uses the basic lift/drag calculation to determine the overall forces produced by a rotor which has some vertical speed component.

(Also I have a master's in Mech. Engineering, so I can understand high level math but I have almost no exposure to aeronautical engineering beyond basic fluid dynamics.)

Thanks in advance :)

Get a book on blade-element-momentum-theory to describe what you're trying to do. It's a non trivial process.

 

[NatSusan]

Hi there!

I can definitely understand your curiosity about modeling the forces on a rotor during auto-rotation. It sounds like you've already put a lot of thought and effort into this, and I commend you for that.

As for resources, I would recommend checking out "Principles of Helicopter Aerodynamics" by J. Gordon Leishman. It covers rotor aerodynamics in great detail and should have the information you're looking for. There are also some online resources, such as the NASA Technical Reports Server, that may have relevant studies or papers on this topic.

I'm also a bit rusty on my aeronautical engineering, so I can't offer much help with the math aspect. However, I'm sure there are plenty of experts out there who could assist you with the integration problem you're facing. Have you considered reaching out to any aeronautical engineering forums or communities for assistance? They may have members who specialize in this area and could offer some valuable insights.

Good luck with your research and calculations! I hope you're able to find the information you're looking for. Happy flying!