# Electric power for lift and torque

One tonne dead-weight is to be lifted in the air and moved horizontally by means of a propeller activated by electric motor.
Questions:
(1) What is the electric power (components U, I) sufficient and necessary for the task?
(2) If, instead of (1), the generated electric field is used to generate a magnetic field, what will be the latter's B and H?
Is this magnetic field sufficient to lift the dead-weight?

Related Classical Physics News on Phys.org
berkeman
Mentor
One tonne dead-weight is to be lifted in the air and moved horizontally by means of a propeller activated by electric motor.
Questions:
(1) What is the electric power (components U, I) sufficient and necessary for the task?
(2) If, instead of (1), the generated electric field is used to generate a magnetic field, what will be the latter's B and H?
Is this magnetic field sufficient to lift the dead-weight?

Propeller? What is the context of your question? What is this propeller acting in? Air? Water?

In the air.

berkeman
Mentor
In the air.
You mean like an electric helicopter? Yikes!

haha,
Yes. I am building a generator and I would like to clear these notions. I would greatly appreciate your help with this.

berkeman
Mentor
haha,
Yes. I am building a generator and I would like to clear these notions. I would greatly appreciate your help with this.
Why does it need to be a helicopter? Why not just a conventional crane vehicle?

K^2
Electric power required would be zero. There is no minimum amount of power required for flight. Consider an object resting on a table, for example. No power is consumed.

What you can do is estimate the power given a certain disk loading. So if you said that you want to have a prop 10m in diameter, then one can say roughly how much power would be required. Bigger prop means less power. Of course, at some point, the weight you add by making the prop larger starts to dominate, and at that point, you no longer win anything from bigger prop.

berkeman:
The total project is larger than this aspect, and a crane would not do.

K^2:
Would you care to enlighten me, please? No power?

Last edited:
K^2
Of course. If an object isn't moving, no work is being done. Fundamental power requirement is zero. A magnet levitating over a superconductor consumes no power. And if you think about it, the object resting on a table is really suspended by electrostatic interaction between the table and the object. Again, no power is consumed.

Want something closer to conventional flight? Consider a helium balloon. It can be weighed to be neutrally buoyant, in which case it is suspended with no energy source required.

Aerodynamic lift wastes power because you have to accelerate air mass. You are moving something while applying force to it, and therefore, you are doing work. That means energy consumption. But the more air you can grab, the less you need to move it, and the less energy it takes. Ever wondered why sail planes have such long wings? If you can make very, very large wings or propeller that weigh nothing, you can be wasting almost no power to keep an arbitrary weight afloat. The question is, how big can you make your lifting surface without it becoming the most massive part of your contraption.

Thank you very much, K^2.

If you do specialize in aerodynamics, would it be all right to contact you through your email or only here?

K^2