# Hovercraft plans (1) - How much i need in voltage?

## Main Question or Discussion Point

I want to rise an object 10 metters from the ground. Its mass is 100Kg, so, to know how much energy i need i have:

E = M * g * h
Where M = Mass Kg, g = 9.8 ~ 10 m/s^2, gravitical force, and h is high in metters.

So i have E = 100 * 10 * 10 = 10KJ (Joules)

Now i'm looking for a power supply that can give me that energy to make a fan or propeller rise up almost to 10 metters and object with almost 100Kg of mass.
How will that power supply be? How much voltage needed? Is it possible to do with any kind of battery?
Think in cars for example, they use gas and electricity.

## Answers and Replies

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I want to rise an object 10 metters from the ground. Its mass is 100Kg, so, to know how much energy i need i have:

At 10 meters off the ground, you don't have a hovercraft, you have a helicopter. That said, the formula you used is not very meaningfull in a design way. It gives the minimum theoretical value, but the reality of generating that power, harnessing it through a transmission of some sort to the final propellers, and OMG, is it an open propeller or a closed (ducted) fan? What pitch? What size? What RPM? You see the actuall values are much higher.

A better way to attack the problem might be to work backwards. IE: A 100kg object suspended by 4 ducted fans. Then figure out the mass of air you need to move per second to keep it suspended. From there you can define a locus of fan size, pitch, speed and duct efficiency that will satisfy your needs. Then you can pick the one that best suits your ability to deliver power to the application in question.

What is a Hovercraft doing at 10 meters anyway? The mass of the skirt itself could become truly problematic.

At 10 meters off the ground, you don't have a hovercraft, you have a helicopter. That said, the formula you used is not very meaningfull in a design way. It gives the minimum theoretical value, but the reality of generating that power, harnessing it through a transmission of some sort to the final propellers, and OMG, is it an open propeller or a closed (ducted) fan? What pitch? What size? What RPM? You see the actuall values are much higher.

A better way to attack the problem might be to work backwards. IE: A 100kg object suspended by 4 ducted fans. Then figure out the mass of air you need to move per second to keep it suspended. From there you can define a locus of fan size, pitch, speed and duct efficiency that will satisfy your needs. Then you can pick the one that best suits your ability to deliver power to the application in question.

What is a Hovercraft doing at 10 meters anyway? The mass of the skirt itself could become truly problematic.
Can you give me a hint of how to do all that? LOL

I'm only 18.. :(

How can i know the speed, the proppelers' diameter (i was thinking on using 2 proppelers, one on the left and other on the right side of the 100Kg object).
Imagine 2 proppelers, holding an object between them using some metallic structure for example.
Lets imagine that the metallic structure has 30Kg, and the object has 100Kg, 130Kg.

Now, according to what data can i see how much air speed i need, and, above all, how much energy i need?

Thanks.

russ_watters
Mentor
How can i know the speed, the proppelers' diameter (i was thinking on using 2 proppelers, one on the left and other on the right side of the 100Kg object).
You pick the diameter arbitrarily. Then key piece of information you need to calculate is the required air velocity. First divide the weight of the craft by the propeller area, which gives you your required velocity pressure. Then, you use Bernoulli's equation to calculate the velocity: p= 1/2 rho*v^2

Then, you find a fan in a catalog that meets your requirements.

Energy is 1/2 MV^2. Fans are usually around 50% efficient.

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ok, thanks! i'll give it a try. ;)