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Lifting carpet for the skycar









Suppose I give you a motor, say a standard good quality car motor. You have to build a little aircraft using that motor. Every simple aircraft uses one or more propellers, so your first thought will be to wonder what kind of propeller you will put on the motor. The key question is the size of the propeller:
Suppose you plan to build a helicopter. So, you place the propeller above the aircraft. The propeller has to lift the whole weight of the aircraft. So you will need to use a big propeller, to get a high pull force. That way your helicopter can stay hanging in the air.

You change your mind and plan to build an airplane. So you change the position of the motor and the big propeller. You put the propeller frontwards. And place wings aside of the aircraft. Problem: the big propeller cannot pull the airplane up to a high speed. Because it propels the air too slowly. You must use a little propeller; it has less pull force yet it blows the air at high speed, which allows to pull the airplane up to a decent speed. (You can use a big propeller to travel at high speed, provided it is cleverly designed. But you won't get a better pull force than with a little propeller.)

So, you have to choose between a helicopter and an airplane. A helicopter can take off vertically and hang in the air. Yet it cannot fly very fast. An airplane needs a runway to take off, in order to accelerate till the wings can lift it. An airplane can fly very fast. It's up to you to choose what you want or what you need. (Helicopters are also more expensive to buy and to operate. Because they use more moving parts, need more fuel and require more ground operations. Airplanes are the most efficient and simple way to stay in the air. That's why helicopters are only used when one's obliged to take off and land vertically or hang still in the air.)

You feel frustrated and compare with you car: it can stand still on the road, it can accelerate up to high speeds, it is efficient and it does not have a huge encumbering pair of wings neither a dangerous propeller. It is perfect. Why can't a sky car be built? It would have no wings, lift off vertically and travel at high speed. Is that science fiction?

Devices that roughly match that idea have been build. One is very successfully operated by the British, US, Spanish and Indian armies: the Harrier fighter plane. Just cut its wings away and shorten its nose and tail, there you get your skycar. The problem is that such a device is utterly expensive and very noisy. In order to get your skycar to lift itself into the air, it needs to be surrounded by propellers (see the M200X Moller Skycar). Or direct an air stream towards the ground like the Harrier does. We want the surface taken by these propellers (or air stream outlets) to be little. Because we're not making a helicopter. As quoted at the beginning of this text, little propellers or outlets have a weak pull force. So we need a more powerful motor to compensate, to get a very fast stream of air. The motor of the Harrier is about ten times more powerful than that of a helicopter of the same weight! So it is ten times more expensive... Dr Moller, the builder of the M200X, had to install the latest and most powerful motors available. Using just good motors his little skycar was not able to really go up in the air. The narrow and fast stream of air is also dangerous and polluting. A rising Harrier would awake a whole neighborhood and destroy every vegetable or mailbox a few meters around. What about the fuel consumption? To hang in the air a Harrier aircraft consumes also ten times more fuel than a helicopter. It is only efficient when flying like a plane.

We want a strong lift force in order to allow the car to hang in the air. To use the least motor power, consume less fuel and produce less noise and dangerous fast air stream, we must use the most possible air blowing surface. The proposal is to place a retractable "carpet" of propellers beneath the skycar:




These are the motivations for the design:
There are several ways to power the propellers:
Some technical problems:
I don't know down to what point the size of one propeller can be reduced. The littler they are, the more the whole system will be reliable and the thiner the carpet made of them will be. The thinner the carpet, the more easily it can be dealt with. Pieces of carpet can unfold aside of the skycar to augment the lift surface and reduce the fuel consumption and noise. A large and thin carpet can even yield a real flying carpet an individual can sit upon (with a seat belt) and fly far away consuming not too much fuel.

Horizontal propulsion was not seriously dealt with but that's a secondary problem. It can use a propulsion system of its own or use the compressed air or electricity produced by the turbines. For sideways movements the skycar can be inclined towards the direction aimed at, like a helicopter does. Or it can use sideways propellers like a submarine does. The skycar can also stay horizontal and incline the lifting carpet. Possibly the carpet can be made of two independent carpets, allowing to incline each half towards another direction for horizontal rotation control. For an efficient horizontal flight the skycar can make use of wings. Maybe retractable wings. If it travels at high speed it can have the shape of a lifting body.

Related data:




As quadcopters became available, I made this test in 2015 with a Cheerson CX-10A. The diameter of a propeller is 30 mm, the piece of cardboard is 18 millimeters above the blades and is 10 mm wider than the longest extent between the tips of two adjacent propellers. The quadcopter obviously needs more power to fly but it flies:


Cheerson CX-10A quadcopter with a
        piece of cardboard above the propellers




Eric Brasseur  -  May 22 2003 till April 10 2015
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