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:
- You can use a little propeller. It will turn at a high speed
and produce a narrow and high speed stream of air. The pull
force will be low.
- You can use a big propeller. It will turn slowly and produce a
huge and low speed stream of air. The pull force will be high.
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
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
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:
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:
- The propellers are placed beneath the car because that way the
air stream is not hampered. The presence of the car body above
the propellers does not hamper them.
- The more propellers are used, the more redundancy you get. A
few propellers can fail without security problem.
- Such a number of high technology propellers can be seen as an
expensive toy. A helicopter just has one or two motors. My
believe is this design will be less expensive because it uses
almost no moving parts. Indeed the machinery around a helicopter
rotor is very impressive. The propeller carpet design only
implies the power of each propeller can be modulated. Than can
be done with nearly no moving parts at all. What's more the
propellers can be mass produced and thus be less expensive.
- On the drawing the propeller blades have a little surface
because I suppose them to turn very fast. This has several
advantages: that way they are less sensitive to turbulences and
air speed changes and require more lightweight and simple
- Half of the propellers can turn an opposite direction. That
way the skycar will not tend to rotate like a helicopter does.
Another or complementary way to achieve this is to use an
aerodynamic grid beneath each propeller to prevent the rotation
of the air flow. This increases a little the yield. The opposite
rotation of pairs of propellers also reduces the problem of
There are several ways to power the propellers:
- Each propeller has its own little fuel motor. This is I
believe not the best choice. Because each motor will be
complicated and expensive and fuel motors commonly have a slow
actuation time. They cannot react very fast to power change
commands. Unless one uses variable pitch blades, which is once
again a complicated feature.
- The skycar contains a set of fuel turbines that feed air
compressors. Air ducts bring the compressed air towards the
propellers to power them. This is the most lightweight solution.
Air valves are used to control the power of each propeller. One
advantage of this system is the propellers can be slow turning
fat propellers. Such propellers are less fragile than fast
turning slim propellers.
- The skycar contains a set of fuel turbines that feed electric
dynamos. Each propeller is powered by an electric motor fed by
redundant electric wires coming from the skycar body. This is my
favorite solution. It may seem too heavy but I believe electric
motors can be lightweight provided they turn very fast. Slow
turning propellers may be possible if the motor of each
propeller is a circular linear motor around the propeller.
- A hybrid solution is to use a standard
little fuel motor for each propeller, but with an electric motor
on the same axis. The fact each propeller has its fuel motor
ensures for a high power and good mechanic yield. The presence
of electric motors (that are also dynamos) allow to share the
power amongst the propellers. Should a fuel motor fail, its
electric motor can take on, with a lower yield, using
electricity produced by the fuel motors of the other propellers.
The electric motors allow for faster speed changes, thus for a
better control of the skycar's attitude. The electric motors can
be a short power supplement to the fuel motors for emergencies,
pumping power on the skycar's high power batteries, main motors
or on other less solicited propellers. The whole requires a
complex network of electric wires, command transistors and fuel
distribution system, but the result is quite optimal.
- One or a few big propellers can be used,
fuel powered. Surrounded by a fleet of little electric
Some technical problems:
- The propellers placed close to the ground are dangerous and
can be destroyed by little stones and the like. If a propeller
propeller breaks, the blades can become very dangerous
projectiles. A chain reaction can even break a few propellers in
just a second. I suppose a kevlar grid above and below the
propellers can reduce the problem. Another way round to reduce
the risks is to use slow turning fat propellers. Yet I prefer
very fast turning thin propellers. Maybe a solution is to make
them out of a strong alloy.
- To synchronize such a set of propellers to get a stable
vehicle is not that easy. To get a reliable system on the long
term for common usage, you need a much higher reliability than
in most today vehicles. That can be achieved by placing a
processor and rudimentary short term inertial reference inside
each propeller cell. The processor of each cell/propeller
receives data from each other propeller and from the skycar's
main computer systems. But it decides on its own of the lift
force it will produce. It can also decide to stop if it
encounters a major problem like high vibration due to a broken
- The way the skycar is drawn above, it has few lateral
stability. It should be placed above a wider lifting carpet to
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.
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:
Eric Brasseur - May 22 2003 till
April 10 2015