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 air stream. The pull force will be low.
You can use a big propeller. It will turn slowly and produce a
huge and low speed air stream. The pull force will be very high.
Suppose you plan to build a helicopter.
So you put the propeller above the aircraft. The propeller has to lift
the whole weight of the aircraft. So you will be obliged to use a big
propeller, to get a high pull force. That way your little 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. So it can 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 and it will be much more
complicated to use.)
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 build? 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 such a device is utterly expensive and very
noisy. In order your skycar can 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 consumed? 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.
So what? Many solutions have been tested out but no one really was
satisfactory. Otherwise skycars would already be for sale. In order to
contribute I would like to propose an idea. (This is the third one I
propose. The two previous ones were nonsense.)
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
ventilators beneath the skycar:
These are the motivations for this design:
The ventilators are placed beneath the car because that way the
air stream is not hampered. The presence of the car body above the
ventilators does not hamper them.
The more ventilators are used, the more redundancy you get. A few
ventilators can fail without security problem.
Such a number of high technology ventilators 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 ventilator carpet design only implies the power of each
ventilator can be modulated. Than can be done with nearly no moving
parts at all. What's more the ventilators 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 motors.
Half of the ventilators 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 ventilator to prevent the rotation of the air flow. This increases
a little the yield. The opposite rotation of pairs of ventilators also
reduces the problem of gyroscopic precession.
There are several ways to power the ventilators:
Each ventilator 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 ventilators
to power them. This is the most lightweight solution. Air valves are
used to control the power of each ventilator. One advantage of this
system is the ventilators 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 ventilator 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 ventilator is a
circular linear motor around the propeller.
A hybrid solution is to use a standard little
fuel motor for each ventilator, but with an electric motor on the same
axis. The fact each ventilator 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 ventilators.
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
ventilators. 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 ventilators. 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 ventilators can be used, fuel
powered. Surrounded by a fleet of little electric ventilators.
Some technical problems:
The ventilators placed close to the ground are dangerous and can
be destroyed by little stones and the like. If a ventilator propeller
breaks, the blades can become very dangerous projectiles. A chain
reaction can even break a few ventilators in just a second. I suppose a
kevlar grid above and below the ventilators 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.
Synchronize such a set of ventilators 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 ventilator cell. The processor of each
cell/ventilator receives data from each other ventilator 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 propeller.
The way the skycar is drawn above, it has few lateral stability.
It should be placed above a wider lifting carpet to gain stability.
I don't know down to what point the size of one ventilator 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 ventilators 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.
