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		   Personal flying machines

	During World War II, it was common for journalists, when otherwise
unoccupied, to speculate about the post-war world.  Unlike present
speculations with similar titles, theirs were generally optimistic, and one
of the themes was that certain new inventions would make our lives more
comfortable.  One such speculation was that helicopters would become as
common as cars and be used instead of cars.  Drawings of cities of the
future showed people whizzing around in small flying machines, propelled by
rotors, rockets, or the artist's imagination.  Forty years have passed, and
this still hasn't come about.  Why didn't it happen?  Is it impossible or can
it still happen?  What is required? Whose fault it it anyway?

	To begin with, what would be the good of a personal flying machine
that could be used like a car, i.e. kept at home and flown to work or to the
store?  To many people, myself included, it seems obvious, but there are many
skeptics and negative thinkers, so it's worthwhile spelling it out.  Here are
some advantages:

	1. If the flying machine was reasonably fast, the comfortable
commuting range would be much larger.  More people could live where they
want, and husbands and wives would be more independent of each other in the
job market.

	2. Intrinsically there is plenty of room in the sky.  With good
enough electronic control, there wouldn't be traffic jams.

	3. Less land would be occupied by highways and there would be less
expense of building them.

	4. Flying is fun.
	
	We will argue that the idea was good, but the speculations were
naive.  With 1990s technology, the dream may be technically and economically
realizable, but it may require innovations in the social mechanisms for
supporting technology in order to get the development done.  It may require
the reversal of some recent innovations in technology assassination in
order that it be allowed to happen.

	To begin with, what's wrong with helicopters?

	1. They are expensive.  A reasonable four place helicopter with
instrumentation costs $150/flying hour for gas and maintenance.  This is not
the decisive problem, because there are a substantial number of rich people
who can afford that and who pay much more for private jets.  If this were
the only problem the rich would lead the rest of us into the helicopter
world just as they led us into the automotive world.

	2. Helicopters are too dangerous unless operating restrictions are
imposed that seriously impair their usefulness.  For a long time helicopters
were regularly used from roof tops, but this practice has mostly been 
replaced by helipads in parking lots.   My impression is that occasional
unpredicted wind gusts caused too many accidents.  Also helicopters have
only recently been able to fly in instrument weather, e.g through overcasts.
They can do this only at similar altitudes to those used by airplanes.
Indeed it may be that the only person who commutes anywhere regularly using
a helicopter is the President of the United States.  Even he probably can't
go to the store by helicopter or even go to Camp David without several
hours notice.

	3. They require too much skill to fly them safely, and a lot of
willingness to cancel trips if the weather appears doubtful.

	4. They are too noisy.  Many cities forbid landings except at
airports, hospitals and a few other designated places.

	5. They have poor public acceptance.  There has always been a
problem of public acceptance of any new annoyance except by phenomena in
whose benefits the public already shares.  Remember the proposed laws about
there having to be a man carrying a flag walking in front of automobiles.
The anti-technological attitudes widely prevalent among intellectuals
combined with egalitarianism and litigiousness will be difficult to overcome.

	Other possibilities than helicopters and airplanes have been mentioned,
but none of the others meet our criterion of possible feasibility according to
present understanding of scientific law.  For example, there is no present
scientific basis for anti-gravity.  Also the one-man rocket or jet propelled
platforms use fuel at such a rate that they can't go a useful distance.  Nor
is their any scientific basis for flying by psi power.

	Here are some ideas about how the problems can be solved.  Helicopters
are still a possibility, but not the only one.

	1. We don't propose anything special concerning cost.  If a large
market develops, competition and automation will bring the cost down.  The
rich will lead the way.

	2. Personal flying machines must be entirely automatically flown.
This is independent of whether there is a big automatic traffic control
system or whether each machine avoids the others with its own detection and
computation apparatus.  Anyone who treats an airplane --- let alone a
helicopter --- like an automobile is asking for a short life.  We humans just
aren't reliable enough.  Airliners which fly fixed routes require at least
two professional pilots to achieve sufficient safety.  Getting sufficient
reliability in computer control is an unsolved but solvable problem.  (Some
computer scientists might disagree with this judgment).  Much of the
mechanical maintenance will have to be automatic or automatically controlled
and inspected.

	3. A new system of navigation and wind observation is required.  The
navigation problem is easier.  The Navstar satellite navigation system is
good to 10 meters, but this must be supplemented by a local system good to a
few inches.

	Wind gusts must be detected and observed.  My candidate for this is
lidar, i.e. radar using light.  The lidar, whether mounted on the flyer or
on the ground, must scan the air mass through which the plane proposes to
fly and determine the velocity field.  This can be done in principle by
doppler reflection from particles suspended in the air.  So far, as I
understand it, the technique has mainly been used for atmospheric research.

	4. I don't know if the noise problem of helicopters can be
sufficiently solved.  If the answer is yes, then helicopters are an obvious
candidate.

	[Are you going to insert comment on problem #5?]

	Another candidate is the airplane.  For this purpose the airplane
must be capable of slow speed flight.  It can keep the noise down by having
a muffler on the motor and a large slow-turning propeller.  Lockheed built
experimental models of such a plane, called the Q-Star, for the Army in the
1960s.

	One possibility for landing is that the airplane land and take off
from a perch like a bird using legs.  If the plane's landing speed is 64
feet per second, and if the legs can extend 16 feet, then an acceleration of
4g will stop the plane in one half second.  I believe that anyone can
withstand this, properly supported, because it isn't necessary to breathe
during that time.  Whether people will find it acceptable is a matter on
which a priori opinions aren't worth much.
	
	In drawings of cities of the future, people are always dressed
very oddly, and their buildings, though fanciful, don't look cosy.  But
those personal flying machines look like something anyone might like to try.
[John-- I think this piece needs a concluding comment or two.  But this one
doesn't seem to me like something you'd write.  Got an alternative?]

	In spite of its great benefits and its probable feasibility, the
prospects for the development of personal flying machines in the next fifty
years are quite small in the present social and political situation.  This
is because the development costs are great --- in the hundreds of millions
to billions of dollars, success is not assured, and the anti-technological
movement is strong enough so that the project might be stopped at any time
from its beginning to legalization of the results.  The latter makes private
investment very risky, since the private investment itself will incite attack.

	Development of the personal flying machine and its institutional
acceptance would be extremely expensive and would face serious political
obstacles.  Judging from the cost of much less revolutionary airplane
projects, hundreds of millions to many billions of dollars would be required.
Then it would face the problem of legalization.

	Here is a possible plan for bringing it about.

	1. First of all, there should be enthusiasm for the idea beyond the
scale of an individual inventor.  This isn't so easy, and most past
innovations have been carried to the point of prototype by individuals.