Cyrano’s balloon:
Recently I described some ideas Cyrano de Bergerac had, including a solar powered ram jet sort of thing.  I have since thought about it some more.  There is no absolute prohibition of a solar powered flying machine.  One has crossed the US and I understand will soon start a trip around the world, or maybe has already done so.  It has solar cells on the wings that drive electric motors for the propellers.

Consider the weight.  The solar cells weigh something.  The Wings have to have enough strength to hold themselves up when the plane is on the ground and to hold up the plane in the air.  The electric motors weigh something.  And there is a pilot or pilots who need their creature comforts.

Consider the losses.  The solar cell can’t be but about 30% efficient.  There are losses in the electric motors.  There is wingtip turbulence and there is the same kind of turbulence at the propeller tips. 

Now build the Cyrano machine.  The heart is a vertical black pipe.  The wall can be as thin as you like, but it has to have some sort of rings or a spiral to keep it from collapsing from the sides as air rushes through.  It does not have to support anything, but hangs from the top.  Around this set a parabolic reflector.  This also can be very light and need only be strong enough to be hung from its top.  The open end of the parabola will point toward the sun and focus the rays on the black pipe.  Close that open end with a transparent shield.  Close the top.  The heated pipe will deliver about half its energy inward and half outward.  The heat coming outward turns it into a hot air balloon that can just about fly anyway.  The inner head causes a rising draft that is directed outward over a circular air foil.  This gives lift. 

The weight is trivial compared with the airplane.  This will not carry a pilot.  There is no propeller, and the airfoil is circular so there is no wingtip.  A few little servo motors adjust vanes that keep the orientation with the sun and tilt the air-foil in the direction of travel and a vent up top if there is too much lift and buoyancy.  It will only work on a still, clear day, but such occasions do happen. 

There needs to be some ballast, so tiny cameras, a microphone, and maybe a tiny speaker are hung from the bottom along with a radio to send pictures and provide guidance.  Sufficient computing power is light.  Some ordinary solar cells power the motors and electronics.

Presto.  The thing is feather light, dirt cheap and provides silent eyes and ears.  If you want to explore an environment, say a bit of wilderness, without disturbing the wildlife, you have your tool.  It collapses into a small package.  There is no need to send up a navigation device since you are going to be monitoring it and can establish its location by triangulation. 

Of course there are those killjoys who would rather just walk around and look, but the wildlife might notice.   

Just a thought.

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