On Jul 30, 11:41 am, "Flash" wrote:

How much weight could that HF engine get off the ground and then at what
cruise? Assuming, of course, that it could be geared suitably. And what
propeller? Eight foot diameter?

Suitable for a minimum parasol? For a Team Airbike?
--------------------------------------------------------

Dear Flash,

I don't know. I'm not an engineer either... I don't even play one on
TV. But the equation for flight sez the lift has to exceed the weight
and the thrust must exceed the drag.

Lift involves air foils and velocity -- for a given wing-area a
particular wing will generate x-amount of lift at a given speed (or
forward velocity). The 'Flyer' grossed-out at about 700 lbs (!!) with
Orville on-board. It had about 500 square feet of lifting surface and
its forward velocity was between 28 and 30 miles per hour.

This is when you begin to appreciate the fact 'horsepower' does not
appear in the flight equation :-)

Abbott's 'Theory of Airfoils' tells you how much lift will be produced
by a given airfoil at a certain speed and angle of attack. Manipulate
that to find out how much wing-area you'll need to generate enough
lift to overcome your weight. Not enough? then increase the size of
the wing... but keeping in mind that one form of drag is a by-product
of lift. You're liable to run out of thrust before you arrive at
sufficient wing area.

Torque can be manipulated to achieve the best match to a particular
airframe. When that happens, the velocity of the thrust-slug will be
a very close match to the cruise velocity of the airframe. This is
where your loses due to drag will be the least. The real genius of
the 'Flyer' is that the Wright's guesstimated 30mph as their flying
speed and designed their system of thrust to match. They knew the rpm
of the engine and how much torque it was producing at that speed.
They geared this down and designed a pair of propellers capable of
converting that amount of torque into thrust and achieved an
incredible 82% efficiency in converting the available torque into
thrust. (The typical light plane of today is lucky if it sees 60%).

I think a more practical approach to the problem would be to define
the airframe in terms of weight, thrust, speed and wing area. You may
then manipulate those factors to see if your engine is a suitable
match. For example, you might consider increasing the area of the
wing.. Of course, doing so will increase the weight. Your goal is to
see if you can arrive at a suitable compromise before the weight
becomes excessive. An even more successful approach is to start with
a clean sheet of paper. With the engine fully defined (or reasonably
so :-) you know about how much work it can do. That can be
translated into a wing having a particular air foil, chord and span,
from which you can determine the weight of the wing. Those factors
would be manipulated as often as requred to determine Worse Case --
which will tell you if the match WON'T work -- and the Nominal Case --
which tells you if the thing will work.. at least, on paper.

-R.S.Hoover