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How
We Made The First Flight
Immediately
upon our return to Dayton, we wrote to a number of automobile and motor
builders, stating the purpose for which we desired a motor, and asking
whether they could furnish one that would develop eight-brake horse
power, with a weight complete not exceeding 200 pounds. Most of the
companies answered that they were too busy with their regular business
to undertake the building of such a motor for us; but one company replied
that they had motors rated at 8 h.p. according to the French system
of ratings, which weighed only 135 pounds, and that if we thought this
motor would develop enough power for our purpose, they would be glad
to sell us one. After an examination of the particulars of this motor,
from which we learned that it had but a single cylinder of 4 inch bore
and 5 inch stroke, we were afraid that it was much overrated. Unless
the motor would develop a full 8 brake horse power, it would be useless
for our purpose.
Finally we decided to undertake the building of the motor ourselves. We estimated that we could make one of four cylinders with 4 inch bore and 4 inch stroke, weighing not over two hundred pounds, including all accessories. Our only experience up to that time in the building of gasoline motors had been in the construction of an air-cooled motor, 5 inch bore and 7 inch stroke, which was used to run the machinery of our small workshop. To be certain that four cylinders of the size we had adopted (4" x 4") would develop the necessary 8 horse power, we first fitted them into a temporary frame of simple and cheap construction. In just six weeks from the time the design was started, we had the motor on the block testing its power. The ability to do this so quickly was largely due to the enthusiastic and efficient services of Mr. C.E. Taylor, who did all the machine work in our shop for the first as well as the succeeding experimental machines. There was no provision for lubricating either cylinders or bearings while this motor was running. For that reason it was not possible to run it more than a minute or two at a time. In these short tests the motor developed about nine horse power. We were then satisfied that, with proper lubrication and better adjustments, a little more power could be expected. The completion of the motor according to drawing was, therefore, proceeded with at once.
While
Mr. Taylor was engaged with this work, Wilbur and I were busy in completing
the design of the machine itself. The preliminary tests of the motor
having convinced us that more than 8 horse power would be secured, we
felt free to add enough weight to build a more substantial machine than
we had originally contemplated.
Our
tables of air pressures and our experience in flying with the 1902 glider
enabled us, we thought, to calculate exactly the thrust necessary to
sustain the machine in flight. But to design a propeller that would
give this thrust with the power we had a t our command, was a matter
we had not as yet seriously considered. No data on air propellers was
available, but we had always understood that it was not a difficult
matter to secure an efficiency of 50% with marine propellers. All that
would be necessar y would be to learn the theory of the operation of
marine propellers from books on marine engineer ing, and then substitute
air pressures for water pressures. Accordingly we secured several such
books from the Dayton Public Library. Much to our surprise, all the
formulae on propellers contained in these books were of an empirical
nature. There was no way of adapting them to calculations of aerial
propellers. As we could afford neither the time nor expense of a long
series of experiments to find by trial a propeller suitable for our
machine, we decided to rely more on theory than was the practice with
marine engineers.
It
was apparent that a propeller was simply an aeroplane travelling in
a spiral course. As we could calculate the effect of an aeroplane travelling
in a straight course, why should we not be able to calculate the effect
of one travelling in a spiral cours e? At first glance this does not
appear difficult but on further consideration it is hard to find even
a point from which to make a start; for nothing about a propeller, or
the medium in which it acts, stands still for a moment. The thrust depends
upon the speed and the angle at which the blade strikes the air; the
angle at which the blade strikes the air depends upon the speed at which
the propeller is turning, the speed the machine is travelling forward
and the speed at which the air is slipping backward the slip of the
air backwards depends upon the thrust exerted by the propeller, and
the amount of air acted upon. When any one of these changes, it changes
all the rest, as they are all interdependent upon one another. But these
are only a few of the many factors that must be considered and determined
in calculating and designing propellers. Our minds became so obsessed
with it that we could do little other work. We engaged in innumerable
discussions, and often after an hour or so of heated argument- , we
would discover that we were as far from agreement as when we started,
but that both had changed to the other's original position in the discussion.
After a couple of months of this study and discussion, we were able
to follow the various reactions in their intricate relations long enough
to begin to understand them. We realized that the thrust generated by
a propeller when standing stationary was no indication of the thrust
when in motion. The only way to really test the efficiency of propeller
would be to actually try it on the machine.
For
two reasons we decided to use two propellers. In the first place we
could, by the use of two propellers, secure a reaction against a greater
quantity of air, and at the same time use a larger pitch angle than
was possible with one propeller; and in the second place by having
the propellers turn in opposite direction, the gyroscopic action of
one would neutralize that of the other. The method we adopted of driving
the propellers in opposite directions by means of chains is now too
well known to need description here. We decided to place the motor
to one side of the man, so that in case of a plunge head first, the
motor could not fall upon him. In our gliding experiments we had had
a number of experiences in which we had landed upon one wing, but
the crushing of the wing had absorbed the shock, so that we were not
uneasy about the motor in case of a landing of that kind. To provide
against the machine rolling over forward in landing, we designed skids
like sled runners, extending out in front of the main surfaces. Otherwise
the general construction and operation of the machine was to be similar
to that of the 1902 glider. |
