In laying out plans for a flying machine the first thing to decide upon
is the size of the plane surfaces. The proportions of these must be
based upon the load to be carried. This includes the total weight of
the machine and equipment, and also the operator. This will be a rather
difficult problem to figure out exactly, but practical approximate
figures may be reached.
It is easy to get at the weight of the operator, motor and propeller,
but the matter of determining, before they are constructed, what the
planes, rudders, auxiliaries, etc., will weigh when completed is an
intricate proposition. The best way is to take the dimensions of some
successful machine and use them, making such alterations in a minor way
as you may desire.
Dimensions of Leading Machines.
In the following tables will be found the details as to surface area,
weight, power, etc., of the nine principal types of flying machines
which are now prominently before the public:
MONOPLANES.
Surface area Spread in Depth in
Make Passengers sq. feet linear feet linear
feet
Santos-Dumont.. 1 110 16.0 26.0
Bleriot..... 1 150.6 24.6 22.0
R. E. P..... 1 215 34.1 28.9
Bleriot..... 2 236 32.9 23.0
Antoinette.... 2 538 41.2 37.9
No. of Weight Without
Propeller
Make Cylinders Horse Power Operator
Diameter
Santos-Dumont.. 2 30 250 5.0
Bleriot..... 3 25 680 6.9
R. E. P..... 7 35 900 6.6
Bleriot..... 7 50 1,240 8.1
Antoinette... 8 50 1,040 7.2
BIPLANES.
Surface Area Spread in Depth
in
Make Passengers sq. feet linear feet linear
feet
Curtiss... 2 258 29.0
28.7
Wright.... 2 538 41.0
30.7
Farman.... 2 430 32.9
39.6
Voisin.... 2 538 37.9
39.6
No. of Weight Without
Propeller
Make Cylinders Horse Power Operator
Diameter
Curtiss... 8 50 600 6.0
Wright.... 4 25 1,100 8.1
Farman.... 7 50 1,200 8.9
Voisin.... 8 50 1,200 6.6
In giving the depth dimensions the length over all--from the extreme
edge of the front auxiliary plane to the extreme tip of the rear is
stated. Thus while the dimensions of the main planes of the Wright
machine are 41 feet spread by 6 1/2 feet in depth, the depth over all is
30.7.
Figuring Out the Details.
With this data as a guide it should be comparatively easy to decide
upon the dimensions of the machine required. In arriving at the maximum
lifting capacity the weight of the operator must be added. Assuming this
to average 170 pounds the method of procedure would be as follows:
Add the weight of the operator to the weight of the complete machine.
The new Wright machine complete weighs 900 pounds. This, plus 170, the
weight of the operator, gives a total of 1,070 pounds. There are 538
square feet of supporting surface, or practically one square foot of
surface area to each two pounds of load.
There are some machines, notably the Bleriot, in which the supporting
power is much greater. In this latter instance we find a surface area of
150 1/2 square feet carrying a load of 680 plus 170, or an aggregate of
850 pounds. This is the equivalent of five pounds to the square foot.
This ratio is phenomenally large, and should not be taken as a guide by
amateurs.
The Matter of Passengers.
These deductions are based on each machine carrying one passenger, which
is admittedly the limit at present of the monoplanes like those operated
for record-making purposes by Santos-Dumont and Bleriot. The biplanes,
however, have a two-passenger capacity, and this adds materially to the
proportion of their weight-sustaining power as compared with the surface
area. In the following statement all the machines are figured on the
one-passenger basis. Curtiss and Wright have carried two passengers on
numerous occasions, and an extra 170 pounds should therefore be added to
the total weight carried, which would materially increase the capacity.
Even with the two-passenger load the limit is by no means reached,
but as experiments have gone no further it is impossible to make more
accurate figures.
Average Proportions of Load.
It will be interesting, before proceeding to lay out the dimension
details, to make a comparison of the proportion of load effect with
the supporting surfaces of various well-known machines. Here are the
figures:
Santos-Dumont--A trifle under four pounds per square foot.
Bleriot--Five pounds.
R. E. P.--Five pounds.
Antoinette--About two and one-quarter pounds.
Curtiss--About two and one-half pounds.
Wright--Two and one-quarter pounds.
Farman--A trifle over three pounds.
Voisin--A little under two and one-half pounds.
Importance of Engine Power.
While these figures are authentic, they are in a way misleading, as the
important factor of engine power is not taken into consideration. Let us
recall the fact that it is the engine power which keeps the machine in
motion, and that it is only while in motion that the machine will remain
suspended in the air. Hence, to attribute the support solely to the
surface area is erroneous. True, that once under headway the planes
contribute largely to the sustaining effect, and are absolutely
essential in aerial navigation--the motor could not rise without
them--still, when it comes to a question of weight-sustaining power, we
must also figure on the engine capacity.
In the Wright machine, in which there is a lifting capacity of
approximately 2 1/4 pounds to the square foot of surface area, an engine
of only 25 horsepower is used. In the Curtiss, which has a lifting
capacity of 2 1/2 pounds per square foot, the engine is of 50
horsepower. This is another of the peculiarities of aerial construction
and navigation. Here we have a gain of 1/4 pound in weight-lifting
capacity with an expenditure of double the horsepower. It is this
feature which enables Curtiss to get along with a smaller surface area
of supporting planes at the expense of a big increase in engine power.
Proper Weight of Machine.
As a general proposition the most satisfactory machine for amateur
purposes will be found to be one with a total weight-sustaining power of
about 1,200 pounds. Deducting 170 pounds as the weight of the operator,
this will leave 1,030 pounds for the complete motor-equipped machine,
and it should be easy to construct one within this limit. This implies,
of course, that due care will be taken to eliminate all superfluous
weight by using the lightest material compatible with strength and
safety.
This plan will admit of 686 pounds weight in the frame work, coverings,
etc., and 344 for the motor, propeller, etc., which will be ample. Just
how to distribute the weight of the planes is a matter which must be
left to the ingenuity of the builder.
Comparison of Bird Power.
There is an interesting study in the accompanying illustration. Note
that the surface area of the albatross is much smaller than that of the
vulture, although the wing spread is about the same. Despite this the
albatross accomplishes fully as much in the way of flight and soaring as
the vulture. Why? Because the albaboss is quicker and more powerful in
action. It is the application of this same principle in flying machines
which enables those of great speed and power to get along with less
supporting surface than those of slower movement.
Measurements of Curtiss Machine.
Some idea of framework proportion may be had from the following
description of the Curtiss machine. The main planes have a spread
(width) of 29 feet, and are 4 1/2 feet deep. The front double surface
horizontal rudder is 6x2 feet, with an area of 24 square feet. To the
rear of the main planes is a single surface horizontal plane 6x2 feet,
with an area of 12 square feet. In connection with this is a vertical
rudder 2 1/2 feet square. Two movable ailerons, or balancing planes, are
placed at the extreme ends of the upper planes. These are 6x2 feet,
and have a combined area of 24 square feet. There is also a triangular
shaped vertical steadying surface in connection with the front rudder.
Thus we have a total of 195 square feet, but as the official figures are
258, and the size of the triangular-shaped steadying surface is unknown,
we must take it for granted that this makes up the difference. In
the matter of proportion the horizontal double-plane rudder is about
one-tenth the size of the main plane, counting the surface area of
only one plane, the vertical rudder one-fortieth, and the ailerons
one-twentieth.