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 th
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:


Surface area Spread in Depth in

Make Passengers sq. feet linear feet linear


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


Make Cylinders Horse Power Operator


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


Surface Area Spread in Depth


Make Passengers sq. feet linear feet linear


Curtiss . . . 2 258 29.0


Wright. . . . 2 538 41.0


Farman. . . . 2 430 32.9


Voisin. . . . 2 538 37.9


No. of Weight Without


Make Cylinders Horse Power Operator


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


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


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


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.