The Aeroplane Speaks

ller is to translate the pow

set at an angle inclined to the direction of motion, secure

divided into two component parts o

ite to it at flying speed. If it falls off in power, then the flying speed must

be conveniently divided into

by the useful thrusting

the rest of the propeller, i.

the friction of the air w

ent of the air caused by t

y of the propeller to produce a cavity or semi-vacuum in which it re

lowing factors: Speed of Revolution.-The greater the speed, the greater the proportion of drift to thrust. This is due to the increase with speed of the pass

ame reasons as in the cas

e Area

Ratio

er.-

he thickness to make a good camber possible. Again, the diameter of the propeller must be limited, having regard to the fact that greater diameters than those used to-day would not only result in excessive weight of construction, but would also necessitate a very high undercarriage to keep the propeller off the gr

NCE OF E

conditions mus

hich the blade is set is known as the pitch angle, and it must be co

er of fact, gives back to the thrust of the blades just as the pebbles slip back as one ascends a shingle beach. Such "give-back" is known as Slip. I

ne plus the slip of the propeller. For example, let us fin

........... 70

lutions..... 1

.............

et the aeroplane will travel

feet (

= 6,160 fee

(mi

revolutions per minute, add 15 per cent. for the

,

cent. = 5 fee

,

s the rest of the propeller. For example, two men ascending a hill. One prefers to walk fast and the other slowly, but they wish to arrive at the top of the hill simultaneously. Then the fast walker must travel a farther distance

st be mounted upon a shaft at right angles to a be

propeller. At that point find, by means of a protractor, the angle a projection of the chor

the angle on

a position making the distance between the two lines equal to the specif

example, if that place is 2 feet radius from the centre, then the circumference will be

e, which is represented above by A-B,

angle is being tested, and it should coincide with the specified pitch. You will note, from the ab

a foot apart, on each blade; and the diagram, provided

itch coincides with the specified

ill produce a diagra

ide with the specified pitch. Angles A, C, and D, are too large, and B is too small. Th

ulty manufacture, (2) distortion, or (3) the sh

ze some fixed object. Mark the point it grazes. Now bring the other tip round, and it should come within 1/8 inch of the mark. If

des should be of e

ngs. Place the propeller in a horizontal position, and it should remain in that position. If a weight of a trifle over an ounce p

the balance of centrifugal force, which comes into play as

points A, B, and C must, of course, be at the same fixed distances from the centre of the propeller as the points D, E, and F. Now revers

hould equa

" "

" "

f error permissible, but if there are any apprec

rea of the blades should be eq

aken must, of course, be at the same distanc

ror permissible. If, however, there is an error of o

the tips of the blades, and (3) the greatest depth of the curve should, at any point of the bla

tes, but a fairly accurate idea of the concave camber can be s

the blade, the observer should look for any irregularities of the curvatur

opened. It is not likely, however, that the reader will have the opportunity of making this test. He should, however, examine all the joints very carefully, trying by hand to see if they are quite sound. Suspect a prope

tips of the blades. Some propeller tips have a speed of over 30,000 feet a minute

its shaft. Test in the same way as for straightness. If it is not straight, it is possibly du

balance, camber, or surface area. It causes a condition sometimes mistaken for

llers is of the greatest importance,

em in a very damp

em where the sun w

n a horizontal position or

ntal pegs, and the position of t

in these notes are not attended to, yo

in less aeroplane speed and climb

lutter" and pos

n the propeller sha

r mounted in front

er mounted behind

d propellers are suitable only whe

d to "interference," they are not s

the distance, measured in the direction of the

s put into motion, with the result that the following blade will not secure as good a reaction

Therefore the four-bladed propeller is only suitable for large pitch, as such pitch produce

to secure a large pitch and consequently a good gap, the four-bladed propeller is usually geared