Part 8 (1/2)

THE OPTIMUM ANGLE OF INCIDENCE is the angle at which the lift-drift ratio is highest In le of incidence possessed by the surface when the axis of the propeller is horizontal

THE BEST CLIMBING ANGLE is approxiles

All present-day aeroplanes are a compromise between Climb and horizontal Velocity We will coned for maximum climb, and the other for maximum velocity

ESSENTIALS FOR MAXIMUM CLIMB:

1 _Low velocity_, in order to secure the best lift-drift ratio

2 Having a low velocity, _a large surface_ will be necessary in order to engage the necessary mass of air to secure the requisite lift

[Illustration]

3 Since (1) such a cli path, and (2) will clile relative to the direction of the thrust_ will be necessary in order to secure the requisite angle relative to the direction of motion

The propeller thrust should be always horizontal, because the ard to cliement of an inclined surface driven by a _horizontal_ thrust--the surface lifting the weight, and the thrust overco the drift This is, in practice, a far e about a vertical axis and producing a thrust opposed to gravity If, when clile as to tend to haul the aeroplane upwards, then it is, in aas a helicopter, and thatinefficient in practice is due to the fact that, owing to mechanical difficulties, it is iht an air-screw of the requisite di so, it would be necessary, in order to absorb the power of the engine, to revolve the coreater velocity than that of the aeroplane's surface As already explained, the lift-drift ratio falls with velocity on account of the increase in passive drift This applies to a blade of a propeller or air-screhich is nothing but a revolving surface set at angle of incidence, and which it is iood deal of detrimental surface near the central boss

4 The velocity being low, then it follows that for that reason also _the angle of incidence should be coe_

5 _Camber_--Since such an aeroplane would be of low velocity, and therefore possess a large angle of incidence, a _large camber_ would be necessary

Let us now consider the essentials for an aeroplane of h lift to get off the ground, but no h velocity_

2 A coreater velocity than the ed for a given surface and time, and therefore a smaller surface will be sufficient to secure the requisite lift

3 _A sle relative to the propeller thrust_, since the latter coincides with the direction of le of incidence_ by reason of the high velocity

5 A comparatively _sle of incidence

[Illustration: ANGLES OF INCIDENCE (INDICATED APPROXIMATELY) OF AN AEROPLANE DESIGNED AS A COMPROMISE BETWEEN VELOCITY AND CLIMB, AND POSSESSING A SLIGHT MARGIN OF LIFT AT A LOW ALtitUDE AND WHEN THE THRUST IS HORIZONTAL]

MINIMUM ANGLE

This gives the greatest velocity during horizontal flight at a low altitude Greater velocity would be secured if the surface, angle, and caned to just ht with a horizontal thrust Also, in such case, the propeller would not be thrusting doards, but along a horizontal line which is obviously a ard the aeroplane merely from one point of view, _ie_, either with reference to velocity or climb

OPTIMUM ANGLE (Thrust horizontal)

The velocity is less than at the sned to-day, the area and angle of incidence of the surface is such as to secure a slight ascent at a low altitude The cale of incidence and velocity The lift-drift ratio is best at this angle

BEST CLIMBING ANGLE