The Aeroplane Speaks [28]
a greater mass of air will be engaged for a given surface and time, and therefore a smaller surface will be sufficient to secure the requisit lift.
3. A small angle relative to the propeller thrust, since the latter coincides with the direction of motion.
4. A comparatively small angle of incidence by reason of the high velocity.
5. A comparatively small camber follows as a result of the small angle of incidence.
SUMMARY.
Essentials for Maximum Essentials for Maximum Climb. Velocity
1. Low velocity. High velocity. 2. Large surface. Small surface. 3. Large angle relative to Small angle relative to propeller thrust. propeller thrust. 4. Large angle relative to Small angle relative to direction direction of motion. of motion. 5. Large camber. Small camber.
It is mechanically impossible to construct an aeroplane of reasonable weight of which it would be possible to very the above opposing essentials. Therefore, all aeroplanes are designed as a compromise between Climb and Velocity.
As a rule aeroplanes are designed to have at low altitude a slight margin of lift when the propeller thrust is horizontal.
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 camber were smaller and designed to just maintain horizontal flight with a horizontal thrust. Also, in such case, the propeller would not be thrusting downwards, but along a horizontal line which is obviously a more efficient arrangement if we regard the aeroplane merely from one point of view, i.e., either with reference to velocity OR climb.
OPTIMUM ANGLE (Thrust horizontal)
The velocity is less than at the smaller minimum angle, and, as aeroplanes are designed to-day, the area and angle of incidence of the surface is such as to secure a slight ascent at a low altitude. The camber of the surface is designed for this angle of incidence and velocity. The lift-drift ratio is best at this angle.
BEST CLIMBING ANGLE
The velocity is now still less by reason of the increased angle producing increase of drift. Less velocity at A GIVEN ANGLE produces less lift, but the increased angle more or less offsets the loss of lift due to the decreased velocity, and in addition, the thrust is now hauling the aeroplane upwards.
MAXIMUM ANGLE
The greater angle has now produced so much drift as to lessen the velocity to a point where the combined lifts from the surface and from the thrust are only just able to maintain horizontal flight. Any greater angle will result in a still lower lift-drift ratio. The lift will then become less than the weight and the aeroplane will consequently fall. Such a fall is known as ``stalling'' or ``pancaking.''
NOTE.--The golden rule for beginners: Never exceed the Best Climbing Angle. Always maintain the flying speed of the aeroplane.
By this means, when the altitude is reached where the margin of lift disappears (on account of loss of engine power), and which is, consequently, the altitude where it is just possible to maintain horizontal flight, the aeroplane is flying with its thrust horizontal and with maximum efficiency (as distinct from engine and propeller efficiency).
The margin of lift at low altitude, and when the thrust is horizontal, should then be such that the higher altitude at which the margin of lift is lost is that altitude at which most of the aeroplane's horizontal flight work is done. That ensures maximum velocity when most required.
Unfortunately, where aeroplanes designed for fighting are concerned, the altitude where most of the work is done is that at which both maximum velocity and maximum margin of lift for power are required.
3. A small angle relative to the propeller thrust, since the latter coincides with the direction of motion.
4. A comparatively small angle of incidence by reason of the high velocity.
5. A comparatively small camber follows as a result of the small angle of incidence.
SUMMARY.
Essentials for Maximum Essentials for Maximum Climb. Velocity
1. Low velocity. High velocity. 2. Large surface. Small surface. 3. Large angle relative to Small angle relative to propeller thrust. propeller thrust. 4. Large angle relative to Small angle relative to direction direction of motion. of motion. 5. Large camber. Small camber.
It is mechanically impossible to construct an aeroplane of reasonable weight of which it would be possible to very the above opposing essentials. Therefore, all aeroplanes are designed as a compromise between Climb and Velocity.
As a rule aeroplanes are designed to have at low altitude a slight margin of lift when the propeller thrust is horizontal.
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 camber were smaller and designed to just maintain horizontal flight with a horizontal thrust. Also, in such case, the propeller would not be thrusting downwards, but along a horizontal line which is obviously a more efficient arrangement if we regard the aeroplane merely from one point of view, i.e., either with reference to velocity OR climb.
OPTIMUM ANGLE (Thrust horizontal)
The velocity is less than at the smaller minimum angle, and, as aeroplanes are designed to-day, the area and angle of incidence of the surface is such as to secure a slight ascent at a low altitude. The camber of the surface is designed for this angle of incidence and velocity. The lift-drift ratio is best at this angle.
BEST CLIMBING ANGLE
The velocity is now still less by reason of the increased angle producing increase of drift. Less velocity at A GIVEN ANGLE produces less lift, but the increased angle more or less offsets the loss of lift due to the decreased velocity, and in addition, the thrust is now hauling the aeroplane upwards.
MAXIMUM ANGLE
The greater angle has now produced so much drift as to lessen the velocity to a point where the combined lifts from the surface and from the thrust are only just able to maintain horizontal flight. Any greater angle will result in a still lower lift-drift ratio. The lift will then become less than the weight and the aeroplane will consequently fall. Such a fall is known as ``stalling'' or ``pancaking.''
NOTE.--The golden rule for beginners: Never exceed the Best Climbing Angle. Always maintain the flying speed of the aeroplane.
By this means, when the altitude is reached where the margin of lift disappears (on account of loss of engine power), and which is, consequently, the altitude where it is just possible to maintain horizontal flight, the aeroplane is flying with its thrust horizontal and with maximum efficiency (as distinct from engine and propeller efficiency).
The margin of lift at low altitude, and when the thrust is horizontal, should then be such that the higher altitude at which the margin of lift is lost is that altitude at which most of the aeroplane's horizontal flight work is done. That ensures maximum velocity when most required.
Unfortunately, where aeroplanes designed for fighting are concerned, the altitude where most of the work is done is that at which both maximum velocity and maximum margin of lift for power are required.