Effect of weight

The table was worked out for a constant weight of 50 kN. What will be the effect of changes of weight such as must occur in practical flight owing to fuel consumption, etc.? The answer to this is not quite so simple.

Suppose the weight is reduced from 50 kN to 40 kN. At the same indicated air speed, the angle of attack would be the same, and the lift would be the same as previously, i. e. 50 kN. This would be too great. Therefore, in order to reduce the lift, we must adjust the attitude, so that the wings strike the air at a smaller angle of attack, or we must reduce the speed, or both. Whatever we do, we shall get a slightly different relationship between air speed and angle of attack: the reader is advised to work out the figures for a weight of 40 kN. Although the relationship will differ from that for 50 kN weight, it will again remain constant at all heights for the same indicated speeds. To sum up the effect of weight, we can say that the less the total weight of the aircraft, the less will be the indicated air speed corresponding to a given angle of attack. A little calculation will show that the indicated air speed for the same angle of attack will be in proportion to the square root of the total weight.