Part 10 (1/2)

[Illustration: R, Direction of reaction of wing indicated

R R, Resultant direction of reaction of both wings

M, Horizontal (sideway) component of reaction

L, Vertical component of reaction (lift)]

In the case of A, the resultant direction of the reaction of both wings is opposed to the direction of gravity or weight The two forces R R and gravity are then evenly balanced, and the surface is in a state of equilibrium

In the case of B, you will note that the R R is not directly opposed to gravity This results in the appearance of M, and so the resultant direction of er directly forward, but is along a line the resultant of the Thrust and M In other words, it is, while flying forward, at the sa sideways, the keel-surface receives, of course, a pressure froreatest in effect towards the tail, then the latter must be pushed sideways

That causes the aeroplane to turn; and, the highest wing being on the outside of the turn, it has a greater velocity than the loing That produces greater lift, and tends to tilt the aeroplane over stilltendency is, however, opposed by the difference in the HE's of the tings

It then follows that, for the lateral dihedral angle to be effective, such angle h to produce, when the aeroplane tilts, a difference in the HE's of the tings, which differencetendency due to the aeroplane turning, but sufficient to also force the aeroplane back to its original position of equilibrium

It is now, I hope, clear to the reader that the lateral dihedral is not quite so effective as would appear at first sight Soners, indeed, prefer not to use it, since its effect is not very great, and since it must be paid for in loss of HE and consequently loss of lift, thus decreasing the lift-drift ratio, _ie_, the efficiency Also, it is sometimes advanced that the lateral dihedral increases the ”spill” of air fro-tips and that this adversely affects the lift-drift ratio

_The disposition of the keel-surface_ affects the lateral stability It should be, in effect, equally divided by the longitudinal turning axis of the aeroplane If there is an excess of keel-surface above or below such axis, then a side gust striking it will tend to turn the aeroplane over sideways

_The position of the centre of gravity_ affects lateral stability If too low, it produces a pendulum effect and causes the aeroplane to roll sideways

If too high, it acts as a stick balanced vertically would act If disturbed, it tends to travel to a position as far as possible froinal position It would then tend, when moved, to turn the aeroplane over sideways and into an upside-down position

From the point of view of lateral stability, the best position for the centre of gravity is one a little below the centre of drift This produces a little lateral stability without any marked pendulum effect

_Propeller torque_ affects lateral stability An aeroplane tends to turn over sideways in the opposite direction to which the propeller revolves

[Illustration]

This tendency is offset by increasing the angle of incidence (and consequently the lift) of the side tending to fall; and it is always advisable, if practical considerations allow it, to also decrease the angle upon the other side In that way it is not necessary to depart so far frole of incidence at which the lift-drift ratio is highest

_Wash-in_ is the terle

_Wash-out_ is the terle

Both lateral and directional stability le of incidence on both sides of the surface, thus:

[Illustration]

The decreased angle decreases the drift and therefore the effect of gusts upon the wing-tips, which is just where they have theto the distance fro axis

The wash-out also renders the ailerons (lateral controlling services) more effective, as, in order to operate thele of incidence as would otherwise be required

[Illustration: Note: Observe that the inclination of the ailerons to the surface is the sale of incidence of the ailerons, the better their lift-drift ratio, ie, their efficiency You will note that, while the aileron attached to the surface ashed-out angle is operated to the sale of incidence is considerably less Its efficiency is therefore greater

The advantages of the wash-in must, of course, be paid for in sole