Berriman, 1913, Some thoughts on stability and control
- Algernon E. Berriman, "Some thoughts on stability and control", Flight 11 January 1913, p. 34.
- (Seems to be only the first section: "I. The Influence of Negative (Down Pressure) Wing Tips on Steering and Balance. Instability and the Rudder." Further installments will probably be found in subsequent issues of Flight.)
In short, Berriman argues that "negative" wing tips—which have a tendency towards downwards pressure instead of lift—may be the most effective way to achieve stability in turning airplanes.
Berriman opens with the proposition that it's useful to share your thoughts in print "as a basis for discussion and criticism" and that the ideas he presents are not settled. He proposes to tackle the issue of "stability", a term which has many meanings within the domain of flight. "By inherent lateral stability in the absolute sense I mean that the wing spars will not cant at all unless the pilot destroys their balance by a movement of the control. "Weathercock" longitudinal stability as means "that the wings tilt and dip in sympathy with the trend of the wind in the vertical plane. In short, a machine that has sensitive weathercock longitudinal stability maintains a constant angle of incidence to the relative wind."
Stability is most difficult to accomplish while turning. He argues that a rudder is not necessary for steering if the wings can be banked properly, and thus direct the aircraft's acceleration appropriately. When the wings are canted for turning the aircraft does not fully compensate for its weight with vertical lift and will therefore accelerate downward (Fig. 2). Reserve power to create additional speed (and thus lift) when turning is therefore vital (Fig. 3). Less banking requires smaller increases in speed (Figs. 4 and 5). More banking than 45° creates excessive demands for increased speed.
He notes that wings which can warp independently enable the operator to differentiate the air resistance and therefore acceleration of each. One wing will accelerate more slowly and the aircraft will therefore turn in its direction. However, he says, in the case of positive wing tips—i.e. wing tips generating upward lift—this will also create a difference in lift between the two wings and cause the aircraft to accelerate downwards on the wrong side.
If a positive lift wing is warped so as to increase the angle, the momentary reaction is obliquely upwards and backwards, being in part added resistance and in part added lift. Of these components the former tends to reduce the velocity in a sense appropriate to the conditions of turning with the warped wing inwards, but the latter tends to cant the wings the wrong way.
Conversely, if the other positive wing is warped to reduce the angle, its resistance and its lift are momentarily decreased. On the one part, therefore, it tends to accelerate and on the other part to descend. A tendency simultaneously to accelerate and to ascend is, however, what is required of the outer wing when initiating a turn.
Clearly, therefore, warping by itself is an unsatisfactory method of steering an ordinary aeroplane, and seems a dangerous operation rather than otherwise.
Berriman suggests that negative wing tips, however, can enable stable turns and in fact have a tendency to self-stabilize:
Suppose one wing tip to have its negative angle increased. The reaction will be obliquely downards and backwards, giving rise to a simultaneous descend and retreat. Both movements are in the proper sense ofr a turn with the wing tips on the increase. But, while the increased negative tip descends and retreats, it decreases its negative pressure, and so resists the movement of descent and retreat. So as soon as the warp ceases, therefore, the bank and the spin also cease; the condition of banking is stable.
See also: Berriman, 1913, Aviation, pp.336–338.
| Original title | Some thoughts on stability and control |
|---|---|
| Simple title | Some thoughts on stability and control |
| Authors | Algernon E. Berriman |
| Date | 1913 |
| Countries | GB |
| Languages | en |
| Keywords | stability, control |
| Journal | Flight |
| Related to aircraft? | |
| Page count | 15 |
| Word count | |
| Wikidata id |
Sources
- Brockett (1921), page 149, entry 6: Berriman, Algernon E. Some thoughts on stability and control. Flight, Vol. 5, Nos. 2-11 (Jan. 11-Mar. 15, 1913), London, pp. 34-37, 61-63, 86-87, 116-117, 305-307, figs. (B2p0149e06)
