4. INTERPRETATION OF PILOT EXPERIENCE
Considerable knowledge of aircraft spin behaviour exists as undocumented pilot experience. In particular, in the area of spin entry and spin recovery, there are no theoretical or experimantal techniques for defining correct control deflections and control sequencing for optimum entry and recovery. These techniques are determined during flight test development and may be refined during operational use.
One particularly sensitive area during spin recovery of a conventional aircraft is the sequencing of anti-spin rudder movement with forward of the elevatgor cobntrol to regain flight trim conditions. If the elevator control is moved forward too soon, two adverse effects can occur: firstly as the aircraft is pitched down, the radius of gyration is momentarily reduced and because of the conservation of momentum, this will lead to an increase in spin rate, secondly as elevator control is moved downwards, the area of effective rudder may be reduced, resulting in a reduction in available anti-spin yawing moment. Alternatively, is the levator control is moved forward too late, the aircraft may enter a spin in the opposite direction.
For aircraft with poor spin recovery characteristics correct pilot technique becomes critical and the subtle nuances of particular aircraftt give rise to much pilot discussion. Accurate flight dynamic models of aircraft spinning are required to enable this pilot knowledge to be interpreted in terms of the aircraft aerodynamic, inertia and control characteristics.
5. CONCLUDING REMARKS
Since the early days of flying, both stalling and spinning have been major causes of aircraft handling accidents, and an economic design solution to the problem of spinning has not yest been found.
The characteristics of the spin manoeuvre has been described in this paper and a brief outline has been given of the design techniques and spin test methods available to the aircraft designer.
The limitations of current design prediction methods are indicated and the need to interpret pilot experience of aircraft spin behaviour in terms of aircraft characteristics is presented.
REFERENCES
1. Gates, S.B. and Bryant, L.W.; The Spinning of Aeroplanes. R&M No. 1001; 1926.
2. Kerr, T.H.; A Criterion for the Prediction of the Recovery Characteristics of Spinning Aircraft. Aeronautical Research Council C.P. No. 195; 1966.
3. Bowman, J.S.; Summary of Spin Technology as Related to Light General-Aviation Airplanes. NASA TN D-6775; 1971.
4. Robelen, D.; Miniature Spin Tunnel. Model Aviation, March, 1980.