Thus, consider an unstaggered biplane at, say, 40 dug. incidence. At values of rotational speed likely to be expected in a spin it will have a iairly large positive value of rolling moment, which means, as we have seen, an inward sideslip. This means in turn less sideslip at the tail leading to difficulty in preserving the spin at a low incidence. ? monoplane spinning at the same incidence would do so with outward sideslip, thereby augmenting the sideslip due to rotation. Inertia moments enter into the question as well, and, in fact, the aerodynamic and inertia moments and the eitects of sideslip are so interwoven as to make any simple separation of cause and effect extremely difficult. An opinion has been expressed that the ordinaiy autorotation experiment has no bearing on the fully developed spin at all but may be important as regards the incipient spin. In the wind tunnel spins have been observed on monoplanes at incidences quite outside the autorotation range.
Crowe, J.H. (1939), "An Elementary Study of the Spin: A Review of Existing Knowledge on a Problem of Ever‐Present Difficulty", Aircraft Engineering and Aerospace Technology, Vol. 11 No. 4, pp. 158-160. https://doi.org/10.1108/eb030471
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