Project Sign Progress Report, 1948

e MARCH S, 1948THE AEROPLANE 280
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Fig. 11.-Willoughby's "Delta 8" experimental
monoplane of 1938.
Thus, an observant student of laboratory tests could have
noticed the extraordinary capacity of circular or square shapes
10 give a very gradual, innocent stall, an~ that at v!!rY high
incidences. Yet, a part from a few broad-minded experimenters,
no designer drew the conclusion that wmgs of such shapes
promised safety in flight, t~oug_h it w~s known f~om ..~rly
practical experience that fly1Dg 10 the second regime, 1.e.,
at the stall, was positively dangerous.
It is true that spinning- Pa rker's "Spiral D ive "-was
attributed. in those days, to high i~cideoces, and that most _of
the lightly loaded rectangular wmgs used at that period
rendered the stall relatively. innocuo us. Howeve_r, :iccidental
~tailing was then, as now. the cause of the maJonty of all
crashes. And the nose dive following inadvertent stalls was well
known to be o f the most serious consequences. .
Eiffel, Riabouchinsky, D ines, . Prandtl, etc., began the_1r
laboratory experiments on aerofoils of very small aspect rauo
and the results were generously published (how closely secret
they would be kept to-day!). Eiffe l showed that the ratio of
the resultant forces reached maxima for small aspect ratios _an~
that slender wings gave the greatest drag at ~ degrees 10c1-
. mcthing like a circular
wing, a nd performance estimates were based on the properties
of such wings. Yet the question of stalling stability did not
a rise, bccau~e of the rotor properties.
The real pioneer of the disc wing was a very able American
research engineer of the National Advisory Committee for
Aeronautics (N.A.C.A.), who proved capable of following
independent lines of development. In about 1930 Charles
H. Zimmermann subjected the properties of disc wings toNND 927545