Project Sign Progress Report, 1948

.. ,. MARCH S, 1948 279 - THE AEROPLANE
-.. The Biology of the Flying Saucer- II
By A. R. Weyl, A.F.R.Ae.S.
In this series of articles the history of low-aspect-ratio aircraft is recounted and
technical aspects of their design discussed. leading up to their use for supersonic flight.
T (Continued from J>Olt 185, February 13 /rut.)
HE SECR ET-CIRCLE "CONSPIRACY;• mentioned pre
viously in connection with circu)ar-aerofoil aeroplanes. did
not lack congenially inventive spirits. Early in 1913 an engineer
in D ijon. M. Bou rgoin. made experiments with an annular
wing aeroplane. The tests were unsatisfactory. One feature
of this design was the provision made for varying the wing
incidence in flight.
More recently, a similar idea was suggested by N. H. Warren
and Th. R. Young (Fig. 8). In 1937 they secured a p atent
( Brit. Pat. Spec. No. 508,022 of December, 1937) for a non
stallable monoplane of rhomboidal shape (i.e., leading wing
swept back and trailing wing swept forwards with the wing lips
merged together). This was provided with a conventional tail
at 1he stern of a long fuselage and a number o f advantage~
Fis. 8.-Project by W arren and Young for a liJht twln
en1lned two-seater of 90 h.p. (1937). The elevator is
fitted between fin and fuselage. There Is no tailplane.
were claimed. lo 1943 a model for a two-seater fighter with
tail turret show~ the separate tail omitt~d; special emphasis
was laid oo the triangular shape o f each wing and the effect of
sweep was relied upon. Nothing more bas become_ known
since however b ut it is worth noting that the proJect had
been'based oa ;ound aerodynamic considerations.
lo 1933 the annular wing of the German sculptor Antes
created a mild s~nsation bc<:ause ?f the good performance oC
models made to th is coocepuon (Fig. 9).
Some.what pecul iar was the aerodynamic ~onceP.tion of the
rhomboidal annular aerop lane of P. Nesbitt W11loughby, a
=
Fis, 9.--Model of the "annular wing " ~f Ant es. 1933.
qualified aeronautical engineer (Fig. 10). The Willoughb}
Delta Co. of London had taken up the development of th,.,
idea in 1931 and sufficient means were available to make rather
extensive tests.
The principle is best described as a tandem monoplane with
two aerofoil-shaped parts connecting the leading wing with the
trailing wing near the tips. The "side wings" had aerofoil
shape not only in their longitud inal cross-section (i.e., in the
direction of flight). but also laterally. This was considered a
characteristic feature and subject to patents. It was claimed
tha t the vortex distribu1ion induced by such shape gave an
unusually h igh aerodynamic efficiency in spite of the small span
of the aeroplane. In addition. it was pointed out that the
maximum lift was shifted to very high incidences. Moreover.
the "side wings" should reduce the drag of engine nacelle,
filled underneath them.
All this was said to be proved by extensive wind-tunnel
experimentation here and abroad. Designs of passenger trans
po n aircraft reaching weights o f 40,000 lb. were prepared on the
basis of model tests made at the National Physical Laboratory
a nd elsewhere. T he results must have been so encouraging
that a n experimental monoplane with two 125 b.h.p. Menasco
e ngines and weighing 2,540 lb. was constructed late in 1938
(Fig. 11). This aeroplane flew indeed and was even publicl~
demonstraled (including one-engine flight) a1 a Garden Party
in May, 1939. Shortly afterwards the experimenter was killed
in an uneitplained c rash during a flight test.
From pressure plots over the "side planes" which have been
published, apparently trim changes could be eitpected at various
aocidences. These components were thus capable of producing
longitudinal inslability a nd it is not improbable that this and
poor control efficiency may have contributed to the accident.
There was a lso evidence of a stall at normal incidences.
although of a very mild character and with little apparent
decrease in the lift c~fficient (which. however, would not
exclude the presence of fl uctuating lift forces).
1 1
Fig. 10.-frinciple or the W illoughby Delta design.
Another suggestion for an annular wing was made by L.
Peel, in 1944. This. however. was concerned less with the
aerodynamic p roperties of such wing systems than with the
arrangement of two engines facing each other with their air
screws. in order to overcome the torque reacuon.
A phenomenon of which aerodynamic experimenters were
alwa)ls well aware. but which aircraft designers failed 10
u1ilizc, was that wind-tunnel tests clearly proved good-natured
stalling p_roperties of wings having very small aspect ratios.
Yet even m the very e_arly days when centres of gravity were far
too far back on the old box-kites, the square shape of tailplanes.
then unaccountably in vogue, ma y have saved the pilot's bacon
more than once by its refusal to stall under eittreme provocation.
Later on science came and proved that a tailplane of "good"
aspect ratio was more eflkient. It was, but it made the stall
worse when the centre of gravity happened to be rather aft.
The interesting thing is that aerofoils of circular or square
shape were tested in the early days at incidences up to 90
degrees, while o n normal aerofoils tests were restricted to rather
small incidences onl y. generally ucluding the range o f stall.NND 927545