Issue No 22 THE AVIATION HISTORIAN 49
fudge on this issue, stating that “the reasons for
this drag rise are not fully understood”.
The largely forgotten but brilliant British aero-
dynamicist, Ernest Ower, had pointed out in a
lecture to the Royal Aeronautical Society (RAeS)
in January 1932 that the better-shaped a fuselage
(or engine nacelle) and wing were, the worse they
would behave when mated together.^4
Ower’s 1932 lecture also referenced the work of
Canadian aeronautical engineer John Hamilton
Parkin and his student protégé, George Klein.
Parkin and Klein met at the University of Toronto,
where the former’s drive as a junior academic had
established a superb windtunnel in the basement
of the engineering faculty. In January 1930 the
pair produced a paper entitled The Interference
Between the Body and Wings of Aircraft, based on
work in the windtunnel. Part of it reads:
“The results of the investigation indicate that
the interference effects are dependent on the
shape of the fuselage, the aerofoil section and the
relative position of the fuselage and aerofoil. The
better the aerodynamic form of the fuselage, and
the thicker the aerofoil section, the greater are the
interference effects. Interference between wing
and body tends, in general, to lower the critical
angle and increase the drag of the combination
as compared with the individual components”.^5
The Hurricane didn’t just have a 20 per cent
aerofoil at root, it was high-camber — almost all
of the curvature of the Clark Y profile was on the
upper surface. No wonder it reacted badly with
a fuselage of “good aerodynamic form” over it.
The “well-fed trout”
By the 1930s it had been long established that
the best shape for any object moving through
air — presuming the idea was to move faster
for a given amount of energy — was the one
noted by Sir George Cayley in his measurement
of a “well-fed trout” in 1809.^6 This form is so
common as to be instantly associated worldwide
with speed, but there is no commonly-accepted
word for it. For the purposes of this article we
will call it a “teardrop”, which almost describes
it, but not quite. Cayley’s illustration is in fact
a graph of area, not a drawing of a fish. Cayley
had essentially “area-ruled” a trout. This is how
aeroplanes had been designed since their design
started being about going forward faster rather
than simply just going up.
A significant issue is that both classic teardrop
fuselages and wings are aerofoils, which are
designed to accelerate the air passing over them
relative to themselves. Essentially, air molecules
don’t care where the aerofoil is that is accelerating
them, or whether it lies in a horizontal or vertical
plane. The air that is moving over the wing root
of a classically streamlined aeroplane is being
accelerated by two aerofoils at once; the one
created by the fuselage’s side area, and the one
created by the wing. The air behaves as if it was
being acted on by one combined “virtual” aerofoil
of much greater camber than the wing alone, a
concept known as “the addition of velocities”.
One aspect of this behaviour is raised drag,
and another is early flow-separation, inducing
buffeting and burbling. Yet another is a greatly
reduced critical Mach number, defined as the
Mach number at which the most-accelerated flow
around a body first becomes locally supersonic,
of which more later.
An illustration of root buffeting, and how serious
it could be, is the first “air disaster” to be reported
as such, and the first for which the accident report
was made public as a matter of policy. On JulyABOVE The prototype Hawker Hurricane, K5083, which first flew in November 1935. Note the small constant-
radius wing fillet, thought to be adequate by its designer, Sydney Camm. The thick wing against the slightly
curved fuselage-side meant that it was not, and the combination of the two resulted in considerable root-drag.
TAH ARCHIVE