Reprinted from - Flight
Magazine and the Aircraft Engineer, December 1935, London,
THE BURNELLI AEROFOIL
By Dr. M. Watter
For very many years Mr. Burnelli has carried out research and
experiment in developing his unorthodox type of aircraft in the
United States. Briefly explained the Burnelli system consists
in using a fuselage of aerofoil section, which gives remarkable
passenger accommodation, and attaching to its sides wings of orthodox
design. The Uppercu-Burnelli Corporation of Keyport, New Jersey,
has granted to W. S. Shackleton, Ltd., the representative rights
The problem of distorted aerofoil body-wing combination would
seem to present rather complex aerodynamic phenomena, and from
a purely theoretic viewpoint its accurate solution is laborious.
The writer felt, however, that for all practical purposes in analyzing
this problem one was justified to resort to the simplifying assumption
of algebraically superimposed effects of aerofoil body and wings.
The following features are indicative of small aerodynamic
interference supporting the above hypothesis. An examination of
the drawing of the latest Burnelli design shows that in view of
the continuity of the upper surface of the wing over the body
portion it is logical to assume that the outer panels have an
effective aspect ratio as if the wings were continuous throughout.
As regards the body which has an aerofoil shape but a very small
apparent aspect ratio it may be remarked that the presence of
outer panels would preclude partial loss of circulation, and besides
that the booms would offer a certain amount of end plating so
that the effective aspect ration must be larger than the mere
shape would suggest. To evaluate the effective aspect ratio of
Burnelli type body the writer assumes an equivalent rectangular
wing having the total area of the wing and body and possessing
the body chord. It is interesting to observe that this simple
assumption was very well verified in two instances by wind tunnel
tests despite the use of two entirely different aerofoil body
shapes. The satisfactory verification is considered to be definitely
supported because of a very close check of the zero lift point,
slope of the lift curve and maximum lift as well as the maximum
L/D of the models.
Let Sb be the area of the aerofoil shaped body having chord
Cb and span bb Sw the area of the wings having an average
Cw and span b. We can write:--
Weight = C1QS hence for equal landing speed and weight C1S
= const. Or aS (dC1/da = const. It can be shown (Fig. 1) that
dC1da = A/(1+2/AR) where A is an experimental constant.
Aspect ratio of wings = b2/Sw
Aspect ratio of body =
In analyzing the relative advantages of the Burnelli monoplane
design we may make the assumption that half of the body width
is indispensable and would be present in any standard design without
the benefit of additional lift effect. Let us take a numerical
example based on one of the recent wind tunnel tests and representing
a 14,000 lb., 14 passenger transport.
Sw = 587 sq. ft. through area S = 163 + 587 = 750 sq. ft. Sb
= 240 sq. ft.; b = 70 ft., and Cb = 20 ft. The effective aspect
ratio can be found from the following equation: --
S/(1+2/AR) = Sw/(1+2S/b2) +
Substituting we find 2/AR = 750/(450+122) -- = .31: AR = 6.55.
In the case of standard design the semispan of each wing would
have been (70-6)/ = 32 and the moment proportional to 32W, while
in Burnelli design the moment is proportional to (70--12) x 450/572
= 22.7W or a saving of 27 per cent. with an additional saving
in wing area of 158 sq. ft.
In this case the amount contributed by the fuselage is 26.5
per cent., which of course is conditional upon the fact that the
zero lift points of both the wing and body aerofoil lift curves
must coincide. A detailed investigation has shown that this condition
represents the best comparison from both the aerodynamic and structural
viewpoints. It results in practically the maximum obtainable L-max./D--min.,
gives high L-max. and contributing lift; it results in somewhat
higher-minimum drag and lower L/D max. than could be obtained
by delaying the lifting action of the body to higher angles of
the wing. One of the other advantages of this setting is decided
simplicity of stress analysis, since the contributing lift effect
of the body is constant for all flying conditions. (Fig. 4).