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National Advisory Committee for Aeronautics, Technical Notes - The Effect of Slots and Flaps on the Lift and Drag of the McDonnell Airplane as Determined in Flight

This note cbntains the results of.flight tests con~
ducted by the Rational Advisory Committee for Aeronautics on
a low—wing monoPlane equipped with leading-edge slots ex—
tending.over the entire wing and flaps extending only to the
ailerons, to find their effect on the lift and drag character»
istics of the airplane. Curves are given showing the lift
and drag characteristics of the airplane for the following
conditions of the.slots and flaps: slots closed and flaps
neutral; slots open and flaps neutral; slots closed and
flaps down; and slots open and flaps down. In addition, the
high and low speeds in level flight and the climbing char—
acteiistics are given.

The results show that the slots used alone increase
the maximum lift coefficient 54 per cent; the flaps alone
increase it 38 per cent; and the slots and flaps in combi—
nation give a total increase in lift coefficient of 94 per
cent. The slots and flaps in combination decrease the land—
ing speed from 60 to 43 m.p.h.; increase the spggg‘range of
the airplane 40 per cent; and increase the-gkide angle at
landing speed 4.20.

It is generally recognized that one of the most impor—
tant problems now confronting-aeronautical engineers is to
improve the airplane in such a-manner-as to increase the
safety of flight. The National Advisory Committee for Aero—
nautics has realized this and is now engaged in a very ex-
tensive program of research. including both wind-tunnel and
flight testing, for the express purpose-o§.increasing the aafe- ;
ty of airplanes.

From- the standpoint of the aerodynamics of the airplane,
it appears that the most promising immediate line of attack
is to find means of decreasing the landing and .take—off—speeds
and of providing adequate control and stability at the atti— ,_
tudes corresponding to these. speeds. Because of their known
ability to increase the maximum lift coefficient, slots and
flaps present one very promising method of accomplishing this
object.

As a part of its general research on Safety, the Committee
has therefore undertaken to investigate the aerodynamic. per—
formanc-e, landing, take—off, stability, maneuverabilit}, and
control. characteristics of an airplane equipped with slots and
flaps so that .the influence of .these d.evices- could be appraised.
not only with respect to safety but also with regard to per—
formance in general. This investigation is now. in progress on _
the thonnell airplane, which was originallv designed for entry
in the. Daniel Gugge.nheim Safe Aircraft Competition. Some pre—
liminary information) th.e presentatiOn of which is the object “
of this report, has been obtained to date.