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National Advisory Committee for Aeronautics, Technical Notes - Use of the Coanda Effect for Obtaining Jet Deflection and Lift with a Single Flat Plate Deflection Surface

During the past 15 years considerable attention has been given to
aircraft configurations utilizing propeller thrust for vertical lift to
support the aircraft at zero ground speed, in order to make a practical
vertical takeoff and landing aircraft (VTOL). The areas of usefulness
for VTOL and STOL (short takeoff and landing) aircraft have been dis-
cussed and evaluated previously (refs. 1 to 4). Within the past two
years Jet engines with favorable thrust-to-weight ratios have become
available. As a result, interest in Jet-supported VTOL and STOL aircraft
has grown.

Since 1955 the NACA Lewis laboratory has been conducting research
on Jet-deflection devices for use on VTOL, STOL, and conventional types
of turboJet-powered aircraft. The emphasis of the research has been
placed on three principal applications of Jet-deflection devices:

(1) devices that provide Jet support for VTOL aircraft oriented in a
horizontal attitude with respect to the ground, (2) devices that provide
Jet directional control forces during takeoff and landing when the air—
speed is too low for aerodynamic control surfaces to be effective or
during flight at high altitudes where the aerodynamic surfaces also may
lose some of their control effectiveness, and (5) devices that augment
the lift of the aerodynamic surfaces either during takeoff and landing
(STOL aircraft) or at high-altitude cruise. In general, the application
of Jet deflection for control and lift augmentation requires only partial
deflection or turning of the Jet; consequently, a large portion of the
engine thrust still is available for axial thrust.

As part of its research program on Jet-deflection devices the NACA
has conducted an exploratory study of the use of the Coanda effect as a
means of Obtaining vertical lift for Jet—powered VTOL and STOL aircraft.
The Coanda effect may be described as the phenomenon by which the prox—
imity of a surface to a Jet stream will cause the Jet to attach itself to
and follow the surface contour (ref. 5). When such a surface is placed
at an angle to the original Jet (or nozzle) axis, the Jet stream will be
deflected. The local pressures on the deflecting surface are less than
ambient air pressure.