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National Advisory Committee for Aeronautics, Report - Full Scale Wind Tunnel Tests of a Propeller with the Diameter Changed by Cutting Off the Blade Tips

Tests were "conducted in order to determine how the
characteristics of a propeller are ejected by cutting of
the tips. The diameter of a standard 10Joot metal
propeller nus changed successirely to 9 feet 6' inches, .9
feet 0 inches, 8_ feet 6 inches, and 8 feet 0 inches. Each
propeller thus formed nus tested at four pitch settings
in the Propeller Research Tunnel ofthe National Advisory
Committee for Aeronautics using an open cockpit fuselage
and a D412 engine.

In the early days of aeronautics it was common
practice to adapt propellers to airplanes by cutting
off the tips until the desired revolutions were attained.
This procedure often led to freak designs and, of course,
at times was the wrong thing to do; but the designer
lacking test data and in many cases pressed for time
and money, found no other course possible. With
the advent of adjustable pitch metal propellers
designed by later and more reliable methods, it may
appear surprising that the practice still continues
The explanation is that a modern propeller will not
be far wrong when initially selected, and with the
higher cost of metal over wood propellers, it is some:
times more economical for manufacturers and custom-
ers to make changes in this manner.

Since accurate measurements of the characteristics
had not previously been made, the tests described
here were conducted in the Propeller Research Tunnel
of the National Advisory Committee for Aeronautics
at Langley Field, Va., with a View to determining
quantitatively the propulsive efficiency, thrust, and
torque of a propeller as its diameter was successively
reduced. For each diameter the propeller was tested
at four blade settings.

The Propeller Research Tunnel, the balances,
torque dynamometer, and testing methods have been
described in Reference 1. The torque dynamometer
was installed in an open cockpit fuselage with a D—12,
425-horsepower engine. This fuselage mounted on the
balance ready for tests is shown in Figure 1.