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• November 2, 2016 Create Date
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National Advisory Committee for Aeronautics, Report - Induced Velocities Near a Lifting Rotor with Nonuniform Disk Loading

A theoretical and eaperimental investigation of the induced
velocities near a lifting rotor has been conducted. The results
are presented in three parts.

Part I presents a method for computing, from available calcu-
lations for uniform disk loading, the eject of nonuniform
circularly symmetrical disk loading on the normal component
of induced velocity in the vicinity of a lifting rotor. Charts of
the normal component of induced velocity are given for the longi—
tudinal plane of symmetry and for the major axes of rotors with
two dijerent, nonuniform circularly symmetrical dish-load
distributions. It is shown that the normal component of in-
duced velocity must be zero at the center of any practical rotor.
A comparison of the results of this report with those for a uni-
form disk loading shows that nonuniform dislc loading has a
powerful eject on the induced velocity distribution and that it
must be taken into account in estimating the eject of the rotor
on most components of an aircraft.

Part II develops certain symmetry relations for the induced
velocities in the plane of a uniformly loaded rotor and also de—
velops relations between the radial load distribution of the rotor
and the radial variation of induced velocities in the wake.

Part III presents the results of an investigation in the Langley
full-scale tunnel of the induced flow near a lifting rotor. Meas-
urements of stream angles and velocities were made in several
transverse planes along and behind the rotor in four dijerent
conditions representative of the cruising and high-speed ranges
of flight.

These measurements indicate that available theory
may be used to calculate with reasonable accuracy the induced
flow over the forward three—quarters of the dish- for these flight
conditions provided that a realistic nonuniform rotor disk—load
distribution is assumed. Rearward of the three—Quarter-
diameter point, calculations of the induced velocity are increas-
ingly inaccurate due to the rolling up of the trailing-vortex
system. Farther rearward, well behind the rotor, the flow may
be represented more accurately by the flow behind a uniformly
loaded wing.