Computer program has been designed and written to predict rotor free-wake positions and resulting rotor blade airloads without requiring time-consuming and tedious calculations. This program was written in FORTRAN IV for use on an IBM-360 computer

Deen, D.

Mantay, W. R.

Sadler, S. G.

English

NASA Technical Reports Server

• Augist 1973	 B73-10239 
•	 NASA TECH BRIEF 
Langley Research Center
	 -4r 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Method for Predicting Rotor Free-Wake Positions and the

Resulting Rotor Blade Airloads 
The problem: 
Accurate predictions of rotor free-wake positions and 
the resulting rotor blade airloads require time-consuming 
and tedious calculations. 
The solution: 
A computer program has been designed and written 
to eliminate this problem. 
How it's done: 
Rotor-wake geometries are predicted by a process 
similar to that used for startup of a rotor in a free Otream. An array of discrete trailing-and-shed vortices is generated, with vortex strengths corresponding to step-
wise radial and azimuthal blade circulations, and is 
limited to an arbitrary number of azimuthal steps 
behind each blade. The remainder of the wake model of 
each blade is an arbitrary number of trailing vortices. 
Vortex element end points are allowed to be transported 
by the resultant velocity of the free-stream and vortex-
induced velocities. Wake geometry, wake flow, and 
wake-induced velocity-influence coefficients are gener-
ated by this program for use in the blade-loads portion 
of the calculations. 
Blade-loads computations include the effects of non-
uniform inflow due to free wake, nonlinear airfoil 
characteristics, and response of flexible blades to applied 
loads. Computed wake flows and blade loads are
compared with experimentally measured data. Predicted 
blade loads, response,- and shears and moments are 
obtained for a model rotor system having two inde-
pendent rotors. The effects of advance ratio, vertical 
separation of rotors, different blade-radius ratios, and 
different azimuthal spacing of the blades of one rotor 
with respect to the other, are investigated. 
Notes: 
1. This program is written in FORTRAN IV for use on 
an IBM-360 computer. 
2. Requests for further information may be directed to: 
COSMIC 
ll2 Barrow Hall 	 - 
University of Georgia 
Athens, Georgia 30601 
Reference: LAR-1 0674 
Source: Dariene Deen and

Wayne R. Mantay
Langley Research Center and

S. Gene Sadler of

Rochester Applied Research Associates, Inc.

under contract to
Langley Research Center
(LAR-1 0674) 
-S
Category 09, 06 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that Such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
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Method for predicting rotor free-wake positions and the resulting rotor blade airloads

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