Changes in angle of attack in system were sensed indirectly by gages which responded to strains induced in wing structure. Output signals were amplified, filtered, and used to activate swashplate actuators. System provided significant reduction in blade loads and desirable changes in hub forces and moments

Alexander, H. R.

Magee, J. P.

Morris, J. J.

English

NASA Technical Reports Server

September 1974
	 B74-10174 
NASA TECH BRIEF 
Ames 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. 
Swashplate Feedback Control for Tilt-Rotor Aircraft 
.
Tilting prop/rotor aircraft are subjected to blade 
loads, hub forces, and moments because of the non-
axial flow which occurs in all phases of operations. 
Steady loads such as occur in scheduled flight opera-
tions may be trimmed out by the application of cyclic 
loads, but when the aircraft is subjected to gusts or 
other transient conditions, some sort of automatic 
system must be used to apply the compensating cyclic 
loads. Additionally, large rotors mounted on a flexible 
airframe may give rise to instabilities at some flight 
conditions when oscillations of the airframe couple 
with blade motion; consequently, an automatic con-
trol system could also be used to suppress structural 
oscillations as well as to augment aerolastic stability. 
Conventional stability-augmentation systems effec-
tively provide static margin and damping augmenta-
tion in the pitch, roll, or yaw degrees of freedom of 
the aircraft; unfortunately, the conventional systems 
respond slowly and cut off at frequencies significantly 
below 1 Hz. 
It has been shown that automatic systems utilizing 
rotor swashplate feedback control with greater fre-
quency response effectively reduce blade vibratory 
loads and damp oscillatory structural modes of the 
airframe and rotor system. The swashplate control 
motions are activated by signals originating in the 
structure or in the airflow relative to the structure. 
In the system which was designed and built to 
demonstrate load alleviation, changes in the angle of 
attack were sensed indirectly by gages which re-
sponded to strains induced in the wing structure. 
Output signals were amplified, filtered, and used to 
activate the swashplate actuators. The system pro-
vided significant reduction in blade loads and desir-
able changes in hub forces and moments. 
The structural stability augmentation/modal sup-
pression system uses an accelerometer mounted at 
the wing tip to sense airframe oscillations; the signal
is conditioned, using filters, then amplified and used 
to drive the swashplate actuators in such a way as to 
make the oscillation decay. The results of the tests 
have shown that increases in damping up to 500% 
are possible under normal operating conditions, and 
that an instability region at overspeed rpm's is com
-
pletely eliminated. 
Notes: 
1. The following documentation may be obtained 
from. 
National Technical Information Service 
Springfield, Virginia 22151 
Single copy at cost 
(or microfiche $0.95) 
References: 
NASA CR-I 14600 (N73-30011), V/STOL Tilt 
Rotor Aircraft Study: Vol. VII, Tilt Rotor Flight 
Control Program Feedback Studies. NASA CR-
114664 (N74-15711), V/STOL Tilt Rotor Air-
craft Study: Wind Tunnel Tests of a Full Scale 
Hingeless Prop/Rotor Designed for the Boeing 
Model 222 Tilt Rotor Aircraft 
2. No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B74-10174 
Patent status: 
NASA has decided not to apply for a patent. 
Source: Harold R. Alexander,

John P. Magee, and James J. Morris of

Boeing Vertol Company

under contract to

Ames Research Center
(ARC-10854) 
Category 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 tree from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19740000174 2020-03-17T13:48:43+00:00Z


Swashplate feedback control for tilt-rotor aircraft

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server