System consists of movable auxiliary aerodynamic sensors mounted on fuselage and connected to trailing-edge flaps by rigid mechanical linkages. System achieves alleviation by reducing lift-curve slope of airplane to such a small value that gust-induced angles of attack will result in small changes in lift

Hewes, D. E.

Phillips, W. H.

Stewart, E. C.

English

NASA Technical Reports Server

October 1975	 B75-10224 
NASA TECH BRIEF 
Langley Research Center 
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 subscri ion 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. 
Gust Alleviation System To Improve 
Ride Comfort of Light Airplanes 
A simple all-mechanical gust alleviation system has 
been developed for light airplanes. This longitudinal 
gust alleviation system was developed to reduce the 
normal accelerations of the airplane at cruise 
conditions. It consists of movable auxiliary aerody-
namic surfaces (sensors) mounted on the fuselage and 
connected to the trailing-edge flaps by rigid 
mechanical linkages. 
The basic components of the system are shown in 
the illustration. The sensors are hinged about a 
chordwise axis adjacent to the fuselage and change 
their dihedral angle in response to gusts. Both sensors 
and both flaps are interconnected so that all deflect 
together symmetrically. As the sensors move up in 
response to an up gust, the flaps are deflected up by 
the flap/sensor linkage. The flaps decrease lift on the 
wing by an amount almost equal to the increase in lift 
on the wing due to the gust which caused the sensor 
deflection. In this way, the lift on the airplane is 
maintained relatively constant regardless of the gust 
encountered by the airplane. 
A loading spring is provided to assure that the 
sensor operates at the most effective angle of attack 
for a given airplane flight condition. The positive
angle of attack is desirable from -a performance 
standpoint, in order that the sensor detract as little as 
possible from the . sic lift-to-drag ratio of the 
airplane. This positive angle of attack results in the 
alleviation of horizontal gusts as well as vertical gusts, 
as the lift on the sensor will change with airspeed. 
Except for low-speed approaches, horizontal gusts are 
of much less importance than vertical gusts. 
This gust alleviation system achieves its alleviation, 
essentially, by reducing the lift-curve slope of the 
airplane to such a small value that gust-induced 
angles of attack will result in small changes in lift. 
This low response to changes in angle of attack 
practically eliminates the ability of the pilot to change 
the flightpath unless some sort of compensation is 
provided. The spanwise pivot axis for changing sensor 
incidence and the pilot's control linkage (see 
illustration) are provided for this purpose. As the 
elevator is deflected, the sensor is rotated about its 
quarter chord so that its angle of attack remains 
constant as the angle of attack of the airplane 
changes. Thus, the flap will not respond to changes in 
angle of attack due to control inputs but will still 
respond to changes in angle of attack due to gusts. 
Flap
(Neutral Position) 
Loading 
Plc	 Spring Flap /Sensor 
Elevator 
Control
Sensor Pilot Control	 Elev 
Linkage	 Spanwise Sensor 	 (Neutral Position) 
Pivot 
for Changing Sensor 
Incidence 
Side View
Trailing-Edge
Flap (Up Position) 
Angle	 Movable 
Sensor 
Front View 
Longitudinal Gust Alleviation System for Light Airplanes
(continued overleaf) 
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.
https://ntrs.nasa.gov/search.jsp?R=19750000224 2020-03-19T20:29:47+00:00Z
Data from static wind-tunnel tests and longitudinal 
short-period analysis revealed that the system 
required some means of increasing longitudinal 
short-period damping. A flap/elevator interconnect 
was installed, because of fewer system design 
complications, which made the flap pitching moment 
more negative. This reduced the normal acceleration 
to about one-half that of the basic airplane, with a 
resulting ride comfort improvement. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Langley Research Center 
Mail Stop 139-A 
Hampton, Virginia 23665 
Reference: B75-10224
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
Patent Counsel 
Langley Research Center 
Mail Stop 313 
Hampton, Virginia 23665 
Source: Eric C. Stewart, William H. Phillips,

and Donald E. Hewes
(LAR-11771) 
Categories: 03 (Physical Sciences) 
B75-10224	 06 (Mechanics)


Gust alleviation system to improve ride comfort of light airplanes

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