Inlet mouthpiece with variable geometry improves low-speed performance of inlet (or ejector) of jet engines by use of reversed cowl-flap mechanism. Flaps can be adjusted mechanically or system can be operated with pressure taps set so pressure on inlet face is always smaller than pressure on back of inlet

Cheng, D. Y.

English

NASA Technical Reports Server

May 1974	 B74-10046 
NASA TECH BRIEF S	 Ames 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 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. 
Reversed Cowl-Flap Thrust Augmentor 
.
The problem: 
To improve the low-speed performance of the 
inlet (or ejector) of jet engines, especially during 
takeoff or landing maneuvers. 
Cowling Pressure	 Thrust Producer 
Induced Flow	 Pressure	 Reversed Cowl Flap Inlet 
	
Separation Region	 and Thrust Augmentor 
No Separation 
Inlet at Low Speed	 High Speed Configuration 
The solution: 
An inlet mouthpiece with a variable geometry made 
possible by use of a reversed cowl-flap mechanism. 
How it's done: 
The inlet flare of the induction duct is contoured 
to prevent sharp turning of streamlines around the 
lip, and the inlet geometry is in the shape of a ring-
wing so that both the open and closed slots are con-
sidered for the lip (as in high-speed air foils). As 
shown by static engine tests, the higher velocity on the 
inner side of the duct creates a pressure difference 
across the lip, which is a source for additional engine 
thrust or the main source of thrust augmentation for 
an ejector. However, when such an inlet is mounted
on an aircraft, the effectiveness of the flare decreases 
and sometimes becomes a source of drag at high 
speeds. In the suggested design, maximum thrust can 
be obtained by means of the reversed cowl-flap be-
cause the angle of the flare can be adjusted according 
to the streamlines created by both the suction and the 
forward speed. 
The reversed cowl-flaps can be adjusted automati-
cally by means of a servo motor driven by a differen-
tial pressure cell in order to maintain favorable 
conditions for streamlines and thrust augmentation. 
Alternatively, the flaps can be adjusted mechanically, 
or the system can be operated with pressure taps set 
so that the pressure on the inlet face is always smaller 
than the pressure on the back of the inlet. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP 74-10046 
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
NASA Patent Counsel 
Mail Code 200-1 1A 
Ames Research Center 
Moffett Field, California 94035 
Source: Dali Yu Cheng
Ames Research Center
(ARC-10754) 
Category 06 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19740000046 2020-03-17T14:00:20+00:00Z


Reversed cowl-flap thrust augmentor

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