Modification of a conventional jet engine internal compression supersonic inlet results in increased shock stability and thus, engine instantaneous response to changes in inlet air properties. This technique provides a large amount of bleed near the maximum pressure recovery at the expense of minor bleed flow during critical operation

Keppler, C. R.

English

NASA Technical Reports Server

To Bleed 
System 
November 1966	 Brief 66-10530 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Perforations in Jet Engine Supersonic Inlet Increase Shock Stability 
To Ble 
Syste 
Supersonic
The problem: 
To match the flow of air to a supersonic jet air-
craft engine with the instantaneous requirements of 
thrust and efficiency imposed on the engine. Proper-
ties of the air flow vary widely, especially as to density 
and pressure, with aircraft speed and altitude and 
with atmospheric variations. 
The solution: 
Modification of a conventional jet engine internal 
compression supersonic inlet that results in increased 
shock stability and thus, engine instantaneous re-
sponse to changes in inlet air properties. 
How it's done: 
Reverse throat perforations are used to change inlet 
performance to match the optimum engine perform 
ance while allowing a variation in engine corrected 
weight flow. Reverse perforations in the throat region 
are desirable because during operation at low pres-
sure recoveries with the "normal shock" downstream 
of the perforated region, the supersonic flow is not 
easily diverted-to go through reverse perforation and
the loss in flow is small. Alternately, during operation 
at high pressure recoveries with the "normal shock" 
located in the region of the perforations, the reverse 
flow portion of the boundary layer is aligned in the 
direction of the perforations and is also at a higher 
static pressure so more flow is bled off. 
Notes: 
1. This technique provides a large amount of bleed 
near the maximum pressure recovery at the ex-
pense of minor bleed flow during critical opera-
tion. This provides an operating point with a 
high pressure recovery and a margin for airflow 
variation (control tolerances) before discharging 
the normal shock. 
2. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Electronic Research Center 
575 Technology Square 
Cambridge, Massachusetts 02142 
Reference: B66-10530
(continued overleaf) 
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=19660000528 2020-03-11T17:43:40+00:00Z
Patent status: 
No patent action is contemplated by NASA. 
Source: Charles R. Keppler 
of United Aircraft Corporation 
under contract to 
Electronic Research Center 
(NEO-8) 
Brief 66-10530	 Category 05


Perforations in jet engine supersonic inlet increase shock stability

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