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Full Flight Envelope Direct Thrust Measurement on a Supersonic Aircraft
NASA/TM-1998-206560

Full Flight Envelope Direct Thrust
Measurement on a Supersonic Aircraft

Timothy R. Conners and Robert L. Sims
Dryden Flight Research Center
Edwards, California

July 1998
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NASA/TM-1998-206560

Full Flight Envelope Direct Thrust
Measurement on a Supersonic Aircraft

Timothy R. Conners and Robert L. Sims
Dryden Flight Research Center
Edwards, California

July 1998

National Aeronautics and
Space Administration
Dryden Flight Research Center
Edwards, California 93523-0273
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1

American Institute of Aeronautics and Astronautics
*Aerospace Engineer, Senior Member AIAA.
Aerospace Engineer.
Copyright

©

1998 by the American Institute of Aeronautics and
Astronautics, Inc. No copyright is asserted in the United States under
Title 17, U.S. Code. The U.S. Government has a royalty-free license to
exercise all rights under the copyright claimed herein for Governmen-
tal purposes. All other rights are reserved by the copyright owner.

FULL FLIGHT ENVELOPE DIRECT THRUST MEASUREMENT
ON A SUPERSONIC AIRCRAFT

Timothy R. Conners

*

and Robert L. Sims

NASA Dryden Flight Research Center
Edwards, California

Abstract

Direct thrust measurement using strain gages offers
advantages over analytically-based thrust calculation
methods. For ight test applications, the direct
measurement method typically uses a simpler sensor
arrangement and minimal data processing compared to
analytical techniques, which normally require costly
engine modeling and multisensor arrangements
throughout the engine. Conversely, direct thrust
measurement has historically produced less than
desirable accuracy because of difculty in mounting and
calibrating the strain gages and the inability to account
for secondary forces that inuence the thrust reading at
the engine mounts. Consequently, the strain-gage
technique has normally been used for simple engine
arrangements and primarily in the subsonic speed range.
This paper presents the results of a strain gagebased
direct thrust-measurement technique developed by the
NASA Dryden Flight Research Center and successfully
applied to the full ight envelope of an F-15 aircraft
powered by two F100-PW-229 turbofan engines.
Measurements have been obtained at quasi-steady-state
operating conditions at maximum nonaugmented and
maximum augmented power throughout the altitude
range of the vehicle and to a maximum speed of
Mach 2.0, and are compared against results from two
analytically-based thrust calculation methods. The
strain-gage installation and calibration processes are also
described.

Nomenclature

A

cross-sectional area, in

2

ACTIVE
Advanced Control Technology for
Integrated Vehicles

F

force, lbf

g

gravitation acceleration constant,
32.2 ft/sec

2

IDEEC
improved digital electronic engine
controller
M
Mach number

P

static pressure, lbf/in

2

absolute
total pressure, lbf/in

2

absolute
S/MTD
Short Takeoff and Landing/Maneuver
Technology Demonstrator
total temperature, °F
USAF
United States Air Force

V

velocity, ft/sec

WACC

station-corrected engine mass ow, lbm/sec

WAT

true engine mass ow, lbm/sec
standard deviation
Engine Stations
0
free stream (ambient)
2
engine-inlet plane

Introduction

For ight-testing applications, direct thrust
measurement using strain gages offers advantages over
traditional, model-based analytical thrust calculation
methods.

1

Depending on the objectives of the ight test
program and resources available to the test facility, these
advantages may permit in-ight thrust measurement that
would not be feasible otherwise.
Depending upon the application, the direct
thrust-measurement method can be less complex and
costly to implement compared to model-based
techniques. The strain-gage sensor arrangement is
typically less cumbersome and costly to procure, install,
and calibrate than the multisensor package required to
collect the input data for traditional analytically-based
P
T
T
T

2

American Institute of Aeronautics and Astronautics

thrust models, particularly if a wind-tunnel calibration of
the analytical model to the specic test engine would
otherwise be required prior to test program
commencement. The computer models are an additional
requirement to which the direct measurement method is
not subject. These models can be very costly for the end
user to procure and maintain, if the models even exist. If
the models do not exist and therefore need to be
developed for the engine in question, then the cost for
procurement can easily be prohibitive.
Although the typical in-ight thrust model has limited
self-tuning capability, if the engine has strayed far from
an average baseline state (for instance, because of
signicant deterioration or damage), then the calculation
accuracy will suffer. Because the strain gagebased
technique measures thrust directly, the technique is not
subject to this type of error.
An in-ight thrust computer program is normally
capable of modeling only steady-state or quasi-
steady-state engine operation. A computer program
typically assumes thermal equilibrium and
stoichiometric fuel-to-air ratios that do not account for
engine acceleration or deceleration schedules, and can
be further limited by the responsiveness of the input
parameters.

2

The strain-gage technique, however, is not
hindered by modeling and input measurement rate
limitation to the same extent. Because of the inherent
high dynamic response of strain gages,