The research being conducted pertains to the determination of the stability and control derivatives of the F/A-18 High Alpha Research Vehicle (HARV) from flight data using the Maximum Likelihood Method. The document outlines the approach used in the parameter estimation (PID) process and briefly describes the mathematical modeling of the F/A-18 HARV and the maneuvers designed to generate a sufficient data base for the PID research

Napolitano, Marcello R.

Spagnuolo, Joelle M.

English

NASA Technical Reports Server

NASA-CR-191216
r
.'--, .,--T'.L/ _'-- _"
Determination of the Stability and Control
Derivatives of the F/A-18 HARV from
Flight Data using the Maximum
Likelihood Method
NASA Grant # NCC 2-759
Semi-Annual Status Report
(May - November 1992)
NASA Technical Contact: Albion H. Bowers
NASA Dryden Flight
Research Facility
Authors:
Principal InVestigator: Marcello R. Napolitano
Graduate Student: Joelle M. Spagnuolo
November 12, 1992
Department of Mechanic_l and Aerospace Engineering
West Virginia University
Moraantown, West Virqinia 26505
(NASA-CR-191216) OETERMINATION OF
THE STABILITY AND CONTROL
DERIVATIVES OF THE F/A-I_ HARV FROM
FLIGiiT OATA USING THE MAXIMUM
LIKELIHOOD METHOD Semiannual Status
Report, M_y - Nov. 1992 (West
Virginia Univ.) 12 p G3/08
N93-12903
Unc I _s
0128459
https://ntrs.nasa.gov/search.jsp?R=19930003715 2020-03-17T10:33:56+00:00Z
ABSTRACT
This document reports on the progresses of the research
conducted for the NASA-Ames Cooperative Agreement No. NCC 2-759
with West Virginia University.
R. Napolitano and graduate
collaborating on the research.
The principal investigator Marcello
student Joelle M. Spagnuolo are
The NASA technical officer for this
grant is Albion H. Bowers, associated with NASA Dryden Flight
Research Facility. The research being conducted pertains to the
determination of the stability and control derivatives of the F/A-
18 High Alpha Research Vehicle (HARV) from flight data using the
Maximum Likelihood Method. The document outlines the approach used
in the parameter estimation (PID) process and briefly describes the
mathematical modeling of the F/A-18 HARV and the maneuvers designed
to generate a sufficient data base for the PID research.
\
\
\
\
Table of Contents
Introduction
PID and Modeling of the HARV--
PID Maneuvers and Tests Completed
References
......
......... •.... 9
INTRODUCTION
The scope of this project is to determine the aerodynamic
stability and control derivatives of the NASA F/A-18 HARV from
flight data. Although a thorough basis of the vehicle aerodynamics
is generated by analytic computations and wind tunnel tests
performed by the manufacture during the design process, the true
aerodynamic characteristics of the aircraft can be derived from an
analysis of flight test data. Therefore, it is beneficial to
compare the results from both the initial design and the flight
data in order to validate the prediction methods of the aircraft
aerodynamics. An additional reason for estimating these parameters
is to update the aerodynamic data bank in the flight simulators.
Using flight data to estimate the stability and control
derivatives of aircraft has been implemented for many years. In
the past, most of the flight testing was limited to conditions in
which linearized aerodynamics and linear equations of motion would
appropriately describe the aircraft dynamic model. For these
cases, the parameter estimation program MMLE3 developed at Ames-
Dryden in the mid 1970's was used. However, recent research
conducted on the F/A-18 HARV related to high angle of attack flight
conditions has generated interest in the parameter identification
for non-linear aerodynamic and dynamic conditions. For this
purpose, the recently developed pEst estimation software, which is
capable of supporting nonlinearities in the dynamic equations of
motion, is being used for this project.
The following sections briefly describe the PID process and
the modifications of the equations of motion within the pEst
software that allow appropriate modeling of the HARV. Furthermore,
the type of maneuvers required to obtain data for PID are discussed
along with some preliminary results of the estimates of the
stability and control derivatives.
PID and Modeling of the HARV
Figure 1 shows a block diagram of the parameter identification
process.
Aircraft I- I Initial Stability a l
Aero- ]-4-- t Control I
dynamics J| Derivatives I
Aircraft I I Measured I
Mathematical Model I I Flight Data I
I Equations ofMotion
"L1
-- Computed Response
Figure i: Parameter Identification Process
It can be seen that the estimation process begins with initial
values of the stability and control derivatives. These values are
generally obtained from previous wind tunnel tests conducted by the
aircraft manufacturer. This set of values in addition to the
aircraft aerodynamic, geometric, and inertial data constitute the
initial mathematical model of the vehicle. The mathematical model
is then used along with the measured flight data, which indicates
the system inputs and responses, in the equations of motion. These
equations are then used to produce a computed response of the
5
aircraft using the initial values of the stability and control
derivatives. Then the difference between the measured and computed
response is assessed and minimized by assigning new values to the
derivatives and iterating the process described above until the
results of the estimated derivatives converge.
The pEst software has a standard set of equations that can be
modified to suit any aircraft configuration. Since the HARV is a
F/A-18 with additional control surfaces and a thrust vectoring
system, several modifications needed to be introduced. For
instance, the extra control surface deflections and the relative
stability and control derivatives had to be accounted for in the
total force and moment coefficient equations. Also, the addition
of the thrust vectoring control system (TVCS) required
modifications in the equations of motion due to the fact that
thrust is no longer limited to act along the x-axis. The TVCS
essentially consists of three vanes mounted on the back of each
engine of the HARV. During vectoring maneuvers, a combination of
the vanes are commanded to deflect, and the amount of each vane
deflection is recorded. These deflections are combined in the
following manner to indicate a single value which represents the
overall deflection in either the pitch or yaw direction.
6v_ 6v3 6v 6 - 6v sI.
6 - ---( + )
yv 2 2 2
where 6 = yaw vane deflection
6_ = pitch vane deflection
,2..6 deflection of individual vane 1,2,3,4,5 or 6
Note the vane numbering system is illustrated in Figure 2.
Upper Van'e Upper Vane
1
Back 6f"
Engine:
Figure 2. Numbering of Thrust Vector Vanes
The additional thrust forces caused by the TVCS are accounted for
by the following terms:
thrust (x) - -cadpvdyv • cos (6pv) cos <6 _) • measured thrust force
thrust(y) - -cydyv , sin(6yv)cosc6p_) • measured thrust force
thrust(z) - -cnormdpv • sin(6pv) COS<6_) • measured thrust force
S
where cadpvdyv = axial force due to combined 6 and 6_pv
cydyv = side force due to yaw vane deflection
cnormdpv = normal force due to pitch vane deflection
The state equations incorporate the above modifications as follows:
v---i [-Dcos_+ Ysin_+ thrust (x) cos_cos_+ thrust (y) sin_+ thrust (z) sin_=os_
m
-mg( cosacos_sinS-sin_sin_cosS-sinacos_cos_cos@) ]
1
wcos_
[-t+ thrust (z) cos_- thrust (x) sin_+mg(cosacos_cos8
+sin_sinS)] + q- tan_ (pcos_ + rsin_)
1 [Dsin_+Ycos_- thrust (x) cosasin_+ thrust (y) cos_- thrust (z) sin_!n i
+mg(cos_sin_sinS+cos_sin_cosS-sinasin_cos_cos@)]+psin_-rcos_
where D = total Drag, (ib)
L = total Lift, (ib)
Y = total Sideforce, (ib)
m = mass, (slugs)
V = Velocity, (ft/sec)
p = roll rate, (rad/sec)
q = pitch rate, (rad/sec)
r = yaw rate, (rad/sec)
= angle of attack, (rad)
= angle of sideslip, (rad)
8 = pitch angle, (rad)
= bank angle, (rad)
These are the changes introduced in the standard set of
equations in pEst. This revised version is to be utilized for the
analysis of requested PID flight test maneuvers which are discussed
in the next section.
PID Maneuvers and Tests Completed
The design of the maneuvers needed for parameter estimation is
based on the need to excite the dynamic modes of the aircraft. It
has been determined in previous work that the system modes are best
excited by maneuvers with frequencies near the system natural
frequencies. This principle implies that optimal inputs would be
those that resemble sine waves at the system natural frequencies.
Hence, the typical maneuver for PID testing is the doublet
performed in the pitch, roll, and yaw planes.
Also, in order to obtain the most accurate results of the PID
analysis, the inputs on every control surface must be independent.
This is extremely important because if two surfaces move
simultaneously during a maneuver, it is practically impossible in
non-linear conditions to distinguish the effects of the two
individual surfaces. Thus, a new set of control laws was developed
at Dryden in order to alleviate correlation among the control
surface deflections. The associated flight control system has been
named OBES which stands for On Board Excitation System. Several
different combinations of surface movements can be programmed into
the computer system to obtain the desired results. However, the
most effective surface deflection combinations and amplitudes are
determined by a trial and error approach in the flight simulator.
The tests for the HARV were conducted in the flight simulator, and
the following inputs were found to be sufficient for good PID
research.
7
Lateral-Directional
Small Amplitude Doublets:
Differential Tail
Rudder
Differential Aileron
Large Amplitude Doublets:
Differential Tail
Rudder
Differential Aileron
Lonqitudinal-Directional
Small Amplitude Doublets:
Inboard Trailing Edge Flaps
Outboard Trailing Edge Flaps
Stabilator
Large Amplitude Doublets:
Inboard Trailing Edge Flaps
Outboard Trailing Edge Flaps
Stabilator
+/- 3 degrees
+/- I0 degrees
-/+ 7 degrees
+/- 6 degrees
÷/- 15 degrees
-/+ i0 degrees
+/- 15 degrees
+/- 13 degrees
+/- 3 degrees
+/- 25 degrees
+/- 23 degrees
+/- 6 degrees
Each doublet is four seconds long (two seconds each way), and they
are performed as the pilot maintains a steady angle of attack.
PID maneuvers were recently tested with the HARV. The points
tested were at 10, 25, 30, 40, 50, and 60 degree angles of attack.
The preliminary pest results were very promising at low alphas, and
the curve fits of the computed and measured responses were quite
accurate. Further analysis of this data has been delayed because
of problems associated with the installation of the pEst software
at West Virginia University. It is expected that these computer
problems will be resolved by mid-November, and the data analysis
can be continued there after.
8
J/
/
/
!
References
i. Maine, R.E., and Iliff, K.W., "Application of Parameter
Estimation to Aircraft Stability and Control -The Output Error
Approach" NASA RP-II68, June 1986f
2. Duke, E.L., Antoniewicz, R.F., Krambeer, K.D., "Derivation of a
Linear Aircraft Model", NASA RP-1207, August 1988.
3. NASA Symposium Report TN-D-7647, "Parameter Estimation
Techniques and Application in Aircraft Flight Testing", Volume
I,II, April 1974.
4. Bowers, A.H., Noffz, G.K., Grafton, S.B., Mason, M.L., and
Peron, L.R., "Multiaxis Thrust Vectoring Using Axisymmetric
Nozzles and Postexit Vanes on an F/A-18 Configuration Vehicle",
April 1991.
q


Determination of the stability and control derivatives of the F/A-18 HARV from flight data using the maximum likelihood method

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server