Flight Control System Design and Test for Unmanned Rotorcraft Flight Control and Cockpit Integration Branch Army/NASA Rotorcraft Division NASA Ames Research Center Moffett Field, CA Chad R. Frost IEEE Santa Clara Valley Control Systems Society Technical Meeting September 21, 2000
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Flight Control System Design and Test forUnmanned Rotorcraft
Flight Control and Cockpit Integration BranchArmy/NASA Rotorcraft Division
NASA Ames Research CenterMoffett Field, CA
Chad R. Frost
IEEE Santa Clara Valley
Control Systems Society Technical Meeting
September 21, 2000
UAV Control Design
Overview
• Background• Design Tools• Design Methods• UAV programs• Example
UAV Control Design
Background• A UAV is an uninhabited, reusable aircraft that is
controlled:– Remotely,– Autonomously by pre-programmed on-board equipment,
– Or a combination of both methods
• Currently >241 UAV systems developed by 31 countriesare operational or in test
• Numerous missions, current and proposed:– Military
– Civilian– Space
Source: Bob Keith, NATO UAV C2 Workshop 1999 (Unclassified).
UAV Control Design
Background
UAV Control Design
Background
• Many vehicle configurations, but rotary-wingedvehicles form a significant and growing portion
• Hover-capable UAVs offer unique capabilities, butcome with unique challenges
UAV Control Design
Background
• Significant industrial and military expertise exists in fixed-wing UAV development.
• Initial work on rotary-wing UAVs did not exploit thecapabilities of the configuration:– Lack of familiarity with rotorcraft issues
– Inability to foresee problem areas
• NASA involvement in rotorcraft UAV developmentsought to take performance to a new level.
UAV Control Design
Background
• Ames is NASA rotorcraft center:– Army / NASA Rotorcraft Division
• NASA: Aerospace Directorate
• Army: Aviation & Missile RD&E Center
– Flight Control and Cockpit Integration Branch
• Expertise in rotorcraft:– Flight control– Modeling– Simulation
• Design tools developed in-house
UAV Control Design
Design Tools
• CIFER®
– Comprehensive Identification from FrequencyResponses
• First flight test with CONDUIT-tuned gains• Aircraft responses did not agree with model
(lon and lat)
0 5 10 15 20 25 30 35 40 45-40
-30
-20
-10
0
10
20
30
40
Time (sec)
Rol
l Atti
tude
(de
gree
s)
Roll attitude command
Roll attitude
UAV Control Design
Flight Test
• Looking for source of discrepancy:– Lon and lat doublets flown closed-loop– CIFER® used to extract frequency responses– Actual sensor and actuator dynamics identified
• Equivalent time delay greater than originallyestimated
UAV Control Design
Flight Test
ComponentEstimated
Delay (ms)Actual Delay
( m s )
Actuators 5 0 107Sensors 2 5 5 3
Computer 2 0 6 0Filters 0 7 0
TOTAL 9 5 2 9 0
UAV Control Design
Flight Test
• Updated Simulink model with identified delays• Added delay results in highly constrained
system
1 10-400
-300
-200
-100
0
Frequency (rad/sec)
Pha
se (
degr
ees)
K-MAX BURRO
XV-15 Tilt Rotor
Narrowed range of stability
UAV Control Design
Flight Test
• Added lead filter to lon& lat attitude feedback
• FCS gains re-tunedwith CONDUIT
• CONDUIT successfullytraded off phasemargin for gain margin
-60
-40
-20
0
20
Gai
n (d
B)
1 10-400
-300
-200
-100
0
Frequency (rad/sec)
Pha
se (
degr
ees)
acceptable range of crossover frequency
CONDUIT-tuned result
UAV Control Design
Flight Test
• CONDUIT tuning results
GM [db]
PM
[deg
]
(rigid-body freq. range)Gain/Phase Margins
0 5 10 15 200
20
40
60
80
GM [db]
PM
[deg
]
(rigid-body freq. range)Gain/Phase Margins
0 5 10 15 200
20
40
60
80
Actuator Rate Saturation
Act
uato
r P
ositi
on S
atur
atio
n
Actuator Saturation
0 0.5 10
0.2
0.4
0.6
0.8
1
Actuator Rate Saturation
Act
uato
r P
ositi
on S
atur
atio
n
Actuator Saturation
0 0.5 10
0.2
0.4
0.6
0.8
1
Bandwidth [rad/sec]
Pha
se d
elay
[sec
]
Bandwidth & Time Delay (pitch)
0 1 2 3 4 50
0.1
0.2
0.3
0.4
Bandwidth [rad/sec]
Pha
se d
elay
[sec
]
Bandwidth & Time Delay (roll)
0 1 2 3 4 50
0.1
0.2
0.3
0.4
LON (ACAH) LAT (ACAH)
LON LAT
PITCH ROLL
After CONDUIT tuning
Baseline gains
UAV Control Design
Flight Test
CONDUIT results:
– Level 2 (8 specs)
– Reduced bandwidth
Real Axis
Eigenvalue Location
1 0.5 0 0.5 1GM [db]
PM
[deg
]
(rigid-body freq. range)Gain/Phase Margins
0 5 10 15 200
20
40
60
80
GM [db]
PM
[deg
]
(rigid-body freq. range)Gain/Phase Margins
0 5 10 15 200
20
40
60
80
GM [db]
PM
[deg
]
(rigid-body freq. range)Gain/Phase Margins
0 5 10 15 200
20
40
60
80
GM [db]
PM
[deg
]
(rigid-body freq. range)Gain/Phase Margins
0 5 10 15 200
20
40
60
80
Crossover Frequency [rad/sec]
(linear scale)Crossover Freq.
0 5 10 15 20
Actuator Rate Saturation
Act
uato
r P
ositi
on S
atur
atio
n
Actuator Saturation
0 0.5 10
0.2
0.4
0.6
0.8
1
Actuator Rate Saturation
Act
uato
r P
ositi
on S
atur
atio
n
Actuator Saturation
0 0.5 10
0.2
0.4
0.6
0.8
1
Bandwidth [rad/sec] P
hase
del
ay [s
ec]
Other MTEs;UCE=1;Fully AttBandwidth & Time Delay (pitch)
0 1 2 3 4 50
0.1
0.2
0.3
0.4
Bandwidth [rad/sec]
Pha
se d
elay
[sec
]
Other MTEs;UCE=1;Fully AttBandwidth & Time Delay (roll)
0 1 2 3 4 50
0.1
0.2
0.3
0.4
Bandwidth [rad/sec]
Pha
se d
elay
[sec
]
Other MTEsBandwidth & Time Delay (yaw)
0 1 2 3 4 50
0.1
0.2
0.3
0.4
Actuator RMS
Actuator RMS
0 0.5 1
Time (sec)
Normalized Attitude Hold(Disturbance Rejection)
0 5 10 15 20
-1
-0.5
0
0.5
1
Dam
ping
Rat
io (
Zet
a)
Attitude HoldDamping Ratio
0
0.2
0.4
0.6
0.8
1
d_theta [deg]
Change in 1 Second [deg]Pitch Attitude
0 1 2 3 4d_phi [deg]
Change in 1 Second [deg]Roll Attitude
0 2 4 6 8d_psi [deg]
Change in 1 Second [deg]Yaw Attitude
0 1 2 3 4 5
Eq.
Ris
e Ti
me
(Tx-
dot, T
y-do
t) [s
ec] Translational Rate Rise Time
1
2
3
4
5
6
7
heave mode, invThdot, [rad/sec]
time
dela
y, ta
u_hd
ot, s
ec
Hover/LowSpeedHeave Response
0 0.5 10
0.1
0.2
0.3
0.4
0.5
COL
LON (ACAH) LAT (ACAH)
PEDLON LAT
PITCH
ROLL
LAT
LON COL
LON
LAT
PED
COL
LON
LAT
PED
PITCH,ROLL
YAW
PITCH ROLL YAW
LON (TRC)LAT (TRC)
UAV Control Design
Flight Test
• Roll response muchimproved; modelresponses agree wellwith flight results
0 5 10 15 20 25 30 35 40 45-60
-40
-20
0
20
40
60
Time (sec)R
oll A
ttitu
de (
degr
ess)
Roll attitude command
Roll attitude
UAV Control Design
Flight Test• BURRO successfully demonstrated to USMC nine
months after start of development
UAV Control Design
Conclusions
•• Design space is very limitedDesign space is very limited– Aircraft dynamics
– Control system hardware– CONDUIT was able to extract the best achievable
performance within design limitations
•• High frequency dynamics were key driver of closed-High frequency dynamics were key driver of closed-loop performanceloop performance– CIFER was useful in identifying system elements
•• Advanced design tools allowed rapid developmentAdvanced design tools allowed rapid developmentof a successful UAVof a successful UAV– 9 month time span– Recovery from added delay
UAV Control Design
Current and Future Work
• Build 1 of K-MAX BURRO UAVsuccessfully demonstrated toUSMC
• Build 2 now in development
• 2000-lb loaded hover– 10-DOF EOM and CIFER ident