The latest version of the NASA Flying Controls Testbed (FLiC) integrates commercial-off-the-shelf components including airframe, autopilot, and a small turbine engine to provide a low cost experimental flight controls testbed capable of sustained speeds up to 200 mph. The series of flight tests leading up to the demonstrated performance of the vehicle in sustained, autopiloted 200 mph flight at NASA Wallops Flight Facility's UAV runway in August 2006 will be described. Earlier versions of the FLiC were based on a modified Army target drone, AN/FQM-117B, developed as part of a collaboration between the Aviation Applied Technology Directorate at Fort Eustis, Virginia and NASA Langley Research Center. The newer turbine powered platform (J-FLiC) builds on the successes using the relatively smaller, slower and less expensive unmanned aerial vehicle developed specifically to test highly experimental flight control approaches with the implementation of C-coded experimental controllers. Tracking video was taken during the test flights at Wallops and will be available for presentation at the conference. Analysis of flight data from both remotely piloted and autopiloted flights will be presented. Candidate experimental controllers for implementation will be discussed. It is anticipated that flight testing will resume in Spring 2007 and those results will be included, if possible

Chambers, Ryan S.

Guerreiro, Nelson M.

High, James W.

Howard, Keith D.

Motter, Mark A.

NASA Technical Reports Server

 
American Institute of Aeronautics and Astronautics 
 
1
A Turbine-powered UAV Controls Testbed  
Mark A. Motter* and James W. High† 
NASA Langley Research Center, Hampton, Virginia, 23681 
Nelson M. Guerreiro‡ 
National Institute of Aerospace, Hampton, VA 23666 
Ryan S. Chambers§ and Keith D. Howard** 
United States Naval Academy, Annapolis, Maryland 21402 
 
The latest version of the NASA Flying Controls Testbed (FLiC) integrates commercial-
off-the-shelf components including airframe, autopilot, and a small turbine engine to provide 
a low cost experimental flight controls testbed capable of sustained speeds up to 200 mph. 
The series of flight tests leading up to the demonstrated performance of the vehicle in 
sustained,  autopiloted 200 mph flight at NASA Wallops Flight Facility’s UAV runway  in 
August 2006 will be described.  Earlier versions of the FLiC were based on a modified Army 
target drone, AN/FQM-117B, developed as part of a collaboration between the Aviation 
Applied Technology Directorate at Fort Eustis, Virginia and NASA Langley Research 
Center. The newer turbine powered platform (J-FLiC) builds on the successes using the  
relatively smaller, slower  and less expensive unmanned aerial vehicle developed specifically 
to test highly experimental flight control approaches with the implementation of C-coded 
experimental controllers.  Tracking video was taken during the test flights at Wallops and 
will be available for presentation at the conference. Analysis of flight data from both 
remotely piloted and autopiloted flights will be presented.  Candidate experimental 
controllers for implementation will be discussed. It is anticipated that flight testing will 
resume in Spring 2007 and those results will be included, if possible. 
Nomenclature 
Fps           =    feet per second 
Mph       =   miles per hour 
FLiC         =   Flying Controls Testbed 
J-FLiC      =    Jet-powered Flying Controls Testbed 
AirSTAR    =    Airborne Subscale Transport Aircraft Research Testbed 
SOM  =  Self Organizing Map 
UAV =  unmanned aerial vehicle 
Disclaimer 
Reference herein to any specific commercial products, process, or service by trade name, trademark, 
manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring 
by the United States Government. The views and opinions of authors expressed herein do not necessarily state or 
reflect those of the United States Government, and shall not be used for advertising or product endorsement 
purposes. 
                                                          
* Controls Research Engineer, Electronic Systems Branch, Mail Stop 488, Member, AIAA, Senior Member IEEE. 
† Engineering Technician, Electronics System Branch, Mail Stop 488. 
‡ Graduate Research Associate, NIA/University of Maryland, 100 Exploration Way, Member, AIAA. 
§ Midshipman First Class, Aerospace Engineering Department 
** Midshipman Second Class, Aerospace Engineering Department 
https://ntrs.nasa.gov/search.jsp?R=20070021748 2019-08-30T01:13:15+00:00Z
 
American Institute of Aeronautics and Astronautics 
 
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I. Introduction 
 
The NASA Flying Controls Testbed (FLiC) project proposed to conceive, develop, implement, and flight 
test highly experimental and perhaps even controversial flight control technologies in a relatively low cost and low 
risk platform. Early efforts in the program focused on developing an inexpensive, small, relatively slow test platform 
controlled by a commercially available autopilot capable of stabilizing, navigating, and recording flight data  This 
initial version of the FLiC was based on the AN/FQM-117B, a surplus Army target drone provided by the Applied 
Aviation Technology Directorate at Fort Eustis, Virginia.  The FLiC served as the experimental testbed for self-
organizing map (SOM) based multiple-model controllers [1] as well as a training and development platform for both 
remotely piloted and autonomous flight operations. On June 27th, 2005, the FLiC performed a fully autonomous 
flight test demo at the Association for Unmanned Systems International (AUVSI) UAV Demo 2005, held at Naval 
Auxiliary Landing Field, Webster Field, MD . 
Concurrently, another NASA project, AirSTAR, was pursuing the goal of testing control upset recovery 
programs on a dynamically scaled transport model. AirSTAR is an unmanned, remotely piloted, 5.5% (seven foot 
wingspan), twin turbine, generic transport aircraft with a sophisticated instrumentation and telemetry package[2]. 
Currently, AirSTAR is remotely piloted by direct visual observation with plans in the near future to be operated with 
ground based computers providing augmented control, based 
on  telemetered data (downlink) and control commands 
(uplink), to research pilots seated in a virtual cockpit.  In 
support of the AirSTAR project, it was desired to investigate 
the feasibility of using commercially available autopilots for 
operations beyond the visual range of the safety pilot and to 
mitigate the consequences of a lost command link.  These 
goals were well aligned with  advancing the capability of 
FLiC, particularly in regards to speed and altitude. The 
resulting collaboration resulted in the development of J-FliC, 
a jet powered version of the FLiC. 
II. Platform Description 
J-FLiC essentially uses the same avionics, i.e. autopilot, radio modem, RC receiver and UAV safety switch,  
as it’s prop-version predecessor, described in detail in [3]. The fundamental difference is in the airframe, engine, and 
autopilot control gains and settings. 
The airframe is the commercially 
available Bob Violett Models (BVM) 
KingCat. The KingCat has been used 
extensively for safety pilot training in 
the AirSTAR program. It is well 
behaved at both high and low speeds, 
recovers from spins and stalls 
predictably, is highly visible, 
particularly in the orange-tipped Navy 
paint scheme, and is easily repaired 
from readily available spare parts.  The 
AirSTAR program has logged several 
hundred flights on various KingCat 
airframes equipped with JetCat P-120 
engines. The P-120 nominally 
produces 26 pounds of thrust,  
providing takeoff distances on the 
order of 400 feet, climb rates in excess 
of 2000 fpm and sustained speeds of 200 mph in the KingCat. Table 1 shows the pertinent specifications and J-FLiC 
is shown in flight in Figure 1. J-FLiC has completed more than 50 flights as of April 2007., with approximately half 
of those flights engaging autopilot control during some segment of the flight.  
Wingspan: 80” 
Length: 94” 
Weight: 40 lbs 
Wing Area: 1600 in2 
Wing Loading: 58 oz./ft2 
Thrust: 26 lbs 
Speed Range: 35-200 mph 
 
Table 1. J-FLiC airframe specifications 
 
Figure 1.  J-FLiC up and away 
 
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III. Initial Flights 
The initial flights of the J-FLiC airframe 
were flown in August 2004 at NASA Wallops 
Flight Facility’s UAV Runway, shown in Figure 
2. These initial flights were manually piloted, 
using COTS radio control (RC) equipment, 
implementing stick-to-surface control with no 
compensation. A total of seven airframe checkout 
flights were performed during early Fall 2004 
prior to the installation of the autopilot. Initially, 
the autopilot was installed in the airframe but not 
connected to the control servos or engine control 
unit (ECU).  Flight data such as airspeed, altitude, 
attitude, body rates and accelerations were 
recorded  in onboard  memory and telemetered to 
the ground control station for display and storage 
on disk.  Another seven flights were conducted in 
this configuration.  Following those flights the 
control surface servo and ECU commands from 
the RC receiver were Y-cables to the autopilot for 
recording. Two test flights in that configuration were conducted in November 2004.  
Setbacks and delays were encountered in 2005. The first flight of 2005, conducted on a blustery day in 
early January resulted in a hard landing requiring extensive airframe repairs which took slightly over three months to 
complete. Three checkout flights without the autopilot installed were conducted in April and May of 2005 without 
incident. During the spring and summer of 2005, the emphasis shifted to demonstrating the SOM-based controllers 
in the FLiC,  participation in the AUVSI’s UAV Demo 2005, and the initial flights of  AirSTAR’s prototype 
dynamically scaled airframe.  Flights of J-FLiC resumed in October 2005.  Some minor damage was incurred during 
an attempted go around initiated with insufficient airspeed.  Repairs were effected over the winter months with new 
hope for progress in the Spring. 
A checkout flight of the repairs was conducted in late April 2006 with the autopilot installed but not 
engaged.  The first flight of J-FLiC with autopilot engagement was on May 25th, 2006.  Initial autopilot 
engagements were up and away, approximately 600 foot altitude at 80 knots, wings approximately level, nose 
slightly up, five degrees.  Figure 3 shows typical pitch and roll responses immediately after autopilot engagement. 
Gain adjustments to the autopilot inner loop controllers, i.e. pitch controlled by elevator and roll controlled by 
ailerons, were adjusted based on a combination of accumulated experience from the FLiC and manufacturer’s 
instructions.  
 
Figure 3. Initial autopilot pitch and roll responses  
 
Figure 2. NASA Wallops UAV Runway (750 ft x 50 ft,  2004)
 
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With the adjustments to the inner loop controllers providing well damped pitch and roll responses it was 
time to proceed on to flying steady circuits within visual range at a moderate airspeed.  A typical ground track 
within visual range is shown in Figure 4, with the autopilot-controlled interval shown in blue, while the remotely-
piloted interval of the flight is red.   During this phase of the flight tests, the throttle was under manual control, 
adjusted to maintain airspeed near 80 knots.  In addition to  inner loop control, altitude and heading were being 
controlled as cascaded outer loop processes by the autopilot. The altitude loop sends pitch commands to the inner 
loop pitch controller and 
the heading loop sends 
roll commands too the 
inner loop roll controller. 
The desired heading is 
usually determined by the 
path required to navigate 
through a 
preprogrammed series of 
waypoints, although the 
autopilot provides the 
option for fixed heading 
commands as input from 
a command script or  
from the ground control 
station.  The altitude 
performance of the 
autopilot during step 
changes of desired 
altitude is shown in 
Figure 5. 
 
Figure 5.  Autopilot  altitude control during initial  circuits 
Figure 4. Ground Track during initial steady circuits at 80 knots – autopiloted in
blue, manually piloted in red 
 
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IV. Speed Build-up Flights 
After demonstrating  the capability to perform steady circuits at 80 knots with good heading, altitude, and 
attitude control, speed build-up flights were cautiously undertaken with throttle still under manual control This 
approach served several  purposes; first, it enabled both the direct visual observation as well as post-flight analysis 
of the dynamic control of the vehicle with relatively small and deliberate increments in airspeed; secondly, it 
provided the basis of a table look-up of throttle settings for a given airspeed in level flight; and it provided a means 
for reducing speed quickly for any undesired transients while still maintaining autopilot engagement.  This phase of 
the testing illustrated the need for elevator trim changes as a function of airspeed.  The significant results of these 
tests were tables of elevator trim increments, pitch inner loop control gains scheduled with airspeed, adjustment to 
the limits of integral (trim) contributions to the elevator and throttle commands,  and a table of  throttle settings 
based on the desired airspeed.   The throttle settings based on desired airspeed table was realized using a C-code 
program developed earlier for the prop-powered FLiC.  The implementation of these user developed programs 
serves as a template for more advanced control concepts, such as identifying the throttle lag associated with the 
turbine spool-up and making predictive or adaptive compensation as in [4,5]. Airspeed, altitude, pitch and target 
pitch from a typical run up to 125 knots during this phase of the testing is shown in Figure 6. Divergence of pitch 
from the desired pitch is a consequence of slightly insufficient down trim with increasing speed, combined with 
limited authority of the integral contribution to the inner loop pitch controller.  This tendency was considered 
preferable to excessive down trim or integral action. However, analysis of the data from the speed build up runs was 
performed to model the trim requirements. 
 
 
Figure 6.  Autopilot control during speed build –up run 
 
 
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The initial analysis of the 
difference between the target and 
current pitch angle versus the current 
airspeed showed a semi-linear trend. 
However, since each flight was 
different and had different flying 
packages, no two were the same. 
Some flights seemed to not have any 
trends at all. It was observed that the 
linear trends were only found in the 
higher range of airspeeds, between 
120 and 160 ft/s. Figure 7 shows a 
linear trend of an increase in pitch 
difference with increasing speed 
during the initial speed build-up run. 
The slope of the trend line shows 
that the difference in pitch angle 
increases by a tenth of a degree for 
every additional foot per second.  
The elevator position was important 
to investigate since it directly affects 
the pitch angle. It was noticed that 
the elevator was increasing in 
deflection as the airspeed was 
increased. This means that it was 
compensating for the fact that the 
aircraft would have changed altitude 
if the elevator did not change as the 
airspeed increased. As the speed of 
the aircraft increases, it climbs. 
Therefore the elevator needs to pitch 
the nose of the plane down in order 
to maintain altitude.  
Figure 8 shows a near 
linear relationship between the 
elevator trim and airspeed during the 
initial speed build-up flight. The 
slope of the line is approximately 50 
fine servo units (fsu) per foot per 
second (ft/s), This corresponds to a 
change in elevator trim position 
corresponding to approximately 5% 
of the total elevator travel over the 
40 knot change in airspeed from 80 
to 120 knots.    
 After several speed build-up 
flights were completed, adjustments 
were made to the elevator trim and throttle position look up tables. Additionally, the inner loop controller gains for 
elevator from pitch were scheduled so as to be reduced with increasing airspeed. Refinements to the airspeed control 
were realized using a limited integral correction along with incorporating the data from the test flights. The typical 
relationship between throttle position and airspeed over the 80-120 knot range is shown  in Figure 9. The throttle 
range is shown in the autopilot’s internal units, representing the range from 1/3  to 2/3 full throttle for the airspeed 
range shown, in level flight.  
 
130 140 150 160 170 180 190 200 210
0
1
2
3
4
5
6
7
Current Airspeed (ft/s)
D
iff
er
en
ce
 in
 T
ar
ge
t P
itc
h 
an
d 
C
ur
re
nt
 P
itc
h 
(d
eg
)
 
 
 
y = 0.1*x - 13
Figure nn.   Pitch Angle Data from June 22 Flight 
 
130 140 150 160 170 180 190 200 210
-5000
-4500
-4000
-3500
-3000
-2500
-2000
-1500
-1000
Current Airspeed (ft/s)
E
le
va
to
r P
os
iti
on
 (F
in
e 
S
er
vo
 U
ni
ts
)
 
 
 
y = 47*x - 1e+004
Figure 8.   Elevator Position Data from June 22 Flight 
 
130 140 150 160 170 180 190 200 210
-5000
-4500
-4000
-3500
-3000
-2500
-2000
-1500
-1000
Current Airspeed (ft/s)
E
le
va
to
r P
os
iti
on
 (F
in
e 
S
er
vo
 U
ni
ts
)
 
 
 
y = 47*x - 1e+004
Figure 7.   Elevator Position Data from June 22 Flight 
 
 
 
American Institute of Aeronautics and Astronautics 
 
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 During August 2006, another series 
of speed build-up flights were 
conducted at NASA Wallops UAV 
runway. The earlier results were 
quickly reproduced with noticeably 
less deviation between the desired 
pitch and the pitch required to maintain 
altitude, indicating an improvement in 
the trim capability. Steady circuits at 
800 feet altitude were performed at 
successively higher speeds, 
culminating in a sustained full – power 
run where the speed stabilized at 175 
knots, slightly in excess of 200 mph.  
The range requirement to stay within 
3000 feet laterally required a nearly 
steady bank angle of 45 degrees. The 
ground track for this flight is shown in 
Figure 10, where it can be seen J-FLiC 
was well within the prescribed 3000 
foot radius.  The corresponding flight 
data  is shown flight is shown in Figure 11. Some oscillation in both pitch and roll were observed in the data at the 
highest speed, but they were bounded and well damped. These results were well correlated with tracking video 
provided by the range. 
 
 
Figure 10. Ground Track during high speed run – autopiloted in  blue, manually piloted in red 
130 140 150 160 170 180 190 200 210
0.8
1
1.2
1.4
1.6
1.8
2
x 104
Current Airspeed (ft/s)
Th
ro
ttl
e 
P
os
iti
on
 (F
in
e 
S
er
vo
 U
ni
ts
)
y=119.95*x-6093.43
Figure 9.   Throttle Position Data from June 22 Flight 
 
 
American Institute of Aeronautics and Astronautics 
 
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V. Conclusion 
  J-FLiC, a turbine powered UAV controls testbed has significantly extended the capabilities of it’s prop-powered 
predecessor, FLiC.  The extended speed range can be directly utilized to demonstrate the efficacy of both on-line 
system identification tools  and adaptive control strategies as replacements for simplistic, albeit effective, gain 
schedules and  look up tables.  Similar to the evolution of FLiC into J-FLiC, it is anticipated that a slow and steady 
progression will ultimately lead to the validation of more complex and demanding issues confronting real-time, in-
flight, on-board adaptive control under parametric uncertainty. 
References 
 
1 Principe, J.C., Wang, L., Motter, M.A , “Local Dynamic Modeling with Self-Organizing Maps and Applications to 
Nonlinear System Identification and Control,” Principe, J.C., Wang, L., Motter, M.A., Proceedings of the IEEE, Vol. 86, No. 11, 
Novemb er 1990. 
2Jordan, T.L., Foster, J.V.,,  Bailey, R.M.,  and  Belcastro, C.M., “AirSTAR: A UAV Platform for Flight Dynamics and 
Control System Testing,” 25th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, San Francisco, 
CA, June 2005 
3Motter, M.A.,Logan, M.J.,French,M.L. and Guerreiro,N.M., “Simulation to Flight Test for a UAV Controls Testbed,” 
Proceedings of the IEEE, Vol. 78, No. 9, 1990. 
4Cho, J., Principe, J.C., Erdogmus, D., and Motter,  M. A., “Modeling and Inverse Controller Design for an Unmanned Aerial 
Vehicle Based on the Self-Organizing Map,” IEEE Transactions on Neural Networks, Vol. 17, No. 2, March 2006, pp. 445-460. 
5Shin, Y., Calise, A.J.., and Motter, M.A.., “Adaptive Autopilot Designs for an Unmanned Aerial Vehicle,” AIAA Guidance, 
Navigation and Control Conference, AIAA-2003-5312, San Francisco, CA, August 2005 
Figure 11.  Autopilot control during high speed  run 


A Turbine-powered UAV Controls Testbed

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