Flight director design for zero and
partial gravity flight
Simulation analysis and experimental results
of the partial gravity maneuver
prof. dr. ir. J.A. Mulder
prof. dr. ir. M. Mulder
Bram Masselink dr. ir. M.M. van Paassen
Department of control and simulation ir. A.C. in „t Veld
Faculty of aerospace engineering ir. M.H. Smaili
Delft
University of
Technology
2-6-2009
Challenge the future

Flight director design for
zero and partial gravity flight
• A flight director is…
• … an aid for a pilot ...
• … on a display …
• … to fly a certain maneuver.
• A zero or partial gravity maneuver is …
• … a flight maneuver …
• … in which during a short period …
• … a sense of weightlessness or microgravity is experienced.
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Reasons to perform partial gravity
flights
• Fundamental research
• Practical research
• Test space equipment before launching it
“To understand in full the mechanisms governing our life and
physics, we need to study what life would be without it (gravity,
edit.)” 1
1 ESA, “ESA Research,” 2008, http://www.esa.int/esaHS/research.html
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FLIGHT DIRECTOR DESIGN
FOR ZERO AND PARTIAL
GRAVITY FLIGHT
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Contents
• Introduction
• The parabolic flight maneuver
• Reference frames and specific forces
• Design of the flight director control law and display
• Experiment 1: flight simulator
• Method
• Results
• Experiment 2: test flight
• Conclusions and recommendations
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Test facilities
• NASA Zero Gravity Research Facility, Cleveland, Ohio
• 145m free fall tower (5.18s zero gravity)
• International Space Station (ISS)
• „unlimited‟ zero gravity
• CNES Airbus A-300 ZERO-G (15 – 20s zero gravity)
• Cessna Citation II Laboratory Aircraft (TUDelft) (up to 10s 0g)
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Parabolic flight maneuver
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Earth vs. body fixed reference frame
Required specific forces in
the body fixed reference
frame:
λg = 0.00g (Space)
λg = 0.17g (Moon)
λg = 0.38g (Mars)
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Specific forces
Specific forces in the Earth fixed reference frame due to the
movement of the center of gravity of the aircraft:
Assume: ΩE = 0 and symmetrical along XB
Rewriting to body fixed reference frame:
Required accelerations (including gravity):
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Flight director objectives
Example of flight director
• Highly accurate partial gravity
flight phase
• Partial gravity flight phase as long
as possible
• Remaining within the safety limits
of the aircraft
• Introducing enough stability
margins
• Limited influence of varying pilot
control behavior
Boeing 737 Primary Flight Display 5
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Design process of the flight director
control law
1. Classical control theory using McRuer‟s cross over model
2. Adjusting and optimizing the flight director control law, because:
• Aircraft dynamics change during the maneuver (VTAS ≠ const.)
• Partial gravity flight phase is short
• Also time domain objectives
• Measurement noise
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Flight director control law
λg Knz Kq
0.00g -0.15 -0.35
0.17g -0.05 -0.25
0.38g -0.15 -0.40
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Dynamics of the controlled element
• Integrator dynamics near the
cross over frequency
• Higher order dynamics for
lower and higher frequencies
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Influence of varying pilot control
behavior
• Increased stability for higher pilot gain, except for lp1
• Constant partial gravity time
Simulation results:
• 15.3 sec (λg = 0.00g)
• 19.1 sec (λg = 0.17g)
• 25.0 sec (λg = 0.38g)
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Display design
1. Air speed indicator
2. Compass
3. Vert. speed indicator
4. Altitude
5. Artificial horizon
6. Spec. force indicator
7. Spec. force error indicator
8. Flight direcotr bar
9. Sequencer lights
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Experiment 1: flight simulator
• Method
• Apparatus / aircraft model and flight conditions / subjects
• Independent variables and dependent measures
• Hypotheses
• Results
• Duration of the partial gravity flight phase
• Accuracy of the partial gravity flight phase
• Workload / safety / flight experience of subjects
• Wing leveler
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Simona experiment
• Apparatus
• Simona Research Simulator
• No motion
• Static control loading
• Aircraft model
• Cessna Citation II
• Incl. auto-throttle
• Flight condition
• 3000m altitude
• 125m/s VTAS
• Subjects
• 4 Citation pilots
• 5 students
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Independent variables
• Partial gravity settings
• λg = 0.00g (space)
• λg = 0.17g (Moon)
• λg = 0.38g (Mars)
• Display modes
• Baseline , (6) & (7)
• Display 1 , (6), (7) & (8)
• Display 2, (6), (7), (8) & (9)
• Wing leveler
• on and off
Baseline display
Display 1
2
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Dependent measures
• Duration
• tλg (±0.050g)
• tλg (±0.075g)
• Accuracy
• RMS ελg (±0.050g).
• RMS ελg (±0.075g)
• Safety
• VTAS, max
• nz, max
• Workload
• NASA TLX Workload rating
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Hypotheses
1. The flight director will improve the maneuver accuracy and
duration
2. The sequencer will improve duration and reduce workload
3. The wing leveler will reduce pilot workload and increase
duration and accuracy
4. The results are not influenced by the flight experience of the
subjects
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Results of the Simona experiment -
accuracy
• Accuracy is significantly better for λg = 0.17g
• The flight director in combination with the sequencer improves
the accuracy significantly
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Results of the Simona experiment -
duration
• Shorter duration for λg = 0.38g than expected
• Significant improvement for the flight director and sequencer
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Workload / safety / flight experience
of subjects
• Workload
• not influenced by the display
• lower workload for λg = 0.17g
• Safety
1. Display 2
2. Baseline
3. Display 1
• Flight experience
• No influence on duration
• No influence on accuracy
• No influence on safety
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Results of the wing leveler
experiment
• Improves duration
• Improves accuracy
• Reduces workload
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Simulator experiment - summary
Hypotheses:
 The flight director will improve the maneuver accuracy and
duration
- The sequencer will improve duration and reduce workload
 The wing leveler will reduce pilot workload and increase
duration and accuracy
 The results are not influenced by the flight experience of the
subjects
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Experiment 2: test flight
method
• Cessna Citation II
• 30 parabolic flight maneuvers
• Four different pilots
• Display mounted in front of
the pilots during flight
• Three partial gravity
conditions
• Two displays (Baseline & Display 2)
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Test flight
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Test flight results
• Comparison to historical values:
• Improved accuracy
• Improved duration
• Due to limited number of flight no significant differences in the
display modes
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Comparison between simulator and
real flight
• Zero gravity flight: better performance in real flight
• λg = 0.17g better in simulator
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Finishing the partial gravity flight
phase
• The partial gravity flight phase is abandoned earlier in the real
flight than in the simulator
• The partial gravity flight phase is abandoned earlier if λg = 0.38g
(due to lack of dynamic pressure feedback to the control loading)
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Conclusions
• The display including the flight director and sequencer improves
the partial gravity maneuver in terms of accuracy and duration
• The flight director does not deteriorate safety and workload
• Performance for zero gravity is better in real flight than in the
simulator
• The partial gravity maneuver is abandoned earlier in the Citation
than in the Simona
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Recommendations
• Use a different workload rating method
• Display design improvements:
• Include audio signals
• Combine the two specific force indicators
• Visualize the safety margins
• Investigate the transition criteria given by Heuvel et al.
• Implement q-feedback on the control loading in Simona
• Investigate the early abandonment of the maneuver in the
aircraft, and try to avoid it
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Flight director design for zero and
partial gravity flight
Simulation analysis and experimental results
of the partial gravity maneuver
2-6-2009
Delft
University of
Technology
Challenge the future

Borrel
Vrijdag 13 februari, 21:00
Café „Het Pakhuis‟
Phoenixstraat 4C
2611 AL Delft
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APPENDICES
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Aircraft transfer functions
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Off line simulation results
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NASA TLX Workload Rating
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Simona ANOVA’s
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Chance of correct flight
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Simona experiment - workload
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Simona experiment - safety
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Display recommendation
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Off-line simulation results
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