Aircraft Flight Dynamics Robert F. Stengel Lecture17 Flight Testing

Stability-and-Control
Flight Testing


Robert Stengel, Aircraft Flight Dynamics

MAE 331, 2012
"
Copyright 2012 by Robert Stengel. All rights reserved. For educational use only.!
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•  Flight test instrumentation"
•  Pilot opinion ratings"
•  Flying qualities requirements"
•  Flying qualities specifications"
•  Pilot-induced oscillations"
Flying (or Handling) Qualities"
•  Stability and controllability
perceived by the pilot"
•  1919 flight tests of Curtiss
JN-4H Jenny at NACA
Langley Laboratory by
Warner, Norton, and Allen"
–  Elevator angle and stick
force for equilibrium flight"
–  Correlation of elevator angle
and airspeed with stability"
–  Correlation of elevator angle
and airspeed with wind
tunnel tests of pitch moment
"
Early Flight Testing Instrumentation"
•  Flight recording instruments: drum/strip charts, inked needles, film,

galvanometers connected to air vanes, pressure sensors, clocks"
Hundreds/Thousands of Measurements
Made in Modern Flight Testing"
Modern Approach to Flight Testing
Instrumentation"
iPhone"
•  3-axis accelerometer"
•  3-axis angular rate"
•  2-axis magnetometer
compass"
•  GPS position
measurement"
•  1 GHz processor"
•  512 MB RAM"
•  32 GB flash memory"

z =

u

v

w
p
q
r
ε
horizontal
ε
vertical

L
λ
h
#
$
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
&
'
(
(
(
(
(
(
(
(

(
(
(
(
(
(
(
First Flying Qualities Specification"
!  First flying qualities specification: 1935 "
!  Edward Warner. Douglas DC-4 transport "
!  Interviews with pilots and engineers"
Flying Qualities Research at NACA"
•  Hartley Soulé and Floyd Thompson
(late 1930s)"
–  Long- and short-period motions"
–  Time to reach specified bank angle"
–  Period and damping of oscillations"
–  Correlation with pilot opinion
"
•  Robert Gilruth (1941-3)"
–  Parametric regions and boundaries"
–  Multi-aircraft criteria"
–  Control deflection, stick force, and
normal load factor"
–  Roll helix angle"
–  Lateral control power"
Gilruth Roll-Rate Criterion [pb/2V]"
•  Helix angle formed by
rotating wing tips, pb/2V!
–  Roll rate, p, rad/s"

–  Wing semi-span, b/2, m"
–  Velocity, V, m/s"
•  Robert Gilruth criterion"
–  pb/2V > 0.07 rad"
NACA TR-715, 1941!
Simplified Roll-Rate Response "
•  Tradeoff between high pb/2V and
high lateral stick forces prior to
powered controls:"
p(t) = p(0)e
at


p(t) = [ C
l
p
p(t) + C
l
δ
A
δ
A(t)]qSb / I
xx
= a p(t) + c
δ
A(t)
p(t) =
c
a
e

at
−1
( )
δ
A
step
p
SS
= −
C
l
δ
A
C
l
p
δ
A
SS
•  Initial-condition response (
δ
A = 0) "
•  Step response [p(0) = 0]"
•  Steady-state response"
NACA TR-868!
IAS, mph"
p
SS
max
,° / sec

Aircraft That Simulate Other Aircraft"
•  Closed-loop control"
•  Variable-stability research aircraft, e.g., TIFS, AFTI
F-16, NT-33A
, and Princeton Variable-Response
Research Aircraft (Navion
)"
USAF/Calspan TIFS!
USAF AFTI F-16!
Princeton VRA!USAF/Calspan NT-33A!
Cooper-Harper Handling Qualities 

Rating Scale
"
NASA TN-D-5153,1969!
Effect of Equivalent Time Delay on
Cooper-Harper Rating
"
Short-Period Bullseye or Thumbprint"
ζ
SP
ω
n
SP
Carrier Approach on Back Side
of the Power/Thrust Curve"
•  Precise path and airspeed control while
on the back side of the power curve"
–  Slower speed requires higher thrust"
–  Lightly damped phugoid mode requires
"coordination of pitch and thrust control"

•  Reference flight path generated by optical
device, which projects a meatball relative
to a datum line
"
Pilot-Induced Oscillations"
•  MIL-F-8785C specifies no tendency for pilot-induced
oscillations (PIO)"
–  Uncommanded aircraft is stable but piloting actions couple
with aircraft dynamics to produce instability"
F-22! Space Shuttle!
Pilot-Induced Oscillations"
•  Category I: Linear pilot-vehicle system oscillations"
•  Category II: Quasilinear events with nonlinear contributions"
•  Category III: Nonlinear oscillations with transients!
Hodgkinson, Neal, Smith, Geddes, Gibson et al!
NASA DFBW F-8 Simulation of Space Shuttle!
YF-16 Test Flight Zero"
•  High-speed taxi test; no flight intended!
•  Pilot-induced oscillations from sensitive roll control"
•  Tail strike"
•  Pilot elected to go around rather than eject
"
Military Flying Qualities
Specifications, MIL-F-8785C"
•  Specifications established during WWII "
•  US Air Force and Navy coordinated efforts
beginning in 1945"
•  First version appeared in 1948, last in 1980"
•  Distinctions by flight phase, mission, and aircraft
type"

•  Replaced by Military Flying Qualities Standard,
MIL-STD-1797A, with procurement-specific criteria"
MIL-F-8785C Aircraft Types"
I.  Small, light airplanes, e.g., utility aircraft and
primary trainers"
II.  Medium-weight, low-to-medium
maneuverability airplanes, e.g., small
transports or tactical bombers"
III.  Large, heavy, low-to-medium
maneuverability airplanes, e.g., heavy
transports, tankers, or bombers"
IV.  Highly maneuverable aircraft, e.g., fighter
and attack airplanes"
MIL-F-8785C Flight Phase"
A.  Non-terminal flight requiring rapid maneuvering precise
tracking, or precise flight path control "
•  air-to-air combat "
•  ground attack "
•  in-flight refueling (receiver) "
•  close reconnaissance "
•  terrain following "
•  close formation flying"
B.  Non-terminal flight requiring gradual maneuvering"
•  climb, cruise "
•  in-flight refueling (tanker) "
•  descent
"
C.  Terminal flight "
•  takeoff (normal and catapult) "
•  approach "

•  wave-off/go-around "
•  landing
"
MIL-F-8785C Levels of Performance"
1.  Flying qualities clearly adequate for the mission
flight phase"
2.  Flying qualities adequate to accomplish the
mission flight phase, with some increase in pilot
workload or degradation of mission effectiveness"
3.  Flying qualities such that the aircraft can be
controlled safely, but pilot workload is excessive
or mission effectiveness is inadequate"
Principal MIL-F-8785C Metrics"
•  Longitudinal flying
qualities"
–  static speed stability"
–  phugoid stability"
–  flight path stability"
–  short period frequency
and its relationship to
command acceleration
sensitivity"
–  short period damping"
–  control-force gradients
"
•  Lateral-directional flying
qualities"
–  natural frequency and damping
of the Dutch roll mode"
–  time constants of the roll and

spiral modes"
–  rolling response to commands
and Dutch roll oscillation"
–  sideslip excursions"
–  maximum stick and pedal forces"
–  turn coordination
"
Next Time:
Advanced Problems of
Longitudinal Dynamics

Reading
Flight Dynamics, 204-206, 503-525
Aircraft Stability and Control, Ch. 13 
Virtual Textbook, Part 18

Supplementary
Material
Princeton Universitys 

Flight Research Laboratory (1943-1983)

Robert Stengel, Aircraft Flight Dynamics, MAE 331, 2010"
•  Forrestal Campus"
•  3,000-ft dedicated runway
"
Copyright 2010 by Robert Stengel. All rights reserved. For educational use only.!
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Helicopters and Flying Saucers"
•  Piasecki HUP-1 helicopter!
•  Hiller H-23 helicopter!

•  Princeton Air Scooter!
•  Hiller VZ-1 Flying Platform!
•  Princeton 20-ft Ground Effect Machine
"
Short-Takeoff-and-Landing, Inflatable
Plane, and the Princeton Sailwing"
•  Pilatus Porter !
•  Goodyear InflatoPlane!
•  Princeton Sailwing"
Variable-Response Research Aircraft

(
Modified North American Navion A)"
Avionics Research Aircraft

(
Modified Ryan Navion A)"
Navion in the NASA Langley Research Center 

30 x 60 Wind Tunnel"
Lockheed LASA-60 Utility Aircraft"
Schweizer 2-32 Sailplane (Cibola)"
Steve Sliwa,

77, landing on Forrestal Campus runway.!
currently CEO, In Situ, Inc.!
Apple iPhone Used for On-Board Data
Processing and Recording

Jillian Alfred, Clayton Flanders, Brendan Mahon

Princeton Senior Project, 2010
"
iPhone Installation! Hobbico NexSTAR!
System Components!

Pitot Tube Placement!
Autonomous UAV Control in a
Simulated Air Traffic Control System

Atray Dixit, Jaiye Falusi, Samuel Kim, Gabriel Savit

Princeton Senior Project, 2012
"
Overview!
System Hardware!
Aerial Refueling"
•  Difficult flying task"
•  High potential for PIO"
•  Alternative designs"
–  Rigid boom (USAF)"
–  Probe and drogue (USN)"
Formation Flying"
•  Coordination and precision"
•  Potential aerodynamic interference"
•  US Navy Blue Angels (F/A-18)"
MIL-F-8785C Superseded by
MIL-STD-1797"
•  Handbook for guidance rather than a requirement"
•  Body of report is a form, with numbers to be filled in for
each new aircraft, e.g.,
"
•  Useful reference data contained in Appendix A (~700 pages)"
UAV Handling Qualities"
•  UAV Handling Qualities You Must Be Joking,
Warren Williams, 2003"
–  UAV missions are diverse and complex"
–  All UAVs must have sophisticated closed-loop flight

control systems"
–  Cockpit is on the ground; significant time delays"
–  Launch and recovery different from takeoff and landing"
•  Suggestion: Follow the form of MIL-F-8785C, FAR
Part 23, etc., but adapt to differences between
manned and unmanned systems"
Flight Testing for Certification in
Other Agencies"
•  Federal Aviation Administration
Airworthiness Standards"
–  Part 23: GA"
–  Part 25: Transports"
•  UK Civil Aviation Authority"
•  European Aviation Safety Agency"
•  Transport Canada"
Even the Best Specs
Cannot Prevent Pilot Error"
On September 24, 1994, a TAROM Airbus A310, Flight 381, from Bucharest on
approach to Paris Orly went into a sudden and uncommanded nose-up position and
stalled. The crew attempted to countermand the plane's flight control system but were
unable to get the nose down while remaining on course. Witnesses saw the plane climb
to a tail stand, then bank sharply left, then right, then fall into a steep dive. Only when
the dive produced additional speed was the crew able to recover steady flight. !
!
An investigation found that an overshoot of flap placard speed during approach,
incorrectly commanded by the captain, caused a mode transition to flight level
change. The auto-throttles increased power and trim went full nose-up as a result. The
crew attempt at commanding the nose-down elevator could not counteract effect of
stabilizer nose-up trim, and the resulting dive brought the plane from a height of 4100
feet at the time of the stall to 800 feet when the crew was able to recover command. !

!
The plane landed safely after a second approach. There were 186 people aboard.
[Wikipedia]!
TAROM Flight 381 (A310

Muntenia

)!
/>!
Pilot Error, or Aircraft
Maintenance, or Both?"
TAROM Flight 371 (A310

Muntenia

)!
/>!
TAROM Flight 371 was an Airbus A310 that crashed near
Baloteşti in Romania on 31 March 1995. It was a flight from
Bucharest's main Otopeni airport to Brussels. The flight crashed
shortly after it took off. Two main reasons are indicated: first the
throttle of the starboard engine jammed, remaining in takeoff
thrust, while the other engine reduced slowly to idle, creating
an asymmetrical thrust condition that ultimately caused the
aircraft to roll over and crash. Second, the crew failed to respond
to the thrust asymmetry.!
!
None of the 10 crew and 50 passengers survived. [Wikipedia]
!