Fly-by-Wire and Fly-by-Light Control Systems for Rotorcraft

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14 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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Fly
-
by
-
Wire and Fly
-
by
-
Light Control

Systems for Rotorcraft


Wichita State University, Embry
-
Riddle Aeronautical University and
University of North Dakota

Team Members



WSU



ERAU

UND

Animesh Chakravarthy* Pat Anderson* Ernie Anderson*

Wilfred
Nobleheart

#
Hever

Moncayo
* Nicholas
Lounsberry
#

Vishwamithra
Sunkara

# Alfonso Noriega

#


* indicates faculty

# indicates graduate student




Project start date: January 15, 2012


Outline



What is Fly
-
by
-
Wire (FBW) and why use FBW in rotorcraft ?



Features of FBW in rotorcraft that are distinct from FBW in fixed
-
wing aircraft.


-

Peculiarities of PIOs in rotorcraft.



-

Time
-
varying dynamics of
tiltrotors
.



-

Additional features.



FBW in the future.



Human factors issues.




What is Fly
-
by
-
Wire (FBW) ?


Control commands from the pilot and the aircraft’s rates/accelerations, etc. are fed
to a flight control computer (FCC) as electrical signals. The FCC then integrates
these various inputs and generates signals to the actuators to move the control
surfaces correspondingly.



Why use FBW in rotorcraft ?



Results
in weight savings (removal of mechanical linkages
).



Reduced
maintenance costs
.



Can reduce pilot workload in the cockpit.



Increases handling capability and maneuverability.



Use of FBW in rotorcraft



Historically, the use of FBW began in fixed
-
wing aircraft (Concorde in 1969),
while its use in production rotorcraft has commenced relatively recently.



Bell
Helicopters has recently unveiled the Bell
-
525 Relentless, which it claims to be
the first commercial helicopter with FBW.



Eurocopter

has developed the
NH90 rotorcraft,
which has FBW.



Sikorsky has developed the H
-
92, incorporated FBW into the UH
-
60M, S
-
92, CH
-
148 Cyclone (which is a derivative of the S
-
92), the X2
-
technology demonstrator,
etc.



Use of FBW in rotorcraft



The US Army has had two previous unsuccessful attempts at incorporating FBW in
rotorcraft


the RAH
-
66 Comanche and the UH
-
60.



It is now ready to try FBW again as it is
considering upgrading the UH
-
60M Black
Hawk with FBW.



The
Marine Corps in the coming years will replace the aging CH
-
53E Super Stallion
with the next
-
generation CH
-
53K heavy lift
helicopter, that will incorporate FBW.



Features
unique to
fixed
-
wing
FBW

Features
unique to
rotorcraft
FBW


Common to
fixed
-
wing

& rotorcraft
FBW

Goal of this Project



To identify research areas important for certification purposes of FBW rotorcraft.



Though many FBW fixed
-
wing aircraft have been certified and flown successfully,
FBW rotorcraft have some
distinguishing

features


and there is a need to lay out
minimum performance metrics by which these can be certified.

FBW and Pilot Induced Oscillations (PIO)


A
pilot
-
induced oscillation (PIO) is an inadvertent, sustained aircraft oscillation which is the
consequence of an abnormal joint enterprise between the aircraft and the
pilot. It involves
sustained
or uncontrollable oscillations resulting from efforts of the pilot to control the
aircraft.


#

“Aircraft and Rotorcraft Pilot Couplings


Tools and Techniques for Alleviation and Detection: Potential triggers for A/RPC”,
Pavel

and
Yilmaz
, 2011.


FBW and Pilot Induced Oscillations (PIO)



In general, the introduction of digital FBW control systems has increased the potential
for adverse interactions between the human pilot and the aircraft dynamics.



Flying
qualities cliff

-

the aircraft is docile and easily controllable one moment, and is
in
severe
PIO the next moment.

Peculiarities of PIOs in Rotorcraft



Rotorcraft PIOs are more
complicated to
analyze
than
fixed
-
wing aircraft PIOs.



The
primary reason for this is that rotorcrafts possess characteristics resulting from the
interactions between the rotating system
-

the rotor, and the fixed system
-

the
airframe. In the past, well
-
known examples of helicopter
PIOs
have been related
to
#
:



a) Excitation
of the low
-

damped main rotor regressive
-
inplane

mode by cyclic

inputs
resulting in aircraft roll and pitch
vibrations.


b) Excitation
of the low frequency pendulum mode of external slung loads by
delayed collective and/or cyclic control inputs due to couplings of the load dynamics via
elastic
cables.


#

“Understanding
the Peculiarities of Rotorcraft
-
Pilot
Couplings”,
Pavel

and
Padfield
,
2008.

Peculiarities of PIOs in Rotorcraft



Rotorcraft can be expected to be more prone to
PIOs
because they are by far less stable
than aircraft, and because they are required to fulfill difficult, high workload missions
.




Some of the recent rotorcraft PIO occurrences include
#
:


a)
Eurocopter

AS350BA (2006)


Yaw initiated PIO caused the helicopter to crash.


b) Bell UH
-
1B (2007)


Pilot caused vertical oscillations due to collective
bounce.


c) Robinson R44 (2009)


Initiated yaw oscillations turned into yaw
-
pitch
PIO.








#

“Aircraft
and Rotorcraft Pilot Couplings


Tools and Techniques for Alleviation and Detection: Potential triggers for
A/RPC”,
Pavel

and
Yilmaz
,
2011.

#

Pilot
-
in
-
the
-
Loop
Influence on Controlled
Tiltrotor

Stability and Gust
Response”,
J.
Serafini
, D.
Muro
, M.
Gennaretti
, 2010.


PIO in
Eurocopter

AS350BA (2006
)



A yaw
-
initiated PIO occurred in January 2006, causing the helicopter to crash.




The
helicopter was equipped with a video recording system that could record images
outside the helicopter and inside the cockpit.

At
43
min
50
sec,
while pointing out a
waterfall to passengers, the pilot states that they are at, "a little over 3,000 feet."
At
44
min
44
sec, a
yaw motion to the right can be observed on the video.

An
aircraft

oscillation

can be observed,
which
quickly increases in magnitude. Treetops become
visible through the right window, and the passengers and pilot start leaning to the left.
The video ends at
44 min
55
sec
as the helicopter
hits
the treetops.



#

NTSB
: LAX06LA072


PIO in
Bell UH
-
1B
(2007)



A collective bounce occurred, causing substantial structural damage to the helicopter.




Collective
bounce is a pilot induced
vertical oscillation
that may
occur at
any flight
condition by a rapid buildup of vertical bounce at
3 Hz (
approx
).




As the helicopter was lifting from the ground, it began to vibrate, that turned into a
severe "hop or a bounce." The pilot climbed the helicopter to about 15 feet; however, it
continued to vibrate. The helicopter then began to nose over and become
uncontrollable. The pilot then
force landed
the
helicopter, due to which it
sustained
structural
damage.


#

NTSB
: SEA08LA043


PIO in Robinson R44 (2009)



In an accident in 2009, initiated
yaw oscillations turned into yaw
-
pitch
PIO, causing the
pilot to force land the helicopter, leading to substantial structural damage.




The
pilot
said
that
a few
minutes into the
flight,
he felt a vibration
and
then a slight
yawing motion developed.

The
vibrations
then turned
to
oscillations
, in both yaw and
pitch, to the point he felt the helicopter was going to come apart.

An
emergency
landing was his only option.




Investigations revealed that the
tendency to enter
an
oscillation regime was exacerbated
by a forward CG (within the CG envelope) and a 30
deg

banked turn to the left.


#

NTSB
: ANC09GA040



FBW and Pilot Induced Oscillations (PIO)



PIOs can be caused due to the presence of position and/or rate limiters, which are
common elements in digital FBW control software.



When these limits are hit, time delays accrue which can cause PIOs.


Tiltrotors


V
-
22 Osprey


BA
-
609

Peculiarities of PIOs in Rotorcraft



Tiltrotors

can fly
in both helicopter
and
airplane mode
-

the configuration of the
aircraft changes depending on the mode of
operation.



Changes
in aeromechanical operation mode
may
require changes in the operation
mode of the FCS, paving the way to changes in the way the pilot perceives the vehicle
response
-

this
represents a potential trigger for
PIO
events.



The V
-
22 Osprey has encountered several such PIO events
#
:


a)
3.8 Hz Symmetric wing chord bending mode caused due to pilot coupling through




longitudinal
cyclic (1991
).


b) A roll mode oscillation occurred due to change in mass balance weight (1997).


c) A PIO
occurred while hovering over a ship (1999
).

#

“Aircraft and Rotorcraft Pilot Couplings


Tools and Techniques for Alleviation and Detection: Potential triggers for A/RPC”,
Pavel

and
Yilmaz
, 2011.

# “
Pilot
-
in
-
the
-
Loop Influence on Controlled
Tiltrotor

Stability and Gust Response”, J.
Serafini
, D.
Muro
, M.
Gennaretti
, 2010
.



Peculiarities of PIOs in Rotorcraft



Most of the existing criteria used to predict susceptibility of an aircraft to PIOs
consider single
-
axis PIOs only.



Since rotorcraft have a higher degree of cross
-
coupling among axes, this necessitates
research into multiple
-
axes PIOs.



Time
-
varying Dynamics of
Tiltrotors



The influence of nacelle rotation is to introduce time
-
varying dynamics in a
tiltrotor
.



If a wind gust hits the
tiltrotor

at the same time while the nacelle is rotating from the
helicopter mode to the fixed
-
wing mode, the response of the
tiltrotor

will be different
from the natural response it would have in either of the two modes. Furthermore, this
response would change depending on the nacelle rotation rate.



There is also the issue of nacelle/blade
-
flap/rotorcraft pitch coupling.



This necessitates research into laying down some minimum performance requirements
of the
tiltrotor

during nacelle rotation.




Time
-
varying Dynamics of
Tiltrotors



Coupling of nacelle/blade
-
flap/rotorcraft pitch can occur.



Oscillations are
induced by the angular
rate of
the nacelles causing rotor flapping which
in
turn generates
pitching moments on the aircraft body.

These
pitching motions are
opposite
in sense
to the pilot input
-

stick forward commands
a forward
rotation of the
nacelles to accelerate forward,
the rotors
flap aft in response and cause a nose
-
up
pitch.
The larger the allowable nacelle rate,
the larger
the pitch
disturbances
#
.

#Flight
Dynamics Aspects of a
Large Civil
Tiltrotor

Simulation
using Translational
Rate
Command, Lawrence,
Malpica
,
Theodore, Decker and Lindsey, 2011.

Additional flight phases/features unique to FBW helicopters



Higher integration of flight and propulsion control



Autorotation and Hover



Retreating Blade Stall



Slope landing



Very low altitude nap of the earth flight.



Requirement to carry slung loads, etc.



At this time, it is unclear as to which of these features are incorporated
using feedback control

in
current FBW rotorcraft but it is not inconceivable for future rotorcraft to do so.

FBW in the future



Active stabilization of sling loads
#



Coupled terrain following/obstacle avoidance using
wideband sensor input.



Automatic landing in brown out conditions.



A super
-
TRC control
system* that allows
both stable
and maneuverable control systems to be active
simultaneously.



# “
Impossible To Resist, The Development of Rotorcraft Fly
-
by
-
Wire Technology,”
Stiles
et al, AHS
60th Annual Forum, Baltimore, MD,
2004


*
http://www.nrc
-
cnrc.gc.ca/eng/news/nrc/2011/07/01/pilot
-
control.html


FBW in the future



In the near future, Fly
-
by
-
Wire technology could evolve into Fly
-
by
-
Wireless
technologies.



Gulfstream tested a fly
-
by
-
wireless system on its G550 advanced flight control system,

by
testing wireless in parallel with other more traditional control methods for spoiler

control
, using fly
-
by
-
light for the inner spoilers and fly
-
by
-
wire for the outboard spoilers.

The fly
-
by
-
wireless architecture includes an internal wireless bus transmitter and external
receiver at the interface for the
actuator
for the mid
-
inboard flight
spoilers
#
.



In future, we could see fly
-
by
-
wireless introduced in rotorcraft too !



#http
://www.flightglobal.com/news/articles/gulfstream
-
fly
-
by
-
wireless
-
trials
-
to
-
continue
-
318170/

Student Participation in this Project



Wilfred
Nobleheart

(
Ph.D

student in Aerospace Engineering at WSU


graduating in 2014)



Vishwamithra
Sunkara

(M.S. student in Electrical Engineering at WSU


graduating in
2013)



Alfonso Noriega
(M.S. student in Aerospace Engineering at ERAU


graduating in 2013)



Nicholas
Lounsberry

(M.S student in Aviation at UND


graduating in 2013)




Are Human Factors Issues Addressed with FBW?


Boeing 787 yoke




vs.


Airbus 330 Side stick



Human Factors


Man vs. Machine (now computer)


Airbus


FBY always in control, not allow pilot to fly outside
envelope, no (or limited) override


Boeing


Allows both pilots to override FBY software


UH
-
60 horizontal stabilizer


experience . . .



Human Factors


Helicopters are Different



What is typical flight envelope?


Low flight profile = more override


potential?


Override automatic or extra effort?


H
-
V flight profile?


Overconfidence?




Helicopter FBW Research Challenges




New compared to fixed wing


Hard to find or. . .


Not in public domain, proprietary


Cost associated with obtaining articles (AHS, SAE, SAGE)










Back
-
up Slides

Development of FBW Technology



Historically, the use of FBW started in fixed
-
wing aircraft.



The first production fixed
-
wing aircraft to use FBW was the Concorde (1969).



The first airliner to use a digital FBW is the Airbus A320 (1987).



The first business jet to use FBW is the
Dassault

Falcon 7X (2007).



The use of FBW in production rotorcraft however has lagged that in fixed
-
wing
aircraft.


Autorotation capability in
tiltrotors



The V
-
22
tiltrotor

does not possess autorotation capability, but such a capability is being
tested on the BA/AW 609
tiltrotor
.



It is important to lay out minimum performance specifications for autorotation in
tiltrotors
.

#
http
://www.flightglobal.com/news/articles/heli
-
expo
-
agustawestland
-
prepares
-
aw609
-
for
-
certification
-
tests
-
368230
/


#
http
://www.ainonline.com/aviation
-
news/hai
-
convention
-
news/2012
-
02
-
11/aw609
-
finally
-
ready
-
its
-
close

Integrated Flight and Propulsion Control



The
flight and propulsion systems
in a rotorcraft are
highly
coupled.



In
fixed wing aircraft,
the dominant variable
that couples the engine to the aircraft is


thrust
, and thrust is not affected greatly by aircraft attitude
or motion.



In
rotorcraft,
the dominant variable that couples
the engine
to the aircraft
is rotor speed,
and the
engines ability to maintain
rotor speed
is affected by the load torques that
result
from
the rotorcraft motion.



It is important to lay out minimum performance specifications to certify an integrated
digital

flight and propulsion control system in a rotorcraft.

FBW in the future



A super
-
TRC control system allows
both stable and maneuverable control
systems to be active simultaneously.

The
blend between stability and agility is
determined by how the pilot moves the control
stick.
Slow, deliberate stick
motions are channeled to a stable control system, whereas fast stick inputs are
channeled to
a more
maneuverable control
system
#
.



Pilots
can be fast and aggressive with the stick when they need agility. At the
next instant, they can be
slow
and cautious, using tiny movements when they
need stability
.



System has been tested on NRC’s Bell 412 Advanced Systems Research
Aircraft.


#
http://www.nrc
-
cnrc.gc.ca/eng/news/nrc/2011/07/01/pilot
-
control.html