Helicopters and Fly-by-wire?
Join Date: Dec 2001
Location: Philadelphia PA
Age: 73
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Fly-by-wire can be a liberating technology and has the potential to change the way we operate.
But only if we think a bit outside the box. For example, just because you can put all the axis on one control doesn't mean you should. Research done by Canada's NRC years ago showed there was nothing for or against any particular controller configuration - a lot depended on the type of response that was needed. Personally, it makes little sense to put up-down on the same controller as the left/right/fore/aft axis when you have to maneuver in all those axis at the same time.
But at least we'll have the option to look at it with FBW.
But only if we think a bit outside the box. For example, just because you can put all the axis on one control doesn't mean you should. Research done by Canada's NRC years ago showed there was nothing for or against any particular controller configuration - a lot depended on the type of response that was needed. Personally, it makes little sense to put up-down on the same controller as the left/right/fore/aft axis when you have to maneuver in all those axis at the same time.
But at least we'll have the option to look at it with FBW.
Comanche had one, seemed to work.
I wonder if the test pilots from that program ever post/read here.
I wonder if the test pilots from that program ever post/read here.
The DLR EC135 flew with just two sidesticks:
DLR Portal - DLR tests new helicopter control system: successful first flight with two active sidesticks
skadi
DLR Portal - DLR tests new helicopter control system: successful first flight with two active sidesticks
skadi
Flying the SHADOW
I had the opportunity to fly many hours in the XS-76 SHADOW flight research vehicle. We flew with traditional 2X cyclic (force controller) full motion collective and force control directional pedals. Next we flew with a 3X cyclic (twist the controller for yaw) and full motion collective. Lastly we flew with a 4X cyclic where up and down on the cyclic controlled the collective. One version back drove the collective so as you moved the cyclic up and down the collective would correspondingly move. This function was disabled with a collective grip switch (lemon squeezer).
The learning curve was pretty steep for all but the 4X control. Yaw control was easy to adapt to as this axis was well damped, much like the Seahawk or Super Stallion where pedal input requirements are minimal. 4X was a different story. The learning curve was very flat. Flying the aircraft everyday allowed us to gain proficiency. If we went a week or so without flying this configuration it was almost like starting from square one. If I has to put my finger on anyone issue it would be the inability to completely separate individual control inputs while doing simple tasks like approach to a hover.
All of this was flown from the front seat in the SHADOW. All in all it was a real kick in the butt. Some of the best flying ever.
The learning curve was pretty steep for all but the 4X control. Yaw control was easy to adapt to as this axis was well damped, much like the Seahawk or Super Stallion where pedal input requirements are minimal. 4X was a different story. The learning curve was very flat. Flying the aircraft everyday allowed us to gain proficiency. If we went a week or so without flying this configuration it was almost like starting from square one. If I has to put my finger on anyone issue it would be the inability to completely separate individual control inputs while doing simple tasks like approach to a hover.
All of this was flown from the front seat in the SHADOW. All in all it was a real kick in the butt. Some of the best flying ever.
Join Date: May 2000
Location: Phuket
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What are the advantages of FBW? Personally I do not like it at all. It is bad enough on something dynamically stable as in an airplane but a helo? When I flew the 9 for the airlines I jump seated on a 320. After we got to flight level I asked the pilots what would happen if we lost all electrics? Captains response was the CP would open the door for the RAT then they would spend the rest of the fuel load trying to get a computer back on line since it would barely fly without a computer, would not land without one.
Jerry
Jerry
Join Date: Nov 2005
Location: Monkeys ride bikes, ever seen one fix a puncture??
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So to develop the FBW question a little..
presumably the pilots preference in any fbw system would be full motion controls with artificial feel units??
presumably the pilots preference in any fbw system would be full motion controls with artificial feel units??
Discussion Points
Fly3est makes a very good point. What is the preferred configuration and what are the benefits?
• Full motion Vs Limited or no fixed force controls. One of the draw backs to limited or fixed motion systems is the lack of feedback for rotor disk position, especially at night. This is also evident when performing ground contact maneuvers. The SHADOW/Comanche system utilized landing gear feed back sensors to assist during ground contact maneuvers.
• Another aspect is control feedback. The C/MH-53E incorporates an artificial aerodynamic feed back system in the pitch axis (FAS – Force Augmentation System). This system increases stick breakout forces and cyclic stick damping as airspeed increases. It also provided stick force per G derived from pitch rate and airspeed. This would be easy to incorporate in a modern fly by wire system.
• Boeing Vs Airbus provides a great study point for future helicopter flight control systems. Airbus elected to go with side arm controllers with little or no feed back and electronic engine throttles that are not back driven. Boeing cloned a traditional mechanical system on the 777 and even back drives the throttles. Both companies would argue that theirs was the best approach.
I am sure that there are many more issues and would enjoy any future discussions.
• Full motion Vs Limited or no fixed force controls. One of the draw backs to limited or fixed motion systems is the lack of feedback for rotor disk position, especially at night. This is also evident when performing ground contact maneuvers. The SHADOW/Comanche system utilized landing gear feed back sensors to assist during ground contact maneuvers.
• Another aspect is control feedback. The C/MH-53E incorporates an artificial aerodynamic feed back system in the pitch axis (FAS – Force Augmentation System). This system increases stick breakout forces and cyclic stick damping as airspeed increases. It also provided stick force per G derived from pitch rate and airspeed. This would be easy to incorporate in a modern fly by wire system.
• Boeing Vs Airbus provides a great study point for future helicopter flight control systems. Airbus elected to go with side arm controllers with little or no feed back and electronic engine throttles that are not back driven. Boeing cloned a traditional mechanical system on the 777 and even back drives the throttles. Both companies would argue that theirs was the best approach.
I am sure that there are many more issues and would enjoy any future discussions.
Join Date: Aug 2013
Location: Andover
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In the Event of loss of Hyds the WAH-1/AH-64 has the Back up control system (BUCS) wich uses linear Variable differential transformers LVDTs wich when activate effectively turned into a FBW Aircraft. (btw thats the limit of my knowledge on it, I only loaded the weapons onthe thing!)
With regards to BUCS on the WAH-64
'Unlike other fielded Army helicopters, the AH-64 Apache has an emergency back
up, electro-hydraulic, fly-by-wire system available to the crew in the event of a jammed
or severed flight control. This back up control system (BUCS) allows the crew to
bypass damaged mechanical flight controls and safely land the aircraft. The BUCS can
be found on both A- and D-model Apaches.
In the AH-64A normal flight control inputs from the pilot or copilot/gunner (CPG)
are relayed to the hydraulic servo-actuators, which control the flight surfaces, using
mechanical linkages (push-pull tubes, bellcranks, etc.). If this mechanical system is
jammed or severed by combat damage or maintenance problems, the BUCS will
recognize the problem and enable fly-by-wire control of the affected axis.
The BUCS uses linear variable differential transducers (LVDTs) to signal flightcontrol
position, and shear-pin-actuated decouplers (SPADs) to separate flight controls
from the mechanical linkages. Eight LVDTs are located in the cockpit to sense flightcontrol
positions from the pilot and the CPG. Other LVDTs transmit the servo-actuator
positions to the Digital Automatic Stabilization Equipment Computer (DASEC). Among
its other functions, the DASEC recognizes problems with the mechanical control system
and enables the BUCS. SPADs are located at the base of each control axis (cyclic
longitudinal, cyclic lateral, collective, and pedals) for each crew station. There are eight
SPADs in all.
When a jam occurs, either crewmember can decouple, or "break out," of the
jammed axis by pushing hard on the affected flight control and breaking the SPAD on
that axis. As soon as the SPAD is broken the BUCS is enabled. All other undamaged
axes will continue to function normally using mechanical linkages. The crew can safely
land the helicopter.
In the event of a severed control linkage, the DASEC recognizes the mistrack
between the flight-control position and the position of the hydraulic servo-actuator. With
sufficient mistrack (17.5 percent, or approximately two inches of control movement), the
DASEC automatically enables the BUCS for the defective axis. All other undamaged
axes will continue to function normally using mechanical linkages. The crew can safely
land the helicopter.'
'Unlike other fielded Army helicopters, the AH-64 Apache has an emergency back
up, electro-hydraulic, fly-by-wire system available to the crew in the event of a jammed
or severed flight control. This back up control system (BUCS) allows the crew to
bypass damaged mechanical flight controls and safely land the aircraft. The BUCS can
be found on both A- and D-model Apaches.
In the AH-64A normal flight control inputs from the pilot or copilot/gunner (CPG)
are relayed to the hydraulic servo-actuators, which control the flight surfaces, using
mechanical linkages (push-pull tubes, bellcranks, etc.). If this mechanical system is
jammed or severed by combat damage or maintenance problems, the BUCS will
recognize the problem and enable fly-by-wire control of the affected axis.
The BUCS uses linear variable differential transducers (LVDTs) to signal flightcontrol
position, and shear-pin-actuated decouplers (SPADs) to separate flight controls
from the mechanical linkages. Eight LVDTs are located in the cockpit to sense flightcontrol
positions from the pilot and the CPG. Other LVDTs transmit the servo-actuator
positions to the Digital Automatic Stabilization Equipment Computer (DASEC). Among
its other functions, the DASEC recognizes problems with the mechanical control system
and enables the BUCS. SPADs are located at the base of each control axis (cyclic
longitudinal, cyclic lateral, collective, and pedals) for each crew station. There are eight
SPADs in all.
When a jam occurs, either crewmember can decouple, or "break out," of the
jammed axis by pushing hard on the affected flight control and breaking the SPAD on
that axis. As soon as the SPAD is broken the BUCS is enabled. All other undamaged
axes will continue to function normally using mechanical linkages. The crew can safely
land the helicopter.
In the event of a severed control linkage, the DASEC recognizes the mistrack
between the flight-control position and the position of the hydraulic servo-actuator. With
sufficient mistrack (17.5 percent, or approximately two inches of control movement), the
DASEC automatically enables the BUCS for the defective axis. All other undamaged
axes will continue to function normally using mechanical linkages. The crew can safely
land the helicopter.'
