Helicopters and Fly-by-wire?

[Stuck_in_an_ATR]

Are there any helicopters using a fly-by-wire system? I'm not thinking SAS/ASE, but a fully blown FBW, like for instance in A-320, or F-16, where pilot's inputs feed the flight control computers, which in turn execute control movements to meet the pilot's demands (like roll/pitch rate, load factor etc.) and there's no mechanical reversion. I am asking, because I think that helicopters, with all the control complexity, cross-coupling, instabilities and generally less-than-perfect handling qualities (at least compared to FW a/c) seem to be perfect candidates for such a system, which could greatly simplify the handling, ease pilot's workload and enhance safety...

So, are such systems currently available, or under developement, or maybe there are some issues precluding the use of FBW in helicopters?

[Turkeyslapper]

yeh I am pretty sure the NH90 (MRH in Oz) is a full FBW aircraft...triple redundancy or something as well?? Not sure about any other types out there though.

[Gymble]

The EC145 is more or less FBW. If hydraulics fail there is no mechanical reversion. For that matter so is the 412 except the wires are a bit thicker. Either way you are still buggered with total hyd failure.
Not quite what you were asking I know!
My point is, we have already taken the scariest step and few of us really noticed.
FBW . Beg deal !! It’s an autopilot.

[skadi]

I think, the NH-90 is so far the only one which comes with full FBW as standard.
The Comanche had FBW and also some other prototypes. For instance, the DLR in Germany is flying an EC 135 testbed with full "fly by light" system.

skadi

[skadi]

The EC145 is more or less FBW. If hydraulics fail there is no mechanical reversion.

:ugh::ugh::ugh:

skadi

[TRC]

... an EC 135 testbed with full "fly by light" system

That's all very well, but what happens at night or on a really cloudy day?

[skadi]

That's all very well, but what happens at night or on a really cloudy day?

Serious question? It will fly as usual!

Fly-by-light EC135 helicopter makes first flight-05/02/2002-Flight International (http://www.flightglobal.com/articles/2002/02/05/142313/fly-by-light-ec135-helicopter-makes-first-flight.html)


skadi

[212_Nightdipper]

The NH-90 is full FBW..not much "monkey skills" or particulary good basic Airwork needed since the sistem "cleans and correct" all the "wrong" inputs....whats left to the pilot is to manage all the systems...which can be challenging as well.....but werent we supposed to be pilots???:confused:...Cheers

[Brilliant Stuff]

I also read the Canadians have a FBW 205 or somesuch doing similar stuff like the DLR 135.

[Tallsar]

Stuck in an ATR....Yep..the NH90 is the only fielded full FBW helo as yet ...and don't forget aspects of V22. You are right in assuming FBW would bring the same and some additional benefits to rotorcraft (depending on size and role) and that the challenge has been more complex and expensive in sorting it. Do not forget that FW FBW took many years of experiment, research and data gathering on specially rebuilt test platforms such as the EAP and a Jaguar at Farnborough..as just in the UK example. Several countries had experimental programmes running from the 80s onwards to sort the development...with only the US and Franco German programmes seeing their results reaching conclusions. The UK spent many years gathering the immense handling qualities data required to understand the control dynamic issues that would lead to the programming of any helo FBW AFCS. This also contributed jointly to the equivalent NASA programme which fed the Commanche AFCS development and design. In the UK we were to have a Lynx FBW development programme but despite it being a high priority research programme it was
cancelled in 1990.....it would have proven of immense value to the EH101 in due course, as well as aircraft such as the new Wildcat...but there we go...the UK committed techno industrial suicide again! :ugh: Also at one stage there might have been some FBW in the Merlin HMA2 upgrade happening now...but the risks were considered to high for the time and money available so it has been dropped. Any other questions..PM me. :)

[IFMU]

The CH-148 variant of the S-92 is also fbw.
Yup. Also Sikorsky has a couple FBW UH60's and the X2. They had the Comanche. The CH53K will also be FBW.

-- IFMU

[Ian Corrigible]

Sikorsky has a couple FBW UH60's and the X2. They had the Comanche. The CH53K will also be FBW

The irony here, given Tallsar's post, being that Sikorsky's FBW is a UK system (BAE).

The BA609, like the V-22, is FBW. Kawasaki's BK117 P5 and NASA's JUH-60 RASCAL demonstrators were also FBW.

The AH-64A and Apache AH Mk1 (but not AH-64D) also have a single-channel FBW system as the Back-Up Control System (BUCS).

I/C

[Matthew Parsons]

I also read the Canadians have a FBW 205 or somesuch doing similar stuff like the DLR 135.

The NRC (National Research Council) runs a 205 and a 412 with one pilot FBW, and the other monitoring mechanical flight controls. The aircraft are used for research and development of FBW control laws, amongst many other things.

The CH148 (S92) is fully FBW, but is still under development. Many successful flight hours so far, but the number of minute aspects that must be managed in developing a full FBW control law is quite overwhelming.


I agree with Stuck-in-ATR's original post, that helicopters are ideal candidates for FBW. There is tremendous potential for vast improvements in stability & control, and reductions in workload. However, there are two issues that make it difficult: one is that the nature of the operation makes the control laws much more complicated, the other is that most helicopters are not economically feasible when the base model gets loaded with expensive avionics or the program suffers huge developmental costs.

Cheers,
Matthew.

[Tallsar]

....ATR....I think you can conclude that overall, helo FBW has been underdeveloped and therefore under-utilised. As MP's post implies...it is very risky and costly to try and design a platform and do all the FBW development on that platform as part of a production programme. V22 and I fear S92 suffers from this approach, Although 609 has gained much from the struggles to get V22 to work. NH90 has had problems but they were in part alleviated by the earlier research work done. Comanche is the irony as it had utilised all the tailored handling qualities research and data gathering done by both NASA and the UK RAE...only to be cancelled! Certainly it is not a sensible approach to assume that a rotorcraft designed with conventional controls and AFCS can quite easily be retrofitted with full FBW...unless you have variable time and an infinite budget of course!

[Dan Reno]

I believe the US Army has paid for some H60 FBW feasibility studies for their fleet.

[Aser]

Yes, I remember reading about it for the uh-60m, a quick google search showed this:
US Army revives interest in fly-by-wire for Black Hawks
By Stephen Trimble


A fly-by-wire upgrade for the Sikorsky UH-60M Black Hawk is back under serious consideration by the US Army.
Army acquisition officials "have a plan" to reinsert funding for fly-by-wire technology, which was removed from the UH-60M programme after 2008, says Maj Gen R Mark Brown, deputy for acquisition and systems management in the office of the assistant secretary of the army for acquisition, technology and logistics.
Brown's remarks come as Sikorsky nears the end of a two-year, 400h flight demonstration programme for the fly-by-wire upgrade, and show a revival of interest in the technology. Fielding an aircraft without mechanical linkages should have arrived with the Sikorsky/Boeing RAH-66 Comanche, but the aircraft was cancelled in 2004.

© US Army

Fly-by-wire was also inserted into the UH-60M upgrade, but the army declined to move the technology into production two years ago.
"We thought it was more important to buy less-capable aircraft faster and relieve our force structure," says Brown.
Inserting fly-by-wire into the UH-60M will save about 220kg (484lb), says Col Neil Thurgood, programme manager for utility helicopters. The technology also enables the army's vision to convert at least some of its Black Hawks into optionally piloted vehicles by the end of the decade.
The key benefit of fly-by-wire, however, is improved handling, says Thurgood. Pilots would no longer have to worry about controlling the aircraft in the last 650ft (200m) of a flight, when their eyes should be scanning the area outside the cockpit, he says.

Regards
Aser

[birrddog]

In talking about FBW, are control inputs and linkages, including force feedback to the controls separable from the system that decides/overrides pilot inputs?

I.e. In creating an electronic control system, is it required to have this aided by a computer, or is that just the next logical progression/justifying factor?

[Matthew Parsons]

birddog,

Theoretically, any control system you can imagine is possible. However, once you get into certifying the FBW system you will find some restriction. Imagine looking at a helicopter cockpit and you see one joystick, nothing else for 4-axis flight control.

In my opinion, this will be a challenge in the future. We can build something that is easy to fly and seems intuitive, but may not meet certification criteria. Not an insurmountable obstacle, but another challenge (=expense) that may delay commercial FBW.

Cheers,
Matthew.

[SilsoeSid]

For instance, the DLR in Germany is flying an EC 135 testbed with full "fly by light" system.

Is that not just a fancy way of saying 'solar powered' ?

I guess if it was the blades that had the solar panels on them, in flight the whole area of the disc becomes a large receptor which becomes vastly larger than the 4/5 individual blades themselves.
As shown in the pic below, instead of just the surface area of the 4 blades themselves producing the electricity, you'd have a panel the size of the red area as shown here;

http://www.aerospaceweb.org/question/aerodynamics/lift/refarea-hel.gif

or you could have a rotor system something like this to accomodate the solar panels;

http://www.inewidea.com/wp-content/uploads/2008/09/image0052.jpg


But I guess the size and number of the batteries required would be the limiting factor for practical use, hence it's only on a testbed....for now.



But where do you stop?
Thermal power units that take the heat from the leading edges or maybe even little wind turbines along the leading edges topping up the batteries, the possibilities are endless... !

[Lonewolf_50]

A few bits and pieces ...

1. Comanche was not only FBW, it didn't have rudder pedals.

2. Sikorsky UH-60 Blackhawk has had a fly-by-wire flight control surface, the horizontal stab, since the A model. (You can revert it to manual control, but in auto mode it exhibits all of the characteristics of a fly-by-wire control surface. It moves to help you without you doing anything.)

At certain airspeeds, this can lead to a bit of "hunting" (depending upon what you are doing), but one place that the automatic programming of the horizontal stab shines is during autorotation.

[Shawn Coyle]

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.

[SansAnhedral]

UH-60MU is FBW

The CH-148 will be FBW, S92 N592SA was the FBW testbed.

[Brilliant Stuff]

SS, the DLR fly by light means they use fibre-optic cabling.

[76ranger]

I can see how a 4 axis cyclic would be tough, but what about 3? Pitch, roll, and yaw.

[Lonewolf_50]

Comanche had one, seemed to work.

I wonder if the test pilots from that program ever post/read here.

[skadi]

The DLR EC135 flew with just two sidesticks:

DLR Portal - DLR tests new helicopter control system: successful first flight with two active sidesticks (http://www.dlr.de/en/desktopdefault.aspx/tabid-1/86_read-20504/)

skadi

[Jack Carson]

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. :)

[before landing check list]

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

[Flyt3est]

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??

[Jack Carson]

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.:)

[Ian Corrigible]

Another S-76 variant, previously referenced by Sir Korsky in a separate (http://www.pprune.org/rotorheads/513373-ec145-unmanned-flight.html#post7980347) thread: Sikorsky launches autonomy research program (http://www.aviationweek.com/Article.aspx?id=/article-xml/AW_08_05_2013_p47-602182.xml)

I/C

[DSquadron]

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!)

[How Nice]

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.'