Fly By Wire

[MERLINMAN]

So the H92 - Superhawk is to have Fly by Wire flight controls eh?

Does anyone have any experience of this technology in a rotary wing context - good/bad/indifferent ?

MM

[Brilliant Stuff]

I know there was a Dauphin which flew by wire.

I also know the Germans are using an EC135 for Fly by light technology.

[212man]

Don't forget the NH-90: first production helicopter with FBW.

[NickLappos]

Comanche was FBW, the fourth FBW helo that I have flown. Works like a charm.

[Robbo Jock]

Strewth! A helicopter with a lift! that must have been one big b######.:}

[JAF0]

Comanche was FBW, the fourth FBW helo that I have flown. Works like a charm.

you flew the comanche?

[Mikester540]

Nick Lappos definitely flew the Comanche!

He was lead test pilot for Sikorsky for like 30 years. He flew just about every modern Sikorsky helicopter. Including the 92.

Now he's at Gulfstream in some cushy executive job. :ok:

Excerpt from Gulfstream Press Release:
Prior to joining Gulfstream, Lappos was a 32-year employee with Sikorsky Aircraft. Most recently, he served as director of the VXX presidential helicopter program. Previously, he was program manager for the S-92 helicopter and director of test engineering for the company's West Palm Beach, Fla., fight-test center. Spending most of his career in research and development, Lappos served as both a test pilot and the chief pilot for R&D. He was also a flight instructor for various Sikorsky model helicopters and has helped train the flight crews of several heads of state, including that of the President of the United States.

[Graviman]

Wow! That's some resume...

Agusta-Westland are getting into FBW too:

http://www.claverham.com/heat.htm

Mart

[Mikester540]

I thought that was to replace hydraulics in a helicopter or something?

[212man]

Mike,
from the link it would appear to be an alternative to hydraulic servos, as you say. However, the link also states that it forms a part of the FBW system being developed.

JAFO,
If you have ever seen the Discovery program about the Commanche; that's Nick in it!

[JAF0]

oh right, ive have seen that program. Hi Nick :}

That is cool though, the comanche looked like a great heli , pitty about its outcome.

[NickLappos]

There are important differences between the various fly-by-wire (FBW) systems that must be discussed. Here are some thoughts, mostly to help spark debate (its getting a bit dull in pprune-land!)

1) FBW is not worth much if all you do is have a computer drive your controls. Control tubes work just fine, and only in truly large sized helos is FBW lighter or simpler.

2) Most FBW systems are just translations of conventional controls into FBW without changing the basic control scheme. That means the aircraft is basically the same as it was, albeit a bit more stable. The pilot still moves attitude to make the machine do its tricks, just like Igor did. Big whoop. That is how NH-90 works, and it is not worth it (in fact, the first 90's flew with iron control tubes, thank you very much!)

3) Given a computer and modern sensors, it is possible for the controls to be radically altered, so that the pilot does less juggling, and the control system does more. Imagine a car that has lane sensors that see the stripes on the road, and motion sensors that see other cars. You could do much to stop auto accidents if you use that system as a stating point for a new way to control cars. Same with helos. The concept of having a pilot juggle an eletric stick in a FBW to do what he has done is old fashioned, and wrong. Take the controls to a new level.

4) A velocity stabilized control system, where the pilot choses ground speed and the controls deliver, it is entirely possible. This system could allow flight in pitch black, zero horizon situations, or in complete white-out/Brown-out. It would have an auto-hover capability, like SAR doppler hover, but fully integrated into the electric stick, so the pilot merely asks for a ground speed, and it delivers. The pilot does not need to juggle pitch and roll attitude, the controls do that. He does not have to walk the pedals, the controls do that too. I have flown this system for several thousand hours in sims, and dozens of hours in helos, and it works wonderfully.

5) The weapons can point the aircraft, so the targeting accuracy and time to shoot drop to half that when the pilot is unaided.


That is Fly by Wire. Comanche had it, and so will the H-92. Nothing else comes close.

[212man]

I don't disagree with your comments, Nick, but do think that much of what you propose could be equally well done with conventional controls. Surely one of the big drivers for FBW, in general, is also damage tolerance and weight reduction (which you suggest is slight for a helicopter), and this is why, thus far, it is only really seen in military designs?

On a similar theme (modern avionics) though slightly off topic; one thing that I find odd, given the progressive nature of the Sikorsky team, is the choice of display symbology for IAS, ALT and Rad-Alt for the 92 i.e. small round gauges. I agree they may be more intuitive for a pilot used to conventional instruments, but I feel they miss the opportunity to deliver the greater situational awareness that tape displays can offer. That initial extra hump in the learning curve during the transition, that may be experienced, is more than offset by the subsequent benefits (I humbly suggest).

[NickLappos]

212man,

The FBW high-order control schemes that I suggest above really can't be done by conventional controls, because the large authorities that the autocontrols need would take large and ghastly stick movements to employ, frankly, the pilot would be disconcerted as the stick did its thing (much as we all feel when we 'follow through" with someone else). This means that the "inner loop" servos would have to be nearly 100% authority. In this case, the protection built into the conventional autopilot would be just like FBW, so there is no savings in it regarding cost or weight. In other words, to do these high order control schemes, you need a FBW computing system, and to build them into conventional controls means you are carrying two systems, a luxury few helos could stand.

Regarding the displays, I agree that many other ways, rather than round dials, can be used. It seems that no one way is preferred by all pilots, I did not fight it when the Sikorsky test pilots and the Collins human factors gurus came up with the S-92 displays. They work, I guess, is the answer!

[ShyTorque]

"but I feel they miss the opportunity to deliver the greater situational awareness that tape displays can offer."

Now THERE is a really good way to start a discussion!

Speaking as a pilot with an analogue brain living in an increasingly digital world....... :\

[212man]

Makes sense Nick; I agree you would need full authority series actuators as well as parallel.

Shy Torque; you are confusing digital and analogue! Last time I looked, climbing higher was a vertical experience and thus quite well suited to a vertical tape display. Hey, you can even portray the ground at a relevant point on the display (from radalt input) as a brown bit, for when you come back down again!

Digital displays just show numbers, that is not what I'm supportingand I agree they are not a good way of interpreting rate change. Tape displays are as analogue as a dial. If the datum moves, the display moves. If it moves quickly, the display moves quickly. Simple really, bit like a needle unwinding quickly.

Having just started flying the S-61 after 4 years of a pure EFIS aircraft I know what I prefer to look at!:{

[bigchopper7669]

just finished test flying the EW 713/2 , by far the best FBW to date

[Si Clik]

212MAN

Whilst the Claverham system will use electric servos in place of the EH101s hydraulic ones it is the intention to also remove the mechanical controls in the system and replace with FBW with the intention of giving it all the gucci control and stability stuff that has been mentioned.

The issue clearly is why retrofit to an existing helicopter at a very high cost (especially when you consider that nearly all Flight Test of the aerodynamic controls will have to be reflown).

I am yet to be convinced after being involved in initial dicussions on the system in question for EH101.

Si

[NickLappos]

Si Clik,

The idea in the EH-101 in going to FBW/HEAT is that they must recover payload, as the aircraft is particularly poor in payload, and has little growth due to rotor limits. I have read that they can gain about 1000 lbs of payload if the system pans out. This would be a nice improvement.

[Graviman]

"The weapons can point the aircraft, so the targeting accuracy and time to shoot drop to half that when the pilot is unaided."

This kind of gets to the heart of the arguement about FBW - what is its intended pupose at the design stage? For general heli use, investment/maintenance cost is the biggest controlling factor.

Maybe control authority should be broken down in various categories:

1. Control augmentation - power enhancement of conventional controls. Achievable through hydraulics or e-servo, since the context is FBW systems.

2. Stability Augmentation - attitude feedback into control system. The simplest mechanical method is the Lockheed gyro (light/training heli), but can become fully digitised if power augmentation also required (using 1.)

3. Flight Augmentation - velocity/climb/position control directly overides pilot input (either parallel or series). This would require e-servos, and a simple electronic controller (including positional sensors).

4. Efficiency augmentation - active trimming, to reduce vibration or fuel burn. Higher harmonic control and any other "tricks" are used to allow a more efficient aircraft.

5. Performance Augmentation - this allows the pilot to explore the limits of the machines envelope, without actually risking the safety of the aircraft. This would require much more sophisticated computer modelling of flight dynamics.

6. Function Augmentation - this allows the pilot to put in high level instructions. The most extreme example is the "destination" command where the heli then completes the entire power-up/take-off/fly/descend/land (pilot can overide at any point).

Clearly the last two augmentation modes in a machine would also demonstate vast advantages as a weapons platform.

Hmmm, good thread

Mart