MD-11 Roll Control Wheel Steering

[DAL2728]

How does the RCWS work on the MD-11? Is this an option that each carrier can utilize or is it something that's always on?

How does RCWS differ from "normal" aileron control with the control wheel? I guess what I'd like to know is what are the benefits and/or downsides of RCWS on the MD-11 and when would you NOT want this option?

Thanks,
Shane

[backofthedrag]

By now , I should know better than to poke my nose into this forum without being totally knowledgeable of the subject, however , as you have had no replies yet , I'll try to keep the ball rolling.
Not rated on the MD11 but I flew the DC10 for a few months twenty years ago.
We had Control Wheel Steering which was pilot selectable ON or OFF . Everyone tried it once, but , as I recall no-one ever tried it twice.
With CWS ON , the autopilot handled the flight controls : the pilot input, instead of via the FCU ( or whatever it was called then ) was via the control column in terms of pitch and roll. If you wanted ten degrees pitch-up you set it via the control column and then left it. The autopilot would maintain the set pitch attitude til you changed it . Similarly with the bank angle.
I am not sure what the reason was for this fit. I have flown Airbus for the last thirteen years . We were taught basic jet flying is about power and pitch attitude , yet nowhere on the FCU can you set pitch - speed or vertical speed will alter pitch but not set it directly. Similarly you cannot set bank angle directly via the FCU.
Perhaps now someone who knows what they are talking about will respond to help you and if they blow me out of the water at the same time - so be it!

[finncapt]

Flew the DC10 about 15 - 20 years ago.

A copilot used it once in very severe turbulence and I seem to recall that was what it was for.

I also recall not being very impressed with it.

If I'm wrong I stand corrected.

[NSEU]

I think we didn't take up the option of CWS on our newer 767's because of a reliability/cost issue. The more complex a system, usually the more likely it is to break down... so extra cost.

[muduckace]

Alike some of the above posters I will claim a humble stance on this reply. The DC-10 and most Airbus airframes I have experience with (A300/310) have a CWS option other than pitch/profile. The MD-11 to my knowledge only has an "auto flight mode". I believe the A/P to be all or nothing in this airframe.

[Flightmech]

I believe RCWS was an MD-11 option. All of the MD-11s I have worked on don't have it. I believe muduckace has also confirmed this.

[Spooky 2]

You are correct as it was an option on the MD11 and not many opted for it. Today I would venture to guess that most if not all operators have deactivated this feature had it been included in the original delivery. HUCK who posts here occasionally would certainly be a good resource for this converation. Calling HUCK, come in please.:}

[ChristiaanJ]

Echo from the past.....
Concorde had CWS, but only as part of its "belt and braces and a piece of string" design approach. It catered for the case of a mechanical jam of the control column or control wheel.

CJ

[DAL2728]

I have used CWS mode on a KC-10 simulator and found it to be a very pleasant experience. I do understand how CWS works on the DC-10 but I am curious if the application on the MD-11 is any different. The name alone implies that perhaps it does not include a pitch control mode (roll control wheel steering).

I also recall seeing in a thread a long time ago that it wasn't something you could switch on or off, and that it was either autoflight mode or autoflight disengaged which reverted to RCWS. I'm looking into the validity of that statement as well.

[Huck]

A HA! A small piece of the aviation world that I can attest to....

I have flown MD-11's with the CWS activated, at Gemini. I fly them now with the CWS deactivated, at FDX.

CWS on the MD11 is only in roll (as I recall). CWS on the DC10 is in pitch and roll.

The theory is that you are inputting your desired attitude into the autopilot - using the aircraft. I roll 10 degrees bank, let go and it holds ten degrees bank.

The only folks I've heard that didn't think it was a complete waste of avionics rack space were tanker guys on the KC10. Evidently it made it much easier to fly with pointy jets attached to your tail.

The downsides were many. The biggest one to me was this insane breakout force to move the ailerons manually - something like three pounds. No way to finesse the aircraft at all.

And there wasn't an approved way to turn it off. I used to just turn off the "paddle" switches and kill all the LSAS with it - until I got a letter from the chief pilot.....

A nasty system, but perfectly in line with McDonnell's philosophy of a push-button airplane. After many many accidents, tailstrikes and close calls we've now as an industry come to the realization that an MD-11 must be flown - as in hand-flown - by real pilots with all their stuff in one sock....

[DAL2728]

When you say breakout force, what does that mean? 3lbs is a lot of force? I've got a trigger pull on a pistol with a 3lb pull but it seems awfully slight to me!

[Huck]

Let's say you're hand-flying and you want to roll the aircraft slightly.

You have to exert a certain amount (it was more than a little) to "break out" of the CWS mode and allow you to move the controls manually.

Then when you returned to neutral, the CWS would kick back on.

The end result was the gracefulness of a hog on ice.

And here's the truly sad part - the MD-11 is a fine-flying aircraft, with wonderful, light controls. But because the CWS was so clunky, pilots would just leave the autopilot on rather than hand-fly it. Thus their piloting skills slipped into disuse.

I got so frustrated I'd slap down the AFS switches and kill the CWS whenever I shot a visual. My argument was that as PIC I had to maintain currency in all phases of automation - and CWS was most certainly deferrable. I needed to make sure I could fly without it.

One of my F/O's (who never ever clicked the autopilot off above 200') turned me in to the standards folks, and they told me to stop......

Oh, I forgot, the only other way to kill CWS was to hold down the autopilot disconnect switch on the yoke. But that made my thumb go to sleep. I tried to use a rubber band but that didn't work!

[DAL2728]

I can definitely see now why the RCWS on the MD-11 wasn't an ideal situation!

How does the aircraft perform in roll without CWS? Doesn't it want to maintain close to the same bank angle when you center the control wheel anyway?

[Huck]

It does fine - all U.S. certified aircraft have to be stable in roll. Like I said, it's a lovely hand-flying airplane. I have no idea why CWS was installed without a way to turn it off.

I had a former Douglas engineer tell me they originally were going to remove the power levers in the MD-11. It would be the world's first "push-button" throttles - you were either in speed mode or max/mct/climb. The MD test pilots rebelled and got them to rethink it.

But it says alot about their philosophy - and again points to why so many of these things end up in a ball. Pilots were told (I was told, by two different companies) to maintain the highest level of automation at all times....

[muduckace]

To say a little more about MDC philosophy, selecting AFS off is to select "AFS OVERIDE" suspecting as the only option to holding the disconnect button. The aircraft was designed for autoflight, given lSAS/ELF and flap limit remained enguaged unless manually disabled.

Never flew with any MD-11 drivers WOA/Gemini who had a big deal with it. The only time I saw a CWS breakover was during windshear.

Biggest gripe I heard from the guys (and felt) was it's inability to slow down when light. We used to do S.A. ops flower runs and often flew one way freight. I remember many tooth filling/vibrating desents when light.

Here at the purple Mecca as well now now and miss the old experience but enjoy the stability of this corperate giant.

It sux to get a inbound AFS call here on a L.P., when in the old world I could have seen and experienced the failure first hand.

[fr8doggie]

Originally posted by HUCK:



"A nasty system, but perfectly in line with McDonnell's philosophy of a push-button airplane. After many many accidents, tailstrikes and close calls we've now as an industry come to the realization that an MD-11 must be flown - as in hand-flown - by real pilots with all their stuff in one sock...."

I didn't know you 'Bama boys wore socks.:)