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Faro
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Control Wheel Steering

Sun Aug 19, 2007 11:44 pm

Does anyone know why the Control Wheel Steering mode in autopilots is going out of fashion? I may be wrong but I believe the 737 series is the only airliner in production which still offers it.

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SlamClick
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RE: Control Wheel Steering

Mon Aug 20, 2007 12:07 am

Well, maybe because nobody ever uses it. I can only recall one occasion when the guy I was flying with used it. It was such an amazing event that we had a thirty minute conversation about it. Turns out he really only uses it because nobody else does. It is good for starting a conversation.

As a philosophical matter I'm not sure it is even a good idea to have it. It can produce an illusion that someone is flying the airplane when no such thing is true. CWS only "points" the airplane. It will cheerfully fly beyond your clearance limit, into restricted airspace, into another airplane or into a mountain. All with the pilot hands-off and thinking he's got it under control. Truth is, it does little more than trim does in a Bonanza.

Most of us prefer to actually fly the airplane unless we are in fully automated flight. CWS is like the worst of both: You don't get to fly and nobody is flying.

When in automated flight, I think most of us prefer to have both lateral and vertical modes engaged.
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Faro
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RE: Control Wheel Steering

Mon Aug 20, 2007 12:19 am

lol Slam, sounds like a case of not eating the cake you didn't have in the first place...

I was intrigued because the thing was used cinematographically once way back, in Airport '75. They had the terror-stricken stewardess slowly turning big fat bank dial on the 747's CWS to make it turn to avoid hitting a big bad mountain top...

I wonder whether it had a historical utility once, maybe on the piston-driven airliners of old.
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Jetlagged
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RE: Control Wheel Steering

Mon Aug 20, 2007 1:25 am

In many ways, a FBW Airbus in Normal Law is like a non-FBW aircraft in CWS mode, only it's a much more pleasant experience.

I recall jump-seating in a 747-200 where the F/O was being checked out. The Capt made the F/O fly a few minutes in CWS just so he got the feel of it. Then words to the effect of "that's probably the first and last time you'll ever want to do that in a 747". Having tried it in the simulator I know exactly what he meant.
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s.p.a.s.
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RE: Control Wheel Steering

Mon Aug 20, 2007 6:14 am

How does this system work, by the way?

In my, perhaps wrong, understanding the crew makes AP inputs via the control yoke.

RS
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SlamClick
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RE: Control Wheel Steering

Mon Aug 20, 2007 6:32 am

Quoting S.P.A.S. (Reply 4):
crew makes AP inputs via the control yoke.

Pretty much it. It provides stability in pitch and roll. If you release the yoke with less than about 6 degrees of roll it will roll wings level and fly that way. You can arm an altitude while in CWS pitch and it will capture and hold that altitude with a change in annunciation status (it will show "alt hold")

I think it might also be possible to arm a lateral nav intercept in CWS roll mode. Been a long time since I flew it or taught it and I don't want to dig up my out-of-date manual just to make the post look more authoritative. If someone is current on a Boeing with the system they can correct me.

[Edited 2007-08-19 23:34:05]
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RE: Control Wheel Steering

Mon Aug 20, 2007 6:51 am

The MD11 uses continously Roll CWS during manual flying... it is kind a helpful if you get used to it once. But only in ROLL mode...

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RE: Control Wheel Steering

Mon Aug 20, 2007 7:08 am

Thanx to one and all for your comments and insight.

Faro
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RE: Control Wheel Steering

Mon Aug 20, 2007 8:30 am

Actually, when Karen Black dials in a heading, that is NOT CWS. That is regular autopilot command HDG mode. In CWS, the autopilot actuates the control surfaces and the control wheel/column tells the autopilot to pitch up/down and bank left, right or level the wings.
 
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RE: Control Wheel Steering

Mon Aug 20, 2007 8:53 am

Older piston airliners with Bendix or Sperry autopilots did not have CWS.

CWS in the Lockheed TriStar is quite useful for low altitude turns such as were required at the old ATH airport, for noise abatement....especially when one is having a bad hair day.

With the TriStar, CWS could be selected when on the ground, ready for action when airborne...except on those select airplanes that were on the British (or associated) register (BA, GF etc....quite likely a UKCAA requirement, just like scarfed pitot tubes and reduced Mmo, not forgetting recovery speed brakes, of course.
 
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RE: Control Wheel Steering

Mon Aug 20, 2007 9:13 am

Despite the explanations above, I'm still unsure exactly what CWS is. If you're using the control wheel, how is that autopilot? What exactly is the form of automation that occurs in CWS?
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RE: Control Wheel Steering

Mon Aug 20, 2007 12:11 pm

It's basically attitude (pitch and bank) hold. You use the control wheel to adjust the pitch and bank angle. When the control wheel is released the autopilot holds that attitude.
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RE: Control Wheel Steering

Tue Aug 21, 2007 12:37 am

Quoting WILCO737 (Reply 6):
The MD11 uses continously Roll CWS during manual flying... it is kind a helpful if you get used to it once. But only in ROLL mode...

WILCO737 (MD11F)

On the UPS MD11s it was deactivated.

Jan
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RE: Control Wheel Steering

Tue Aug 21, 2007 1:49 am

Quoting Jetlagged (Reply 11):
It's basically attitude (pitch and bank) hold. You use the control wheel to adjust the pitch and bank angle. When the control wheel is released the autopilot holds that attitude.

Sounds rather Airbus-y to me!
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RE: Control Wheel Steering

Tue Aug 21, 2007 5:57 am

Quoting MD11Engineer (Reply 12):
On the UPS MD11s it was deactivated.

Didnt know that, we still use it and its not bad once you get used to it...

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troubleshooter
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RE: Control Wheel Steering

Tue Aug 21, 2007 7:22 pm

Quoting Faro (Thread starter):
I may be wrong but I believe the 737 series is the only airliner in production which still offers it.

The EMB135/145 have CWS installed.
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qslinger
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RE: Control Wheel Steering

Wed Aug 22, 2007 6:41 am

Quoting Faro (Thread starter):
Control Wheel Steering

Here is a question for u guys, What is a CWS??? What does it look like? 

[Edited 2007-08-22 00:06:11]
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RE: Control Wheel Steering

Wed Aug 22, 2007 8:56 am

Quoting Troubleshooter (Reply 15):
The EMB135/145 have CWS installed.

It is referred to as TCS on the ERJ's... "Touch Control Steering"

it does the following:

- Allows manual maneuvering of the airplane without disengaging the autopilot. The airplane may be maneuvered to any desired pitch attitude while the TCS button is pressed. When the button is released the following occurs:
1. Primary servos reengage.
2. The computer synchronizes itself to the new pitch attitude and vertical mode and maintain it.
3. Lateral control is returned to the previously selected lateral mode (return to the later mode is filtered to prevent rapid maneuvers).
- After glide slop capture in APR (approach) mode with the autopilot engaged, if the TCS button is pressed and released, the autopilot will resume the controls and turn the airplane to the ILS center beam.
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Jetlagged
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RE: Control Wheel Steering

Wed Aug 22, 2007 11:23 pm

Quoting Qslinger (Reply 16):
Here is a question for u guys, What is a CWS??? What does it look like?

Here's what Control Wheel Steering looks like:


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Click here for bigger photo!

Photo © Juan Carlos Guerra - APM



Look at the autopilot engage "paddles" on the glareshield mode control panel. AP B is in CMD (command) mode, under that is CWS position, then OFF. Moving the paddle down to CWS engages this mode. The paddle will also automatically trip to CWS under certain conditions, for example: the command mode is invalid.

Basically CWS is an alternative to AP Manual mode. The pilot uses the control wheel rather like when hand flying, pull or push the column to adjust pitch angle, turn the wheel to adjust bank angle. When the desired attitude is achieved, the pilot releases the control wheel and the AP maintains the current attutude. However when bank angle is close to zero when it controls to wings level, on the assumption that that is what is required.

AP Manual is similar except rather than using the control wheelas the input, a separate manual pitch and turn control is installed. Both AP Manual and CWS are attitude hold modes, the only difference being how the attitude is adjusted.

The picture below shows a 747-200 which has manual AP controls, though some 747-200s had CWS. The turn knob is on the centre pedestal, just aft of the throttle quadrant. There is a pitch wheel either side of the turn knob. Note the autopilot MCP engage paddles are labelled CMD/MAN/OFF in this case.


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Photo © Andrea Buzzacchi



Many modern autopilots do not have CWS or manual modes. The basic modes in such cases are usually vertical speed and heading.
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