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Bruce
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Pressure On The Yoke, Rudder

Tue Apr 20, 2004 12:49 am

When the plane is on the ground parked, there is a certain amount of pressure (usually not much) required to move the yoke, either left/right or pitch (move it forward/backward) and also when you step on the rudder pedal.

Now, when in flight, and with increased speed and pressure of air against these control surfaces, does that increase the amount of physical pressure required to move the yoke by hand and rudder in the cockpit?

bruce
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FredT
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RE: Pressure On The Yoke, Rudder

Tue Apr 20, 2004 1:43 am

Yes, it does. At high speeds, it can feel as if the stick is moulded into a block of concrete! Quite unnerving, but also good as you would be very likely to overcontrol had this not been the case.

In aircraft with powered controls, much work goes into recreating this. It is called q-feel, and essentialy makes sure that the controls get stiffer along with the (square of the) increasing airspeed, just as they would have had the controls been all manual. When the q-feel system goes out, you have a real problem. You still have control, but you really have to be careful not to overcontrol.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
goboeing
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RE: Pressure On The Yoke, Rudder

Tue Apr 20, 2004 1:50 am

Bruce,
There are also some things that are done on aircraft that help the controls get "heavier" as the airspeed increases. They are called anti-servo tabs and do the opposite of servo tabs. Like a trim tab, they are connected to the trailing edge of the horizontal stabilizer or stabilator and move in the same direction as it does. This creates more resistance as the pilot moves the controls. A servo tab does the opposite.

Nick
 
Klaus
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RE: Pressure On The Yoke, Rudder

Tue Apr 20, 2004 5:36 am

The Airbus sidestick has no feedback whatsoever, as far as I know;

The flight laws take care of an automatic adaptation to different speeds, however: Stick deflection commands a certain g-force in the respective direction, and it´s up to the flight computers to determine the control surface deflection required to satisfy the request.

So the same deflection of the sidestick will result in less elevator/aileron deflection at higher speeds, but will achieve a comparable g-load.
 
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Bruce
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RE: Pressure On The Yoke, Rudder

Tue Apr 20, 2004 6:07 am

I see. I wondered about this because when i moved controls on a parked plane I thought, if they dont get "heavier" it would be so easy for the pilot to even bump it and send the plane spiraling out of control at altitude!

does anyone know exactly how much force is required on a typical stick at cruise altitude/speed? i.e. pounds of force?

bruce
Bruce Leibowitz - Jackson, MS (KJAN) - Canon 50D/100-400L IS lens
 
phollingsworth
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RE: Pressure On The Yoke, Rudder

Tue Apr 20, 2004 6:16 am

The increase in control input forces with speed only occur for reversible controls. Most of the large transports and fighter aircraft have irreversible controls; therefore, unless there is an artificial feedback loop to compensate for this, control input forces would remain constant.
 
ArmitageShanks
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RE: Pressure On The Yoke, Rudder

Tue Apr 20, 2004 6:20 am

Just how hard are the average controls to move in say a 737, 777, or CRJ? I was recently in a 727 sim and they seems incredibly hard to move. I could not fly easily with one hand. On the contrary the 747-400 seemed very easy to manipulate with one hand.
 
PhilSquares
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RE: Pressure On The Yoke, Rudder

Tue Apr 20, 2004 6:49 am

If my memory serves me correctly, it's been about 4 years since I've flown the 320, but below 50' or so there is nose down trim applied to simulate some control force for the flare. I can't remember the exact parameters, but I do remember that in the flight control laws.
Fly fast, live slow
 
Klaus
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Philsquares

Tue Apr 20, 2004 7:00 am

I can only speak from earlier discussions of the subject and from what I´ve read so far; As far as I remember, "flare law" would primarily disable the autotrim feature so that after finally getting the mains down, the plane wouldn´t be in a nose-up trim with too little authority to get the nose gear to the ground properly... Could that have been it?
 
FredT
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RE: Pressure On The Yoke, Rudder

Tue Apr 20, 2004 7:00 am

Some positive elevator pressure is usually wanted for the final part of the approach... I always trim a little nose-heavy myself for better control and there's a similar function in many FBW fighters...

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
A3204eva
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RE: Pressure On The Yoke, Rudder

Wed Apr 21, 2004 4:18 am

Yes there is pressure (as you've probably guessed by now). It feels very different on the ground and in the air

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