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747-400 Elevator Feel

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747-400 Elevator Feel

Old 18th Sep 2000, 10:59
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Question 747-400 Elevator Feel

For all the 400 experts out there....

The 400 elevator Feel Computer/ Feel Unit are designed to provide artificial feel forces to the control column to simulate changes in both airspeed and horizontal stabiliser position.

I can see how the amount of effort required to move the stick would increase as the aircraft flew faster, but what effect does stabiliser position have on the stick... Does it make it harder/easier to move... or somehow changes the neutral/centre position of the stick?(Looking at the design of the computer, I can't see how it can do the latter. Also, the tests listed in the Boeing Maintenance Manual do not offer any insight into Elev Feel ops).

Thanks for any input.
Old 18th Sep 2000, 13:35
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The feel force is controlled by the feel computer, and is exerted by the feel actuator acting through the feel unit.

In each of the two groups of components in the computer, a Qc-sensing(pitot) bellows acts through a leaf spring upon a pivot linkage to displace a force balanced slide valve. A cam, connected by linkage to the horizontal stabilizer, acts through another leaf spring in opposition to the Qc-sensing bellows.

The sum of these two forces, together with hydraulic return pressure, loads the force balance valve to pressurize the associated chamber of the feel actuator. The force balance valve closes when the force exerted by feel pressure on the opposite end of the valve balances the input forces. The feel pressure acts on the feel actuator rams to apply a force which resists rotation of the feel unit cam.

As the cam is connected to the aft quadrant, this resistance plus feel unit centering spring tension resists control column displacement from neutral.

[This message has been edited by CCA (edited 18 September 2000).]
Old 18th Sep 2000, 16:33
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Thanks for the insight re opposing forces, QCA.

I take it from this, that the column resistance ONLY changes, not the column neutral point(?). Also, is the force required to pull the stick backwards the same as it is to push it forwards for any given speed/trim setting?

Old 19th Sep 2000, 08:59
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Thumbs up

Yep, that's it - the stick neutral position never changes. You move it, trim it then put it back. Feels odd for the first hour or so, then you forget about it.

I don't know about stick force vs push or pull - it just feels right. Sort of like an ad. for sports shoes!!!
Old 20th Sep 2000, 05:44
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"Feels odd for the first hour or so, then you forget about it."

Thanks, Mustafa....
I gather from this sentence that this is totally different from a light aircraft with absolutely no "real" feedback from the elevators back through the hydraulic actuators to the stick.... As one gentleman put it, like a computer joystick[Albeit with adjustable springs].


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