Why do military jets sometimes have elevators in a depressed position when parked?Why couldn't Air Moorea Flight 1121 use pitch trim to land safely?Do aerodynamic forces and moments change aircraft pitch and yaw in the same way?Why does the Boeing 737 have a pitot tube on the tail?Why does the DHC-6 have only one set of elevator cables?Why don’t airliners use stabilizer movement to assist with large pitch control inputs?Why does the MCAS use the horizontal stabiliser rather than the elevators?
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Why do military jets sometimes have elevators in a depressed position when parked?
Why couldn't Air Moorea Flight 1121 use pitch trim to land safely?Do aerodynamic forces and moments change aircraft pitch and yaw in the same way?Why does the Boeing 737 have a pitot tube on the tail?Why does the DHC-6 have only one set of elevator cables?Why don’t airliners use stabilizer movement to assist with large pitch control inputs?Why does the MCAS use the horizontal stabiliser rather than the elevators?
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Why do they have elevators in such a position as if the joystick is pushed forward, even though there's nobody inside the cockpit?
elevator
asked 8 hours ago
stackzebrastackzebra
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Why do they have elevators in such a position as if the joystick is pushed forward, even though there's nobody inside the cockpit?
elevator
asked 8 hours ago
stackzebrastackzebra
2192 silver badges6 bronze badges
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Gravity? ........
$endgroup$
– TomMcW
7 hours ago
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$begingroup$
Why do they have elevators in such a position as if the joystick is pushed forward, even though there's nobody inside the cockpit?
elevator
asked 8 hours ago
stackzebrastackzebra
2192 silver badges6 bronze badges
$endgroup$
Why do they have elevators in such a position as if the joystick is pushed forward, even though there's nobody inside the cockpit?
elevator
elevator
asked 8 hours ago
stackzebrastackzebra
2192 silver badges6 bronze badges
asked 8 hours ago
stackzebrastackzebra
2192 silver badges6 bronze badges
asked 8 hours ago
stackzebrastackzebra
2192 silver badges6 bronze badges
asked 8 hours ago
stackzebrastackzebra
2192 silver badges6 bronze badges
asked 8 hours ago
stackzebrastackzebra
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2192 silver badges6 bronze badges
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Gravity? ........
$endgroup$
– TomMcW
7 hours ago
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$begingroup$
Gravity? ........
$endgroup$
– TomMcW
7 hours ago
$begingroup$
Gravity? ........
$endgroup$
– TomMcW
7 hours ago
$begingroup$
Gravity? ........
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– TomMcW
7 hours ago
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1 Answer
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It generally means that the hydraulic actuator (power control unit) driving the surface has an "idle" facility that allows fluid to move internally between the two sides of the actuator piston, or just circulate in the pressure/return lines, and when unpressurized it acts more or less like a hydraulic damper even though the input spool valve is at its "null" (no command) position.
The result is that when unpressurized it's free to move (although damped) and if gravity wants to pull the surface in one direction it'll do so. As soon as hydraulic pressure is applied, it'll snap back to whatever position is being called for by the input system.
Sometimes you have PCUs that are "non-idling" and when unpressurized they are hydraulically locked which is only broken when there is a control input to the controlling spool valve. Such surfaces stay where they are even when the hydraulic pressure has bled off, unless you move the controls to break the hydraulic lock.
On the CRJs, the elevator PCUs are idling, and the elevators sag when unpressurized. The aileron PCUs however are non-idling, and the ailerons don't sag when unpressurized. If you try to move an RJ's aileron when its hydraulics are off, it is totally rigid.
answered 7 hours ago
John KJohn K
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1 Answer
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1 Answer
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$begingroup$
It generally means that the hydraulic actuator (power control unit) driving the surface has an "idle" facility that allows fluid to move internally between the two sides of the actuator piston, or just circulate in the pressure/return lines, and when unpressurized it acts more or less like a hydraulic damper even though the input spool valve is at its "null" (no command) position.
The result is that when unpressurized it's free to move (although damped) and if gravity wants to pull the surface in one direction it'll do so. As soon as hydraulic pressure is applied, it'll snap back to whatever position is being called for by the input system.
Sometimes you have PCUs that are "non-idling" and when unpressurized they are hydraulically locked which is only broken when there is a control input to the controlling spool valve. Such surfaces stay where they are even when the hydraulic pressure has bled off, unless you move the controls to break the hydraulic lock.
On the CRJs, the elevator PCUs are idling, and the elevators sag when unpressurized. The aileron PCUs however are non-idling, and the ailerons don't sag when unpressurized. If you try to move an RJ's aileron when its hydraulics are off, it is totally rigid.
answered 7 hours ago
John KJohn K
43.9k1 gold badge78 silver badges152 bronze badges
$endgroup$
add a comment
|
$begingroup$
It generally means that the hydraulic actuator (power control unit) driving the surface has an "idle" facility that allows fluid to move internally between the two sides of the actuator piston, or just circulate in the pressure/return lines, and when unpressurized it acts more or less like a hydraulic damper even though the input spool valve is at its "null" (no command) position.
The result is that when unpressurized it's free to move (although damped) and if gravity wants to pull the surface in one direction it'll do so. As soon as hydraulic pressure is applied, it'll snap back to whatever position is being called for by the input system.
Sometimes you have PCUs that are "non-idling" and when unpressurized they are hydraulically locked which is only broken when there is a control input to the controlling spool valve. Such surfaces stay where they are even when the hydraulic pressure has bled off, unless you move the controls to break the hydraulic lock.
On the CRJs, the elevator PCUs are idling, and the elevators sag when unpressurized. The aileron PCUs however are non-idling, and the ailerons don't sag when unpressurized. If you try to move an RJ's aileron when its hydraulics are off, it is totally rigid.
answered 7 hours ago
John KJohn K
43.9k1 gold badge78 silver badges152 bronze badges
$endgroup$
add a comment
|
$begingroup$
It generally means that the hydraulic actuator (power control unit) driving the surface has an "idle" facility that allows fluid to move internally between the two sides of the actuator piston, or just circulate in the pressure/return lines, and when unpressurized it acts more or less like a hydraulic damper even though the input spool valve is at its "null" (no command) position.
The result is that when unpressurized it's free to move (although damped) and if gravity wants to pull the surface in one direction it'll do so. As soon as hydraulic pressure is applied, it'll snap back to whatever position is being called for by the input system.
Sometimes you have PCUs that are "non-idling" and when unpressurized they are hydraulically locked which is only broken when there is a control input to the controlling spool valve. Such surfaces stay where they are even when the hydraulic pressure has bled off, unless you move the controls to break the hydraulic lock.
On the CRJs, the elevator PCUs are idling, and the elevators sag when unpressurized. The aileron PCUs however are non-idling, and the ailerons don't sag when unpressurized. If you try to move an RJ's aileron when its hydraulics are off, it is totally rigid.
answered 7 hours ago
John KJohn K
43.9k1 gold badge78 silver badges152 bronze badges
$endgroup$
It generally means that the hydraulic actuator (power control unit) driving the surface has an "idle" facility that allows fluid to move internally between the two sides of the actuator piston, or just circulate in the pressure/return lines, and when unpressurized it acts more or less like a hydraulic damper even though the input spool valve is at its "null" (no command) position.
The result is that when unpressurized it's free to move (although damped) and if gravity wants to pull the surface in one direction it'll do so. As soon as hydraulic pressure is applied, it'll snap back to whatever position is being called for by the input system.
Sometimes you have PCUs that are "non-idling" and when unpressurized they are hydraulically locked which is only broken when there is a control input to the controlling spool valve. Such surfaces stay where they are even when the hydraulic pressure has bled off, unless you move the controls to break the hydraulic lock.
On the CRJs, the elevator PCUs are idling, and the elevators sag when unpressurized. The aileron PCUs however are non-idling, and the ailerons don't sag when unpressurized. If you try to move an RJ's aileron when its hydraulics are off, it is totally rigid.
answered 7 hours ago
John KJohn K
43.9k1 gold badge78 silver badges152 bronze badges
answered 7 hours ago
John KJohn K
43.9k1 gold badge78 silver badges152 bronze badges
answered 7 hours ago
John KJohn K
43.9k1 gold badge78 silver badges152 bronze badges
answered 7 hours ago
John KJohn K
43.9k1 gold badge78 silver badges152 bronze badges
43.9k1 gold badge78 silver badges152 bronze badges
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Gravity? ........
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– TomMcW
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