Rudder deflection when aircraft on stand

[Coopz67]

Why do most of the aircraft I see at the gates have the rudder deflected what looks to be full left. Is it a required lock position when parked or something else ?
Thanks
Coopz 67

[HEATHROW DIRECTOR]

....and why did DC-9s have one elevator fully and one fully down??

[hatchetman]

without hydraulic power applied to the flying controls the rudder is subject to whichever way the wind is blowing

[Coopz67]

As simple as that !

Thanks

[Bullethead]

Coopz67,

The control surfaces are very finely balanced and as hatchetman says they blow with the wind when there is no hydraulic power available.

HD,

Dunno about the DC9 elevators but the B707 ones did the same, one balanced the other and if one went up t'other went down, again dependent on the wind.

Regards,
BH.

[HEATHROW DIRECTOR]

OK, but not being too clued up I thought both elevators would be linked so that they moved in unison.

[Wizofoz]

HD,

It's actually a certification requirement that flight controls have independent activation. In the event of one control column becoming stuck, they can be de-linked so the un-stuck one has control of one elevator and one set of ailerons/roll spoilers.

[HEATHROW DIRECTOR]

Wiz.. Ok, many thanks for that. Resolved about 30 years of curiosity!!

[Dairyground]

I always thought that there were locks to prevent the control surfaces flapping about and damaging themselves on widy days - and that there had been the occasional accident caused by pilots attemptong to take off with controls still engaged (light GA, rather than transport - perhaps there is a difference there).

One thing that always puzzeled me: parked Comets always had flaps fully extended, but on other types they are fully retracted, even before vacating the runway.

[HEATHROW DIRECTOR]

Dairyground. I think if you check this and subsequent pages you'll find a few Comets with their flaps retracted, although a few do have them out..
Air-Britain : DH.106 (http://www.abpic.co.uk/results.php?q=DH.106&fields=type&sort=latest&limit=50)

[wiccan]

And BR31 Britannias [sp?] when they engaged reverse pitch, the elevators would move in opposit direction....[left UP, right DOWN....then change :confused:]

[etsd0001]

707 elevators were 'free floating' the Control column's were connected to elevator servo tabs that moved the main surface aerodynamically. To assist with this, fwd of the elevator surface they were large balance panels that help the surface movement. When the elevator was moved, the air pressure on one side of the balance panel reduced as the air was drawn out by an increased gap between the stabiliser and the L/E of the elevator. The higher pressure on the other side of the panel then assisted in elevator movement

[Ixixly]

DairyGround: Most of the locks you refer to in GA are placed on by the pilot outside the aircraft, quite literally like a block of wood that stops them moving. Thats why its bigger problem in GA because a pilot has forgotten to do a proper walk around and hasn't spotted in and then hasn't checked all control surfaces free and moveable before take-off!! Or the other common type is simple a rod that goes through the control column that stops the control column moving and thusly the control surfaces. Depends on the aircraft and which surface it is.