rjpieces
Posts: 6849
Joined: Mon Nov 24, 2003 8:58 am

What Controls The Spoilers?

Sun May 23, 2004 2:21 pm

I was wondering if the spoilers are activate manually upon touchdown, or are they programmed to do so?

Any help is appreciated. Thanks.
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QantasA332
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Joined: Sat Dec 13, 2003 5:47 pm

RE: What Controls The Spoilers?

Sun May 23, 2004 2:22 pm

I was wondering if the spoilers are activate manually upon touchdown, or are they programmed to do so?

In the case of most commercial/large aircraft, the spoilers are armed to deploy automatically on landing...

Cheers,
QantasA332
 
NWA742
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RE: What Controls The Spoilers?

Sun May 23, 2004 3:38 pm

On almost all commercial aircraft, the pilots will arm the spoilers right after deploying the landing gear.

To do this, it just requires pulling the spoiler handle back just a hair to the arm position. Whenever the rear wheels touch down, there is probably a sensor to let the system know that the aircraft is on the ground, and the spoilers will deploy automatically.

Just watch a cockpit video of a landing and you can see the spoiler handle go all the way down by itself on touchdown.



-NWA742
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MD11Engineer
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RE: What Controls The Spoilers?

Sun May 23, 2004 6:58 pm

You´ve got to distinguish between the flight spoilers, which are either controled by a control wheel input through a spoiler mixer and assist the ailerons (coming up on the downwing side during a turn in direct ratio to the control wheel deflection), the speed brakes (controled by the speed brake handle, come up during flight symetrically, often the same surfaces as the flight spoilers, just a different control input. Actually, the control wheel input and the speedbrake input are often overlaid. E.g. I´ve got the speedbrakes out at maximum flight deflection, now I´m turning my control wheel, the upper wing spoilers will actualy retract). The amount of deflection is usualy limited in flight. Taking the MD-11 as an example, the maximum deflection for lateral control (spoilers to assist ailerons is 60° assymmetricaly, as speedbrake 30° symmetricaly and as ground spoiler (to kill the residue lift on landing) 60° symmetricaly. The extension of the speedbrakes is inhibited mechanically if the flaps are extended (I´ve heard from pilots that you can, theoreticaly, deploy the speedbrakes first and then the flaps, but the plane would turn into a brick). There is also a mechanically interlock from the nose gear ground shift mechanism, which prevents full symmetrical deployment of the spoilers if the nose gear strut isn´t compressed (means you can´t pull the speedbrrake lever into the ground spoiler / 60° position unless the nose gear is on the ground. For automatic ground spoiler deployment there exists an electric actuator under the center pedestal, which, if the spoilers are armed by pulling the handle up out of the "down" detent, will move the speedbrake lever back on landing (or a rejected take-off), to 30° on landing the moment there isd a wheel speed input from the rear wheels of the MLG boogies and to 60° once the nose wheel touches the ground.
There is no space in here now to get into the details of the groundspoiler control logic, just to tell you, it gets inputs from the FADECs, flap position transmitter, wheel speed sensors, ground sensing relays and the radio altimeters.

Jan
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rjpieces
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Joined: Mon Nov 24, 2003 8:58 am

RE: What Controls The Spoilers?

Mon May 24, 2004 2:17 am

Thanks for the responses guys!  Smile
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N766UA
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RE: What Controls The Spoilers?

Mon May 24, 2004 4:05 am

Mind you if the spoilers are not armed the pilot simply has to pull the handle back to deploy the spoilers. Or, in some cases, push a lever down. Either way it's a simple mechanism just like the flaps or gear.
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DeltaGuy
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RE: What Controls The Spoilers?

Mon May 24, 2004 8:30 am

Great reply MD11Engineer! Always learning something in TechOps

Some aircraft are weird about spoilers...on the Mad Dog, you have to have the gear down and locked beforeyou can arm the autospoilers. I understand you could technically do the reverse on a Boeing, but it's not standard practice?

Usually there's an interlock or something to prevent inadvertant deployment...i.e. squeezing the lever to pull in the handle, unlocking the lever...

DeltaGuy
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