Please explain spoiler terms

[Robi77 0]

The B-747 and other aircrafts have different spoiler options,for example armed,disarmed and then there is a DET position as well.What are all these different settings used for ?I noticed that when I press the "/" key the spoilers depoly and retract regardless of the settings above.Therefore I am somewhat confused and hope somebody can explain.ThanksHubert Werni

[Flamin_Squirrel 71]

They may be called different things, but essentially they work in the same way for the majority of aircraft.Their purpose is to destroy lift, which is useful in two sitiations.1) Remove lift generated by the wings on touch down to allow the full weight of the aircraft to settle onto its wheels, allowing the brakes to work to their full potential. Spoilers depolyed full up on the ground are known as ground spoilers.2) It allows you to slow down more quickly at a given altitiude, descend at a faster rate at a given speed, or a combination of both. Speed brakes, basically. It's not safe in flight to use ground spoilers in flight, so in flight their upwards movement is limited, which is what the DET (detent) is about.Disarmed: Spoilers are down and will stay that way in any situation.Armed: Spoilers are down but will deploy automatically to the ground position on touch down.

[MorsAbAlto 19]

Speedbrakes and spoilers are two different systems. Speedbrakes are used to add drag, while spoilers are use to kill lift, although on many airplanes the only distinction between spoilers and speedbrakes is the angle at which they deploy relative to the airfoil and their position on the wing. There are several different types of speedbrakes and spoilers, depending on the aircraft type. Spoilers are deactivated for safety reasons when airborne.The ARMED setting will cause the spoilers and speedbrakes to deploy to the fully extended position under certain circumstances, like a rejected take-off or on touchdown.DET means "detent". There is a "Flight Detent" to limit the extension of the speedbrakes in-flight to a certain amount. Pulling the speedbrake lever any further can result in heavy vibrations and damage to the aircraft, the worst case being loss of control. This is why there is some kind of locking mechanism to prevent this. You can override it on some aircraft, but this should only be done in emergency situations.I am not sure, but I think using the spoiler key in-flight will only cause the speedbrakes to extend to the flight detent.

[yos233 1]

As far as I know, "/" will deploy full spoilers, everything. To arm your spoilers so they auto-deploy on touchdown you press Shift+/.

[Flamin_Squirrel 71]

Speedbrakes are used to add drag, while spoilers are use to kill lift.

In flight that amounts to the same thing.

[MorsAbAlto 19]

In flight that amounts to the same thing.

I am not a qualifyied pilot in the real world, but from my basic arm chair theoretical knowledge I tend to disagree. The opposing force of lift is weight. The opposing force of drag is thrust. So the addition of drag does not necessarily mean a decrease in lift and vice versa. It's possible that the speedbrakes on e.g. a 737 do also decrease lift, due to their position on top of the wings, but airplanes like the Fokker 100 and many military jets have their speedbrakes near the tail (think F16).

[Tabs 2,790]

Anything you stick up into the airstream going over the wings destroys lift because it's disrupting the normally smooth airflow while creating drag.I've always thought that "speedbrakes" is the term when drag devices exist that aren't attached to the wings - for example on an F/A-18, it's a big panel that pops up on the rear of the fuselage that purely creates drag, it doesn't affect the airflow over or under the wings.

[Flamin_Squirrel 71]

The opposing force of lift is weight. The opposing force of drag is thrust.

Not that simple. If you're pitched up, you'll have a portion of the weight component acting to slow the aircraft. So you can pitch an aircraft up to slow it down faster, but then you'll climb (or reduce your descent rate). You can prevent the aircraft from doing so by deploying spoilers, so in effect increasing drag and decreasing lift have the same effect.

[MorsAbAlto 19]

If you're pitched up, you'll have a portion of the weight component acting to slow the aircraft.

How so?

So you can pitch an aircraft up to slow it down faster, but then you'll climb (or reduce your descent rate).

I find that to be consistent with what I wrote so far. The aircraft in your example is slowing down because of both, the increased drag at high AOAs and simultaneous reduction in forward thrust, as the thrust vector moves downwards.

...so in effect increasing drag and decreasing lift have the same effect.

No, I disagree. A decrease in lift will result in a "downward" momentum. An increase in drag will result in a "backwards" momentum. While it is true, that the speedbrakes/spoilers of certain airliners do affect both parameters, I believe the above statement to be incorrect.My last post was a little inaccurate, since the devices on the top of the wings of aircraft are really called spoilers. But since they are only extended to a certain angle when airborne, their main purpose is to act as speedbrakes when in the air. Apparently there is no such thing as a "pure" speedbrake on most larger aircraft. They are more common on regional aircraft (Fokker 100, BAe 146) and fighter jets.

[FACA 0]

There is a special feature for Boeing aircraft too. When you do high bank turns, the inner spoilers of the wing going down opens to help coordinate turns, so the pilots won´t have to apply rudder all the time. I heard this from a pilot. Has anyone else heard this?

[yos233 1]

It happens in FSX default, AND PMDG. I'd say it really happens.

[StevenHPerry 20]

Sorry, squirrel, but weight isn't affect by pitch or angle of attack. Weight is gravity. If you stand up, your weight goes to the ground "through" your feet. If you lay down, your weight still pulls you to the ground, not skidding along the ground in the direction of your feet.Centripetal force is the force you are perceiving to swing your weight away from vertical down. But even in a perfectly flown loop with a constant velocity, your "g-force" sensed will be 2gs higher at the bottom than it is at the top.FACA - those are "spoilerons". They're for roll control primarily, not yaw. There may be "rudderons" but the only thing I can think of that qualifies would be on the space shuttle.Steve Perry[edit for name, as is usual for me]

Edited September 25, 2010 by StevenHPerry

[Tabs 2,790]

There is a special feature for Boeing aircraft too. When you do high bank turns, the inner spoilers of the wing going down opens to help coordinate turns, so the pilots won´t have to apply rudder all the time. I heard this from a pilot. Has anyone else heard this?

The spoilers assist in roll control at slow speeds as far as I know, not to help coordinate turns - coordinating turns has to be done by the rudder, the spoilers basically just act as large ailerons in that mode.

[WestAir 2,522]

No, I disagree. A decrease in lift will result in a "downward" momentum. An increase in drag will result in a "backwards" momentum. While it is true, that the speedbrakes/spoilers of certain airliners do affect both parameters, I believe the above statement to be incorrect.

Alex,As an aside, it sounds (from my usually incorrect perspective) that you're trying to separate the four forces into two separate interactive groups. As you know, all four forces acting on the aircraft (Lift/Drag/Weight/Thrust) interact with each other. I think in the analogy about an increase in drag resulting in a backwards momentum, the decrease in speed will decrease the airflow over an aircraft's airfoils and decrease lift. Effectively, that drag manages to slow down the aircraft and kill lift. I believe that is what they were trying to say when they said speed brakes killed lift regardless of if it was just a measure of countering the thrust/drag relation.

[asdf987 0]

A decrease in lift (due to spoilers) will be counteracted by the pilot/autoflight system by increasing angle of attack. This increases induced drag. You shouldn't really analyse thrust/drag alone, as all forces acting upon the aircraft are relevant. When your speedbrakes increase drag, you may compensate for this by decreasing pitch, thus AoA and downwards velocity.It is far easier to consider the aircraft's state by its energy state.. While in flight, you have kinetic energy (in the form of momentum) and gravitational potential energy (in the form of altitude). In straight and level flight, the engines provide sufficient energy to counteract "energy decreasing" effects of parasitic and induced drag and the lift generated by the wings counteracts vertical acceleration due to gravity. With the engines at idle and producing little/no power, there is insufficient thrust to counteract drag, thus your energy state is decreasing. You must either descend, thus using gravitational potential energy to counteract drag forces or accept a reduction in speed (less preferable in case of loss of power as you will need to increase AoA to compensate for loss of speed, which causes more loss of speed, until you finally stall), or a combination of both. By extending drag devices, you further decrease energy state.Nick Jones