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Robi77

Please explain spoiler terms

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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

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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.

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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.

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

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Speedbrakes are used to add drag, while spoilers are use to kill lift.
In flight that amounts to the same thing.

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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).

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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.

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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.

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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.

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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?

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

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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]

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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.

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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.

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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

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Sorry, squirrel, but weight isn't affect by pitch or angle of attack. Weight is gravity.
If you pitch up/down from straight and level your trust/drag vector will have a component acting vertically, at which point weight, lift drag and thrust will all have an effect on eachother.

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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.
Precisely! The decrease in lift is caused by the decrease in speed (and thus airflow), not the increase of drag. These are two different things. If you counteract the increased drag by adding more thrust, nothing happens. Please note that I am refering to the aircraft as a whole and not just the airfoil, where drag will affect lift at a given speed (L/D ratio).
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.
I don't. They are still four distinct forces that affect the aircraft in different ways. Still, the opposite of drag is thrust.
It is far easier to consider the aircraft's state by its energy state..
Yes, it is easier because it a more generalized approach, that does not factor in aerodynamic effects on the aircraft much. It's more relevant in military aviation, where you see all kinds of funny maneuvers away from the horizontal attitude and where energy conservation is important. Since you will normally not see acceleration significantly exceeding 1g on an airliner or bank angles in excess of 45 degrees, I feel it does not matter much in civil aviation.
If you pitch up/down from straight and level your trust/drag vector will have a component acting vertically, at which point weight, lift drag and thrust will all have an effect on eachother.
Yes, but unless the lateral acceleration is exceeding 1g, weight will only work in the vertical, from what I understand. I do not understand, how it would slow down the aircraft.It would be nice if a rated pilot could chime in to this discussion. By the way, what's your real name Squirrel? I always think of some sort of cartoon, when I read your nickname...

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Gents,This is a complicated issue and all points so far have relevance. As i understand it, as pointed out the four forces of the aircraft act together resulting in the actual state of the aircraft. An increased component of drag will require an increase in thrust to maintain a given airspeed, should thrust not be altered then the aircraft will slow and eventually increase the AOA. Lets remember that an aircraft needs two things to fly, AOA and RAF when these two hit the sweet spot the wing produces lift so yes the AOA does directly affect the weight in the sense it is required to produce lift to counteract the weight. once the critical AOA is reached the wing stalls and the aircraft will no longer produce lift, so drag has a relationship towards lift in that respect in the sense that the wing has reached the critical AOA. If you descend the AOA changes therefore not producing as much lift for a given weight component (assuming the airspeed has not changed), remembering that when we descend the weight component comes into play and less thrust is required to maintain a given airspeed if we add drag then we can maintain a faster rate of decent even with no thrust component applied because the aircraft can be pitched down and the weight can act as a force to replace thrust. Basically if you increase drag thrust must be applied to maintain straight and level flight, since we would not logically use speed brakes in straight and level flight being you could reduce thrust to slow the aircraft down anyway. You would logically only be using speed brakes in a decent which would therefore increase drag and if you are looking to slow the aircraft on its given decent path without altering power then speed brakes would assist that (because drag has been increased). That being said we can also reduce thrust and apply drag (speed brakes) which would give a much steeper decent path being that lowering the pitch attitude will increase the effect weight has on the aircraft in the sense AOA is reduced, therefore lift is reduced (given the airspeed remains constant) therefore as the nose lowers more and more, the lift component lowers due to AOA and the weight then plays its part.I am a rated pilot however im not sure if what i said needs any clarification but im more then happy to elaborate on any part of it, My apologies if its come out scrambled! (its getting late!) Fly safe Captains-Dan Parker

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Yes, but unless the lateral acceleration is exceeding 1g, weight will only work in the vertical, from what I understand. I do not understand, how it would slow down the aircraft.It would be nice if a rated pilot could chime in to this discussion. By the way, what's your real name Squirrel? I always think of some sort of cartoon, when I read your nickname...
Lateral? That's side to side, and doesn't apply to this discussion.And you don't have to be accelerating for weight to affect the lift/drag couple. See image below.force_vector_climb.gifMy names Jordan, and I'm a private pilot if that counts.

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Sounds like the stuff we learn for the PPL isn't that evident after all...
The funny part is that several of us who replied have hundreds of flight hours, aeronautical degrees, and/or time in turbine-powered aircraft. :(

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Looks like the frame of reference is what has us all on different pages.I like to think that my football teams is moving the ball down the field for a touchdown, rather than the football is just "being" while the field moves from right to left. Potatoe, potato.Let's get Dan Quayle's opinion.Steve Perry

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Let's get Dan Quayle's opinion.Steve Perry
Steve,"Verbosity leads to unclear, inarticulate things." - Dan Quayle. :( . You hit the nail on the head, though.

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Lateral? That's side to side, and doesn't apply to this discussion.And you don't have to be accelerating for weight to affect the lift/drag couple. See image below.force_vector_climb.gifMy names Jordan, and I'm a private pilot if that counts.
Hey Jordan.as you can tell I am not a native speaker, so a wrong expression might slip in here and there. Sorry for that. I guess what I meant was the vertical axis. Okay, so after staring at the diagram for 10 minutes I can see your point. In fact I had a very similar image in my mind. It seems I was right about weight only acting downwards (in an absolute sense). But somehow I had a hard time to realize how this affects the thrust/drag axis when the pitch changes. Actually it makes a lot of sense now. So, thanks for clearing that up.

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Spoilers "spoil" laminar airflow over lift generating devices. They may/will also create dragAir brakes or speed brakes do not spoil flow over LIFT generating devices but only create dragStraight%20Face.gif

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