Hello everyone,I would like to know if the tail spoiler and under fuselage spoiler perform differently from wing spoiler. Is the primary purpose of wing spoiler to reduce the lift but not reduce speed?As I know some aircraft approach with their tail spoiler or fuselage spoiler extended, like the Fokker 28, F16 and many others. WHY ??? Isn't this practice inefficient? I do believe there is a strong reason to behind.http://www.airliners.net/open.file/735963/L/Moreover, is the tail spoiler, fuselage spoiler a pure device for speedbrake purpose only? Generate Drag but not kill any lift?Anyone can share their experience of the different characteristics of these spoilers when in operations?? Any pros and cons?Thank you for reading!www.alkit.nethttp://alkit.fotopic.net

As you say really.Speed breaks add drag to reduce the speed, but can also used to make the aircraft more controlable. Jets have two specific problems on approach: low drag and slow engine spool times. Creating drag lowers minimum power and min drag speed on the drag curve, reduces speed and allows the engine to maintain a high RPM from which TOGA power can be quickly extracted. If the engines were allowed to idle on approach it would take too long to get full power and the aircraft would probably touch down before being able to execute the go around.Spoilers are used instead of ailerons in the cruise to roll the aricraft. The roll spoilers are part of the lift dumper set of spoilers on the wing. When lift is dunmped on touch down all the spoilers extend. When the aircraft is banked in the cruise, only one or two of the spoilers are exteneded. If the aircraft wants to bank right, then the right roll spoiler is extended by the required amount. That reduces lift on that wing causing that wing to drop a little. The reason ailerons can be used is that the forces involed at M.75 are large, they also cause the wing to twist and can cause wing tip flutter which can be fatal.

You see Alkit ..isnt AVSIM fantastic! :)Thankyou for the info Kefuddle ...very interesting!re: "Speed breaks add drag to reduce the speed, but can also used to make the aircraft more controlable. Jets have two specific problems on approach: low drag and slow engine spool times. Creating drag lowers minimum power and min drag speed on the drag curve, reduces speed and allows the engine to maintain a high RPM from which TOGA power can be quickly extracted. If the engines were allowed to idle on approach it would take too long to get full power and the aircraft would probably touch down before being able to execute the go around."I would like to try this with the Fokker-100 in the sim! :)I presume real world pilots use increments of the air brake on approach and not just full on as in most airbrake gauges....?regardsEdhttp://forums.avsim.net/user_files/101978.jpg

>>Thankyou for the info Kefuddle ...very interesting!My pleasure. It is useful for me to help with this information so that my ground school knowledge doesn't become stale whilst I continue with my training. I have also learned one or two things myself here when others chip in and add more detail.>>I presume real world pilots use increments of the air brake on approach >>and not just full on as in most airbrake gauges....?Most aircraft have a range of possible settings. The pilot will be looking to achieve an engine N1/EPR setting in combination with a descent rate and a speed. I imagine that the speedbrakes on 146s must come in pretty handy on the 5.5degree glideslope into London City airport.I am merely a trainee so am not really upto speed on detailed operational procedures yet. My understanding is that in normal approach scenarios (3deg glideslopes) flaps and gear are sufficient for approach. But occasionally speedbrakes will be used to help stabilise the approach, especially if asked to maintain a higher than normal speed by ATC.The usual use of speedbrakes will be used on engine idle to speed the descent rate without increasing speed. FWIW, professional pilots will usually endeavour to descend with the engines idling to save fuel (and hence money).

Thank you Kefuddle for your detail answer!!That's about spooling time of the engine! Is that why this spoiler extend approach method only used by "older" type of jetliner? I guess the modern engine have a better spooling performance.Moreover, I heard of many simmers said the nose go up when wing spoiler out (in various different types of plane). Is this true? Why it will push your nose up when it actually reducing the lift force? Will the same happen to spoiler underneath fuselage.Ed: good recommendation to put me here for this question. ^_http://alkit.fotopic.net

>I presume real world pilots use increments of the air brake on>approach and not just full on as in most airbrake gauges....?>That all depends on the aircraft.Some aircraft have airbrakes which extend in stages, but most do not and it's all or nothing.Some may have 2 automatic stages, one which functions in the air and another one (with larger deflection) for use on the ground.

>I would like to know if the tail spoiler and under fuselage>spoiler perform differently from wing spoiler. Is the primary>purpose of wing spoiler to reduce the lift but not reduce>speed?>yes, that's their primary purpose. The reduction of speed due to increased drag is a secondary effect.>As I know some aircraft approach with their tail spoiler or>fuselage spoiler extended, like the Fokker 28, F16 and many>others. WHY ??? Isn't this practice inefficient? I do believe>there is a strong reason to behind.>These aircraft have generally high idle power (especially military aircraft) and a high approach speed.Braking in the air on final approach reduces the rollout distance. As someone else said, long spoolup times for the engines may also be a factor as with such engines you may want to approach with more power than the speed you want needs.>Moreover, is the tail spoiler, fuselage spoiler a pure device>for speedbrake purpose only? Generate Drag but not kill any>lift?>yes, and therefore it's not a spoiler at all but it's called an airbrake.

>That's about spooling time of the engine! Is that why this>spoiler extend approach method only used by "older" type of>jetliner? I guess the modern engine have a better spooling>performance.>many modern engines do have shorter spoolup times yes. But still you may want to keep power up as long as possible (and therefore be a little fast on the approach).For example if you're coming in with your Fokker 100 and there's a 747-200 coming up close behind (which has a higher approach speed than you would like to use) you may be told to stay fast by ATC. You'd then extend the airbrake on final to slow down to final approach speed more quickly than you'd do normally.>Moreover, I heard of many simmers said the nose go up when>wing spoiler out (in various different types of plane). Is>this true? Why it will push your nose up when it actually>reducing the lift force? Will the same happen to spoiler>underneath fuselage.>Lift goes down so the autopilot pushes the nose up to compensate and prevent the rate of descent from increasing.This also causes your speed to drop which is the reason many simpilots use spoilers in the air...So the nose up attitude when using spoilers is not an effect of the spoilers but rather a reaction of the (auto)pilot to counter the loss of lift by compensating for it, thus achieving another effect.

I was under the impression that roll spoilers (spoilerons) located closer to the fuselage on the wing were used at lower airspeeds because that is where the airflow is concentrated especially with swept wings. At high speeds (cruise) the minimaslly sized ailerons (because of the reasons you state) have the most effect because the airflow is concentrated toward the outer wing portions and the high speed airflow only requires minimal control surface area.Do I have this backwards?

Ronzie,I think it depends on the aircraft. Many actually have two sets of ailerons, inboard and outboard, with the inboard ones helping the roll spoilers. The inboard ailerons may be used to act as flaps (flaperons). I think the 727 has inboard, outboard ailerons and spoilers.My understanding is that you are sort of correct in sating that most of the airlow is near the wing root at low speeds. I think that really only applies to the extent you express when the wing is stalling.In the normal range of flight consitions, the outboard ailerons provide best response and control at lower speeds because of the significant secondary yaw effect with roll on swept wing aircraft (generally speaking). I too think it is true to say that, in the cruise, the outer portions create most lift. I suppose this is why the outer aileron needs to be restricted or locked in the cruise because of the torsional effect on the wing. My assumption is that the designers must think that inboard ailerons and/or roll spoliers do the sufficiently allowing them to build a thinner more efficient wing rather than one that needs to withstand the kind of twisting forces described.I think the inboard ailerons are sometimes needed to supliment the roll spoilers in the cruise because when a spoiler is extended a little bit, it actually can increase the lift on the wing, so the inboard aileron starts the process and the spoiler extends to its first lift reducing position to help. Again a situation that may not be the case on some aircraft.There is another problem with roll spoilers. As they maybe on the same system as speedbrakes, if the speedbrakes are fully extended, the roll spoilers then have to reduce the speed brake effect as in order to roll the aircraft right, a left spoiler has to retract slight to increase the left wings lift. Inboard ailerons help with this situationt too.BTW, when I say inboard aileron, it is usually positioned outboard of the flaps.I am rather short on specifics here. Maybe somebody else can add some aircraft specific detail?