Difference between flaps and spoilers?

[Qavion 19]

"And another very important aspect of landing flaps is the increase in your approach angle - meaning they will permit you to descend at a greater angle than would be possible without flaps."Why would you want to descend at a greater angle? The glidepath is only 3 degrees.Are we talking about nose up or nose down?RgdsQ>

[cowpatz 243]

Handy to get down onto the slope if you have been held high. Without the drag the airspeed would increase significantly. Speed brake is also not that effective at the slower speeds.Steve

[Qavion 19]

"Without the drag the airspeed would increase significantly. Speed brake is also not that effective at the slower speeds."But doesn't this make Victor Lima's argument, that flaps were not designed for drag, rather mute?In simming, I use flaps to generate drag when I'm high, too ... but don't you get rapped over the knuckles in the real world by check pilots for using flaps to slow you down?Don't airlines emphasise gear and spoilers for this kind of thing?Cheers.Q>

[Guest ZOTAN]

It may be completely different in a B744, but in my C-152 (Real world) flaps are used also when we come in to high. By dropping the flaps down, we can increase our angle of descent without increasing airspeed. Thats the definition of flaps on the Written PPL exam also.

[cowpatz 243]

You are quite right when you say that flaps should not be used to slow the aircraft down as this causes premature flap wear. However if you look at a descent at min flap up speed clean, or with flap out, you will notice a significant difference in descent ability between the two. At low weights the speeds are well below the max placarded speeds. The gear can be used and is very effective, however if used at too high a speed it is also very noisy and can be quite disconcerting to the passengers. In my experience using speedbrake below about 220 kts just shakes the aircraft and that is about it. Getting flap out allows the aircraft to be slowed and have a steeper approach angle. Try descending down the slope clean at min flap up speed (gera up)and then try it again at the same speed with flap 5 or 10 (depending on weight)also with the gear up. You will find that flying it clean will cause the airspeed to increase.RgdsSteve

[Guest jumpjet]

OK ....... the next topic for discussion is ...... SLATSHeheh! ;)CheersGraham

[victorlima01 2]

>"Without the drag the airspeed would increase significantly.>Speed brake is also not that effective at the slower speeds.">>But doesn't this make Victor Lima's argument, that flaps were>not designed for drag, rather mute?>>In simming, I use flaps to generate drag when I'm high, too>... but don't you get rapped over the knuckles in the real>world by check pilots for using flaps to slow you down?>>Don't airlines emphasise gear and spoilers for this kind of>thing?>>Cheers.>Q>>>Indeed it does. Except that there's real world ops for large jets and then there's real world ops for small props. In the plane I fly in the real world, I often land using 15 degrees of flaps. However, if I'm rather high above the ideal glidepath I'll add a couple more degrees of flaps. Like someone else said here, that will permit me to increase my descent angle so I will intercept the ideal glidepath without gaining extra speed. But notice I didn't add the extra flaps to slow down, but rather to increase my descent angle. Like I said earlier, drag created by flaps is pretty much collateral damage but it does come in handy. I descended to itercept my ideal approach path without gaining any speed. The whole reasoning behind flaps is the following. They are not there to slow you down. They're there to provide extra lift in takeoff and landing settings and this in turn provides for slower speeds. There is a mathematical formula for lift which shows this very clearly:L=CL*S*V(squared)/2Where L is lift, CL is lift coefficient, S is wing surface area and V is speed. Basically, flaps increase the CL thus increasing lift. Since you increased CL you can decrease speed a little while mainting adequate lift, which in turn won;t make you stall... see?In large turbojets you don't operate flaps by feel, like you do in piston single engine acft. There's a procedure, and the flaps are used specifically to increase your descent angle and to allow for slower approach speeds. I know what your next question is going to be: "But you just said flaps were not made to slow us down!" Think about it for a minute. You extended flaps in your jumbo jet, that created some considerable drag which wasn't there, which in turn helps slow the acft down. BUT, it also increased Lift significantly (remeber, it's number one purpose), which now allows the airplane to fly at a slower speed without stalling.As for you second question, you are absolutely right. Wanna slow down? Extend your gear or your speedbrakes, but don't rely on your flaps. Better yet. Wanna be a little more smooth and graceful? Plan your approach ahead and don't rely on any of the above but adequate throttle use to slow down. That will score you some points with in your checkride!I sincerely hope this has cleared up a thing or two for you Greg, but I'm horrible at expressing these aviation thingys better. I'm no engineer after all... just a private pilot who thinks too much! :-coolPlus I think Qavion really explained it better with his first post!Best Regards,Victor Limahttp://www.precisionmanuals.com/images/forum/800driver.jpg

[Guest hlm65]

The standard ILS G/S is 3

[Qavion 19]

"if I'm rather high above the ideal glidepath I'll add a couple more degrees of flaps. Like someone else said here, that will permit me to increase my descent angle so I will intercept the ideal glidepath without gaining extra speed. But notice I didn't add the extra flaps to slow down, but rather to increase my descent angle. Like I said earlier, drag created by flaps is pretty much collateral damage but it does come in handy."I'm not totally convinced, Victor.To the novice aerodynamicist and Newtonian physicist(like me), it seems that if you wanted to increase your descent angle, you would simply point the nose down.However, if you point the nose down, the aircraft is going to build up speed.How do you slow down your aircraft (if your engines are already at idle)?As far as I can see, the only way to do this is to create more drag.How do you create extra drag if (say) you can't extend the gear or use spoilers? You can't.The flaps have to be creating the drag to do this. Isn't this what "induced drag" is? http://selair.selkirk.bc.ca/aerodynamics1/Drag/Page6.htmlDrag is the natural consequence of lift. More flaps = more lift ...or am I getting in (water), way over my head here? :)Cheers.Q> (Drowning not waving)

[victorlima01 2]

>"if I'm rather high above the ideal glidepath I'll add a>couple more degrees of flaps. Like someone else said here,>that will permit me to increase my descent angle so I will>intercept the ideal glidepath without gaining extra speed. But>notice I didn't add the extra flaps to slow down, but rather>to increase my descent angle. Like I said earlier, drag>created by flaps is pretty much collateral damage but it does>come in handy.">>I'm not totally convinced, Victor.>>To the novice aerodynamicist and Newtonian physicist(like me),>it seems that if you wanted to increase your descent angle,>you would simply point the nose down.>>However, if you point the nose down, the aircraft is going to>build up speed.>>How do you slow down your aircraft (if your engines are>already at idle)?>>As far as I can see, the only way to do this is to create more>drag.>How do you create extra drag if (say) you can't extend the>gear or use spoilers? You can't.>Hi Qavion. I couldn't agree more with what you said, specially the last line. If you increase Lift necessarily drag is also increased. After all these two forces are not really two seperate entities, they are vectors of one single force. This drag created by the flaps certainly is important to help slow the aircraft, as you pointed out in your example. However, you should not used it primarily for that reason, that is my point. Flaps are used to allow for flight in lower speeds, and they can be used as a means to get there (in aircraft such as the one I fly in) but you will be frowned upon if you use your flaps as airbrakes in boeings, and I think it isn't healthy to think of flaps as airbrakes. Maybe this last statement of mine cannot be held as true for light airplanes with fixed gear and no spoilers. Perhaps in this scenario you are more correct than I am in that flaps are often used as speedbrakes. However I never thought of them that way. I always thought of them as a means to increase my descent angle without increasing speed. The obvious flaw with that reasoning and continuing to defend it is that something that allows for a greater descent angle without any increase in speed is pretty much an airbrake! So I concede this point to you, but I will bravely stand by my layman's notion that flaps shouldn't be thought of as airbrakes (although they are), but rather as lift "generators"I'm getting way over my head here and a little confused now... An aeronautical engineer could certainly aid us in settling this matter!>The flaps have to be creating the drag to do this. Isn't this>what "induced drag" is? >>Drag is the natural consequence of lift. More flaps = more>lift I learned that induced drag is drag generated at the wingtip due to the creation of a vortex. This vortex is created because the air under higher pressure under the wing tends to escape towards the wing's upper side where static pressure is lower. However, the more you increase the difference between static pressures under and over the wing, the more induced drag you'll have. Flaps generate more induced drag since they increase lift which in turn decreases static pressure over the wing.Anyway, this has been a very productive discussion, but I think I should stop for now because it's starting to go to places I can't follow. If I add anything else here it will be pure speculation. This is as far as my limited knowledge will carry me! :)Best Regards,Victor Limahttp://www.precisionmanuals.com/images/forum/800driver.jpg

[Guest Dean Cross 4C]

Hey, If I can just add my $0.02; bare in mind I don't fly them, I just fix 'em :)High Lift Devices :: Flaps The purpose of the flaps is to reduce take-off and landing distances OR in the case of take-off carry a greater weight from the same distance. These distances depend on the speed which are flown, there are minimum values given per regulations and these are universally defined as 1.2 times the stalling speed for take-off, and 1.3 times the stalling speed on landing. The stalling speed is determined by CLmax (the maximum lift you can get from the aerofoil in any configuration). To get the lowest possible distances the CLmax has to be as high as possible becuase you want the maximum amount of lift at low speeds. Generally considered to be the main factor in determining CLmax is the camber of the wing. The chord of an airfoil is the imaginary straight line drawn through the airfoil from its leading edge to its trailing edge. The camber of an airfoil is the curve of its upper and lower surfaces. This curve is measured by how much it departs from the chord of the airfoil. Tests have shown that by increasing the camber the you increase your lift at all Angles of Attack ((AoA) Angle of attack (α, Greek letter alpha) is a term used in aerodynamics to describe the angle between the airfoil's chord line and the direction of airflow wind, effectively the direction in which the aircraft is currently moving) and increas CLmax. Therfore, for tkaeoff and landing you want a high-cambered wing, but this causes high drag at cruising speed and nose-down pitch which is undesirable at high-speed - G&T slipping off your tray and onto ones lap. What aircraft designers do is they have a low-camber aerofoil for high-speed flight and modify the aerofoil camber for take-off and landing. How do you modify the camber. Trailing edge (TE) flaps. Flaps are a hinged portion of the trailing edge of the aerofoil that deflect downward so-as to produce an increased camber. TE flaps are suitable for low-speed flight but for high-speed as in most commercial transports a Leading Edge High Lift Device is used i.e slats, slots, kreuger flaps, etc. I am not going to go over all flaps designs, so lets concentrate on the B747-400 design. The TE Flap is what is known as a Fowler Flap. The Fowler flap moves rearwards AND down as oppose to a slotted flap that onlu moves down e.g Embraer 145. The B747-400 has a tripple-slotted fowler flap which means the flap is divided into three sections which allows airflow to re-energise the upper airflow allowing for a greater deflection of air. The fowler flap increase wing area and camber which gives us greater lift, an increse in CLmax but also gives the least drag of all flaps because of the decresed thickness:chord ratio of the flap itself. Coming onto what Victor Lima has said, the Fowler flap results in a change of pitch moment. Why does it do this? Due to the rearward movement of the flap and greater area the Centre of Pressure (The Center of Pressure (or CoP) is the point on a body where the sum of the total pressure acts.) moves rearwards because of the increase in the length of the cord of the aerofoil. I hope you are still following :) This can be desirable to increase visibility on landing and to allow as Victor Lima has stated an intercept of the glideslope (which, while not a dig at any pilots, I would consider bad practice - a unrushed, well-planned approach would negate the need to intercept the glideslope so hurridly; but I realise there are other factors such as ATC :). Do I redeem myself :) ) Let's talk about this drag. There are lots of types of drag, and I am not going to get into them. We know that drag opposes thrust and that it wants to slow us down. Flaps do increase drag, the greater the deflection - the more flap you put into the airflow - the more drag is created whilst giving an increase in lift. Drag increments and flap increments are not constant, the increments in drag increase as flap angles increase.Spoiler(s) Spoilers can serve to functions on an aircraft. They can provide roll control (to augment (B747-400) or replace ailerons (Airbus A300)). The spoilers are panels on top of the wings that are hinged at the front and are normally attached to the rear-spar of the wing. They are hydrualically actuated. To function as roll control the down-going wing (upward pointing aileron) deflect the spoilers up whilst the up-going wing (downward pointing aileron) do not deflect the spoilers. Let's clarify, if I want to bank to the left I command via the yoke a left movement which deflects the left-wing aileron upwards, the left-wing spoilers upwards, whilst the ring-wing aileron points downwards and the right-wing spoilers stay stowed and vice-versa. Unlike ailerons, spoilers cannot give an increase in lift, so any roll control with spoilers will cause a loss of lift on that wing. Benefits of using spoilers for roll control is they don't flutter, there is decrease wing-twist due to them being mounted further forward on the chord and you can have greater span trailing edge flaps to increase lift.Speed Brakes Speed brakes utilise the same overwing panels to increase drag when you want to slow down OR increase your vertical speed. Simply, most of your outboard spoilers will deflect upwards resulting in an increase in drag, and loss of lift which is what you want when you want to slow-down (higher-pitch) or descend (lower-pitch, greater thrust). We don't normally want to use all spoilers in flight because you can abrutly change you flight angle and you don't generally want to dump the lift at the root of the wing hence why the inboard panels aren't normally used.Ground Spoiler(s) When you land your brakes and thrust reverser provide your decelerating forces. The efficiency of your brakes depends on the aircraft having it weight on the wheels but this is reduced if your wing in still providing lift. What we want to down is get rid of all that lift when we touchdown. As soon as the main wheels touchdown we want all those panels upwards to increase drag and get rid of this lift so we can get the weight on the wheels. Generally, the spoilers deflect on different timings, generally the middle, working outwards and inwards so as not to induce a large pitch-down moment which would cause stress on your nose oleo. They still deflect darn fast, but enough to cushion the nose-wheel touch-down. If it's done correctly, the pilot should be able to hold his pitch on touchdown and the aircraft will gently lower it's nose - that's the plan. I hope that explains all the terms, as sorry guys if you already know all this I don't want to spoon feed those that know.Please feel free to correct, like I said - I'm not a pilot :)Kind Regards,Matt

[Guest JTH]

Wow, thanks for the many detailed comments.Someone mentioned slats, anyone mind explaining what they are? Also, I thought speedbrakes and spoilers were the same thing... but judging from what Dean Cross 4C says above, are speedbrakes just spoilers deployed only half way instead of all the way?Thanks in advance!

[Guest jumpjet]

I'm the one who mentioned SLATS, I threw it in there for fun!Slats perform the same function as flaps (that is, they temporarily alter the shape of the wing to increase lift), but they are attached to the front of the wing instead of the rear. They are also deployed on takeoff and landing.CheersGraham

[Guest JTH]

Cool. I assume they deploy automatically when you deploy the flaps?

[Qavion 19]

"I assume they deploy automatically when you deploy the flaps?"Never assume ;) (but you are right)The Leading Edge (LE) flaps are the first ones out during flap extension (deployment)... and the last one's in during flap retraction. From 0 to 1 unit of flaps, only the leading edge flaps extend (not all of them, however...just certain groups). At Flaps 5, you have all your leading edges extended and your trailing edges at 5 units.Unfortunately, the pictures of the LE flaps provided in the previous message don't really show the design of the 744 flaps. There are two types, Kruger (6 panels) and Variable Camber (22 panels). The Kruger panels are the inboard panels (closest to the fuselage). These are flat panels, but have a small, curved, foldout nose section (presumably to smooth the airflow).The Variable Camber panels are flat when stowed, but curved when deployed (they have thin flexible panels which are bent by the cam mechanism behind the panel). They also have a small, curved foldout nose section. The Variable Camber flaps have small air gap between the wing and the panel (when deployed).Re spoilers/speedbrake panels....The max extension of all 12 panels is 45 degrees.On the ground, all panels extend to 45 degrees if the speedbrake lever is all the way back.When the panels are being used as speedbrakes in flight, some panels do extend to the max, some go to a lower angle (assuming the "Flight Detent" on the Speedbrake Handle is working properly)... some don't extend at all in flight.However, the panels are dual function... They also serve as spoilers for roll control. Similar to the speedbrake function, some panels do extend to the max, some don't, and some don't move at all (but not necessarily the same panels that move/don't move when you move the speedbrake lever).Hope this makes sense.Cheers.Q>