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Guest JTH

Difference between flaps and spoilers?

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Guest JTH

Excuse me if this is an extremely novice question but in an aircraft like the PMDG 744 (my favourite payware aircraft) what exactly is the difference between flaps and spoilers? As far as I understand it, both serve the same purpose - a small piece of metal sticks up on the wing and "spoils" the airflow, therefore causing drag and slowing the plane down. So why have two? Why not just have either flaps or spoilers? I'm very interested to see what the answer to this is as it's something I've been thinking about for a while now. Thanks in advance, Greg.

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Flaps do create drag (especially at full extension), but they also create lift (to help the aircraft get into the sky at lower speeds). Spoilers (on top of the wing) create drag... and _negative_ lift... so they really do the opposite thing to flaps ;)If you stick your hand out of the window of a moving car and simulate flaps and spoilers... it's easy to see the result. If your car is moving across the page from right to left and you do this "" your hand will be forced up by the airstream. If you do this "/" (if you are flexible enough), it will go down.... or break off :(Hope this helps.Cheers.Q>P.S. Children... don't try this without the supervision of your parents... or where there are laws against sticking your hands out of moving vehicles :(

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Guest JTH

Great explanation, that has really cleared it up - thanks! By the way though in your analogy about the car should it not be the other way around? The way I think of it now it seems that holding your hand like this / would cause it to go up (like flaps), and holding it like would cause it to go down (like spoilers). Let me know.By the way, why are flaps used on landing instead of spoilers? If spoilers cause the plane to descend and lose speed would the not be preferable during approach to flaps, which cause the plane to slow but gain altitude?Thank you once again.

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Guest andyman

>Great explanation, that has really cleared it up - thanks! By>the way though in your analogy about the car should it not be>the other way around? The way I think of it now it seems that>holding your hand like this / would cause it to go up (like>flaps), and holding it like would cause it to go down (like>spoilers). Let me know.>No Mr. Qavion is correct re-read his statement and try to visualize.I like to think of flaps having one purpose(ignoring the fact that they create drag) which is to create lift so you can fly at lower speeds, this way you can slow down on your approach and use less braking on the runway.Spoilers will slow you down very quickly, and you already need power on approach to keep the plane going, so extending spoilers will only cost your airline more money(fuel burned). Also it will decrease lift requiring a higher pitch to maintian lift. This will probably result as a very firm touchdown.EXPLAINATION: Extending speed brakes require you too raise the nose 2-3 degrees to maintain VSI. When it comes time to flare you would need another 3 degrees,{pose as a tailstrike risk too] and the speed will decay quickly when you idle the throttle. This will increase the descent rate further. Now yes, some people will know some things in this post are wrong, but I'm just trying to provide a simple explaination.

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Hi, just a supplement, another function of the flap is to allow the aircraft to pitch the nose down (is it calls angle of attack can't remember) for a fews degree without increase the airspeed nor V/S, as a result, the crew can have a better view for approach..bb

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"The way I think of it now it seems that holding your hand like this / would cause it to go up (like flaps), and holding it like would cause it to go down (like spoilers). Let me know."I think you get what I mean... it's just that your hand is moving in the wrong direction across the page(arm and, hopefully, car direction) <---- _____ (hand and arm) = flaps. Relative wind direction = -----> "By the way, why are flaps used on landing instead of spoilers? If spoilers cause the plane to descend and lose speed would the not be preferable during approach to flaps, which cause the plane to slow but gain altitude?"Actually, spoilers _can_ be used for slowing in the air... and they are used after landing. Unfortunately, spoilers tend to be very "dramatic" so they should not be used close to the ground (or you will land very heavily). The airplane already has a natural tendency to fall out of the sky (because of gravity).... spoilers amplify this effect.Also, using spoilers with lots of flaps tends to put excessive strain on the wings. Thankfully, your 744 will remind you not to use your spoilers at very low altitudes or with landing flaps set.Hope this makes sense.Cheers.Q>

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>Great explanation, that has really cleared it up - thanks! By>the way though in your analogy about the car should it not be>the other way around? The way I think of it now it seems that>holding your hand like this / would cause it to go up (like>flaps), and holding it like would cause it to go down (like>spoilers). Let me know.>>By the way, why are flaps used on landing instead of spoilers?>If spoilers cause the plane to descend and lose speed would>the not be preferable during approach to flaps, which cause>the plane to slow but gain altitude?>>Thank you once again. Flaps help to maintain a lower than flaps up speed ;-) and on approach to landing this is critical otherwise you would never reach VREF speed other than when your plane started to drop out of the sky. Spoilers would be a real problem close to the ground or having them depolyed while performing a go around but these are not issues with flaps. ...............Randy J. Smith................A PROUD MEMBER OF THE PMDG BETA TEAM[h4]Evolution is a process that results in heritable changes in a population spread over many generations[/h4]


Randy J Smith

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Hi Greg,During an approach, the spoilers are armed, but not raised. When the aircraft settles onto the runway, the spoilers are raised to disrupted the airflow and keep the aircraft firly on the ground. I think it also provides better tire traction on the runway.Ken.

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Flaps basically alter the chord of the aerofoil (wing). It would be easier to understand through drawings, but flaps will increase the curvature of the wing, thus increasing the wing's lift Coefficient (Cl).This in turn dramatically increases Lift generated by the wings, which finally allows for flights in lower airspeeds. If you did not lower flaps for approach you'd never be able to land at 150 kt, for example, because you would be way past stall speed. So flaps decrease stall speed and increase lift. 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. However, flaps also increase drag generated by the wings and lower the critical angle, which can be practically witnessed in Boeing aircraft: once you lower flaps a Pitch limit indicator appears on the PFD. Best Regards,Victor Limahttp://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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To add a couple more points: think about the name spoilers for a minute. Doesn't it sound like something that spoils? Well, that's the spoiler's business. It spoils the airflow on the wing's upper surface which creates a dramatic reduction in lift and also a dramatic increase in drag, thus used to lower and brake an airborne aircraftContrary to what some people posted here flaps were not designed to increase drag and reduce airspeed. That's the spoiler's business. Flaps were created to provide extra lift during approach and takeoff settings thus allowing for slower speeds (making landings smoother, using less runway etc) The extra draf created by flaps' deployment is pretty much collateral damage. I realize thi is kind of hard to grasp but if you know how a wing works to create lift for flight you will easily grasp how flaps and spoilers work!Best Regards,Victor Limahttp://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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Guest JTH

Thanks for the many replies. I think I get it now. Thanks!

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Guest airspace

Nice flying jumbo jet animation, Steve -Darren:)

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Thanks...not mine tho just borroewed. Buggered if I know why it came out twice though.....still getting to grips with this signature thing.CheersSteve


Cheers

Steve Hall

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Yeah others basically got it right:Spoilers - designed to disrupt the normal airflow over the wings, create drag, and rapidly slow the plane or increase the rate of descent.Flaps - designed to increase lift at slower speed by changing the camber (curvature) of the wing. Flaps do result in a slowing effect, but that is not what their purpose is, it's totally about increasing lift so as to not have ridiculously high V speeds that would risk blowing the tires etc.


Ryan Maziarz
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