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convair880mfan
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Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Tue Oct 26, 2021 4:59 pm

I have heard contradictory things about this. I know flaps create some drag while increasing lift and that the first flap settings creates a lot of lift for a small amount of drag compared to landing flap configurations relatively speaking.

Reading up on this subject I have learned that flaps lower the speed at which the wing stalls. But I am not clear if flaps can be used to actually slow an aircraft or whether they are only used to reduce the stall speed of an aircraft after it has already been slowed by other means.

A very long time ago I flew on a Boeing 707-100 series aircraft and when the flaps were lowered for landing I felt a definite deceleration. I was a teenager though and maybe the power was reduced simultaneously or something else. My memory fails me.

I think that the so to speak kosher ways to reduce speed revolve around thrust reduction, speed brake usage and elevator movement. Or am I wrong about that?

Thanks for any expert information!
 
Woodreau
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Tue Oct 26, 2021 5:10 pm

I use flaps to slow the aircraft when ATC doesn't specify a speed to fly on approach.

I'd wager it's personal technique.

But the landing gear works better

I also use the landing lights as well. Speed brake is one of the last things - i usually use it to correct vertical profile vs airspeed
 
N1120A
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Tue Oct 26, 2021 9:39 pm

It really depends on the airplane. On a fixed gear airplane, especially with a slick wing, reducing power and adding pitch only gets you so slow in a descent. Good technique is to allow the flaps to assist in slowing you. In some retractable aircraft - usually lighter ones - the gear speed is high enough that it is often your best speed brake. In others, you may need flaps to help get you to gear speed. Flaps definitely will slow the airplane down though.
 
Flow2706
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Tue Oct 26, 2021 10:46 pm

As mentioned before, it's really depending on the aircraft type. On the A320 (and I think on most other large airplanes as well) flaps will definitely increase drag and could be used to slow down from a purely aerodynamic point of view. However flap wear increases by *a lot* when extending the flaps close to the limit speed (and maintenance is expensive), so it's not good airmanship to use flaps to slow down - depending on the situation, the speed brake or gear extension is the far better choice.
 
Max Q
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Tue Oct 26, 2021 10:48 pm

Flaps should not be used to slow an aircraft, they are there to allow you to fly slower


Using flaps to decelerate is poor airmanship


That’s what the speed brake is for
 
CosmicCruiser
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Tue Oct 26, 2021 11:18 pm

Max Q wrote:
Flaps should not be used to slow an aircraft, they are there to allow you to fly slower


Using flaps to decelerate is poor airmanship


That’s what the speed brake is for

Agree, we always told not to lower flaps at their max operating speeds to prevent unnecessary stress on the flaps.
 
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Starlionblue
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Tue Oct 26, 2021 11:49 pm

As mentioned, flaps are for flying slower, not for slowing down.

The speedbrake is great for slowing at higher speeds but gradually loses effectiveness at lower speeds, at which point the gear comes in handy.


In case of a non-normal situation, however, you use what you have to best effect. For example if you have an uncontrollable fire, you'd keep the speed up until the last possible minute, drop the gear at Vle, and then definitely use the flaps to help you slow down.
 
benjjk
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 12:48 am

Just to be clear, in most cases, flaps have a maximum speed at which they can be extended. So whilst the added drag will have the effect of slowing the aircraft down, even if you wanted to rely on them you'd have to slow down by other means first.
 
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Starlionblue
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 7:56 am

benjjk wrote:
Just to be clear, in most cases, flaps have a maximum speed at which they can be extended. So whilst the added drag will have the effect of slowing the aircraft down, even if you wanted to rely on them you'd have to slow down by other means first.


Indeed. Vfe (max flaps extension speed) for Flaps one on the A330 is 240 knots. And Flaps one doesn't give you a lot of drag anyway. Vfe Flaps two is all the way down at 205 knots, and Vfe Flaps three at 186 knots.

Not tremendously useful if you want to get down from cruise speed to approach speed quickly since by the time you can use the more draggy flap settings you're almost at approach speed anyway.

On the other hand, using the speedbrake over 200 knots roughly halves the deceleration distance in level flight compared to flight idle only.
 
Woodreau
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 12:38 pm

I’ve always waited until 10kts below flap limit speed to extend the flaps as that is company procedure. For the A320 Vfe Flaps 1 is 230kts, Vfe Flaps 2 is 200kts, Vfe Flaps 3 is 185kts, Vfe Flaps Full is 177kts.

So the flaps come out at 220kts, 190kts, 175kts, and 167kts. I use the flaps to slow from there. To get to the speeds for flap extension, I plan to have a level segment or a 300-500fpm descent segment at some point in the descent to decelerate to the point where I can extend the flaps.
 
bluecrew
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 3:01 pm

The E190 doesn't have the greatest spoilers, so it's a fairly common exercise to run out Flaps 1 (15 degrees of slats and 7 degrees of flaps) to induce a bit more drag when you've got a little too much energy. VNAV has improved a little over time, but it used to love an aggressive descent right at the edge of the speed restriction set, and really wouldn't give you any time to slow down once you hit an altitude and speed restriction, besides 250/10k.

Depends on the plane I'd say.
 
DarQuiet
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 3:06 pm

I'm curious. At what purpose/reason you will use flaps to slow the aircraft? And by slowing the aircraft, it means speed is reduced.

What I know and also as mentioned here, flaps will enable you to fly at slower speed and can increase your margin before aircraft can possibly enter stall.
 
bluecrew
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 3:10 pm

Woodreau wrote:
I’ve always waited until 10kts below flap limit speed to extend the flaps as that is company procedure. For the A320 Vfe Flaps 1 is 230kts, Vfe Flaps 2 is 200kts, Vfe Flaps 3 is 185kts, Vfe Flaps Full is 177kts.

So the flaps come out at 220kts, 190kts, 175kts, and 167kts. I use the flaps to slow from there. To get to the speeds for flap extension, I plan to have a level segment or a 300-500fpm descent segment at some point in the descent to decelerate to the point where I can extend the flaps.

Do you always use flaps to slow? Technique I was taught was to bum around at Flaps 1, then extend further at the S and F speeds unless you really need the drag, but the boards are pretty effective for that if memory serves.

DarQuiet wrote:
I'm curious. At what purpose/reason you will use flaps to slow the aircraft? And by slowing the aircraft, it means speed is reduced.

What I know and also as mentioned here, flaps will enable you to fly at slower speed and can increase your margin before aircraft can possibly enter stall.

Flaps will increase induced drag in addition to providing lift, this is why we have flap extension speeds, the induced drag at speeds higher than that damages the flap.
Flaps extended during a descent, for example, generate more lift and more induced drag, but you compensate by adjusting pitch downwards. The extra drag is usually enough at the same speed and power settings to get a few extra hundred fpm in descent.

Practical examples? Late off-schedule descent into JFK with tailwinds on an airplane that doesn't like to slow down in the first place - there if you ask for some extra track miles, they're really gonna give you extra track miles. Depends on the plane, but in all aircraft at some point you'll find yourself with a little too much energy, be that from an aggressive flight computer VNAV path calculation, ATC instructions, or just making a mistake; sometimes the easiest solution is a notch of flaps and smooth but careful application of the speed brakes.
 
DarQuiet
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 3:18 pm

The way these are written "flaps have a maximum speed at which they can be extended" and "max flaps extension speed" can be interpreted how quick the flaps extend at max flap setting? ;)

It should be VFE is the allowed maximum speed of aircraft with flaps fully extended.

Starlionblue wrote:
benjjk wrote:
Just to be clear, in most cases, flaps have a maximum speed at which they can be extended. So whilst the added drag will have the effect of slowing the aircraft down, even if you wanted to rely on them you'd have to slow down by other means first.


Indeed. Vfe (max flaps extension speed) for Flaps one on the A330 is 240 knots. And Flaps one doesn't give you a lot of drag anyway. Vfe Flaps two is all the way down at 205 knots, and Vfe Flaps three at 186 knots.

Not tremendously useful if you want to get down from cruise speed to approach speed quickly since by the time you can use the more draggy flap settings you're almost at approach speed anyway.

On the other hand, using the speedbrake over 200 knots roughly halves the deceleration distance in level flight compared to flight idle only.
 
DarQuiet
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 3:28 pm

Thank you for the example. But is it not that the primary control you can use to slow the aircraft is by reducing power?


bluecrew wrote:
Woodreau wrote:
I’ve always waited until 10kts below flap limit speed to extend the flaps as that is company procedure. For the A320 Vfe Flaps 1 is 230kts, Vfe Flaps 2 is 200kts, Vfe Flaps 3 is 185kts, Vfe Flaps Full is 177kts.

So the flaps come out at 220kts, 190kts, 175kts, and 167kts. I use the flaps to slow from there. To get to the speeds for flap extension, I plan to have a level segment or a 300-500fpm descent segment at some point in the descent to decelerate to the point where I can extend the flaps.

Do you always use flaps to slow? Technique I was taught was to bum around at Flaps 1, then extend further at the S and F speeds unless you really need the drag, but the boards are pretty effective for that if memory serves.

DarQuiet wrote:
I'm curious. At what purpose/reason you will use flaps to slow the aircraft? And by slowing the aircraft, it means speed is reduced.

What I know and also as mentioned here, flaps will enable you to fly at slower speed and can increase your margin before aircraft can possibly enter stall.

Flaps will increase induced drag in addition to providing lift, this is why we have flap extension speeds, the induced drag at speeds higher than that damages the flap.
Flaps extended during a descent, for example, generate more lift and more induced drag, but you compensate by adjusting pitch downwards. The extra drag is usually enough at the same speed and power settings to get a few extra hundred fpm in descent.

Practical examples? Late off-schedule descent into JFK with tailwinds on an airplane that doesn't like to slow down in the first place - there if you ask for some extra track miles, they're really gonna give you extra track miles. Depends on the plane, but in all aircraft at some point you'll find yourself with a little too much energy, be that from an aggressive flight computer VNAV path calculation, ATC instructions, or just making a mistake; sometimes the easiest solution is a notch of flaps and smooth but careful application of the speed brakes.
 
GalaxyFlyer
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 3:32 pm

Yes, thrust to idle, speed brakes as needed, once on the approach, use configuration changes to slow to Vref. We don’t use the boards at 180 knots to slow to 160 knots for the next flap setting.
 
Woodreau
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 5:19 pm

bluecrew wrote:
Do you always use flaps to slow? Technique I was taught was to bum around at Flaps 1, then extend further at the S and F speeds unless you really need the drag, but the boards are pretty effective for that if memory serves.


DarQuiet wrote:
I'm curious. At what purpose/reason you will use flaps to slow the aircraft? And by slowing the aircraft, it means speed is reduced.


Going in to LAX, one of the things SOCAL likes to do is keep you at 250, then 210 or greater, then 170 or greater. I make sure that I am below glideslope during the entire approach, while staying on the arrival profile altitudes.

Once I'm released from the 250kt speed assignment and given 210kts or greater, I'll leave DES mode and switch to VS -200 and start decelerating to 210, making sure that the glideslope is still above me. If it appears that I'll intercept the GS then I'll add speed brakes, but the aircraft slows to 210kts at THR IDLE without speedbrakes. FLAPS 1 at 220kts. then either intercept the GS or go back to DES at 210kts,

Once SOCAL assigns 170kts or greater, if I'm still below the GS, then I'll go back to VS-200 to slow, FLAPS 2 at 190kts, continue decel to 180kts and intercept the GS.
If I've already intercepted and descending on the GS, the landing gear comes out, and FLAPS 2 at 190kts, continue decel to 180kts.

I find it rare to need speedbrakes when kept at 250kts by SOCAL, as long as I haven't intercepted the glideslope and am not off the VNAV descent profile.

I've never really thought it about as slowing using the flaps, but it's a 10kts decel with FLAPS 1- which is only the slats from 220 to 210kts, and then 10 more knots with FLAPS 2 from 190kts to 180kts. Then 40-ish knots from 175kts to Vapp using FLAPS 3 and FLAPS FULL.

I've never been told that what Im doing is wrong. no check airman has never mentioned anything I'm doing wrong on any line check or simulator check. So this is the first I've heard that it's bad technique to slow using flaps.
 
bluecrew
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 7:47 pm

Woodreau wrote:
bluecrew wrote:
Do you always use flaps to slow? Technique I was taught was to bum around at Flaps 1, then extend further at the S and F speeds unless you really need the drag, but the boards are pretty effective for that if memory serves.


DarQuiet wrote:
I'm curious. At what purpose/reason you will use flaps to slow the aircraft? And by slowing the aircraft, it means speed is reduced.


Going in to LAX, one of the things SOCAL likes to do is keep you at 250, then 210 or greater, then 170 or greater. I make sure that I am below glideslope during the entire approach, while staying on the arrival profile altitudes.

Once I'm released from the 250kt speed assignment and given 210kts or greater, I'll leave DES mode and switch to VS -200 and start decelerating to 210, making sure that the glideslope is still above me. If it appears that I'll intercept the GS then I'll add speed brakes, but the aircraft slows to 210kts at THR IDLE without speedbrakes. FLAPS 1 at 220kts. then either intercept the GS or go back to DES at 210kts,

Once SOCAL assigns 170kts or greater, if I'm still below the GS, then I'll go back to VS-200 to slow, FLAPS 2 at 190kts, continue decel to 180kts and intercept the GS.
If I've already intercepted and descending on the GS, the landing gear comes out, and FLAPS 2 at 190kts, continue decel to 180kts.

I find it rare to need speedbrakes when kept at 250kts by SOCAL, as long as I haven't intercepted the glideslope and am not off the VNAV descent profile.

I've never really thought it about as slowing using the flaps, but it's a 10kts decel with FLAPS 1- which is only the slats from 220 to 210kts, and then 10 more knots with FLAPS 2 from 190kts to 180kts. Then 40-ish knots from 175kts to Vapp using FLAPS 3 and FLAPS FULL.

I've never been told that what Im doing is wrong. no check airman has never mentioned anything I'm doing wrong on any line check or simulator check. So this is the first I've heard that it's bad technique to slow using flaps.

Not saying it's wrong - it's just not the technique I was taught for normal operations. It makes sense in specific situations like that, the example I used for the Flaps 1 and speedbrake out seems to happen in N90 all the time, similar with the erratic speed control, the constant descend and slow instructions, tight airspace, late descent, etc. The initial post didn't have context, I remember the Bus as being very happy to start slowing down without the flaps unless you had a gnarly tailwind, 100% agree on using the slats to slow down though. Rule of thumb we always used was slats out and 210 knots or so was a pretty good energy state.

Granted my experience in the Airbus was shortlived and abroad, in a country that while busy, *ahem* approaches the level of decent air traffic control 50-60% of the time. Lots of low and slow and early speed restrictions.
 
Max Q
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Re: Can flaps be used to slow an aircraft or only to allow it to fly safely at slower speeds?

Wed Oct 27, 2021 11:19 pm

I always try to avoid extending flaps anywhere close to their limit speed

While slowing, selecting each position at 10 knots above the maneuvering speed or when the trend arrow reaches that setting works well


This minimizes vibration, wear and tear on the flaps and positions high lift devices to be ‘in place’ by the time your speed has decreased


If you’re doing it right there should be next to no vibration or excessive air loads


Similarly on departure selecting the next lower setting when the trend arrow reaches that maneuvering speed gives a nice smooth retraction / clean up schedule


Pushing flap limit speeds is just bad airmanship

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