Flaps

[Idasam]

Does the Mirage have flaps? I can't seem to find them, the switch, the toggle or the key(s) that activate them.

[jojo]

No flaps on Mirage 2000.

And the SLATs retract when you extend landing gear. You only extend SLATs (BECS) manually if you have to land power loss on engine.

[exodios93]

The mirage doesn't have flaps but it does have leading edge slats that automatically deploy at low airspeeds.

[Goldsmack]

I did the same thing when the m2000c first came out. I always bind the axis and maps gear and flaps....took me a good 15 mins :music_whistling:

[Frederf]

I don't know of any delta wing configuration that has trailing edge flaps. The trailing edge control surfaces are generally for pitch control. The trailing edge surfaces are altered slightly in the landing config automatically. If you want to consider that "flap action" I guess you could think of it that way but it's beyond pilot control.

 

I never understood the logic in the leading edge devices (slats technically but LEF is practically the same) being forced retracted during landing.

[azm]

Should be number one question in M2000 FAQ.

We have M2000 FAQ, right? ))

Edited October 3, 2016 by azm

[Frederf]

I couldn't find a good distinction between LEF and LE slats other than the LEF seem to always be simply hinged and slats are often slotted aerodynamically. LEF are for increasing camber ratio while LES are to increase critical AOA?

 

In any case I thought it might be a safety issue as one could accidentally find themselves at an AOA on approach (not normal but accidents happen) and have a crash that normally-scheduled becs might have helped recover from. Becs start to come out at 17.5° which isn't too far from approach AOA.

 

Maybe the landing FBW program isn't made the schedule becs? Do they have a chance of asymmetrical deployment upset? Takes too much hydraulic power? You want the wind to stall after touchdown? I was curious why not schedule them as normal in this phase of flight. Sure they wouldn't normally extend at normal approach AOA but to prevent them entirely?

[jojo]

Becs start to come out at 17.5° which isn't too far from approach AOA.

 

With landing retracted, the "Becs" start to extend at 4° AoA, and are fully extended at 10° AoA.

 

From what I have been told, on M-2000 the "Becs" mainly reduce drag. So extending them for landing would lead to too flat approach flight path.

Therefore in normal landing Becs are retracted to use the wing drag like "air brake".

 

On the other hand, in landing configuration, air brake would destroy lift. This is why pilot are instructed not to use them before touch down in final approach.

[vparez]

Here is a nice picture of the effects of slats and flaps:

 

http://aviation.stackexchange.com/questions/1734/what-is-the-difference-between-flaps-and-slats

 

You see that slats do not have an effect on lift until near critical angles of attack; probably this is why they are not used in landing. There is no need for them and possibly could aggravate the situation in case of a one-sided failure.

 

The flaps in this picture are not entirely accurate, as they should reduce the critical AOA (curve is shifted upwards but also to the left), not keep it the same as in the clean configuration. This is due to the additional drag caused by the flaps (quite a lot of it).

 

Hinged LEF have the same aerodynamic purpose as their trailing edge flap counterparts: change the camber of the wing. They are in the F-16 and F-18 I believe. Since they rotate downwards, they certainly increase profile drag, but one needs to look at this with respect to the general characteristics of the wing design. There is probably a good pay-off when they are used, in spite of added drag, but I would expect the effect to be similar to flaps. In addition to this, they can also be used to optimize the airfoil profile for high-speed flight.

 

Slats (as in the M2000c) are designed to separate from the wing leading edge, providing a slot through which the incoming air is accelerated, which then energizes the top wing boundary layer (which delays flow separation as previously mentioned). Since slats are extended mostly to the front of the airfoil (and very slightly upwards) they do not create much additional profile drag, and by their action of controlling the boundary layer, they keep the drag of the whole wing remain lower than if they werent used (not really in level flight, the effect is only at higher AOA where you have flow separation on the top).

Edited October 3, 2016 by vparez

[Azrayen]

I never understood the logic in the leading edge devices (slats technically but LEF is practically the same) being forced retracted during landing.

As jojo said, without slats your [edit] DRAG is higher. Hence your engine runs higher. Hence it's quicker to accelerate to MIL/Full AB if you need to go around.

 

(originally I wrote AoA instead of drag; thanks to vparez to point this error to me)

Edited October 3, 2016 by Azrayen

[vparez]

As jojo said, without slats your AoA is higher. Hence your engine runs higher. Hence it's quicker to accelerate to MIL/Full AB if you need to go around.

 

I don't think this is the reason; have a look at my previous post. Also, if you engine runs higher RPM to maintain flight, there is more chance of a disaster if your engine dies. So, that's not a great design decision.

[vparez]

If the engine dies on final it makes absolutely no difference if the engine would have been running at a higher RPM, slats are in or out etc. as you wouldn't be able to reach the runway with a dead engine in any case.

The reason why you want to maintain a certain minimum RPM on approach is that most jet engines accelerate very slowy out of idle (many planes for this reason automatically increase idle thrust once e.g. the flaps are extended).

 

Well I don't know if you can make such a general statement. I think it heavily depends on the plane type and the aerodynamic design philosophy. In my pilot training the first thing I was told was that the take-off is the most critical phase with respect to engine failure, not the landing. This makes sense, since at landing you are slowing down continuously while on take off you struggle to accelerate.

 

Now, all I am saying is that I do not believe that you would purposefully need engine power to land, while at the same time being near a critical flight regime. IMHO the design of the plane would first ensure that your flight regime is with a nice margin, and only then would a designer worry about the engine response in extraordinary situations. You don't sacrifice the safety during a normal landing so that you can have better options if you need to brake off. How many times in a plane's life do you land normally and how many times do you go around in an emergency?

 

But this is all beside the point, the point is what Azrayen said: without slats your AOA is higher. This is what I don't agree with since in the textbook definition slats do not change your AOA for most of your flight envelope, but only near the critical regime; and you don't land in the critical regime.

 

What are the critical AOA for stall for the "clean" Mirage and what is the normal AOA at landing?

I will test it tonight after work if nobody does it before.

Edited October 3, 2016 by vparez

[Azrayen]

have a look at my previous post.

Just did that:

"Slats (as in the M2000c) are designed to separate from the wing leading edge"

Errr... no. No slot between the slats and the wing on the M2000.

Perhaps "slats" is not the right word in English (in your opinion at least) and LEF would better correspond. But they're not "hinged" per se on the M2000 either.

 

That doesn't sound convincing as the slats themselves add only very little to camber and area, hence the actual increase in lift at identical AoA is very small.

Furthermore extended slats add drag

Indeed slats do not increase lift at identical AoA (or not enough to be noteworthy) (and that's why I didn't talk about lift earlier). Slats extend the range of available AoA (with slats: critical AoA = higher value).

But you're wrong on your second sentence: at high AoA (such as approach AoA ~14°), extended slats lower induced drag.

[edit] and I corrected an error on my part; perhaps it's more "convincing" now?

 

If the engine dies on final it makes absolutely no difference if the engine would have been running at a higher RPM, slats are in or out etc. as you wouldn't be able to reach the runway with a dead engine in any case.

Agreed.

 

The reason why you want to maintain a certain minimum RPM on approach is that most jet engines accelerate very slowy out of idle (many planes for this reason automatically increase idle thrust once e.g. the flaps are extended).

The M53 is not so bad in that aspect, but still as all jets it needs time to accelerate.

 

So yes, that's the reason. No slats = more Cx (more drag) = more thrust needed = higher RPM = better engine response time.

 

Of course as jojo said, if you have thrust (engine) problems, the rule changes.

Edited October 3, 2016 by Azrayen

[Azrayen]

Well I don't know if you can make such a general statement. I think it heavily depends on the plane type and the aerodynamic design philosophy.

I don't think it was a general statement.

OTOH, it's a statement that fits the M2000.

 

Now, all I am saying is that I do not believe that you would purposefully need engine power to land, while at the same time being near a critical flight regime.

Did you fly a lot of delta-winged high performance aircraft?

How do you define (how much is) "near" critical flight regime?

 

But this is all beside the point, the point is what Azrayen said: without slats your AOA is higher. This is what I don't agree with since in the textbook definition slats do not change your AOA for most of your flight envelope, but only near the critical regime; and you don't land in the critical regime.

Oh my god. :doh: You're totally right, brainfart on my account.

I should have written "your drag is higher".

Very sorry about the induced confusion. I will edit my post right away.:blush:

 

What are the critical AOA for stall for the "clean" Mirage and what is the normal AOA at landing?

It's a good thing to ask those questions. :)

AoA FBW limit (A/A mode): 29° (27° under 100kt)

AoA pilot limit (CHARGES mode): 20°

Approach AoA: 14°

[Azrayen]

Every item that you exend into the airflow causes additional drag.

Sounds logical indeed :)

But the extended item may also change the aerodynamics of the entire wing in such a way that the induced drag reduction is more important than the drag added by the item itself.

That's what happens in the case we're discussing.

[vparez]

Just did that:

"Slats (as in the M2000c) are designed to separate from the wing leading edge"

Errr... no. No slot between the slats and the wing on the M2000.

Perhaps "slats" is not the right word in English (in your opinion at least) and LEF would better correspond. But they're not "hinged" per se on the M2000 either.

 

Did you fly a lot of delta-winged high performance aircraft?

How do you define (how much is) "near" critical flight regime?

 

It's a good thing to ask those questions. :)

AoA FBW limit (A/A mode): 29° (27° under 100kt)

AoA pilot limit (CHARGES mode): 20°

Approach AoA: 14°

 

Then they are not slats, and since they don't rotate they are not LEFs. They are a totally unique piece of french engineering like a 2CV! :D

 

There is a gap between slats and wing LE. The separation of the two profiles creates circulation around each one, and the interaction between these yield the benefits to the drag and lift.

Do you agree that the gap provides the primary physical mechanism of how slats do their thing? Otherwise, please explain to me through which physical mechanism do BECKS in the Mirage change lift/drag/AOA.

 

Check around 9:15 here:

 

https://www.youtube.com/watch?v=q_eMQvDoDWk

 

No, I never flew a delta wing fighter. Is this the only way one could be able to define what is a critical or near critical regime? I always thought such knowledge came BEFORE the first flight, from engineering calculations or wind tunnel testing. And I did a lot of wind tunnel testing. ;)

 

I would define a near-critical regime for AOA for which you don't have a linear relationship between CL and AOA. But that's just a criterion of the top of my head, I would have to look into it more to see what does literature say. Most likely there is no fixed definition, or there are multiple definitions like for a boundary layer thickness.

 

Thanks for the data, but I was thinking what is the critical AOA if you don't use slats, nd compare it to the max AOA used in landing. I am quite curious to try it out. Also, since you know a lot of stuff about the Mirage, could you confirm what another member posted earlier about the AOA at which slats are deployed? If his numbers are correct (from 4deg AOA onwards) it could be a good clue in this discussion.

 

One thing I don't understand from your posts is what you are saying about slats and drag. Drag cannot be HIGHER in the clean configuration than in the deployed slats configuration. The deployment of slats slightly increases the profile drag, but the increase in lift also increases induced drag. So, I don't see how slats can be used to REDUCE drag. But maybe we missunderstand each other.

 

In any case, nice discussion! ;)

[Azrayen]

1.Yes they are.

Thanks :)

Indeed "slat" is used in RL documentation/cockpits of "english" M2000s.

 

 

The point Azrayen was trying to make was that if AoA remains the same, the slats (sealed or not) reduce the required AoA to maintain the same amount of lift, thereby reducing induced drag, but only at the same AoA.

Uh? Not sure to follow you here.

 

"if AoA remains the same" + "reduce the required AoA" in the same sentence => sounds illogical to me?

 

My understanding is that at "high" (approach/14°) AoA, Cx will be lower if slats are extended.

So, with slats retracted (= auto mode when L/G down), Cx will be higher, needed thrust (to maintain AoA & flighpath) will be higher.

 

I you have low thrust issues (engine problems) the last thing you want is a higher Cx. In this case, you'll switch the slats to "extended" manually.

 

No, I never flew a delta wing fighter. Is this the only way one could be able to define what is a critical or near critical regime? I always thought such knowledge came BEFORE the first flight, from engineering calculations or wind tunnel testing. And I did a lot of wind tunnel testing. ;)

Of course it's not the only way. Wrote that because you told about your experience ;)

 

Drag cannot be HIGHER in the clean configuration than in the deployed slats configuration.

It can't? Damn.

Why did I read the contrary on a RL documentation related to this specific aircraft?

(I'm not an aerodynamician, nor a mathematician)

Edited October 3, 2016 by Azrayen

[jojo]

As we already said with Azrayen:

- for landing, SLATS are retracted to increase drag, which allows to land with higher RPM (like Azrayen said), so better engine reactivity. It's a pretty common practice on jet airplane to increase drag on landing, to have better engine spool up time. It's easier for the pilot.

Watch this F-16 with AB deployed during final leg:

It doesn't mean you're at 90% RPM !

 

- Why not to deploy AB on Mirage then ?

As I said earlier, in landing condition AB destroy lift (they are on the wing).

So not a good idea.

[vparez]

@Jojo and Azrayen,

 

could you please share the text from the official documentation where it elaborates on the clean configuration having more drag than configuration with slats deployed? I am guessing that there is another context in which this applies and that we are discussing ad infinitum because we dont have this context.

 

I stand by what I said before: if you deploy slats the profile drag might slightly increase but it is usually not very much, but if the slats increase lift, then your induced drag will also increase. So, for constant AOA, slats = + drag

 

Now, about the context... if your lift is increased more than total drag then your finesse will increase which is usually a good thing for a glide-like flight. So, what your technical documentation says must be looked at in the correct context. Any possibility to see this doc? I would be really interested.

 

@Azrayen,

 

Yes, I see what I wrote and how you might have taken it the wrong way. No, no I certainly don't have any hands-on experience with jet fighters! I just land my little ULM with throttle on idle, and yes I knwo its not the same as Tanguy and Laverdure! :D

 

@bbrz,

 

I stand corrected, there are sealed slats. Thanks!

Do you know how do they function? Is their job to increase wing surface?

Edited October 3, 2016 by vparez

[mvsgas]

I probably got this wrong, but I thought in tailless delta configure aircraft (Mirage 2000, V, III, F-102, B-58 etc.) The Leading Edge Flap (LEF) or slats, move the center of lift forward. This make the aircraft a bit more sensitive in pitch, good for rapid pitch movement (like in a BFM scenario) but not desirable on landing or take off. AFAIK or understand, this is why so few aircraft with tailless delta configuration use slats or LEF. IIRC, only Mirage 2000 and F4D-1 Skyray are the only two tailless deltas with LEF flaps/Slats that I can think off.

Edited October 3, 2016 by mvsgas

[jojo]

I probably got this wrong, but I thought in tailless delta configure aircraft (Mirage 2000, V, III, F-102, B-58 etc.) The Leading Edge Flap (LEF) or slats, move the center of lift forward. This make the aircraft a bit more sensitive in pitch, good for rapid pitch movement (like in a BFM scenario) but not desirable on landing or take off. AFAIK or understand, this is why so few aircraft with tailless delta configuration use slats or LEF. IIRC, only Mirage 2000 and F4D-1 Skyray are the only two tailless deltas with LEF flaps/Slats that I can think off.

 

Mirage 2000 and Rafale, Gripen, Typhoon, J-10, J-20...all fly by wire delta fighters.

 

You're right, SLATS increase instability. But FBW can handle it very smoothly.

[Azrayen]

could you please share

Sorry, best I can do here is quoting the following, from the § about Becs (slats) an old RL manual:

Les becs automatiques sont asservis à l'incidence. (...)

 

Train sorti, les becs sont automatiquement rentrés.

 

(...)

 

NOTA - Pour couvrir certains cas de panne du moteur conduisant à de faibles poussées en approche, on peut avoir, train sorti, les becs plein sortis (position "SORTIS" de l'interrupteur "BECS" situé en banquette gauche).

 

I hope your read French; for those who don't, the NB at the end explain what I wrote earlier i.e. the slats can be manually extended with L/G down, in case of engine loss of thrust in approach.

 

= = = = = =

 

but if the slats increase lift

I'm not an aerodynamician, but I don't think slats do that.

They are not flaps.

 

= = = = = =

 

[edit]

IIRC, only Mirage 2000 and F4D-1 Skyray are the only two tailless deltas with LEF flaps/Slats that I can think off.

Well, there is also the Rafale and Typhoon. Granted they're not pure deltas, but delta-canards.

Edited October 3, 2016 by Azrayen

[vparez]

@Azrayen,

 

thanks a lot mate for the reply! (no problems with french) ;)

 

Ok, I totally understand why you would manually extend slats in case of power loss. Power loss means less speed, means higher AOA to keep the same lift. As you push to higher AOA you are approaching critical stall, so you extend slats manually to delay a critical AOA to a higher value.

 

I would suppose that they advise manual extension so that the slats are fully extended ("on peut avoir, train sorti, les becs plein sortis") so that a pilot doesn't have any surprise if the automatic system malfunctions or if the computer suddenly (for whatever reason) decides to change the configuration at a critical moment. You need a stable configuration on landing. (this is just my thinking I dont have any info)

 

I agree that slats do not create lift, and I misspoke there. What I was trying to say is that at the AOA where slats are working, the lift is greater than at any other smaller AOA. As lift increases so does the induced drag. The induced drag originates from the recirculation around the wing tips from the lower to the upper wing side. If you have lift then the pressure on the top is smaller than the pressure on the bottom, hence this recirculation.

 

But I am sure that slats cannot decrease drag compared to a clean config. :)

[jojo]

@Azrayen,

 

thanks a lot mate for the reply! (no problems with french) ;)

 

Ok, I totally understand why you would manually extend slats in case of power loss. Power loss means less speed, means higher AOA to keep the same lift. As you push to higher AOA you are approaching critical stall, so you extend slats manually to delay a critical AOA to a higher value.

 

I would suppose that they advise manual extension so that the slats are fully extended ("on peut avoir, train sorti, les becs plein sortis") so that a pilot doesn't have any surprise if the automatic system malfunctions or if the computer suddenly (for whatever reason) decides to change the configuration at a critical moment. You need a stable configuration on landing. (this is just my thinking I dont have any info)

 

I agree that slats do not create lift, and I misspoke there. What I was trying to say is that at the AOA where slats are working, the lift is greater than at any other smaller AOA. As lift increases so does the induced drag. The induced drag originates from the recirculation around the wing tips from the lower to the upper wing side. If you have lift then the pressure on the top is smaller than the pressure on the bottom, hence this recirculation.

 

But I am sure that slats cannot decrease drag compared to a clean config. :)

 

You keep repeating the same thing.

 

1st: forget your story about stability issue. It's a FBW aircraft. And as long as FBW is nominal there isn't any issue with extended SLATS.

SLATS become an issue only in case of FBW malfunction.

 

2nd: with landing gear retracted, the SLATS start to extend at 4° and are fully extended at 10°

https://forums.eagle.ru/showpost.php?p=2916585&postcount=9

So on subsonic flight it's pretty much always working.

Edited October 3, 2016 by jojo

[vparez]

You keep repeating the same thing.

 

1st: forget your story about stability issue. It's a FBW aircraft. And as long as FBW is nominal there isn't any issue with extended SLATS.

SLATS become an issue only in case of FBW malfunction.

 

2nd: with landing gear extended, the SLATS start to extend at 4° and are fully extended at 10°

https://forums.eagle.ru/showpost.php?p=2916585&postcount=9

So on subsonic flight it's pretty much always working.

 

1st I dont have a story about the stability issue. It is not me who said that. I am saying that it could be a risk in the case of malfunction so thanks for agreeing with me.

 

2nd, you mean with l/g retracted?

 

What am I repeating?