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Messerschmitt leading edge slats


Denford

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Can anyone explain why all small Messerschmitt aircraft had leading edge slats?

Only rarely do photos show them extended: in what circumstances were they used, and how were they deployed: manually or automatically?

If they were worth what must have been significant extra manufacturing and maintenance effort, why did no equivalent contemporaries use them?

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The leading edge slats were a Handley-Page patent. They work by airflow/gravity, and are not inter-connected. They are there to delay the stall, or at least to delay the stall in the outboard region of the wing. This makes for a happier experience for the pilot, as he still has aileron control while the wing has begun to stall in the inboard region. Disadvantage for a fighter: when they opened they could throw your aim off a bit, especially if one opened a bit before the other.

They often open on the ground, because of gravity, but I think they were pretty "neutral" on the taildraggers, so could be pushed closed and would (probably) remain closed.

Other aircraft used fixed slots (Avenger, Dauntless, Ventura...) which are draggier than slats. The Whirlwind was initially built with pretty-much full-span slats, but I believe that these were completely disposed of. Some Russian fighters also used slats, as I recall.

bob

p.s. I forgot Swordfish, Tiger Moths, and who knows what else!

Edited by gingerbob
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The 109 slats were deployed automatically and in conjunction with trailing edge flaps are designed to increase lift at low speeds. This means landing speeds are lower and take off is shorter than they would be without the devices.

From what I have read, the Luftwaffe pilots had issues with them deploying during aerobatic maneuvers. I'm not sure if this problem was rectified or not

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The 109 slats were deployed automatically and in conjunction with trailing edge flaps

True, but they are not in any way connected mechanically to the trailing edge flaps. They are totally independent surfaces. Just like the slats on the F-86 Sabre, 109 slats were simply gravity/air flow operated. You often see them closed on the ground becaue the 109 is a tail dragger. The leading edge of the wing sits more or less level with the ground when the a/c is parked. As on the F-86, the slats could be pushed closed and would stay there because there was nothing to cause them to re-open. As soon as you start jostling the airplane by starting the engine and/or taxiing it, the slats would fall to the open position. They would stay open until the air flow over the leading edge of the wing pushed them closed. Same exact system on the Sabre.

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Sorry I should have written that statement more concisely. What I meant was the slats were automatically operated and when slats are used in conjunction with trailing edge flaps the wing will produce more lift at lower speeds when compared with a wing that has neither device.

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Am I correct in assuming that the trailing edge of the slat sits on the upper surface of the wing when closed and so should be 'wafer thin' so as not to leave a 'step' which would surely disrupt the airflow.

Likewise,when open there is not a step showing in the wing for the slat to sit up against when it is closed.

I say this because I have seen on several (if not all) kits which feature separate slats, a rebate is provided for the slat to fit flush with the wing if you are modelling it in the closed position. I suppose this is understandable.

However, I wonder how many modellers remember to fill in and make flush this rebate and thin the trailing edge of the slat if they are showing open slats.

deecee

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A flap will give you more lift at any angle of attack, but won't affect the angle at which you will stall. A leading-edge slat will give the same lift at low angles of attack but allows the flow to remain attached at high angles, permitting greater angles and hence lift before the stall.

The problem with automatic leading edge slats in combat is that they will open asymmetrically in a turn, which will induce unwanted roll and ruin the aim. This is unnerving to less experienced pilots, but the more experienced ones will simply continue to pull through until both open and behaviour becomes more predictable again.

The slat sits in the wing not on it. Or rather against the smooth curved internal surface, leaving a small gap on the upper surface. The presence of this gap is a trade-off against the benefits gained.

Edited by Graham Boak
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The slat sits in the wing not on it. Or rather against the smooth curved internal surface, leaving a small gap on the upper surface. The presence of this gap is a trade-off against the benefits gained.

It looks more like flat surface under the slat

ES4F2001_zps846da251.jpg

Photo of G6

Michael

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The interesting aircraft is the Lysander, which has four slats (2 per wing.) The outer pair open automatically, as usual, at a set speed, and stay open on the ground (unless someone has wired them shut - which did happen.) The inner pair operate with the flaps, so flaps down = slats open, flaps up = slats closed. So far no kit manufacturer has got it right.

Edgar

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You have to understand that injection molding styrene has limitations. You can't mold something to scale thickness - as the trailing edge of a slat - and get it to come out of the mold properly. There are always compromises on things like that.

The real slats sit almost totally flush with the wing surface.

When you say "not as aerodynamic as I thought" - keep in mind that it was designed for a function. There was no need to over-design it so as to make it absolutely perfect. The 109 flew in the 350 mph range, and the aerodynamic 'slickness' of the slat design was perfectly adequate for that kind of speed range.

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The flow inside the slat would have been smoother had the facing wing surface been smooth, as in later designs. That's what I was thinking. Your comment however is more true than you suggest, because the slat was not required in the 350mph range, only attainable with a smooth wing at low angles of attack. The slat operates at high angles of attack and hence slower speeds all the way down to stalling speed. At these angles and speeds the lift induced drag is dominant. Drag due to the flow between the slat and the wing is insignificant.

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Indeed, though it could have gone faster without them. It may however not have been quite so effective an weapon: these things are always trade-offs and no aircraft designer adds an excrescence without somebody having a good reason for it.

The point I was trying to make in my last posting was that although a messy shape between slat and wing would create some drag, this would not affect the top speed because the slat would not be open there. It would have contributed some drag and hence some deceleration in the turn, but less than that provided by being at high AoA in the first place.

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