Auto leading edge slats of the 109

[Sternjaeger]

Crump, can we please go back to our conversation now please? 

[Bearcat]

Yes .. quickly .. because I may find my keys before that and just lock this puppy.

[Crump]

Sternjager says:

 

Crump, can we please go back to our conversation now please?

 

http://forum.il2sturmovik.com/topic/2035-auto-leading-edge-slats-109/?p=49779

 

Key phrase being:

 

Crumpp says:

 

The aerodynamics are explained already.  

 

 

AND

 

Crumpp says:

 

So please just leave me out of this

 

 

There is no conversation to have..... Sternjager. 

[Sternjaeger]

it's your call Crump, I just don't understand why you turn all defensive and avoid questions when asked.

 

My friendly advice is to argument your points, if anything because your positions are quite unorthodox, and posting some links is not enough to support your points. 

[Crump]

Sternjager,

 

I don't feel like reinventing the wheel in some silly internet discussion about whether or not engineering convention as is taught in most major universities is correct.  I am sure the game developers understand slats, how they operate, and the benefits. 

[MiloMorai]

Sternjager,

 

I don't feel like reinventing the wheel in some silly internet discussion about whether or not engineering convention as is taught in most major universities is correct.  I am sure the game developers understand slats, how they operate, and the benefits. 

 

So why get involved in these discussions?

[Sternjaeger]

Crump, I only asked if you could confirm my thoughts, not reiventing the wheel. It's either a yes or a no mate.

[Crump]

check your pms

[Sternjaeger]

I did, but I would like you to answer in public, please. I'm sure this is a conversation that everybody can benefit from? 

 

Let me remind you the question: do we agree that the efficiency of a wing is dependent on the behaviour of the airflow on the upper surface, and that when we reach a certain AOA (namely 15 degrees and above), the airflow starts mutating from laminar to turbulent, causing eventually the wing to stall?

 

The answer is a simple yes or no.

Edited November 20, 2013 by Sternjaeger

[Venturi]

Don't feed the trolls

[DD_bongodriver]

No he is asking the troll a question.

[Sternjaeger]

it won't happen, it's a shame cos he had a cracking theory on the use of slats..

[Furio]

I think that we could leave aside, for the moment, laminar or turbulent flows. Too much theory for this thread, I feel. “Laminar”, if I interpret correctly Stern, has nothing to do here with laminar airfoils, for example.

 

What we can safely say is that slats allow wings to fly at higher angle of attack. They can be used on the whole leading edge to attain STOL performances (think of the Fieseler Storch) or on the outer part of the leading edge to retard tip stall.

As there are many ways to obtain the same result (wing twist being another method), it’s not surprising that slats were not common on WWII fighters, and sometimes were introduced to tame bad stalling behaviour, as in the Mig 3.

If they were adopted for the production Bf109, it’s sure that the Messerschmitt needed them, in spite of the weight, cost, complexity and maintenance complication they added, not to mention the drag increase they produced.

[Sternjaeger]

Furio, the distinction between laminar and turbulent is very important, as is the one between a slat (on the Bf109) and a slot (on the Storch). 

 

The nature of the debate here is that a slat, as you rightly said, allows wings to be efficient at a higher angle of attack, but according to one person the slat does this by increasing the turbulent airflow, which is conceptually wrong, but good luck convincing this guy otherwise... 

[Venturi]

Slats should be slotted right into the discussion, always that leading guy flapping round the forward edge of the conversational airflow, yet really doesn't seem to understand. Rah rah rah

[Furio]

I think this thread is worthwhile, so I’ll try to line up some facts, keeping these clear from my opinions.

 

There are several types of leading edge devices. Most of these are meant to allow the wing to reach higher angle of attack, thereby enhancing maximum lift or retarding tip stall in the interest of safety. Mobile slats or fixed slots are nothing more than a small wing placed in front of the main airfoil’s leading edge, their aerodynamic effect being to alter the airflow above the main wing. I don’t want to enter the debate about aerodynamics and physic’s’ laws, but the end result is that airflow stay attached to the wing upper surface at higher angle of attack, and the onset of stall is delayed. Perhaps we can agree on this without further discussion, can’t we?

 

A similar result can be obtained with leading edge cuffs and/or vortex generator placed on leading edge or just above it. There is at least one light plane that was produced with fixed slots – Storch style – but lately switched to vortex generators, obtaining more or less the same performances, with less weight and cost. Another one switched from cuffs to leading edge “teeth”, which proved more effective.

 

The ICP Savannah with leading edge slots...

 

… And  the same plane with vortex generators above leading edge. What look as three antennas are airfield's fence.

 

Early VariEze with cuffs on main wing's leading edge...

 

And later model with leading edge teeth. Another form of vortex generator.

 

However, as far as I know, only slats and slots were successfully used during WWII. On the Bf109 specifically, they moved automatically and were not interconnected, so you could end up with one slat extended while the other was retracted. This was perfectly logical, as wings operate at different speeds during a turn, and the slats come out when wind pressure drops below a certain limit (actually, we should talk of pressure differential, but we can live with some simplification). I never read that this asymmetry caused any controllability problem.

 

So, I think we can say:

The Bf109 didn’t use slats to obtain STOL performances, but as a mean to retard tip stall and spin entry while manoeuvring.

They were good enough to offset their weight, complexity, cost and drag.

I don’t believe they pose a particular problem to the developers, because their effect is small and their operation is limited to low speed.

As the Bf109 is generally acknowledged as a good B&Z fighter, any wise pilot would always keep speed up and slats closed.

[DD_bongodriver]

109 slats were not really designed to improve high speed  manoeuvring characteristics, and of course they were not STOL devices either but they were primarily intended to improve low speed handling qualities so the aircraft didn't have to land at high speed, given that the 109 was tricky to handle on the ground high speed is really not desirable on the landing roll, in fact by their very nature automatic slats are not an ideal device for manoeuvring given it is well documented that asymmetric deployment was a reality, the tiger moth had automatic slats that were specifically required to be locked closed during aerobatic manoeuvres, 1 because of asymmetric deployment and 2 because under load slats open with force that sometimes the structure cannot handle and slats can be broken off, another poster with experience as a USN A-4 pilot has already described this very problem and that is on a ruggedly built jet designed to be slammed into the moving deck of an aircraft carrier.

As the Bf109 is generally acknowledged as a good B&Z fighter, any wise pilot would always keep speed up and slats closed.

 

This +100, but of course it cannot be dismissed that a 109 in the hands of a highly skilled pilot could use the 109 in a turning fight.

[Kurfurst]

in fact by their very nature automatic slats are not an ideal device for manoeuvring given it is well documented that asymmetric deployment was a reality, the tiger moth had automatic slats that were specifically required to be locked closed during aerobatic manoeuvres, 1 because of asymmetric deployment and 2 because under load slats open with force that sometimes the structure cannot handle and slats can be broken off, another poster with experience as a USN A-4 pilot has already described this very problem and that is on a ruggedly built jet designed to be slammed into the moving deck of an aircraft carrier.

 

This +100, but of course it cannot be dismissed that a 109 in the hands of a highly skilled pilot could use the 109 in a turning fight.

 

Hmm.

 

Erwin Leykauf, German fighter pilot, 33 victories:

 

"The Bf 109s also had leading edge slats. When the 109 was flown, advertently or inadvertently, too slow, the slats shot forward out of the wing, sometimes with a loud bang which could be heard above the noise of the engine. Many times the slats coming out frightenened young pilots when they flew the Bf 109 for the first time in combat. One often flew near the stalling speed in combat, not only when flying straight and level but especially when turning and climbing. Sometimes the slats would suddenly fly out with a bang as if one had been hit, especially when one had throttled back to bank steeply. Indeed many fresh young pilots thought they were pulling very tight turns even when the slats were still closed against the wing. For us, the more experienced pilots, real manoeuvring only started when the slats were out. For this reason it is possible to find pilots from that period (1940) who will tell you that the Spitfire turned better than the Bf 109. That is not true. I myself had many dogfights with Spitfires and I could always out-turn them. 

One had to enter the turn correctly, then open up the engine. It was a matter of feel. When one noticed the speed becoming critical - the aircraft vibrated - one had to ease up a bit, then pull back again, so that in plan the best turn would have looked like an egg or a horizontal ellipse rather than a circle. In this way one could out-turn the Spitfire - and I shot down six of them doing it." 

 

Franz Stigler, German fighter ace. 28 victories:

 

"- Did pilots like the slats on the wings of the 109? 

Yes, pilots did like them, since it allowed them better positions in dogfights along with using the flaps. These slats would also deploy slightly when the a/c was reaching stall at higher altitudes showing the pilot how close they were to stalling.....this was also useful when you were drunk "

 

Walter Wolfrum, German fighter ace. 137 victories:

 

"Unexperienced pilots hesitated to turn tight, bacause the plane shook violently when the slats deployed. I realised, though, that because of the slats the plane's stalling characteristics were much better than in comparable Allied planes that I got to fly. Even though you may doubt it, I knew the Bf109 could manouver better in turnfight than LaGG, Yak or even Spitfire."

 

And this is from an ex-Yugoslavian pilot. Yugoslavia had quite an aircraft park after the war, with 109s, Yak 3s, Spitfires, Hurricanes and even P-47s!

 

»The main shortage of Jak 3 was its obsolete technique. Its cockpit was spartan, everything had to do be done manually. Particular problem was when you had to get air compressor into its second gear when rapidly changing altitude. In such situations engine is not receiving the right mixture of air and fuel and is loosing power, so you had to be very concentrated in doing it all synchronized and in exact moment. The same applies for the oil cooler which was adjusted with an mechanical wheel, during the dive the cooler had to be closed and during the climb opened as the engine needed more air. All of it was automatio on the Messerschmitt. In Jak 3, throttle handle and the propeler pitch handle were beside each other and you had to move them simultaneously, so all the time you pulled the throttle you had to think about the pitch. So imagine when you are in a midst of a combat, chasing and being chased, turning the wheels, setting the handles, adjusting the pitch, setting the gunsight and at the same time manouvring and trying to hit your enemy. Messerschmitt had it all automatic.

Messerschmitt had  leading edge slots ("predkrilca") to prevent it from stalling and Jak stalled even on highest speed. In sharp turns Messerschmitt provoked a black-out and that was not possible with the Jak since he would stall. On other hand Jak easily came out of the spin and Messerschmitt stalled slowly but when it did it was hard to get it out due to small command surfaces which would become »shaded«. Therefore it was neccessary to give a hard contra with the food pedals, full gas or sometimes to lower the gear. Messerschmitt had the electrical loading of weapons, and Jak mechanical, I remember how it clicked. 

In all, Jak 3 had marvelous flying performance and excellent manouvrebility, it was invented for peacetime flying and aerobatics, but you had to have »a hand« for it. On other hand Messerschmitt was much more simple to fly, especially in air combat, of course once you learned to cope its small rudder on take-off and landing.« 

 

On the side note - how is "asymmetric" slat opening is supposed to be a bad thing for maneuvering? The slats open when the wing (one, or both) exceed the critical angle of attack for the airfoil, and when the slat opens on one or both wing it restores it. The wing does not stall, even when the slats open asymmetrically (if you mean that only one wing has the slats open) it means that this particular wing would stall otherwise.

[DD_bongodriver]

Pilot annecdotes

[Kurfurst]

Pilot annecdotes

 

vs. internet nerd's opinion.

[JtD]

On the side note - how is "asymmetric" slat opening is supposed to be a bad thing for maneuvering? The slats open when the wing (one, or both) exceed the critical angle of attack for the airfoil, and when the slat opens on one or both wing it restores it. The wing does not stall, even when the slats open asymmetrically (if you mean that only one wing has the slats open) it means that this particular wing would stall otherwise.

The slats didn't deploy upon stall, the deployed well before it. The "bad" thing about the asymmetric deployment the the extra drag created by the open slat, which causes the plane to yaw.

[DD_bongodriver]

vs. internet nerd's opinion.

 

yes, with a commercial pilot's license and experience in flying aircraft with automatic slats witnessing first hand the pitfalls of asymmetric opening of slats.......you are just an internet nerd.

Edited November 23, 2013 by DD_bongodriver

[Kurfurst]

The slats didn't deploy upon stall, the deployed well before it. The "bad" thing about the asymmetric deployment the the extra drag created by the open slat, which causes the plane to yaw.

 

They open when the air starts the become turbulent over the wing and the pressure distribution sucks the slats open - on the onset of stall if you like. Assymetric deployment occurs when only one of the wings start to enter a stall, usually when you already have some slideslip and the angle of attack is greater on one wing than on the others - which also means you are not making the turn right! With slats, that wing won't stall, and yes, drag will be greater, but not because of the slat but because you have greater angle of attack one wing, which means more lift, and thus, more drag on that wing.

 

Without slats, that wing would simply stall out and you would probably enter flick roll and spin. So please do not tell me how assymetric slat opening and drag is actually "caused" by leading edge slats, it actually caused by uncoordinated flying and the slats save your butt from a spin in that situation...

yes, with a commercial pilot's license and experience in flying aircraft with automatic slats witnessing first hand the pitfalls of asymmetric opening of slats.......you are just an internet nerd.

 

Let's see your licence then and your logbook of hours in Bf 109s... And no, I am not a pilot, you could say I am just an internet nerd who OTOH reasearched the Bf 109 for some 15 years and who has yet to find an account or document of bad stall handing or bad stall behavior due to slats.

 

You, however is not arguing my internet nerd opinion, you are just another internet nerd arguing the combat experience of highly successful and experienced Bf 109 combat and test pilots.

[Rama]

Well.... and it all come down again to personnal disputes.

Too bad, like other thread, it was quite interesting at start.

 

Locking.