109G/la-5/7 and the slats

[joeblogs]

"Handley Page had acquired his own wind tunnel during the war [WWI], and among his early tests were trials of a wing with multiple narrow chordwise gaps which he hoped might delay the stall. It did not work. However, when a single narrow spanwise cut was tried the results looked more promising. Moving the slot close to the leading edge increased maximum lift by 25 percent, and refinement of the slot position and size soon raised this to a dramatic 50 percent. Patents were obtained and in march 1920 a D.H. 9 was tested with 'slats' fixed ahead of the wing leading edges to form the slot. This confirmed the wind tunnel results, the aircraft flying as slowly as 38 mph. Soon afterwards a young German pilot-engineer, Gustav Lachmann, chanced on a photograph of this D.H. 9 in an aviation magazine and saw its resemblance to the multi-slotted aerofoil he had attempted to patent early in 1918. He had stalled and crashed his aircraft the year before, and the idea of slots to delay the stall had occurred to him while recovering in the hospital. The German patent office was dubious, however, and rejected his application. Inspired by Handley Page's example, Lachmann now had his triple-slotted section tested at Gottingen; it increased lift by over 60 percent. With this confirmation his patent was not only granted, but it was backdated to February 1918, just prior to Handley Page's. HP went to Berlin to meet Lachmann. They got on well and agreed to pool their rights, and in return HP employed Lachmann as a consultant with a research grant at Gottingen, the start of their long collaboration."

Patrick Hassell, "Advances in Aerodynamics," in Philip Jarett, Biplane to Monoplane. London: Putnam Aeronautical, 1997

-Blogs

Originally posted by HoHun
Hi Blogs,

>Handlye Page And a German engineer obtained patents on slats at essentially the same time. It was a case of independent invention. They cross-licensed with each other.

Actually, Gustav Lachmann got his first patent in 1917 and then was hired by Handley-Page, where he acquired a second patent in (I think) 1919. He was the inventor, but Handley-Page as his employer was the owner of the patent rights. I don't know what patents Handley-Page held before 1919, but everything seems to have been pretty typical business practice here. Aviation was an international business even back then.

Regards,

Henning (HoHun)

[Angus]

Time to revive this, for there is some data inbound.
I modestly earned my place on HoHUn's mighty ignore list for the lack of evidence of the possible downside of automatic slats.
Here is the sentence from the judge.
"Hi Angus,

>All you have is nothing, resulting in total refusal.

You're the one to make claims, you're the one who has to bring the evidence.

You haven't brought anything, so I can't refuse anything.

You want to prove the Me 109 slats had problems, you bring proof specific to the Me 109.

One single claimed (but unverified) quote from one pilot who reportedly said something vaguely negative on the slats is worth nothing, and you haven't even posted that quote verbatim yet. "

THat pilot he refers to is Gunther Rall. I replied after having a conversation with Rall, - which is of course not documented.
However, I did not see my reply, but, presto, found it in his new book, in German, MEIN FLUGBUCH, look at website meinflugbuch.de.
It's in German, - here follows my translation. p.45, Rall has just shot down a Curtiss and is hit by another one. He takes a vicious turn to evade. What happens?
"...I turn the Messerchmitt to get out of the line of fire. My turn is so sharp and steep that the outboard slat jumps out and the aircraft whips out of the turn, - a betrayal of the Messerchmitt, which in this war I am to curse many more times."

I can post this in German later on if needed.
I also have yet another report on the 109's quirks, which touches the subject of slats slightly. Next post.

[Overlag]

it stalled cos he turned too hard, not cos the slat came out. slats are great, they dont STOP stalls, just increase the AOA you can use, but they arnt miracle (spelling?) workers

[StarOfAfrica2]

I think he was only posting to provide proof the statement had been made, not to make a claim one way or the other on the performance of the 109 slats.

[Grits]

Saw this thread late, but I have something to add. My Dad was an A4 Skyhawk pilot, the A4 had simple mechanical automatic slats exactly like the AH planes. He said that they DID open asymetricly under the right conditions and it would cause (sometimes severe) instability  until the other one popped out. While the Blue Angels flew the A4 Skyhawk they had the slats fixed shut so they would not deploy on one wing and not the other. At 36" separation you cant afford to have that kind of destabilizing event.

How does this correspond to AH? I made a film of me flying a 109 and flew around making the slats open and close, both in level flight evenly, and in different attitudes so that they opened unevenly. Dad said that was exactly how they were supposed to act, and he was quite impressed with that kind of detail.

I can not tell you anything about 109's slats in real life, if their pilots liked or loathed them, if they were or were not wired shut (and dont really care), but I can tell you that the slats in AH work exactly as they did in RL.

[StarOfAfrica2]

Cool!  Thanks for sharing Grits!

[VO101_Isegrim]

If the slats open assymetrically, that is because it just happens that one wing has less lift available at high angle of attack. Now if there wouldn`t be slats, what would likely follow is an extremely case of instability, a snap roll towards the stalling wing as the different lift vectors act on the airplane. See spitfire, and esp. the 190/Mustang stall characteristics.. This is also more likely to happen if the pilot doesn`t keep the ball centered in the turn. Now if he has slats, then they would open on the lower lift wing, restoring lift, but as the slats are open in one wing and not on the other, there will be some difference, but not nearly as violate as if one wing would suddenly loose all lift due to flow separation, what the slats would prevent (or more like delay) happening.

And yes, slats are no magic wands for a stall free enviroment. The stall will just occure later with them.

[Charge]

"I also have yet another report on the 109's quirks"

I can hardly wait...




-C+

[Overlag]

main problem with AH slats is they are either open or closed which means 100% or 0% effect, causing the issues we have.

in real life they came out smoothly i would have thought?

[Charge]

"in real life they came out smoothly i would have thought?"

That is how they are modelled in IL2 but in stories of 109's slats they are always described as coming out at once with a "clunk" sound being heard even inside cockpit. The Russian planes had a different hinge system than 109s, so those might have worked differently as the axial torque of the hinge does not hinder the movement of slat as it MAY do in 109. Dunno for sure because I do not have an accurate drawing of 109 slats.

Anyway, as their deployment happens by sufficient air entering the underside gap of the slat I'd imagine that flow to force the slat open at once. Maybe you could get them to move into closed position slowly by very slight movements in nonturbulent air but I think their principle of function suggests they always bang open unless regulated somehow (but that would be once again a potential place for mechanical failure).

-C+

[MiloMorai]

Anyway, as their deployment happens by sufficient air entering the underside gap of the slat I'd imagine that flow to force the slat open at once.

Think you have this wrong charge. The slats were held closed by air pressure and there was no gap until the slat opened.

How much AoA is there when the a/c is landing. It is said that the slats came out during the turn to final. (the a/c is basically level, so 0* AoA.)


We need  Straiga  to come and tell us how slats work, him being an aviation expert and all.

[Grits]

Originally posted by Overlag
in real life they came out smoothly i would have thought?

Well, I cant say for the WWII planes, but Dad says on the A4 they pop open, and they are either open or shut, and its a very sudden movement like in AH. He said you cant hear them, but you can feel them.

[Charge]

"Think you have this wrong charge. The slats were held closed by air pressure and there was no gap until the slat opened. "

I can't seem to confirm this Milo. In some pictures I thought I saw the gap but in some pictures it is totally invisible. If there is no gap I don't understand how they can be forced open against the airstream?

In "http://109lair.hobbyvista.com" there are very detailed pictures of slats but they gave me no evidence if there really was a gap on the underside.

edit: Bf 109G-6 "MT-452" W.Nr. 165227 has some pictures where a very slight gap is visible and a bigger gap in the vertical portion on the outer end of slat. Not a big gap, though...

-C+

[Angus]

Well, Rall uses the expressions "jump" or "pop" or "Snap".
And note, that he mentions that this is something he would curse many times.
However, when I asked him whether he would have preferred no slats, he said they were necessary, - without them the landing speed would have been much to high.

So, it was the slats interfering in a rough turn he did not like.

Bear in mind that he flew many allied planes as well, including the P51 and the Spitfire.

[Charge]

Angus, if I would go to same lengths of reading what I want to see I'd say that because he was a "sniper" ie. could shoot accurately from very long distances he didn't like the slats because while tracking the target he many times gently pulled over the threshold level when the slats suddenly popped open, ruining his aim -from long range.

In banking turns the slats may come out asymmetrically but having disastrous effects on handling? Of course you can pull an evasive in 109 which would come out as a stall and cannot be saved even by the slats and that would be even easier in a Spit.

As i see it that comment on losing control in sudden evasive is just him blaming somebody else than himself.

-C+