Author Topic: 109G/la-5/7 and the slats (Read 8176 times)

VO101_Isegrim · « **Reply #105 on:** March 02, 2005, 12:25:08 PM »

Quote

Originally posted by Angus

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.

Maybe he would prefer a violent 180 degree flick roll instead of slats in rough turns, a la Mustang/Spitfire? I doubt.

Tilt · « **Reply #106 on:** March 02, 2005, 06:25:03 PM »

Slats are sucked open due to a combination of speed and angle of attitude (incidence) and held open by negative pressure whilst the combination of incidence and speed are maintained.

They are balanced to open rapidly and positively.

Their task is to inject a stable boundary layer of air (thru the slot created)over the upper surface of the wing which prevents loss of air flow in near (or otherwise) stall conditions.

Their primary disadvantage is that the final onset of stall (once the incidence is so high as to defeat the slat) is very rapid.................... hence if your ac was to loose lift over only one wing due to the manouvre under consideration then the subsequent loss of lift from that wing could be seen as violent compered to other wings ....like a spitfire for instance.

Charge · « **Reply #107 on:** March 03, 2005, 04:19:35 AM »

Nice info Tilt thx.

I don't really see why you people are talking about Spitfire when regarding slat behaviour? P51 has a similar shaped wing as the 109 except for profile, but he Spit does not. I have never read of Spitfires flip stalling 180 deg. AFAIK Spitfires leading edge is curved to even out the pressure build-up on the leading edge aiming for least drag. This in turn for its part causes the whole wing to lose its lift at the same time if max AoA is exceeded. Washout helps by giving warning of the stall and by delaying the stall but when elliptic wing stalls it is "total". Tapered wing stalls more gently but in turn produces more drag. AFAIK that is...

-C+

Tilt · « **Reply #108 on:** March 03, 2005, 08:45:02 AM »

I thought spit wings were slightly twisted to soften the onset of stall which also gave an audible sound near the wing roots during their departure.

Could the reference to "flick" departures be limited to high speed stalls.

Angus · « **Reply #109 on:** March 03, 2005, 11:26:30 AM »

Ok, here goes. From 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. "
A former LW wingco who worked with Rall in the Bundesluftwaffe (RET, working with history now!) told me that he considered Rall to have been the finest shot of the old LW. Better than Marseille.
(Rall considers Marseille to have been the best, but that's just being modest I think.)
Anyway, Rall excelled at deflection shooting, while Marseille was famous for plonking around at no speed and shooting his foes right in the eye at no range. Using the slats there BTW, but that's enough for a whole thread.
So, yes, you have a point, Rall complained about the slats throwing one off the aim. He said he preferred the slats for anything but combat basically.
Then Tilt came along with this:
"Their primary disadvantage is that the final onset of stall (once the incidence is so high as to defeat the slat) is very rapid.................... hence if your ac was to loose lift over only one wing due to the manouvre under consideration then the subsequent loss of lift from that wing could be seen as violent compered to other wings ....like a spitfire for instance."
Very nice, I could never have put this so well. The slat plonks out quite swiftly, changing the game, and at high speed a lot will happen before the pilot has the chance to respond to it. I belive that must be what it's all about (look at the question in the start of the thread), - but still......

Now on to quirks.
What I so far found was the slats need to be well balanced and glide easily to have the required effect.
Recently I aquired a document which I may quote. Will post in less than an hour or so. It basically states that it is necessary for the 109 to be "flown in" properly for the slats needed to be set correctly.
Ok, I made some folks mad on this thread by suggesting that the negative effect of slats could possibly have their roots in damage or bad cirkumstances. Anyway, I honestly am a tad baffled now, for both explanations seem to be rather valid.
Ok, will post as soon as I dig up that doc and type from it.

Tilt · « **Reply #110 on:** March 03, 2005, 01:29:51 PM »

Quote

Originally posted by Angus
The slat plonks out quite swiftly, changing the game, and at high speed a lot will happen before the pilot has the chance to respond to it. I belive that must be what it's all about (look at the question in the start of the thread), - but still......

If you look at the CL curve for an La7 (I dont know about a 109) it is smooth across the slat opening point.

Slats do little to actually add lift they simply preserve laminar air flow over the upper wing as the angle of incidence increases beyod the wings natural departure point. However when they are no longer able to sustain the laminar flow then the characturistic of departure is sudden.

Handling is not changed as they "plonk out" it is drastically changed as they are defeated.

Notem.

Stated above that slats do little to add lift. Of course as they allow the wing to operate at higher levels of incidence then they of course allow the wing to generate more lift thru this increased angle. They do not add lift due to their extension alone as a product of increased wing area or such like.

Angus · « **Reply #111 on:** March 03, 2005, 01:54:51 PM »

THX in advance

Charge · « **Reply #112 on:** March 04, 2005, 03:41:56 AM »

"What I so far found was the slats need to be well balanced and glide easily to have the required effect. "

I agree. If you find out that they had problems with the slat mechanism it would be interesting info. If they changed the mechanism from 109E to 109F there probably was a good reason, which is not documented anywhere for some reason. Maybe the first version really was prone to jam because of dirt or icing and the second version installed in 109F/G cured some or all of this, but then again the Russians chose to use a different kind of hinge?

OTOH it is interesting that the German pilots rarely even say anything about slats in their books just as if they didn't even notice them in flight. It was either that they were so smooth in operation or that they usually flew in the fast part of flight envelope so the slats usually didn't deploy in any part during flight.

-C+

Angus · « **Reply #113 on:** March 05, 2005, 07:08:58 AM »

But, you can stall at any speed basically.
Now on to the dirt and ice.
I had mentioned that dirt and ice issue before, whith little popularity actually. But it seems rather logical, for the LW was having a really diffucult time in their retreat from the eastern front particularly, sometimes staying only for a day on a temporary airfield.
There is something about the hinges somewhere above in this thread, but overall it is a very simple design.

Still bothers me why they are not used in modern light aircraft if they were as some here have claimed, almost perfect and totally simple.
Just a Cessna 172 or a Cherokee will stall at 60 kts, - those are little aircraft with mere 150-200 hp or so. If slats were that great why are they not used on small aircraft today?

Overlag · « **Reply #114 on:** March 05, 2005, 07:15:25 AM »

Quote

Originally posted by Angus

Still bothers me why they are not used in modern light aircraft if they were as some here have claimed, almost perfect and totally simple.
Just a Cessna 172 or a Cherokee will stall at 60 kts, - those are little aircraft with mere 150-200 hp or so. If slats were that great why are they not used on small aircraft today?

why would you need slats on a Cessna? not as if you are pulling high G turns is it?

they are used on modern fighter jets, they are just much more advanced

MiloMorai · « **Reply #115 on:** March 05, 2005, 07:38:52 AM »

Quote

Originally posted by Overlag
why would you need slats on a Cessna? not as if you are pulling high G turns is it?

they are used on modern fighter jets, they are just much more advanced

Why would the Stringbag need slats, and it did have them, for it did not pull high G turns. The Storch had them as well. Made for a much lower landing speed, it did.

Angus, I would speculate it would be because of safety > if one came out and the other didn't, the civvy pilot would not be able to correct in time so close to the ground.

GScholz · « **Reply #116 on:** March 05, 2005, 07:45:41 AM »

GScholz · « **Reply #117 on:** March 05, 2005, 07:49:21 AM »

Quote

Originally posted by MiloMorai
Angus, I would speculate it would be because of safety > if one came out and the other didn't, the civvy pilot would not be able to correct in time so close to the ground.

Slats do not add lift. If only one slat pops out nothing happens unless the pilot is unaware of the situation and stalls the other wing by continuing to lower speed/tighten turn.

pasoleati · « **Reply #118 on:** March 05, 2005, 10:52:09 AM »

Quote

Originally posted by Angus

Still bothers me why they are not used in modern light aircraft if they were as some here have claimed, almost perfect and totally simple.
Just a Cessna 172 or a Cherokee will stall at 60 kts, - those are little aircraft with mere 150-200 hp or so. If slats were that great why are they not used on small aircraft today?

For the simple reason: modern Cessnas are pieces of **** first, aeroplanes second. Every measure is taken by the maker to make it as cheap as possible and sell it at highest price they dare to ask.

As fas as stalling at 60 kts goes, Typhoon stalls at some 65 mph IAS at light loadings...

Angus · « **Reply #119 on:** March 05, 2005, 02:36:44 PM »

Hehe. true. Build an aircraft with so little weight that still needs several hundred yards of runway. And Cessna stalls like a *****!
Same goes with the Cherokee, - needs a long way to get airborne, - however gentle to no departure charactericstics.
(Been in them when deliberatly being brutally stalled)
Anyway, Scholzie, nice collection. Do you have the types of those?
And again, something to debate on. What is the world without a debate anyway.....

"Slats do not add lift. If only one slat pops out nothing happens unless the pilot is unaware of the situation and stalls the other wing by continuing to lower speed/tighten turn."

Well, they lower the stall speed, and correct a stall about-to-happen very quickly. Now with both slats operating, before the other wing stalls, the slat there should also deploy. The first wing to stall should (in a turn for instance) be the outboard wing. So I think you have it wrong there.
The outboard wing stalls before, and then the stall is quite cruel. However, with no slats the stall would have occured before anyway.
In a ROUGH turn as Rall describes it, this can happen differently, for this is very quick. The slat jumps out and corrects the beginning stall procedure so viciously that the aircraft flicks out of the turn. This is how he describes this anyway, and boy, that guy made many a rough turn!