Leading Edge Slats on the Me-109

[VO101_MMaister]

You are amazing guys... How the hell did you end up on the spit`s high speed stall characteristic in a thread about the leading edge slats of the 109?????

There are no spinproof airplanes, there ones which are hard to put in a spin. The wing is stalled when the airflow become turbulent over the whole upper wing area and so it looses its lifting effect. The slats ensure a laminar flow over the outer wing around the ailerons at low speed so you have some more control before the wing stall. No magic here. It can postpone the stall but it won`t eliminate it.

The spin is when only one of the wing is stalled due to the assyimetrical flow. The slats could open independently, so they could prevent a spin by opening only on the wing which was just about the stall. But again it was only postponing the spin in this case and gave you more control.

On the other hand the slats could make a fuss, when only one of them opened due to some mechanical failure, and it resulted an assymetrical lift and so an unpredicted spin at low speed. Also they raised the drag when they were open, what meant quicker de-accceleration.

I have never flown an aircraft with slats, so no practical experience here, but as I understand Crumpp did, and he gave a quite good description about the acting of such an airplane.

I also feel that the 109 in the game is a bit sensitive, but hey, I can`t tell if it is right or not. Can you? I have never flown one, and I have never read a review of the current flight modell by a real life 109 jockey. Have you? There are quantitive specs what can be measured and checked in numbers and graphs. And then there are the sensations. It is quite hard to translate a pilot`s story into an accurate flight model. In these stories you can only get what that particular guy felt in that particular situation, and then how he can recall it after maybe 60-70 years. Well it is not bomb proof for sure. Now translate it into a computer game for guys who are flying in an office chair, and they pull as hard as they want without feeling the punishment of the real G-forces or the physical exhausting of an aerial battle. So we can have a depute on it for 1000 years and we never gonna agree.

[Crumpp]

As to how to replicate the buffet in the game

Start another thread, it is pretty easy to simulate correctly the effect.

Crumpp completely ignores the 95% of positive report on the Spitfire but emphasises the negative 5%

Nothing to do with any emotional attachment one way or the other to the Spitfire. I like the airplane.

With certain posters on these boards though there is no reason to repeat the strengths of the design as that is all they emphasize.

Therefore anybody who seeks the historical balance is stuck in the position of repeating what has has already been pointed out AND adding in the overlooked qualities OR just stating the overlooked qualities that achieved that balance!

[Crumpp]

Originally Posted by VO101_MMaister

You are amazing guys... How the hell did you end up on the spit`s high speed stall characteristic in a thread about the leading edge slats of the 109?????

There are no spinproof airplanes, there ones which are hard to put in a spin. The wing is stalled when the airflow become turbulent over the whole upper wing area and so it looses its lifting effect. The slats ensure a laminar flow over the outer wing around the ailerons at low speed so you have some more control before the wing stall. No magic here. It can postpone the stall but it won`t eliminate it.

The spin is when only one of the wing is stalled due to the assyimetrical flow. The slats could open independently, so they could prevent a spin by opening only on the wing which was just about the stall. But again it was only postponing the spin in this case and gave you more control.

On the other hand the slats could make a fuss, when only one of them opened due to some mechanical failure, and it resulted an assymetrical lift and so an unpredicted spin at low speed. Also they raised the drag when they were open, what meant quicker de-accceleration.

I have never flown an aircraft with slats, so no practical experience here, but as I understand Crumpp did, and he gave a quite good description about the acting of such an airplane.

I also feel that the 109 in the game is a bit sensitive, but hey, I can`t tell if it is right or not. Can you? I have never flown one, and I have never read a review of the current flight modell by a real life 109 jockey. Have you? There are quantitive specs what can be measured and checked in numbers and graphs. And then there are the sensations. It is quite hard to translate a pilot`s story into an accurate flight model. In these stories you can only get what that particular guy felt in that particular situation, and then how he can recall it after maybe 60-70 years. Well it is not bomb proof for sure. Now translate it into a computer game for guys who are flying in an office chair, and they pull as hard as they want without feeling the punishment of the real G-forces or the physical exhausting of an aerial battle. So we can have a depute on it for 1000 years and we never gonna agree.

Good post. Your right, the thread is getting off track and needs to get back on.

The behaviors of the Bf-109 are fairly well documented and we have some measured data. There is enough there to construct a reasonable facimile. Unfortunately the RAE did not have a standard or the measuring equipment developed by the NACA until later.

Also other reports and the Operating Notes give some really good clues about the stability and control of the Bf-109. For example, the Bf-109 (in a trimmed condition) was limited by design to about 5G's. This keeps the pilot safe and allows maximum attainable manuverability with gusting. You can see this in the turn performance evaluation by the RLM/Mtt of the Bf-109E.

5600/140 = 40 lbs MINIMUM control force required on the elevator at 1G and we require a stick force per G greater than 8lbs/g.

I would think CloD FM is sophisticated enough to use sections. If that is the case, simulating the slats effect on stall behaviors should be a matter of doing exactly what the designers did.

Adjust the coefficient of moment of the elevator accordingly with the outboard wing sections and stalled main portion wing sections.

At the forward CG point where our elevator requires the most moment, the airplane should not spin. As the CG moves rearward, the ability to enter a spin is increased until at its most rearward position a spin entry is possible with deliberate effort.

Reading the synopsis of the Mtt spin trials the Bf-109 at rearward CG reminds me of a C-172 spin qualities at the Cessna forward CG. You must enter a power on stall and give a vigorous rudder input to the direction you want to spin. The break is crisp as the rudder feel is noticeably sloppy near the break but solid until that vicinity. The airplanes settles into more of a corkscrewing dive than a developed spin. The PARE can be pretty sloppy in a 172, letting go of the controls will effect recovery many times. Reducing power and stepping on the high wing results in immediate recovery. You can just about ignore the A and E in PARE in a C172 as long as they are not extreme.

[ACE-OF-ACES]

Originally Posted by robtek

Now there you have to bring some proof that the assymetric action of the flaps, which was intended, was causing spins.

First you 'flip' and said 'with such arguments I am soo far out'.. Now you 'flop' and want me to provide proof of such arguments that are too far out?

Why bother, Ill just give you a few more min to 'flip' back and poo poo it again.

Originally Posted by robtek

And the points you've brought are as usual black and white with no room for intermediate.

Agreed..

But I can not take all the credit for these points.. I was simply pointing out what pilots who have flown the 109 had to say about the uneven slat activation.

[Crumpp]

Stalling the 109
Me 109 E:
"The airplane was equipped with a 60 foot trailing static head and a swiveling pitot head. Although, as may be imagined, operation of a trailing static from a single-seater with a rather cramped cockpit is a difficult job, the pilot brought back the following results:
Lowering the ailerons and flaps thus increases CL max of 0.5. This is roughly the value which would be expected from the installation. Behaviour at the stall. The airplane was put through the full official tests. The results may be summarized by saying that the stalling behaviour, flaps up and down, is excellent. Both rudder and ailerons are effective right down to the stall, which is very gentle, the wing only falling about 10 degrees and the nose falling with it. There is no tendency to spin. With flaps up the ailerons snatch while the slats are opening, and there is a buffeting on the ailerons as the stall is approached.. Withs flaps down there is no aileron snatch as the slats open, and no pre-stall aileron buffeting. There is no warning of the stall, flaps down. From the safety viewpoint this is the sold adverse stalling feature; it is largely off-set by the innocuous behaviour at the stall and by the very high degree of fore and aft stability on the approach glide.
It is important to bear in mind that minimum radii of turn are obtained by going as near to the stall as possible. In this respect the Bf.109E scores by its excellent control near the stall and innocuous behaviour at the stall, giving the pilot confidence to get the last ounce out of his airplanes turning performance."- RAF Royal Aircraft Establishment (RAE) Farnborough handling trials,Bf.109E Wn: 1304. M.B. Morgan and R. Smelt of the RAE, 1944.

Me 109 E-4:
"I was amazed at how docile the aircraft was and how difficult it was to depart, particularly from manoeuvre - in a level turn there was lots of warning from a wide buffet margin and the aircraft would not depart unless it was out of balance. Once departted the aircraft was recovered easily by centralizing the controls."
- Charlie Brown, RAF Flying Instructor, test flight of restored Me 109 E-4 WN 3579. Source: Warbirds Journal issue 50.

Me 109 G:
"- How the Messerschmitt reacted to hard pull? Did she stall?
There is the general opinion that you could not make her stall by pulling but she could 'slip'."
- Kyösti Karhila, Finnish fighter ace. 32 victories. Source: Interview by Finnish Virtual Pilots Association.

Me 109 E:
"I was particularly interested in the operation of the slats, the action of which gave rise to aileron snatching in any high-G manoeuvres such as loops or tigh turns so I did a series of stalls to check their functioning more accurately. The stall with the aircraft clean, with half fuel load and the engine throttled right back occurred at 105 MPH (168 km/h). This was preceded by elevator buffet and opening the slats about 20 mph (30 km/h) above the stall, these being accompanied by the unpleasant aileron snatching as the slats opened unevenly. The stall itself was fairly gentle with the nose dropping and the port wing simultaneously dropping about 10 degrees."
- Eric Brown
- The author writes about an "unpleasant" event. Nothing catastrophic! Surely all of the planes of that time had features, that were unpleasant, just as well as many planes today have. Curtiss Hawk 75 was surely unpleasant to fly with the rear fuselage fuel tank filled, as flying acrobatics could get you killed. P-51 was at least unpleasant with fuselage tanks filled.

Me 109 E:
"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. This advantage to the Bf 109 soon changed when improved Spitfires were delivered."
- Erwin Leykauf, German fighter pilot, 33 victories. Source: Messerschmitt Bf109 ja Saksan Sotatalous by Hannu Valtonen; Hurricane & Messerschmitt, Chaz Bowyer and Armand Van Ishoven.

Me 109 E:
"And there I discovered the first thing you have to consider in a 109. The 109 had slots. The slot had a purpose to increase the lift during takeoff and landing. In the air automatically it's pressed to the main wing. And if you turn very roughly you got a chance, it's just by power, the wing, the forewing, comes out a little bit, and you snap. This happened to me. I released the stick immediately and it was ok then. "
- Major Gunther Rall in April 1943. German fighter ace, NATO general, Commander of the German Air Force. 275 victories. Source: Lecture by general Rall.

Me 109 E/F/G: - The plane had these wing slats and you mentioned they pop open uneven?
"Two meter slots on fore wings. The reason was to increase the lift during low speed take off and landing. To reduce the length of runway you need. In the air, if you make rough turns, just by gravity, the outer slot might get out. You can correct it immediately by release of stick, you know? Only little bit, psssssssht, its in, then its gone. You have to know that. And if you know it, you prevent it."
- Major Gunther Rall. German fighter ace, NATO general, Commander of the German Air Force. 275 victories. Source: Lecture by general Rall.

Me 109 G:
"- How often did the slats in the leading edge of the wing slam open without warning?
They were exteneded always suddenly but not unexpectedly. They did not operate in high speed but in low speed. One could make them go out and in by moving the stick back and forth. When turning one slat functioned ahead of the other one, but that did not affect the steering. In a battle situation one could pull a little more if the slats had come out. They had a positive effect of the slow speed handling characteristics of the Messerschmitt.
- Could the pilot control the leading edge slats?
No. The slats were extended when the speed decreased enough, you could feel when they were extended. "
- Kyösti Karhila, Finnish fighter ace. 32 victories. Source: Interview by Finnish Virtual Pilots Association.

Me 109 G:
"- In a battle, which was the case: did the pilot endure more than the Messerschmitt could do or vice versa?
The fact is that when you pulled hard enough the wing leading edge slats slammed open. After that the pilot could not tighten the turn. The plane would have stalled. I don't know, I never tried to find out what the plane would do after that. I never heard anybody else saying that he would have banked so hard that the slats came out. I did that a few times, for example once over the Isthmus I tried to turn after an enemy, banking so hard that both slats came out, but I had to give up.
- How did the slats behave in such a situation, did they go in and out ?
It depended on speed, if you pulled more,they came out, then back in
The slats came out completely, never half-way?
I never came to watch them so intensely. You just knew they had come out, you could see them and feel that the lift increased pretty much.
- So the plane warned that now you are on the edge.
Yes, you knew the plane is about to spin."
- Antti Tani, Finnish fighter ace. 21,5 victories. Source: Interview by Finnish Virtual Pilots Association.

Me 109 F/G:
"- 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 "
- Franz Stigler, German fighter ace. 28 victories. Interview of Franz Stigler.

Me 109 G:
"As CL max is reached the leading edge slats deploy - together if the ball is in the middle, slightly asymmetrically if you have any slip on. The aircraft delights in being pulled into hard manuevering turns at these slower speeds. As the slats pop out you feel a slight "notching" on the stick and you can pull more until the whole airframe is buffeting quite hard. A little more and you will drop a wing, but you have to be crass to do it unintentionally."
- Mark Hanna of the Old Flying Machine Company flying the OFMC Messerschmitt Bf 109 G (Spanish version).

Me 109 G:
"There was nothing special in landing the plane. It was heavy but the wing slats opened up when speed slowed down and helped flying in slow speed."
-Kullervo Joutseno, Finnish fighter pilot. Source: Hannu Valtonen, "Me 109 ja Saksan sotatalous" (Messerschmitt Bf 109 and the German war economy), ISBN 951-95688-7-5.

Me 109 G:
"It was beneficial to keep the throttle a little open when landing. This made the landings softer and almost all three-point landings were successful with this technique. During landings the leading edge slats were fully open. But there was no troubles in landing even with throttle at idle."
-Mikko Lallukka, Finnish fighter pilot. Source: Hannu Valtonen, "Me 109 ja Saksan sotatalous" (Messerschmitt Bf 109 and the German war economy), ISBN 951-95688-7-5.Source: Hannu Valtonen, "Messerschmitt Bf 109 and the German war economy"

Me 109 G:
"We didn't have time for acrobatics but we weren't forbidden from doing them, though. Snap roll was fast and easy, and the engine didn't cough as in older planes. Immelman turn was splendid when you tightened the stick a bit on the top. The automatic wing slats did their trick and you didn't need ailerons at all for straightening the plane."
-Otso Leskinen, Finnish fighter pilot. Source: Hannu Valtonen, "Me 109 ja Saksan sotatalous" (Messerschmitt Bf 109 and the German war economy), ISBN 951-95688-7-5.

"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 it [Bf109] could manouver better in turnfight than LaGG, Yak or even Spitfire."
- Walter Wolfrum, German fighter ace. 137 victories.

http://www.virtualpilots.fi/feature/articles/109myths/

[taildraggernut]

Originally Posted by Crumpp

Nothing to do with any emotional attachment one way or the other to the Spitfire. I like the airplane.

Nobody mentioned emotional attachments.

Originally Posted by Crumpp

With certain posters on these boards though there is no reason to repeat the strengths of the design as that is all they emphasize.

They tend only to repeat the positive aspects after certain posters go out of their way to emphasise the minor negative aspects.

[taildraggernut]

Originally Posted by Crumpp

At the forward CG point where our elevator requires the most moment, the airplane should not spin. As the CG moves rearward, the ability to enter a spin is increased until at its most rearward position a spin entry is possible with deliberate effort.

So basically you aknowlege the RAE evaluation that the aircraft was 'too stable' for a fighter, if you are having to use up elevator effect simply to counter the CoG then you have afairly impeded manouverability.

[Crumpp]

If you have never flown a slat equipped aircraft, it is a different experience despite the slats being totally unnoticeable for the vast majority of their operation.

Once you have, the idiosyncrasies of the slats becomes part of the airplane and the tactile clues are comforting acknowledgements that everything is working as it should.

Once you explore the low speed performance of a slat equipped aircraft you will miss them on airplanes that lack such a device.

[II/JG53 Rolf]

One of the most amusing threads I have ever read... You can learn so many details about slats and its function while there is an agreement that in-game Bf-109 E doesn't have realistic stall and spin characteristics... Well done chaps.

[ACE-OF-ACES]

Originally Posted by Crumpp

http://www.virtualpilots.fi/feature/articles/109myths/

LOL

Leave it to Crumpp to cut-n-paste quotes from a website with the title 109 myths as PROOF that uneven slat activation could NOT cause spins.. Yup no chance of bias at that website! NOT! One glance at that site and anyone can see that site goes way out of it's way to interpret what was said about uneven slat activation in the best possible light for the 109

With that said, instead of 'words' from a biased Internet website, how about 'words' from actual Bf109 pilots in a book by David Isby called The Decisive Duel: Spitfire vs 109? Will this meet your standards of proof robtek?

Originally Posted by Oberleutnant Erwin Leykauf

Less experienced pilots could put a Bf 109 into a stall and spin when the slats deployed on one wing and not the other in a tight turn. When slats deployed unevenly in tight turns, they would disrupt the airflow, causing the ailerons to ‘snatch’ enough to shake a Bf 109, spoiling the pilot’s aim

Now it is decision time.. As in who are you going to belive?

1) A biased website quote posted by Crumpp.
2) A quote of an actual WWII Bf109 pilot.

The choice is clear, but I am sure that some folks like Crumpp, Tomcat, and robtek will find creative ways to disregard what this actual WWII Bf109 pilot had to say about the slats causing spins..