Qualities that made for a great aircraft that don't show up in performance stats.

Schweik · Oct 27, 2018

The slats were needed because it was a small, thin 32' wing with only 173 square feet of wing area. The small thin wing is part of the streamlining - what allows it to fly so fast, accelerate so well, retain it's speed so well. As we all know the slats allowed it to turn reasonably well in spite of the low drag wing, unlike many other small fast planes. If it had a 40' wing span it wouldn't have needed them (though it may have needed some aileron boost).

Again it's not that it was particularly unusual to have this or that specific feature, but to have the combination of so many was remarkable. I'm not at all surprised to see some clunky old prototype in England with leading edge slats, but I think properly working leading edge slats on a fighter in 1940, along with a good highly functional radio, an engine / supercharger combo which performs well from Sea Level to 25,000 feet, constant speed prop, fuel injection, and the overall high dive speed and excellent rate of climb, is pretty impressive.

I'm not some Luftwaffe fanboy pretending the Bf 109 was magical unbeatable 'uber-thing', nor have I ever stinted on praise of the Spitfire. I'm just saying the 109F, the Franz was unusually advanced for when it came out. I don't think the Spitfire needed leading edge slats because of the amazing wing it had, but many other fighters of the era could have used them. Certainly the ability to set the flaps at various settings including for combat was also a useful feature which was all but universal in fighters by the end of the war.

Of course many of the technologies in wide use in the 1940's were developed in the 1930's or even back in the 20's or during WW I (like superchargers or the alluminum alloy skin used by almost all warplanes put into production after 1940). The thing is, many of them were still struggling to realize their potential in the pre-war era, and all to often during the war itself. Some of the features of the Franz didn't work quite right in the Emil as we know, including specifically the leading edge slats.

What makes the Franz impressive to me (especially for as early as it was available) is that it had so many advanced features in the same very small, nicely streamlined package and in good working order. This gave the German pilots a lot of tools to use.

I think it's also worth pointing out how lightly armed the plane was. More proof that you didn't need huge guns or tons of guns to shoot down enemy planes, precision and flying characteristics mattered at least as much if not more. Thinking of the Ki-43 and many of the Russian and Italian fighters here.

swampyankee · Oct 27, 2018

Schweik said:
The slats were needed because it was a small, thin 32' wing with only 173 square feet of wing area. The small thin wing is part of the streamlining - what allows it to fly so fast, accelerate so well, retain it's speed so well. As we all know the slats allowed it to turn reasonably well in spite of the low drag wing, unlike many other small fast planes. If it had a 40' wing span it wouldn't have needed them (though it may have needed some aileron boost).

Again it's not that it was particularly unusual to have this or that specific feature, but to have the combination of so many was remarkable. I'm not at all surprised to see some clunky old prototype in England with leading edge slats, but I think properly working leading edge slats on a fighter in 1940, along with a good highly functional radio, an engine / supercharger combo which performs well from Sea Level to 25,000 feet, constant speed prop, fuel injection, and the overall high dive speed and excellent rate of climb, is pretty impressive.

I'm not some Luftwaffe fanboy pretending the Bf 109 was magical unbeatable 'uber-thing', nor have I ever stinted on praise of the Spitfire. I'm just saying the 109F, the Franz was unusually advanced for when it came out. I don't think the Spitfire needed leading edge slats because of the amazing wing it had, but many other fighters of the era could have used them. Certainly the ability to set the flaps at various settings including for combat was also a useful feature which was all but universal in fighters by the end of the war.

Of course many of the technologies in wide use in the 1940's were developed in the 1930's or even back in the 20's or during WW I (like superchargers or the alluminum alloy skin used by almost all warplanes put into production after 1940). The thing is, many of them were still struggling to realize their potential in the pre-war era, and all to often during the war itself. Some of the features of the Franz didn't work quite right in the Emil as we know, including specifically the leading edge slats.

What makes the Franz impressive to me (especially for as early as it was available) is that it had so many advanced features in the same very small, nicely streamlined package and in good working order. This gave the German pilots a lot of tools to use.

I think it's also worth pointing out how lightly armed the plane was. More proof that you didn't need huge guns or tons of guns to shoot down enemy planes, precision and flying characteristics mattered at least as much if not more. Thinking of the Ki-43 and many of the Russian and Italian fighters here.

Oh, I won't argue that the Bf109 wasn't a good fighter --- possibly the best of its generation, which was the same generation as the Hurricane -- but automatic leading edge slats were not only far from unique to the Bf109, but the fact that no other fighter designer found them necessary may be indicative of an initial poor wing design, with the outer portion of the wing stalling before the root. Automatic LE slats have been used, and removed, from other fighters, with one example being the Saber.

Automatic LE slats were actually used on quite a few production aircraft before WW2, not just "some clunky old prototype." The thing is that slats improve lift coefficient by increasing the angle of attack at which the wing stalls (so do leading edge flaps), but this frequently makes visibility on landing more problematic, especially with the relatively long nose of fighter aircraft. It also means that the high lift isn't necessarily available on landing, when one tends to want the main gear to take landing loads, not the tail wheel.

tomo pauk · Oct 27, 2018

Shortround6 said:
...

The Spanish built fighters are real can of worms. Yes they figured out how to put a Hispano cannon in each wing. On the other hand by the time they got the planes built and flying they were totally obsolete as fighters and the Spanish intended them for use as ground attack machines even while under construction. Spanish industry was in such bad shape in the late 40s and early 50s that many parts could not be produced in Spain and had to be purchased in some cases from Switzerland (landing gear forgings/casting) and in other cases they had to wait for the original german companies to be rebuilt to supply the needed parts (like wiring harnesses).

I have no idea if the Spanish built versions were intended for the same ultimate load factors as the German planes or not or if the Spanish were willing to accept lower performance or changes in roll response that the Germans in WW II were not. Speculation on my part.

The book "Hispano Suiza in Aeronautics" by Manual Lage makes no mention one way or the other but goes into more detail on the production problems and explains the switch to the Merlin engine.

Spanish did two things in order to fit the big Hispano cannon and still retain stenght of the wing. They introduced a short, auxilary spar, located between the main spar and the leading edge, and made a hole in the main spar. Greg posted the pic many months ago: link.

But then, a Bf 109 with MG FFM with 90 rd drum in the wings, or, even better, with belt-fed MG FFM, would've gave a good service IMO.

Schweik · Oct 27, 2018

As far as the slats go, I'm thinking more of their value for combat maneuvering than for landing approach. The Bf 109 was a high speed plane, relied on speed in air to air combat, but sometimes the speed wasn't enough. When they are in their rolling scissors or forced to turn fight, the slats could make the difference between survival and doom. The same could have helped with many other aircraft with a higher wing loading.

swampyankee · Oct 27, 2018

Schweik said:
As far as the slats go, I'm thinking more of their value for combat maneuvering than for landing approach. The Bf 109 was a high speed plane, relied on speed in air to air combat, but sometimes the speed wasn't enough. When they are in their rolling scissors or forced to turn fight, the slats could make the difference between survival and doom. The same could have helped with many other aircraft with a higher wing loading.

It may not have been wing loading, per se, but unacceptable departure characteristics without slats.

Shortround6 · Oct 27, 2018

It is this instance that the slats helped maneuverability (helped decrease turn radius) that is what I find in error.

the slats do nothing, sip, bupkus, nada, zero until the angle of attack exceeds about 13 degrees and if your wing is inclined 13 degrees or more from the direction of travel you are generating a huge amount of drag.

And the 109 fans seem to confuse effects of full span slats (as used on the Fi 156, the Westland Lysander and others) with partial span slats. The slats on the 109 affected around 33-40% of the wing area even if they covered a bit more span. Sorry, a 10-20% increase in lift (or even 33%) over 40% of your wing doesn't really help if the rest of the wing has stalled (providing no lift)
What they did do was give warning of an approaching stall, which helped the pilot fly closer to the edge, and if one or both wings stalled they helped maintain aileron control so the pilot was better able to keep the plane from flicking into a spin. Many green or inexperienced pilots never came close to reaching the limits of the aircraft in a turn do to both fear of stalling/spinning and lack of experience in high G maneuvers. Try telling the difference between 4 1/2 Gs and 5 1/2 Gs by the seat of your pants or how close to blacking out you are.

Shortround6 · Oct 27, 2018

I would also note that the 109 was designed as a 2000-2200kg aircraft with a 700hp (or under) engine. Wing loading would have 27lb/sq/ft or under in initial design.

Claiming it was advanced because they shoehorned a much bigger engine into it rather than design a new airplane may be giving it too much credit.

pbehn · Oct 27, 2018

I don't think you can discount the need for these slats for landing, I would think that's where they were needed most of all.

Schweik · Oct 27, 2018

Don't the slats effectively lower the stall speed?

pbehn · Oct 27, 2018

Schweik said:
Don't the slats effectively lower the stall speed?

Yes.

Schweik · Oct 27, 2018

pbehn said:
I don't think you can discount the need for these slats for landing, I would think that's where they were needed most of all.

I'm not discounting that need by any means, but I know they were very helpful in combat. Landing characteristics were more critical for less experienced and less well trained pilots. In 1940 German pilot quality was quite good, on average. I think slats helped with landing but due to the other characteristics of the Bf 109, were more necessary for combat. Not every combat of course. But perhaps analogous to pilot armor or even a pilot parachute. It was a very important feature for emergency situations, such as are routine in fighter combat.

Landing characteristics, even marginally more difficult ones, were certainly important though. Without a doubt they led to huge numbers of accidents, lost aircraft and pilot deaths on the Allied side mainly due to pilots with insufficient aircraft familiarization training on the type of plane they were flying.

Schweik · Oct 27, 2018

Shortround6 said:
I would also note that the 109 was designed as a 2000-2200kg aircraft with a 700hp (or under) engine. Wing loading would have 27lb/sq/ft or under in initial design.

Claiming it was advanced because they shoehorned a much bigger engine into it rather than design a new airplane may be giving it too much credit.

If the design didn't allow for dramatic improvements to things like engines, increased fuel capacity, armor, more weapons and various other factors, it wasn't such a good design. That is one of the main traits that defined a good aircraft in WW2.

In fact per the thread title, it's probably one of the less obvious but most important traits of a good warplane - the capacity for improvement and modification, as a subset of overall versatility. That is the difference between a lot of the other 1930's designs like the Curtiss Hawk, I-16, MS. 406 and the Hurricane: they were pretty good in their day, and remained formidable for a few years, but ultimately didn't have room for the dramatic improvements needed for the rapidly accelerating pace of aircraft design and the swiftly soaring requirements for an expanded flight envelope for the ever more dangerous combat environment of WW2.

Schweik · Oct 27, 2018

Shortround6 said:
It is this instance that the slats helped maneuverability (helped decrease turn radius) that is what I find in error.

I know 'maneuverability' is a slippery term but it does mean more than just turn radius..

What they did do was give warning of an approaching stall, which helped the pilot fly closer to the edge, and if one or both wings stalled they helped maintain aileron control so the pilot was better able to keep the plane from flicking into a spin. Many green or inexperienced pilots never came close to reaching the limits of the aircraft in a turn do to both fear of stalling/spinning and lack of experience in high G maneuvers. Try telling the difference between 4 1/2 Gs and 5 1/2 Gs by the seat of your pants or how close to blacking out you are.

Riding a stall is critical in a low-speed dogfight, especially when using common Luftwaffe tactics like a rolling scissors. Low speed dogfight was of course not the optimal situation for them but being able to ride the stall was very helpful. Also when in a vertical climb (such as used when shooting an enemy aircraft from below) it helped manage the stall at the peak of the climb and allow the pilot to control his descent without going into a spin.

Normally, in a low speed turning fight they would not be pulling a lot of G's.

S

pbehn · Oct 27, 2018

Schweik said:
I'm not discounting that need by any means, but I know they were very helpful in combat. Landing characteristics were more critical for less experienced and less well trained pilots. In 1940 German pilot quality was quite good, on average. I think slats helped with landing but due to the other characteristics of the Bf 109, were more necessary for combat. Not every combat of course. But perhaps analogous to pilot armor or even a pilot parachute. It was a very important feature for emergency situations, such as are routine in fighter combat.

Landing characteristics, even marginally more difficult ones, were certainly important though. Without a doubt they led to huge numbers of accidents, lost aircraft and pilot deaths on the Allied side mainly due to pilots with insufficient aircraft familiarization training on the type of plane they were flying.

Without the LE slats the landing speed is increased because the stall speed is increased.

Schweik · Oct 27, 2018

pbehn said:
Without the LE slats the landing speed is increased because the stall speed is increased.

Yes I'm well aware - but given that the slats didn't work well or always in the (similar and sometimes heavier) 109E, I assume the higher landing speed was within the capabilities of most of the pilots & on most of the fields they were using. Is that an incorrect assmuption?

Dimlee · Oct 27, 2018

Kevin J said:
There is no word for cousin in the Russian language, your cousins are your brothers and sisters.

Well...
I'm Russian and now I have to learn something new about my mother tongue. Should I go back to grade school...

pbehn · Oct 27, 2018

Dimlee said:
Well...
I'm Russian and now I have to learn something new about my mother tongue. Should I go back to grade school...

There was speculation that the word "cousin" would disappear from Chinese due to the single child policy.

XBe02Drvr · Oct 27, 2018

swampyankee said:
The thing is that slats improve lift coefficient by increasing the angle of attack at which the wing stalls

If they're full span automatic slats. In a BF-109 style installation, all they do is make sure the wing center section stalls before the tips, a function served in other aircraft (perhaps less efficiently) by wing twist.
Cheers,
Wes

pbehn · Oct 27, 2018

Schweik said:
Yes I'm well aware - but given that the slats didn't work well or always in the (similar and sometimes heavier) 109E, I assume the higher landing speed was within the capabilities of most of the pilots & on most of the fields they were using. Is that an incorrect assmuption?

In my opinion, especially with the Bf109 the lower the landing speed the better things are. The 109 was best landed in a three point landing, so slower the better as I see it

swampyankee · Oct 27, 2018

Shortround6 said:
It is this instance that the slats helped maneuverability (helped decrease turn radius) that is what I find in error.

View attachment 514597
View attachment 514598

the slats do nothing, sip, bupkus, nada, zero until the angle of attack exceeds about 13 degrees and if your wing is inclined 13 degrees or more from the direction of travel you are generating a huge amount of drag.

And the 109 fans seem to confuse effects of full span slats (as used on the Fi 156, the Westland Lysander and others) with partial span slats. The slats on the 109 affected around 33-40% of the wing area even if they covered a bit more span. Sorry, a 10-20% increase in lift (or even 33%) over 40% of your wing doesn't really help if the rest of the wing has stalled (providing no lift)
What they did do was give warning of an approaching stall, which helped the pilot fly closer to the edge, and if one or both wings stalled they helped maintain aileron control so the pilot was better able to keep the plane from flicking into a spin. Many green or inexperienced pilots never came close to reaching the limits of the aircraft in a turn do to both fear of stalling/spinning and lack of experience in high G maneuvers. Try telling the difference between 4 1/2 Gs and 5 1/2 Gs by the seat of your pants or how close to blacking out you are.

The slats kept the ailerons operational by forcing the root section to stall before the tips; this can be (and usually is) done by twist or camber changes, e.g., leading edge droop. In general, one wants to have the roots stall first, but for a tapered wing without twist, the tips tend to be both more highly loaded and will stall before the root, and that stall will make the ailerons less effective, or even completely ineffective. I've not been able to find the polars of the airfoil used by the Bf109 (
NACA 2R1 14.2 tapering to NACA 2R1 11.35; see The Incomplete Guide to Airfoil Usage). As an aside, airfoils and wings continue to produce lift after stall. They just tend to do so while creating very large amounts of drag and also tend to have the amount of lift fall off as angle of attack increases.

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