Bf 109 Landing Gear Geometry Issue

cimmex said:

It is really amazing how some people blame aircraft engineers who probably belonged to the best of the time that they were too dump to understand the basics of wheel dynamics when the decided that no toe out or toe in was the best for the 109 there surely were some reasons for this. Especially this kind of modification would not cost a lot so even Prof. Messerschmitt who is known as a very money saving man could not deny if necessary.
just my 2c
cimmex

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The reason for the geometry is supposed to be due to the transport requirements of the design laid out in 1933 (Taktische Forderungen fur das Jagdflugzeug (Land) ). One requirement was that the aircraft be small enough to be transported by rail. It was not a requirement as far as is known for the undercarriage to be attached to the fuselage (neither the Ar 80 nor the He 112 had this feature though the Fw 159 did) but this is what Messerschmitt decided to do. Once the undercarriage is attached to the fuselage, or more specifically a truss which also accepted the front attachment point of the wings and the lower attachment of the engine bearers, it HAS to splay out to be functional. Even splayed the track is still barely 2 metres. All the other problems stem from this. Altering the angle of toe or making other minor adjustments to the geommetry is like sticking an Elastoplast on an axe wound.

Prof. Messeschmitt may have been known as a money saving man, but don't forget it was two fatal crashes of the M20 transport and the subsequent refusal of Deutsche Luft Hansa to accept the type that led to the 1931 bankruptcy proceedings against BFW AG.
Later the **** up that was the Me 210, also designed by the illustrious professor, cost Messerschmitt AG an estimated 38,000,000 RM and led to Prof Messerschmitt's removal from the business side of the company.
He was certainly one of the very beat designers of his time, but when he did get it wrong it was very expensive indeed.

Cheers

Steve

Milosh said:

An aviation expert (??) by the name of Crumpp has stated that 'toe out' is better than 'toe in'.

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Darrol Stinton, who was an aviation expert, reports the same thing.

Probably in the tanslation Cimmex, but I didn't understand what you are saying.

We noted the high incidence of takeoff and landing accidents, the opinions of German pilots, and wondered why it wasn't corrected. Willy WAS a good engineer, but his Bf 109 landing gear surely could not prove that. The other main fighers had nowhere NEAR the ground accidents the Bf 109 did.

That says something about the design of the gerar and nothing about the Bf 109 once airborne. Once it was flying it was surely one of the best in the world at the time, even near the end of the war if flown by a competent veterant pilot. But the landing gear was abysmal compared with other top line fighters.

swampyankee said:

Darrol Stinton, who was an aviation expert, reports the same thing.

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It depends on the aircraft, and the pilot.
We had one customer in a C-180 who continually had problems bouncing on landing. We rigged the undercarriage with toe-out. Because of the undercarriage type (spring steel), when weight came on the wheels, both wheels tracked outwards, and reduced the tendency of the spring steel to bounce the aircraft back into the air.

stona said:

Once the undercarriage is attached to the fuselage, or more specifically a truss which also accepted the front attachment point of the wings and the lower attachment of the engine bearers, it HAS to splay out to be functional. Even splayed the track is still barely 2 metres. All the other problems stem from this. Altering the angle of toe or making other minor adjustments to the geommetry is like sticking an Elastoplast on an axe wound.

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How did the Grumman F4F Wildcat deal with this?

gjs238 said:

How did the Grumman F4F Wildcat deal with this?

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Or any of the Cessna tail-wheel aircraft series? (or cub, maule, or any number of more modern tail-wheel aircraft?)

Okay gents I found an article from the summer 2001 issue of "Best of Flight Journal Fighters". That issue has an article called, "Flying the Bf109", by the late Mark Hanna and Capt. Eric Brown. On a post somewhere in here it was asked the source of the "information / rumor" of 109 accidents. This might be it (these excerpts are from the portion written by Capt. Eric Brown).

Here is a quote from page 54:

"The more than 33,000 Bf 109s produced from 1938 to 1945 gave the Luftwaffe an abundance of continuously updated air weapons. They were capable of beating their implacable enemies, even in the terrible conditions of Russia and North Africa. Many Luftwaffe Bf 109 pilots racked up scores in the hundreds that will dazzle the minds of air historians and fighter buffs for years to come.

But the Bf 109's deficiencies almost equal its fabulous assets. The Luftwaffe lost 11,000 of these thoroughbred fighting machines in takeoff and landing accidents, most of them at the end of the War when they needed them most. The inexcusably poor visibility from the cockpit greatly reduced their pilots' ability to fight. The snatching of the automatic wing slats not only caused many of the numerous ground accidents but also contibuted to a great many aerial accidents. The slat, canopy and landing-gear problems all had known simple production fixes. Perhaps Prof. WIlly Messerschmitt and the Luftwaffe generals were too busy patting themselves on their backs and counting Bf 109 victories to find time to listen to the pilots or to digest the significance of the Bf 109's accident rates.

The Bf 109 was, indeed, a prolific, necessary and timely fighter but was not as great as the Spitfire, the Mustang or the Hellcat, which all many fewer vices for the wartime pilots to overcome."

On page 51 he remarks about handling:

"From the handling viewpoint, the Bf 109E had two pluses and four minuses. On the credit side, it had a steep angle of climb that made it difficult to follow, and it could also bunt into a dive without its direct-injection engine cutting out under the negative G, thus leaving a pursuing British fighter behind as its carburetor-fed engine faltered. On the downside, the 109 had poor harmony of control: no rudder trimmer, which meant it was easy to inadvertently pick up skid and ruin one's sighting airm; in tight turns, the slats snatched open, giving lateral twitching and again ruining the pilot's aim. Finally, when the speed was allowed to build up rapidly in a dive, the elevators became increasingly heavy until at 440mph, they became virtually immovable."

Finally from page 53:

"Control harmony was poor because the rudder was light, the ailerons moderately light and the elevators extremely heavy. Control harmony in a fighter should be achieved with light ailerons, slightly heavier elevator and rudder heaviest."

I'm just the scribe and not the source...

Cheers,
Biff

While I'm sure the Luftwaffe pilots got used to the elevator heaviness, it cannot have helped their agility at high speeds. Riggind a rudder trim is easy, so it's tough to understand the lack of it. I can understand no rudder trim in something like and Aeronca Champ or a Piper Cub, but not in a 1,000+ HP front line fighter.

All that does not detract from the incredible record of the Bf 109 in the slightest, but it could have been much better.

I am glad it wasn't!

Didn't the Bf109 have a airfoil shape built into the vertical stabilizer that provided some push toward the side.

Not perfect, I'm sure. Not too effective in low speed, high power situations, like takeoff, and go arounds.

Yes, it did. Unfortunately, it doesn't substitute for rudder trim.

It is possible the lack of rudder trim might have been exacerbated by the airfoil in the tail, but Willy Messerschmitt would have known that.

One of our older American fighters at the Planes of Fame is a Seversky AT-12 Guardsman. It only has 975 HP and has rudder trim. The newest American fighter we have without rudder trim, other than the Bf 109, is a Boeing P-26 Peashooter. It has a fixed rudder trim tab and is only about 550 HP. Ours is trimmed for cruise flight.

However, the Yak-3 also does not have rudder trim, but is not adversely affected by this. It does not have an asymmetric airfoil in the vertical tail.

So, the question would be whether or not the US - British pilots who flew these fighters for comparative tests were simply used to rudder trim while the Germans were not, and that made the difference in flight reports ... or whether the lack of rudder trim was really a big factor. Since fighters spent MOST of the time at cruise, and not in combat, I'd lean toward it being not much of a factor unless the combat dragged out for awhile.

But that is backseat quarterbacking from 80 years later, so I don't really know except that the few former Luftwaffe pilots we have had make presentations never mentioned the rudder trim in any of their talks. That doesn't mean it wasn't a factor, but also doesn't mean it was. All it means is they didn't talk about it at the time. Given the fact that they were addressing an American audience, it would not be surprising if aircraft faults were not mentioned even if present and remembered. They might talk about it among themselves, but saying it to an Americn audience might not ever happen. I can't say either way, and did not ask at the time.

I heard Saburo Sakai give a talk once at the old Champlin Fighter Museum on Falcon Field in Mesa, Arizona (back in about 1991 or so). He mentioned that the Japanese pilots envied the speed and climb of the Hellcats. He didn't say the Zero had shortcomings, but he did say he admired the Hellcat. Perhaps that is the same thing as saying the Zero was outclassed, but I would not put words into his mouth.

I also have never met anyone who had flown a Spitfire that has much bad to say about it, but we all know it had faults. It is probably natural to concentrate on the good things and ignore or minimize the bad ones when you are talking about a machine that you flew in a war or are flying now as a restoration / toy airplane.

Another thing I have mentioned before in here, we have had many Mustang pilots claim the P-51 was the best fighter in the world. I have asked maybe 3 of them what other fighters they flew in the war, and those three said they only flew the Mustang. I have serious doubts about someone who makes a claim gthat his mount was the best ... but never flew the others!

It is quite possible the german fighter pilots who flew the Bf 109 to such incredible victory totals never flew anything else. Not all, because we KNOW Erich Hartmann flew the Fw 190 when he wanted to do so, but stayed with the Bf 109. But many of the other Bf 109 pilots may not have flown any other German fighter or any captured American / British / Soviet fighter either, so maybe they simply didn't know the lack of a rudder trim was a handicap in the first place because that was all they knew about.

tyrodtom said:

Didn't the Bf109 have a airfoil shape built into the vertical stabilizer that provided some push toward the side.

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It did, I've seen the tail in profile from above it is definitely an asymmetric shape...but I can't understand why a simple trimming device wasn't used, if only to relieve pilots of the, er, 'leg-work' in normal flying and to make life easier for novice pilots.

The canopy I can understand as the best shape they could come up with at the time to extract the best aerodynamic performance but the undercarriage was so obviously an issue (given the huge casualty list) it beggars belief that they couldn't or wouldn't 'fix' it.

Pretty interesting information fellas.

Is this value of 11k lost to accidents an estimation or backed by hard data?
The wing slats as major cause of accidents is new to me.

Good question, Denniss,

I have seen that figure many times, but never with a quoted reference! I have head some Germans say many were lost to takeoff and landing but, again, no numbers .. and no references. So, like you, I wonder where that number came from.

I hope not from William Green!

Since your sig says you are from Germany, Denniss, do you know of a German reference where the number of Bf 109's lost in takeoff and landing accidents is shown? If so, have you seen the reference and do you recall the number? It would be nice to dispell the rumor or, at best, get some sort of accurate number with a good reference. Even for a partial time period, say ... something like 1941 - 1944, which would be representative of typical wartime losses even if not complete.

Of course, just a loss number without sorties flown also does nothing for us because we cannot the nfind the losses as a percentage of flights.

This gets worse as we work our way through it logically, huh? I'd expect the losses on the Russian Front to be worse than for the Western Front due to primitive forward airfields and operation from mud in the spring. But I don't know for sure.

Maybe some of our German friends DO know and HAVE references.

The idea of wing slats causing problems might be more suggestive of allied opinions of the (enemies) automatic aerodynamic-pressure operated slats; though I would've thought that combat damaged slats could've aided in control issue problems leading to some slight additional percentage of loss than the rarer lesser chance of loss due to assymetrical opening/closing of them.

Well, if one slat was combat damaged and would not open, and if the pilot didn't know it ... and if he pulled to hard at low altitude, it would snap-stall in the direction of the stuck slat.

I have not heard of that in combat reports I've read from either side. Additionally, most people shot at the canopy-engine area, not the wingtip.

So, in practice, I seriously dount it was a major factor, though ir certainly might have happened. I am under the impression that combat in the ETO was very much more high altitude than in other theaters, so maybe it happened and the pilot simply recovered and retreated to fight another day. If I had a major control issue with my plane at 20,000+ feet, I don't think I'd stick around to see if I could die that day.

I too Greg, think it (the slats) were mostly insignificant in the problems that lead to losses, because they'd be more serious and dangerous other damage and problems than those from the slats on there own.

The slats are in sight of the pilot, if they're battle damaged he's very likely going to see it.

Wouldn't you think a pilot noticing damage around the slats, would check out their operation before he got low and slow.

Why try to force them to deploy via an aggressive control action and risk the damage locking or causing more structural damage trying to get them to work for a test... surely if the wing in that area is damaged, you either try to escape towards safe lines and worry about low speed when coming to land or bail when it is safe to do so if you/they could see the damage was bad enough...

tyrodtom said:

The slats are in sight of the pilot, if they're battle damaged he's very likely going to see it.

Wouldn't you think a pilot noticing damage around the slats, would check out their operation before he got low and slow.

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He might not notice if there was any damage if the damage was internal like a piece of of something stuck in the track or if a small caliber bullet had bent a rod.