Bf 109 Landing Gear Geometry Issue

Discussion in 'Aviation' started by GregP, Jan 15, 2014.

  1. GregP

    GregP Well-Known Member

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    #1 GregP, Jan 15, 2014
    Last edited: Jan 15, 2014
    I was asked to clarify the landing gear geometry issue in the Bf 109 by a visitor to the museum last weekend. Attached is a front view drawing of a Bf 109.

    Bf109_LG_Geom.jpg

    When the tail is up, the tires are pointing parallel to eash other and straight down the runaway. No problem,

    Now imagine for a second that the aircraft is pointing straight up, but is sliding forward in the direction of the belly. See the layout of the landing gear below the aircraft drawing. It is easy to see that if the gear is moving in the direction of the center arrow, the tires would be trying to slide outward from each side.

    The aircraft cannot do this physically, but as the aircraft tips backward, the alignment track of the tires becomes increasingly toe out and, by the time the tailwheel is on the ground, both tires are toed out to a significant degree. The leanback angle is about 13°. If one tire or the other gets significantly more pressure (or weight on it) than the other, as in a crosswind where one wing lifts a bit, then the main gear will move in the direction of the wheel with the greater weight on it. If the pilot isn’t very quick with the rudder or brake or both, a groundloop can easily result.

    Fitting a tailwheel lock helped but did not eliminate the problem.
     
  2. stona

    stona Well-Known Member

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    Which is why a three point landing was the method taught to Luftwaffe (and modern) Bf 109 pilots. The problem with this is that in this attitude the view forward is poor and this makes it difficult to detect any swing developing, which brings us back to your last sentence :) Inexperienced pilots tended to over react with inevitable results.
    The geometry is the problem, the track of the Spitfire under carriage is significantly less than a Bf 109.
    Cheers
    Steve
     
  3. Milosh

    Milosh Well-Known Member

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    The track of the Spitfire was ~6" less than that of the Bf109.
     
  4. bobbysocks

    bobbysocks Well-Known Member

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    none of the front line fighters were too friendly to inexperienced pilots. but most allied pilots had 300+ hours before getting into one and then had several hours of orientation. the LW didnt have that luxury. i dont know how many hours they were getting before stapping into 109s late in 45 but it wasnt a whole lot......

    At some point during this period, Robert told me he was preparing for his first solo ride in the P-51. I advised him against the same mistake I made on my first take-off in a P-51. Had taxied to the end of the runway, got clearance to take-off,crammed the throttle forward and the horrendous torque developed by that very powerful engine and huge 4 blade prop jerked my nose about 30 degrees to the left and I darted off the runway. I knew if I reduced power I would mire in the January English mud and flip over. Not an option so I kept the power on, got it off the ground, got the wheels and flaps up and barely cleared the airport tower, so close that I took the wind sock with me. I am considering taking this with me on my next trip to Leiston airbase and advising them that I am returning the wind sock to their museum.
     
  5. Aozora

    Aozora Well-Known Member

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    The Spitfire's legs were vertical, with some toe-in of the wheels, therefore the legs were resistant to being pushed sideways. The legs of the 109 could be forced sideways by lateral forces because they were already splayed. In addition the structures that secured the 109's pivot points to their mounting points on the main bulkhead/spar were liable to be distorted by heavy landings (eg; the 109K):

    [​IMG]

    take a look at the support structure 3, 21, 24, which was cantilevered and could be bent out of shape by lateral forces

    [​IMG]

    vs Spitfire, supported at both ends and, being a tube, was less likely to be bent out of shape, albeit heavy landings could and did force the leg up through the wing (eg Seafires were prone to this)

    [​IMG]

    Any lateral twisting or outwards movement was resisted by the hydraulic piston:

    [​IMG]
     
  6. GregP

    GregP Well-Known Member

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    I've never understood why Willy didn't toe-in the wheels so they were parallel in the 3-point attitude and toed-in during a wheel landing.

    It would have corrected the worst of the faults and was almost ridiculously simple to accomplish. Then the swings on landing and takeoffs would have disappeared. Further, I'm surprised no crew chief came up with field mod to handle it.

    It may well have been a case of simple pride that they didn't need a "fix" to handle this fighter, I can't say and would not care to speculate.
     
  7. gumbyk

    gumbyk Well-Known Member

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    And a CofG that is well aft will make it all the harder to correct before it becomes unrecoverable.

    Thanks for the clear, easy-to-follow description, Greg
     
  8. Aozora

    Aozora Well-Known Member

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    Later variants, from the G-4 onwards had bigger mainwheels (from 650 x 150 mm to 660 x 160) and the geometry of the hubs was changed so the wheels were more vertical - the bigger wheels and more upright position meant that the kidney-shaped fairings were needed on the upper wings. Some late G-14s, most G-10s and all K-4s adopted larger 660 x 190 mm wheels which required the larger, rectangular upper wing bulges.
     
  9. gjs238

    gjs238 Well-Known Member

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    This drawing seems to show how an inverted V engine produces a sort of triangle shaped engine cowl with presumably less visibility restriction for the pilot.
     
  10. GregP

    GregP Well-Known Member

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    You're welcome for the text and, yes, I believe an inverted Vee does result in slightly better visibility over the nose and down, but seeing a small bit closer to the plane is not very important since almost ALL Vee engine WWII fighters have a poor, but better than with a radial engine, view over the nose.

    None except maybe the Hellcat offer a view ahead. Can't see much down and to the side, but you CAN see the runway in front of a Hellcat about 80 yards ahead or so. At least, I can if sitting on a parachute.

    In the air, all you have to do is bank slightly one way or the other to get a view ahead and down.
     
  11. gumbyk

    gumbyk Well-Known Member

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    I'm not convinced that visibility was such an issue.
    I've been trained to use a combination of a point in the clouds, and peripheral vision to judge swing.
     
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  12. Milosh

    Milosh Well-Known Member

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

    GregP Well-Known Member

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    #13 GregP, Jan 15, 2014
    Last edited: Jan 16, 2014
    Guess he never read a basic aerodynamic text that addresses conventional landing gear.

    Of all the conventional gear WWII fighters, I believe the Bf 109 is the only one with toe out. I could be wrong there, but if so, not by much.
     
  14. MikeGazdik

    MikeGazdik Member

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    #14 MikeGazdik, Jan 15, 2014
    Last edited: Jan 15, 2014
    Not sure with airplanes, but in a car, "toe in" creates a very twitchy vehicle. Toe out is more stable. But a car does not go through the dynamics of a landing plane.

    I could see, toe in or toe out, that on landing this would be much more of a problem than on take-off. On take-off the load on the gear would become less important as speed increased, whereas on landing it would keep increasing and become more important.

    And if load transferring from side to side, would create a toe-in and toe-out fluctuation, that would be tough.

    This video shows a lot of directional instability on landing. (regardless, what an awesome looking, sounding, and flying airplane. love it ! )
     
  15. stona

    stona Well-Known Member

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    That's exactly what Luftwaffe (and I suppose everyone else's) pilots were trained to do. The problem was with inexperienced pilots who fund it hard to see the swing developing and then over reacted with coarse control inputs to correct it. The Bf 109 is very unsympathetic to clumsy reactions like this which is why it was challenging for these inexperienced pilots. There are numerous accounts from the 'experten' explaining how they kept the aircraft straight using well judged control inputs and, on landing, the brakes, but this was beyond the ability of some young pilots.
    All these powerful, single engine aircraft of WW2 had adverse reactions to the engine torque, it's just that in the case of the Bf 109 this was compounded by various other factors and notably the title of this thread, to make it at the very least 'tricky' to land and take off.

    The Spitfires undercarriage track is indeed about 15cm/6" less than the Bf 109. I'd call that significant since for the reasons explained by others above the Spitfire does not suffer the same problems as the Bf 109, despite this. The problem lies with the geometry, not the width of the Bf 109s under carriage and yet time and time again, both in print and all over cyberspace, you will see the assertion that it was the Bf 109's narrow track undercarriage that caused innumerable landing and take off accidents.

    Cheers

    Steve
     
  16. Lefa

    Lefa Member

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    #16 Lefa, Jan 16, 2014
    Last edited: Jan 16, 2014
  17. stona

    stona Well-Known Member

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    Maybe you should go back and read what some of those reports say. Experienced pilots could handle the Bf 109 with relative ease but it is the less experienced pilots flying an unforgiving aircraft that were the problem. I can't quote every reference to this but Antti Tani sums it up nicely in the link you gave.

    Antti Tani: The first starts were often risky for many pilots. Many of them went in the forest, there was a "Messerschmitt corner " at Utti.

    It's also worth considering what the men who flew them at the time said. Even those who liked the Bf 109 would support what Tani said. Time and time again they comment on the difficulty that inexperienced pilots had handling the aircraft on or close to the ground.

    The reports from test pilots and experienced pilots on the Me 210 are invariably positive. For inexperienced pilots it was a different story. Johannes Kaufmann of ZG 1 wrote.

    'The Me 210 certainly impressed us... In comparison with the Bf 110, the Me 210 was faster.......climb performance was much better, diving characteristics conformed to the demands placed on it....The warning of danger on take off was justified as it needed some corrections to be made with rudder and the engines to stay on a straight line course........The approach and landing caused no problems.
    Coming from Regensburg on the landing approach to Tours, I saw a most unusual picture. There were some crashed aircraft lying on the airfield which were evidently new and consisted of Me 210s......These crashes were due to exclusively to the young, still inexperienced pilots, so that a revised decision was forced upon the aeroplane. This came very quickly. The Me 210 was withdrawn...'


    The Bf 109 did not have some of the malicious handling characteristics of the Me 210 and was of course never withdrawn from service. It was nonetheless a handful for inexperienced pilots and killed a lot of them.

    I will repeat that I don't believe that the Bf 109, as it entered service with the Luftwaffe, would have been accepted by the RAF.

    Cheers

    Steve
     
  18. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    #18 FLYBOYJ, Jan 16, 2014
    Last edited: Jan 16, 2014
    Ok folks, a few pokes here...

    Describe "experienced."

    300, 400, 500 hours in tail draggers? 1000 combat sorties? A complete combat tour?

    I've known pilots with just a few hundred hours who were more proficient and safe than pilots with thousands of hours. Additionally what kind of operations were 109 drivers subjected to? Planned calm mission sorties or hectic scrambles with little time to focus on basic aviating. Airfield conditions - moguls and holes all over the place or long and wide paved runways?

    It was also mentioned that these aircraft were flown with no checklists, a huge risk factor recognized and remedied in the post war years as "lessons learned."

    AFAIK the "old school" philosophy was to make 3 point landings as a norm, but as mentioned there are field of vision problems with the nose of the -109 being so long so peripheral vision would have to play here, throw in poor runway conditions as well as gusty crosswinds and this elevates the risk.
    After considering this and reading some of the comments I guess is crystal clear why the tail dragger disappeared in post WW2 combat aircraft.
     
  19. stona

    stona Well-Known Member

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    I don't think you can put a number on it. An old hand with many hours on other types might be able to apply that experience to flying the Bf 109 and would have a much lower chance of disaster.
    A young pilot with relatively few hours, but who had survived a number (pick one !) of take offs and landings in a Bf 109 would also be much less likely to come to grief.
    Cheers
    Steve
     
  20. Lefa

    Lefa Member

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    I have read, and although Finland used the plane until 1954, I have not read than one fatal accident, some broken machines, though. If anyone has information about the Bf 109 accidents in Finland, put the information here. Of course they are some, but I have not seen statistics
    I think a bad reputation came from Germany where late in the war, after very short pilot training, young pilots entered the plane.
     
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