Bf 109 variable pitch gearbox

Discussion in 'Other Mechanical Systems Tech.' started by wrbrd, Dec 23, 2006.

  1. wrbrd

    wrbrd New Member

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    I'm trying to find out how the internal planetary gear sytem works in the variable pitch gearbox for the propeller. I have limited information and a sectional view but with little detail. If anyone could explain it to me or direct me to someone who might know it would be most appreciated. I do have the maintenance manual for the VDM prop but it gives no explanation of the internals.
    Thanx and have a Merry Christmas!!! :D
     
  2. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    OK - first off there is no real planetary gear/ gear box in a WW2 constant speed propeller. It is actuated by a hydraulic piston or electrical (Curtiss) solenoid. Regardless of the manufacturer the principal is the same. Here is a real basic diagram for all constant speed propellers..


    I am not totally familiar with the prop on a Bf 109 but the principal should be about the same. Hope this helps.
     

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  3. mkloby

    mkloby Active Member

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    wrbrd - hope I can help you. It's 4am and I can't sleep!

    The basic operating principle behind the constant speed prop, in the aircraft I have flown, is as flyboy said. The max efficiency prop RPM will be determined by specific powerplant considerations. However, tension of the speeder spring can be adjusted w/ a prop rpm lever, or also a combined prop RPM/condition lever as I've seen in some A/C, which will adjust the operating RPM that the governor will maintain prop speed at, below max. The propeller governors will act to monitor and adjust propeller blade angle to maintain this prescribed max prop efficiency.

    If you are running your prop at maximum RPM, let's say 2200, and you increase engine power, at the same given prop blade angle, you would create an overspeed condition. The governor's function is to be able to sense this overspeed condition, and correct by adjusting prop blade angle to bring prop RPM back to it's maximum efficiency.

    The prop governor acheives this monitoring and adjusting of prop blade angle through the basic components that were shown in flyboy's above post. So, we'll continue w/ our example: you increase power, creating an overspeed condition. The flyweights serve to sense this momentary overspeed condition, as centrifugal force will force them outward in their rotation. This will open the pilot valve, which will drain pressurized oil from the dome assembly. The high pressure oil acts to exert force upon a servo-piston(the force in this case is decreasing), which resists a feathering spring and bladeshank counterweights to increase blade angle (since the piston's counterforce is decreased because we drained the high pressure oil) and maintain the desired prop RPM.

    The opposite is true if you decrease your power setting. The flyweights will move inward in their rotation, increasing flow of high pressure oil through the pilot valve, increasing force exerted on the servo piston and overcoming the bladeshank counterweights and feathering spring and decreasing the prop blade angle.

    Hope this quick rundown of how a constant speed prop works helps. They also include a feathering provision, and can employ a backup or overspeed governor in case the primary governor fails. If you would like to know how anything else functions - just ask!

    Matt
     
  4. the lancaster kicks ass

    the lancaster kicks ass Active Member

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    all makes for a very interesting read gentlemen, well done :thumbright:
     
  5. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Thanks Lanc!

    Damn Matt, ever thought of getting your A&P and becomming an instructor? That's a better explination then some textbooks I have! :thumbright:
     
  6. mkloby

    mkloby Active Member

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    I'm proof that military education works :D Break things down barney style - and they're easy to understand... even for us Marines :lol:

    Somehow I think the military would object to me moonlighting w/ another job! :D However, it's always a possibility in the future after my service is complete...
     
  7. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    hehehehe...

    Hey, I found out the Bf 109B used a Hamiliton Standard prop made under license. Here's one from a a "D."

    [​IMG]
     
  8. mkloby

    mkloby Active Member

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    Great pic - shows nicely some geometric twist!
     
  9. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Yep - I suspect the gear on the aft plate drive an accessory, maybe the prop governor.
     
  10. mkloby

    mkloby Active Member

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    Here's a schematic of the TC-12B prop system and a pic of the prop governors on a TC-12B....
     

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  11. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Cool! What model PT6 are on those?
     
  12. mkloby

    mkloby Active Member

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    PT6A-41 baby. 850shp, max transient 5 second 1150shp!
     
  13. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Very Cool! We have -34s on the Twin Otters we take care of for the USAFA.
     
  14. Denniss

    Denniss Active Member

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    License contractor was VDM, the Bf 109B with this prop got the unofficial name B-2 instead of B-1 with the fixed pitch wooden prop built by Schwarz (AFAIK was a deHavilland license). The B-2 designation was never officially used by RLM or Mtt.
     
  15. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Gotcha - the point here early Bf 109s used a Ham Standard prop.

    Here's a nice cutaway of a Gustav prop.

    [​IMG]
     
  16. mkloby

    mkloby Active Member

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    Very nice pic. Shows the clean installation of the powerplant.
     
  17. wrbrd

    wrbrd New Member

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    Thanx for all that information, however it's not the correct variable pitch system used on a Bf 109E.
    Due to a cannon running through the prop shaft the VDM company designed an electric variable pitch prop for the Bf 109. It could not use a hydromatic propeller for this reason. The pitch mechanism consisted of a planetary gear setup installed around the propeller shaft and activated by an electric motor. It was a manually controlled prop until somewhere around 1940 where they did incorporate an automatic or governing feature.
    What I need to know is how did this planetary system work?
    Thanx!
     
  18. mkloby

    mkloby Active Member

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    Sorry buddy... I don't know a damn thing about that!
     
  19. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Again, I think semantics are getting in the way here - a planetary gear is used to reduce turning ratios within a gear box. Prop hubs don't have planetary gears, in the case of electric propeller there should be an electric solenoid geared to the end of the prop shank which changes propeller pitch.

    Here is a Curtiss Electric propeller used on the P-39. I believe the set up would be very close to the bf 109E.

    Now full feathering propellers did have a gear box in the front portion of the hub which housed an electric motor. This is where you might be thinking planetary gears and gearbox...



    I know I have a Bf 109E hub cutaway somewhere and again I think it's operation is very similar to the set up shown for the P-39.

    [​IMG]
     
  20. wrbrd

    wrbrd New Member

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    The curtiss prop is a totally different system altogether. The gearbox used on the Bf 109 uses a planetary system to change the sun gear to which it drives the gears on the prop hub and by way of worm gears turns the blades.
    In the gearbox are planet gears, sun gear and what have you. At the back end of this gearbox is an input gear driven by an electric motor which in turn (this is what I'm trying to find out) drives the forward gear which operates the blades. I need to know the set up of the gearing so this blade change can be accomplished.
     
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