3 Blade vs 4 Blade props

Discussion in 'Other Mechanical Systems Tech.' started by Thorlifter, May 23, 2007.

  1. Thorlifter

    Thorlifter Well-Known Member

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    Can anyone tell me the advantages / disadvantages of each. Seems to me the more blades the more air it would grab.
     
  2. comiso90

    comiso90 Active Member

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    Good question....

    I imagine the more blades, the more complicated the feathering mechinism would have to be.
     
  3. FLYBOYJ

    FLYBOYJ IP/Mech THE GREAT GAZOO
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    The number of propeller blades are determined by engine HP, Blade length and engine RPM. based on this engineers determine how to get the most "bite" from the engine and propeller combination. There was an aircraft flown with a one blade propeller said to be the most efficent.
     
  4. comiso90

    comiso90 Active Member

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  5. Cyrano

    Cyrano Member

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    #5 Cyrano, May 23, 2007
    Last edited: Jul 21, 2011
    [​IMG]
     
  6. FLYBOYJ

    FLYBOYJ IP/Mech THE GREAT GAZOO
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    No, it was offset with a counterweight.
     
  7. Thorlifter

    Thorlifter Well-Known Member

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    That makes sense. But how do you explain, for instance, the Corsair. They had 3 blades and 4 blades, but it was the same engine, give or take 100 hp.
     
  8. Wurger

    Wurger Siggy Master
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    FlyboyJ is right.Look at early WW2 fighters ( Spitfire,Bf-109,).At first, they were equipped with two-blade propellers, but when their engines became more and more powerful they had to be fitted with 3 or 4 blade props ( Spitfire Mk.XIV and later with 5-blade prop even,Griffon engine had really a big power) to make the props working effectively.It seems that the German engineers chose a different way to solve the problem.Fw 190s,Bf 109s and other later a/cs were equipped with props that had very wide blades.As far as F4U Corsair is concerned.The plane had so powerful engine that if its prop would have to work correctly the blades had to be very long.As a result the Vought firm made the fighter using the "W" shape of the wings ( in front view) to equip the plane with the engine and prop.It seems that the 4-blade prop worked much more effectively with the powerful engine.
     
  9. FLYBOYJ

    FLYBOYJ IP/Mech THE GREAT GAZOO
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    In actuality when the Corsair went from a 3 blade to a 4 blade prop, the engine did change (different dash number) as well as altitudes the later models were operated at. I think this was at the thinking of the engineers who made these changes.

    Check this out...

    A Single-Bladed Prop? What the h....?
     
  10. comiso90

    comiso90 Active Member

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    Wurger...

    You have the best "sig pic". did u make it yourself?
     
  11. Wurger

    Wurger Siggy Master
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    Yes I did :) using some components for the collage.
     
  12. Tony Williams

    Tony Williams Member

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    I think you meant to type two-blade: AFAIK only model aircraft have been made with one-blade props. You can balance the weight of a one-blade prop with a counterweight, but you can't balance the thrust - and the forces generated by a powerful engine would probably destroy the propeller shaft.

    For any engine of a given power, there were a number of options facing designers. The more blades you had, the more thrust you could obtain within a given propeller diameter, but the closer the blades were together the less efficient they were, as each blade disturbed the air for the following one. Another variable was the chord of the blades - how wide they were. As with aircraft wings, a long, narrow shape is the most efficient in terms of the maximum thrust for the minimum drag, but a large propeller diameter causes practical problems, not just with undercarriage height but with propeller tip speed approaching the speed of sound, when performance falls off badly.

    Designers of the early WW2 fighters like the Spitfire and the Bf 109 had the problem of coping with engine power which increased steadily through the war, so the props had to be upgraded to cope with the power. There was only a very limited opportunity to increase the prop diameter because of undercarriage length, so they had the choice of adding more blades (the Spit went from 2 to 3, then 4, then 5, then 6 in a contraprop) or making the blades wider (the Germans generally chose this). Why the Germans didn't add more blades has been the subject of much debate, but one of the reasons was probably their reliance on synchronised guns: the more blades you have, the more precise the timing of gun firing has to be to ensure that the projectiles pass between the blades.
     
  13. davparlr

    davparlr Well-Known Member

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    Good entry. Clear and concise.
     
  14. renrich

    renrich Active Member

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    The F4U1 could turn up only about 2000 HP and had 3 blade prop. The F4U4( the first Corsair with a 4 blade prop) could develop more than 2400 HP. Thus the 4 blader. My brother has a Saratoga 10 or 20 years old. Recently had a complete overhaul and went from a 2 blade to 3 blade prop. Says it climbs a little better but probably no faster but seems a little smoother.
     
  15. Wurger

    Wurger Siggy Master
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    Certainly, yes.Some troubles with the translation into English.:lol:
     
  16. Soren

    Soren Banned

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    Exactly.

    As to the one blade prop, well that'll be an uncomfortable ride :)
     
  17. DOUGRD

    DOUGRD Member

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    DITTO!!! Now for another question: Why is the front set of blades on some counter-rotating props longer than the rear set? The RAF Shackleton for an example.
     
  18. Graeme

    Graeme Well-Known Member

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    According to 'Jane's' 1959-1960, the Shackleton's props are all 13' (3.96m) in diameter. What source tells you differently? Bradford's accurate(?) 3-views also depicts them as equal diameter.
     
  19. DOUGRD

    DOUGRD Member

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    Iceland 1981: Flew in WR960 the Shackleton that is now displayed in the Manchester museum. We played "rabbit" in the clouds while two USAF F-4s played "fox" and tried to get a heat seek lockon. One of the Mechs pointed it out to me. He said it was to prevent the tip turbulence from playing havoc with the tips on the rear prop blades. Made sense to me at the time?
     
  20. Cromwell

    Cromwell Member

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    Some model planes fly with a balanced one-blade prop as it is supposed to be more efficient

    Problem is this

    its not just about weight in a still balancing situation, its also about unbalanced aerodynamic forces when rotating

    Then what do you do ?


    Crommie - whatever happened to the first Brit Repbulic ?
     
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