4 bladed props

Discussion in 'Aircraft Database' started by richardc7, Jun 30, 2008.

  1. swampyankee

    swampyankee Active Member

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    Umnh, no. Since I did prop aero for a number of years, I know that the statement "three blade prop has a higher efficency[sic]" is, at best, an oversimplification. Induced losses are reduced with a greater number of blades; the loss of efficiency with greater blade numbers will occur if individual blade chords are excessively large or if there is interference between blade roots; the latter does not tend to be problematic with as few as six blades, and not until speeds that are greater than the operational speeds of almost all ww2 aircraft (modern propellers, such as those on the A400M, have the spinners contoured to eliminate that problem This requires cfd tools that didn't exist 30 years ago and weren't possible 50 years ago). There is a constraint on minimum blade chord; this is usually that the blade operates with large regions of separated flow and with highly angular airflow in the propeller in some flight regimes, especially takeoff, and this dictates the thickness at the blade root, which will tend to dictate the minimum chord.
     
  2. gumbyk

    gumbyk Well-Known Member

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    That may or may not have anything to do with flexing. There are many reasons for a prop to shed a blade.
    MacCauley have been trying for 20 years to get one of their propellers to work with the one of the Lyc IO-360 series engines (I can't remember which one off the top of my head) and just can't get it to work. After 20 hours of operation, the blade shears off at the root. There is something happening that the engineers just can't quite nail down, and these aren't high-powered engines.
     
  3. Westfield Charlie

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    Some of the early WWI English biplanes had four-bladed propellers. The BE 2-C, described charitably as 'perhaps the worst plane ever made" (up to that point). British ace Albert Ball summed it up as "a bloody awful aeroplane".

    As early as 1915, the B.E.2c entered service as a pioneer night fighter, being used in attempts to intercept and destroy the German Zeppelin airship raiders. The interceptor version of the B.E.2c was flown as a single-seater with an auxiliary fuel tank on the centre of gravity, in the position of the observer's seat. After an initial lack of success while using darts and small incendiary bombs to attack airships from above, a Lewis gun was mounted to fire incendiary ammunition upwards, at an angle of 45°, to attack the airship from below. The performance of the B.E.2 was inadequate to intercept the Gotha bombers of 1917, but the techniques it pioneered were used by the later night fighters.


    View: https://www.youtube.com/watch?v=yvA-154kgrM
     
  4. GregP

    GregP Well-Known Member

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    #24 GregP, Feb 17, 2015
    Last edited: Sep 29, 2015
    sqrt = square root.

    The ideal diameter of a 2-blade prop in inches would be 22 * sqrt(HP).

    The diameter of a 3-bladed prop would be 18 * sqrt(HP).

    The diameter of a 3-bladed agricultural prop would be 20 * sqrt(HP).

    The 4/5-blade I don't have yet, but these ar VERY close ... and the REAL diameter depends on use and landing gear length. A Naval fighter would need a shorter prop than an Air Force fighter due to carrier landing thumps.

    Good place to start your prop investigation ...
     
  5. Elmas

    Elmas Active Member

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    MP_1937 C161_02w.jpg


    Caproni Ca 161 bis - the airplane with which Col. Mario Pezzi achieved the world record height for propeller driven aircraft, still unbeaten with 17.083m, october 1938.
     

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  6. Wurger

    Wurger Siggy Master
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  7. GregP

    GregP Well-Known Member

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    Now THAT's a propeller!
     
  8. Wurger

    Wurger Siggy Master
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