Wood Scimitar Propellers - reliability?

Discussion in 'Firewall Forward / Props / Fuel system' started by SteveR, Apr 11, 2011.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Apr 11, 2011 #1

    SteveR

    SteveR

    SteveR

    Active Member

    Joined:
    Jan 12, 2005
    Messages:
    37
    Likes Received:
    0
    Location:
    Norman, OK
    Are scimitar propellers more prone to breakage than "standard" straight propellers? Some scimitar shapes have quite an aggressive curve, and it seems to me that the strength of the propeller would be reduced. I have heard of one instance where a tip broke off, but one incident doesn't really prove anything.

    I'm considering buying a scimitar type propeller, but I want to make sure it is safe. I have a baby on the way this month so I'm thinking about these things more than before. Any thoughts would be greatly appreciated. If anyone can recommend me to someone who is an authority on the subject, that would also be greatly appreciated.

    [​IMG]
     
  2. Apr 11, 2011 #2

    JMillar

    JMillar

    JMillar

    Well-Known Member

    Joined:
    Jan 18, 2007
    Messages:
    233
    Likes Received:
    0
    Location:
    Antigonish, NS, Canada
    I would suspect that the lamination of the wood is tailored to ensure that strength remains high despite the curve. But I am certainly no expert.
     
  3. Apr 11, 2011 #3

    Dan Thomas

    Dan Thomas

    Dan Thomas

    Well-Known Member

    Joined:
    Sep 18, 2008
    Messages:
    4,786
    Likes Received:
    2,017
    The old guys thought they were OK.

    Beautiful.jpg

    1926-alexander-Ealgerock-simitar-prop.jpg

    Model_L_Front_242.jpg

    Some homebuilders have made such props with an extreme sweep and claim that higher thrust loads pull the tips forward, which reduces the pitch of the prop and lets the engine rev a little higher and make more power. In cruise they flex back and increase the pitch.

    I dunno.

    Dan
     
    DangerZone likes this.
  4. Apr 11, 2011 #4

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,443
    Likes Received:
    3,180
    Location:
    Memphis, TN
    what is more important is the linage. if it was made by a company that knows what they are doing they are fine. if you know the history that is important too. If you are worried send it back to be inspected. Some of the new high performance props are being made this way.
     
  5. May 14, 2011 #5

    Hugh Lorimer

    Hugh Lorimer

    Hugh Lorimer

    Well-Known Member

    Joined:
    Feb 14, 2008
    Messages:
    298
    Likes Received:
    99
    Location:
    Stair, Ayrshire, Scotland.
    All the props that I have designed and made , had a performance improvement over commercial props. On the subject of twisting? I made the neutral axis of the blade section at the 18% chord line to encourage the de-pitching ( slightly ) under load. The laminated mahogany core had carbon fibre sandwiched also, then the complete shape was encapsulated in c.f. ( Fibre glass would have allowed slightly more twist?.)Hughie
     
  6. Feb 7, 2015 #6

    Retroflyer_S

    Retroflyer_S

    Retroflyer_S

    Banned

    Joined:
    Nov 3, 2014
    Messages:
    411
    Likes Received:
    29
    Location:
    Michigan
    Sounds like a reasonable idea. Anyone ever laminated prop blades in a mold ?
     
  7. Feb 8, 2015 #7

    Jan Carlsson

    Jan Carlsson

    Jan Carlsson

    Well-Known Member

    Joined:
    Jan 11, 2009
    Messages:
    1,860
    Likes Received:
    387
    Location:
    Sweden
    All propellers can suffer from flutter and loosing a blade or part of a blade. that's why all propellers is or should be tested on the engine it is supposed to go on.

    A propeller like the on in the OP is looking like WW1 style, they where wide and slow turning on multi cylinders engine often. put that on a few cyl direct drive, with a high aspect ratio propeller and you might get problem. Or not!

    A pure scimitar prop will have a small radius mean line. and need the wood planks to be glued in a S shaped mould with the planks standing instead of flat.

    On a small slow airplane I don't think there is any gain in having a scimitar prop over a standard shape propeller. the speed range is to small.
    But a good propeller will win over a poor propeller any times.
     
    DangerZone and dcstrng like this.
  8. Feb 9, 2015 #8

    DangerZone

    DangerZone

    DangerZone

    Well-Known Member

    Joined:
    Sep 5, 2011
    Messages:
    2,107
    Likes Received:
    369
    Location:
    Zagreb HR
    Just to confirm the old guys were (and still are) right, the most efficient propellers are almost identical in shape... It's like going back to the roots, old school style, the most advanced Hartzell props for piston engines have a sort of scimitar blades.

    Hartzell-Propeller-3-blade-7605-composite-piston.jpg
    0710_HPC_FOD1.jpg
    0710_HPC_FOD4.jpg
    Hartzell-Propeller-Composite-Piston-Header.jpg

    I know a guy who made wood prop blades and then vacuumed the glass and carbon around the blades and installed a stainless steel leading edge protection more than twenty years ago. Amazingly, last year at the Aero Expo in FH Germany Hartzell has shown a cut through of the ASC-I and ASC-II which seem to have an identical structural technique.
     

Share This Page

arrow_white