Wood Constant Speed Prop Blades

Discussion in 'Firewall Forward / Props / Fuel system' started by Monty, Jan 31, 2015.

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  1. Jan 31, 2015 #1

    Monty

    Monty

    Monty

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    A lot of older constant speed props used wooden blades. The Germans, including MT continue to use wood core composites. The retention system is a series of lag screws in a stainless steel cup that interfaces the bearing in the hub. Does anybody have ANY info on:

    1.) the lag screws (they are long to short and distribute the load from the blade to the hub. any sources?)

    2.) Installation proceedures

    3.) Acceptable practices glues, woods, lamination schedules etc. Do you pre drill the holes for the lag screws? Do you use epoxy in the hole....etc.

    4.) Leading edge erosion strip installation practices.

    These types of blades were used on everything from the Spitfire to the FW190. I know there has to be some technical documentation somewhere. I've searched high and low on the inter webs and come up empty. The best thing I have found is on the Aeromatic website, but that is just a picture.
     
  2. Jan 31, 2015 #2

    BBerson

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    I think the Hoffman HO-V62 manual is at the website. Shows the brass leading edge and some other stuff.

    Certainly lag screws are pre-drilled to shank size.
     
  3. Jan 31, 2015 #3

    TFF

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    Aeromatic has wood blades. Sometimes they can be real cheap in un-airworthy condition. Good for dissection . You can probably get some old blades for nothing. I know the Aeromatic has wood screws holding the ring. The contention of the AD, although the prop that caused the AD was un airworthy in multiple ways. I believe the screws are installed dry, but they are still made to a 30's type cert.
    Most modern wood props cheat and have a prop tape on the blades. Fiberglass or carbon have been used too. You want tit to be sacrificial and renewable, which is why most use the tape. Metal requires some real skill and tooling to pull off.
    MT uses aprox 1/2" square wood stock that is glued together; that is a lot of gluing. I would be using plank wood. How thick is up to you and the wood and speed. I have seen for fixed pitch 1" thick and I have seen 1/4" and in between. I would personally use resorcinol, but epoxy are used by some and plastic resin are being used too.
     
  4. Jan 31, 2015 #4

    4trade

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    Finnish use some fighter models (WW 2) hamilton standard hub copy and laminated wood prop blades. Those wood laminate use very thin blanks, some cross lamination too. Lamination was closer to plywood thickness than blanks. I check my books, do i find more for that construction and assembly.
     
  5. Jan 31, 2015 #5

    Jan Carlsson

    Jan Carlsson

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    Other method is to have a big course thread on a taper shank where the metal ferrule is. or both.
     
  6. Jan 31, 2015 #6

    Propman

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    The first 40 Bonanzas had multi-lam wood blades. one was Reklaw flyin last October. Had an interesting conversation with the owner.
     
  7. Feb 1, 2015 #7

    4trade

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    Those WW 2 props was birch laminate in Finland. Laminate thickness was 0.3 mm and every tenth veneer was 90 degree angle. Wood quantity was 70% while there was bakelite type of material rest of 30%. Those prop blades lamination was hot, compress lamination, 115 C and 25 kp/ cm2. Wood laminate was extreme tough and hard.

    This is not gonna help you...i think that you are after more conventional wood prop building.
     
  8. Feb 1, 2015 #8

    Monty

    Monty

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    You are correct, the densified wood type is not what I'm looking for. For those who might be interested AEHS has some info on the public portion of their site: here

    If you are a member they have some more info on the manufacturing process used to make these blades. The threaded blade roots were made of densified, and resin infused wood. The leading edges are brass and the blade is coated with bakelite. Not something a homebuilder is going to be able to do. The MT method of using lag screws in regular wood laminate is what I'm after.
     
  9. Feb 1, 2015 #9

    Jan Carlsson

    Jan Carlsson

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    I don't think MT is using regular wood in the shank, it is compressed beech, and then light weight spruce in the blade.
     
  10. Feb 1, 2015 #10

    Toobuilder

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    I know you're looking for wood construction, but that guy who was building that V-8 powered Lancair IV "looking" ship was also doing his own blades in CF. IIRC, there were some good pictures on his site... Might give you some ideas.
     
  11. Feb 1, 2015 #11

    4trade

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    Bob Barrows, Bearhawk designer, build wood blades for constant speed prop too. He maybe can give some help.
     
  12. Feb 1, 2015 #12

    Monty

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    Something like this is what I had in mind. IIRC Barrows made his using a Hoffman hub. I am pretty sure they have a lot larger shank on the blades than a Hartzell. I know they use a different wood in the shank than the blade core. I'll look into the V8 "Lancair" composite blades.

    I suppose I could just make them of aluminum, I can do that, but want to save weight. I'm pretty sure the blades are made from forgings, and then machined and heat treated or vice versa. I'd have to start with billet. Not sure about the internal stress issues. I could use T651 to address that problem. The reason for all this monkey motion is my engine turns the wrong way, and I'm not going to spend $13-20K on a prop. I won't have that much in the airframe and engine combined.
     
  13. Feb 1, 2015 #13

    4trade

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    Autoconversion? Marine (auto) conversion have several type of V8 that can run opposite direction than autoengine. Cams and cam gears are cheap for marine V8.
     
  14. Feb 1, 2015 #14

    Toobuilder

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    Monty, I was thinking of the LP1. Sorry, it took me a bit to remember.
     
  15. Feb 2, 2015 #15

    TFF

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    I would stay away from homemade aluminum because of the resonance issues. $13-20K would buy you a new CS Hatrzell if not close to two at 20K. Anything over 5K and you can buy something used but good.
     
  16. Feb 2, 2015 #16

    Monty

    Monty

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    Unfortunately, that is not an option in this case. A reverse rotation prop is the easiest solution.
     
  17. Feb 2, 2015 #17

    Monty

    Monty

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    Yes, resonance issues are a problem with aluminum, thus my interest in wood. I do have access to what I need to measure the blade resonance and could even put strain gauges on them. My installation is weird enough that the factory stuff just doesn't work. The only prop in the HP/speed range is way too big in diameter, and too heavy, rare and expensive.....

    Trust me I've looked.
     
  18. Feb 2, 2015 #18

    TFF

    TFF

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    OK your probably low at 20K. How much HP and diameter limitation?
     
  19. Feb 2, 2015 #19

    Monty

    Monty

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    320 hp, 72 inch diameter, reverse rotation, 19.5 inch spinner, 3 blades

    No way around custom blades-unless you know a secret.
     
  20. Feb 2, 2015 #20

    TFF

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    Even with 3 blades you are still 8-10" short on dia. with that hp. Yep, 4 bladed MT with custom blades for rotation.
     

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