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Thread: Props - Wood vs. Metal

  1. #11
    RetroAcro's Avatar
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    OK, didn't have the time or motivation to get all scientific, but made some notes about the propellor swap-out on the 85hp stock Reed Clipped J-3 Cub that I fly. Sensenich 72GK44 wood prop was replaced with a metal Macauley CF71-44 . First thing you'll notice is that the heavier metal prop takes longer to spin up to the RPM you've got the throttle set to when starting, which gives you even more time to get your hand on the throttle as the engine "spins up" after propping it from behind. J-3's were made for this. Another nice thing about metal is that you can prop it with less effort if you bounce it a little against compression and get the prop moving downward before pulling it through...the momentum does a lot of the work.

    I can't say I noticed any obvious increase in takeoff/climb performance with the metal prop. Hard to say without doing comparison tests. Not sure if I'll get around to it like I did with the Pitts, but it would be interesting to get some good climb numbers flying the two props back-to-back so that density altitude conditions are similar. It turns up about 50 RPM less on climbout (engine developing less power), and leveling off, setting 2,350 RPM, it indicated 79, which is about 5 MPH faster than the wood prop at that RPM. Nope, Clipwing Cubs are NOT faster than the longwing J-3. Not sure yet if fuel flow is going to be the same at it was before at this RPM.

    As expected, the stick feels heavier in flight with the metal prop due to the slight move forward of the CG, as well as the gyroscopic (pitch) resistance of the metal prop vs. wood. I went through the reverse of this when changing from a metal prop to composite on the Pitts...it's quite a bit lighter in pitch now.

    Idle RPM can be set lower with a metal prop - more flywheel effect, which allows for a lower steady idle RPM. The difference shows up during landing - it seems to be a little less "floaty" due to less residual thrust at the lower idle. It also seems to drop altitude more dramatically in a slip than it did with the wood prop...I assume for the same reason. I consider these to be good things.

    Due to the CG move, I noticed that I must now pull the stick just a little further aft and put it on the stop to get a true 3-point touchdown power off. Before, you could touch down very slightly tailwheel first if you pulled the stick to the stop just before touchdown.

    So a very slight performance advantage (speed, not climb) with the metal prop, but it very much changes the entire "feel" of the airplane. I actually prefer the lighter feel of the airplane with the wood prop, but there's enough good about the metal prop that I think it'll stay.
    Last edited by RetroAcro; 07-17-2012 at 08:47 AM.

  2. #12
    WeaverJ3Cub's Avatar
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    Nice "science" and explanation, RetroAcro. I don't have a dog in this fight , but it's very interesting nonetheless.

  3. #13

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    Wood vs. metal? There's another kind. Way back when, I came back from globetrotting with USMC and made another run at my PPL. My instructor mentioned that all that stuff we practiced was to satisfy the CAA. We now had the FAA and they had other ideas for what a PPL should know. For a J-3 to haul a battery, generator, radios,etc the A-65 was upgraded to 75HP and a Beech R-003 controllable pitch prop was mounted. At that time it was called a Beech-Roby. It sure made the Cub climb. It was controlled by crank in the cockpit. Looked a lot like a window crank from a 52 Desoto.

    Bob

  4. #14

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    Wood blades are generally used for lower power engines ( <100 hp) because they are lighter, absorb energy pulses better than aluminum (damping) and are frangible in case of a prop strike. But drawbacks include shape control in manufacturing, moisture absorbtion which can effect balance and mass and contour changes. They don't have the same stiffness as metal so can't maintain resistance to bending for given loading and that limits power capability. Cost is usually lower than other materials and esthetics are pleasing. I have a GSC 2-blade, ground adjustable wooden prop on Rotax 912 with good performance and smooth operation.

  5. #15

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    Bob, the Spiteful, with wooden blades had a Griffon with 2500 horsepower.
    But , then again that was just Supermarine, and they probably didn't know that wood was only for low power engines under 100 hp.

  6. #16

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    Mulitblade wood props were made during the war to conserve metals, but I assumed this thread was about GA aircraft with relatively low power ( <100 hp) Cub class engines as initially stated. If you try hard enough, you can find exceptions to any normal application. For consistent shape control, balance, strength, low rotating mass and relatively good damping, a composite blade is hard to beat. If you fly in rough places where a prop strike is possible, wood props will disintegrate like an energy fuse, protecting the engine from damage. I had that happen and was thankful for a $300 wood blade replacement cost instead of thousands for a metal blade and the associated thousands more cost of engine teardown and repairs.

  7. #17
    rosiejerryrosie's Avatar
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    Where did you get a wood blade for $300.00?
    Cheers,
    Jerry

    NC22375
    65LA out of 07N Pennsylvania

  8. #18

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    GSC in Canada makes a ground adjustable wood prop; wood blades and an aluminum hub for around $500 delivered. If blades are broken, a new pair runs around $300.
    I fly from a high altitude airport and need to be able to tweak blades for density altitude operations so an adjustable blade system is necessary. I also have a 3-blade Warp Drive in reserve but the esthetics of the wood blades are appealing and should there be a prop strike, the wood blades disintegrate and save the engine from damage.

  9. #19
    rosiejerryrosie's Avatar
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    Great. The last wood prop I bought cost me $1300.00. I'll have to research GSC. Are they good at making recommendations as to what size prop to use?
    Cheers,
    Jerry

    NC22375
    65LA out of 07N Pennsylvania

  10. #20

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    If you Google GSC Systems, will get their website. Can probably send a note and get answers from technical man Rick. Remember, their props are intended for lower HP engines so a Lyc 360 would be too powerful for their products.
    I live/fly my Pulsar at 7000' so density altitude is a factor and having the gnd adj prop works well.

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