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Thread: Consequences of replacing heavy alluminum Prop with lite weight wooden prop?

  1. #1

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    Consequences of replacing heavy alluminum Prop with lite weight wooden prop?

    This is on a hand propped a-65 with impulse coupler mag. Airplane came from a higher elevation and needed a prop change. Because of cost I went with a wooden prop. What will the effects be on the engine. Now understand this wooden prop is not pitched the same as the one removed. The one removed was pitch around 40 this new prop is pitched and 60. Its a Sterba Prop and Ed said this was the prop to start with for my setup.
    But how will this lite weight prop effect engine performance and running? Or will it? I would say it would in some way. Thoughts...

    Tony

  2. #2

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    Best bet is stay in contact with Ed Sterba and follow his advice. I found a link to his site on the Great Plains engine site. Its a neat site and even has a prop calculator. I don't see any way that a lighter prop will hurt an engine. Are diameters the same or is the new one much smaller?


    http://www.greatplainsas.com/edrules.html


    A wood prop is generaly a little smoother than a metal prop. Going from a 40 inch pitch to a 60 is a fairly big leap. I'm guessing that the engine will never get up to a meaningful RPM range if the 40 was any way close. Example: Grumman American AA-1, AA-1A and AA-1B use 53 inch or 54 inch pitch. These are good combinations for t.o. & cruise. A 57 inch cruise prop is also approved. However, using that prop on a hot day or high altitude gives owners a real disappointing t.o & climb performance. If any.


    Wood props are not my favorite down here on the Gulf coast where rain is a fact of life. The finish suffers. I had one a couple of airplanes ago and it looked like it had been dragged behind a pickup truck.


    Good luck, Bob

  3. #3

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    Bob the airplane came from an elevation of 5000'. It had to have this prop to reach rpm at this altitude. Ed said this should be really close to what I need if not right on for my elevation of 600'. This is going on a Sonerai with an a-65 engine on her. She is the sonerai 2 stretch built as a single seat because of the extra weight of the a-65.

    Tony

  4. #4

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    I used to know O-145s, A-65s and A-75s because I learned in Cubs. Wow. Talk about apples and oranges. An airplane designed for a 80 HP 3300 RPM VW now has a 65 HP 2300 RPM Cont. Diameter has to be, what, about 65 inch or so. If you kept the original 71 in dia, you would dig divots down the RW. I bet this is not the only Cont Sonerai ever built. Have you contacted the Sonerai users for a starting point?. Trying props, one after another could add up.
    A small change in pitch makes a big change in RPM. I used to have a Luscombe 8A with an A-65. It had a Beech R-003 prop for which it was STCed. It was controlled in pitch with a hand crank on the panel. This crank looked somewhat like late 40s DeSoto. I rebuilt her from a wreck. The metal prop was no longer airworthy and the extra Beech prop went with the plane. I had previous experience with the R-003 prop and had no reservations about it when I trained on the Piper J-3 instrument trainer. ( I won't cloud your mind with those details)
    After I had the hung the prop, I just had to fiddle with it. I marked the blade shank and the prop hub and ran it from high to low pitch. There was very little apparent change. After she was returned to service by my AI, the prop seemed to function well. I had a few pilot error incidents when I neglected to go into low pitch on final. Full throttle on climb out resulted less than full RPM. I just cranked real fast and the 65 started to howl and dug out.
    I'm just trying to say that just a little change in a prop has a huge effect on RPM. I hope you don't have to go through too many props before you find the right combination. Ed Sterba has a good rep.


    Bob

  5. #5

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    I am a member of the Sonerai site. They build to plans and do not like it when others build different or stray from the plans. Saying this we do have a few flying the sonerai with other engines besides a VW but they keep to themselves. There have been a few built using the a-65 but these people are gone today. One needs to remember the sonerai has been around since the 70's. Some have changed hands many times over all the years.

    Ed told me if its not correct send it back and he would make it right, but he believes it will be real close. I want a static run up of around 2200-2250. In cruise I am looking for 2300-2350. Ed said he has used this same prop on another sonerai with an a-65. I trust him. I was wondering how the effect of the lite weight would be compared to the heavy aluminum prop. But if its not correct it will go back to ED. What a very nice man Ed Sterba is.

    If I remember correctly someone from the sonerai site mentioned the Harmony Rock is a Modified Sonerai and the man would not call it a Sonerai out of respect for the designer of the sonerai. I would like to call mine something else to, but its already registered as a Sonerai IILS with an A-65.
    The new prop is a 60x60.
    Tony
    Last edited by 1600vw; 03-17-2014 at 12:17 PM.

  6. #6
    cub builder's Avatar
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    So why not have a prop shop put some pitch into the metal prop? That usually costs around $100 if you aren't asking for paperwork and log book entries.

    FWIW, I find about 150 RPM difference in my planes (one slow plane and one fast plane) between operating from airports at 7000' vs airports at sea level (I am based at over 7000'). That can be made up by a pitch change of roughly 4". A pitch change of 20" is huge. They do measure them differently from manufacturer to manufacturer, but I have flown behind Sterba props before and his pitch measurements aren't that different from the rest of the world. On the other hand, Ed has been in the business a long time and will work with you to get the prop right for your plane.

    FWIW, based on my experience with a number props from a number of manufacturers on various planes and engines over the years, I'm guessing the 60x60 will have a bit more bite than desirable for an A-65 on a Sonerii, but should be close. It would be a lot closer than a 40" pitched prop. I suspect the 40" number may have been misread or otherwise incorrect (as in the prop was repitched, but not restamped) That's significantly less bite than you'll find on a 75 mph Cub with an A-65, typically swinging a 68x44 prop.

    As for effects on the plane? Metal props generally turn smoother due to the weight acting like a fly wheel. But the wood prop is smoother in that it doesn't have any harmonics. If you hit the prop it just shatters, so you don't need to tear your engine down. Sterba uses a tough polyurethane leading edge that will protect the prop from rocks and rain damage, but keep it varnished to protect while sitting. The airfoil on a wood prop is typically thicker, so isn't as efficient as a metal prop. However, Sterba has been working with the KR crowd for a long time and has his props dialed in nicely for planes in that class.

    The #1 thing it will affect is your W&B. Make sure you check it.

    -CubBuilder
    Last edited by cub builder; 03-17-2014 at 04:15 PM.

  7. #7
    RetroAcro's Avatar
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    All things being equal, the switch to the wood prop will give you a little less performance, less vibration, much less stress on the crank flange (if you're into acro), less flywheel effect (may need to bump up your idle), and less weight on the nose, obviously. The prop is also more prone to complete stoppage should your idle be set too low, and you are doing spins. This again, is the much lower flywheel effect. They are nicer on the fingers to prop, though.

  8. #8

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    Quote Originally Posted by cub builder View Post
    So why not have a prop shop put some pitch into the metal prop? That usually costs around $100 if you aren't asking for paperwork and log book entries.

    FWIW, I find about 150 RPM difference in my planes (one slow plane and one fast plane) between operating from airports at 7000' vs airports at sea level (I am based at over 7000'). That can be made up by a pitch change of roughly 4". A pitch change of 20" is huge. They do measure them differently from manufacturer to manufacturer, but I have flown behind Sterba props before and his pitch measurements aren't that different from the rest of the world. On the other hand, Ed has been in the business a long time and will work with you to get the prop right for your plane.

    FWIW, based on my experience with a number props from a number of manufacturers on various planes and engines over the years, I'm guessing the 60x60 will have a bit more bite than desirable for an A-65 on a Sonerii, but should be close. It would be a lot closer than a 40" pitched prop. I suspect the 40" number may have been misread or otherwise incorrect (as in the prop was repitched, but not restamped) That's significantly less bite than you'll find on a 75 mph Cub with an A-65, typically swinging a 68x44 prop.

    As for effects on the plane? Metal props generally turn smoother due to the weight acting like a fly wheel. But the wood prop is smoother in that it doesn't have any harmonics. If you hit the prop it just shatters, so you don't need to tear your engine down. Sterba uses a tough polyurethane leading edge that will protect the prop from rocks and rain damage, but keep it varnished to protect while sitting. The airfoil on a wood prop is typically thicker, so isn't as efficient as a metal prop. However, Sterba has been working with the KR crowd for a long time and has his props dialed in nicely for planes in that class.

    The #1 thing it will affect is your W&B. Make sure you check it.

    -CubBuilder
    I called the company who makes this aluminum prop. They told me they never cut their prop to 60 inches. They said this is wall art, they told me not to use it. They said they tested their props and not to make it shorted then 67 inches. Because of this I did not want to have this prop repitched.

    This man also told me he does not like dealing with Experimentals or homebuilts because those who fly them do not listen to what others tell them. I told him not to worry, this prop was not going back into service or use. His attitude changed when I said this and he started to talk to me a little more. Before hanging up I reassured him this prop was not being used again.

    I am all over the WB. This airplane will not be flown until its all worked out and recorded in the logs. I thought about adding another fuel tank but as I use fuel I will lose the benefit of the fuel or weight so that won't work. I then thought about adding a starter, but with the cowl it has, that won't work not without a lot of mods to the cowl. So it looks like weight will be added in the forum of ballast. I will first check to see is any ballast can be removed from the tail.
    Tony
    P.S. I do not fly acrobatics.
    Last edited by 1600vw; 03-18-2014 at 05:26 AM.

  9. #9

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    Be careful regarding RPM Tony. When A-65s were everywhere, the Continetal crowd used 2300 as the red line and cruised at 2150. Of course, tachometers are notorious for being dead right all the time. BTW, I have an old one somewhare that that was working when removed from my Luscombe. I upgraded to a C-85 and the Tachs turn the other way. If you need it, its free for the postage.


    ACS has one manual that covers operators, parts and overhaul.


    Not going to do aerobatics in a Sonerai? Yeah they all say that at first.


    Good luck, Bob

  10. #10

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    Bob I will take that tach. Let me know what you need for the postage. The prop that was on it, I could have hit over 3000 rpm. I never wanted to do that so it was replaced.

    The only way I will ever do aerobatics is with some training. I doubt I will try to teach myself this.

    Thanks Bob

    Tony

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