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newby questions

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  • garywolf@rogers.com
    I have joined and read back to December so that I am not going over too much old ground but I still have some questions. I am looking for an engine to sub for
    Message 1 of 4 , Jul 9 3:22 AM
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      I have joined and read back to December so that I am not going over too much old ground but I still have some questions.

      I am looking for an engine to sub for a half VW in a light plane with 150 square feet and a gross of about 800 pounds. I think that 40 hp would be enough for this. If possible I would like to use direct drive but am concerned that there has been some crank breakage.

      Which engine has the best crank and what does it weigh? Am I better to start with a lower hp engine for lighter weight and improve the breathing, or should I get an off the shelf 40 hp engine and live with its weight?

      I am intending to limit prop size to under 60" so that 3600 rpms could be used for takeoff.

      Thanks in advance

      Gary Wolf
    • Norman Heistand
      I like the Generac 33hp. You can get the weight down to 70 lbs if you give up the electric start. I believe this engine and the small block 750cc type
      Message 2 of 4 , Jul 9 10:12 AM
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        I like the Generac 33hp. You can get the weight down to 70 lbs if you give up the electric start. I believe this engine and the "small block" 750cc type engines are quite a bit lighter than the "big block" 40hp engines. For the Kohler V-Twin a pusher prop should be on the flywheel end, a tractor prop should be on the power shaft end since the crank thrust bearing is on the power shaft end. It is also questionable to put a prop on one end of the crank and a flywheel on the other end. Note the 1/2 VW has no flywheel and has the crank thrust bearing to support a tractor prop.

         The flywheel weighs 18 lbs or more on these industrial v-twins. The starter weighs 7 lbs. A battery weighs 7 lbs. So if you will give up the electric start, you can save 24 lbs by cutting the flywheel down to 8 lbs. I am speculating that the 70 lb 33hp engine may perform as well as a heavier 40hp engine. And the Generac can be found at lower cost. Generac also makes a 40hp engine that might work for you. These are being used on powered parachutes with a pusher configuration.

        Even 40hp may seem under powered for 800 lb gross. 500 lb gross is more typical for ultralights. I have a 50hp water cooled snowmobile engine on my Texas Parasol. You would probably like a Rotax 503 with gearbox or I could give you a good deal on my water cooled 50hp.

        Norm Heistand  my .02




        On Tue, Jul 9, 2013 at 5:22 AM, <garywolf@...> wrote:
         

        I have joined and read back to December so that I am not going over too much old ground but I still have some questions.

        I am looking for an engine to sub for a half VW in a light plane with 150 square feet and a gross of about 800 pounds. I think that 40 hp would be enough for this. If possible I would like to use direct drive but am concerned that there has been some crank breakage.

        Which engine has the best crank and what does it weigh? Am I better to start with a lower hp engine for lighter weight and improve the breathing, or should I get an off the shelf 40 hp engine and live with its weight?

        I am intending to limit prop size to under 60" so that 3600 rpms could be used for takeoff.

        Thanks in advance

        Gary Wolf


      • Peter Walker
        Hello 60 @ 3600 is over the recommended revs for a wood prop 947 /minute @ 60mph  The numbers my prop calculator gives for 40HP @ 60mph  Climb Prop Service
        Message 3 of 4 , Jul 9 4:30 PM
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          Hello
          60" @ 3600 is over the recommended revs for a wood prop 947'/minute @ 60mph 
          The numbers my prop calculator gives for 40HP @ 60mph 
          Climb Prop

          Service or Peak Efficiency Prop

          Cruise Prop

          Diameter =57inchesDiameter =54inchesDiameter =51inches
          Pitch =18inchesPitch =19inchesPitch =20inches
          Prop efficiency=0.55
          Prop efficiency=0.57
          Prop efficiency=0.65
          J =0.31
          J =0.32
          J =0.35
          Est. airspeed =59.4
          Est. airspeed =60.0
          Est. airspeed =62.6
          S.L. Static thrust =222lbs (approximate)S.L. Static thrust =227lbs (approximate)S.L. Static thrust =237lbs (approximate)
          Prop Tip Speed=898ft/secProp Tip Speed=856ft/secProp Tip Speed=801ft/sec
          What plane is it going on? The thrust line may dictate a redrive The redrives that seem to work use some method of moving the resonance of the prop outside of the operating area or use a vee drive and sacrifice belt life to limit torque Jeron posted of a redrive at Oshkosh that coated the engine in black dust as the belt is sacrificed to save the crank Lifing a belt used in that manner is easy Weigh it and when it reaches a 90% weight replace it
           A prop is NOT a flywheel as they are normally thought of  Think of it as the board you carry on your shoulder At most walking speeds it stays steady on your shoulder But at one speed it starts flapping up and down till it bounces off your shoulder 
           
          However too much advance is likely to be pushed as the reason for crank breakage Strangely it seems to be only on airplanes and air boats
          Peter
           


          From: "garywolf@..." <garywolf@...>
          To: Small4-strokeEngines@yahoogroups.com
          Sent: Tuesday, July 9, 2013 6:22 PM
          Subject: [Small4-strokeEngines] newby questions

           
          I have joined and read back to December so that I am not going over too much old ground but I still have some questions.

          I am looking for an engine to sub for a half VW in a light plane with 150 square feet and a gross of about 800 pounds. I think that 40 hp would be enough for this. If possible I would like to use direct drive but am concerned that there has been some crank breakage.

          Which engine has the best crank and what does it weigh? Am I better to start with a lower hp engine for lighter weight and improve the breathing, or should I get an off the shelf 40 hp engine and live with its weight?

          I am intending to limit prop size to under 60" so that 3600 rpms could be used for takeoff.

          Thanks in advance

          Gary Wolf



        • garywolf@rogers.com
          Norm and Peter, Thank you very much for your insightful replies. You have saved me a lot of time. Also, I just read the latest post which has an attachment
          Message 4 of 4 , Jul 11 3:53 AM
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            Norm and Peter,
            Thank you very much for your insightful replies. You have saved me a lot of time. Also, I just read the latest post which has an attachment about cam timing. It is excellent.

            Thanks again,
            Gary Wolf

            --- In Small4-strokeEngines@yahoogroups.com, garywolf@... wrote:
            >
            > I have joined and read back to December so that I am not going over too much old ground but I still have some questions.
            >
            > I am looking for an engine to sub for a half VW in a light plane with 150 square feet and a gross of about 800 pounds. I think that 40 hp would be enough for this. If possible I would like to use direct drive but am concerned that there has been some crank breakage.
            >
            > Which engine has the best crank and what does it weigh? Am I better to start with a lower hp engine for lighter weight and improve the breathing, or should I get an off the shelf 40 hp engine and live with its weight?
            >
            > I am intending to limit prop size to under 60" so that 3600 rpms could be used for takeoff.
            >
            > Thanks in advance
            >
            > Gary Wolf
            >
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