Pietenpol-List: Re: A-75 Prop
Posted: Sun Feb 17, 2008 2:10 pm
Original Posted By: "Bob Hassel"
Oscar & Mike,This mirrors my experience with an A-75 and a Hegy 72 x 42 prop. Fresh A-75, rebuiltStromberg (yes, it's exactly the same as the A-65), new mags, etc, in otherwords, a strong A-75. Other than what y'all mentioned below, the only otherinternal difference is greater piston to cylinder clearance.Pulled about 2150 static and about 2200 in a 50 mph climb on a cool day, maybe50rpm less on a hot day. At WOT it would pull 2400 rpm in level flight at 600ft about sea level in cool weather (2J0 is about 10' above sea level). A perfectA-65 prop, but about 250-300 rpm low for an A-75. This prompted me to buy a 73 x 39 from Clark at Performance Propellers. Itwas a prop he had made for his Cub, for hot, high density altitude conditionswith a passenger. On a hot day it pulls 2500+ in a 50 mph climb, and 2600 incool weather. It's really too much of a climb prop for cool weather, but perfectfor hot weather, which is what we have most of the year. It's also a realwork of art. 54 laminations of hard maple, thinner than the Hegy in profile,but thicker and larger thru the hub. The difference was AMAZING. Climbs out like my neighbor's Cub with a C-85 (well,almost), and seems to be much smoother and happier cruising at 2400-2450and 62-65 mph at about half-throttle, whereas before it was 2150 (rated cruisefor an A-65) and maybe 2/3 throttle for 67-72 mph. I'm referring to actual throttlemovement here. I thought about installing a vacuum guage to see just howmuch throttle I'm really giving it, but then came to my senses (Hey, it's aPietenpol! not a Cessna!).I may trim the Hegy a bit (71 x 42, or 70 x 42...) and see if I can make it actlike something in between the two, maybe 2400 in climbout and 2600 at WOT, toget back a little cruise speed. Then again, it's not about speed anyway, isit? :-)Dave MordecaiNX520SFPanacea, FL> MikeD wrote- > > >The torque curves are very close up to A65 rpm levels and if you load it the> same > >it will perform about the same. You need to load it so that it reaches it's> higher > >cruise/max rpm to produce full power, therefore you need less load than a 65.> > Correct. The torque curves should be more than just very close... they should> be exactly the same because the A75 is the same engine as the A65. The rods are> drilled to provide more oil at the higher rated RPM and the pistons are > different > (waffle pattern on the underside or some such thing), plus a few minor > tweaks, but they are one and the same engine. I've looked at the Continental> specs for the carb venturi for the two engines (when using the NA-S3A1) and it> is unclear but I believe they both use the 1-1/4" venturi, too. > > Bottom line is that if I put my Hegy 72x42 prop on the A75 it will perform > exactly > like my A65 and I'll never see the additional 10HP because I won't be able > to crank it up to 2600 RPM to get full rated 75HP out of it. > > Oscar Zuniga > San Antonio, TX > mailto: taildrags(at)hotmail.com > website at http://www.flysquirrel.net Oscar & Mike,This mirrors my experience with an A-75 and a Hegy 72 x 42 prop. FreshA-75, rebuilt Stromberg (yes, it's exactly the same as the A-65), new mags,etc, in other words, a strong A-75. Other than what y'all mentioned below,the only other internal difference is greater piston to cylinder clearance.Pulled about 2150 static and about 2200 in a 50 mph climb on a cool day, maybe50rpm less on a hot day. At WOT it would pull 2400 rpm in level flight at600 ft about sea level in cool weather (2J0 is about 10' above sea level). A perfect A-65 prop, but about 250-300 rpm low for an A-75. This prompted me to buy a 73 x 39 from Clark at Performance Propellers. It was a prop he had made for his Cub, for hot, high densityaltitude conditions with a passenger. On a hot day it pulls 2500+in a 50 mph climb, and 2600 in cool weather. It's really toomuch of a climb prop for cool weather, but perfect for hot weather,which is what we have most of the year. It's also a realwork of art. 54 laminations of hard maple, thinner than the Hegy in profile, butthicker and larger thru the hub. The difference was AMAZING. Climbs out like my neighbor's Cubwith a C-85 (well, almost), and seems to be much smoother and happier cruisingat 2400-2450 and 62-65 mph at about half-throttle, whereas before it was 2150(rated cruise for an A-65) and maybe 2/3 throttle for 67-72 mph. I'm referringto actual throttle movement here. I thought about installing a vacuumguage to see just how much throttle I'm really giving it, but then came tomy senses (Hey, it's a Pietenpol! not a Cessna!).I may trim the Hegy a bit (71 x 42, or 70 x 42...) and see if I can makeit act like something in between the two, maybe 2400 in climbout and2600 at WOT, to get back a little cruise speed. Then again, it's not aboutspeed anyway, is it?
Dave MordecaiNX520SFPanacea, FL > MikeD wrote- > > >The torque curves are very close upto A65 rpm levels and if you load it the > same > >it willperform about the same. You need to load it so that it reaches it's > higher> >cruise/max rpm to produce full power, therefore you need lessload than a 65. > > Correct. The torque curves should be morethan just very close... they should > be exactly the same because theA75 is the same engine as the A65. The rods are > drilled to provide moreoil at the higher rated RPM and the pistons are > different >(waffle pattern on the underside or some such thing), plus a few minor >tweaks, but they are one and the same engine. I've looked at the Continental> specs for the carb venturi for the two engines (when using the NA-S3A1)and it > is unclear but I believe they both use the 1-1/4" venturi,too. > > Bottom line is that if I put my Hegy 72x42 prop on the A75 it will perform > exactly > like my A65 and I'll never see the additional 10HP because I won't be able > to crank it up to 2600 RPM to get full rated 75HP out of it. > > Oscar Zuniga > San Antonio, TX > mailto: taildrags@hotmail.com > website at http://www.flysquirrel.net ________________________________________________________________________________
Oscar & Mike,This mirrors my experience with an A-75 and a Hegy 72 x 42 prop. Fresh A-75, rebuiltStromberg (yes, it's exactly the same as the A-65), new mags, etc, in otherwords, a strong A-75. Other than what y'all mentioned below, the only otherinternal difference is greater piston to cylinder clearance.Pulled about 2150 static and about 2200 in a 50 mph climb on a cool day, maybe50rpm less on a hot day. At WOT it would pull 2400 rpm in level flight at 600ft about sea level in cool weather (2J0 is about 10' above sea level). A perfectA-65 prop, but about 250-300 rpm low for an A-75. This prompted me to buy a 73 x 39 from Clark at Performance Propellers. Itwas a prop he had made for his Cub, for hot, high density altitude conditionswith a passenger. On a hot day it pulls 2500+ in a 50 mph climb, and 2600 incool weather. It's really too much of a climb prop for cool weather, but perfectfor hot weather, which is what we have most of the year. It's also a realwork of art. 54 laminations of hard maple, thinner than the Hegy in profile,but thicker and larger thru the hub. The difference was AMAZING. Climbs out like my neighbor's Cub with a C-85 (well,almost), and seems to be much smoother and happier cruising at 2400-2450and 62-65 mph at about half-throttle, whereas before it was 2150 (rated cruisefor an A-65) and maybe 2/3 throttle for 67-72 mph. I'm referring to actual throttlemovement here. I thought about installing a vacuum guage to see just howmuch throttle I'm really giving it, but then came to my senses (Hey, it's aPietenpol! not a Cessna!).I may trim the Hegy a bit (71 x 42, or 70 x 42...) and see if I can make it actlike something in between the two, maybe 2400 in climbout and 2600 at WOT, toget back a little cruise speed. Then again, it's not about speed anyway, isit? :-)Dave MordecaiNX520SFPanacea, FL> MikeD wrote- > > >The torque curves are very close up to A65 rpm levels and if you load it the> same > >it will perform about the same. You need to load it so that it reaches it's> higher > >cruise/max rpm to produce full power, therefore you need less load than a 65.> > Correct. The torque curves should be more than just very close... they should> be exactly the same because the A75 is the same engine as the A65. The rods are> drilled to provide more oil at the higher rated RPM and the pistons are > different > (waffle pattern on the underside or some such thing), plus a few minor > tweaks, but they are one and the same engine. I've looked at the Continental> specs for the carb venturi for the two engines (when using the NA-S3A1) and it> is unclear but I believe they both use the 1-1/4" venturi, too. > > Bottom line is that if I put my Hegy 72x42 prop on the A75 it will perform > exactly > like my A65 and I'll never see the additional 10HP because I won't be able > to crank it up to 2600 RPM to get full rated 75HP out of it. > > Oscar Zuniga > San Antonio, TX > mailto: taildrags(at)hotmail.com > website at http://www.flysquirrel.net Oscar & Mike,This mirrors my experience with an A-75 and a Hegy 72 x 42 prop. FreshA-75, rebuilt Stromberg (yes, it's exactly the same as the A-65), new mags,etc, in other words, a strong A-75. Other than what y'all mentioned below,the only other internal difference is greater piston to cylinder clearance.Pulled about 2150 static and about 2200 in a 50 mph climb on a cool day, maybe50rpm less on a hot day. At WOT it would pull 2400 rpm in level flight at600 ft about sea level in cool weather (2J0 is about 10' above sea level). A perfect A-65 prop, but about 250-300 rpm low for an A-75. This prompted me to buy a 73 x 39 from Clark at Performance Propellers. It was a prop he had made for his Cub, for hot, high densityaltitude conditions with a passenger. On a hot day it pulls 2500+in a 50 mph climb, and 2600 in cool weather. It's really toomuch of a climb prop for cool weather, but perfect for hot weather,which is what we have most of the year. It's also a realwork of art. 54 laminations of hard maple, thinner than the Hegy in profile, butthicker and larger thru the hub. The difference was AMAZING. Climbs out like my neighbor's Cubwith a C-85 (well, almost), and seems to be much smoother and happier cruisingat 2400-2450 and 62-65 mph at about half-throttle, whereas before it was 2150(rated cruise for an A-65) and maybe 2/3 throttle for 67-72 mph. I'm referringto actual throttle movement here. I thought about installing a vacuumguage to see just how much throttle I'm really giving it, but then came tomy senses (Hey, it's a Pietenpol! not a Cessna!).I may trim the Hegy a bit (71 x 42, or 70 x 42...) and see if I can makeit act like something in between the two, maybe 2400 in climbout and2600 at WOT, to get back a little cruise speed. Then again, it's not aboutspeed anyway, is it?
Dave MordecaiNX520SFPanacea, FL > MikeD wrote- > > >The torque curves are very close upto A65 rpm levels and if you load it the > same > >it willperform about the same. You need to load it so that it reaches it's > higher> >cruise/max rpm to produce full power, therefore you need lessload than a 65. > > Correct. The torque curves should be morethan just very close... they should > be exactly the same because theA75 is the same engine as the A65. The rods are > drilled to provide moreoil at the higher rated RPM and the pistons are > different >(waffle pattern on the underside or some such thing), plus a few minor >tweaks, but they are one and the same engine. I've looked at the Continental> specs for the carb venturi for the two engines (when using the NA-S3A1)and it > is unclear but I believe they both use the 1-1/4" venturi,too. > > Bottom line is that if I put my Hegy 72x42 prop on the A75 it will perform > exactly > like my A65 and I'll never see the additional 10HP because I won't be able > to crank it up to 2600 RPM to get full rated 75HP out of it. > > Oscar Zuniga > San Antonio, TX > mailto: taildrags@hotmail.com > website at http://www.flysquirrel.net ________________________________________________________________________________