Pietenpol-List: prop for A-75
Posted: Mon Nov 26, 2007 9:30 am
Original Posted By: Ryan Michals
>From the archives, more than you ever wanted to know about picking a prop foryour A75 Piet. And Chuck Gantzer followed up with a post that recommended checkingyour mechanical tach with a digital/optical one, which turned out to bea good recommendation in my case because my mechanical tach reads 200 RPM highat cruise and I was under-utilizing the engine. I run a Hegy 72x42 on the A65on 41CC.============================In a message dated 9/23/2006 9:21:49 AM Central Standard Time, Andimaxd(at)aol.com writes:Hey guys,I have become a lurker, but, I need some feedback from you guys on props. I have a prop off of a 65hp Aeronica mounted to my A-75 piet. I'm developing 2300-2400 rpm's. I was curious what others are using with their piets with A-75's and what kind of number they're getting. I was visiting with Jim Markleand he dug this up for me: An A-75 is merely an A-65 that is rated at a higher rpm. The pistons are different and the rods are drilled for extra cooling of piston skirt at the higherrpm. The carb has a slightly larger venturi and different jetting. The motor is timed slightly different. The prop is the only thing that actually makes a difference in performance; the other changes are only for longevity at higher rpm. A65 is rated at 2300,2150 cruise. A75 is rated at 2650,2300 cruise. The extra rpm is the only thing increasing horsepower: if your prop is not allowingthe motor to wind up to proper rpm you simply have an A65. If you have an A65 that turns 23-2400 in a climb you have the performance of an A75. There was a C-75 which was a slow running version of C-85, but A65 to A75 conversions are much more common. A75 prop generally would be slightly less diameter and 2-3 inches less pitch than A65, but generally rpm is the only big change. With proper prop A75 will climb slightly better and cruise about same as A65, but athigher rpm.With an A65 prop an A75 will climb exactly the same(because it is the same!) but you could cruise at 2300 which would be several mph faster. Regardless, in the real world the weight of the airplane will make more differencethan A65 vs. A75. In my opinion a metal prop is far superior to wood in thrust. Wood has less inertia and better throttle response, but metal definitelyperforms better. I like an A65 to turn about 2300 in 75 mph climb. [I think hemust have meant an A75 should perform like this, not an A65! -OZ] That means about 25-2600 straight and level. Cruise about 2250 and you are still less than75% at cruise. P. S. There was no C65 only A65's .A series was A40,A50, A65,A75,and A80. C series had slightly more displacement(188 cu .in. vs 173 cu. in.). C series wasC75,C85 at 188 cu.in.and C90 at 200 cu .in.All that being said, I would like some exact performance numbers, prop numbers and manufactures, so I'll know what to start looking for. Currently Ihave a Univar 72 X 42, and according to the above I've got a 65hp engine on my aeroplane. NX101XW is a little on the heavy side and so is the pilot, so I would like all of the potential climb that I can get (Without going to an O-200 or something!). I think I would like to stick with a wooden prop, unless there is just a huge amount of additional thrust/climb from metal. Well, let me knowwhat you guys think, hell, maybe I should just stick with what I've got. It (engine) would be de-rated and should last longer?Any comments/help is greatly appreciated and as usual, thanks in advance, later.Max DavisArlington, TX.NX101XW (Reserved)Oscar ZunigaSan Antonio, TXmailto: taildrags(at)hotmail.comwebsite at http://www.flysquirrel.net________________________________________________________________________________Date: Mon, 26 Nov 2007 07:51:24 -0800 (PST)
>From the archives, more than you ever wanted to know about picking a prop foryour A75 Piet. And Chuck Gantzer followed up with a post that recommended checkingyour mechanical tach with a digital/optical one, which turned out to bea good recommendation in my case because my mechanical tach reads 200 RPM highat cruise and I was under-utilizing the engine. I run a Hegy 72x42 on the A65on 41CC.============================In a message dated 9/23/2006 9:21:49 AM Central Standard Time, Andimaxd(at)aol.com writes:Hey guys,I have become a lurker, but, I need some feedback from you guys on props. I have a prop off of a 65hp Aeronica mounted to my A-75 piet. I'm developing 2300-2400 rpm's. I was curious what others are using with their piets with A-75's and what kind of number they're getting. I was visiting with Jim Markleand he dug this up for me: An A-75 is merely an A-65 that is rated at a higher rpm. The pistons are different and the rods are drilled for extra cooling of piston skirt at the higherrpm. The carb has a slightly larger venturi and different jetting. The motor is timed slightly different. The prop is the only thing that actually makes a difference in performance; the other changes are only for longevity at higher rpm. A65 is rated at 2300,2150 cruise. A75 is rated at 2650,2300 cruise. The extra rpm is the only thing increasing horsepower: if your prop is not allowingthe motor to wind up to proper rpm you simply have an A65. If you have an A65 that turns 23-2400 in a climb you have the performance of an A75. There was a C-75 which was a slow running version of C-85, but A65 to A75 conversions are much more common. A75 prop generally would be slightly less diameter and 2-3 inches less pitch than A65, but generally rpm is the only big change. With proper prop A75 will climb slightly better and cruise about same as A65, but athigher rpm.With an A65 prop an A75 will climb exactly the same(because it is the same!) but you could cruise at 2300 which would be several mph faster. Regardless, in the real world the weight of the airplane will make more differencethan A65 vs. A75. In my opinion a metal prop is far superior to wood in thrust. Wood has less inertia and better throttle response, but metal definitelyperforms better. I like an A65 to turn about 2300 in 75 mph climb. [I think hemust have meant an A75 should perform like this, not an A65! -OZ] That means about 25-2600 straight and level. Cruise about 2250 and you are still less than75% at cruise. P. S. There was no C65 only A65's .A series was A40,A50, A65,A75,and A80. C series had slightly more displacement(188 cu .in. vs 173 cu. in.). C series wasC75,C85 at 188 cu.in.and C90 at 200 cu .in.All that being said, I would like some exact performance numbers, prop numbers and manufactures, so I'll know what to start looking for. Currently Ihave a Univar 72 X 42, and according to the above I've got a 65hp engine on my aeroplane. NX101XW is a little on the heavy side and so is the pilot, so I would like all of the potential climb that I can get (Without going to an O-200 or something!). I think I would like to stick with a wooden prop, unless there is just a huge amount of additional thrust/climb from metal. Well, let me knowwhat you guys think, hell, maybe I should just stick with what I've got. It (engine) would be de-rated and should last longer?Any comments/help is greatly appreciated and as usual, thanks in advance, later.Max DavisArlington, TX.NX101XW (Reserved)Oscar ZunigaSan Antonio, TXmailto: taildrags(at)hotmail.comwebsite at http://www.flysquirrel.net________________________________________________________________________________Date: Mon, 26 Nov 2007 07:51:24 -0800 (PST)