Pietenpol-List: proper prop for A-75 piet
Posted: Sat Sep 23, 2006 9:13 am
Original Posted By: Rcaprd(at)aol.com
Subject: Pietenpol-List: proper prop for A-75 pietHey 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 Markle and 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 higher rpm. 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 athigher 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 allowing the 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 bigchange. With proper prop A75 will climb slightly better and cruise about sameas A65, but at higher 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 severalmph faster. Regardless, in the real world the weight of the airplane will make more difference than 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 definitely performs better. I like an A65 to turn about 2300 in 75 mph climb. That means about 25-2600 straight and level. Cruise about 2250 and youare still less than 75% 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 was C75,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 myaero plane. 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, unlessthere is just a huge amount of additional thrust/climb from metal. Well, letme know what 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)________________________________________________________________________________
Subject: Pietenpol-List: proper prop for A-75 pietHey 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 Markle and 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 higher rpm. 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 athigher 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 allowing the 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 bigchange. With proper prop A75 will climb slightly better and cruise about sameas A65, but at higher 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 severalmph faster. Regardless, in the real world the weight of the airplane will make more difference than 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 definitely performs better. I like an A65 to turn about 2300 in 75 mph climb. That means about 25-2600 straight and level. Cruise about 2250 and youare still less than 75% 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 was C75,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 myaero plane. 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, unlessthere is just a huge amount of additional thrust/climb from metal. Well, letme know what 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)________________________________________________________________________________