Pietenpol-List: in defense of the Corvair
Posted: Sun Dec 08, 2002 8:29 pm
Original Posted By: "Christian Bobka"
John writes:>I have heard that he is running direct drive at a fairly high rpmYes, that's correct. There has only been one Corvair flown with a redrive recently (the Rinker gearbox, on Dave Stroud's formerly Subaru-powered Christavia), and in the normal application the engine is run direct drive at between 3000 and 3400 RPM depending on prop used. But William advertises the engine output as 100 HP @ 3200 RPM and continuous output of 90 HP @ 3000 RPM, torque of 160 ft-lb @ 2800 RPM.>but where do the curves show the horsepower at THIS rpm, not at the>top of the curve?For one, they are posted on Mark Langford's website at http://home.hiwaay.net/~langford/corvair/specs.html if you'll scroll down a bit you'll find the graph for the stock 2700 cc engine with OT-10 cam, which is what William was running. The plots are from a program that simulates operation, but have been found to be quite accurate and validate William's claimed output values. William did not ever put his engine on a dyno... his numbers (published in his manual and on the website long before Mark ever ran the simulation on Dyno) were based on measured thrust and static RPM with known props. Anyway, you'll find the cited values of HP and torque on this graph as close as my eye can see 'em, anyway.>I for one, would like to see the actual curves published on his web>site, not just his claims.There has been talk of putting the engine on a dyno and generating actual curves, but it hasn't been done yet.>But I don't believe that one in his enthusiasm for the engine should>overrate it's output at the ACTUAL RPM'S that are used to turn a prop>in a plane.I don't believe he's overrated its output at the actual RPMs used to turn a prop. He flew the airplane for quite some time and demonstrated its performance, and has further demonstrated the engine's claims time and time again turning the same pitch and diameter prop turned by known engines to measure thrust and static RPM to directly compare the engines. Obviously he can't use the exact same prop because the Corvair turns counter to the direction of Lyc/Continentals, but using the same manufacturer's prop with same pitch and diameter.>I would worry that someone not too knowlegable would attempt to put an>over-rated Covair into an air frame that is designed for, say a 100 hp>Lycoming and then find that the performance is disappointing.Has this happened to someone you know? And what is an "over-rated" Corvair? An airframe designed and flown with a 100HP Lycoming will never know any difference if it's flown with a 100HP Corvair or with a 100HP Subaru. It has to be matched with the correct prop, but that's part of the equation whether we're talking Subaru, Corvair, Lyc, or Warner, isn't it?>Probably would spend the rest of his days bad mouthing auto>conversions!And that's what we're trying to avoid.>I would not pit my 111 hp engine against a 145 hp engine.Darn. I still think you'd give him a run for his money.>And it is actual, not guessed at, horsepower that will determine the>rate of climb.Yep. There is no fooling actual performance. Paper and calculations are one thing, but real-world performance can't be faked.>But put my plane against a CLAIMED 110 hp Corvair Pietenpol and I'll>be willing to bet the farm that my plane would win!Well, alright!!!!!!! Now we've got something fun to look forward to when guys like D.J. gets his in the air. Anybody else with Corvair power willing to toe the line with John? I wish William's Piet were still alive today, but the airframe is toast (the engine is alive and well, though). Even though you claim your Subaru produces 111 HP, we wouldn't handicap you against our 110 HP ;o)Guys, this is fun. This is what makes for good hangar talk and for challenging competitions at fly-ins. And like I said, the proof will be in the pudding no matter what the numbers say.Oscar ZigaSan Antonio, TXmailto: taildrags(at)hotmail.comwebsite at http://www.flysquirrel.net________________________________________________________________________________
John writes:>I have heard that he is running direct drive at a fairly high rpmYes, that's correct. There has only been one Corvair flown with a redrive recently (the Rinker gearbox, on Dave Stroud's formerly Subaru-powered Christavia), and in the normal application the engine is run direct drive at between 3000 and 3400 RPM depending on prop used. But William advertises the engine output as 100 HP @ 3200 RPM and continuous output of 90 HP @ 3000 RPM, torque of 160 ft-lb @ 2800 RPM.>but where do the curves show the horsepower at THIS rpm, not at the>top of the curve?For one, they are posted on Mark Langford's website at http://home.hiwaay.net/~langford/corvair/specs.html if you'll scroll down a bit you'll find the graph for the stock 2700 cc engine with OT-10 cam, which is what William was running. The plots are from a program that simulates operation, but have been found to be quite accurate and validate William's claimed output values. William did not ever put his engine on a dyno... his numbers (published in his manual and on the website long before Mark ever ran the simulation on Dyno) were based on measured thrust and static RPM with known props. Anyway, you'll find the cited values of HP and torque on this graph as close as my eye can see 'em, anyway.>I for one, would like to see the actual curves published on his web>site, not just his claims.There has been talk of putting the engine on a dyno and generating actual curves, but it hasn't been done yet.>But I don't believe that one in his enthusiasm for the engine should>overrate it's output at the ACTUAL RPM'S that are used to turn a prop>in a plane.I don't believe he's overrated its output at the actual RPMs used to turn a prop. He flew the airplane for quite some time and demonstrated its performance, and has further demonstrated the engine's claims time and time again turning the same pitch and diameter prop turned by known engines to measure thrust and static RPM to directly compare the engines. Obviously he can't use the exact same prop because the Corvair turns counter to the direction of Lyc/Continentals, but using the same manufacturer's prop with same pitch and diameter.>I would worry that someone not too knowlegable would attempt to put an>over-rated Covair into an air frame that is designed for, say a 100 hp>Lycoming and then find that the performance is disappointing.Has this happened to someone you know? And what is an "over-rated" Corvair? An airframe designed and flown with a 100HP Lycoming will never know any difference if it's flown with a 100HP Corvair or with a 100HP Subaru. It has to be matched with the correct prop, but that's part of the equation whether we're talking Subaru, Corvair, Lyc, or Warner, isn't it?>Probably would spend the rest of his days bad mouthing auto>conversions!And that's what we're trying to avoid.>I would not pit my 111 hp engine against a 145 hp engine.Darn. I still think you'd give him a run for his money.>And it is actual, not guessed at, horsepower that will determine the>rate of climb.Yep. There is no fooling actual performance. Paper and calculations are one thing, but real-world performance can't be faked.>But put my plane against a CLAIMED 110 hp Corvair Pietenpol and I'll>be willing to bet the farm that my plane would win!Well, alright!!!!!!! Now we've got something fun to look forward to when guys like D.J. gets his in the air. Anybody else with Corvair power willing to toe the line with John? I wish William's Piet were still alive today, but the airframe is toast (the engine is alive and well, though). Even though you claim your Subaru produces 111 HP, we wouldn't handicap you against our 110 HP ;o)Guys, this is fun. This is what makes for good hangar talk and for challenging competitions at fly-ins. And like I said, the proof will be in the pudding no matter what the numbers say.Oscar ZigaSan Antonio, TXmailto: taildrags(at)hotmail.comwebsite at http://www.flysquirrel.net________________________________________________________________________________