Original Posted By: "Gordon Bowen"
Subject: Re: Pietenpol-List: Big Bore&Short Stroke Versus Small Bore&Long StrokePiet Friends,I have to pitch into this subject.1 - There is no relationship between PCU (Power Cylinder Unit: piston, rings and cylinder) wear and bore X stroke combinations. A large range can be made to achieve expected life limits.2 - For aircraft engines, the overriding design objective is lightness and lower BSFC (Brake Specific Fuel Consumption). Minimizing thermal losses (hencelower BSFC) favors big bores and few cylinders. Given more displacement per cylinder, less of the same are necessary to generate the power needed, hence less weight. Example: 4 cyl. Lyc.O-360 versus 6 cyl. Cont. O-360: both are real 200HP engines. The Lycosaurus has lower BSFC (more mpg) and vibrates more.The Contisaurus has higher BSFC (less mpg) and is smooth as silk. Smoothness comes from lower thrust loads (the force pistons exert on cylinder walls) and better balancing of primary/secondary forces and internal binaries, a natural with 6 cyl. configuration. So, a large displacement per cylinder rotatingat lower speed is capable of generating the same power as a lower displacement rotating at higher speed. Short strokes, as said before, implies high conrod angularity and higher thrust load. Higher thrust load generates friction losses and greater wear, if same materials are used.3 - Given the above, large bores predominate. Thus large valves can be used, resulting in filling efficiencies (so called volumetric efficiency) far in excess of those achieved by the run-of-the-mill automotive engine. However, large valves do not induce the high turbulence levels needed for fast combustion. Thus the extreme sensitivity of our slow revving, big bore aircraftengines to fuel Octane rating. Higher Octane fuels are needed to preclude detonation but this slows combustion even more! Therefore, twin spark plugs areneeded to expedite things. In effect twin spark plugs slice the combustion chamber in 2 and ensure freedom of detonation under high loads. Incidentally, this isthe root explanation for speed loss when checking magnetos. Normal combustion is, paradoxically, very slow (20 to 100 m/s). Very high revving engines(Ferrari V12 comes to mind) have tiny pistons/combustion chambers and get awaywith a single spark plug.4 - Our Lycosaurus and Contisaurus are not perfect (...and in some aspects irritably so, example in point carbs and mechanical fuel injection, not to mention single timing magnetos...) but are unbeatable in their primary function:reliability/safety.5 - Can one turn an automotive engine into a good aircraft engine? The answer is an unequivocal YES.6 - Done properly, almost any automotive engine should have at least 1000h TBO.Sorry for the lengthy mail. Intention was to contribute +.Cheers,Miguel AzevedoPA22/20-150________________________________________________________________________________
Re: Pietenpol-List: Big Bore&Short Stroke Versus Small Bore&Long Stroke
Re: Pietenpol-List: Big Bore&Short Stroke Versus Small Bore&Long Stroke
Original Posted By: AzevedoFlyer(at)aol.com
Miguel:All that said, the direct drive Corvair engine as per William Wynne's recipeis consistently proven and in quite a reasonable sample that it can be donesafely, by the average pedestrian and a low a cost as you can get.As you mention dual plugs helps prevent detonation and this is one of thefinicky points in the Corvair running on single plugs. But once you replacethe cam to relocate peak torque, replace cast pistons for forged in order towithstand the occasional occurrence of detonation and sort out the finetuning out to keep it from happening, 100 hp with no redrive can beaccomplished on that engine at a reasonable cost.I personally have become quite partial to the Mazda 13B rotary. No valves,no pistons, few moving parts and no opposing powerstrokes to shake it allappart.http://www.rotaryaviation.com/For this one you do need a redrive to achieve reasonable numbers. But onceover the 3000$ expense for that fine piece of machinery most of the rest ofit is quite within the "beer money" means of this working stiff. A completerebuild kit for a used core can be had for 500$ and a savable core can behad for a couple hundred. A "short block" (sans accessories) rebuilt enginecan be had for 2500$ from various road racing suppliers if you opt to notrebuild a used core yourself. And it has no valves to burn out. It will do150 to 180 hp and that is really babying it, as the folks in the trackracing world are making 3 and 4 times that running at 9 thou RPM. Yes a bitmuch for the Aircamper, but the point is that affordable and proven autoengine conversions are out there to be had.SaludosMichael in Maine. (previously of Caracas where I was also once known asMiguel)http://rides.webshots.com/album/147451245dhnmgI ----- Original Message -----
Miguel:All that said, the direct drive Corvair engine as per William Wynne's recipeis consistently proven and in quite a reasonable sample that it can be donesafely, by the average pedestrian and a low a cost as you can get.As you mention dual plugs helps prevent detonation and this is one of thefinicky points in the Corvair running on single plugs. But once you replacethe cam to relocate peak torque, replace cast pistons for forged in order towithstand the occasional occurrence of detonation and sort out the finetuning out to keep it from happening, 100 hp with no redrive can beaccomplished on that engine at a reasonable cost.I personally have become quite partial to the Mazda 13B rotary. No valves,no pistons, few moving parts and no opposing powerstrokes to shake it allappart.http://www.rotaryaviation.com/For this one you do need a redrive to achieve reasonable numbers. But onceover the 3000$ expense for that fine piece of machinery most of the rest ofit is quite within the "beer money" means of this working stiff. A completerebuild kit for a used core can be had for 500$ and a savable core can behad for a couple hundred. A "short block" (sans accessories) rebuilt enginecan be had for 2500$ from various road racing suppliers if you opt to notrebuild a used core yourself. And it has no valves to burn out. It will do150 to 180 hp and that is really babying it, as the folks in the trackracing world are making 3 and 4 times that running at 9 thou RPM. Yes a bitmuch for the Aircamper, but the point is that affordable and proven autoengine conversions are out there to be had.SaludosMichael in Maine. (previously of Caracas where I was also once known asMiguel)http://rides.webshots.com/album/147451245dhnmgI ----- Original Message -----
Re: Pietenpol-List: Big Bore&Short Stroke Versus Small Bore&Long Stroke
Original Posted By: Matt Dralle
Subject: Re: Pietenpol-List: Big Bore&Short Stroke Versus Small Bore&Long StrokeMichel,Fully agree with your appreciation of Mazda rotaries!I think highly of these powerplants and have been told by people from Washington State that even TBO is quite meaningless in this case. Somebody fromPuyallup area stated that only when you cannot start easily is when you are being told that a rebuild is in order. The guy had 2000+h in one engine...I do not understand - maybe I do - why home builders have not zoomed into Wankels a long time ago.Almost no vibration, light, insensitive to Octane rating (heck, our military uses Curtiss-Wright designed Wankels with JP4 as fuel, direct injected and twin spark ignited...!), very compact frontal area, exceedingly robust internals, garanteed long TBO and so forth... What else do you want?Problem areas are higher BSFC ( more than compensated by lower frontal area and weight) and safely handling the extreme exhaust heat. A solution to the last is the modern, space age heat blankets from Federal Mogul Corp (USA). Like any 2 stroke engine, Wankels benefit greatly from tuned exhaust systems but mutting exhaust noise might prove difficult. However, almost everybody loves the famous P51/Spitfire/Hurricane exhaust noise. Well, Wankels are closer to that than anything else out there...Nice to have met you.I am a Brazilian by birth and living here in this God's country for the last 10 years. Becoming an American Citizen this year!Cheers,MiguelN8714DPA22/20-150________________________________________________________________________________Date: Sat, 8 Sep 2007 13:46:49 -0700
Subject: Re: Pietenpol-List: Big Bore&Short Stroke Versus Small Bore&Long StrokeMichel,Fully agree with your appreciation of Mazda rotaries!I think highly of these powerplants and have been told by people from Washington State that even TBO is quite meaningless in this case. Somebody fromPuyallup area stated that only when you cannot start easily is when you are being told that a rebuild is in order. The guy had 2000+h in one engine...I do not understand - maybe I do - why home builders have not zoomed into Wankels a long time ago.Almost no vibration, light, insensitive to Octane rating (heck, our military uses Curtiss-Wright designed Wankels with JP4 as fuel, direct injected and twin spark ignited...!), very compact frontal area, exceedingly robust internals, garanteed long TBO and so forth... What else do you want?Problem areas are higher BSFC ( more than compensated by lower frontal area and weight) and safely handling the extreme exhaust heat. A solution to the last is the modern, space age heat blankets from Federal Mogul Corp (USA). Like any 2 stroke engine, Wankels benefit greatly from tuned exhaust systems but mutting exhaust noise might prove difficult. However, almost everybody loves the famous P51/Spitfire/Hurricane exhaust noise. Well, Wankels are closer to that than anything else out there...Nice to have met you.I am a Brazilian by birth and living here in this God's country for the last 10 years. Becoming an American Citizen this year!Cheers,MiguelN8714DPA22/20-150________________________________________________________________________________Date: Sat, 8 Sep 2007 13:46:49 -0700