Serge and Colin and KRNetters, I have really resisted hitting the reply button...But I feel now is as good a time as any to reply on this subject. There are profound General Design differences between automobile engines, and aeronautical engines. Which make these engines very application specific.
Let's start with basic components: 1.) Crankshaft-(Load Support) The Automobile engine's crankshaft is is designed to turn a flywheel, clutch and input shaft of a transmission(or torque converter). Dynamic Thrust forces are relatively small. More importantly, look how the automotive engine handles or supports these loads. The flywheel (clutch etc.)or torque converter is supported by the crankshaft main thrust bearings and transmission input bearings (front pump bearings for the automatic). This allows the dynamicly loaded power application device to be supported on both ends. In engineering we call this simply supported. The Aero engine's crankshaft is designed to turn a propeller. Dynamic thrust forces are enormous. The aero engine doesn't have the luxury of a transmission bolted to it to support the opposite end of the load. This is why aero engines have very large thrust bearing journals. This allows the dynamicly loaded power application device(propeller) to be supported on only one end. In engineering we call this a cantalever. To illustrate this point, place a board between two saw horses. Place a weight in the middle of the board. That's now a simply supported beam. Now remove one of the saw horses. This is now a cantalevered beam. Keep the board level. See what it takes to keep the ends of the board level? This is how an aero engine handles the load. The closer you get to the load the easier it is to support it. This is the same reason why aero engines have such large thrust bearing surfaces. 2.)Cylinder heads. (Tolerances) Automobile engines combine the combustion chambers into a single unit(s). Aero engines use one cylinder head /combustion chamber per cylinder. Automobile engine production volumes will boggle the mind with the huge amount of volumes each car company produces every year. Aero engines volumes are a tiny fraction of what automotive production volumes are. This isn't the only reason, only part of it. Aero engines operate in a much harsher environment than automobile engines operate in. The aero engines tolerances are much closer than automobile engines in order to get the expected life from the engine. Tighter tolerances drive up cost. The aero engine would not survive in it's harsh environment if automotive production volume tolerances were applied. The Individual Cylinder head allows the aero engines deck height and therefore compression ratio be tightly controlled. Even and smooth power output is the end result. Automobile engines have anything but even and smooth power output because the compression ratio and deck heights cannot be closely controlled, but rather compromised between the best and worst deck heights, at best. Bores are typically within .015 of each other. That's 10 times the tolerance of an aero engines production bore tolerance. Do you know why Chevrolet finally stopped Corvair production? It wasn't because of Nader, it was because the engines were too costly to produce in the needed production volumes. Ignition systems: (failure mode, redundancy & Time). I hear this all the time folks complaining about magnetoes, and how much better electronic ignitions are. reliability etc. etc. Ever have a "Check Engine Light" come on it your car when driving it? There's plenty of cars on the shoulder because the engine just quit. There are no shoulders to pull over on if the electronic module quits on a flight engine. Ask William Wynne, he does not advocate using an electronic ignition on his Corvair Conversion. Typically, when an electronicly controlled automotive engine illuminates, the computer tries to retain the last know set of variables, and goes into what's called the "limp-in" mode. In an aircraft, if that computer ever commanded a limp-in mode, guarrenteed, you are not staying airborne. Failure mode of a Magneto is a gradual performance degridation, which allows the pilot to time to plan where he can make a landing. Time. Aero engines have to completely independant, redundant ignition systems. Mags, wires and Plugs. If you foul or burn a plug because the pilot wasn't paying attention to his workload...You are more than likely to suffer only a small degridation in performance, again allowing: Time An auto engine does not have independant, redundant ignition systems. If you foul a plug, burn a rotor, or chafe through a coil wire, you are in serious trouble, and must take immediate action, because you don't have: Time This is referred to in engineering as single point of failure. There are too many single point of failures in a single electronic ignition system. The same thinking can be applied to electronic fuel injection: Too many single point of failures. Porsche experimented with a certify-able aero engine I believe for Mooney?? It was a behemoth weight-wise. and also a dismal failure. Why? because is had redundant alternators, fuel injectors, ignitions, computers and even a cooling fan... To get around the single point of failure problem. An Aero engine operates in a completely different environment than an auto engine operates in. The differences in design, weight, systems, and even how they are manufactured are profound. Todays auto engines are even more application specific, and are completely designed and optimsed for a specific power-output, price range, fuel economy and class of vehicles, even the kind of terrain they are intended to operate in. Aero Engines are designed for a specific output, aircraft class, and are designed to turn a propeller. Which means they too are designed to operate in a specific kind of "terrain". Because of these profound differences, converting an automobile engine for aircraft use is possible, maybe sometimes economicly feasable. But these significant differences should be addressed, good conversions do, however, a converted automobile engine will never perform as well in an aircraft, as the aero-specific designed engine will. Just as an aero engine doesn't perform as well in a automobile as an automobile engine will. Specicly for Serge: I'M NOT SHOUTING, JUST THAT MY REPLIES TO YOUR MESSAGE WILL BE EASIER TO PICK OUT: --- "Serge F. Vidal" <serge.vi...@ate-international.com> wrote: I fail to understand what exactly is the benefit of an aircraft engine over an automotive conversion. SEE TEXT ABOVE. Certified aircraft engines are overpriced, Fuel -guzzling, noisy, tricky and unreliable beasts. NOISY BECAUSE THEY ARE AIRCOOLED. THE COOLING FINS RADIATE ALOT MORE THAN JUST HEAT, THEY AMPLIFY NOISE ALSO. IF YOU OVERHEAT AN AIRCOOLED ENGINE, REDUCE POWER AND ENRICH THE MIXTURE, THE ENGINE WILL COOL DOWN. IF YOU OVERHEAT A LIQUID COOLED ENGINE, THE RESULT IS COOLANT LOSS. ANOTHER SINGLE POINT OF FAILURE. ALL OF THE LIQUID CONNECTIONS IN A LIQUID COOLED ENGINE ARE POTENTIAL FAILURE POINTS. AERO ENGINES ARE FAR MORE RELIABLE THAN AAUTO CONVERSION, AS FAR AS FUEL GUZZLING, FUEL BURN RATES ARE A DIRECT RELATIONSHIP TO POWER OUTPUT. They lag 70 years behind automotive technology, and due to the cost of certification that prevents anything better from showing up, these engines will keep > contributing to the high cost of flying. HAVE YOU SEEN THE LYCOMING/HONDA? ELECTRONICLY CONTROLLED DUAL.....MAGNETOS. OVERHEAD VALVES.... CAM IN BLOCK. Any car manufacturer producing engines that heavy on cost, maintenance and fuel, and so unpractical and unreliable, would be out of the engine business pretty soon. SERGE, SEE ABOVE. AUTO ENGINES AND AERO ENGINES OPERATE, AND ARE DESIGNED FOR COMPLETELY DIFFERENT ENVIRONMENTS. AERO ENGINES ARE VERY RELIABLE, FAR MORE RELIABLE THAN A AUTO ENGINE. COMPARE APPLES WITH APPLES. ARE YOU SAYING THAT NEW AERO ENGINES ARE UNRELIABLE, FUEL-GUZZLING AND UNPRACTICAL? OR ARE YOU REFERRING TO OLD USED, TIMED OUT, WORN OUT, PIECED TOGETHER FROM OTHER JUNK ENGINES, AND COMPARING THAT TO A NEW CAR? IF A NEW AERO ENGINE IS AS YOU STATED ABOVE, THEN IT WOULD NEVER BE CERTIFIED FOR USE NOW WOULD IT? ===== Scott Cable KR-2S # 735 Wright City, MO s2cab...@yahoo.com __________________________________ Do you Yahoo!? Yahoo! Hotjobs: Enter the "Signing Bonus" Sweepstakes http://hotjobs.sweepstakes.yahoo.com/signingbonus
