You are right, remember for example Rotax 912, it is typical automotive sized engine with an reduction drive. And that is OK, who will say they aren't perform well? Subaru vs. Rotax, how many differences will find between them? Of course, they are very different from a REAL aircraft engines, I will not complain this. But remember ours aircraft, is not enough for them an Subaru? And finally, there are many failures in any REAL aircraft engines, just read some reports.
BR, Alex -----Original Message----- From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net] On Behalf Of David Mikesell Sent: Monday, January 12, 2004 7:41 PM To: Ron Eason; KRnet Subject: Re: KR>These 7 things: Auto vs Aero Engines for Aircraft Well the crank shaft on a auto engine in most cases is supported by the use of a reduction drive to get the maximum efficency....and I don't see how good logic comes into play to say single ignition systems are and will fail............be honest with a modern electronic ignition and fuel injection system that is in every car produced, what is the actual failure rate in a direct proportion to aircraft magnetos that are rebuilt every year and I am only counting the ones rebuilt due to failure???? Well all of the shops I have talk to about magneto (since I am always doing business with them for my customers) say 10 out of every 65 mags they send out rebuilt get returned in 2 to 3 years due to failure..........yet I have had 3 cars all with electronic ignition and each one with over 100,000 miles that are sitting outside right now just like millions of other people who have never every had anything done to the ignition or fuel injection system except changing the spark plugs and! wires. David Mikesell 23597 N. Hwy 99 Acampo, CA 95220 209-609-8774 skyguy...@skyguynca.com www.skyguynca.com ----- Original Message ----- From: "Ron Eason" <r...@jrl-engineering.com> To: "KRnet" <kr...@mylist.net> Sent: Monday, January 12, 2004 7:56 AM Subject: Re: KR>These 7 things: Auto vs Aero Engines for Aircraft > Very good. Good engineering logic and purpose. This is one for the achieves. > When thinking about engines. > > KRRon > > Sent: Friday, January 09, 2004 8:11 PM > Subject: RE: KR>These 7 things: Auto vs Aero Engines for Aircraft > > > > 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. > > > > _______________________________________ > to UNSUBSCRIBE from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/instructions.html _______________________________________ to UNSUBSCRIBE from KRnet, send a message to krnet-le...@mylist.net please see other KRnet info at http://www.krnet.org/instructions.html
