| The most important issue being missed is the torsional resonance the auto crankshaft receives from the propellor. The application of viscous couplings is often tried to isolate the auto crank from the propellor with some success but the weakness still remains. An automotive crankshaft will fatigue fail if the engine is in aircraft service for more than a few hundred hours in most cases. The fancy billet cranks offer little relief from the fatigue problem. Keep in mind that the propellor blades are constantly flexing under the air loads which translates into fatigue flexing of the crankshaft along it's entire length. Just look at a side by side picture of an auto crankshaft and a comparable power aircraft crankshaft. The aircraft unit is substantially heaver. This weight is not added to the aircraft engine for no reason.
The second issue is the high power requirement. The auto industry indeed designs their engines for high RPM/HP operation but the assumption is that this output is required for a very small percentage of the engines usage profile. Both fatigue and wear are dramatically increased at near red line operation (the rotational loads are square law to RPM). Others have commented on the high cooling load at near red line operation which can be managed. The take away from the high cooling load should jog thoughts of fatigue and wear rates.
I am all for enjoying home built engine experimentation, but the IV is not a good platform for the fun.
Jack Morgan On Jun 1, 2011, at 6:00 AM, Lancair Mailing List wrote:
Date: May 31, 2011 1:41:38 PM EDT
Subject: Re: [LML] Re: L-IV Choice of Engine
Swaid,
Your comments below are part of what drives me nuts in this conversation. A fuel line failure is NOT an engine issue. It is a systems issue that applies to every aircraft that ever flew (except electrics). Thus, using it as a condemnation of a one-off application is not germane to the topic.
Electronic ignition systems are as reliable as the day is long. Solid state electronics generally last longer than whatever they're stuck in. And I have redundant computers, with automotive exhaust oxygen sensors to let me get the induction and ignition maps exactly right.
LS-1 coils at 1 per plug are as reliable as the day is long. Millions of cars have proved that, and there's no high-altitude issue, because of their construction.
Automotive injectors are incredibly reliable, and I've got two sets, user selectable, so if my wiring fails to one, the other will work. (BTW, I expect to select alternate injectors and computers on a calendar basis, so all will be known-good all the time.)
The engine internals are designed to be able to run all day at 7,000 RPM, but I'm rev-limiting to 3,500. I can't imagine needing more than the 600 hp I make at that speed. The hydraulic roller lifters should have no problem, since billions of them run forever with no problems.
Where do we have concerns? The gearbox. It was designed with the help of Timken's helicopter people to run at 1,000 HP continuously. It has separate lubrication and oil cooling, with a full suite of sensors. It also has three helical cut gears so that it has 3.4 teeth engaged at all times, unlike spur gear setups with 1 tooth engagement. The thrust bearing is designed for 1,000 HP.
Garrett turbochargers and wastegates are reliable as the day is long, and run on Continentals and Lycomings every day.
Have I missed something? Maybe. The designer is very experienced, and Don Goetz flies behind a Continental he prepared. He's designed everything from stationary power generator engines to Indy race engines to aircraft engines for DARPA. I think he's answered a lot of questions. Did he miss anything? Maybe. That's what testing is for. But as for the internals, any speed shop can repair the engine for a lot less than your Lyconental. The only part that isn't field repairable is the gearbox.
Do I have a risk of failure? Yes. Do you? Yes. The prime difference between us is that Lyconental failures are better known from a large statistical database. Mine are somewhat predictable, but don't have the experience yours have.
I expect to start testing today. News when available.
Ted Noel
N540TF
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