Alternative Engine Information Preference

Discussions of alternative engines tend to generate alternate points of view. A common debate involves the type of information available. One view says prospective customers desire only total hours flown vs failure rate, as they generally don't understand engineering data. The opposing view says shoppers do understand most engineering test data, and consider it important in their decision making.

Poll participants are asked to carefully consider the questions in the context of ALL alt-engine vendors.

Dan,
I have a difficulty with the poll covering all alt engines when all the threads have been with the egg units.
Perhaps you can give a 3rd choice. Given the amount of info already out there, I'm very content with an hours/incidents approach if talking about the eggenfellner engines.

So my vote would be for more tech info if I wanted to know more about an engine with no info available but if you're going to extrapolate from the overall poll to discuss egg engines, I would vote for hours/incidents.
Tom Hanaway

I think most potential clients prefer both here (more info is usually better) but very few will buy something that has no flight hours or extensive ground testing at least. The proof is in the pudding- I want to see something actually working, not just a bunch of theory saying that something should work.

In the ideal world, I'd want to see as much detail as possible on the design, stress analysis, vibration analysis, testing to destruction and finally a pile of trouble free flight hours. The question is, what is the price of the hardware when all this is said and done?

While my preference would be time flown vs. failure rate (since I'm not an engineer and don't relate to lots of numbers and charts), one of my biggest deciding factors was talking to other customers of the same package and seeing if they are satisfied with the product and with the manufacturer.

Comfort zone

Some don't look at either. Some just like being different. Not that they don't care about safety, but in aviation, even experimental, pilots assume or expect a certain level of safety, especially from a FWF package.

May be some pilots feel they can handle any situation, even loss of power. I am not discounting the severity of loss of power, but it's like riding a motorcycle, you have to check out some thoughts of safety and security when riding one. You still can get killed in a car, but some people accept more risk, whether real or precived. There is no doubt on a motorcycle, even with experience, leathers and a helmet, you are more exposed. I know a lot of careful experienced skilled motorcycle riders that got wiped out, to no fault of their own. As a old and wise philosopher once said, stuff happens.

The question is, does an experimental engine and installation expose you to more risk? Would detailed engineering assure you no tragedy will befall you? Will 2,000 hours on an engine by one owner make you feel better? If its a contest of service experience, the certified aircraft air-cooled direct drive engines are so far ahead, no other engine will catch up in out life time.


How will we know when this new technology in GA engines arrives (if ever)? We will know it when we see it. It's like going from rag-n-tube bi-planes to aluminum monocoque cantilever mono-wing planes, it's just better aerodynamically. (A Stearman is still awesome.) When jets hit the commercial market, DC8, B707, the piston planes days where numbered in commercial aviation. There was no doubt. Will Subaru's, Mazda's and Chevy V6's or V?'s ever rule the sky? Probably not. I am just worried GA will die out all together. As gas goes up, we will be looking back at the $100/barrel as the good old days.

If an experimental engine is flown under flight test conditions, with detailed instrumentation, under sever operations to some high water mark, that would impress me. However that would be an expensive and long term program. The service life and reliability of alternative engines is hard to nail down. Many are being flown normal or nominal conditions, quietly some where, but at this rate it's statistically insignificant. However at the same time 100,000's of hours are being logged by Lycs and TCM's.

Would detailed engineering assure you no tragedy will befall you?

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It's not about a guarantee that no "tragedy" will happen. It's all about an assurance that no tragedy will happen due to apathy or ignorance on the part of the alternative part designer. That really speaks to value as much as safety. If the design specs. and testing protocol is made available, a prospective buyer can do some checking and perhaps verify that the part he is buying will have more than a 200hr TBO, for example. For sure, some select handful of nerds would run the numbers, and word would get out fairly quickly if there was trouble brewing.
It wouldn't be giving the competition much of a leg up either. To use the example of the PSRU, it's a low volume part that really needs to be custom designed for a given engine. Just not enough return on investment for companies to get all excited about cloning someone else's design. If there was, some company could buy one and easily reverse engineer it.

I have always wondered,.... how do you extensively test an auto conversion that almost by definition will always be a short run of a couple of hundred engines. Sure, the basic block design may be stable but timing, valve train, ignition, etc can change with each new model year. It seems to me that it is rare to see an alternative engine fail on the basic design, it's usually something to do with the related systems such as ignition, cooling, fuel system, etc that seems to bring them down. (Also applies to Lycs as well)

Bill S
7a Ark

BillSchlatterer said:

I have always wondered,.... how do you extensively test an auto conversion that almost by definition will always be a short run of a couple of hundred engines. Sure, the basic block design may be stable but timing, valve train, ignition, etc can change with each new model year. It seems to me that it is rare to see an alternative engine fail on the basic design, it's usually something to do with the related systems such as ignition, cooling, fuel system, etc that seems to bring them down. (Also applies to Lycs as well)

Bill S
7a Ark

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Yep, whether it is a Lyco or auto engine, fuel or fire issues usually cause the power loss, not a catastrophic mechanical failure. We must add data from the electrical system on battery dependent engines as well as the PSRU on auto engines.

I'd say in the last 2 years, data sharing on fuel and electrical systems on auto conversions is slowly showing some basic agreement on layout and getting somewhat standardized. Some of the bad PSRU designs are now off the market and being replaced by ones with better track records and even some actual engineering and validation behind them.

Not as much good work has been done with low drag cooling systems but some is coming down the pipeline.

I wish to add one point which at least interest me personally:

When these Lycoming clones came to the market, did you considered them immediately as "aircraft engine" ever since from the first units? Or how long it took or how many units they had to sell (/make fly) until you put them in the same category as Lycomings?

Lycoming has history -- a long one. So why would those alternative engines differ so much from Lycoming clones, which has been just a while at market? Does anyone have years when these clones has become available? I haven't noticed any dates while jumping around their web pages.

Or if I'd copy the Lycoming and manufacture it in China, it will be popular from the beginning with new fancy names for components like "super hyper roller tappets"^tm?


What comes to the original question, I prefer experimentalism if builder has knowledge about the subject (engine in this case). I'm personally don't consider myself ace in this area and therefore as I wish to live long I'll choose safer route -- at least this time at "any cost". What comes to information, if you know what you are doing, why not do it yourself -- collect the information needed. If you only look for FWF package, then you obviously can't have too much data.

Pirkka said:

When these Lycoming clones came to the market, did you considered them immediately as "aircraft engine" ever since from the first units? Or how long it took or how many units they had to sell (/make fly) until you put them in the same category as Lycomings?

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This is a very interesting comment. What constitutes an aircraft engine? Is it an aircraft engine because it is designed and built from scratch for aircrafts? Or it is an aircraft engine because the design, production, maintainance, QA procedures, TBO etc have gone through (and is constantly going through) the quality check and testing the aerospace industry and authorities demand of the engine to be able to install it in an aircraft - a certified aircraft engine?

I don't know how these clones came into existence, but unless they have gone through the same QA as certified Lycomings, they are every bit as alternative as a well designed, but uncertified auto engine conversion in my opinion.

It is interesting to see what Rotax say about certified and uncertified versions of their engines. They say that only the certified engines (912 A/F/S) have been tested as per aeronautical standards for safety and TBO. The uncertified engines (912 UL/ULS) have not been tested for safety and TBO, and are for use in aircrafts and vehicles in which an engine failure will not compromise safety, but they also say that those engines confirm to BRP-Rotax quality standards. Page 17
The interesting part is the TBO. That is the only thing that gives a usable number that can be related to failure rates or MTBF (mean time between failure). I would assume that the Rotax quality standards are high, but according to Rotax they are not high enough so they can say what the TBO will be for their uncertified engines. On the contrary, they say the engine can stop at any time, meaning the MTBF is unknown - it could be 10h or 5000h and anything in between.

The same thing must be valid for certified and uncertified Lycomings. The MTBF for an experimental Lycoming is also unknown, but at least we know that the engine is built according to Textron's quality standards which we can assume is high because their main business is production of certified aero engines. But what about the clones? Do they have vast experience and knowledge of what it takes in terms of quality to produce "real" aircraft engines? Do they have any more experience and knowledge than the people that convert auto engines? Afterall, the core component in a Subaru conversion, the engine, is built according to very high quality standards, at least as good as Rotax, which has shown to be just as good, if not better than Lycoming.

Regarding the original question, I think that total hours flown vs failure rate for uncertified/experimental engines doesn't realy mean that much because the failure rates can be caused by lots of other things like wrong maintainance, wrong operation, poor installation and so on (Rotax also clearly points this out in their manual). Only for certified engines following a certified maintainance schedule, certified installation etc will such a number have any valuable meaning. For experimental engines, all that matters is that the engines are built according to some quality standard, or in other words, that the persons building it knows what they are doing. Unless those persons or that company have an undisputable reputation like Rotax or Lycoming have, the only way to show that they do know what they are doing, is to show engineering data.

SvingenB said:

I don't know how these clones came into existence, but unless they have gone through the same QA as certified Lycomings, they are every bit as alternative as a well designed, but uncertified auto engine conversion in my opinion.

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It's because they've been making FAA approved replacement parts for Lycomings and Continentals for a long time.

L.Adamson --- 0360 Lycoming