# Lack of twin engine E/ABs

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#### pfarber

##### Well-Known Member
Yep...that's how statistics work. A ~25% failure rate means that a quarter of the examples in a group will suffer a failure, not that a particular example has a 25% chance of failure.

Yes, a properly designed, properly constructed, properly operated, and properly maintained auto engine conversion can be reliable. The problem is, statistics show that the average homebuilder is unable to accomplish this. If you're a mechanic with 30 years' experience working on engines, you've got a VERY good chance of a successful conversion. If you're an average Joe barely capable of adding oil, and scrimping on every purchase to hold the costs down, your chances aren't so good.

I'd love to look at the changes needed to make to a Corvair to make them reliable...because, according my data, it hasn't happened yet.

About 40% of the accidents happening to Continental O-200-powered homebuilts are due to a loss of power for any reason (including pilot error). That percentage is 65% for Corvair-powered homebuilts. As far as accidents due to engine mechanical issues (including errors by builders or mechanics), there were six such accidents occurring to BOTH the O-200 and Corvair-powered homebuilts in the 22-year period covered by my data. But there were 120 O-200-powered homebuilt accidents in my database, and only 24 Corvair-powered ones.

According to the FAA registration database as of January of this year, there are about 700 O-200-powered homebuilts, and 56 homebuilts with Corvairs. Even if you assume the Corvair numbers are ten times higher than the FAA records show, that's STILL a higher rate of mechanical failure for Corvairs.

I'm not deliberately picking on Corvairs, since the data for most conversions is as bad or worse. I fully support people who want to use alternate engines...they just need to understand the risks are greater.

Ron Wanttaja
I think we agree on what the numbers mean, people doing things that may or may not be the best decision but all they have is thier own experience.

A new clean sheet design would recommend best practices. Car motors work great when the proper design is implemented.

You can use a simple screwdriver incorrectly and injure yourself or damage a part. Now take a complex design like a car motor FWF and now that same person who can't use a screwdriver properly is gonna figure is out?

#### pfarber

##### Well-Known Member
Ron, thank you for your even-handed analysis, as usual. As one who has been following Corvairs for some time, I do think there are more than 56 flying. I’ve looked over at least 15 or 20 installations in person without going that far out of my way (OSH for the last ten years or so and one Corvair College) and I have a hard time believing this represents roughly 30% of the fleet. 500 is probably a reasonable top set estimate in my judgment. Regardless, your point stands that “alternative” installations have not met the reliability record of certified engines (even if many of those are now experimental by virtue of those performing maintenance on them or non-compliant modifications). It shouldn’t surprise even the most rabid supporters of “alternative” installations that amateur builders on the whole haven’t matched Lycoming and Continental and a fleet of trained A&P/IA maintainers. In the end, it comes down to the individual installation (including scores of details unrelated to the engine itself) and what is being asked of the engine relative to its capabilities.

@Dan Thomas, I would suggest that there are reasons in addition to mere cost that might steer one toward an engine with automotive origins. There are probably a number of folks who would prefer this approach who would willingly admit that it’s not necessarily that much cheaper, but still prefer to experiment. They’re probably the ones who educate themselves on engines generally, pay particular attention to the ingredients that tend to yield reliability and safety, and understand that there’s no free lunch.

I don’t think experimental aviation is served well by either the viewpoint that 1) traditional powerplants are always superior, or 2) automotive engines are a panacea. Still, I’m grateful we have the ability to do our own research, make out own choices about our individual priorities, and ultimately to be the ‘PIC’ of the reliability of the engine we choose

Car motors are not a panacea. I would bet a warm diet cola that if an STC for an LS1 for a 172 was $20k installed i bet you would see all those old tired lyc/conts hit the used market almost overnight. #### dog ##### Well-Known Member Car motors are not a panacea. I would bet a warm diet cola that if an STC for an LS1 for a 172 was$20k installed i bet you would see all those old tired lyc/conts hit the used market almost overnight.
You get that STC and I will be ready to take all the
lyc/conts off your hands and ,then,give you
a real special introductory rate on your insurance

#### Wanttaja

12 years ago the STC'd SMA diesel conversion for a 182 was $100K or better. Again, more than the whole airplane was worth at the time. Price for that STC'd kit now? Not the whole airplane, just the engine change kit: View attachment 130144 And that is FIVE years ago. https://www.soloy.com/uploads/9/0/6/9/90692509/c182_sales_with_order_form_v5_final.pdf @Dan Thomas, they need to add 30% (100hp) and charge 30% more. Wait! There is things like that. Called turboprop! I'm not sure if a quater of a mil is justifiable for a (relatively small) piston engine. #### Dan Thomas ##### Well-Known Member @Dan Thomas, they need to add 30% (100hp) and charge 30% more. Wait! There is things like that. Called turboprop! I'm not sure if a quater of a mil is justifiable for a (relatively small) piston engine. A turboprop conversion will cost a lot more than a quarter million. #### arj1 ##### Well-Known Member A turboprop conversion will cost a lot more than a quarter million. Hi Dan, According to the link below, not that much more (engine cores could be bought fairly cheap). And you get a T/P not a piston! #### dog ##### Well-Known Member Hi Dan, According to the link below, not that much more (engine cores could be bought fairly cheap). And you get a T/P not a piston! link is for the overhaul only,core cost,shiping,motor mount,prop and install and systems integration would be on top where there can be some awsome "deals" are on turbo prop coversions that didnt quite get finished,or ones that have been finished but the fuel and other costs have people looking to sell useualy a couple of turbo pipers on the market and recently a turbo maule with the small rolls #### arj1 ##### Well-Known Member link is for the overhaul only,core cost,shiping,motor mount,prop and install and systems integration would be on top where there can be some awsome "deals" are on turbo prop coversions that didnt quite get finished,or ones that have been finished but the fuel and other costs have people looking to sell useualy a couple of turbo pipers on the market and recently a turbo maule with the small rolls @dog, I get it, but my point is that diesel piston cost shouldn't be on the same order of magnitude as turboprop engine. #### dog ##### Well-Known Member @dog, I get it, but my point is that diesel piston cost shouldn't be on the same order of magnitude as turboprop engine. point taken.its all a bit much. and my only real world solution is to make more money the thing that comes up as the real basic economic/technical hold up is any system that can give a significant increase in efficiency/range/power density whatever way you term it,just is not there and if it was, with a 65% fuel to thrust efficiency then the whole game changes or at least it does for industry,but for us there will just be greater fees or purchase costs,lost time waiting for something that might never get here and when it does,its still going to be dependent on manufacturing equipment,plants and employ'es that are very expensive to set up and get running smoothly. go price state of the art casting and machine tools,the buildings to put them in,and what it costs to get someone competent to stand in front of each machine and sit behind each desk that will make you cough #### arj1 ##### Well-Known Member point taken.its all a bit much. and my only real world solution is to make more money Well... Or buy an AVGAS/MOGAS engine? In the end, if a diesel engine costs twice the AVGAS engine for a tiny decrease in fuel consumption, then what's the point? Being a GTBA member, I understand why the turbines cost that much and why you pay them that much - higher reliability, good high-alt performance etc. But diesel? Sorry, I digress and it is now too far away from the twin-engine experimentals OP. #### aeromomentum ##### Well-Known Member There have been a few converted auto engines that have even been certified including Franklin, Thielert, Continental Diesel, Continental spark ignition, Austro, Volkswagen, Toyota and Orenda. An interesting aside is Franklin started with air cooled auto engines (both inline and opposed), then air cooled aircraft engines, then auto engines (Tucker, liquid cooled) then back to air cooled aircraft engines. Another interesting aside is Tucker designed a light fighter aircraft in early WW2 than never flew. The idea here is that the use of auto engines as a base or basis for successful aircraft engines is an proven and established fact. But of course that does not mean that every or even most conversions are successful or cost effective. There are a few areas where effort needs to be spent in developing any engine. In terms of auto engines, the development of the basic engine is already done before you start. Of course you still must do the development on the conversion. With Aeromomentum we chose to start with a well developed and proven base engine and then look what others have done both successfully and not and used this to help direct our engineering efforts. Not directly copying like Superior and others did but still leveraging the work and experiences of others to more quickly get to the goal of a reliable engine conversion. This leveraging is very important due to the small number of engines in aircraft. Much more important for the cost of the auto based aircraft engine is the cost savings by using the high volume production numbers of the base engine to save on parts cost. This is huge and makes for very substantial savings over that of low quantity traditional aircraft engine parts prices. Our upright 100hp AM13u is$10K. This would be perfect for a wing or pylon mount twin and ok for a push/pull twin. The equivalent Rotax 912iS is $24K. You will get the same performance with the AM13. Both are about the same weight, fuel burn, displacement, etc. What we do not have is the years of installation experience and expertise that Rotax has. They have shipped over 60,000 912 based engines, have seen just about every possible installation issue and have very detailed and exact installation instructions. If you follow their installation and operating instructions just like if you follow ours, you will have a fantastically reliable engine. If you do not, you will have problems. #### gtae07 ##### Well-Known Member In the end, if a diesel engine costs twice the AVGAS engine for a tiny decrease in fuel consumption, then what's the point? I guess it depends on what fuels are available to you and what their relative cost is. In the US, it's most likely not in your favor, especially if you can self-fuel with mogas. Even with the eventual 100UL costing a little more, in the long run the cost difference may be a wash and almost all small airports will carry it (not all will have Jet A). In other parts of the world, avgas isn't common or easily available, but diesel and jet are--or the avgas is much more expensive. In those cases a diesel might make much more sense. I remember an Avweb article asking why people weren't clamoring for diesel conversions on Cessnas--after all, the cost breakeven was only 20 years out! #### Dan Thomas ##### Well-Known Member Hi Dan, According to the link below, not that much more (engine cores could be bought fairly cheap). And you get a T/P not a piston! PT-6 cores won't be "cheap." They're a popular engine. Add that core price to the overhaul prices, and you get a much fatter price. The overhaul prices listed are probably based on not needing replacement of any expensive parts such as compressor or turbine wheels that cost tens of thousands. This place sells used engines with time remaining. The prices are for an exchange, with you sending them your core. P&WC Engines for Sale - Pratt & Whitney A clip from that. Look at the price of the first one. That's a new engine.$1.44 million.

You don't see many PT-6s in homebuilts. You see more Allison (Honeywell) TPE-331s because they're cheaper. Fixed instead of free turbine, simpler construction. Fewer airplanes use them, and as airframes are damaged or timed out, their engines become available.

At any rate, the turboprop is far beyond the reach of 99.9+% of us.

#### wrmiles

##### Active Member
Car motors are not a panacea. I would bet a warm diet cola that if an STC for an LS1 for a 172 was \$20k installed i bet you would see all those old tired lyc/conts hit the used market almost overnight.
Can't be done unless you certificate (both type and production) the engine also.