# Spark redundancy.

### Help Support HomeBuiltAirplanes.com:

#### Dan Thomas

##### Well-Known Member
In most aspects, my personal use of conversion engines rather than conventional aircraft engines has less to do with buy-in economy and much more influenced by running cost and technology. Most people, if they are honest, will admit that an auto conversion is not initially cheaper than a used Lycoming. The costs start mounting when you have to rebuild the mags often, perform top end rebuilds, etc. after relatively low hours in your homebuilt because well, you bought a used motor. At that point, the auto conversion that was a fresh rebuild really starts to earn its keep.
The redundant systems argument for certified "aircraft" engines remains something of a mystery to me. All auto conversions I am aware of- and that is not to say I am aware of them all, I am especially fuzzy on V6 and V8 auto conversions- have spark redundancy developed for them. Many use electronic fuel injection which is so much more reliable than a carburetor that even ignoring the efficiency and control provided by EFI it is laughable to attempt to argue a carb is in any way meaningful way safer or better. The fact is that GA would have converted a decade ago if the FAA had not, as per usual, made it so prohibitively expensive that to even consider it makes your bank account slit its wrists.
I did an Subaru installation in a Glastar for a third party. By the time it was done he could have bought the Lycoming and been flying a year earlier, and not had to have me spend a lot more time working out the bugs. It's neither cheap nor simple, especially if it's not a bolt-it-on conversion.

Used Lycs are fine if they've been looked after. I took them off the flight-school airplanes at TBO, with compressions still in the high 70s and no metal in the filters. There were another 1500 hours in them for a homebuilder. Magnetos need 500-hour inspections, with replacement of points and condenser usually at the second inspection. After 2K hours they should be overhauled or replaced and then they're good for another 2K.

EFI and EI will make it into GA if GA survives long enough, but someone is going to have to pay the shot and find some way to amortize it so it makes sense to buyers, or the FAA is going to have to get a lot friendlier and stop hindering progress with so many onerous fees and requirements for near-perfection. GA is 99.9% safe now, but they want 100%. They can't have that no matter how many rules they make. As long as humans are involved, accidents will happen, either through pilot error or though cheapskate maintenance as per owner demands. Even here on HBA we occasionally get people that want a stall/spin/accident-proof airplane that flies itself so they'll never get hurt. They can't have that, either. Risk aversion is far bigger now than it was when I was young, and maybe that's part of the decline in GA. And the media's hyping of every little aircraft incident or accident, while ignoring the carnage on the highways, isn't helping.

#### Dan Thomas

##### Well-Known Member
The point is that in a Lycosaurus you might have noticed, checked it out, and found nothing at all, then a few flight hours later had a bad time.
One more point: a good aircraft mechanic knows almost instantly what's wrong with the Lycosaur if it acts up. The engines and their systems are simple enough for that and they're easy to fix. There are only so many thing that can go wrong with them. Computerized EFI and EI troubleshooting is fine, but it was driven by the awesome complexity of the systems. No mechanic would ever have the training to know immediately what was causing an intermittent power loss that didn't resemble any problem experienced by a vintage vehicle.

There's a common myth among homebuilders that Lycosaurs are unreliable. They're absolutely not if they're maintained as the manufacturer tells you. I was the director of maintenance for a flight school fleet for 12 years or so, with the cumulative flight hours of seven aircraft being maybe 30,000 or more in that time, and never had an engine failure of any sort. It all comes down to proper maintenance, just as it would with an auto conversion. Further, the engine-failure accident rate among homebuilts is much higher for those with auto conversions than with Lycosaurs. Ron Wantajja can elaborate on that. Many of the failures involve fuel or ignition systems rather than the engine structure, but things like crankshaft failures are common as well.

#### rv6ejguy

##### Well-Known Member
In the 2 Subaru videos I recently did on YouTube, (10 airplanes in total, 7500 flight hours) NONE of these folks spent more than what a fresh Lycoming costs and most spent a lot less. That argument is tired and inaccurate for most people who understand these engines and can wrench themselves. Non-gearheads shouldn't do auto conversions though, just as they shouldn't do maintenance on a Lycoming.

Broken cranks? Not common at all. I've heard of one (in an airplane) where the guy ditched the factory harmonic balancer and installed a lightweight aluminum one. Bad idea. I know there are hundreds of times more Lycs flying but also know of broken cranks on these, multiple ADs and SBs. They break sometimes too. Anything can break.

Last edited:
103

#### dwalker

##### Well-Known Member
In fairness, I was comparing NEW auto conversions to USED Lycomings as far as expense. because, we all know a fresh (let alone NEW) longblock Lycosaur starts around 30K and climbs quickly from there. I have seen an invoice for a Franklin 6 that was new in the crate for 39K.
Broken cranks fuel/air issues yada yada... apply to all engines.. HOWEVER, antique mag technology which will barely light off the spark plugs reliably is not something to brag about, and one must question the continued acceptance of barely adequate.

I will give you that with maintenance and use, Lycosaurs are fairly reliable. The same is true of all engines. The issue is that it is no longer 1960, and airplane reliability pales in comparison to pretty much anything in modern automotive. It is no longer true that a Lycosaurus flown 10 hours a month, maintained by the cheapest AP on the field that only recommends replacement of pretty much anything only after critical mass is imminent, and receives the quickest of walk-arounds prior to flight, will perform reliably enough to get the pilot up and down safely. It is common knowledge that the GA "technology" is a joke, andis stuck using 1930's tractor technology.

On the other hand, automotive and marine tech has grown by leaps and bounds. Marine engines that live day in and day out at two setting- idle and WOT- run for thousands of hours without missing a beat maintained by owners who push maintenance so far it is a joke because they do not want to be off the water. Automotive technology has come so far a 24hr race is no longer an endurance test, it is a sprint race from start to finish. We are at the point that after a 24hr race the cars are checked over and other than changing the tires and brake pads are ready to go another 24hours.

I like this discussion because you illustrate one side of the point very well- regularly flown certified aircraft have few issues with regular maintenance from actual techs. On the other hand, it is insulting to even insinuate that is a normal circumstance, as I feel like we should all be able to agree that a privately owned aircraft is lucky to see 10 hours a month average a year.

Now I will strongly disagree with you about the "simple" Lyco being transparent and easily diagnosed by an A&P. That is crap. I have personally witnessed oil cooling, fuel, and other "intermittent" issues chased for months by A&Ps that could do nothing more than replace parts and hope they were replacing the right things.

On the other hand a literal idiot can understand "Knock Sensor #1 out of range" when it appears on the screen, or "Cyl #3 misfire", etc. when it pops on the screen and go check those things out. I understand that those used to dealing with carburetors and older technology fuel injection feel like they are complex and inherently tricky things to work with, but that era has passed. Modern- and by modern I mean anything built/marketed after about 2004- EFI systems are easy to work with and most importantly, easy to diagnose and LOG. Data is everything and being able to look at the data log file and SEE a misfire occur at the same instance fuel pressure dropped or the wideband showed lean for a split second is invaluable, especially since the pilot may have never noticed a thing. I routinely helped drivers understand they were overslowing or had speed left in the car, as they would report being "flat" (foot to the floor) when the data showed the throttle at 70%, or would say they felt they had the corner down and could not carry more speed through, when on an identical corner at another part of the track they were 5 or 10 MPH faster and smoother. Data does not lie, and the more we have the better off we are.

#### TFF

##### Well-Known Member
The first person who wants to jump on an auto conversion is the person who shouldn’t. Apples to apples means buy and bolt on. For everyone who has a successful auto conversion, I want a qualification of past experience that allowed it to work successfully. If you raced cars for 30 years and did more than write a check, that went into the cost of that “$5000” engine.$200,000 of experience counts. You had to gain the experience to spend it.

Certified engines generally have two reasons for broken cranks. Bad manufacturing and prop strikes. Over the years a few cranks break and the FAA hammers down. Way fewer people than what the auto world would trigger. Lycoming and Continental have both had it happen. Each time they had tried to sub out the manufacture. Autos break cranks too. It happens at different milestones. I have seen daily driven Ford Focus, Chrysler 4s,Mercedes Diesel, BMW 645 break or crack cranks, much less race cars. No one would keep score if they never broke. What autos don’t usually have is prop strikes. It doesn’t happen often anymore because of cost, but strike and bolt on a new prop was pretty common. If it’s only flying 10 hours a year, it will probably be decades before it breaks.
Comparing any of it with a straight face without spouting an agenda is just like my statement above, true but skewed. It’s not ever apples to apples. The info will never be equal. Pool of money or pool of talent. The truth is you have to have a pool of something extra which ever side you stand on.

#### Dan Thomas

##### Well-Known Member
Now I will strongly disagree with you about the "simple" Lyco being transparent and easily diagnosed by an A&P. That is crap. I have personally witnessed oil cooling, fuel, and other "intermittent" issues chased for months by A&Ps that could do nothing more than replace parts and hope they were replacing the right things.
I said a good mechanic would know almost instantly what was wrong. There are many mediocre technicians, and most of them are just not interested in studying stuff and learning more. The US A&P is almost a joke, way too easy to obtain, compared to the Canadian AME license, which I hold. Far more training and experience required.

#### dwalker

##### Well-Known Member
I said a good mechanic would know almost instantly what was wrong. There are many mediocre technicians, and most of them are just not interested in studying stuff and learning more. The US A&P is almost a joke, way too easy to obtain, compared to the Canadian AME license, which I hold. Far more training and experience required.
I can not fault anything in that statement.

#### Daleandee

##### Well-Known Member
The US A&P is almost a joke, way too easy to obtain, compared to the Canadian AME license, which I hold. Far more training and experience required.
Reminds me of my shop instructor way back in high school. He was teaching us how to rewind the coils on an old mechanical voltage regulator. I commented that (at that time) I could walk down the street and buy a replacement for eight bucks. He made me understand that I couldn't do that when it broke in the middle of nowhere ...

#### aeromomentum

##### Well-Known Member
We should also not discount the fuel fuel savings of a modern EFI, high compression, 4 valve per cylinder auto conversion over a Lycoming or carb Rotax. This fuel savings is almost the cost of the engine over a 2000 hour TBO. Keep in mind that even a Lycoming O-235 will use $60,000 to$80,000 in fuel over the TBO. This better fuel economy also provides about 20% more range or a little more useful load.

#### dwalker

##### Well-Known Member
We should also not discount the fuel fuel savings of a modern EFI, high compression, 4 valve per cylinder auto conversion over a Lycoming or carb Rotax. This fuel savings is almost the cost of the engine over a 2000 hour TBO. Keep in mind that even a Lycoming O-235 will use $60,000 to$80,000 in fuel over the TBO. This better fuel economy also provides about 20% more range or a little more useful load.
I am not sure this is the place for logic and reason!

#### Dan Thomas

##### Well-Known Member
I am not sure this is the place for logic and reason!
Yup. Few of us fly to save money.

The diesel conversions were supposed to pay for themselves by burning less fuel, and since Jet-A is cheaper, that was supposed to save more. But the cost of the conversions were so high that there were no savings at all and there are few flying worldwide. They make sense in places like Africa where the refineries don't make 100LL and it has to be tankered in and transported all across the continent. When I was there in about 2006, my friend was paying between $8 and$11 per US gallon for 100LL. He was interested in the SMA diesel but the STC didn't cover his model of 182. Another organization there is now operating two SMA 182s. I did some work on one of them before it was shipped over there.

#### rv6ejguy

##### Well-Known Member
The SMAs also were a disaster mechanically as they had serious case fretting issues and most lasted less than 400 hours before being changed out. Insufficient testing again by a company with massive testing facilities available. When will they learn... Continental has redesigned all the weak aspects of the original design now (hopefully).

#### dwalker

##### Well-Known Member
Yup. Few of us fly to save money.

The diesel conversions were supposed to pay for themselves by burning less fuel, and since Jet-A is cheaper, that was supposed to save more. But the cost of the conversions were so high that there were no savings at all and there are few flying worldwide. They make sense in places like Africa where the refineries don't make 100LL and it has to be tankered in and transported all across the continent. When I was there in about 2006, my friend was paying between $8 and$11 per US gallon for 100LL. He was interested in the SMA diesel but the STC didn't cover his model of 182. Another organization there is now operating two SMA 182s. I did some work on one of them before it was shipped over there.
So I did *some* development work with the newish Mazda 4cyl diesel, and its a pretty neat package, but I am not sure I would want to even begin an attempt to convert it for an aircraft.

Weight? HP?

#### Dan Thomas

##### Well-Known Member
The SMAs also were a disaster mechanically as they had serious case fretting issues and most lasted less than 400 hours before being changed out. Insufficient testing again by a company with massive testing facilities available. When will they learn... Continental has redesigned all the weak aspects of the original design now (hopefully).
When I worked on that one ten years ago the factorywas already on its third generation of that design. They'd worked out many of the problems we found on this one.

#### Toobuilder

##### Well-Known Member
HBA Supporter
Log Member
We should also not discount the fuel fuel savings of a modern EFI, high compression, 4 valve per cylinder auto conversion over a Lycoming or carb Rotax. This fuel savings is almost the cost of the engine over a 2000 hour TBO. Keep in mind that even a Lycoming O-235 will use $60,000 to$80,000 in fuel over the TBO. This better fuel economy also provides about 20% more range or a little more useful load.
You are suggesting that in an aviation application, an auto conversion, by nature of it's basic architecture (high compression, multi valve, etc) has a significantly better BSFC than a Lycoming? I'd like to see that data, because frankly, a Lycoming even with mechanical FI and a simple EI cranks out some very impressive BSFC numbers when LOP.

#### dwalker

##### Well-Known Member
You are suggesting that in an aviation application, an auto conversion, by nature of it's basic architecture (high compression, multi valve, etc) has a significantly better BSFC than a Lycoming? I'd like to see that data, because frankly, a Lycoming even with mechanical FI and a simple EI cranks out some very impressive BSFC numbers when LOP.
Why do you think that?

#### Toobuilder

##### Well-Known Member
HBA Supporter
Log Member
Why do you think that?
Which part? If the first, its because aeromomentum said:

"...We should also not discount the fuel fuel savings of a modern EFI, high compression, 4 valve per cylinder auto conversion over a Lycoming or carb Rotax..."

And unless my reading comprehension has decreased radically, the discriminating characteristics described by the author were related to architecture. If he had just mentioned "EFI", then that would be an accessory, and NOT a discriminator because EFI is available for the Lyc.

#### dwalker

##### Well-Known Member
Which part? If the first, its because aeromomentum said:

"...We should also not discount the fuel fuel savings of a modern EFI, high compression, 4 valve per cylinder auto conversion over a Lycoming or carb Rotax..."

And unless my reading comprehension has decreased radically, the discriminating characteristics described by the author were related to architecture. If he had just mentioned "EFI", then that would be an accessory, and NOT a discriminator because EFI is available for the Lyc.

I am curious why you think any Lycoming is anywhere near efficient as a modern engine as described. I have limited experience with the cutting edge Lycosaurs, so am willing to be educated here, but my understanding is they are in no way an example of efficiency.

#### Toobuilder

##### Well-Known Member
HBA Supporter
Log Member
There is much discussion on this subject on this forum, and Ross, who has a lot of skin in the game with both efficient Lycomings as well as auto conversions, may point out some very specific numbers.

But for those of us that actually fly Lycomings efficiently can attest, it's old news. The fact is, the low RPM tractor like mission of the typical light aircraft is very much in the sweet spot for the large bore, 2 valve loose clearance, air cooled aircraft engine architecture. Run WOT with the prop pulled back, LOP and with optimized spark, it's tough to beat. And aside from the very rare example, auto engine conversions do not exhibit noticeable gains in efficiency when flown head to head with a Lyc. Not only do they not show anywhere near 20% improvement, they are often actually worse than the Lyc.

Now, if you throw a 4 banger Lyc in a Honda Civic and run the EPA dyno profile - its going to be awful. But by the same token, running the 4 valve jewel from the Honda at WOT, max load and LOP dragging a Cherokee around for hours on end, the BSFC numbers are going to be MUCH closer. People often berate the Lyc as ancient- but it is actually a very specialized piece which has nothing except the bare minimum required to satisfy a very specific task - turn gasoline into torque - and it does that quite well.