Jet A vs gasoline

Dan Thomas said:
The certified engine would have cost less in the end, believe me. And the performance would have been better. The Subaru has a 5600 RPM redline, but with the reduction the prop runs at around 2550 at that speed. It did not like cruising anywhere near that redline; the noise and fuel consumption was awesome, even leaned out. If you lean it aggressively it will burn valves instantly. Subaru's valves are tiny and depend on EFI to keep them happy. So anyway, the cruise of this Glastar with the 130 HP Soob was only 100 MPH or so at 4600 RPM. The 135-HP Lyc it was designed for could be cruised at anything up to redline (2700 RPM), and at 75% power it cruised at 130 MPH.

Converting an engine? It's not nearly as simple or as good as it sounds. Some guys have done it successfully, but it takes a lot of time and money.
Click to expand...
Actually, I'll be starting with a 3.6 six-banger; at least, that's the plan. In retirement, I'll have all the time in the world (until I die, of course.) I understand the challenges, and I understand that I may not be able to meet them all. But the enjoyment is in the journey, at least for me.
 
genna said:
That's interesting, but .... Honda made a jet, yet, at least in USA, new GA piston engine planes outsell GA jets about 2-1. So far they produced about 90 of them... I took them nearly 20 years to make the damn thing

Sure, they make more $$ on each jet than they may on a piston engine. But that emboldened sentence may not be completely accurate.
Click to expand...

I'm not trying to be a jerk (I promise!) but that sentence you bolded is a question so not sure if a question is ever really accurate or not accurate but the second part is just facts that you can look up yourself. 31M+ engines per year is what Honda cranks out. The GA piston industry collectively is 4+ orders of magnitude smaller than that. That's just a fact.

And as it pertains to the jet, 1) the margin per delivered jet must be at least 100X what it would be per delivered engine, 2) it's a halo product that Honda can use in their glossy brochures and marketing materials (like the NSX but at a much higher level), and 3) it helps them push their technological innovation further and is probably viewed internally as a management proving ground division for aspiring leaders. Getting into piston GA OEM market would not tick any of these boxes. Believe me, I'm as big a GA superfan as anyone on this board but it would make no business sense whatsoever for Honda to get into GA piston aircraft manufacturing and if I were a shareholder/board member (I'm not btw), I would not view it as a good move.
 
RudyP said:
I'm not trying to be a jerk (I promise!) but that sentence you bolded is a question so not sure if a question is ever really accurate or not accurate but the second part is just facts that you can look up yourself. 31M+ engines per year is what Honda cranks out. The GA piston industry collectively is 4+ orders of magnitude smaller than that. That's just a fact.

And as it pertains to the jet, 1) the margin per delivered jet must be at least 100X what it would be per delivered engine, 2) it's a halo product that Honda can use in their glossy brochures and marketing materials (like the NSX but at a much higher level), and 3) it helps them push their technological innovation further and is probably viewed internally as a management proving ground division for aspiring leaders. Getting into piston GA OEM market would not tick any of these boxes. Believe me, I'm as big a GA superfan as anyone on this board but it would make no business sense whatsoever for Honda to get into GA piston aircraft manufacturing and if I were a shareholder/board member (I'm not btw), I would not view it as a good move.
Click to expand...

Yup. It's not that the Lyco/Conti designs can't be improved upon, it's that there is no cost justification for an engine manufacturer to do-so. I'd think if a manufacturer wanted to make an aircraft-specific block that ran on 91/93UL or Jet-A, it wouldn't be too difficult to do. They can adapt things like direct injection, FADEC/electronic ignition timing/etc into the design and probably come out with a small-but-not-insignificant fuel savings or increase in HP per lbs. However, since it makes no financial sense to invest the R&D and certification costs, no one will undertake it. It would require someone like a Howard Hughes character to take on the project.
 
genna said:
That's interesting, but .... Honda made a jet, yet, at least in USA, new GA piston engine planes outsell GA jets about 2-1. So far they produced about 90 of them... I took them nearly 20 years to make the damn thing

Sure, they make more $$ on each jet than they may on a piston engine. But that emboldened sentence may not be completely accurate.
Click to expand...

Honda partnered with GE on the engine. GE did the core (which is the really hard part) and Honda did the low pressure section (which is only a little hard). Ultimately the jet is a much different economic proposition.
 
Ted DuPuis said:
Honda partnered with GE on the engine. GE did the core (which is the really hard part) and Honda did the low pressure section (which is only a little hard). Ultimately the jet is a much different economic proposition.
Click to expand...
And it took several years longer than projected! Definitely a "halo" project.
 
Kenny Phillips said:
And it took several years longer than projected! Definitely a "halo" project.
Click to expand...

Programs always take longer than projected, that's nothing new. However the HondaJet took a LOT longer than projected, largely because it was a first of type in many, many ways. Engine wise my understanding was Honda went in doing the core themselves, realized just how hard it is to build a core, and then partnered with GE (GE-Honda Engines I believe was the partnership company).

There were a lot of very interesting things with that engine.
 
Ted DuPuis said:
Programs always take longer than projected, that's nothing new. However the HondaJet took a LOT longer than projected, largely because it was a first of type in many, many ways. Engine wise my understanding was Honda went in doing the core themselves, realized just how hard it is to build a core, and then partnered with GE (GE-Honda Engines I believe was the partnership company).

There were a lot of very interesting things with that engine.
Click to expand...
Yep, that was one of my company's projects. They had entire working engines more than a decade ago, of which approximately zero ended up in the finished project.
 
SoonerAviator said:
Yup. It's not that the Lyco/Conti designs can't be improved upon, it's that there is no cost justification for an engine manufacturer to do-so. I'd think if a manufacturer wanted to make an aircraft-specific block that ran on 91/93UL or Jet-A, it wouldn't be too difficult to do. They can adapt things like direct injection, FADEC/electronic ignition timing/etc into the design and probably come out with a small-but-not-insignificant fuel savings or increase in HP per lbs. However, since it makes no financial sense to invest the R&D and certification costs, no one will undertake it. It would require someone like a Howard Hughes character to take on the project.
Click to expand...

They would do it if there was a demand for it, but pilots want it to be proven technology before they'll fly behind it, and so there is no demand for new technology.

Actually, some new technology is creeping in. Years ago, Lycoming and Continental wouldn't even think about roller tappets. Now you can get them. I don't know why it took so long. Less wear because of less friction, and also less wasted power, also because of less friction. I'm sure there are factors they had to address that I don't know about, but they are now available.

I guess its evolution, not revolution in aircraft engines.
 
Also keep in mind, the cheapest thing in the airplane is the pilot. Sure Lycoming could upgrade the engine, but if it added $1 to the cost of the engine it would deter at least some from buying it.
 
Crashnburn said:
They would do it if there was a demand for it, but pilots want it to be proven technology before they'll fly behind it, and so there is no demand for new technology.

Actually, some new technology is creeping in. Years ago, Lycoming and Continental wouldn't even think about roller tappets. Now you can get them. I don't know why it took so long. Less wear because of less friction, and also less wasted power, also because of less friction. I'm sure there are factors they had to address that I don't know about, but they are now available.

I guess its evolution, not revolution in aircraft engines.
Click to expand...

Pilots aren't demanding "proven technology for they'll fly behind it", the tech has already been proven. The costs of certification are what kill it before pen ever meets the paper. Plenty of Experimental guys have been running E-MAGs, FADEC, etc. on their aircraft. It's proven to be reliable and efficient. However, putting that onto a certified aircraft is prohibited without lots of red tape and high costs. Same goes for designing an engine to retrofit into any certified aircraft. The certification costs make any attempt futile.
 
Crashnburn said:
Actually, some new technology is creeping in. Years ago, Lycoming and Continental wouldn't even think about roller tappets. Now you can get them. I don't know why it took so long. Less wear because of less friction, and also less wasted power, also because of less friction. I'm sure there are factors they had to address that I don't know about, but they are now available.
Click to expand...

One of the catches with certification is making changes that can be retrofitted without invalidating previously existing performance data. Roller cams are inherently better in almost all aspects, and a roller cam would make it easier to add power. But... now your performance data gets invalidated.

So when Lycoming went to roller tappets, the goal was to make sure the cam profile matched the flat tappet so that the argument could be made for it being backwards compatible with older aircraft.

On the whole this worked out, although they got the profile off a bit and because of this the end result was that some engines (primarily turbo) actually lost some horsepower with the roller vs. flat. So engines like Navajo engines are still sent out with flat tappets, but @Bill Jennings will get roller tappets in his new engine and in that engine there will be no power or efficiency loss.
 
The airplanes I learned to fly on used unleaded avgas, back when Pontius was a pilot!
 
SoonerAviator said:
Yup. It's not that the Lyco/Conti designs can't be improved upon, it's that there is no cost justification for an engine manufacturer to do-so. I'd think if a manufacturer wanted to make an aircraft-specific block that ran on 91/93UL or Jet-A, it wouldn't be too difficult to do. They can adapt things like direct injection, FADEC/electronic ignition timing/etc into the design and probably come out with a small-but-not-insignificant fuel savings or increase in HP per lbs. However, since it makes no financial sense to invest the R&D and certification costs, no one will undertake it. It would require someone like a Howard Hughes character to take on the project.
Click to expand...
Continental Motors (when it was Teledyne Continental Motors) did produce a FADEC certified engine, it was the engine for the Liberty XL2. I think it was on O-240 modified into the IOF-240-B. Not many buyers AFAIK for the plane or the engine.
 
Cap'n Jack said:
Continental Motors (when it was Teledyne Continental Motors) did produce a FADEC certified engine, it was the engine for the Liberty XL2. I think it was on O-240 modified into the IOF-240-B. Not many buyers AFAIK for the plane or the engine.
Click to expand...

Sure, but I'd think if there was a modern engine which was a direct replacement for IO-360/520/540 to be installed in ANY aircraft originally equipped with the Lyco/Conti engines with minimal extra cost, there'd probably be some moderate demand. It's like doing an LS swap in the auto world. If you could get the same or better performance out of an alternative engine for roughly the same price as the OEM engine, you'd probably see people make the switch. Easier hot/cold starts, potentially better mileage, one or two less knobs to mess with at the same cost as the factory engine? Sure, why not! Alas, those pesky FAA certification rules for performance and flight testing come and ruin it for everybody! :)
 
Cap'n Jack said:
Continental Motors (when it was Teledyne Continental Motors) did produce a FADEC certified engine, it was the engine for the Liberty XL2. I think it was on O-240 modified into the IOF-240-B. Not many buyers AFAIK for the plane or the engine.
Click to expand...

What I heard about the XL engine is pilots didn't like not having control over the mixture. Also, the useful load, is pretty low. It's not an LSA, but many LSA's have a better useful load. Also, the engine sound is really annoying.
 
SoonerAviator said:
Sure, but I'd think if there was a modern engine which was a direct replacement for IO-360/520/540 to be installed in ANY aircraft originally equipped with the Lyco/Conti engines with minimal extra cost, there'd probably be some moderate demand. It's like doing an LS swap in the auto world. If you could get the same or better performance out of an alternative engine for roughly the same price as the OEM engine, you'd probably see people make the switch. Easier hot/cold starts, potentially better mileage, one or two less knobs to mess with at the same cost as the factory engine? Sure, why not! Alas, those pesky FAA certification rules for performance and flight testing come and ruin it for everybody! :)
Click to expand...

I've probably spent more time flying and otherwise running FADEC piston engines than anyone else on here (just an assumption since it's in the thousands of hours including ground running). You're not looking at better performance or economy. You're looking at equal performance, generally worse economy, but easier starts and single lever control. There are a lot of nuances of aircraft specific installations that can make things harder than anyone things on paper. Even something as silly as changing the intercooler setup can cause some weird dynamics. We think that, because our cars are all so well-behaved, that this is easy, but those of us who are involved in R&D know how much effort goes into making everything as smooth and seamless as it is. Anyone who's done significant modification to cars has seen the rabbit hole you can go down when you start changing things.
 
SoonerAviator said:
Yup. It's not that the Lyco/Conti designs can't be improved upon, it's that there is no cost justification for an engine manufacturer to do-so. I'd think if a manufacturer wanted to make an aircraft-specific block that ran on 91/93UL or Jet-A, it wouldn't be too difficult to do. They can adapt things like direct injection, FADEC/electronic ignition timing/etc into the design and probably come out with a small-but-not-insignificant fuel savings or increase in HP per lbs. However, since it makes no financial sense to invest the R&D and certification costs, no one will undertake it. It would require someone like a Howard Hughes character to take on the project.
Click to expand...
NOT easy. SMA did it. I worked on one in a 182 a few years ago. At that time SMA told us that they had 50 engines flying worldwide, and they had spent one billion dollars on the project. How many other manufacturers do you think are going to tackle that after seeing SMA's experience?
 
Dan Thomas said:
NOT easy. SMA did it. I worked on one in a 182 a few years ago. At that time SMA told us that they had 50 engines flying worldwide, and they had spent one billion dollars on the project. How many other manufacturers do you think are going to tackle that after seeing SMA's experience?
Click to expand...

That was the point I was making . . . It isn’t easy and the costs/ROI don’t make much sense compared to other projects. As I said before, the only way it likely gets done is with a Howard Hughes-type who pursues the project regardless of cost or payback period.


Sent from my iPhone using Tapatalk
 
You guys are so involved in fixing the engine problems you're missing the real issue. Fuel. Simple truth here is that while diesel can be produced around the world with pretty much the same characteristics and no problems with vapor pressure or turning into a neat polymer, unleaded gasoline can't seem to say the same. Sure Porsche and the others made engines that would run on pump gas but since the composition of the fuel coming out of the pump is never the same its like shooting at a moving target and for piston engines thats tough to hit. I've never seen a diesel with vapor lock but I've seen a lot of gasoline engines with that issue. If the lot of fuel isn't right or the same as the last batch than what can you do....engine can't fix the issue.

Frank
 
SoonerAviator said:
That was the point I was making . . . It isn’t easy and the costs/ROI don’t make much sense compared to other projects. As I said before, the only way it likely gets done is with a Howard Hughes-type who pursues the project regardless of cost or payback period.


Sent from my iPhone using Tapatalk
Click to expand...
No, I was responding to the "not too difficult to do" remark you made. It IS difficult. There are many aspects that have to be considered, and many more that show up during testing and early in-service. The one I worked on was a first-generation engine and had numerous problems even after only a couple hundred hours. SMA was on their third iteration by then and they sent us a bunch of parts to fix the shortcomings. SMA is a division of SNECMA, IIRC, who has deep pockets. Otherwise the whole thing would have died long before any engines were sold. Continental bought the technology from SMA.
 
BiffJ said:
You guys are so involved in fixing the engine problems you're missing the real issue. Fuel. Simple truth here is that while diesel can be produced around the world with pretty much the same characteristics and no problems with vapor pressure or turning into a neat polymer, unleaded gasoline can't seem to say the same. Sure Porsche and the others made engines that would run on pump gas but since the composition of the fuel coming out of the pump is never the same its like shooting at a moving target and for piston engines thats tough to hit. I've never seen a diesel with vapor lock but I've seen a lot of gasoline engines with that issue. If the lot of fuel isn't right or the same as the last batch than what can you do....engine can't fix the issue.

Frank
Click to expand...

Diesel and Jet-A are different. SMA, for instance, has their engine certified for Jet-A only. Diesel has less lubricity or something and the pumps don't like it. I'm sure they could have fixed that easily enough (after all, millions of diesels on the road have pumps that tolerate diesel) but they were, I'd bet, concerned that diesel fuel would vary widely in composition and quality, and any fuel not specifically for aviation could cause an accident, or at least be in the tanks at the time of an accident, and SMA would be a named defendant in consequent lawsuits if they had ssaid diesel was satisfactory.

Back in the 1980s we had a trucker from Texas show up in BC, Canada, to pick up a load of stuff. It was one of the coldest Decembers in recent memory, and he had last fuelled up in coastal Washington state. We told him to leave his engine idling all night or he'd never get it started in the morning. Asked him about his antifreeze and if that diesel was winter fuel. He laughed, thinking we were funning him. Next morning he called from the hotel. Truck wouldn't start. He had to wait a day or two before a tow truck could pull it to a truck shop and put it in a heated bay for two days to thaw out the antifreeze AND the diesel fuel. It had jelled. And there's a warning: kerosene-based fuels can do that, and airliners have to keep their fuel tanks warm at altitude. A GA diesel using summer diesel fuel could suffer engine failure due to jelled fuel.
 
Last edited:
Dan Thomas said:
Diesel and Jet-A are different. SMA, for instance, has their engine certified for Jet-A only. Diesel has less lubricity or something and the pumps don't like it. I'm sure they could have fixed that easily enough (after all, millions of diesels on the road have pumps that tolerate diesel) but they were, I'd bet, concerned that diesel fuel would vary widely in composition and quality, and any fuel not specifically for aviation could cause an accident, or at least be in the tanks at the time of an accident, and SMA would be a named defendant in consequent lawsuits if they had ssaid diesel was satisfactory.
Click to expand...

You have that backwards on the lubricity. Jet-A has less lubricity than diesel, and you need special fuel system components to make Jet-A work in a diesel. You also end up with somewhat different calibrations for optimal running because Jet-A and diesel have slightly different burn characteristics.

Technically, diesel would work fine in a piston engine that can run Jet-A. But certification wise that probably doesn't work out so well because of all the things you need to account for with certification.
 
If Jet-A is available around the world, and Jet-A works in a diesel motor (simply referring to the compression causing ignition instead of spark plugs), then that seems like the better place to start on a new engine design. The alternative is some sort of other gasoline type fuel, which others have made clear the issues there.

Didn’t Daimler invent the compression ignition engine?
 
You must log in or register to reply here.
Back
Top