It really doesn't change anything. Still available just cutting out the middle man. Cessna would build and certify each Diesel 172 with a Lycoming. Then, a Cessna pilot would fly it to Alabama for a Diesel conversion. The Cessna pilot would come back down to Alabama and fly it back to Independence for delivery.

So, they're basically streamlining the process. It makes sense.

The majority of planes can run on mogas.

Unfortunately, the vast majority of 100LL sales are to airplanes that can't run on mogas. Also, the majority of fleet value are planes that can't run on mogas.

So no 100LL without a replacement means basically the end of piston GA as we know it. It would be a disaster, even for the planes capable of mogas.

Mike C.

There can't be preignition, fuel is not introduced until top of stroke, and the engine is designed to operate with detonation, so I thought the engine would still run but perhaps at reduced power.

Curious what the destruction mechanism is here. Can you explain or point me to an explanation?

(I know the reverse is true, diesel/jet in a 100LL airplane destroys engines with preignition)

Mike C.

I just threw a guy out of a meeting this morning, who uttered those exact words as part of his argument to keep building something - that we are not going to build anymore if i have my way. Science fair projects are fun. but in the real world you have to sell product to stay in business.

Diesel engines ignite the fuel by heat of compression. We refer to a parameter called the fuel's ignition delay. basically it's the time between the start of injection and the first identifiable pressure increase from combustion.

With gasoline you worry about AKI which is the resistance to self-ignition. You want a lot of resistance to gasoline starting by itself. With diesel it's the opposite - we want the fuel to be easy to get started burning. Diesel fuel has a parameter called cetane number which is inversely proportional to the ignition delay. Higher cetane = easier to get the fire started.

So you see the fuels are polar opposites in what they are designed to do. Put diesel in your spark ignited engine and you get huge pre-ignition, because that's what diesel is supposed to do. Conversely, put petrol in your diesel engine and it has an enormous ignition delay. When the fuel finally starts to burn it's going to be at a point in the piston travel with very high compression, plus the rate of burn will be much higher than with diesel. So the pressures and temperatures go through the roof (actually through the piston, literally)

There can't be preignition, fuel is not introduced until top of stroke, and the engine is designed to operate with detonation, so I thought the engine would still run but perhaps at reduced power.

Curious what the destruction mechanism is here. Can you explain or point me to an explanation?

(I know the reverse is true, diesel/jet in a 100LL airplane destroys engines with preignition)

Mike C.

Mike - here's a visual aid - it doesn't take much petrol contamination in diesel to significantly alter the ignition delay.

That’s a useful distinction, thanks.

Perhaps I’m over-simplifying, but if a 2-seat trainer and a 4-seat ‘station wagon’ can be operated on mogas, all is not lost. Yes, it would be transformative. Many planes would be retired. It would certainly impact the fast singles (Cirrus, Lancair, Bo, 210) and the light twins, though I suppose the early O-470 powered 310s and Barons would get the last laugh.

It would also move the needle (again!) on SETP as a step up airplane.

The major advances in aviation have historically been driven by advances in propulsion. I presume that a reborn GA would be shaped by fuel availability, favoring the lower-compression traditional engines and Rotaxes and such.

Another nail in the coffin of the light twin, and this time the high-performance single would go down with it. Sigh.

Currently the jump to turbine power is pretty steep, even at the low end of SETP (Malibu jetprop, P210 Silver Eagle, early TBM700s). An affordable and decently efficient 300-ish hp turboprop (1/2- of your TPE-331!!) would be transformative, in a good way, whereas the disappearance of 100LL would be transformative, in a bad way. But I do think GA would survive. People want to fly.

My $0.02

Mark

All of this is true ... but if there's any viable niche after such an event ... it will be basic trainers. Lots of reasons to have diesel 172's but loss of 100LL isn't among them.

Dive into the technicalities of it and it becomes rather obvious that low cost, small and efficient gas turbine engines will never happen. Fighting too many realities of physics and manufacturing technology. First is just the reality of moving air vs. small passages. The second is the advances in efficiency require very difficult steps of manufacturing. Above a certain size, gas turbine engines make sense, simply due to size alone.

Gasoline is a perfectly good fuel for aviation, and the gasoline piston (Otto) engine is perfectly good choice for aircraft up to a certain size. We're kind of stuck in the hole of the existing technology is "good enough" and implementing new technology is "too expensive". An incredible amount has been learned in the car industry, since the last piston aircraft engine was designed. But the size of the fleet, the cost of development and the substantial resistance to anything new will prevent it.

I believe 100LL cessation is a "when" not "if" question. There's no particular reason a piston power plant that does the job of a TSIO550 and runs on regular highway gasoline can't be built, but there's simply not the market to warrant the investment of developing that engine.

We must have been attending different courses on streamlining, but I have a really hard time seeing how putting additional flight time and wear on gasoline engine (used to ferry the skyhawk down to Alabama) and spending double (or more) the labour cost on installing, removing and reinstalling an engine as streamlining.

If anything I see additional costs, delays, MIF risks and diluted liability (warranty or legal).

This is it, plain and simple.

PWC, Williams, Garrett, Allison, and a few others have put a lot of R&D money into this over the years, each of them trying to get a commercial edge over others. Nobody is hiding a magic bullet for a small jet engine or turboprop, the magic bullet just doesn't exist.

I just threw a guy out of a meeting this morning, who uttered those exact words as part of his argument to keep building something - that we are not going to build anymore if i have my way. Science fair projects are fun. but in the real world you have to sell product to stay in business.

Having had experience with a diesel conversion (SMA 182).

In the US market....

I can say that all the efficiency and ease of operation benefits were realised. It was also extremely reliable.

On the downside, limited maintenance facilities and limited sources of parts and oil drive costs up.

Combine that with the engine having a few additional maintenance inspections that are unique to diesel and that it they are life limited and can NOT be overhauled. There you go, you just gave up most of your savings.

It doesn't help that these units are undergoing active development and see a lot of changes. The manufacturers don't have the scale to support multiple versions.

Oh yeah first post yadda yadda.

you are assuming that "cool new technology" equals "long term business model" . Far, far from being true.