Wolfi, your arguments have already been offered here, and countered. The price argument applies in Europe only, it bases on government’s tax policies only. But Europe is only a small part of the G/A scene. And mostly in Europe but even in the US, G/A is on the decline, however much we may regret it. Also, availability of AvGas seems to be guaranteed for the foreseeable future by a Polish refinery.
And yes, the US engines do create reliability by using big volumes, to the expense of fuel burn. (no substitute for cubic inches, as they say over there. As a bass guitar player and cabinet designer I grudgingly agree…)That’s a compromise, aviation is full of compromises, and this compromise has been seen to work well since WW2.
Also been said before: the future will be decided by the emerging economies (India, Brazil, and mostly China) but up till now the growth of G/A has been inexistent there, or next to. Whatever China chooses will be the future, as things stand today. For as far as I can see, there are some tries there with Rotax-powered two-seaters…
I think the old Lyco engines deliver the best SFC of any petrol engine currently operating – if one is comparing engines running at a constant 65% or 75% power.
Second order improvements should be achievable with electronic ignition, via variable ignition timing, allowing low RPM to be used to reduce mechanical losses. But for some reason Lyco etc are dragging their feet getting this certified… maybe they worry about getting too far ahead of the US market?
Diesel engines deliver a better SFC because they have a much higher compression, not because they have FADEC.
I think the old Lyco engines deliver the best SFC of any petrol engine currently operating
Hm, I can’t help asking for some reference there. My understanding was always that the Lyco’s were not good at SFC at all, preferring reliability and long life, and probably to good reason. I certainly believe the Rotax 912/914 have much better SFC, but don’t have any figures at hand.
Perhaps it is not a good idea to discuss Lyco’s as a whole, there might well be significant differences between models.
Yes, large displacement and low rpm can lead to higher efficiency due to reduced friction – which is one reason ship engines run at between 100 and 200 rpm. The limit in that direction is that combustion becomes problematic with a spark ignition engine when the cylinders reach a certain size – and the ability to run large cylinders at low rpm is in fact an advantage of the diesel.
The other reason to build a low rpm, large displacement engine is to match the propeller speed without a gearbox, and the lack of a gearbox is a reliability benefit. It may or may not have an affect on weight – all the manufacturers have done it both ways and market experience pushed them to direct drive for higher powered engines. The Russian M14 is an interesting design that went in a different direction: geared, supercharged, and nine cylinders to make only 360 HP… but radials are otherwise mechanically simple.
Jan, the Rotax does not have particularly good SFC but takes less operator input to achieve it. This comes along with the relative complexity of two motorcycle carbs with their rubber diaphragms and moving slides. Or electronic fuel injection. As you correctly pointed out above, engine management is not necessarily the same thing as engine design.
This is one of the many areas where it is easy to throw down a gauntlet but digging out the answers takes more time than most people have 
A very quick google finds this. You can wade through this and much else. There are links there to follow.
I recall a debate in Usenet (those were the days – c. 10 years ago) where a car engine designer laid out a load of data showing the car engines were all slightly worse. That should be on google somewhere.
Higher RPM and gearboxes lose power. Not a lot; maybe 20%. But the notion that the old Lycos have poor SFC is totally wrong. At some specific power setting, they are pretty well optimal.
I find it very hard to believe that car engines have constantly improved since the 50es and GA ignition engines have by a magic stroke of luck attained the perfect optimal design 50 years ago just because it is easy to optimise an engine running at constant RPM.
Even supposing that is true (considering the antiquated instrumentation used to measure said performance in flight I highly doubt the accuracy and repeatability of results) – the world ex US does not have the easy “i can buy a lot of avgas for that engine price” argument. The US won’t have it for long either – certified private pilot numbers are in constant decrease since 1991, student numbers as well, while FI numbers increase (the myth of the "commercial pilot shortage " seems to be a myth after all) – you don’t have to trust me, it’s the FAA data… The result of that will be less and less demand for engines and higher and higher costs.
The reliability of the total package leaves to be desired as well (maybe the US consumer population thinks it’s ok to have a great BSFC but have the mags checked every 500h hours – if they even get there, the spark plugs crack, the exhaust crack and so on. Supposedly because it’s “hard” to design an engine that does 75% hours in a row. Since car engineers have managed to design production series road-going engines that manage to sustain 95-99% rated power for 24 h in a row w/o falling apart, I cannot believe it’s “impossible” to design a better aero engine which after all has a lesser set of constraints to fulfill or so i’m told. So what are the real operating numbers when adding maintenance costs on top of fuel costs? At Swiss manpower prices personally i’d rather avoid going to the shop every so often.
If GAis to be saved, it is going to have to come up with a product which is pretty much turn-key to operate and doesn’t need to be babied all along and have its ancillaries replaced every so often in order to appeal to those markets where growth can come from. Otherwise the GA numbers will keep shrinking until not even the US flyers will be able to afford to do it any longer, not even on an experimental basis.
650k for a new plane of which 70k (!) for an engine which is designed for ONE constraint set only?
The key is constant power.
Aero engines run at a constant power, and quite a high power too.
It’s easy to optimise an engine for that. You can even do it with fixed ignition timing.
To achieve anything like reasonable MPG with a car engine you need complex controls. These engines run at about 20% of max rated HP on average, the power output varies wildly, and even 70mph is only about 30% (for a typical 2 litre car). My VW 2L diesel does an amazing 50MPG+ in city traffic, if crawling along at a constant speed just above idle; a petrol car would be doing 5-10MPG. The emissions regs throw in more complexity; those who tweak their engines (reprogram the ECUs) can get substantially more MPG, but they don’t meet the emissions regs anymore (it’s IMHO cynical to burn more fuel to reduce emissions).
Aero engines run at a constant power, and quite a high power too.
If you’re honest, you have to admit that the majority of piston GA engines are operated on short flights and traffic patterns for most of the time. Also most of them are not equipped with a complete engine monitor. That makes this “SFC is not that bad in cruise” argument a lot weaker. A lot can be gained from more modern engines.
And 1950s aero engines are as modern as 1950s car engines. A big block V8 from the 1950s will work in today’s environment, too and as reliably as an aero engine. The Soviets also thought the 1960s licensed Fiat 124 produced as Lada was the pinnacle of car development and didn’t need improvement.
I find it very hard to believe that car engines have constantly improved since the 50es and GA ignition engines have by a magic stroke of luck attained the perfect optimal design 50 years ago just because it is easy to optimise an engine running at constant RPM.
It’s optimal within the economics of which it is operated. I don’t see many cars with turbines either, even though turbine (jet and turboprop) is used in all larger airplanes.
GA is a tiny niche in the aviation industry. Cars are not niche, it’s one of the worlds largest industries. The basic design of the Lycoming/Continental is hard to beat with its simplicity. What you can improve is manufacturing processes (better tolerances, better materials) making the engine lighter, stronger and more reliable. You can improve the governing of the engine from 100% manual to FADEC, making it simple to operate and assure optimal operation all the time. But, these engines already exist. They are called Rotax, ULPower and D-motor. They will eat their way into Lycoming land from beneath. Already the smallest Continentals are gone for ever. The (i)O-200/230 is also soon to be a thing of the past. Airplanes in this class are replaced with LSA/VLA using Rotax and ULPower. 320 size is next, but it will take some time before new aircraft is developed. 360 and up will remain for a looong time.
Aircraft engine management will I’m sure develop toward single power lever control that sets propeller rpm by density altitude, mixture and ignition timing by (probably) a multi-axis look up table, and then finally power by a fly-by-wire throttle opening depending on throttle setpoint. Percent power available and in use will be calculated and displayed to the pilot. All that will make flying easier but not greatly more fuel efficient.
I’m not sure however that any of that is going to appeal greatly to the average private aircraft owner. One of the reasons I fly an out of production certified aircraft with an O-320 is because it is a very inexpensive way to do the job and have fun. Less expensive in my case than an RV which is what I guess is what I might otherwise be flying. Either way, the engine’s lack of complexity gives me freedom that I would never sacrifice. That is a much more important to me than single lever engine operation.
There are around 700 aircraft living at my base. If you look around for the equivalent of car dealerships, ready and waiting to service your aircraft for big money, the only thing vaguely like that is a Piper dealer that works only on the Meridian and Matrix type aircraft. The rest are maintained largely by independent A&Ps working in their own or the owners hangar, buying parts wherever they can buy them, i.e from multiple suppliers and independent of any dealer. Owners like it that way and I’d guess anything that makes that unfeasible is, in the end, not going to fly in the market.
