How much innovation has there been in biro manufacture over the past 30 years?
They haven't yet prevented them marking aircraft interiors....
whilst a Rotax has a pleasantly lower fuel consumption than a Lycoming
Not wishing to disagree otherwise, but AFAIK the SFC (fuel flow per HP) of a Rotax is no better than that of a Lyco, when the latter is operating at peak EGT i.e. anytime in cruise.
The Rotaxes are low HP engines and when you fit one in a little 2-seater with a small volume cockpit you get a plane which does say 130kt at 20 litres/hr, which is superb, and there is a big market segment for that sort of capability, but you would have got the same result with a little Lyco, say an O-200, except that few people are going to use a Lyco in a new design when the Rotax is lighter etc.
I recall seeing a table of SFCs, some years ago, produced by a car engine designer, and the Lyco/Conti direct drive engines beat the whole lot. No "car" petrol engine was as good. But that's not suprising; the mechanical losses at say 5000rpm are a lot more than at say 2500rpm, plus the gearbox...
If modern engines delivered a say 20% better MPG than the old ones, that would be a big driver for change, but they don't and as soon as this is realised, the primary case disappears.
Not wishing to disagree otherwise, but AFAIK the SFC (fuel flow per HP) of a Rotax is no better than that of a Lyco, when the latter is operating at peak EGT i.e. anytime in cruise.
You keep saying that and I keep responding: that is only true in theory as in reality you spend a considerable portion of your flight in climb / full rich and the consumption is so awful that you will never be able to get back to anything close to Rotax' SFC just by flying long enough.
I operate my turbocharged O-540 with ca. 38l/h but in initial full rich climb it's 97l/h.
PS: I read a side by side comparison of the Rotax 912S and the new 912iS with electronic ignition in two identical Fk14 microlights. To my surprise, the 912iS showed much better consumption and performance, most likely due to the non optimal carburettors and auto-leaning of the 912S.
Maybe, but you or I are not driving the market.
the 912iS showed much better consumption and performance, most likely due to the non optimal carburettors and auto-leaning of the 912S.
How can it?
Power can come only from burning fuel, so if the engine is running near peak EGT, and the ignition is timed right for that RPM etc, what the carb does is irrelevant.
Power can come only from burning fuel, so if the engine is running near peak EGT, and the ignition is timed right for that RPM etc, what the carb does is irrelevant.
Indeed, because with the 912S it does not always run at peak EGT due to the way the mechanical auto leaning works (I think they call it "altitude compensation"). Apparently its effectiveness depends on the altitude/atmosphere. The carb creates the air/fuel mixture and that needs to be exactly at the optimal stoichiometric ratio to reach book SFC.
Unfortunately the 912iS is both heavier and more expensive while not producing more horse power. They should have at least added a few hp, that is always possible. It will probably take quite some time for it to succeed. Well, Rotax is basically without competition so why innovate?
Apparently its effectiveness depends on the altitude/atmosphere. The carb creates the air/fuel mixture and that needs to be exactly at the optimal stoichiometric ratio to reach book SFC.
I don't think this can be done accurately enough over the full range of altitude. One needs to be measuring mass flow to do it properly - or else do what they do in cars which is to use an oxygen sensor. But oxygen sensors on cars pack up fairly frequently...
I recall that Conti used altitude compensation in their fuel servos. There is a nasty failure mode in that whereby the pressure sending diaphragm bursts at altitude. The result is an engine stoppage - until you realise what's happened and lean massively.
Well, Rotax is basically without competition so why innovate?
Same goes for most things. Improvements are at most very marginal.
I think Rotax was motivated towards EFI by the unavailability of better carbs than the CV Bings for their specific engine. The Bings could in principle be OK but they were not designed for the same level of reliability as a simpler aircraft carb: a vacuum controlled moving piston, a thin rolling rubber diaphragm to seal it, hose clamp mounting and spring return cables are fine for a 1972-96 BMW motorcycle (the main application for these carbs), but aren't optimum for aircraft. Plus the Rotax engine by design needs two carbs versus one, and they must be synchronized, which is a lot of 'monkey motion'. The constant velocity carb does provide a useful measure of auto lean (as do some aircraft carbs BTW, see http://en.wikipedia.org/wiki/Bendix-Strombergpressurecarburetor) and I can imagine Rotax looking at their options, seeing nothing else available in side draft aircraft carbs with or without auto lean, and thinking that EFI was the only way forward despite it having no advantage in power plus complexity and component obsolescence issues.
I like the simplest possible setup myself, and admire the original designers of the flat aircraft engines in coming up with a very simple carburation solution, positioning a purpose-designed single carb under the engine to minimize leakage issues and fire potential.
How much innovation has there been in biro manufacture over the past 30 years?
Good point! Actually I was thinking as I submitted the last post several examples in the natural world where evolution hasn't taken place for a long time. Crocodiles haven't changed at all - in evolutionary terms they clearly have little need for improvement. Dinosaurs also. But what these things have in common is that whilst they are around for a long time, when they go, they go very quickly. Evolution (as opposed to revolution) is a good thing.
The original point was made in regard to CofA aircraft. Permit/experimental aircraft (and their Jabiru/Rotax etc powerplants) have come along leaps and bounds, and are a perfect example of what I argue hasn't happened in the CofA world. And like most innovations, these are still treated with derision by a significant proportion of the GA community, even though (notwithstanding their limited mission profile) many quietly agree they are vastly superior to their older CofA counterparts.
I'd be inclined to agree that if you can run a old aero engine in a steady state for a long period, you may well get great efficiency. However, I would suspect that as an ensemble, the average old aero engine spends more time, a very long way from its optimum efficiency, that it does operating at it's optimum efficiency. You can argue that's operator error, but you could argue that's just reality. Using modern engine management removes all doubt - you get an engine that operates at it's peak efficiency all the time.
Quick question: Does anyone think that having automated engine management has potential greater benefits for the longevity of an engine? Poor engine management can certainly reduce an engine's life expectancy. And presumably, the closer you run an old aero engine to it's optimal efficiency, the finer the margins for error before you unknowing start causing damage.
Hard to prove unless you conducted a controlled scientific experiment, but it would be interesting to know what effect it might have for an "average" aero engine in the hands of an "average" pilot. As with fuel efficiency, this is really the performance that matters.
these are still treated with derision by a significant proportion of the GA community
I don't think they are treated with derision. What I see happening is that, on the old UK pilot forums, there is a very much "them and us" positioning, and the "Rotax crowd" (I use that term loosely) carries along a small number of individuals who are very vocal in pushing their position, often adding inflammatory stuff e.g. the demise of Avgas and the closure of GA airfields would be just fine (because "I" have my own farm strip, with mogas), etc etc etc.
The way I see it is that there is room for everybody.
Personally, I would never trade my TB20 for a smaller machine because I need that mission capability for the trips that I do (mostly with Justine, on holidays, and carrying a load of stuff) which make flying really worthwhile for me.
the average old aero engine spends more time, a very long way from its optimum efficiency, that it does operating at it's optimum efficiency.
It probably does. A 30 minute burger run is just that.
Using modern engine management removes all doubt - you get an engine that operates at it's peak efficiency all the time.
It's an interesting Q but I would be suprised if you could run say an IO540-C4 (250HP) at 250HP in all phases of flight, at stochiometric, with any kind of engine management. You would need water cooling, and a turbo to substantially pump up the MP. Then you are looking at a different engine. Would it be more reliable? I am certain not.
Does anyone think that having automated engine management has potential greater benefits for the longevity of an engine?
It must have, but will it be delivered in a reliable form and at a price people will pay?
My experience with motorcycle EFI (1500-2000 people use my work now) is that its very hard to produce results that better carbs, including fidelity of control. The reasons its used in that application are (1) more power without affecting idle quality, due to high pressure delivery and no venturi in the intake, and (2) the ability to tune a narrow digitially defined band of the operational range to pass emission tests without affecting the broader range of operation.
In the motorcycle application, it might surprise you to know that when well equipped, high volume manufacturers switched over to EFI, economy typically dropped 10-20%. That's not to say it can't be done well, but EFI is not a panacea for engine control.
The biggest potential advantage of EFI for aircraft engines is automatic altitude compensation. Certainly for me that is inconsequential compared to the complexity of owning and maintaining a certified EFI system over decades.
