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light aircraft engines

Old 23rd Nov 2021, 13:09
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light aircraft engines

As a non-pilot, I read so much in these pages about engine failures, accidents and near-accidents in light aircraft due to such things as carburettor icing, lean or rich mixture, plug fouling, poor power output etc. All of these were also common in car engines in the 1960's or 70's but are almost unheard of in modern cars, which are very reliable, and mostly have fuel injection and often turbos as standard, as well as plenty of automatic control over adjustments for temperature and air density. Given the negative consequences of engine failure in the air are far greater than in a car, why is it that so many relatively modern light aircraft apparently have such antiquated power plants, and require so much manual adjustment and control? Obviously, historic aircraft are a different matter, but updated engines with modern automation etc would reduce the pilots workload and improve reliability and safety enormously. (forgive my ignorance)
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Old 23rd Nov 2021, 14:23
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The prevailing design requirements for certification are "old", by today's standards, but based upon simple wisdom. A lot of this wisdom has been born of experience, a lot of it from WW2 airplanes. Within these requirements, an engine for a certified aircraft, must itself be certified. That process is very expensive and burdensome. And, referring to the [present] engine certification design requirements, certain simplicities are required. One of those is that the engine must be able to run without an external source of electricity - hence magnetos. Nearly all legacy horizontally opposed piston engines are direct drive, which is simple and reliable, but contrary to modern engine design. Certainly some modern engine installations are being certified with variations on these requirements (by "special conditions"), but it's expensive. So, for a brand new airplane design, with a modern engine, it may be worth the investment. But, for an airplane designed in the 1960's, and built '60's to '80's, it may not be worth a million dollar program to certify a more modern engine, when you can just keep rebuilding the original one.

Present light airplane engines (Continental and Lycoming) are surprisingly simple, and lightweight for the power that they produce. They are comparatively reliable, when I consider the "computer" problems I have experienced with modern car engines! Many of the failures you may read about are a result of improper operation, rather than the engine itself failing mechanically. But yes, they are old and very basic in design. To get modern engines into the general aviation fleet, will require lots of money, and regulatory advancement (= money + time). The general aviation industry is not known for having excess money!
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Old 23rd Nov 2021, 15:00
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Some of the most common light planes are quite old designs, and use engines of corresponding age. Especially those from the US: C150/152, C172, PA28, Beech Bonanza, ...

From Europe comes the Rotax family, which still uses carburettors but has no need for carb heat nor for mixture control. And they now have an injected version too, though I do not see it achieving great commercial success.

The only engines for light aircraft that are with the times are the diesels, Austro, (ex-)Thielert, and others more.
[ added: plus some adaptations of car engines, like the Viking 110/130 by Mr. Eggenfellner of Subaru fame, but I don't think these are certified ]

Last edited by Jan Olieslagers; 23rd Nov 2021 at 15:58.
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Old 23rd Nov 2021, 17:20
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Size of the market (tiny cf automotive)
Different requirements, eg power to weight ratioRotax and ULPower are doing some good stuff.
I could argue that you don't hear about engine failures in modern engines exactly because they are more reliable.
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Old 23rd Nov 2021, 17:47
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Thank you for the information. I realise that old aircraft will have old engines, but given the complications and difficulties in managing them and the drastic consequences of their failure, surely some updating or re-engining would be necessary. If only for the safety of the pilots. It's quite surprising that the authorities haven't mandated this: similar failings with fatal consequences in a road car would have resulted in recalls and compulsory modifications. I assume that economics come into this: cheaper to re-fit a recondition engine of the same type, than a new one. And certifying new engine designs is probably not economic for manufacturers either.

But also, maybe, part of the charm and attraction of flying small planes is perhaps actually mastering the complications and idiosyncracies of each plane, and managing the enhanced risks. Its a world I know very little of, and respect and admire those who can and do those things.
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Old 23rd Nov 2021, 19:15
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Please don't assume that an engine failure in a light airplane is always going to have drastic and/or fatal consequences (your words). Au contraire, it's an eventuality that pilots are very well trained to deal with and practice frequently. An airplane with a stopped engine can glide down under control to make a perfectly safe landing in many circumstances. There are phases of a flight where dealing with an engine failure is more tricky, like just after take off, but even that is usually survivable.
Let me put it this way. I'd rather have an engine failure in my aircraft at 2000' in the cruise, than a blow out on a front wheel in my car cruising at 70mph in the middle lane of the M6 in the rush hour.
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Old 23rd Nov 2021, 19:27
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'I am interested to see Jan O saying that carburetted Rotaxes don't need carb heat. I have had a couple of instances of rough running which I thought was carb icing, and which application of carb heat - or really carb warm - appeared to cure, in a Eurofox. Why is carb heat not generally required for carburetted Rotaxes please?
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Old 23rd Nov 2021, 23:51
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My 582 has a water heated entrance ring to the carbs. This warming ring is always on, fed by the engine cooling water.
AFAIK this is standard fitting for the 582.
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Old 24th Nov 2021, 00:06
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Given that 'cold' and 'warm' are vague terms the Rotax engine runs on a warm air mix and so generally avoids carburettor icing but they are not immune from it. The cylinder heads are liquid cooled maintaining temperatures. Engine failure, of some Rotax engine installations, owing to carburetor icing is not uncommon. Rotax subsequently introduced what is placarded as Carburetor heat although it does not add hot air. The Rotax carb. ht. control shuts off the cold air part of the intake air mixture therefore causing the intake air temperature to rise, hopefully, out of the icing range. The Rotax engine is altitude limited, presumably due to its limitations to cope with the range of temperatures and the needle and float carburettor mixture control limitations for air density.

For power the densest of air possible is required. The colder the air the better and rammed in (even without a turbo) is preferable. Most light engines are not altitude limited other than by performance. Hot air is reserved for when it is required to prevent or dispel icing. The range of temperatures an aircraft regularly experiences is far greater than the automatic systems a car is expected to deal with. Regarding the mixture, an aircraft passes through a vast range of air density and therefore a large range of mixture control is required. There are automatic systems for both of these issues but obviously adding weight, complexity and cost.

Last edited by Fl1ingfrog; 24th Nov 2021 at 00:34.
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Old 24th Nov 2021, 00:39
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Originally Posted by lightonthewater View Post
As a non-pilot,...........
Let me know which auto engine will produce 70-80 % of it's maximum rated power for 2000 hours.
Most auto engines don't even produce rated horsepower until you get up to 5,000 or so RPM, that would require a gearbox or belt
reduction system.
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Old 24th Nov 2021, 01:06
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Paul Bertorelli did a few videos of his opinions about this. I think he has some interesting points and worth looking at.




Last edited by jonkster; 24th Nov 2021 at 01:26.
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Old 24th Nov 2021, 07:21
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It only takes like 40hp to drive a modern car at 60mph while itís max output is many times that number.
So for the majority of its life a car engine runs at a fraction of what itís rated for.
In my illustrious career Iíve managed the get the check engine light on twice by spirited drivingÖ.in rental cars.

As mentioned before the light airplane market is a mere fraction of the automobile market.
As far as cars keep in mind that a manufacturer often uses an existing engine with some slight modifications or some additional electronic jangles installed.
Point being even in the automobile industry they donít design a new engine for every new model car and they can recoup R&D cost over literally hundreds of thousands of units if not millions.

There are some ďnewĒ aviation engine designs available, even for the retrofit market.
But itís hard to justify a $70k engine installation on what is a $40k used airplane.
New airplanes even simple ones are eyewateringly expensive even with a prehistoric engine.
Let alone the recertification proces to now install a new engine design.
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Old 24th Nov 2021, 10:04
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A similar discussion went on in this thread

Just for Info -
Automotive V8 Engine Conversions for Aircraft
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Old 24th Nov 2021, 10:07
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Here is a newly developed V12. Kerosene/Jet-A1 burning and certified.

Car engines are tricky to convert as Porsche learned the hard way. However the Thielert, Austro and such are based on a car engine (Mercedes A170) and seem to work finally well.

Last edited by Less Hair; 24th Nov 2021 at 10:29.
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Old 24th Nov 2021, 11:07
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Thanks to all of you.
Heston: I realise that engine failure doesn't always mean disaster, (far from it) and that aero engines run far harder for much longer than car engines are required to do.
The curiosity I had was more to do with the level of automation (or lack of it). For example, in my old 1960's car I had to start the engine from cold with a manual 'choke' , carefully adjust the mixture as it warmed up, and it would stall immediately if I got it wrong, although the consequences when it did were just inconvenience. And now , thanks to fuel injection, I don't need to bother with this. Fuel injection would remove all risk of problems due to carburettor icing and incorrect mixture, and the potentially more serious inconvenience, as well as alleviating the pilots workload and anxiety levels.
But of course I understand that it's not an option in older aircraft , which seem to form the majority of the private flying fleet, as seen via Prune forums.
However, I guess that safety might be much improved if some way was found to retrofit some level automation.
Thanks again for answering my question.
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Old 24th Nov 2021, 12:58
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Fuel injected engines add a layer of complexity to aircraft systems. Justified sometimes, put undesirable in for other types. One of my first certification projects back in the late 80's was to remove the injection system, and revert to carburettor for the Cessna 185, it was a great simplicity for the plane, and improvement for float operations.

Here is a newly developed V12. Kerosene/Jet-A1 burning and certified.
This is one of my present projects, I'll be doing the testing and compliance for this engine into the deHavilland Beaver and STC approval. I'm expecting to be involved in ground run test early in the new year, and hopefully flying it in the spring:


I'm looking forward to this new technology engine (being a VW diesel owner for decades), but it's use in an airplane has presented the need for some complex fuel and electrical system changes, and will require agreement from the authority for special certification conditions.

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Old 24th Nov 2021, 13:19
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My decades of experience is that Lycomings and Continentals, from 1930s agricultural origins,, whether normally aspirated or injected, can often be a pain to get going (requiring techniques my wife would never master if they were needed to start a car) but once started they keep going and (as PF says above) continuously produce their rated power output.

Contrast that with modern fangled motor cars where I have had various problems with engine management systems over the years which require sophisticated (read expensive) diagnostic equipment to investigate. The last car I could properly get to grips with if it failed to start was my 1974 MGB.
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Old 24th Nov 2021, 13:58
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The videos suggested by Jonkster answer all my questions and make perfect sense. Basically customer resistance to change, and lack of cash all round.
Very interesting .

Pilot DAR:
Good luck with the project. Will be interesting to see if it changes minds.

David Gittiins:
I have owned cars from those built in the 1950's until the present day (including a Morris Minor, MGB, Landrover, VW and Mercedes). Since then, none built with modern electronics have ever failed to start first time, or given me any trouble at all, although I guess that, if they had failed, it might have been expensive to fix. But maybe I don't drive them hard enough or have just got lucky.

Will get back into my shell: thanks everyone.
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Old 25th Nov 2021, 12:51
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Oh yes , I've had minis, 1100's, a Morris1300, an Imp, an MGB and a couple of Mk III Cortinas and fixed 'em no problem until I got an XR3i

Have had engine management box problems on an 02 BMW 320 and an 04 Saab 9-3. The BMW introduced me to "can only be diagnosed by a main dealer" prices of £120/hr in 2008 and a few hundred quid for a new electronic box (couldn't get a spurious one). I'd be heartily upset if I was at 2,000 ft when the engine decided to go into "limp home" mode.
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Old 25th Nov 2021, 13:41
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I had a 1984 Audi Quattro, which I loved. But the engine started to run really rich, to the point it really wouldn't run. It was a very first generation of computer controlled, so I could still mechanically over rule the computer a little, but fixing was needed. The advice I received was: "Remove the glovebox, loosen the computer module behind it to get access to the end of the box. Remove the screw and the end cover, and pour the water out, and let it dry. Reassemble when dry, and run engine." Yup, it worked like a charm! 'Turns out this was a known thing with these cars, which Audi really did not want to admit. The windshield leaked, and dribbled right into the computer. With a shield over the computer box, I drove that car for years, and loved it.

We've been having long discussions about the computer which runs the diesel RED engine being installed in the Beaver. I've directed that the plane will have to have two independent electrical systems, as the RED engine will not run without electricity. There's going to be a lot of analysis and test to demonstrate equivalent safety to simple magnetos!
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