An alternate engine question

[Guest Rocko]

Hiya folks

 

There's something that's been intriguing me for a long time now, but I've never had a good answer for it. So, I thought I'd whack it on the board and ask youse all ;)

 

Apart from Jabiru and Rotax, all the other engine manufactured seem to be in the fairly small usage category. Yet there are literally hundreds of potential engines out there, that really could be brilliantly converted to light aircraft use, and that'd be more economical and much less expensive.

 

I know a lot of the problems in alternate aircraft stems from the fact they run full flogged a lot of the time, limiting their life, and making malfunctions more feasible. As always, I hear people questioning the use of automotive engines in aircraft, when the RPM's and loads (not to mention dry weight) are so much higher. But car engines aren't the only source out there.

 

My alternate hobby is using a Jetski. I personally have a Polaris MSX140. It's a 3 cylinder, 2 stroke, 140 HP, EFI, that happily revs out to well over 6000rpm, and goes like a friggin rocket. No gearbox, but it doesn't need it. Fuel usage is ridiculously low. I can go 240km on a single 70litre tank, when many newer high performance engines may only go 60-70km. VERY economical. And yet, i've never heard of anyone using anything like this for an aircraft. If you were concerned about the rpm's, then limit them by 1000, to keep the stress down. Sure, there are issues, like dual ignition, gearbox, cooling (although already water cooled), and programming the EMS, but heck, anything can be achieved!

 

After all, look at the Rotax 2 strokes. Really, all they are is a primitive (because of the carby) alternate path of the Rotax Bombadier engines used in Seadoo Jet ski's! And a LOT more research is done into PWC engines that light aircraft engines, but why no substantial cross-over? You take a Rotax 2 stroke PWC engine, and stick it next to a 582. Apart from the extra cylinder, they look extremely similar.

 

Even more interesting, is the huge range of 4 stroke engines out there, modified from motorbikes, now used in jetski's. We're talking non-turbo engines with 160 plus HP, AND relatively light!! They rev out to near 12000rpm, so surely with a bit of tweaking, gearbox mods, and stuff mentioned above, etc, they could readily be adapted to aviation? Yet, where are they?

 

I know carby's are thought by many as "tried and true", but some facts can't be helped. They can be bloody temperamental, crap themselves with ice, guzzle fuel unnecessarily, and personally, I hate the thought of tinkering with the little buggers. EFI is the "way of the future"...at least, it was a decade ago. Yet, in recreational aircraft, we're still sharpening sticks on carbies with other primitives.

 

And for $14K to $19K, personally, I think we should all be asking for a damn sight more for our engines than ice age technology. Do none of these companies do real R&D on aircraft engines? Not just tweaking current designs, but really looking to advance their engines?

 

When was the last time we heard of a REAL engine improvement from Jabiru or Rotax? Sure, they are damn good little engines. But they still sell basically the same 2 strokes and 4's they have for years. The 582...the 2200 Jab...the 912 Rotax...sure they've been "tweaked", but they've remained the same basic gear for years. No, you don't want to break a good thing when you have it, but if the good thing is getting a little long in the tooth, where's the effort from them in introducing new technology? In the same period of time, Rotax have brought the Seadoo engines from around 140HP max, to 215HP turbocharged....AND even more power is in the pipelines, with the PWC manufacturers striving madly to out-engineer each other for market share. Yamaha have just released their latest Super High output ski's, that are now only 339kg in total weight, AND Pump out what We've heard is much more than 250HP!!!

 

Imagine having a 160HP 4 stroke engine in a light aircraft, with the reliability of EFI, and good fuel economy, AND a much cheaper price (Given an entire Yamaha SHO jetski with engine costs about as much as a Rotax 912S, and has 2 1/2 times to HP, you'd expect they could do an engine alone much cheaper). Would you want one? I sure would!

 

So, anyone done this sort of thing? I'd be real interested in hearing from them.

 

Scotty

 

 

[Steve L]

HI Scotty,

 

there are a few other engines out there that may be suitable for a/c. One I like myself is a Harley engine from http://www.skyray.us/ EFI, light and a good slugger around 4000 rpm. Another is a chev corvair engine at http://www.flycorvair.com/ dont know much about the corvair but theres good feedback about it.

 

Steve

 

 

[Modest Pilot]

I think the basis problem is that direct drive engines in aircraft really require a heavy bottom end and a light top end, the exact opposite of most other designs. Gearboxes need to be much heavier (as per standard engineering tables) than is practical in most light aircraft. The same designer did the basic design work for all three US flat engines in the 30's. I guess times change but Physics are forever.

 

 

 

[Guest ozzie]

see photo of new honda 1750cc turbo 4 strk in engine thread

 

 

[Guest brentc]

Last time I was at the boat show, they appeared to have fitted a 912 4 stroke equivalent in the latest SeaDoo because it is better than anything else available at the time. I suspect that they have eventually "caught up" to aircraft so it might be the opposite of what you say.

 

I have a 900 cc Kawasaki Jet Ski - I get 8,000+ RPM out of it and it's a brillant looking 3 cylinder machine but I don't think it would be suitable in an aircraft because I don't think it could handle the load. Perhaps if it had a gearbox and was de-rated, but I'm not sure. I remember when a mechanic was helping me rebuild it he said it was one of the best designed and built engines he had ever worked on, which is interesting as you don't hear that about Jabiru engines!

 

 

[Guest airsick]

I remember when a mechanic was helping me rebuild it he said it was one of the best designed and built engines he had ever worked on, which is interesting as you don't hear that about Jabiru engines!

That's the first time I have ever heard "best designed" and "Jabiru engines" in the same sentence and taken it seriously.

 

 

[Guest palexxxx]

The same designer did the basic design work for all three US flat engines in the 30's.

I'm guessing that two of the US flat engines you're talking about are Lycoming and Continental, but what is the third?

 

 

[Guest basscheffers]

Beyond Rotax and Jabiru, Lycoming and Continental also produce engines in the 100-125HP range that could be used. But they do not produce anything smaller. Nothing else small and 80HP being available is what got Jabiru in the engine business to begin with.

 

Aircraft engines may be designed to withstand constant running at 75% rpm, but that design feature should not preclude modern ignition systems being used.

 

Some say "tried and true" but I say "tried and known to fail". My car says I average 45km/hour. That means after 1500 hours (TBO for a Rotax) it would have done less than 70,000KM, hardly time for a rebuild and not the tiniest hint of unreliability. Now it wouldn't often have run at RPMs as high for long, but it does rev up and down all the time, I wonder what would be harder on an engine?

 

But what about aircraft engines needing to work in both 40 degree heat at ground level as well as freezing at 8,000 feet? Modern car engines cope just fine with that too; people do live in or regularly go to areas like Colorado ski areas that high without trouble. Not to mention that they turn the key and drive off, going from freezing cold to full power in seconds - aircraft owners are much more careful with their engines.

 

As others have pointed out, they obviously have not been designed to fit aircraft, but that doesn't mean people that design engines for aircraft use couldn't base their designs on modern engines and enter the 21st century.

 

I wonder though if it would be hard to get certified; in the syllabus they go into great detail on how an aircraft engine works, something that would be turned up its head when that design changes.

 

 

[Guest ozzie]

I'm guessing that two of the US flat engines you're talking about are Lycoming and Continental, but what is the third?

Franklin Engines had a nice black one at the show

 

 

[Guest pelorus32]

Three further issues with the likes of Textron Lycoming and TCM:

 

1. Our aircraft are severely weight constrained. A Rotax 912 gives peak output of 100hp from an engine that weighs in at about 70kg installed. None of the standard flat motors from TL or TCM can match that;
    
    
   
2. Specific fuel consumption. Again the Rotax figures do not appear able to be matched by the TL or TCM competition;
    
    
   
3. AvGas is a fuel of the past and Mogas is becoming increasingly "non-spec". It is now impossible in large swathes of the world to get AvGas for much of the year and the ethanol in Mogas makes it increasingly unacceptable.
    
    
   

 

 

Bottom line is that all the mainstream companies in the aero engine world have been lagging badly in their R&D. What should long ago have been on the market is a flat four that weighed 70kgs, delivered 100 - 115hp peak output and runs on JetA1 or Diesel and has a specific fuel consumption akin to the Rotax - all FADEC controlled. What's so hard about that - all demonstrably possible? The main answer is that the americans are so wedded to AvGas that they just don't get it. And as for Rotax - it ditched development of its V6 aero engine for unspecified reasons and that at the point that the thing was designed and built. Explain that.

 

Regards

 

Mike

 

 

[BigPete]

It comes down to plain economics. If Jabiru, Rotax, Continental or Lycoming were turning out 500,000 engines each per year, things may be better. :thumb_up: And don't forget they are all air cooled (Rotax heads are water cooled) and have to run bigger tollerances.

 

I don't care too much if my jetski, snowmobile or car suddenly quit - inconvienient, but hardly life threatening. I do however want my aircraft engine to keep running. :raise_eyebrow:

 

One of the reasons we enjoy the sophistication and advancement of modern car engines is the R&D costs per unit are quite small. This is because they make so many of them. :thumb_up:

 

regards

 

:big_grin::big_grin:

 

 

[Guest basscheffers]

I don't care too much if my jetski, snowmobile or car suddenly quit - inconvienient, but hardly life threatening. I do however want my aircraft engine to keep running.

I'd like to hear some statistics on this, but from the anecdotes I hear it seems aircraft engines quit a lot more often on a hours-between-failure ratio than cars do!

Sounds to me like when this engine design was laid down it probably was more reliable than the average car engine, but the tables have now turned.

 

One of the reasons we enjoy the sophistication and advancement of modern car engines is the R&D costs per unit are quite small. This is because they make so many of them.

That makes no sense; the R&D spent on car engines can be applied to aero engines as well. When an engine is designed, it is not done so from scrap and known design principles and often existing components are simply brought together.

Obviously, aero engines will always be more expensive as they will be made on lower-volume production lines with lower tolerances and higher quality control. But if more parts were borrowed from the auto industry, they need not be as expensive as they are now (i.e.: the cost of a small car!) and would likely be more reliable.

 

 

[facthunter]

car engine comparo.

 

I don't want to be a party pooper, but we have had this argument many times before on these forums, and we go through the same old points. The suggestions for car engines as suitable alternatives are many, and the successfull ones are very few.

 

If anybody cannot assess the difference between a Continental/ Lycoming product and a thing like a Chev Corvair, there is not much that I can contribute to assist them here. I don't want to be put in the position of defending these engines as defect-free or the ultimate thing, but before you bag them, at least realise that they are a certified (and that is a task in itself) product, with a useful TBO usually in excess of 2,000 hours, built to very high standards of materials, dimensions, inspection and assembly. They are purpose-built to the extent (as an example) where the IO- 360, one of the most common "clunker" flat-fours, when built to take a turbo-charger, that only maintains the power at altitude that it had at sea level, has virtually No parts in common with the basic model. Everything is built heavier and designed to get the heat out. ie more fins and the pistons are cooled with a jet of oil, & has a stronger crankcase etc. Just an example. Nev...

 

 

[Guest Flyer40]

Rocko a while ago I posted a similar question here with criticism of the safety and efficiency of carburetors, and received an unfriendly response from a group of people who seemed to be happy to have their personal safety (ie engine reliability) firmly rooted in the 1940's.

 

That said a lot about the safety culture in rec aviation and helps explain why market forces haven't compelled aero engine manufacturers to move with the rest of the world. I am encouraged that you haven't been loudly criticised. Hopefully things are changing for the better.

 

I'd like to hear some statistics on this, but from the anecdotes I hear it seems aircraft engines quit a lot more often on a hours-between-failure ratio than cars do!

Personally I am very uneasy about the number of members here who have posted about their personal experiences of engine failures. It seems that some guys accept that engine failures go with the territory.

 

I'm happy to say that I find the current probability of an engine failure intollerable and will refuse to participate until that improves. And I'll wait for as long as it takes because I will not spend the equivilent of a medium sized car on an aero engine that has a carburettor, poor efficiency, complex operating procedures, suspect metallurgy, poor reliability and high maintenance demands. There is no technical justification for these deficiencies. All of these issues are resolvable, but we only see a small number of low-volume companies tackling them and attempting to create a modern aero engine. One of them will get my money as soon as they tick the reliability box.

 

 

[Yenn]

I am not convinced that the reliability of electronics in engines is really good. In my small circle of flying friends, one has a Honda with electronic fuel injection. It is permanently in for repair and they don't seem to be able to fix it.

 

I have flown in carburetted engine aircraft for 40 years and never had a carburettor problem of any consequence except carby ice, which once caused me to abort a takeoff and wear in the float pins on a Bing carby which caused a massive increase in fuel consumption. I should have caught the wear earlier if I had been diligent.

 

If the carby has been working for many years with little trouble and electronics have been breaking down, why change.

 

I agree that spark control is still in the dark ages in aero engines.

 

 

[Guest basscheffers]

I don't want to be put in the position of defending these engines as defect-free or the ultimate thing, but before you bag them, at least realise that they are a certified (and that is a task in itself) product.

Certification can only assure a consistent quality, it does not imply nor guarantee a high level of reliability; the best it can do is provide a minimum level. And if you set that minimum level to 1960s expectations...

 

 

[Guest basscheffers]

I am not convinced that the reliability of electronics in engines is really good. In my small circle of flying friends, one has a Honda with electronic fuel injection. It is permanently in for repair and they don't seem to be able to fix it.

I don't think you can judge this by one car! Obviously, there are millions on the road that are not "permanently in for repair"...

 

I have flown in carburetted engine aircraft for 40 years and never had a carburettor problem of any consequence

I don't think we are talking specifically about carburetor problems. Engines fail for many reasons. Apparently, the (Rotax 912ULS powered) aircraft that I am training in had quite a bad engine poop in its early life, a brokern crankshaft, I believe.

Did you ever have any engine failures? If so, what was the cause of them?

 

 

[facthunter]

Reliability level.

 

I don't agree with your last bit . IF the reliability is not there, the TBO/certification is reviewed. IF the reliability is improved then the TBO can be extended. This is a dynamic situation, but the certification (safety based) process does act conservatively. Just because most engines are flat fours or sixes, doesn't mean that changes haven't occurred internally, since the 60's.

 

The break-throughs can occurr in the "experimental" area where a lower level of safety is accepted in principle, and I still don't see much happening there. I personally believe that the reciprocating internal combustion engine is a self destructing piece of machinery, in almost any form, but it produces more power for the fuel used than just about any other propulsion unit. The high by-pass ratio turbofan is getting pretty efficient, but it will never be for us. We don't fly high enough and you can't build little versions of it that don't use lots of fuel. Nev....

 

 

[Guest basscheffers]

Overhauls don't replace the entire engine and some parts are bound to fail before the overhaul regardless, so there is a bit more to quality standards than just setting the TBO.

 

Conservatism also means not switching to something that is better simply because you do not know that it is better or safer.

 

The only thing that seems to be happening in the experimental arena is car-conversions. While some good success has been made here, especially using the Mazda rotary engines, I am not a big fan of the practice because these engines were built for cars, after all, and there are simply too many unknowns. What it would take is for an engine to be engineered from the ground up for aero use, but modeled on modern engine manufacturing technology and that is likely to share designs of parts, even if those part will then be manufactured to a higher specification.

 

I don't think anyone can do that experimentally from their shed or even a smaller company like Jab was when they started on their engines. It would take either one of the big boys or someone seriously loaded up to back a start-up against all odds. (not to mention bureaucracy)

 

 

[Guest Rocko]

A little off the topic, but....

 

I realise a lot of the comments above are related to auto engines. My question was more specific than that.

 

Related primarily to the smaller, high tech engines used in Jetski's.

 

As a general rule, the Polaris engine I have is one of the most reliable engines on the water. Sure, if you crap an impeller, or a bearing in the driveshaft, or even worse get water in them after a flip, they can be a problem. It's just not an issue in aviation.

 

However, and again I ask, taking the example of the Seadoo PWC's, fitted with a 215 hp: Supercharged Intercooled Rotax® 4-TEC® engine, weighing under 80kg, then isn't that somewhere in the class we need? Detune it, to take off the additional stresses, and you'd still have 150HP, in an pretty lightweight system. That'd kick some butt, seriously. Get away from the supercharged models, and they're 160HP. Again, a VERY serious potential aircraft engine, and even lighter. As far as the stresses involved, while I accept aircraft engines run at high revs for long periods, PWC engines are made to be robust....going from 0-100+kPH, with a weight with rider of 450 odd KG, and having the guts revved out of them repeatedly. That's no stand at home car engine. It's a high performance thing, made to handle some pretty high stresses. Consider how much torque is applied to the drive shaft, when accellerating a 450kg bit of equipment, through the resistance of water, to 110kph, in just a few seconds? Less than a propeller? I'd be somewhat surprised if it was.

 

Scotty

 

 

[Guest Rocko]

Although...

 

Admittedly, I don't like the reliability of seadoo/Rotax engines in PWC's ;) I was just using it as an example. The Yamaha engines are quite reliable tho

 

 

[hfrensch]

I have read with interest the speculation of aero engines verses automotive engines over many different threads and feel that the reliability issue needs to be cleared up.

 

In my previous life I was involved in the development and testing of engines for a major vehicle manufacturer for thirty years, managing the engine development area prior to my retirement in 2003.

 

The test regime on an engine is very severe with even a minor change to a piston ring for example requiring a number of 400hour wide open throttle (WOT) throttle test at maximum power(not 70%) to be conducted. These would run non stop except for regular oil change intervals. At the end of this test the engine would be torn down and inspected. Some engines would be rebuilt and run another 400 WOT test if required.

 

 

We would also conduct hot and cold cycle tests where the oil temp was elevated to 150+ deg C and coolant at 120+ deg C (under pressure) at WOT for 25 mins. The engine was then shut down all the coolant dumped. Cold coolant filled and started brought up to max temp at WOT for another 25 mins. This would be repeated for 500 cycles or more depending on what we were testing for.

 

 

The engine dynos were all computer controlled and calibrated regularly.

 

I have spoken to Rod Stiff a number of times on engine testing and he assures me that there is no aircraft engine manufacturer that conducts tests that are this severe or even come close, except for jet engines.

 

 

I have no doubt in my mind that automotive engine is far more efficient, reliable, economical and better built than most existing aircraft engines.

 

 

Cheers Helmut

 

 

[pylon500]

I can see where you're going Rocko, and we tend to have two camps on the subject.

 

 

 

Those saying "I want my aircraft for safe reliable transport" (which it isn't until it's the size of a 747 or at least a Dash-8) , and the other camp willing to say, "I want to fly for fun, and am ready to accept all the educated and informed risks involved." :thumb_up:

 

To maintain the simplicity of air-cooling (and accept the fuel consumption) there are a lot of motor-bike engines out there that could fit the bill.

 

Molt Taylor had a Kawa-1000 in a Piper Cub back in the '70s!

 

Modern gearboxes, and multi-cylinder layouts to reduce shaft pulses could be the way to go.

 

As for marine engines, you need to be sure of dissapating the heat from an engine designed to run on raw cold water.

 

 

 

Arthur.

 

 

[vk3auu]

Helmut, can you give us a clue as to which major vehicle manufacturer that was. I would like to buy one next time I change motor cars.

 

David

 

 

[Brett]

Love your post about the engine testing helmut ,, I once had a good chat to the people that were testing the EF-EL ford motors before they came onto production yrs ago (pity they didnt check the head gaskets better :) and couldnt agree more about the rigorous testing and abuse they get on the dyno ,, only thing about car engine though is most have cast iron blocks ,,, bit of a problem with weight i'd imagine . I'd however love to put a big $$$$ bet on for say a rotax 912 and a late model toyota collora engine alloy block ,,same dyno ,same testing , wonder wich one would win ??? I know who i'd put my money on ..