Lycoming, Continental and Rotax

[Jabawocky]

Maths time.

52LPH or 81.4lb/hr
HP=213
BSFC 0.382

Now this is at 82% power and as the HP drops off, the fixed losses take a bigger % effect, so at 75% 0.4 is probably correct. But this photos is at a higher power.

Plenty more DATA where that came from.

Oracle, this is not OPINION.You have an opinion, I can have an opinion, but DATA does not.

Confucius say; do not tell a man something impossible when he already doing it.

Do you want me to do some O-360's or IO520's or IO550's, or O-320's. I have the data?

My apologies if my tone seems extreme, I thought it was more focussed on the absurdity of a coroners report and much misinformation backed by opinions of the ill informed, including whoever made the claim about the BMEP

[Oracle1]

I apologise as well we should all be here to learn. ok how are you arriving at the horsepower figure of 213 I might learn something. BTW has a coroner ever said anything sensible

[Jabawocky]

Was the extra RPM from running a coarser pitch or finer pitch?

Was the extra HP achieved by extra RPM? Same BMEP but more RPM?

Think about this for a minute the MP could only be ambient less induction losses. So how did the BMEP get increased so drastically? And how did a coarser pitch do this?

The max power of the Rotax is what 5800? and max continuous is 5500 or something? The peak torque generated is sub 5000 rpm, so from that the conclusion can only be the peak pressure and peak BMEP is not at 5800 RPM at all. Thus any prop pitch that derives an RPM in the max continuous range will result in a higher BMEP anyway.

If one used a finer pitch prop, to extract max RPM and thus max HP as the airspeed increased what would have happened to prop efficiency? So why would the pilot do that too? To go slower?

If my memory serves me correctly, the time was over the ground so tailwind had some influence, so in the accident aircraft calculating power required etc without knowing the winds would be a very in-exact science would it not?

The crank failed from the deceased owner operating an engine with severe out of balance states, nothing was documented well in scientific terms other than the owners notes conferring with the supplier, and the actions thereafter did not inspire me with any confidence.

I have had no contact with the supplier nor deceased, but I have read the reports including those prepared for the coroner. None give me the impression the Rotax or its previous owners use were to blame. The deceased owners input is another matter.


PS Oracle no problem Its late will explain more tomorrow.

nomorecatering....same, time for zzzz but I do have some useful info on that too

[Sunfish]

Here we go again - conflating about Five different issues....

1. Why don't car engine conversions make good aircraft engines? Blah blah and by implication why do aircraft engines cost so much?

The answer in Two words is duty cycle. - the actual time at horsepower over the expected life for the engine. A Holden Commodore may be advertised as developing "200 horsepower" (say), however it will only be required to generate that amount of horsepower (if it can) for mere seconds during accceleration, in fact at 100KPH the car only requires about 19 hp to overcome rolling and air resistance.

Contrast that with an aircraft engine which is required to generate between 55% and 100% of its advertised horsepower every flight for the term of its natural life. This is a whole other world of durability.

To put that another way, yes, you can get 400 hp out of a turbocharged intercooled Subaru engine, but not for long, and certainly not if you leave it parked in the weather for months between operations.

Even more extreme, consider marine diesels of any size. My yacht has a 13HP Volvo Penta that can operate full throttle all day, all night (2100 rpm) and has done for 41 years with only injector work - but its 385 lb of good swedish cast iron.

2. Why don't aircraft engines use four valves per cylinder, pent roof combustion chambers, overhead canms,variable valve timing, electronic fuel injection, electronic ignition and a host of other automotive technologies? The answer is because they don't need to.

Your car has to deliver power across a rev range of say 2000 to 4000 rpm while producing acceptable fuel economy and pollution levels. What is your aircraft engine rev range between full power and minimum loiter/ cruise? 2100 to 2750 rpm? Say 650 revs? Lycoming and Continetal don't need all that extra weight to optimise for that rev range. Simplicate and add lightness.

Yes, you could build an engine that would use all that technology to produce say !000 hp on takeoff and then turn down to say 200hp in cruise and the aircraft performace would be spectacular.....once you had worked out how to fit a Ten foot diameter propeller and the triple slotted flap arrangement for the tiny wings to obtain an acceptable stall speed on approach.

3. Why have a mixture control when carburettors can be made to compensate? Blah Blah.

Read the Rotax and Jabiru web forums about the problems with allegedly "compensating" Bing carbs and the ensuing misery of cracked rubber, air leaks, needle positions, jet sizes, cylinder balancing, etc. Some people even modify the carbs to regain control of mixture.

4. Not being able to hand starting a Rotax? Lethally Dangerous Myth

Hand Propping a Rotax 912 - YouTube

5. The Rotax 912iS fuel injected engine? This is actually a very different beast from the 912ULS, exactly how different I may eventually find out. Jonathan Porter in Africa has been reporting fuel flows around 12 -13 l/h in cruise.

The engine uses a purpose designed ECU arrangement where everything is redundant, there are two oil cooled alternators, one for the engine and one for the aircraft systems in the engine with automatic fail over. eight injectors and most interestingly four EGT probes which makes me think that this system is a little different from your average Bosch injection. The torque curve now also approximates the propeller power curve.

6. Manifold pressure gauges with constant speed propellers? How else are you going to comply with the manufacturers explicit operating instructions?

7. The fatal crash? Apparently evidence was presented that the crankshaft geometry had changed due to some slippage between the built up components that destroyed the geometry. This had manifested itself in a history of unusual vibration. Ultimately the crank failed.

The cause of the crank vibration, if I remember correctly was atrributed to mishandling of the engine or perhaps a prop strike, but the actual persons involved was unclear.

There, I hope I have offended everyone.

[Typhoon650]

I'd just like to point out that auto engines are not near as frail as many here are pointing out.
Many, many manufacturers randomly pull an engine out of production and subject it to extensive, punishing dyno work. Even in the 60's, Chrysler would run production V8's at max rpm/load on dynos to the point of failure or 1000 hours often easily going well over 1000 hours with no failure.
Let's not even start on plain old auto engines which are converted for marine use which run at a constant load and power setting for hours on end.
Certified aircraft engines are great things, they are light, simple and reliable, but they are not even close to being optimised for what they do. They are old designs optimised for what they have to do, but no way are they an example of the perfect solution for the job.
The only reason they are still what they are is certification costs and lack of manufacturing volume to justify new designs.

[tecman]

Sunny and Bob, let me swiftly and gracefully concede the point on the Rotax hand prop. As Dr Johnson might have said, it wasn't done easily but you're surprised to see it done at all. I definitely can't do it with my 912S2, with an exercise in trying some time ago resulting in no spark at all and a lingering case of cricketer's elbow. Admittedly, the S2 has various accessories that may make it harder. There may also be differences in electronics modules but, for the record, I always regard a prop of any type as live. And, as an observation, these days I see fewer new pilots doing a dead-cut check on shut-down of the magneto ignition engines. Having once identified a floating ground problem in a club aircraft it's not a check I skip.

[owen meaney]

Course pitch effects BMEP

Would increase of prop pitch increase BMEP?

[Aussie Bob]

Tecman, another thread worth a read

Not an easy to prop start engine but it is nice to know that it can be done if you are stuck.

[Jabawocky]

Owen, no it doesn't.

[Oracle1]

Indicated Mean Effective Pressure

Jabawocky

It has been a very long time since I looked at piston engine theory and Random Access Memory is at a premium in my alcohol ravaged mind.

I dusted off my piston engine theory texts today and you are correct About BMEP. I have used the incorrect term to describe what was happening. BMEP occurs when friction losses are minimal at peak torque and BFSC is lowest. We can extract more horsepower past this point but it is a diminishing marginal return as a function of increasing RPM. However I stand by my physical understanding of what was happening in the engine. High power settings combined with a coarse prop settings would have increased IMEP and increased the frequency of resonance in combination with the gearbox.

BMEP+FMEP = IMEP

The friction losses in a Rotax would be higher than a direct drive because of the higher RPM and larger change in RPM. The rotax is also driving a water pump impeller. A coarser pitch would also cause a more rapid oscillation in crank RPM as the prop decelerated after the power pulse and the gearing worked to accelerate the crank.

I also rang the guy who pulled the engine down and the even two metallurgists couldn't agree when the failure was initiated. There was evidence of a minor manufacturing fault in the crank but it was deemed that in normal service it wouldn't have caused a failure. What everyone does agree on is that the engine was abused. I respect your opinion on this Jaba but do you know the nodes of resonance on this engine and where they occur? I am sure you can easily work them out but have you? Did the manufacturing fault respond to a particular frequency? If mechanical engineering was perfect science engines would never fail.

Its immoral to operate an engine outside factory limits and we will never know what initiated the failure, but it certainly introduces an element of doubt? Its the same as over stressing an aircraft and not telling people about it,

It is also very poor form to bag the pilots landing, whatever his shortcomings. None of us know how we will react when the time comes and if we will be found wanting. My opinion on the circumstances of this event have not changed.

[Jabawocky]

What everyone does agree on is that the engine was abused. I respect your opinion on this Jaba but do you know the nodes of resonance on this engine and where they occur? I am sure you can easily work them out but have you? Did the manufacturing fault respond to a particular frequency? If mechanical engineering was perfect science engines would never fail.

Ok so now we are getting closer to the mark. No I have not and have no desire to waste my money on doing a torsional analysis of a crankshaft nor can anyone quantify the extent of the severe out of balance prop. Noted by the deceased.

My concern here is the abuse you believe that everyone agrees on is that of the deceased owner, not the previous owner. The significant vibration issues were the problem induced by the deceased as best my memory serves. I could be wrong!

If the abuse as you allege was from pitching the prop to extract maximum speed, how on earth could that have exceeded any manufacturers tolerances. It almost defies logic, and if it was pitched finer, to extract max RPM thus HP (less prop efficiency drops) then that may be considered abuse, however I doubt that Rotax have a crank designed so close to the limits. If they do I will suggest that nobody I know will ever fly behind one again. I bet Rotax run them at 5800 RPM at full load for hundreds of hours in testing. I would be surprised if they have not. But I could be wrong.

The ATSB report said "The appearance and 45 degree angled progression of the crack in the number one connecting rod journal was consistent with fatigue through cyclic torsional loading." So while you may not see anything different here, I wonder how this is most likely to happen? Continuous operation at 5800 RPM for a few hours in a row or by many hours of a severely out of balance prop?

Just because the coroner could not see through this does not mean it is not the most likely cause.

I concede my view of this accident might not be the case, but it stands up to the logic of physics far better than anything in the court room ever did. I will say again, the alleged paperwork and other issues that the seller may have been guilty of had nothing to do with a crank failure. Lets blame Boeing for the SFO crash shall we.

I have nothing more to add. Punters can read all the material if they have access to it and make up their own minds, of course be wary folks of what you read and believe, tomatoes will kill you!

I am quietly confident that Rotax make a very well engineered and robust engine. I have spent maybe 100 hours behind them, and I would say from what I have seen of maintenance they are no less reliable than a Lycoming or CMI engine. That being said, the old technology dinosaur engines are equally or more efficient, and do provide more HP for those who need it.

Remember the fuel debate, 80% of the fuel is used by the fleet section that MUST have an aviation fuel equal or better than 100LL, so an UL low octane can't work. Same goes for HP....the major uses of HP are the big guys, and they cant do it on a 912. They would need 6-8 of them.

So horses for courses

[Oracle1]

Poor Maintenance by the owner?

On September 21, 2006, JG had the prop inspected and balanced by Mr McCarthy, a Licensed Aircraft Maintenance Engineer (LAME), who was then the manager of an aircraft maintenance centre at Albion Park. Mr McCarthy explained in detail to the court the procedures he adopted to balance the prop. Extraordinarily, when he removed the weights attached to the prop upon arrival, its balance improved. In his experience this was abnormal. He then proceeded to achieve what he thought the optimum balance, to within a tolerance of 0.2 inches per second.
JG advised Mr McCarthy later that the prop appeared to have been well balanced and that he was more than satisfied with the job.
The evidence revealed the probability that the problems as to vibration were inadvertently attributed to the propeller being out of balance. As it turns out, this does not appear to have been the actual source of the problem. Mr Brian Nicholson, an aviation consultant, now retired, but still a LAME, stated that the adjustments to the prop potentially masked the true source of the vibration, namely, torsional twisting of the crankshaft, which was revealed to be out 15 degrees. Consistently, Mr McCarthy’s evidence that unusually the balance improved when he removed the weights also suggests that the propeller was not the cause of the imbalance.
What is very clear is that throughout the nearly 2 ½ -year period of JG’s ownership of the aircraft, he was diligent in ensuring, and recording, all required servicing, and all necessary maintenance including constant attempts to address any deficiencies. The only suggestions to the contrary were made by Mr Coates and Mr Allen. They were not disinterested, to say the least, and all other evidence allows me to reject their criticisms outright



Does a LAME not know how to balance a prop?

Sounds to me like the crank was already on the way?



The records kept by JG reveal that he had constant problems with the aircraft after purchasing it from Mr Michael Coates on September 1 2004. These problems are corroborated by others, including Mr Coates and his friend and associate Mr Allen.

Initially, JG’s concerns focused on the Woodcomp electrical adjustable aircraft propeller and vibrations that appeared to emanate from it.

The guy flagged straight up he was having problems with the prop and made attempts to fix it, misguided or not, even the LAME didn't pick up the crank might be on the way. He certainly sought expert help.

AND FINALLY the real classic

One could be forgiven for doubting whether any maintenance or servicing was ever performed on the aircraft while owned by Coates. His record keeping was so appalling and to the extent that it existed at all, inaccurate, that we will never know. Very little if any of his two days oral evidence could be accepted other than his own admission as to his deceptive, or fraudulent dealings with RA Aus in relation to the registration of aircraft and use of unregistered aircraft, his ‘re-registering’ of an unregistered plane, his continued use of Czech registration in Australia in contravention of requirements, and his wrongful use of the serial number of an aircraft in Australia, on an aircraft in the USA. He compounded the litany of dishonesty by having prepared the Condition Report in August 2004 required for the sale to JG despite being prohibited from doing so by his pecuniary interest (i.e. ownership) of the aircraft on which the report was compiled, and further, without the qualification required to do so. There is a strong likelihood that records which he did produce to the court were prepared for court production, and also that ‘Logs’ were not contemporaneous but may have been fictionally backdated to ensure a sale. He admitted that much of what was written by him in his Sting newsletters stretched the truth or were ‘sales puffery’ for marketing purposes.
He claims that he set several speed or endurance records in the original Sting, which he then sold to JG. It is not clear whether JG knew of these claims; their significance, if true, is what effect that may have had on the engine, apart from whether he maintained regular if any servicing. It became necessary for Mr Coates to be granted a Certificate pursuant to s 33AA of the Coroners Act 1980 in so far as his evidence was concerned relating to the registration of the aircraft and his participation in the false affixation of the same registration details to another aircraft.

Small paperwork problems eh Jaba?

A few hours at MAX RPM? I would say lots


The teak tough little crank was probably already moving and the owner may have been chasing a balance problem that never sat still because it may have been caused by the terminal injury to the crank. If it hung for another hundred hours its another testament to the german engineers

[Jabawocky]

You are being selective with the facts as presented. What happened with all the matters noted from 2004 through to 2006 which involved many prop issues and parts changed or replaced or whatever. Sourced from suppliers other than the OEM/dealer???

All of which was prior to Mr McCarthy doing work on it? Is it any wonder when McCarthy removed weights the IPS improved? And that is unusual as noted by the LAME. I do assume the LAME knew what he was doing. Prop balancing is a black art, but not hard to do, by the way I never accept anything at 0.2, if it is not under about 0.07 we keep going, but I digress.

So the issues are not about McCarthy at all, it is all the stuff in the year and a half before that. Much of which I question by virtue of who was doing the work, including balancing, which I assume is where the weights (noted by McCarthy) came from.

Maybe the notes I read were far more detailed than those you had access to, but it does not change the fact that the greatest risk to crank failure was REALLY bad prop balance in my view, all of which was under the control of the deceased and prior to the LAME.

Go check the dates and events.

like I said before....I really have nothing to add (despite the words above), I think from what you are telling me that the Rotax is very susceptible to high RPM and or balance beyond what I call acceptable. So I best not fly behind one.

So in the debate of Lyc/CMI or Rotax......I will stick to the LYC/CMI's in future.

[Ultralights]

in my experience, i have flown 700hrs behind Rotax 912's never had a problem.
similar hours behind Lycomings and Contis,with only carby icing causing a few blips on what would be perfect operations, even 50 in front of a 2 stroke 503 rotax,
only ever had one engine failure. in a jabiru.

[Sunfish]

Typhoon:

I'd just like to point out that auto engines are not near as frail as many here are pointing out.
Many, many manufacturers randomly pull an engine out of production and subject it to extensive, punishing dyno work. Even in the 60's, Chrysler would run production V8's at max rpm/load on dynos to the point of failure or 1000 hours often easily going well over 1000 hours with no failure.
Let's not even start on plain old auto engines which are converted for marine use which run at a constant load and power setting for hours on end.
Certified aircraft engines are great things, they are light, simple and reliable, but they are not even close to being optimised for what they do. They are old designs optimised for what they have to do, but no way are they an example of the perfect solution for the job.
The only reason they are still what they are is certification costs and lack of manufacturing volume to justify new designs.

This is bull****.

1. You still don't understand duty cycle. It is not "running 1000 hours at full throttle".

For an aircraft engine it is:

(a) cold soak on wet aerodrome for one to three weeks.

(b) start engine, warm for ten minutes or less.

(c) Apply full throttle for Five minutes. Then cruise power.

(d) Repeat this cycle of thermal loading for at least Five years, with periods of abuse like subzero starting, high temperatures etc. thrown in.

2. New designs offer no benefit. Because of the limited operating rev range of the propeller and consequentely the engine. All of the new technology stuff in auto engines is to improve fuel economy through reducing volumetric losses or to improve the shape of the power curve by widening the band where efficient combustion is available..

If an aircraft engine was required to have a power band from say 1500 rpm to 5000 rpm you would be right, but it doesn't.

3. The marine variants of automotive engines are derated by between 50% to 66% of their advertised "automotive horsepower, except for the "consumer" outboards whose duty cycle is similar to a car anyway.


Jabawocky you are confused about power curves. It is possible to seriousy bugger an engine. The performance is optimised as a torque/rpm combination

The curves you see are actually advertised torque at maximum power for the specified rpm.

To put that another way, you can strangle the engine, it will run over torqued,, but at less power.

[Typhoon650]

No, your statement is BULL****. I clearly understand duty cycle and have provided two examples of many that show auto engines can easily run at full load for extended periods.
Please cite your references for marine engines being designed for 50-66% of duty cycle, that is bull****.
As for the rest of it, every day auto engines are abused far, far more than any aero engine. Cold soak? Big deal, millions do it daily. Full throttle from dead cold? Again, millions do it. AND they do it with lack of oil changes or any maintenance whatsoever in many cases. Not like a fragile aero engine which will **** itself if you don't change the oil after 100 hours.
Of course, of modern aero engines were liquid cooled, we wouldn't have to worry so much about their "advanced, optimised" design being shock cooled or running at full power after a short taxi and run up....
You clearly do not understand marine engines at all. They are under a constant load, just as an aero engine is. Yes, even outboards.
As I said before, we have what we have because the market doesn't justify expenditure for new technology, nor does the regulatory system.

[Jabawocky]

Sunny,

Jabawocky you are confused about power curves. It is possible to seriousy bugger an engine. The performance is optimised as a torque/rpm combination

The curves you see are actually advertised torque at maximum power for the specified rpm.

To put that another way, you can strangle the engine, it will run over torqued,, but at less power.

No confussion, I have been working with Torque v Speed curves all my life. Chuck a prop on the end instead of a load like a hydraulic pump doing a constant torque job, and you have a big fan. The laws of phsics are the same to all things.

The curves you see are actually advertised torque at maximum power for the specified rpm.

Care to explain that in english?

you can strangle the engine, it will run over torqued,, but at less power.

Ahh I don't think so. An engine can only generate so much torque, it can't create more. An elevctric motor can produce more than FLT, simply load it up, the RPM starts falling, and she backs up the Torque V Speed curve quite nicely. We use this to our advantage some times, in fact quite often . Of course what does happen is the current draw starts climbing at a rapid rate, effective but not efficient, but who cares.

Combustion engines do not work that way.

You can apply an instantaneous peak torque by suddenly stopping the propellor, such as a "Prop Strike", this has X amount of torque from the engine plus Y amount from the sudden deceleration of the prop (inertia conversion) and bingo the crank sees a torque spike many times the maximum the engine could ever produce.

That is why you bulk strip em

[Oracle1]

Auto Conversions

Automotive engines are optimised to operate at constantly changing power settings. Aircraft engines are optimised to operate at a constant power settings . They are designed to do completely different things. Do not make the mistake of thinking the actual structure of aircraft engines are fragile. They are very robust.

This does not excuse the intellectual and engineering laziness and the extortion racket that is american aircraft engine manufacture. Thanks to the explosion of LSA Ultralight and experimental categories the american manufacturers have been dragged kicking and screaming to the table to develop better engine management systems. There is no way a 6cyl direct drive is worth 60,000. When the chinese begin to copy and adapt the direct drives the price will drop significantly. Execute a few parasite lawyers and we could drop the price as well.

If you could shove a car engine into an aircraft at low cost everybody would be doing it.

[Jabawocky]

Oracle,

Do you know how much of the say $26K for a Rotax is for the engine and how much is a result of insurance alone?

I wish I could recall the figure, but it is staggering, something like 40%, maybe someone here can shed some light.

What CMI and Lycoming haf to contend with is having civil cases rammed down their throats because pilots kill themselves and passengers from VFR into IMC, or faulty carby's on an engine built 38 years ago and rebuilt once or twice.....and the fault was....Loss of control, or carby ice or both!

Seriously it is STUPID, I had this discussion with Bill Ross, the Manager of Factory services at Continental about 4 months ago. He attended the APS class we were teaching at and his response was one of frustration at the level of stupidity. So is it any wonder.

Fix that problem alone and GA might grow again.

[Oracle1]

Robinson Helicopter

I heard a figure that profit from 3 out of 10 helicopters off the production line go towards liability. I am well aware of this issue, my family are all commercial solicitors

as I said,

Execute a few parasite lawyers and we could drop the price as well.