Which Engine???

[Yenn]

Rotax and Jabiru are well known with plenty of flying time. Most of the others are relatively rare. Rotax may have a slightly better failure rate, but you need to compare costs as well. I would stick with either one of them personally. I say this with absolutely no Rotax 4 stroke ownership, but happily own a 2200 jab.

 

 

[Jethro Belle]

I say this with absolutely no Rotax 4 stroke ownership, but happily own a 2200 jab.

Hi Yenn, Would you elaborate on what makes you happy about the Jab 2200? How many hours do you have on yours? What generation is is? Any hint on how you have avoided some of the reported problems? Pro Jabiru postings are about, but not elaborated except the capital/parts cost.

 

 

[Jethro Belle]

Today we have some other choices

Yes indeed.

Of those in your linked video the D-Motors are the standout interest (IMHO and on several other forums). Based on American prices they cost a 60% premium over the roughly comparable 4 and 6 cylinder Jabiru motors. For that you get 92Vs80 and 130Vs120 horses with the more powerful D-Motor producing power at 10% lower revs and a few kg less weight (including radiator)!! The D-Motors only come with electronic controlled fuel injection and ignition, but you can get dual ECUs.

 

As Stol1 questions

 

I look at the D motor, love the simple design, and basic direct drive, like the Jabiru, but what are the weak points of this engine that time usually reveals? What are the parts availability, and support? Who's flying behind it?

D-Motor promotes that Germans are developing helicopters using it, and flygfabriken in Sweden are impressed (they considered the Jab motor). I also note somewhat ironically the the D-Motor Australian agent is fitting it to a Jabiru!!!

 

With Jabiru addressing its reliability issues and the D-Motor coming online, Rotax petrol/avgas supremacy is being challenged (IMHO and I put Rotax at least the equal of Lycomtinental quality/reliability from an engineering perspective).

 

 

[facthunter]

When the 912 came out it was extremely reliable (The 80 HP version). Like all things that get more complex and older in service, they can be neglected and made less reliable. A liquid cooled motor has extra parts and an oil cooler has extra hoses. If this stuff is not kept up to scratch it will let the engine down. The final reliability is up to the operator more so as the plane gets older and more fiddled with. Not as many people these days are familiar with engine internals as was the case 60 years ago. Fit and forget doesn't really apply to aeroplanes. They have to be monitored (oil filter opening visual check for leaks listen for unusual noises on start up etc) and serviced/ checked according to a realistic and practical schedule.. The engine spluttered but it came good and it's OK now doesn't fit with aeroplanes. Nev

 

 

[Jethro Belle]

When the 912 came out it was extremely reliable (The 80 HP version). Like all things that get more complex and older in service, they can be neglected and made less reliable. A liquid cooled motor has extra parts and an oil cooler has extra hoses. If this stuff is not kept up to scratch it will let the engine down. The final reliability is up to the operator more so as the plane gets older and more fiddled with. Not as many people these days are familiar with engine internals as was the case 60 years ago. Fit and forget doesn't really apply to aeroplanes. They have to be monitored (oil filter opening visual check for leaks listen for unusual noises on start up etc) and serviced/ checked according to a realistic and practical schedule.. The engine spluttered but it came good and it's OK now doesn't fit with aeroplanes. Nev

Agree entirely. I am a mechanical engineer with fluid dynamics/CFD, structural and materials background so engines are one thing that I feel able to offer opinions on (I am not an expert and decisions to install should not be based upon my posted opinions). I have been watching Rotax since ANO95.10 days. The fact they have proved reliable is a testament to Rotax getting it right. They are high revving complex things that should fail and wear out quickly, all other things being equal. Clearly they are not, hence my pot shots at Lycomtinentals. They are probably the most reliable, but they are so simple, basic, tested, and with an extensive 'well' trained/governed maintenance structure, it would be hard for them not to be.

 

Since the D-Motor is simpler (if you ignore the electronics or have faith. 4Cylinder variant has 35 moving parts and a TBO rebuild kit for $US 5000 as I recall) than Lycomtinentals , if it has the build quality of Rotax it is a potential game changer, if prices are right. They have had all the woes of other manufactures to take advantage of. They seem to be well backed by Belgium government and the EU (not sure Jabiru enjoys that). Only time will tell and I am looking forward to results (statistically consistent facts) from early adopters.

 

I want good safe reliable affordable and the D-Motor seems to be pushing in that direction. If Jabiru can match it at Jabiru prices everyone is a winner.

 

 

[skippydiesel]

Hi Jethro,

 

You would seem to support the "revs = rebore's" (R=RB) philosophy "they are high revving complex things that should fail and wear out quickly". I view the R= RB concept as American propaganda (the country of the large capacity engine) that has not been born out in the real world that is overwhelmingly populated by small high revving engines that can achieve extraordinary levels of performance & longevity, when well designed/constructed and serviced "by the book" (particularly when motivating a vehicle that pays more than lip service to efficiency).

 

I love my Rotax 912 ULS - it almost seems to be everything the "Lycomtinentals" is not - smooth, quiet, economical, light weight and despite the addition of liquid cooling and a gear box (both very familiar to me) straight forward and easy to work on (being metric also is a big plus in my book).

 

In the unlikely event of being in the market for a larger HP than Rotax can currently supply I guess I would reluctantly have to look at a "Lycomtinental" but I would also check out the Subaru conversion area (Rotaxy like concept) as being much more aligned with my philosophy.

 

 

[Jethro Belle]

Hi Jethro,You would seem to support the "revs = rebore's" (R=RB) philosophy "they are high revving complex things that should fail and wear out quickly". I view the R= RB concept as American propaganda (the country of the large capacity engine) that has not been born out in the real world that is overwhelmingly populated by small high revving engines that can achieve extraordinary levels of performance & longevity, when well designed/constructed and serviced "by the book" (particularly when motivating a vehicle that pays more than lip service to efficiency).

I thought I was stating what was widely known SkippyD . Maybe I should have made it clear by stating ""they are high revving complex things that should fail and wear out quickly IN THEORY RELATIVE TO A LOW REVVING ENGINE" ", all other things being equal.". I thought the last part of my sentence, that you omitted, implied that.

 

Certainly many North Americans promote it because it is true, and they have never faced tight vehicle engine displacement regulations and high fuel prices. In their world there is no substitute for cubic inches:cheezy grin:. Rotax also sells well in USA I believe! The D-Motor is Belgium based, so they must be following American propaganda also.

 

I am aware of enough reduction-drive failures to know you have to do it right, it comes with extra weight and failure risk, favoring the low revving unstressed direct drive engine. To get the power at low revs requires displacement. It is the laws of physics (engineering), not American propaganda. There is no doubt the Rotax is more complex and highly stressed engine. I mean engineering complexity, not just arrangement and parts count.

 

I am impressed by the 4 strokes Rotax has created and their TBO/reliability and would be relaxed in a safe aircraft powered by one. I also don't think Lycomtinentals are doing it as well as they could (so my comparison may imply that Lycomtinentals could have extended TBOs in theory ).

 

I am not sure why you have drawn the conclusions you have given the above is what my post said. I did caveat that it was my opinion based on my background. Like much in engineering is is not just the correctness of the design, but also the build quality that determines the final reliability and performance. The Rotax is a valid design solution that makes up for low CC by high revs giving similar swept volume per horsepower as stoichiometry requires. Simplistically doubling engine speed should double the wear rate and halve the engine life! ...

 

My point was there are now serious contender engines (to be proved by D-motor) available regardless of which camp you sit, so everyone can be a winner, and these are interesting times I will take your post as a sound vote for the Rotax approach and delivery.

 

 

[mnewbery]

The maths is in the mean piston speed.

 

A piston with a 2 inch bore is travelling 4 inches every revolution.

 

The 2.4 inch stroke Rotax 912 continuous setting of 5,800 rpm yields a mean piston speed of 11.8 m/s

 

The continental O-200 has a 3.88 inch stroke which at 2400 rpm yields a mean position speed of 7.88 m/s which is about 2/3 of the Rotax. TBO for the Rotax is between 1500 and 2000 hours, the O-200 is 1800 hours. They are apples and oranges so the numbers really only start a new argument rather than informing an existing one.

 

Compare this to the speed of sound which is the maximum speed a flame can propagate in the absence of detonation ~350 m/s and it clear these pistons are moving relatively slowly but changing direction a lot.

 

@fly_tornado the mean piston speed of a R1150 at 6000 rpm is 14.1 m/s. To get the same piston speed as the Rotax the engine would need 5000 rpm. It's not going to be a problem with your application because the engine will only see light and very occasional use.

[skippydiesel]

Jethro & MNebery,

 

I did start out to try & convert you both but thought better of it as I think we probably developed our respective bias over many years, so I will spare you my zealot like enthusiasm for what I see as European engineering excelance, as apposed to what Uncle Sam dishes out.

 

Jethro - I am not apposed to direct drive engines in small aircraft but believe that Rotax has conclusively demonstrated a better way. I am disappointed that this model is not more widely adopted and expanded on (viable competition might bring the price down). Direct drive is very much about the KISS principal, which I like to follow but I also know that it is just that - a guide and that it does not always work (what has happened to the Wankle rotary aircraft engine?)

 

My reference to American propaganda is shorthand for their dominance in the aircraft piston world and their apparent unwillingness to evolve or allow others to do so (my God they still measure everything in US Imperial).

 

MNebery - I fly behind a Rotax that is not certified but the very same engine is available at a certified unit, both with the same 2000 hr TBO - the Rotax is capable of delivering the same service as a 100 hp Lycomtinental, at less weight, noise, vibration & fuel consumption - nothing "light and very occasional use" about that ( I understand the US military favour Rotax engines in their small drones - I wounder why??).

 

There is no doubt that the aviation world owes much to the USA but perversely much of what the world has to offer aviation is pinched or stifled by the USA .- - Yes Rotax is popular in the US (they are not all Donald's) just as European and Asian cars are but it is a grudging acceptance always in danger of being considered unpatriotic.

 

I would not like you to think that I despise "Made in the USA" - there is much that I admire - Cummins & CAT diesels, Mooney M20, P51 Mustang (lot of British influence) , the RV range & Mustang II, etc etce

 

 

[mnewbery]

I have about half my hours behind or in front of Rotax engines. I didn't express an opinion either way

 

 

[Thruster88]

Skippy could you explain how the USA aero engine maker's are holding anyone back from having a go, Porsche PFM, Thielert? diesel and others have been a raging success

 

 

[fly_tornado]

one year of the R1150 fleet has more miles on it than all of the rotax 912s ever built, never heard of any issues related to the piston speed but you are the expert's expert @mnewbery

[mnewbery]

Here (post #37) we have yet another example of someone arguing with maths. Please don't because its embarrassing. Anyone who thinks a motorcycle idling away on the side of the road charging a battery for some traffic cop 10 hours a day is representative of an aero engine application, please start a club of your own or something.

 

Actually, scratch that. @fly_tornado please do tell us here how many thousands of trouble free hours your flying motorcycle engine has accumulated since 2010. Surely that's enough flying time to be able to give a representative real world example?

[biggles]

The maths is in the mean piston speed.A piston with a 2 inch bore is travelling 4 inches every revolution.[/quote

 

2 inch stroke ?

[mnewbery]

Yes. Sorry

 

 

[fly_tornado]

Actually, scratch that. @fly_tornado please do tell us here how many thousands of trouble free hours your flying motorcycle engine has accumulated since 2010. Surely that's enough flying time to be able to give a representative real world example?

 

There are hundreds of BMW powered microlights running around the EU, Takeoff in Germany has been pumping out BMW conversion kits since before you flying the A380

[mnewbery]

I like the design principle of the D-Motor in that the valve design isn't interference. Its a side valve.

 

I was drooling over this 115Hp lycosaurus experimental which apparently still doesn't benefit from electronic fuel metering

 

233 Series

 

 

[M61A1]

The maths is in the mean piston speed.

The bearing speeds are probably more important, but still easily calculated.

 

 

[mnewbery]

Excellent point @M61A1. I was going to mention the shear gradient in the lubricating film that depends on the bearing surface speed but I stopped. For those interested there are some really easy-to-read articles that show the effect of (bearing or piston) surface speed on oil film shear and how the speed gradient contributes to friction, heat and wear. Just google this for one example.

 

Then I thought of the audience

 

Bottom line, the surface speed of a bunch of tiny things rotating very quickly might be less than one big thing rotating slowly and doing the same job. Or it might not. Maths, its hard to argue with but I am sure some will still try. Remember, a room full of mathematicians made nuclear bombs possible. Everyone else just tested the results.

 

I went googling for the number of R1150 engines made. Its less than 99,999 because that's how many digits there are in the engine number sequence. The highest number I can find is ~52,000 for a 2004 model so a good guess would be ~60,000 examples by the end of 2006 of which a very tiny number would have ever been documented for overall condition prior to being scrapped because nobody cares. I am sure for $10,000 you can still get one with 500 hours (40,000 kms) on it and a free motorcycle!

 

Another fun math fact, Rotax made and sold 50,000 "912" engines in 25 years to 2014. By 2020 if Rotax keep going at the same rate that number will be 62,000 new 912 engines. It reminds me of the joke conversation between God and Arthur Davidson about God's design of "Woman".

[Thruster88]

How fast would the BMW bike go at 75% power, would be ok on the autobahn but most would be running under 20%.

 

 

[fly_tornado]

How fast would the BMW bike go at 75% power

depends on the model, if its a GS it won't get it past 200. the motors are happy running at any speed above 5000

 

 

[mnewbery]

@Thruster88 theoretically *wink wink* the R1100 90Hp engine would propel the R1100RS to 215 Km/h before hitting the redline and it really is struggling to accelerate past 205 Km/h. Using the square/square root for the power demand against drag, this suggest 75% power would be around 186Km/h and 6200rpm. Those numbers agree with my dimly remembered experience. Something else to consider is that the R1150 engine was routinely called out for not putting much beyond 77Hp to the ground even when in the best state of tune. In the case of the R1150 I have no idea other than "more than 186 Km/h" because it was a 6 speed.

 

One case in point is the Takeoff-ul TBM12 which is based on (their own modification of) the BMW R1200 motorcycle engine. The engine configuration first appeared on the Merlin weight shift microlight in 1998 with the R1100 based modification. One modification was three spark plugs per cylinder (why? why?)

 

The TBM12 unit is claimed to produce 75Kw at 7200 RPM and weighs a claimed 58Kg.

 

I'm not going to speculate how long that output can be sustained for because I don't care and the original thread was for a CH-701 not a microlight. The $10,500 Euro (~$17k in Australian zloty) purchase price plus the delivery fee could be a bit more off putting than other features. The R1100 version (TBM11) requires a new centrifugal clutch every 400 hours (won't wear out if you never fly it @fly_tornado, I want your personal experience not some Euro fleet numbers).

 

As far as the claim that "hundreds of BMW powered microlights are running around Europe" well maybe they are, in the back of trailers.

 

Takeoff-ul have been going since the mid 1970's so hundreds of engines since 1998 is ... laudable?

 

This document in English from 2003 shows a number of equipment failures and concerns that occurred in a single example of the TBM11 over 1000 hours of operation. It makes for exciting reading and puts a definite qualification to the statement that your BMW R1150 will provide reliable thrust.

[Jethro Belle]

Then I thought of the audience Bottom line, the surface speed of a bunch of tiny things rotating very quickly might be less than one big thing rotating slowly and doing the same job. Or it might not. Maths, its hard to argue with but I am sure some will still try. Remember, a room full of mathematicians made nuclear bombs possible.

I try to be respectful to whoever is happy to read my posts .

 

My posts, that seems to have re-sparked this thread, simply observed that the D-motor is closer to the Lycomtinentals (large displacement, low revving, simple, but at surprisingly low weight for water cooling) than the Rotax. Side valve aside, if D-Motor have done what Lycomtinentals should have done, then we are in interesting times (have improved materials and build quality). You can look at the reliability of Lycomtinentals or do the maths: they will both indicate these motors should be long lived and reliable.

 

I checked your linked paper Mnewbery and it is a theoretical hydrodynamic journal bearing paper (that is a long way from useful in applied engine tribology). The wear and friction of greater concern is rings/cylinders, valve guides .... It doesn't matter what speed: more revolutions = more wear, so a higher revving engine should wear out sooner. The fact Rotax lasts is testament to their build and material quality (NiCrSil). When it comes to stressing, in any engine the highest loads on high-speed engines are generated by acceleration and deceleration of the pistons, each revolution. The Rotax generates proportionately higher stresses due to its higher speed. You don't have to do any calculations to see that. Another engineering measure of 'stress' is power output per cc. The higher it is, the more stressed the motor is mechanically and thermally. Cylinder wear rate is closely related to BMEP, meaning turbocharged engines require special attention in design and build.

 

Sometimes things that appear very simple to the consumer/maintenance have some very complex engineering in them (Tribolgy is incredibly complex, but almost invisible to the consumer except from service life). When I stated the Rotax was complex compared to the Lycomtinentals I was including this in my assessment.

 

I repeat again that my engine explanations are simplistic to avoid lesser details that confuse the fundamentals while not changing the truth.

 

It is great to see post solidly supporting Rotax (I expected it). I was hoping some-one may know more about the D-Motor and D-Motor installs they might like to share.

 

PS: I appreciate you awarding blame for Nuclear Weapons to mathematicians not the engineers :ecstatic:I not sure they viewed themselves to be.

 

 

[mnewbery]

(...) a long way from useful in applied engine tribology

Blame @M61A1 for that, he started it . Even the electrical load robs the engine of some power but try going anywhere without it.

 

During my engineering classes (yes @fly_tornado I did engineering) the lecturers were at pains to discuss the trap of adding more pistons, valves and other gubbins in the pursuit of more specific power. It might work for a while but useful stuff gets optimised away like being able to idle the engine or having acceptable oil consumption or manageable complexity ... or mass.

 

I do like how designers have cottoned on to intercoolers in an effort to increase turbo engine TBO back to something like the naturally aspirated aero engine times.

[mnewbery]

I worked with a guy in Bundaberg who built his own drag racing engines. He showed me a lot about the relationship between ignition timing, BMEP and torque over the operating range. He showed me clearly why some 1970s two-stroke engines start with a relatively advanced spark that retarded back to zero degrees near the redline. It was very simple but it worked to keep things safe.

 

His "small" drag bike was a 2000cc turbo monster that produced 400bhp at 14,000 rpm using one rotary valve instead of camshafts. His big issue was that the class didn't allow electronic aids which meant no boost referenced advance and the turbo took ages to pick up off the line.

 

Totally the opposite of an aero engine!