Jump to content
WayneL

Motors - another VW variant.

Recommended Posts

For the same rated HP as a 912ULS, it's a lot thirstier.  22 - 30 lph, all on Avgas.

Share this post


Link to post
Share on other sites

It doesn't seem to actually bring any benefit/improvement to small HP aircraft engines - just more of the same. In my totally unbiased (ha!) opinion Rotax 912/914 range is still the class leader,  which is a little disappointing given the way the automotive industry continues to make (admittedly small) incremental improvements.

Share this post


Link to post
Share on other sites

 The VW engine has had fatal flaws for years. Weak cases drive shaft weaknesses Head porting in the wrong place to name a few. These are all addressed here, but I don't like the siamesed heads, but there's little remaining of the original design (thankfully) but the "thing" would have been better to start from scratch. I recognize this is hard to do in a real sense. It's still a simple engine and if the cost is right including including operating cost it might have a future.

  I think the Rotax design is  now all over the place. IF it's the answer the question is wrong. The 80 HP was ok at the time but still a complex installation. Too many external pipes radiators etc and too expensive for Parts. Growing the motor always has problems. A good aero motor dewsign is already on the limit or it's too heavy. Consequently the "derived " engine will have a shorter  (and more interesting ) life. ALL fours have torsional vibration problems that are worse than other configurations. Flat fours have a long history in cars of broken cranks and exhaust and inlet systems are hard to get right. Nev

Share this post


Link to post
Share on other sites
6 hours ago, Marty_d said:

For the same rated HP as a 912ULS, it's a lot thirstier.  22 - 30 lph, all on Avgas.

And double the capacity.....for that 100 hp. Alot of the fuel consumption would be from having air cooled heads and a lack of power probably from lower compression.

Can't see it being a particularly cheap engine also...which was essentially WHY people used them....

 

As Nev said, they went to alot of trouble to cast all their own parts so it baffles me why serious design changes weren't made.

Perhaps they were also catering to the offroad buggy/car market with the same parts?

 

I would have gone with water cooled heads personally...... not hard to incorporate a pump if your making your own castings..

 

 

 

 

Share this post


Link to post
Share on other sites

The specs for the engine say that it has a compression ratio of 8:1, yet they say to tun it on 100LL. At that compression ration, there's more than CO2 and water going out the exhaust pipe.

 

I can't give a source for this graph, but is seems to be one commonly used in the "Which octane rating for my compression ratio?" discussions

 

[âIMG]

 

As you can see, an engine with an 8:1 compression ratio should operate OK on 84 octane fuel. Since the lowest you can get at a pump is unleaded 91 octane, that should be OK in this engine. 

 

What I don't like about published engine specs is that they only ever state the maximum horsepower and the RPM at which that is achieved. 

 

You can calculate torque if you know the horsepower at a given RPM using the formula:

T(lbf.ft)= k x HP(lbf.ft/min)/( RPM)

Where k is the unit-less constant 5252

 

So, if the engine produces 100 HP @ 2900 RPM then.

T = (5252.100)/2900

T = 181 lbf.ft   (or in metrics 245 N.m)

https://www.youtube.com/watch?v=fgLNO3ThGD4

 

The question an operator wants answered is who much torque does my engine need to produce to operate my propeller efficiently?

 

Share this post


Link to post
Share on other sites

The truth is that all engines have strength & weakness -  What matters is the best engine for the application, cost (both purchase & running) as perceived by the prospective purchaser/owner.

 

The simplicity of the air cooled/direct drive engine is seductive but non (in the 80 -115 hp range) have won me over quit as much as the Rotax. 

 

Air cooled direct drive engines have many drawbacks just as fluid cooled gearbox drive engines - nothing is perfect but for my application (motivating a nice little two seat composite) the Rotax 912/914 range is a match made in heaven - smooth, quiet, economical and so far (@ 850+ hrs) reliable.  So far service parts have not been costly (less than my car). The one repair - I have replaced the sprag clutch,  a bit of a stinker but not completely outrageous but then I use my own labour. 

Share this post


Link to post
Share on other sites

 At 100 HP for nearly 3 litres that's not necessary.  IF you can air cool it's simpler to  build and maintain. It doesn't look to be as lightly built as it could be.. Individual liguid cooled heads are a bit twee and a crankcase with separate cylinders lacks strength and rigidity it could have had otherwise.. People probably like it to LOOK as if it is an aeroplane motor. Some very slow revving motors are very fuel efficient.( Container ships engines) High power for a capacity is not the absolute critera we are looking for. Nev

Share this post


Link to post
Share on other sites
Posted (edited)

  Gear redrives are not easy to design. The Rotax one is quite complex and requires (expensive) service occasionally. It's also pretty noisy and clunky, starting and stopping. One advantage of THAT red . gear is more choice of a prop and easy  mechanical in  flight variable pitch. Planes which operate under 110 knots don't need variable pitch prop. It all weighs and costs. The built up crank on a Rotax is an odd thing that I see  as a downside. Just pressing parts like that together sucks. It's a known weakness.

 Torque equates to thrust which you need to get you moving Gears multiply torque. but there's a loss involved. Octane rating s vary because of more than compression ratio. Smaller bores can allow more compression to be used. A four valve head with central plug will run a higher compression as it needs less advance. IF you direct inject it doesn't matter what the octane is but it's a pretty specialized pump sensitive to grunge. Nev.

Edited by facthunter

Share this post


Link to post
Share on other sites
1 hour ago, old man emu said:

As you can see, an engine with an 8:1 compression ratio should operate OK on 84 octane fuel. Since the lowest you can get at a pump is unleaded 91 octane, that should be OK in this engine. 

Depends if it's MON or RON.....

Share this post


Link to post
Share on other sites

The following info was posted on a US facebook group, Microlight and Ultralight aircraft.

Wayne.

 

VW Conversion: 100hp ASTM Certified Engine by MotorAV
100 hp @ 2900 rpm, Direct Drive
189 lbs ( 85.7 kg ) Minimum runnable dry weight including the alternator.
TBO 1200 hours. 2,000 hours after ASTM Certification.

Magnesium Alloy AS41 Engine Case;
Nitrided Crankshaft with integral propeller flange;
Throttle Body Injector;
Hydraulic Valve Lifters;
Dual Spark Plugs;
Dual Electronic Ignition;
Primary Alternator 12V/20A;
Secondary optional alternator 12V/50A;
The suggested price of $12,900.
Mr Bill Brogdon, the design consultant, is a former Chief Engineer of Continental Motors.

Share this post


Link to post
Share on other sites

Working from memory (risky) this company already cast the VW Brazillian engines, so took it over when VW wanted to sell. They then hired a Continental engines design engineer and this motor is the result. 

Ken

Share this post


Link to post
Share on other sites
4 hours ago, facthunter said:

  Gear redrives are not easy to design. The Rotax one is quite complex and requires (expensive) service occasionally. It's also pretty noisy and clunky, starting and stopping. One advantage of THAT red . gear is more choice of a prop and easy  mechanical in  flight variable pitch. Planes which operate under 110 knots don't need variable pitch prop. It all weighs and costs. The built up crank on a Rotax is an odd thing that I see  as a downside. Just pressing parts like that together sucks. It's a known weakness.

 Torque equates to thrust which you need to get you moving Gears multiply torque. but there's a loss involved. Octane rating s vary because of more than compression ratio. Smaller bores can allow more compression to be used. A four valve head with central plug will run a higher compression as it needs less advance. IF you direct inject it doesn't matter what the octane is but it's a pretty specialized pump sensitive to grunge. Nev.

From (imperfect) memory, my gear box only requires a service at 1,200 hrs - do not know the cost. If its noisy I cant hear it and its one hell-of-a -lot quieter than the Jabs & LyCons in my area.

 

Clunky stop/starting not so much an issue if you either stop/start on one ignition or fit "soft start" in part or whole.

 

Cant comment on crankshaft construction/assembly (it works) however I think its  Continental that use a silk thread between the  crankcase mating surfaces. - now that's weird!

 

As for your other comments - seem to relate to the fuel injected 912 - no experience and at the price only of interest to aircraft doing high hours (schools? ) or people with very deep pockets - the fuel saving would take me a lifetime to pay off..

Share this post


Link to post
Share on other sites

 What's so weird about a cotton thread (as well as compound) between the surfaces?. Its a common proven  practice. Built up pressed together cranks are suss and there's been a few associated failures. The gear drive end is also subject to inspections . The cam faced friction damped  shock absorber is fairly unique but needed and if there's metal or excess noise you pull it and have it checked.. I think you are a bit one eyed about your Rotax.. I'm not out to bag it for the sake of it but just add a few facts which is what we should be dealing with in these matters.  Nev

Share this post


Link to post
Share on other sites

I reckon that an aero engine should be built on the KISS principle. The simpler it is, the less there is to go wrong. The advances on aero engine design should be directed at weight reduction; efficient combustion; heat dispersal. 

  • Like 1
  • Agree 1

Share this post


Link to post
Share on other sites

Particularly in U/L applications where they get all kinds of treatment, and we are generally doing it the way we are to keep the budget (ours) in control. Nev

Share this post


Link to post
Share on other sites
11 hours ago, facthunter said:

 What's so weird about a cotton thread (as well as compound) between the surfaces?. Its a common proven  practice. Built up pressed together cranks are suss and there's been a few associated failures. The gear drive end is also subject to inspections . The cam faced friction damped  shock absorber is fairly unique but needed and if there's metal or excess noise you pull it and have it checked.. I think you are a bit one eyed about your Rotax.. I'm not out to bag it for the sake of it but just add a few facts which is what we should be dealing with in these matters.  Nev

Guilty as charged - definitely an enthusiastic 912 fan.

 

Whats weird is that these very old practises (good in their day) belong to an industrial era where repeatable super accurate machining was not available - there are now better ways of achieving the same result more repeatable result without the need to develop an artistic skill

 

"The gear drive is subject to inspections" ??? must have missed that in the Rotax manual.

 

No offence Nev but it seems to me , after following your comments for some time now,  that you have a significant anti Rotax 912 bias - For example in your above comments "if there's metal or excess noise you pull it and have it checked" this is not Rotax specific, so what are you saying???. and again "The cam faced friction damped  shock absorber is fairly unique but needed" your point is ?????  

  • Agree 1

Share this post


Link to post
Share on other sites
11 hours ago, old man emu said:

I reckon that an aero engine should be built on the KISS principle. The simpler it is, the less there is to go wrong. The advances on aero engine design should be directed at weight reduction; efficient combustion; heat dispersal. 

I agree with you ---- up to a point. If the more complex system delivers a significant improvement over the simple that is the direction most users/operators will go. Most engineers, by training or inclination, admire the simplicity of many past technologies - that doesn't mean they want to  return to that era/technology (I always lusted after a steam powered launch). In the HP range Rotax is more complex than most but then (in my opinion) it does everything better.

Share this post


Link to post
Share on other sites
Posted (edited)

Once again, the Brazilians have spent a heap of time, money and effort producing something that provides no real engine benefits, no technological advances, no weight reduction, and no fuel economy gains. 

I really do wonder what the aims of these engine development programmes are, and if anyone actually wrote down attainable and important targets for their redesign.

At $12K for a MotorAV engine, you might as well go and buy a Revmaster 2300 for under $9K and have a VW engine that was designed and refined over 40 years or so, by a bloke who is an engine design expert.

The bragging rights about snaring Bill Brodgen from Continental Motors doesn't hold any water for me, Continental were still manufacturing 4 and 6 cyl side valve industrial engines with abysmal power output in the mid-1970's.

These engines designs dated from the early 1930's. I'd like to think that engine technology has advanced at a pretty exciting rate over the last 40 years, at least - but companies like Continental are classic industrial dianosaurs - "We've always done it this way! - it works, why do you need to change anything?"

 

If the Japs were into aircraft engines like they're into automotive engines - by today, we'd have a Japanese IC aircraft engine available, that weighed 50 kgs, produced 200 reliable HP, ran as smooth as silk, and had a 3000 hr TBO.

Honda are producing their new i-DTEC 1.6L diesel with aluminium heads and block, high-swirl combustion chambers, chrome-moly steel pistons, a variable geometry ECU-controlled turbocharger with intercooling - and it produces 118HP at 4000RPM and weighs 47kgs less than their previous 2.2L diesel engine.

This new engine features weight-saving in every single engine component, high plateau bore honing to reduce friction, plus a special synthetic oil designed specifically for the engine. All this translates into 3.7L per 100kms on the highway in a Honda Civic.

If Continental had advanced with their technology and design like the Japs have done, they just might be producing hundreds of thousands of lightweight aircraft engines today, instead of being an industrial and technological laggard.

Edited by onetrack
  • Like 2
  • Winner 1

Share this post


Link to post
Share on other sites

Facthunter was correct. The gearbox of the Rotax does have an inspection schedule set by the manufacturer.

 

You would be surprised at the accuracy that can be achieved by skilled machinists. The problem engineers had up till relatively recently was getting over the poor metallurgical properties of the materials they were using. Now engineers have access to ceramic coatings, more suitable alloys and such. You could build a 4-cylinder copy of a Lycoming or Continental that was a whole lot lighter and more efficient than their usual products. 

Share this post


Link to post
Share on other sites

I agree with the KISS design, but I am amazed at the success of the distinctly non KISS Rotax. Just look at the installation, it is a maze of pipes and extra bits all over the place, but there is no doubt that it works and works well.

Look at a Lycoming or Jabiru and you can immediately see what each bit does, but the question is which works best? I have been involved with spark ignition engines for many years and still like to see simplicity.

Share this post


Link to post
Share on other sites
1 hour ago, old man emu said:

Facthunter was correct. The gearbox of the Rotax does have an inspection schedule set by the manufacturer.

 

You would be surprised at the accuracy that can be achieved by skilled machinists. The problem engineers had up till relatively recently was getting over the poor metallurgical properties of the materials they were using. Now engineers have access to ceramic coatings, more suitable alloys and such. You could build a 4-cylinder copy of a Lycoming or Continental that was a whole lot lighter and more efficient than their usual products. 

Other than the 1200 hr  G box detailed internal inspection, I believe all other "inspections" are in situ checks of dog clutch, movement of prop flange, signs of leakage, etc. When you "know" your engine you are getting a pretty good "handle "on these

as part of the pre-flight checks - hardly onerous.

 

 "You would be surprised at the accuracy that can be achieved by skilled machinist" no I wouldn't but I think you have pretty well made my point - skilled machinists are now by-enlarge confined to "bespoke" one off/ultra low production runs - its an art form.

 

1 hour ago, Yenn said:

..................................................distinctly non KISS Rotax. Just look at the installation, it is a maze of pipes and extra bits all over the place, but there is no doubt that it works and works well.

.............................................

Well there you go - from the perspective of a long time bush mechanic, mostly on agricultural equipment but also car's, & motorbikes I actually find the Rotax to be pretty simple. A bit messy true - I can speculate about all the pipes (instead of being part of the case/heads etc) but what impresses me is that it just works and very well  and its very easy to work on (provided you follow" The Book"). 

Share this post


Link to post
Share on other sites
1 hour ago, onetrack said:

I really do wonder what the aims of these engine development programmes are, and if anyone actually wrote down attainable and important targets for their redesign.

Yeah, got me baffled as well..

Next they'll be designing drum brakes.....great design and metallurgy. ....but in the end, well, they'd still be just "drum brakes".

 

It's all a bit of a shame that all that effort went into producing what looks (as in visually) like a great engine but just underperforms in nearly every aspect.

I can't fathom why you would get an ex Continental employee involved. It's like getting a designer of the Holden HQ on board for your new car...lol.

 

I so wish Honda would make a competing engine to the Rotax, just out of spite and in response to it's absurd pricing. (Monopoly)

Including the same mounting points. I imagine a "junior" design team, using Honda's data base, could knock up a 100hp engine in a few months.

They wouldn't even have to use advanced or current technology to beat Rotax in EVERY preformance level.

 

Rotax marketing must totally dumbfounded why no one has had a serious crack at the crown ..... for over 20 yrs.

DESPITE the purchase price and DESPITE the hundreds of percent markup on parts.... most being off the shelf commercial/industrial/automotive products.

 

 

  • Like 1

Share this post


Link to post
Share on other sites
2 minutes ago, Downunder said:

... I so wish Honda would make a competing engine to the Rotax, just out of spite and in response to it's absurd pricing. (Monopoly)

Including the same mounting points. I imagine a "junior" design team, using Honda's data base, could knock up a 100hp engine in a few months....

 

 

I'm totally with you, 1T. After years of riding chain-driven bikes I'd had a bellyful of them, especially the oil thrown all over the frame.

I got excited about the new shaft-driven bike Honda was rumoured to be developing. Apparently, as you suggest, this blank-slate project was given to a new batch of engineers. The CX-500 they came out with was pretty revolutionary.

I got to ride the very first one in the country (the Black Shadow used in the ads) before it was given to some of the journos, one of whom pranged it. The one I bought was the most dependable bike I ever owned. It had some quirky features but was so well-engineered that many are still on the road today. Some of these engines are running aircraft.

  • Like 1

Share this post


Link to post
Share on other sites

Technological advancement requires complexity. It's the "trade-off" for better engine perfomance, weight, and economy.

This VW type engine is the perfect example of what "simplicity" gets you. Low power, poor economy, poor tbo and heavy weights.

If you want simplicity,  you need to accept the other negative features. 

 

The Rotax (the carb version and somewhat the injected models) I see as semi-advanced engine.

The water cooled heads allow higher compression (better fuel economy and power). Full alloy barrels and the gbox again, advance the performance criteria.

I imagine dual carbs goes into that mix as well.

 

A modern engine. Well, I don't think there is one.

The turbo and injected 915 would have to be closest I guess....injected, turboed, gbox and water cooled heads.

 

 

  • Agree 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×