Those Cr@ppy Rotax Engines

[Jerry_Atrick]

On 18/11/2020 at 9:53 PM, old man emu said:

This Trump crap is getting boring. How about we start a thread bagging Rotax engines? We could mount a campaign in favour of Jabiru engines. Now there's a campaign that would be interesting!

OK - I shall 😉

 

I have only flown a Rotax powered aircraft once... on a navex.. I know I could do this on rec flying, but since my engineering talents are limited, this seems more appropriate for me..

 

It was in a Diamond something or other.. Not sure of the engine model; maybe a 912... maybe a Victa lawnmower engine.. couldn't tell the difference... Noisy, vibraty, whiny... Never wanted to be behind one again..

 

Too many tubes for a pre-flight as well... And an extra radiator/cooler... And more wires than an old patch panel from a 1980's computer room.

 

Back to the chomotosed serentiy of a PA28... ahhhhh...

 

Discuss.... Non tech though, otherwise, we have to shift this to rec flying...

 

Edited November 21, 2020 by Jerry_Atrick

[Bruce Tuncks]

I flew from Gawler to the sunshine coast in Qld behind a Rotax and it went just fine.  But I still don't like them. Apparently their crankshafts are made in bits and pressed together. And they are only about 1300cc's, running at 5000rpm and driving a prop through a reduction gear.

They have about three times the parts a Jabiru has and cost about 3 times as much.

 Their spare parts cost big money and to stay legal you have to buy some expensive stuff. Like rubber stuff every 2 years at $2000 a go.

I reckon they are the engines for rich but culturally cringing guys.

I'm a Jabiru supporter as you can see.

[pmccarthy]

Rotax engines sound nice as they go past, sort of like a Hyundai with extractors, which as you know are very common. Whereas the old fashioned sort of aeroplanes make a loud noise that makes people look up and ask “ what is that?”. I think the Rotax ones are made by the Singer sewing machine company, they have that sort of rhythm to them, but you don’t need to thread a shuttle.

[Yenn]

I would liken it more to a screech.

[nomadpete]

The two stroke Rotaxes all scream. It's a noise that's right up there alongside hearing jetskis when I'm trying to relax at the beach. 

 

The 912 is pretty quiet compared to just about every Lycosoarus that I've listened to......

 

And I'd never complain about the music of a big radial or V12 flying past.

 

BTW, does anyone know where I can get one of those bumper stickers that says "I love aircraft noise"?

[Bruce Tuncks]

I tried to look up one on google nomad, but no luck. There are a bunch of places which do custom ones, but you need to order a whole bunch. If you do, I'll buy 2 for sure.

[facthunter]

A lot of the "larger" motor noise is from the prop.(tip speed) and worse on take off when people hear it the most.

  . Generally a FLAT motor with 6 cylinders is much smoother than the 4 cyl types and sounds nicer.. A reduction gear is  a part that has to be engineered properly. Sun and planetary are the best but NONE if you can get away with it is OK. (lighter and cheaper). Stub exhausts as on a Gypsy Major etc are too hard on the ears. Noise and vibration on long flights is a pain. Some re drives set up harmonics between the engine and the prop because of the ratio they use.'

 Fuel economy affects range and the weight of the fuel reduces payload. That's the incentive to get specific fuel consumption low. The biggest capacity Piston engine had the best specific fuel consumption (a 3340 Cu in Four row radial) with  3 turbine power recovery units.. It's not about power /litre. It's about power /Lb and specific fuel consumption. Lbs /HP/Hr.. Reversals( RPM) affect component life  and friction etc is V squared law.. Gears can  lose 5-10 % easily. Chains are better.. but nothing is best. where it works OK. Nev

Edited November 24, 2020 by facthunter
typo

[old man emu]

The more the number of cylinders the smoother the engine. For brevity, let's call a combustion event a "bang"

A single cylinder 4-stroke goes "bang" every second revolution of the crankshaft. (720 degrees)

A cylinder in a twin goes bang once per revolution. (360 degrees)

A cylinder in a 4-cylinder - two bangs per revolution. (180 degrees)

A cylinder in a 6-cylinder - three bangs (120 degrees)

A cylinder in an 8 cylinder - four bangs (90 degrees)

A cylinder in a 12 cylinder - 6 bangs (60 degrees)

 

The smoothness of an engine depends initially on how often there is a combustion event creating a pressure impulse on the piston.The faster it operates, the more frequent are the pressure impulses. Those impulses cause vibrations and the more vibrations per minute, the closer the peaks come together and we can't sense the gaps in between so well.  So the engine feels smoother.

 

 

[onetrack]

You have to hear a Cadillac V16 or a Ford Lincoln Zephyr V12, to understand the real definition of a "smooth engine". The magic commences at 0.36 secs in the first video, and at 13.13 in the second video.

 

 

 

Edited November 25, 2020 by onetrack

[Jerry_Atrick]

My last car in Aus was a VS Commodore "executive", which was the base model.. And for its time, it was basic. But tht 3.8V6 was much smoother than the '96 2.8V6 Audi A6 I had in the UK. I miss both cars immensly; reltively simpel and sturdy (I am sure the Falcon equivalent was great, too). The Audi was better built.. The Commodore was a lot more fun to drive, despite the Audi feeling like it had very similar performance, though at higher revs...I owned them at the same time.. I bought the Commodore before I left Aus and bought the Audi in the UK... When I would go back to Aus, I would drive the Commodore. After a week with the family, I would jump in it and head off.. I miss those days... Only  thing better would be to have flown to wherever it was I was driving to..

 

Edited November 26, 2020 by Jerry_Atrick

[Bruce Tuncks]

I had a Leyland P76 when I worked with this guy who had an Audi. The Audi guy thought the P76 was better.

Another guy bought a Volvo " for the reliability" he said. In fact the P76 was at least twice as reliable as that Volvo.

 

[nomadpete]

Lucky sod.

You must have got the good one.

[nomadpete]

A close friend of mine worked for the "Vehicle proving department" of Leyland Australia, not long before they closed down. He was asked to blueprint a small number of vehicles for a rally - he said that he couldn't even snatch a matching set of distributors that opened the points equally for all cylinders. The QC was terrible. If built properly, their cars were great. Sadly, not many were. ( And before you start, I do know they didn't make their own distributors but you get my drift)

[Jerry_Atrick]

I bought a Volvo for relaibility, too.. How wrong was I..

[onetrack]

The early Commodore 3.8L V6 (the "Buick" motor) was pretty much unbreakable. But the rest of the Commodore was crap. However, from 2005, Holden used 3 different models of motor and they were all crap.

 

AFAIC, the last great Holden built was the totally-Australian designed WB series. They are collectors items now.

 

I have a WB 1-tonner ute in good condition, its a real survivor, because all the Holden 1-tonners either got worked to death, or turned into drag utes with 350 Chevs and other hot-rodding ideas, that destroyed any semblance to the original.

[Yenn]

given a complete rebuild and additional spot welding of the body, the P76 was a good enough car to win the Dakar rally, if I remember correctly.

They were really just about the start of the best buying advice I ever heard. Buy British, buy bad.

When I left Britain I had just bought a new pair of shoes, especially built for hard country work. They lasted less than 6 monthe. British raincoats were absolutely useless. When I bought an Australian raincoat, not a drizabone, I was amazed that it kept me dry all day, even riding a horse. Such a coat was unheard of in Britain.

The Poms used to say what they made was the best in the world and the Japs and also the germans couldn't compre for quality, but it was rather the same as donald trump is now. Say something long and loud enough and people will believe.

[Jerry_Atrick]

There are very few manufacturers that have always got ir=t right.. Sometimes it's commercial pressure (e.g. Boeing of late); sometimes it's unforeseen issues from yet to be discoverd science (e.g. deHavilland Comet). After many decades of automative engineering experience, the original Mercede's A series was found to roll easier than an old East German Trabant... and the head engineer tragically took his one liife as a result.

 

In 2018 (from memory), Britain was the world's 8th largest manufacturer - at least by value.. Yes, there was a chunk that was food (ready meals are massive here, and you can get very decent ready meals at reasonable prices). The UK's cheeses are world beating and now their wines are coming up to (though the good ones are still dollar for dollar a bit expensive). But their precision engineering industries are very strong; as is their tooling industries. An old schoolfirend of mine has a lighting manufacturing business in Melbourne handed down from his parents - and they only buy their spinning lathes and other bits from the UK.. they are the only ones who make them to the quality required..

 

Britain's consumer manufacturing has always been a bit off the quality stakes.. But I remember a discussion I had with a German about 10 years my junior at work one day.. We were talking about the strengths of Germany v Britain.. I mentioned that Britain is a very strong engineering country and he was most indignant, pointing to all the consumer goods that Germany produce... I reminded him of the Lancaster, the Spitfire, and that most nuclear isntallations in the western world involve British designs (and also, the Brits gave the Germans the jet engine). The problem with Britain these days, is it is too short sighted...

 

Back to Rotaxes... I am sure they are great engines.. But I too whiny and high reving for me... I will take a IO-540 any day.... (I know, different class)...

 

 

[Yenn]

IO-540 compared to a Rotax? No comparison. If you need 250 plus HP Rotax will never do the trick. If you need 80HP an O-540 would be far too heavy.