Why Do Rotaries Suck?

[jame88]

See my post above. Once again, it all comes down to what does capacity mean? Yes we are repeating ourselves here, and really, call it 1.3L or 3.9L, it doesnt really matter as long as you know how to relate that to how piston motors are rated you can make valid comparisons and assesments

I agree.

Sorry to repeat but the only reason i wouldn't say 3.9L is because in that method of measuring capacity, a 1000cc 2-stroke would be a 2000cc.

I think this thread is slowly coming most to an agreeance.

[Smity42]

Perfectly right there, but the "how much it pumps per cycle" seems to work for the current ratings of 4-stroke and 2-stroke, and it can relate to a Wankel, so i thought it is a good way of rating it. Perhaps the Engineers at Mazda thought similar.

The only way you could fairly do that is if you do it off the crank cycle. But again, this doesn't even work between 2 and 4 stroke.

So if you do it on the cycle of the 'combustion medium', whats the cycle of a rotor? One movement or Three? Its debatable... and one way you get 1.3L and the other you get 3.9L

Maybe we should average the two and call it a 2.6L

Edited September 30, 2009 by Smity42

[GT-R32]

Well done all. The time relative and relationship to piston counterparts is fully out there now. The whole unit is considered and understood. Now we are at that stage my question is: If you know how it works and can relate it accordingly, does it really matter how exactly it is rated?

This is a better discussion than was had on AusRotary about this exact thing!

[jame88]

The only way you could fairly do that is if you do it off the crank cycle. But again, this doesn't even work between 2 and 4 stroke.

So if you do it on the cycle of the 'combustion medium', whats the cycle of a rotor? One movement or Three? Its debatable... and one way you get 1.3L and the other you get 3.9L

Sure is debatable, refer to my post above and have a close look at this 2-stroke animation and see if you can see what i mean.

2-stroke

[Smity42]

Sure is debatable, refer to my post above and have a close look at this 2-stroke animation and see if you can see what i mean.

2-stroke

Yes, I can see both arguments clearly, which is why i said it is debatable. I was sold on it being when the original face of the rotor gets back to its original position (ie 3.9L), but now I am fence-sitting. It could be either...

But as we have been saying, it doesnt matter how exactly you rate it as long as you understand how that particular method of rating it relates to the equivalent piston capacities

[Smity42]

Well done all. The time relative and relationship to piston counterparts is fully out there now. The whole unit is considered and understood. Now we are at that stage my question is: If you know how it works and can relate it accordingly, does it really matter how exactly it is rated?

This is a better discussion than was had on AusRotary about this exact thing!

Agreed! An excellent discussion. Hopefully there is more understanding out there now

[Birds]

Well done all. The time relative and relationship to piston counterparts is fully out there now. The whole unit is considered and understood. Now we are at that stage my question is: If you know how it works and can relate it accordingly, does it really matter how exactly it is rated?

This is a better discussion than was had on AusRotary about this exact thing!

Not at all. You'd have to be a pedantic bastard to actually give a shit that some ignorant fellow might think 1.3 litres worth of rotary is the same as 1.3 litres worth of piston 4 stroke.

[jame88]

Ok so its:

2-stroke = amount of air for 2 rotations of output shaft

4-stroke = amount of air for 2 rotations of output shaft

Wankel = amount of air for 3 rotations of output shaft

or:

2-stroke = amount of air for 1 rotations of output shaft

4-stroke = amount of air for 2 rotations of output shaft

Wankel = amount of air for 1 rotations of output shaft

Which is what everyone used before it was suggested otherwise.

(Also 2.6L for a 13b is a good way to compare to a 4-stroke, but the engine itself has little to do with 2.6L)

Guess it just depends on if you believe the evil insane LIES invented by the greedy heads of the evil multinational corporations in their secret plan for world domination.

[DRD-00F]

I have read this thread since the day it was created. For about 2 weeks now, this discussion on rotaries was a very exciting thing for me, I bored my girlfriend about it, I discussed it with those at work and I talked about it with mates.

The reason I was so interested in it is because at the start of it all, I had a VERY basic understanding of how it all worked. Now, thanks to everyones tuition, I am pretty confident that i understand it. Not just that infact, I would say that I can comprehend where each person is deriving their information from and how they deem it to be the most important way to class this engine.

Personally, I disagree with probably about half of you, but I've taken what has been said, understood it, and made my own conclusions as how to come about the answers I was after. In the end, it's quite obvious that most people here would be concidered 'correct' in what they are saying. People are just looking at it from different angels. Much like a pyramid, from the side, it's a triangle, but from the top, it's a square.

To be honest, I don't think this will ever be 100% settled unless some sort of almighty power comes down, cause at the moment, you can't even agree on the definitions of the terms that you're trying to prove.

I'm going to keep reading, and I'm going to keep thinking that half of you are bringing up unnecessary information and moot points, but I'm going to enjoy it

[Jez13]

I was wondering when you were going to post doof - your name has been sitting down there for weeks. I figured you left your computer with this page open and then went on a holiday to hawaii.

This discussion went mainly wrong from the start because we were trying to compare the mechanics of a rotory to a piston engine. The problem is they are so different that all the principles related to pistons are different for a rotory. Like how you would class an RPM or what would determine a full cycle for a rotory engine. If you look at how a piston works and then apply it to a rotory you will not find the correct answer. You need to start your mind with a clean slate on the rotory - thats why I feel that my perception is more accurate because I learnt how a rotory works before I learnt how a piston works.

[jase-r34]

EPIC thread, and a great read over the last few pages. Some of you guys sure know your shit. Hats off to you and I am much the wiser for having read your posts.

[DRD-00F]

I've made a few posts to try and come to a conclusion, but everything I said was basically repeated, and has been repeated about 5 times since, so there's not much point in me posting much anymore. Plus, I'm more a student in this then a teacher

I've learnt enough to make my mind up on the subject, and as such, I can't debate it because I now see all sides as being correct in their own way. Any literage anyone now says to me about the 13B will have a reply of 'Well that depends...', no matter what is said.

To be honest, I do believe one way more then the other, but my compassion for fairness gets the best of me and I could argue either point now.

[madbung]

I'd say because pistons and rotars both use compression and ignition they're very similar in principle ie: both basic combustion engines.

The "wankle" is nothing more than a renamed elliptical engine/pump re-engineered for modern internal combustion uses.

There's nothing new or modern in it's design, in fact the principles it uses outdate the piston combustion engine by a long way.

Why was it not employed as much as the piston engine? simply because it is not as efficient in either application (pump/engine)

Cheap to build though.

Edited September 30, 2009 by madbung

[Sydneykid]

Ok so its:

2-stroke = amount of air for 2 rotations of output shaft

4-stroke = amount of air for 2 rotations of output shaft

Wankel = amount of air for 3 rotations of output shaft

or:

2-stroke = amount of air for 1 rotations of output shaft

4-stroke = amount of air for 2 rotations of output shaft

Wankel = amount of air for 1 rotations of output shaft

Which is what everyone used before it was suggested otherwise.

(Also 2.6L for a 13b is a good way to compare to a 4-stroke, but the engine itself has little to do with 2.6L)

Nope I see it as

2-stroke piston engine = amount of air for 1 complete cycle of the pumping media (the piston/s)

4-stroke piston engine = amount of air for 1 complete cycle of the pumping media (the piston/s)

Wankel engine = amount of air for 1 complete cycle of the pumping media (the rotor/s)

Ooooo look they are all the same, that's why I think my view is more correct.

Guess it just depends on if you believe the evil insane LIES invented by the greedy heads of the evil multinational corporations in their secret plan for world domination.

Nope, just Mazdas using marketing spin to sell a product under false pretences. Of course no other company has ever done that sort of thing.

Cheers

Gary

[jame88]

So "1 complete cycle of the pumping media (the piston/s)" for a 4-stroke is the piston going up, down, up, down?

[Sydneykid]

So "1 complete cycle of the pumping media (the piston/s)" for a 4-stroke is the piston going up, down, up, down?

Yep that would be a full combustion cycle, 4 strokes if you like. Hey, maybe that's why we call it a 4 stroke. When measuring the capacity of the engine we don't care that that's 2 revolutions of the crankshaft

Then a full combustion cycle for 2 stroke would be up, down. Well whadya know, maybe that's why we call it a 2 stroke. When measuring the capacity of the engine we don't care that that's 1 revolution of the crankshaft

You know where I'm going now ..............wait for it............

One complete combustion cycle for a rotary would be, one complete revolution/rotation/orbit of the rotors. When measuring the capacity of the engine we don't care that that's 3 revolutions of the eccentric shaft.

Well, any logical person wouldn't care, as they say you can lead a horse to water but you can't make it drink.

Cheers

Gary

[fuzzy_scuz]

Actually an Automotive Engineer would be.

[GT-R32]

How do CAMS get to their 1.8 multiplier of Mazda's rating?

[fuzzy_scuz]

From thin air I hear.

No it based on the manufacturers specifications.

[madbung]

This has been done I'd guess, but I'll ponder anyway.

3 shaft revolutions to 1 revolution of the rotors (full cycle)..

intake, compression, ignition and exhaust chambers all taken care of by the elliptical design of the of the gearset between e-shaft and rotor housed in a "round" block.

it runs a 3-1 crank to rotor (rotation) ratio

it has 3 rotor faces

it creates 4 chambers, via it's elliptical movement, intake, compression,ignition,exhaust.

it uses ports, not mechanical valves.

with every 3 crank rotations it does 1 full rotor cycle (intake, compression,ignition,exhaust)

So it creates 4 chambers with every 3 crank revolutions or if you prefer it creates 4 chambers with every full revolution of the 3 rotor faces..

Mmmm I think the only way to accurately compare the wankel with a 4 stroke would be to compare cfm @ ?? rpm (rpm measured at the rotor).... for efficiency.

1 full combustion cycle with every 3 turns of the crank (or full cycle of the rotars).

It's a wankel, i'm not game to label it anything else.

Edited September 30, 2009 by madbung