[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)

This was my first reaction on the MOTA engine simulation program Luc once gave me....
I still think such programs are usefull, but practice results ALWAYS come first!

Jan Thiel a écrit:

This was my first reaction on the MOTA engine simulation program Luc once gave me....
I still think such programs are usefull, but practice results ALWAYS come first!

No doubt Jan !
But that is not the issue here !

Jan Thiel a écrit:

I bought all Blair's books, I used to buy all tuning books!
But for my work, looking for more power, they were mostly useless to me.
Except for 1 very good writer's articles: Kevin Cameron.
He made you THINK!
In my opinion thinking is far more important than calculating!

I am studying the text book by GPB and in that text book, it is noted on several occasions that sonic flow is of minor importance in internal combustion engines. GPB also makes no reference to the "optimal" 180 degree exhaust timing (which is not optimal, if we take into account the actual port timings of the RSA engine, for example). So when Frits Overmars makes a statement about port timing and sonic flow, I start to THINK. Then I take the equations in the text book, substitute some values, and my result does not support Frits Overmars' assertions. So I continue to THINK. Who is wrong, who is right?

Jan Thiel a écrit:

This was my first reaction on the MOTA engine simulation program Luc once gave me....
I still think such programs are usefull, but practice results ALWAYS come first!

As any complex piece of machinery, a 2T engine has tens, if not hundreds of free parameters: bore, stroke, crank length, inlet diameter, ..... It is unthinkable that one would be able to optimize such a system relying only on "practice results". Any successful attempt to optimize such a machine relies on theory and calculations to "zoom in" on a relevant range of the parameters.

I am always a bit disappointed when people "with practical experience" make disparaging remarks about theoretical work ("only results on the dyno count!") and numerical simulation ("garbage in, garbage out!"). People who make such remarks do not understand (the nature of numerical) simulation. I would challenge anybody to design and build a working 2T engine without any reference to theory - see how far you go.

As Einstein said, "theory is when you know everything, but nothing works, practical is when it works but no one know why".
Numerical simulation is a great help, but in the end, it's true that only the final result on the dyno (I would say even on the track) is important. You cannot win races in a simulation software.

I’m always very desapointed when someone wants to earn for nothing what somebody spend a whole Life to reach!
If it was so simple to calculate with computers, racing départments would note have any chance to live anymore and cagiva or swissauto should have been world champion.

Regarding operational 2 cycle engines, theory untested in a laboratory/dyno/racing setting can not meet any functional criteria of a "strong proof".

Well, if you want to play this game.....

"simulation" is any analysis of a system on the basis of calculations rather than measurements.

"simulation" does not necessarily require a "computer" (the term "programmable digital computer" would be more precise as there are other "computing machines" besides the common programmable digital computer). Simulation is not the same as "numerical analysis". Honestly, it is impossible to design any machine without simulation. Do you think steam locomotives were designed solely based on "practical experience" and "measured data"? If "practical experience" is the only road to success, you can never make anything "new". Do you think the first airplane was designed based on "practical experience"? Or even the first internal combustion engine, for that matter?

As an example: a engine builder wishes to determine the optimum shape of a conrod. First of all, the builder must decide which performance parameter is relevant: engine lifetime? Fuel consumption? Vibration? Peak power? Reliability? In practice, the builder is interested in all such aspects, thus the overall performance parameter is a weighted sum over the "partial" parameters.

The empirical approach would be to fabricate several conrods, build several engines with those conrods, measure each performance parameter and then determine the "overall performance" of each conrod. Then the builder can select the "best" conrod. However, this "best" conrod is, in general, NOT the optimal conrod. To optimize the conrod, you need to use theory and calculations to figure out where the stresses are, how high the stresses are, etc, so that you know how to improve the conrod. Thus, the simulation will show you the "road" towards the goal.

Simulation is much more important than most people think. There are many systems for which simulation is the only possibility. Consider a system such as the International Space Station. Do you honestly think you would be able to make a successful ISS by simply building 10 different versions of the ISS and see which one works best? Do you honestly think that the safety evaluation of a commercial airliner can be done on a purely "experimental" or "practical basis"? Good luck, see how many experiments you need to obtain data for all possible configurations of the airliner in all possible atmospheric conditions.

Designing a racing engine is like trying to find an obscure address in a big city where you've never been before. Simulation is like a GPS tool that guides you to within a certain range of the address (say, 15 meters) - after that you'll have to walk. This can be interpreted as: "the GPS is useless because I have to walk the last part anyway" or "without the GPS it would be very unlikely that I would ever find this address". I advocate the second interpretation (the first interpretation is rather short-sighted)

So only further simulations can supply further improvement in an operational 2 cycle engine and the method of successive approximations (trial and error testing) has no role?

Gentlemen,

The purpose of this thread (and the other 4 before it) is for Jan and Frits to share their knowledge with the rest of us. Jan is an empiricist with more than 50 years worth of practical experience and his engines has won at GP level since the 60's, Frits is half empiricist and half theoretician that wrote small programs to help him understand what is happening better. Between the two of them they have graciously and selflessly shared that combined knowledge of over a 100 years worth. Most of us are extremely grateful and respectful of this.

There are other forums where you can debate the value or not of simulation software and try and shoot holes in the physics behind finite wave theory. Please do not dilute this thread with petty bickering and posturing.

Frits, Jan and Marc, forgive me if I have overstepped my bounds but this is getting in the way of allowing the two gentlemen from sharing more. There is a lot more, you can see it on the Dutch site where they have been queried a lot more extensively but it is unfortunately in Dutch!

Neels

Thank you Neels!
I was about to give up on forums.

At Aprilia there once was a program from LOTUS.
Some exhaust pipes were designed and made with this.
They were completely useless!!!
The program was returned to LOTUS....

Allow me one last time to state my case.

Frits Overmars made a comment about a "pressure ratio" and if it "exceeds 2 you reach Mach 1".

I cannot confirm (or deny) this claim based on my personal knowledge and based on what I read in text books.

So my question is simple: please show me (and the others) what you precisely mean with your statement.

Similar for the assertions about the "compound Helmholtz resonator". None, I repeat: __none__ of the text books I have consulted consider the "compound Helmholtz resonator" as a "mode of operation" of a 2T engine. Is this an oversight of other authors? Is this so specific that only experienced tuners know the details? I am very interested to learn about the details, precisely because Frits Overmars is considered an expert.

Virgil Tripp a écrit:

So only further simulations can supply further improvement in an operational 2 cycle engine and the method of successive approximations (trial and error testing) has no role?

I will not say "only simulation", but simulation may show options for improvement which even an experienced "practitioner" may overlook or fail to grasp intuitively.

The reason I entered this thread was because Frits Overmars is/was making claims which are not supported by theory and which seem physically unreasonable. Thus, I like to hear more detailed explanations about why Overmars is right (and apparently, several well-known authors in the field are wrong).

I don't really care that much about simulation of 2T engines - apart from the fact that I do "simulation" and "numerical analysis" for my profession and I fully understand the power, and the limitations of simulation.

ReinanRacing a écrit:

Allow me one last time to state my case.

Frits Overmars made a comment about a "pressure ratio" and if it "exceeds 2 you reach Mach 1".

I cannot confirm (or deny) this claim based on my personal knowledge and based on what I read in text books.

So my question is simple: please show me (and the others) what you precisely mean with your statement.

Have a look at equation 2.16.13 in Blair's 2T book.

But rather start a separate thread to discuss this, the issue is not with what you state but the thread in which you do.

Vannik a écrit:

Have a look at equation 2.16.13 in Blair's 2T book.

Finally, we have an answer. Thanks, I will study those sections.

Vannik a écrit:

But rather start a separate thread to discuss this, the issue is not with what you state but the thread in which you do.

And how many people would I attract if I open this thread (prospective title: "About choked flow phenomena in the exhaust port of a 2T engine") from zero?

[quote="Vannik"]

ReinanRacing a écrit:

But rather start a separate thread to discuss this, the issue is not with what you state but the thread in which you do.

I am very surprised Neels.

If Frits makes his statements here, then questions should be asked about this here.

Everyone here reading the statements did want to know if it is correct, or am I the only one?

If Frits won't real questions about his statements than he should not post them here.

Vannik a écrit:

Frits, Jan and Marc, forgive me if I have overstepped my bounds

On the contrary Neels. I am grateful for your kind words.
I've been holding myself back from reacting, trying to preserve some dignity instead of speaking my mind   .

LucF a écrit:

Vannik a écrit:

But rather start a separate thread to discuss this, the issue is not with what you state but the thread in which you do.

I am very surprised Neels.

If Frits makes his statements here, then questions should be asked about this here.

Everyone here reading the statements did want to know if it is correct, or am I the only one?

If Frits won't real questions about his statements than he should not post them here.

LucF has made statements on this forum about the performance of the Ryger engine. Many people have asked about it, but none have gotten an answer. Everyone here wanted to know if the statements were correct, but .....
It was a useless discussion.

This whole discussion should be deleted from this topic, as it will leed to nothing. ASAP.

Frits Overmars a écrit:

On the contrary Neels. I am grateful for your kind words.
I've been holding myself back from reacting, trying to preserve some dignity instead of speaking my mind   .

Feel free to speak your mind - then at least we will be free from the self-imposed censorship about what kind of questions are "appropriate", about what is "understandable" for other forum members. Perhaps then we can finally have an adult discussion between experts and interested amateurs.

JanBros a écrit:

This whole discussion should be deleted from this topic, as it will leed to nothing. ASAP.

All hail the censor and his red pen, protecting innocent minds from inappropriate information.

I have stated it before and I will state it again: Frits Overmars made a statement about sonic flow in the exhaust of a 2T engine. As an interested amateur, I could not verify that statement so I ask about it - only to be told that such questions are "inappropriate" and that Frits Overmars had decided that the answer was "not understandable to other forum members".

Neels van Niekerk has kindly pointed me to a section in the text book by GPB. I will study that section and trust me, I will be back with more questions after that.

ReinanRacing a écrit:

Frits Overmars made a statement about sonic flow in the exhaust of a 2T engine. As an interested amateur, I could not verify that statement so I ask about it - only to be told that such questions are "inappropriate" and that Frits Overmars had decided that the answer was "not understandable to other forum members".
Neels van Niekerk has kindly pointed me to a section in the text book by GPB. I will study that section and trust me, I will be back with more questions after that.

Shall we get the facts straight, Reinan? I told you beforehand that I would be glad to answer all your questions on one condition: this is not the place for in-depth physics. There are other forums where Neels, myself and others explore these matters in depth. You choose to ignore my condition and now you are complaining that you don't get an answer. What makes you think I owe you anything?

Furthermore, you wrote that you studied professor Blairs book. As professor Van Niekerk pointed out, the answer to your question is right there in the book. You must have seen it without understanding it, and I saw no sense in repeating what professor Blair already explained.

You talk about self-imposed censorship. Yes, I censor myself in order to stay within the spirit of this forum that offers Jan Thiel and myself the opportunity to share our findings with other enthusiasts. We try to do this in a way that is pleasant for the majority of the forum members.

As professor Van Niekerk suggested, why don't you start your own thread? Then you can ask any questions you want without interfering with the thread that bears our names.

Frits Overmars a écrit:

Shall we get the facts straight, Reinan?

That's "professor Reinan" for you, or better yet, "professor Van Rooijen", or even better yet, "prof. dr. ir. Van Rooijen"; if you refer to "vannik" as "professor Van Niekerk" then please extend me the same courtesy.

Frits Overmars a écrit:

I told you beforehand that I would be glad to answer all your questions on one condition: this is not the place for in-depth physics. There are other forums where Neels, myself and others explore these matters in depth. You choose to ignore my condition and now you are complaining that you don't get an answer. What makes you think I owe you anything?

You don't owe me anything. You are free to make your decision and not answer my question. And I am free to have an opinion about your refusal to answer the question Then again, you did not bother to point me to those other "forums".

Frits Overmars a écrit:

Furthermore, you wrote that you studied professor Blairs book. As professor Van Niekerk pointed out, the answer to your question is right there in the book. You must have seen it without understanding it, and I saw no sense in repeating what professor Blair already explained.

Another interpretation could be that you were too lazy to look up the relevant section in the book to point me in the right direction. That's quite all right. When I tell my students: "you can show on the back of an envelope" then I really mean "it takes four hours of dedicated work and I am too lazy to do that."

Frits Overmars a écrit:

You talk about self-imposed censorship. Yes, I censor myself in order to stay within the spirit of this forum that offers Jan Thiel and myself the opportunity to share our findings with other enthusiasts. We try to do this in a way that is pleasant for the majority of the forum members.

I cite JanBros:

JanBros a écrit:

This whole discussion should be deleted from this topic, as it will leed to nothing. ASAP.

If that is not censorship then I don't know what is. Furthermore, you refer on several occasions that questions are "too difficult", and that the discussion is "not understandable for other forum members". I find that a rather arrogant stance - who are you to decide about such aspects? I realize there are certain rules for each forum; it is up to the moderators to react when forum members ignore those rules, but it is not up to __you__ to decide what kind of contents is acceptable and what is not. If you want control over the contents of this thread (because it bears your name), then that's fine: then put a lock on this thread and review each message before publication.

Frits Overmars a écrit:

As professor Van Niekerk suggested, why don't you start your own thread? Then you can ask any questions you want without interfering with the thread that bears our names.

I will open a thread on this forum to discuss these things in details, and if you're interested, you are invited to join. I will post a link here when I open the new thread.

ReinanRacing,

I really don't know who you are and similarly you do not know really who I am.
However I am disappointed with your attitude and manner towards this thread and also Frits who has been able to generously provide many answers and insights to both the Aprilia 125 and 2 stroke performance for many years.
I therefore look forward to you not making any more comments to this thread and going away and doing your own thing.

Goodbye.

Ken Seeber a écrit:

ReinanRacing,

I really don't know who you are and similarly you do not know really who I am.
However I am disappointed with your attitude and manner towards this thread and also Frits who has been able to generously provide many answers and insights to both the Aprilia 125 and 2 stroke performance for many years.
I therefore look forward to you not making any more comments to this thread and going away and doing your own thing.

Goodbye.

Hello Ken, are you a moderator? If so, then please inform me in detail of any violations on my part of the forum rules, and then take appropriate action, such as an official warning. If you are not a moderator, then you should consider your words carefully. As a forum member you are asking another forum member to go away - because you are "disappointed with my attitude".

I am disappointed with your attitude and manner. I am looking forward to reading more of your posts so that I can react to them with WORDS that __you__ don't like

If you (or anybody else) wants to set some kind of "standard" for what is acceptable and what is not acceptable in this thread or in this forum, then the thread or forum should be closed and all contributions should be reviewed and approved before publication.

I suggest you close your eyes, and go to your Happy Place, where it is Christmas 365 days per year and there are endless renditions of "Imagine" by John Lennon.

Hello

I want build a rotary valve using a belt on CVT engine 54X50, what measures recommend for use on the shape intake and timing for the valve ?
[Vous devez être inscrit et connecté pour voir cette image]
Thanks