[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked)

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

hi

has anyone tried if it makes a difference what angle has the cylinder? (vertically or horizontally or something in between). did this gives a difference in performance and has to be changed the balance factor of the crankshaft?

thanks Manuel

Nombre de messages : 62 Localisation : Denmark Date d'inscription : 12/02/2012

Frits Overmars a écrit:

Mic a écrit:: During the expansion stroke the rotation direction of the crank determines which side of the cylinder wall the piston is pushed towards.

Mic, to be exact you should write: "which side of the cylinder wall the piston is pushed or pulled towards".
The con rod angle, together with the force in the con rod (push or pull) determines which side that is. And after reading the Big Bang story you may find that is is not the side you were originally expecting.

Citation :: Here I thought that you would see a difference between having the piston push toward the exhaust port where the big port gives less supporting surface area vs. towards the C port side where the wall surface area is much bigger.

You are right, but if I remember correctly, Jan Thiel's tests have not shown a distinct difference between the two situations. So the difference, if any, is small.

Have just finished reading your big bag story again. Yes you're of course correct. Right after TDC the crank pulls the piston in the direction of the rotation. After this I then guess the pistion is pushed against the opposite side when it start to apply positive force to the crankshaft?

When Jan mentioned the power loss between RSW250 and RSA250 he only mentioned the reversed rotation and not the change in big end pin diameter. Why didn't they change back to the pin size and conrod from the RSW if that was better? Sounds like a rather simple operation.

I remember the RSW use the top crank to drive the input shaft of the gearbox while on the RSA the chassis designer wanted a higher placed output shaft. So here the input shaft was lowered and the lower crank was used to drive the gearbox and then the rotation needed to be reversed.

Manuel Rainer a écrit:: has anyone tried if it makes a difference what angle has the cylinder? (vertically or horizontally or something in between). did this gives a difference in performance and has to be changed the balance factor of the crankshaft?t

I guess thousands of people have tried that over the past hundred years, Manuel. And no, it does not make any difference in performance. But it does require different balance factors.
In a single cylinder engine without a balance shaft you have to choose between strong vertical vibration or strong horizontal vibration or a bit of both. And since vertical vibration is more unpleasant for the rider, we try to concentrate on compensating the vertical unbalance. That means a high balance factor for an engine with a vertical cylinder and a low balance factor for an engine with a horizontal cylinder.

Mic a écrit:: When Jan mentioned the power loss between RSW250 and RSA250 he only mentioned the reversed rotation and not the change in big end pin diameter. Why didn't they change back to the pin size and conrod from the RSW if that was better? Sounds like a rather simple operation.

It was not that simple. The RSW had pressed-in big end pins. The RSA250 had completely different cranks with forged pins.

Nombre de messages : 86 Localisation : Australia Date d'inscription : 05/05/2012

Frits Overmars a écrit:

Mic a écrit:: When Jan mentioned the power loss between RSW250 and RSA250 he only mentioned the reversed rotation and not the change in big end pin diameter. Why didn't they change back to the pin size and conrod from the RSW if that was better? Sounds like a rather simple operation.

It was not that simple. The RSW had pressed-in big end pins. The RSA250 had completely different cranks with forged pins.

Frits what half had the big end as part of the crank wheel & would you upload some pictures ?

Frits Overmars a écrit:

Institute of TwoStrokes a écrit:: 4 Inlets an EXACTWELD 250 with variable valve timing

The Exactweld tandem twin is a very nice engine, though I haven't seen one with variable valve timing yet.
But it is even more complicated than a normal tandem twin; the primary gears have to be small because of the inlet ducts, and the cranks must be contrarotating to keep the engine from vibrating itself to pieces. So there are more gears, and more losses.

[Vous devez être inscrit et connecté pour voir cette image]

Exactweld was made many years before the Kiwi Big Horn engine, if it the engine makes more power do we worry about the loses?

Nombre de messages : 62 Localisation : Denmark Date d'inscription : 12/02/2012

Frits Overmars a écrit:

Manuel Rainer a écrit:: has anyone tried if it makes a difference what angle has the cylinder? (vertically or horizontally or something in between). did this gives a difference in performance and has to be changed the balance factor of the crankshaft?t

I guess thousands of people have tried that over the past hundred years, Manuel. And no, it does not make any difference in performance. But it does require different balance factors.
In a single cylinder engine without a balance shaft you have to choose between strong vertical vibration or strong horizontal vibration or a bit of both. And since vertical vibration is more unpleasant for the rider, we try to concentrate on compensating the vertical unbalance. That means a high balance factor for an engine with a vertical cylinder and a low balance factor for an engine with a horizontal cylinder.

Mic a écrit:: When Jan mentioned the power loss between RSW250 and RSA250 he only mentioned the reversed rotation and not the change in big end pin diameter. Why didn't they change back to the pin size and conrod from the RSW if that was better? Sounds like a rather simple operation.

It was not that simple. The RSW had pressed-in big end pins. The RSA250 had completely different cranks with forged pins.

I think this is RSA250 cranks although it doesn't not fit with Frits's description. Perhaps an early model
[Vous devez être inscrit et connecté pour voir cette image]

The engine in the lower picture is an RSA250 allright, but the cranks in the upper picture are RSW.

Invité

Frits Overmars a écrit:

fpayart a écrit:: Frits, Without wishing to denigrate the great work of JBB. I do not understand what you find so great about the configuration of this engine.
Apart from compactness of width and length, and a perfect primary balance, what are the benefits?
I found against by a number of disadvantages: the lack of rigidity of the crankshaft? the difference in length of the intake ducts.
To fill my loopholes, could you comment on your arguments in favor of this configuration. You surely have good reasons that escape me.

You already summed up some good reasons: compactness of width and length, and a perfect primary balance.
Further: simplicity (low number of parts) and hence low weight and low friction; reduced torque fluctuation during each crankshaft revolution thanks to the 90°/270° firing phase (more about this at [Vous devez être inscrit et connecté pour voir ce lien] This means less stress on clutch, transmission and tires, and the possibility to use softer, grippier tire compounds.
The air box can be smaller because both cylinders are not trying to suck air at exactly the same time. Regarding these last two items a tandemtwin engine is at a clear disadvantage.
You are right about the inlet tract lengths being unequal and about the crankshaft being less rigid, but on the other hand the crankshaft main bearings are less stressed because the connecting rod forces partly even each other out thanks to the common big end pin.
Maybe I forgot to mention some aspects, in which case I hope that Jean-Bertrand Bruneau will correct me Wink

..

Sorry i can answer in English.
Malheureusement je n'ai pu achever la mise au point de ce moteur, il est donc difficile de juger de son potentiel et de la pertinence de mes choix architecturaux.
Le point délicat était la flexion du manneton, c'est sur ce point que j'ai du travailler en priorité.
Pour avoir en même temps travaillé sur un twin Rotax avec la Rotax-JBB en 1984, je peux dire que le fonctionnement de ce moteur était assez étonnant. Il se passait des trucs bizzares qu'il aurait été intéressant d'étudier. Au niveau performance je n'ai pas de relevé de banc, mais il était largement équivalent au Rotax, mais plus vif.
Merci pour votre intérêt pour ce moteur.

Mr. Bruneau,

Merci!

Google Says:
Unfortunately I was unable to complete the development of this engine, it is difficult to judge its potential and relevance of my architectural choices.
The tricky part was bending the crank pin is on this point that I had to work first.
For at the same time working on a twin-Rotax Rotax with JBB in 1984, I can say that the operation of this engine was pretty amazing. He spent bizzares stuff that would have been interesting to study. The performance level I'm not reading bench, but it was largely equivalent to the Rotax, but alive.
Thank you for your interest in this engine.

What diameter was the crank pin?

Can you give me any details of the separation disk?

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Riley Will a écrit:: What diameter was the crank pin?

Can you give me any details of the separation disk?

Sur l'image présenté par Francis: à gauche le 1er vilebrequin avec bielles de Yamaha et 2 segments fonte pour l'étanchéité, étanchéité dynamique donc par labyrinthe.
à droite l'avant dernière version avec des bielles mécanosoudées réalisées par moi-même, l'étanchéité est assurée par deux segments acier minces et manneton de diamètre 24 mm.
au dessus (démonté) la dernière version avec bielles Honda (gp 3 cylindres) retouchées et segment idem.

La 1ère version avait le cylindre vertical dans l'autre sens, échappement vers l'arrière. Question pour Fritz: perdons nous de la puissance dans ce cas? ou le transfert arrière est-il moins bien rempli du fait que le vilebrequin ne tourne pas dans le sens du remplissage de ce transfert?

BRUNEAU a écrit:: ...La 1ère version avait le cylindre vertical dans l'autre sens, échappement vers l'arrière. Question pour Fritz: perdons nous de la puissance dans ce cas? ou le transfert arrière est-il moins bien rempli du fait que le vilebrequin ne tourne pas dans le sens du remplissage de ce transfert?

We have two effects here: a possible difference in sealing whether the exhaust port is on the thrust side of the cylinder or on the opposite side, and a difference in transfer flow balance. This second effect will be there, but it can be positive as well as negative.
Both effects occur at the same time; one effect cannot be separated from the other, let alone measured separately.
All I can say is that the combined effects do not seem to make a noticeable difference in power.

Nombre de messages : 62 Localisation : Denmark Date d'inscription : 12/02/2012

Frits Overmars a écrit:

BRUNEAU a écrit:: ...La 1ère version avait le cylindre vertical dans l'autre sens, échappement vers l'arrière. Question pour Fritz: perdons nous de la puissance dans ce cas? ou le transfert arrière est-il moins bien rempli du fait que le vilebrequin ne tourne pas dans le sens du remplissage de ce transfert?

We have two effects here: a possible difference in sealing whether the exhaust port is on the thrust side of the cylinder or on the opposite side, and a difference in transfer flow balance. This second effect will be there, but it can be positive as well as negative.
Both effects occur at the same time; one effect cannot be separated from the other, let alone measured separately.
All I can say is that the combined effects do not seem to make a noticeable difference in power.

So RSW125 has good exhaust port sealing and bad C port transfer flow while RSA125 has the opposite?

Invité

Frits Overmars a écrit:

BRUNEAU a écrit:: ...La 1ère version avait le cylindre vertical dans l'autre sens, échappement vers l'arrière. Question pour Fritz: perdons nous de la puissance dans ce cas? ou le transfert arrière est-il moins bien rempli du fait que le vilebrequin ne tourne pas dans le sens du remplissage de ce transfert?

We have two effects here: a possible difference in sealing whether the exhaust port is on the thrust side of the cylinder or on the opposite side, and a difference in transfer flow balance. This second effect will be there, but it can be positive as well as negative.
Both effects occur at the same time; one effect cannot be separated from the other, let alone measured separately.
All I can say is that the combined effects do not seem to make a noticeable difference in power.

Thank you Fritz.
Merci pour cette réponse précise car sur ce sujet j'ai entendu tout et son contraire. Personnellement je n'ai pas constaté de différence, mais je n'ai pas réellement fait d'essai comparatif pour pouvoir l'affirmer.

Mic a écrit:: So RSW125 has good exhaust port sealing and bad C port transfer flow while RSA125 has the opposite?

Maybe; maybe not; maybe the opposite. As I said, you cannot measure these effects separately, so there is no way to know.

Nombre de messages : 62 Localisation : Denmark Date d'inscription : 12/02/2012

Frits Overmars a écrit:

Mic a écrit:: So RSW125 has good exhaust port sealing and bad C port transfer flow while RSA125 has the opposite?

Maybe; maybe not; maybe the opposite. As I said, you cannot measure these effects separately, so there is no way to know.

I guess C port transfer flow is better on the RSA125 where crank rotation fits with the transfer flow direction of the C port. But the exhaust port sealing if difficult to predict. Right after TDC the crankshaft pulls the piston towards the exhaust port and makes a good sealing but after the piston reaches its maximum velocity and the crank has to slow it down it changes side and is now pushed towards C port side but now the exhaust port also starts to open and the sealing is gone anyway.

Nombre de messages : 62 Localisation : Denmark Date d'inscription : 12/02/2012

Jan Thiel a écrit:: The RSA engine was a bit of a disappointment to be true.
It only gave marginally more power.

Jan,

Was an APF cylinder ever tested on the RSW125?

Just wondering when the performance of RSW and RSA was so close and with the RSA having a better cylinder. It would then have been interesting to see this together with the almost straight exhaust of the RSW.

The first RSA tests were done at Derbi.
An RSW cylinder type APE was used.
In the beginning with a straight exhaust .
The later bent exhaust gave less power.
The APF cylinder was made at Aprilia in 2006.
It had the same transfer and exhaust ducts as the APE type Y
But it gave more power through better cooling.
It was tested on an RSW engine, as all cylinder development was done using an RSW engine.
Only once a cylinder already tested on the RSW was tested on the RSA on the same day.
On the RSA it gave slightly more HP
The biggest gain was at around 11.000 rpm, about 1 HP

Jan Thiel a écrit:: Only once a cylinder already tested on the RSW was tested on the RSA on the same day.
On the RSA it gave slightly more HP. The biggest gain was at around 11.000 rpm

[Vous devez être inscrit et connecté pour voir cette image]

Mic a écrit:

Frits Overmars a écrit:

Manuel Rainer a écrit:: has anyone tried if it makes a difference what angle has the cylinder? (vertically or horizontally or something in between). did this gives a difference in performance and has to be changed the balance factor of the crankshaft?t

I guess thousands of people have tried that over the past hundred years, Manuel. And no, it does not make any difference in performance. But it does require different balance factors.
In a single cylinder engine without a balance shaft you have to choose between strong vertical vibration or strong horizontal vibration or a bit of both. And since vertical vibration is more unpleasant for the rider, we try to concentrate on compensating the vertical unbalance. That means a high balance factor for an engine with a vertical cylinder and a low balance factor for an engine with a horizontal cylinder.

Mic a écrit:: When Jan mentioned the power loss between RSW250 and RSA250 he only mentioned the reversed rotation and not the change in big end pin diameter. Why didn't they change back to the pin size and conrod from the RSW if that was better? Sounds like a rather simple operation.

It was not that simple. The RSW had pressed-in big end pins. The RSA250 had completely different cranks with forged pins.

I think this is RSA250 cranks although it doesn't not fit with Frits's description. Perhaps an early model
[Vous devez être inscrit et connecté pour voir cette image]

The 250 RSA had normal crankshafts, with pressed-in crankpins.
It gave slightly less power, I think because of the rotation change.
This was compensated for by fitting the APF cylinders.
The end result was a slightly less powerful 250RSA compared to the RSW
I think crankpin diameter was the same as the RSW.
Once a 21,3 mm crankpin was tried on the RSW125.
It gave less power, I suppose there was more friction.
For the RSA125 a 22mm crankpin was chosen by the technical director, against my will!
He also decided on the very troublesome 8 mm disk drive shaft!
Now he is expected to resolve all Ducati's problems!
Of course I wish him good luck!

Nombre de messages : 62 Localisation : Denmark Date d'inscription : 12/02/2012

Jan Thiel a écrit:: For the RSA125 a 22mm crankpin was chosen by the technical director, against my will!
He also decided on the very troublesome 8 mm disk drive shaft!
Now he is expected to resolve all Ducati's problems!
Of course I wish him good luck!

Crazy of Gigi Dall'Igna not to listen to the guys with the knowledge

Mic a écrit:

Jan Thiel a écrit:: For the RSA125 a 22mm crankpin was chosen by the technical director, against my will!
He also decided on the very troublesome 8 mm disk drive shaft!
Now he is expected to resolve all Ducati's problems!
Of course I wish him good luck!

Crazy of Gigi Dall'Igna not to listen to the guys with the knowledge

The reason was that he did not want 3 main bearings, like the RSW had.
All I can say about that is that we tried the RSW without the 3rd bearing a couple of times.
In this condition it always gave less power!
Because the 3rd bearing made the crankshaft flex less!
The most logical thing to do, I thought, was to fit 4 main bearings.

22 years ago I had an interesting experience.
Working on a certain engine we had crankshafts with 20 and 22mm crankpins.
With a 22mm crankpin there was a LOT more power.
After some track time I repeated the same test again.
The power difference had disappeared completely!

Jan Thiel a écrit:: 22 years ago I had an interesting experience. Working on a certain engine we had crankshafts with 20 and 22mm crankpins.

That must have been the Rumi engine. But didn't we use a 24 mm crankpin then, Jan?

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

Frits Overmars a écrit:

Manuel Rainer a écrit:: has anyone tried if it makes a difference what angle has the cylinder? (vertically or horizontally or something in between). did this gives a difference in performance and has to be changed the balance factor of the crankshaft?t

I guess thousands of people have tried that over the past hundred years, Manuel. And no, it does not make any difference in performance. But it does require different balance factors.
In a single cylinder engine without a balance shaft you have to choose between strong vertical vibration or strong horizontal vibration or a bit of both. And since vertical vibration is more unpleasant for the rider, we try to concentrate on compensating the vertical unbalance. That means a high balance factor for an engine with a vertical cylinder and a low balance factor for an engine with a horizontal cylinder.

hi

thank Frits
So you can say that the balance factor of the crankshaft has no influence on the performance, only indirectly by reducing the vibrations in the motor and with this the mixture in the carburator is more stable. like Jan said.
is this right?

thanks manuel[/quote][/quote]

» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)