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

Frits not Fritz

Sorry

Frits Overmars a écrit:

Nice logic, Marc! OK, the engine produces 52 hp. But if you remove the spark plug, it produces zero hp. So the spark plug alone produces 52 hp? Let's build twin spark engines then! Or triple spark. Or quadruple spark. Or ..... what comes after quadruple ?

Hi Frits,

dont spread out too much information - those French might become to competetive once they decide to join our SOBW championship for 2011! :)
just teasing - very usefull information

jenne

Don't worry, Jenne, everybody is welcome; the more the merrier.

ridley a écrit:

have you ever used ceramic bearings on your crankshaft, and what do you think of this application.

Yes I have, but not the way you probably expect. We did not use them in a 125 cc engine, but we do use hybrid bearings (steel rings and ceramic balls) on a 6,5 cc model aero-engine named the MB40, which is used in F3D pylonracing. It's not doing too bad (world champion for the last 8 years or so). Like most model engines it has a hollow crankshaft serving as a rotary valve. The ceramic balls run directly in a groove in the crankshaft. A set of balls cost €7 if I am not mistaken, and they last forever.

Engine data: bore 21 mm, stroke 19 mm, compression 14:1, exhaust timing 190°, transfer timing 128°, maximum rpm 35.000, fuel is methanol (no nitro!) with 20 % oil (I would be happy with 4% oil but you have to use the fuel that is supplied by the organizers).
The biggest difference with other model engines is the cylinder; to make it thermally sound I designed a sleeve-less cylinder with a chrome bore. Nikasil is necessary when you use chrome-plated piston rings, but there is no piston ring in the MB, so we don't need nikasil; chrome is good enough.

O yes, top speed. A couple of years ago I tried to clock a model with a radar gun. Flying straight towards me would have given the best speed reading, but I objected to that.... I clocked it from behind while it was in mid-turn. The speed then was 346 km/h.
We also put a g-sensor in a model to measure the lateral acceleration in corners, but we still don't know how many g's it was pulling, because the sensor only went to 36 g....

EDIT: I also found a little impression on YouTube. The guy with the white ear-warmers, that's me 8)


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Frits Overmars a écrit:

EDIT: I also found a little impression on YouTube. The guy with the white ear-warmers, that's me 8)
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Blood and guts!! what a mosquito sound! and it seems working very well!!!!


the cylinder really looks like a "real" sportbike one!

R/C cars is one of my hobbies, and "our" cylinders are really different...


is there any kind of carb on these engines ?
why is there a landing (good word??) in the crankshaft, juste close to the web ? there is'nt any interior cage on these bearings ?


thanks Frits

Shining a écrit:

the cylinder really looks like a "real" sportbike one!

R/C cars is one of my hobbies, and "our" cylinders are really different...

yeah I noticed that too. impressive design for an RC.

Frits said that the ceramic balls of the bearing run directly in the groove in the crankshaft, so there isn't the inner ring.

sorry, I didn't notice

Shining a écrit:

is there any kind of carb on these engines ?

No. The inlet is always fully opened. The pressure of the exhaust pipe is used to pressurize the fuel tank; the fuel is injected through a needle-regulated spray tube. To shut off the engine a servo-motor pinches the fuel line shut.

Citation :

why is there a landing (good word??) in the crankshaft, juste close to the web ?

Sorry, I did not understand this question. Please try again in French (or Dutch, or German, or Italian, or Spanish 8) )

Citation :

there is'nt any interior cage on these bearings ?

There is no internal ring; the balls run directly on the crankshaft, as nasone32 explained. There is a cage hower, as you can see at one of the pictures. We take a normal ball bearing apart and use its outer ring and plastic cage in combination with our ceramic balls..

Frits I'm wondering if the dimensions of the expansion pipe changed when the disc was moved to the rear? The rearwards facing exhaust was very straight, which would be very efficient compared to the conventional expansion pipe mounted under the the engine?

Frits Je me demande si les dimensions de la conduite d'expansion a changé quand le disque a été déplacé vers l'arrière?
Le dos à la route d'échappement a été très simple, qui serait très efficace par rapport à la conduite d'expansion classique monté sous le moteur de la?

Are the model aircraft had to see at those speeds. I watched a ducted fan model flying and it was difficult to see when going fast, the pilot had to bank it over periodicaly.

Institute of TwoStrokes a écrit:

Frits Je me demande si les dimensions de la conduite d'expansion a changé quand le disque a été déplacé vers l'arrière?
Le dos à la route d'échappement a été très simple, qui serait très efficace par rapport à la conduite d'expansion classique monté sous le moteur de la?

The Aprilia RSA with the curved forward-facing exhaust and the older RSW with the straight rearward-facing exhaust use the same pipe dimensions - in theory at least, because you simply cannot keep everything identical, like external surface area, for example. A straight pipe should be better, but the difference was hardly noticable.
There was a much bigger difference elsewhere: in handling. Because of the forward-facing exhaust the RSA's engine had to be mounted further away from the front wheel. That changed the weight distribution (Eric Offenstadt might correct me and call it mass distribution 8) ). Many former RSW-riders could not get used to this and complained about front fork problems and lack of feedback. The problem still exists...

Very interesting explaination.

Thank you Frits!

oops I forgot, Frits is the patten that is machined into the disc housing there for any reason other than lubrication?

Oops j'ai oublié, Frits est le patten que c'est usiné en le disque logement là pour une raison autre que lubrification?

Institute of TwoStrokes a écrit:

Frits est le patten que c'est usiné en le disque logement là pour une raison autre que lubrification?

Yes: to reduce friction. As any mechanics student will tell you, dry friction only depends on the force that pushes two surfaces together, and on the material of those surfaces. How large the area of these surfaces is, does not matter.
That is, until you put oil between the surfaces. Oil reduces the dry friction between the surfaces, but at the same time introduces an unwanted phenomenon: viscous drag. And that is dependent on the size of the surface areas. The picture below shows an RSW, simply because it is the clearest photo I could find; the RSA has an identical surface.
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Frits Overmars a écrit:

Citation :

why is there a landing (good word??) in the crankshaft, juste close to the web ?

Sorry, I did not understand this question. Please try again in French (or Dutch, or German, or Italian, or Spanish 8) )

Citation :

there is'nt any interior cage on these bearings ?

There is no internal ring; the balls run directly on the crankshaft, as nasone32 explained. There is a cage hower, as you can see at one of the pictures. We take a normal ball bearing apart and use its outer ring and plastic cage in combination with our ceramic balls..

you've just give an answer @ the question you didn't understand.

in fact i just didn't remember the answer was in your previous post



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holly shit!! it can breathe very well!

Frits, I would be glad to have your help.
I am promoting the culture of two stroke in the Italian scooter scene, which is getting very big and with massive two stroke developement, everybody must know that this engine is still alive and has still much room for development.
An Italian Journalist, Pierluigi Mancini, believes that he is the two stroke-god on earth and thinks he knows everything about this engine, he is completely closed-minded and he doesn't want to listen to me even when i explain everything deeply and with much data. he is blocking the development of two stroke engine doing this.

I posted the photo of your fantastic 24/7 reed valve and he says it doesn't work, he says he phoned to Joe Romano and other things so I would like you to write just two words about your valve. not one word more, I know you must have very little free time so I don't ask anything more.
I don't know if this forum allows external links, but if you want to give a rapid answer, here is the topic (in italian).
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I've been accused to be stupid, senseless and else, while i'm only trying to make people think, go deep on how this engine works so we altogether can make this engine better and give him longer life.
thanks

j'en connais un du côté nord de Lyon qui doit se régaler de lire tout ça sans en perdre une miette, et dont les propres productions n'ont pas grand'chose à envier à Aprilia.
Allez relire un peu le topic FPE pour voir...

Merci JP
C'est vrai qu'il y a beaucoup de similitudes avec nos moteurs.
Malgré tout, je dois reconnaître qu'il y a une foule de choses intéressantes même pour nous, j'aimerais avoir toute la science de Frits

In the end, looks like the debate on the other forum has come to an end. for now.
suddenly appeared a lot of people that broke an entire reed with the engine in the power band, and the engine kept running. this confirmed your theory Frits.
but a small post from you would be greatly appreciated if you want.

the RC engine has a breezing sound, that thing really runs fast as hell

Hi Nasone,
I've just spent over an hour reading pages 359 through 369 of the discussion at [Vous devez être inscrit et connecté pour voir ce lien] and I got the impression that you're doing fine without my help.
The video [Vous devez être inscrit et connecté pour voir ce lien] made me smile and several readers reported their personal experiences of engines that kept running with a broken reed, so that should strengthen your confidence.
Anyway, I try to promote two-stroke knowledge in general; I do not want to force my ideas upon anyone. If your opponent wants to stick to his convictions, I have no desire to make him change his mind.

EDIT: there were questions about the rpm range in which the 24/7-system could function. Let us call the the rpm of maximum power RMP. Then the system should work from about 0,8*RMP to 1,12*RMP.
An example: the Aprilia RSA delivers its maximum power at 13000 rpm. On this engine the 24/7-system should work from 10.400 rpm till 14.500 rpm. And this is without taking into account the effect of the exhaust power valve. With the power valve influencing the exhaust frequency, the 24/7-system might work from 9.500 till 14.500 rpm.

Thank you very much Frits.
You are right, if he wants to stay in his convinctions, let's leave him do. I was disappointed because he is considered like a sort of guru, while he is only a journalist with an average knowledge and a really closed mind.
but our work is promoting knowledge and we should not force anyone in this process. (I know maybe one hundredth of what you do, but i really feel like i'm involved )
Reading your answer here to my post made me very happy, really. And you are a really kind person, i am grateful.

edit: hai ragione ora di dormire, but you are awake too!

Hi Frits,
Last time I told you I will show you some new drawings of a construction idea for the 24/7 inlet, but I have little time at the moment. So I don’t wanted to waste time for drawings and I decided last Sunday(a little in hurry) to build a pretty simple kind of 24/7 valve. Here some pics of it.

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And this afternoon I put it on a engine at the dyno, (90cc, 50mmbore46mmstroke, 6speed Minarelli AM6, ReedValve engine).At first the engine stops running if I opened (I opened by 11.000 rpm, engine got max hp by 13.400,max torque 12.900)the valve by full throttle on resonance rpm, but after some hours of carburetor setting the engine took on gas with an really nasty sound!! I will do some test at the dyno tomorrow and will tell you what’s happened. So I can say there is no question if it works or not , there is only the question how long does it take to cultivate the system.

Well done, Michael. And so quick! I wish all my ideas were realised as quickly as this one...
The best way to adopt your engine to this system is probably to make the crankcase volume really large, but that is not something you can do in a hurry. What you can do in a hurry, is putting exchangeable distance pieces of different lengths between carburettor and valve.
What carburettor diameter did you use?

Its an 35mmKeihin and I use a 57mm long cone before the carb.

Michael Burgard a écrit:

Its an 35mmKeihin and I use a 57mm long cone before the carb.

35 mm is certainly big enough. With your 'cone before the carb' do you mean between the carb and the outside world? It is better to have a short bellmouth with a big radius at the outside of the carb, and distance pieces between carb and valve.
The carb should be more or less on the outside end of the intake tract; if it is somewhere in the middle, the pulses in the tract have a much stronger influence upon the fuel level in the needle holder, and that may be very confusing. Maybe you could ask for an injection system for Christmas....