Vespa Dry Lake Racer lives...

[RGV]

Thanx for that Paul, very interesting results. I will have to rethink exhaust wrap on the RGV. I was going to do it to increase the RPM that the exhaust peaked out at.

I suppose the theory is there but in such a small amount that its not worth going ahead with.

[internetscooter]

Thanx for that Paul, very interesting results. I will have to rethink exhaust wrap on the RGV. I was going to do it to increase the RPM that the exhaust peaked out at.

I suppose the theory is there but in such a small amount that its not worth going ahead with.

One caveat on the results is that I did not bother checking the air/fuel - it is possible that I needed to change the jetting with the exhaust wrap. I'll leave it on and do some more tests when I have the new manifold (since that will definitely require jetting checks). I've decided to split the engine and do my final gear change so it may take a while till the next run.

[RGV]

Hey Paul i was wondering if you have messed with crank case volume at all, easy with reed valve motors. Just a matter of spacing out the reed block. Old school was to pad cases to increase crank case compression. New thinking is to increase case volume and decrease pumping losses as the piston comes down. It gives a slower charge but you have a larger volume to get the charge from. A well designed expansion chamber will draw the charge through the reeds as long as the transfer ports are open. Would be interesting to see a before and after dyno on that.

[ChrisACT]

You're right, RGV.

Crank case stuffing is very old thinking and it was the way to get more torque before they worked out expansion chambers. With a good pipe, the forces involved inside it are much bigger than those inside the crankcase. The piston does not push the air/fuel mix into the combustion chamber on the down stroke. The pipe sucks the air/fuel mix up through the transfer ports. So there's no point decreasing the crankcase volume in an attempt to force more air/fuel through the transfer ports unless you're trying to increase torque when the engine is off pipe.
Increasing the crankcase volume will allow the engine to rev a bit more freely. You lose a tiny bit of your low down torque but you can pick that up again with good pipe design. A good place to start is a crankcase compression ratio of about 1.33:1. So, if your running a 125cc engine, you'd want a 375cc crankcase volume or thereabouts.

[internetscooter]

Ok - before I start this update I'll state upfront that won't be able to make racing in 2012 but the good news is that I have the go ahead for 2013

This is a long post as I have had a few things on the go and they are all just starting to produce results now, which means in 2013 I should have a pretty mean machine!!!

1) CFD Modelling

After many many hours of banging my head against free OpenFOAM CFD software I am now getting sensible results with my 3D scanned Vespa I am able to calculate drag and how much power I need at what speed. I can also visualise the problem areas. I've evolved the motorbike example, which comes with the software, from 20 minute "toy" result, to something that is way more accurate that runs over 24 CPU hours (with more accurate runs planned). I can do a decent run over night, so this gets me a few hundred virtual salt runs before '13 and so I can tweak the body work and make it perfect

2) Bits and Pieces

The next part of the puzzle was producing the said bits above (plus also that reed manifold extension mentioned). Last week I took delivery of my CNC set-up Jeremy who fitted the KDX head, kindly retrofitted steppers to my mill head. So now I can model the bits in CAD, pop them on my virtual Vespa, race it on my virtual salt track, and then use the CNC to help produce them!



3) Gearing and better manifold

The last dyno run told me I needed taller gearing and/or higher rpm. So I rebuilt the bottom end with a taller 4th (which wasn't available to me a few years ago) and built a new shorter, free flowing manifold. I dyno'd the scoot also last week and using the CFD results and the actual power results I should hit 105 mph!!! The bad news was the manifold had an air leak, the good news is we found lots jetting improvements with the old one (and more to come with more jets).

Below is the dyno measured rear wheel power plotted against the calculated power I need to overcome drag.


So I have a lot to keep me busy preparing. Especially since I have now changed my target. It was 100mph, however Tony O'Brien in the UK just got 100.5mph. So I am now aiming for 107+mph with better aerodynamics and some radical engine modifications (more on that later when I have something to show for it). Oh - am I planning a Philip Island trip this year to confirm top speed and get used to riding it at those speeds

Cheers,

Paul

[RGV]

Thats a nice bit of gear you have there Paul. Beats my grinder and drill.

You should be able to make some cool bits for the Vespa.

So some one has got to the magic 100 mph, nice. What sort of revs are you planning on pulling?

Ive fitted some reed spacers to my bike and it seems a bit off song, Ill be able to do a with and with out up on the lake.

Good luck with your development.

[internetscooter]

So some one has got to the magic 100 mph, nice. What sort of revs are you planning on pulling?

At the moment my 100mph = 8,250rpm, so I am not anywhere near the piston speed limit. If the power was there she should pull 10,000rpm safely (and I have done that in 3rd). I only have 4 gears, so I can't put peak power up high as I need something down low to get me there

[RGV]

A guy experimented with water injection into the exhaust to cool the gas and slow the pulses. That lowered the effective peak of the chamber, opposite to exhaust
wrapping. Ill see if i can find the article.
Or maybe a programmable ignition might help give some mid range and still have over rev. Im not sure what your running, Zeeltronic has some nice features and could fire water injection as well as electronic power valves. this system can also run 2 switchable 3D ignition curves. Ive had some dealings with this guy, he is very knowledgeable on these things.
http://www.zeeltronic.com/page/home.php

[ChrisACT]

The Ignitech unit is very good and not expensive.

http://www.ignitech.cz/english/aindex.htm
http://www.ignitech.cz/english/dccdip/dccdip.htm

[RGV]

I thought you needed a laptop to program the Ignitech but you can use a hand controller for the Zeeltronic?
http://www.zeeltronic.com/page/programmer.php
But I could be wrong about the Ignitech. Both have very similar features.

Paul here is a link to the water injection i mentioned earlier.
http://www.suzuki-rg500.com/water.htm

[ChrisACT]

Yep, a laptop is required to program the Ignitech.

[JonB]

Hi Paul

What is the learning curve for OpenFoam like?
I have an old laptop I could partion and put Linux on part.
I struggle with CAD, though I did manage to make a loft of my shell in Solidworks.

Thanks
jon

[internetscooter]

What is the learning curve for OpenFoam like?
I have an old laptop I could partion and put Linux on part.
I struggle with CAD, though I did manage to make a loft of my shell in Solidworks.

I Jon - it is very high BUT I am going through and working out what bits I need to know and this can be applied to all similar projects i.e. salt lake racing Fortunately I work in high performance computing and have picked OpenFOAM as my learning project for computational science, so work is sending me on an OpenFOAM course next week

I am documenting how to do it here: http://www.vespalabs.org/Projects/Vespa_CFD%2f%2f3D_Model and once I have done the course I will be adding more accurate information. If you have a model, then I can help you CFD it...

Now the model is the hard part too, unless you have really simple geometry, it is going to be really hard to make an accurate one. I got my scooter 3D scanned, which was expensive but I don't even know how I could do it manually. Most people are after "looks" and create models from photos, mine is accurate to about 0.05mm.

As an update - I have been running lots of runs with different parameters, what that is showing me is that I need to go on the course Some changes I do which should not change the results much, change it a lot. So my Cd (drag coeffiecient) result I trust in the range of +/-10% and this needs to be a lot less if I am going to measure subtle changes. The amount of effort I am putting into this though, I am confident I can get it working (more) nicely.

[JonB]

Thanks for getting back to me Paul.

My shape is pretty simple, a couple pics of the plug for the mold in my build thread;
http://www.landracing.com/forum/index.php/topic,11024.0.html
Will just have a 100mm of the wheels hanging out the bottom.

What I'm mainly interested in is yaw stability, is that something you can do?

Do you work for beer?

Thanks
Jon

[internetscooter]

Ah - yes that should be easy to model - I dreamed of building a Vespa streamliner replica and actually started modelling a similar shape by hand (i.e. generating the points through code). There are some tools mentioned in this thread that can generate airfoil shapes http://www.dlra.org.au/forum/viewtopic.php?f=6&t=1030 e.g. JavaFoil

Yaw - I am not touching yet, but I will keep it in mind while going through stuff. It could be as easy as placing the model at an angle relative to the oncoming air. I will definitely be looking at the lift forces, so it probably won't be too different. Wind gusts though I think will too hard for me and I am also guessing modelling rotating wheels.

Yes I work for beer - work is the scourge of the drinking classes I have no problems sharing what I do, it helps me learn, see if you can create a model and we'll give it a whirl.