mick1 wrote:Does the riders weight effect these results, if so how is that inputted as a variable ?
yes it does affect performance like riding with a passenger for some ,theres loads of input screens to put the data into
engine / gearbox / clutch / chassis+rider / conditions
Adam_Winstone wrote:"ps we ran a huge 3.7 gearing on the group 6 look at the huge drop 1st to 2nd"
So, running a 5-speed (if one proves to hold together in such a powerful motor) and the right ignition profile, so that it is back onto the power quicker between gears, and you could ride it without feeling the massive dip in power between changes? Long gearing and the power to span the changes, now there's an idea
Adam
for road use/ease of riding (as u know better than me) better to select a power curve from pipe and porting with a wider spread of power than try to improve a bad curve ,if you look at the dyno graphs area youll see various power curves ,its good to look at the shape of the power curve and the resulting shape of the torque curve as initial perceptions normally think the opposite if you were to solely look at the hp graph ,you need a rising to a peak power curve to achieve a table top shaped torque curve
take a look at 4th gear from its base thru to its peak ,you can see how close it runs to the resistance curve meaning its very close to being maxed out on its ability to pull much higher gearing as doing so it just wouldnt pull 4th gear
Darrell Taylor wrote:This is the info i pulled together when Ian Campbell visited me, i put his weight and my gearing data in and the revised power figure it made with the fan removed (43.6bhp) to do the Elvington 1-mile sprint. The data below is as per Monday's runs at 117 and the 2nd day we ran just 1 tooth less on rear and it ran 118.6mph. This is as per rich settings as ran on Dan's dyno, apart from fan removed. It didnt get up to temp on that jetting so dropped a few jet sizes to acquire the correct temps and the times came good.
So forgetting full bodied scooters for a while and concentrating on world record breaking scooters with mega speed records, what does all this technical stuff mean? Can you tell us for example what power is needed to pull either 132 or 138.5mph? The reason i ask this is because Madspeed say on their site that they have a sprinter which did 138mph http://www.madspeedperformance.co.uk/TU ... fault.aspx is this even possible? Aside from Madspeed, Keith Terry is said to have done 132mph on the Kursaal Flyer using a cast iron barrel with pacemaker box and 22/46 gearing, which means he would have had to hit 10,000rpm at least to hit 132mph.
Can you do simulations on your software to say what BHP would be needed in both these instances?
Are there any other record holders over 120mph or just Madspeed and Keith?
Darrell Taylor wrote:the only conclusion ive drawn is to do as im told the americans do and look for repeatability and/or machine history
the official record events/2 way pass is the most reliable
That sounds vague? What do you mean?
I dont follow sprint records, but i will be doing from now on as I'm having a crack next year.....i know Stuart Owen has a wealth of results behind him and those are consistent and repeatable as i understand. However i didnt even know Madspeed did sprinting? And, dare i ask....apart from the one 132mph run we have all read about from Keith, are ANY of his other runs close to that in any way shape of form from his sprinting history?
drunkmunkey6969 wrote:I know Avantone did a bit on this and am waiting to hear back from him, i cant remember what his calcs said but im sure he had some sort of graph/resistance curve also???
It was something I posted in 2008 on the old forum.
The point I was trying to make on the Super Monza thread was that at those sorts of speeds, aerodynamic drag is having exponential impact in terms of power vs speed, so you get to the point where drag is a bigger factor than power. Hence why I said...
Avantone wrote:Over 60 it's all about aerodynamics - machine AND rider.
You could do it on 30 and fail with 50 depending on the above.
Think I worked out that you could hit 70mph with just 13bhp, but would need to more than double that for an extra 20mph (90mph). To achieve just 10mph more and reach 100mph would need at least another 10bhp! (almost the same power that originally got you to 70mph)
This is because head on, standard scooters have horrible aerodynamics in every aspect. On Darrell's model different machines would have different aerodynamic profiles, and as the gains achievable in increasing power diminish, you'd have to look at either a design or changes that would flatten the drag profile. That way you could go faster with the same amount of power with the appropriate gear ratios. You'd also have to have a steady enough power profile to prevent a flat spot causing drag to overcome power at that point and therefore stopping you moving further up the RPM/Power curve.
The rider also makes a massive difference, and how small (in volume) and prone a rider is will make a difference to that drag profile. Ideally the rider would be invisible head-on with legs forward behind the legshields, and a very flat back and no gap between their chest and knees (how many of us can still do that?). You could argue that if you can't get in that position and have poor flexibility, having a low sports seat is a bad idea, and you'd be better with a higher seat to enable you to get a flatter back and lower shoulders.
Without a windtunnel it would be difficult to improve a standard scooter, but the shape of the trailing edge on the legshields is a favourite for subtle improvement, followed by the headset, front mudguard, wheel/fork profile and underneath. You then get into consolidating smaller gains with questions like "why is the gear-changer in it's least aerodynamic position at it's highest speed?"
There is some basic but interesting CFD modelling which shows how and where drag builds as speed increases
Red indicates high pressure areas, grey indicates low pressure areas (drag)
Last edited by Avantone on Fri Dec 13, 2013 4:25 pm, edited 1 time in total.
drunkmunkey6969 wrote:I know Avantone did a bit on this and am waiting to hear back from him, i cant remember what his calcs said but im sure he had some sort of graph/resistance curve also???
It was something I posted in 2008 on the old forum.
Thats the post i have been looking for! No wonder i couldnt find it, as it was on the old forum.
Here's what the old thread said all those years ago (in case you cant be bothered to click the link!)
Avantone wrote: I think it’s fairly well accepted that compared to modern day bikes and scooters, Lambretta’s (and Vespa’s) are pretty brick-like and heavy which makes getting significantly better performance both difficult and expensive.
I’ve also been thinking for a while, how fast a standard engined scooter could go with the benefit of some wind tunnel modelling. Now the challenge here is to do something that helps the aero profile of the scooter whilst still retaining it’s clear identity.
If you go down the power route to increase speed, doubling the maximum speed requires an 800% increase in power!
I’ve based the table above on the power required to increase the top speed of a 65MPH/11HP scooter. As you can see, to hit 90MPH needs an almost 300% power increase.
Wouldn’t it be easier to improve aero dynamics? (Mostly talking racers here for the purists). We see cutdowns, but does that really help? It generally doesn’t improve the frontal area, and actually hinders the way airflow is managed round the rider.
So any thoughts? Any budding aerodynamicists out their? Anyone want to lend me a wind tunnel?……………….
