Dry Lakes Racers Australia

The blower is a centrifugal one so it gets more efficient at higher RPM. This should in theory make the power curve more like the power to overcome drag curve, so I get power where it's missing (i.e. it keeps heading north after 95 mph). It was also to change my class as chasing 130+ is kinda hard (especially with no tyres rated that high), chasing zero is a bit more doable

Still packing... heading off Saturday morning...

Ok it's been a long drive back - I will do a full write-up and add a link - the short version is that I did 89.664 mph after lots of challenges. That time was a flying mile!!! Due to lake issues the track was moved and instead of measuring the time over 1/4 mile I had to do full throttle for a full 1 mile, through what felt like a beach which had loads of 4wd tracks through it - my arms are still aching.

The main issue was that I could not sit in the low down position I did all my calculations on as it was WAY too unstable When my weight went past the rear axle it felt like I was riding backwards. If I had taken the screen and the track was good and had only 1/4 mile timing I might have got 95mph (so still more work required for 100mph+)... Also I need to factor in the parasitic loss of the salt...

Thanks Tiny, Bob, Graham and Ross for the support!

It was a great week and thanks to all the organisers you have done a brilliant job!

Well done Paul,
The salt is a harsh Mistress

Chris

Yes indeed - I still am scratching my head and need to dyno the scoot to see what is up. I went through my old dyno results and mapped it against gearing and even adding a 20% increase in frontal area (because I could not sit as low) and 20% increase in Cd I still should have seen 100mph. The way the scoot behaved (struggling to change from 3rd to 4th and keep accelerating) suggested I had half the power I thought I had. Or maybe if my chest is at a certain height, I became like a parachute directing air into the void rather than over the top?

For those that did 100mph+ what was the Hp you needed?

Hi Paul,

To answer your question, and i might sound stupid for saying this after 300 dyno runs: 'I think' I had about 35HP, but it's a very very flat curve. Still still trying to calibrate the model (which is a bit rough at best). Guessing 0.85-0.95 drag & 0.46 frontal. Was hoping to catch up with you on the salt.

1st & 2nd are short shifted

Hi Paul

It was good to finally meet you, big effort setting a PB, congratulations.

When I ran the stock RGV in 2010 in M-G-250 I discovered the importance of Aero and Frontal Area.

If I lifted my Head just the slightest little bit, my Speed dropped and I could not go over 180kph. I eventually went 119mph on the GPS track twice, so that was maxed out with about 60 Dynojet rwhp.

So I would say getting yourself as low as possible is your Big challenge.

Pete

Yes - low as possible is on my list but there are a few other things I am pursuing as the possible contributors...

I estimate that 30 Hp should be enough for 100mph and after that a rapid increase in Hp is required to make small improvements (as we all know). dplecko your results support this theory, thanks for sharing them!

One thing I am looking at is the possibility that I have generating negative pressure under my sidepanel where the carb sits. So as I get faster my power will drop.

I did a quick map of negative pressure in my simulation and indeed I see a negative pressure region developing where the carb inlet is. I have a pressure sensor which I dusted off last night and I will try an measure some real values to see what they tell me. Below is a image showing a "skin" around a negative pressure value, everything inside the "skin" is more negative than everything outside.



edit: Or it could be the cowl restricting the air outright - I don't think I have dyno'd it with the cowl on!!!

Paul, dose the "closeness" of the web indicate negative pressure regions, ??,,

Stayt`ie wrote:Paul, dose the "closeness" of the web indicate negative pressure regions, ??,,

No that is just resolution of the mesh it was calculated with - think of it as a balloon in "opposite world" - if you could blow up a balloon with negative pressure that is the shape it would make. Hope that helps explain

yep,yep, thanks,, ,

More evidence that 32Hp should be enough - Tony O'Brien just got 116.2 mph in the UK! He has approx 32Hp but a lower frontal area.

http://79.170.44.125/green-hornet.co.uk/?p=1030



I need to get to a dyno...

Nice result but the big white dyno seems to suck top speed. No way my bike will get to redline in the top 2 gears on the lake. No over rev. It hits max HP and stops. Get this guy out to the lake.

Dave

Here are some numbers from our bike at Speed Week,

21 rear wheel HP - 94.8mph - with fairing, but head and shoulders still way above. Also bike 170 pounds rider 187 pounds.
Without Fairing 93.5mph bike same weight but rider 154 pounds.

I think you will need 30 plus some, its a big wall you are pushing, and for me 94.8 to 100mph is going to take a few more HP. Remember that guy who ran on the scooter in post above was top speed, its another game to hold it flat out for a mile and another mile run in. We also had wheel spin even at low HP, it like the salt just moves, so another 5% loss there.

Why bugger around, boost her up for kill and grab 40hp and blow through that 100mph .

Great meeting you at Speed Week.

JP

Agreed with JP. Unless you want to chop your bike half, HP is gold. Just make sure that it makes more HP the longer it runs (one minute @ 100%) not the other way around...