Blisters and bubbles aren't the ideal aerodynamically - a homogeneous shape is better as there is less parasitic drag, but if you are designing a circuit racer (or road machine), as opposed to a Battle Mountain machine, then it has to be practical for use in a wide range of conditions otherwise that theoretical speed will never, or rarely, be realised.

In terms of side wind stability as opposed to efficiency, a profile that maintains attached flow in a side wind will probably be less stable as it will act like a wing or sail to create a larger side force.

New smoother nose below.

Jeff.

Looks rather good by the way 

I hope I fit in it though, wouldn't mind a spin in it, not literally of course!

A couple of thoughts about it though; with the height and length of the foot/knee bubbles seeing the apex of a bend might be a problem, of course if you take a nice safe line it won't matter, but if you want to running with a tyre on the edge of the grass it might, also i think you might have overestimated the gap between knee bulges. However without seeing scale drawings it's hard to tell, it also depends on the width of your hips and what width BB you are using of course, just sit and stick your legs out and see what width you have between your knees and then allow clearance for the bubbles, believe me knees and bubbles don't go together, and if they do blood will soon flow.

 

Oh i do like a bit of bike porn 

Bit of a curiosity question, 

When you use your cfd package to determine the flow over the shape how do you know that your predictions are close to real world(tm)? The speeds are much slower than with automotive design and with that the error factor will be larger no? 

The reason for asking is in any kind of cfd you need to calibrate your model other wise its dare I say bullsh*t in bullsh*t out? As we found with flow optimisation in a previous life playing with water treatment equipment. 

Will you expand a little.

But other wise a very sleek and lovely looking machine.. I am jealous :-)

Karl

As I said in the article, CFD is only a comparative tool at this level, so all you can do is do a baseline run and try changing things to see the effect I haven't got past the baseline yet, but do have a comparison with another shape (similar to Bubble & Squeak) using the same settings. Speed shouldn't be so much of an issue as CFD should correct for Reynolds Number, whereas this can be a problem for scale models of cars and aeroplanes in wind tunnels. So yes you're right, you have to correct against real world data to get a realistic figure (this is true for wind tunnels too). As an illustration of the problem, Miles is getting less than half the drag force with his CFD package at the same speed for a very similar shape (not mine) on the system I used (or was used for me).

We're just shining a torch into the vast darkness - we can't afford floodlights!

Russ

One step at a time...

Things such as hand/wheel interaction when turning, heel strike when getting tired, knee strike when pushing hard and accelerating, adjusting brakes, removing rear wheel for tyre change, siting of computer, drinking etc.

Also i'm interested if you are designing in Ackermann steering geometry, B&S didn't have it, i changed in as far as i could although it was still a little short, it increased tyre life and reduced twitchyness. 

 

All the things you've mentioned are things I've already considered (which is not the same as getting them right of course). I plan to do an article in the next mag about the mechanical bits but I had already been advised strongly to get the Ackermann right by someone who knows about these things.

If you could tell me your vital statistics Ian then I might be able to tweak the design so that you'll fit as well. My problem is that I have short legs, even for my height, which tends to mean lack of knee clearance etc. for others...

That's spot on as a design brief, any engineer would be happy to work from that.  Good to see you're using English measurement units.

Barney

By the way, I AM a forum moderator <Fx: evil laugh>

Cant wait to see it in the flesh.

Update: Unfortunately the resin to make the moulds was delayed at the Channel Tunnel until after the end of my week off so I won't have the opportunity to make the moulds until I get another break. I've redesigned the rear suspension as a full five link system, which, although it looks more complicated, will be easier to make. It also gives good anti-squat geometry. Images to follow in a bit.

I've started making the moulds for the bodyshell - pictures below:

 

I'd best get my skates on and build something to compete against you in.. mind you your performance at the last race I'll have my work cut out keeping up regardless of what your in!!

Karl

Would be great to see a faired Speedy on the tracks again Karl! They were in their ascendancy when I first attended BHPC races back in the early 1990's. You can get your own back then, although you'll probably only have to wait til Hillingdon to do that...

 

Not made much progress recently but here's a few more. The BHPC magazine (LaidBack Cyclist) often has build articles. This year you can get 5 PDF copies for just £6 (click on the logo at the top of this page and go to 'Shop').

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