Talbot Frameworks PRJCT SLVLSS

The head tube is right out there in the breeze, and a circular cross section is really bad for your aeros. Almost anything you do to the leading edge is likely to be an improvement.

Trailing edge, surely? A teardrop shape is as aerodynamically efficient as it gets, with a rounded front end and a pointy tail. If you look at any fast road or TT bike which has had wind tunnel time, it'll have a rounded front edge on the HT and then a tapering section behind it.

The majority of the drag doesn't come from the air hitting the rounded front of the head tube - it comes from the vortices from the trailing side of a round tube which are eliminated (or at least substantially reduced) by a tapered trailing edge.

In which case, some sort of webbing between the TT and DT would be optimal...

The Central section of the headtube only needs to Clear the 1 1/8" steerer. So could be squished a bit.

Possible. I could turn up some steel sinks for the bearing seats, make an elliptical tube block and vise it, it's not very thick.

Yep. A bit of the DT material with the front cut off, and then opened up to 31.7mm (I'm assuming you're going for a 1" fork) would do nicely I would've thought.

I agree with tester about the TT though - I can't see stiffness being and issue, and given that vertical stiffness is guaranteed from the tube shapes, I would've thought a flat oval TT, with the thick plane being horizontal, would be best.

P.S. Also agree with tester about the external headset cups - the thinner HT is a worthwhile trade-off.

This^

With bottle Mounts on the tt.

what sort of volume would be described by the inside of the top tube if a highly ovalised profile was used? Over a litre?

Y U UCI compliant?

ITU build rules FTW.

And even then - even for AG events, nobody really checks...

Weeeeell, and yes, I can see where you're going here (internal drinks bottle), let's say the TT has the same width as the DT and ST (24.8mm) and has a half-inch depth (12.5mm) and is 530mm long. If the tube is a perfect elipse then the cross-sectional area is 12.5 x 24.8 x pi = 973.71mm2, giving a total volume of 516k mm3, or just over half a litre.

The difficulty in using the TT as a drinks bottle would be getting the fluid from the TT into the rider's mouth. The aero testing I've seen on BTA drinks bottles shows that straws poking up from BTA bottles are horribly un-aero, and I'd assume the same would apply to anything poking up from the TT.

Would also be a bit shit as a drinks receptacle with parallel TT, so either slope TT, or have normal(ish) hydration system. Love that phrase...

normal(ish) hydration system. Love that phrase...

The journey to full slvless is almost complete.

You need to talk about nutrition plans now.

Now this is getting really good! What about keeping the round HT but have a custom made fabricated hydration receptacle that slotted in behind, providing a super aero 'tear drop' shapped HT/TT/DT junction. The straw could be a long retractable thing that spent most of the time IN the receptacle and could be pulled out via a hole in the TT to drink then quickly pushed back in. Only an inch or so of straw would be poking out behind the stem. You might have to anchor the bottom of the straw to the bottom of the receptacle with a clip or something.

fires up CAD

Edit. The fabrication could be a structural part of the frame. Then you'd just need a bladder of a similar size and shape.

Statistically, if you all keep saying what you think someone will get it right in the end...

Sounds like a plan. Commence rabble.

Monorail! That's right, monorail!

Some sort of magnet system maybe?

Trailing edge, surely?

Trailing edge is for marginal gains, all the hard work is done by the leading edge. A circular cross section so fucks things up that there's almost nothing you can do apart from starting again with something wider that's a good shape, that's why the best aero rims are now wider than the tyres in front of them. It's also why those 90s "Aero" tubes which grafted a trailing edge onto a round tube ended up working better when turned around, and it's why a proper Kamm tail has so little effect on total drag.

The front half (i.e. from leading edge to maximum thickness) of a minimum drag aerofoil is rounded, but it's nothing like a semicircle.

But how do we know when that is?

rabble rabble rabble

I'm not sure that's correct. My understanding, admittedly based on motorsports wind tunnel testing and CFD work rather than for bicycles, is that it's the trailing edge which is most important, hence why a teardrop shape has a much lower Cd figure than a reverse teardrop shape:

Also, if you had the pointed end at the front then the drag profile would be very susceptible to yaw. It might be aerodynamic if the airflow was from directly ahead at all times, but as soon as the airflow started coming at it from an angle you'd get horrible vortices off the sharp leading edge.

I think the Cervelo RCA white paper shows it most clearly at Figure 16. If the leading edge was most important, then the oval shape would be superior to the teardrop aerofoil shape.

Edit: Found figure 16 as a .gif, it's here:

P.S. It also shows that a Kamm tail (the third profile) is better than a circle, but still nowhere near as good as a teardrop shape with the same front area.

My point really was that if the front half of your shape has fucked the airflow, you can't get much back with the back half, and a semicircular front half has already fucked your flow. If you imagine modifying this aerofoil into two competing shapes, one with the original nose followed by a semicircular tail and one with a semicircular nose followed by the original long tail, you should find that the one with the original nose has the lower drag.

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a Kamm tail (the third profile)

I don't think that's a true Kamm tail, it turns out that you can't chop off the whole tail and still feel the benefit, you have to leave it until the thickness is about half the max thickness.

Drag cofficient (Cd) is not a constant. It depends on size and speed (reynoldsnumbers and so on...). At bike speeds, Cd for different shapes (including airfoils) are much higher than for airplane/car speeds.

Model airplane aerodynamics seems to be the closest match for bikes.

Hmmm, I wonder if that's right. Might have to call in a favour from a friend studying CFD.