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Vents

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GeoffBird View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GeoffBird Quote  Post ReplyReply Direct Link To This Post Topic: Vents
    Posted: 29 October 2019 at 9:17pm
Yes, the rear of an airfoil is a high pressure zone and the widest point, a low pressure zone, so you'd expect air to enter the rear wheel aperture and exit the front wheel aperture.
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Balor View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 29 October 2019 at 9:38am
Something does not add up - shouldn't air move from high pressure to low pressure?
I think you meant that rear wheel is "high" pressure area, which makes sense given airfoil pressure distribution.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2019 at 4:16pm
The rear wheel usually runs in a low pressure area so air usually goes in rather than out at the rear wheel. Completely Overzealous is designed to use that effect for ventilation.

Roy 
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simon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote simon Quote  Post ReplyReply Direct Link To This Post Posted: 16 October 2019 at 9:07pm
You need airflow so I was wondering how to exhaust better than just around the back wheel which can’t be that good ,or if the wheels were covered so it couldn’t exhaust ,would a side duct of any type be better than a hole at the rear end where the two sides join
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brucey Quote  Post ReplyReply Direct Link To This Post Posted: 09 October 2019 at 9:54pm
there are two problems with internal airflow

1) internal drag; the airflow inside the machine isn't for free. 
2) external drag; subtracting air from the flow and then adding it again may increase the drag significantly. 

If you want to estimate the 'cost' of the internal  airflow, just imagine what it would take in the way of fans (when the machine is stationary) to shove the air in the directions it goes in when the machine is on the move. 

Estimating the effects on the external drag is more difficult.  It is not too difficult to arrange a reasonably efficient air inlet (eg at a stagnation point on the front of the machine) and even 'scraping' some of the flow off the outside of the shell (e.g. via a slot) probably isn't that bad either. The biggest problems come with the exhaust; you stand every chance of generating turbulent flow, or even  inducing flow separation on the lee side of the machine. 

I have always thought that perhaps,  if the exhaust were configured in the right way, it could possibly be made to help the flow remain attached rather than hinder it.  Sure, there would likely be some kind of an (increased internal drag, probably ) penalty for altering the exhaust, but maybe this could be made to 'pay for itself' by allowing a different fairing shape, eg allowing a more adverse pressure gradient, and a smaller wetted area or something?

FWIW NACA ducts, even as inlets, may not be the best solution for HPVs. They were designed as a low(er) drag inlet vs a raised scoop, for use at high speeds.  However they have consequences; one of which is that the boundary layer downstream of the duct is pretty messed up and  this is unlikely to be desirable on an HPV. With a NACA duct you lose much of any ram effect; is it, I wonder, possible that a smaller duct which retains more ram effect could be a better duct at low speeds because it flows better?

cheers
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GeoffBird Quote  Post ReplyReply Direct Link To This Post Posted: 28 September 2019 at 9:37pm
With a streamlined bike, the air probably exits out of the hole for the front wheel, as long as it's not sealed, as this is a low pressure region.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 28 September 2019 at 9:08pm
For better cooling insulating (foam-core or even foam-sheet) shells are preferable, painting it white and it might be possible to incorporate some evaporative cooling as "low-tech" temperature control. We already have some built in, but it is possible to lose water to sweating faster that it is possible to absorb it, so having a spray bottle handy might be helpful.
More advanced, semi-automatic methods might be employed for indirect evaporation cooling in case of high humidity, like making some shell panels of absorbing (think melamine sponge) material and wetting them out using capillary action or low-powered pump.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 28 September 2019 at 8:21pm
That's a good point... however, both leading AND trailing edges of a streamlined body are high pressure zones, and dumping ventilation airflow at the sides would likely lead to bad aerodynamics.
I think using battery powered fans is a better idea, but it is not a strictly HPV solution (so are battery-powered lights though).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2019 at 9:16pm
Probably only an issue if it was possible to build a sealed bike, but as long as it has wheels in contact with the road......

Roy 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote simon Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2019 at 3:24pm
After the worlds this year I was wanting to increase air flow to the rider and we noticed no out vents on faired bikes
SIMON
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