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Old 10-07-2020, 12:10 PM   #861 (permalink)
aerohead
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numbers @ DARKO

Quote:
Originally Posted by JulianEdgar View Post
Based on quoted top speed compared to the standard vehicle, I work it out at Cd=0.33.

Addition: When Aerohead was sending me details on his vehicle for inclusion in my book it soon became obvious that a lot of what he was saying was of somewhat doubtful validity - like an absurdly low Cd measured in a tiny wind tunnel. I then asked for the top speeds in standard and aero-modified forms, did the calculations and got a Cd of 0.37. Dr Wolf then corrected my maths and got a Cd of 0.33, the one I have quoted above. I chose not to run any claimed Cd figure next to the truck.
Some things to ponder:
1) You're comfortable publishing Cds from A2 Wind Tunnel.
2) DARKO's design consultant was Gary Eaker, designer of the A2 Wind Tunnel.
3) You have expressed a threshold of 5% blockage ratio for automotive wind tunnels.
4) Alan Pope allows 10% blockage ratio for 1:1 - scale automotive tunnels. Hucho allows 10% blockage ratio for automotive wind tunnels.
5) Hucho allows 20% blockage ratio for curved-walled tunnels.
6) Hucho allows 30% blockage ratio for adaptive-wall wind tunnels.
7) Hucho allows in excess of 30% blockage ratio for adaptive- wall tunnels if only zero-yaw measurements are targeted.
8) Hucho allows even higher blockage ratios if 'streamlined' vehicles are tested at zero-yaw in an adaptive-wall tunnel.
Please explain your conclusion about 'tiny' tunnels.

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