Quote:
Originally Posted by Piotrsko
What do you think? I think not. And suprise, there is a reason for the question if you are a fan of 12-25% thicknesses NACA airfoils of the laminar persuasion with the max thickness aft of of 40%
Has to do with boundary layers being undefined subsonic (low reynolds) but still creating a very low drag profile @ low speeds
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* Well, at least you got a 'subsonic' out of freebeard. Which was the correct answer.
* And I might have further qualified the caveats with 'sub-transonic' flow.
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* I'm not a fan of any airfoils. 'ANY.'
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* If you want to 'go there,' we can sure do that. Here, where it will all get lost, and no one will know it's here, or we can parse it out into it's own, dedicated thread, which will survive into the future, and can be referred to when anyone else brings this subject up.
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I'm presently doing a sample problem with a NACA 63,sub 4 -021, LBL, symmetrical airfoil, which is probably a 'worst-case' for a 'laminar' profile.
She's rated @ Cd min=0.006, at Rn 1,000,000, to Rn 10,000,000, based upon length, 85.86 km/h ( 53.32-mph ), standard air kinematic viscosity.
21.42% thickness, occurring at 34.28% chord, provided by Professor Schlichting, 'Boundary-Layer Theory', 7th-Edition, Figure 2.21, page 38.
* I've set the section thickness to 49.3-inches ( 1252.2mm ) in order to provide the driver and front seat passenger as much vertical interior clearance as a Toyota Prius.
* It's not looking so good so far, but I'll save the gory details until I've completely hashed it out.
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* If you wanted to select a more 'traditional,' non-symmetrical, laminar section of your liking, you could also scale it's section thickness to 49.3-inches, for easy comparison.
* At the thickness ratio of your choosing, that will fix the car's total length.
* That will allow Rn calculation at any given road velocity in calm air.
* Which will tell us what the boundary-layer is going to be like.
* The wheel placement will need to respect the 16-degree, double-10-degree, and 10-degree, SAE 'approach, breakover, and departure' angles from the roadway.
* That will fix the car's ground clearance and overall height.
* Which will also fix it's effective fineness ratio in mirror image reflection.
* Which will inform us about the lowest Cd it would be able to achieve at supercritical Reynolds number.
* Then we can compare it to other architectures.