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Author Topic: Anybody smart here?  (Read 11341 times)

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Offline Bratfink

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Re: Anybody smart here?
« Reply #15 on: August 22, 2017, 09:18:07 AM »
Just wondering if anybody would have any idea how to calculate how much down force a rear pro mod wing would generate with different total surface areas for length and width and then say if you increased height of the back end of the wing by say 5-7 degrees max.

From what I understand the wing allows the air going over the top of the car off the back end to have a less turbulent boundary layer that creates rearward suction and drag.  

Can anybody point me in the right direction? Thanks!

Short answer is: Depends on the NACA profile.

There are L/D plots for angles of attack published for most NACA's. However, a Promod wing will likely not be in the published tables. The NACA tables are not published by calculation but by physical testing. Any test data on race car wings is usually propitiatory.

Since stall positions are affected by more than just airflow (particularly in cars on the ground) Lift and Drag profiles are not necessarily going to reflect the NACA tables either. And even CFD struggles to predict this (which is why you need to take most CFD data with a pinch of salt unless there is serious tested verification to prove the model).
Can it be calculated? Yes. Do you want to? No. Best solution = A day in a Wind Tunnel.

Now which wind tunnel.... that is a whole new can of worms! Tunnels can be wrong too.

Look for: Reynolds Sensitivity, Boundary Layer Displacement (Rolling road vs Static ground), Blockage Ratio and Static Pressure Gradient. If they can't answer any of those questions, look elsewhere. (And even if they can answer them, make sure they are the right answers).