I'm going to have to pull my BE (Aero) out here and agree that the bottom of the windscreen is a HIGH pressure area. But why would you believe me just because i read a few books, did a bunch of experiments, another bunch of assignments, and passed some exams?
How we can prove it is high pressure scientifically is not with tape or tufts, that will only tell you direction of flow if there is any and if it is turbulent or laminar flow. It is not a measure of pressure.
To measure pressure you need to build yourself a U-tube manometer, which is a device for measuring relative pressures. Graham will be familiar with the calibrated manometer that he uses for flow testing heads, but this is a little less than mobile because it is designed for a specific purpose and mounted to the bench.
The simplest way to build one is to get some clear plastic tubing long enough to reach from inside the cabin to the area you want to measure relative pressure and tape/clip/glue it in a U shape to a piece of white board that you can mount in the cabin, or have your assistant hold. Fill the tube with just enough water, mixed with food colouring to make it easier to see against the board, so that you can mark the movement of the water one way or the other on the board. Each end of the tube can now be taped to the position you want to take relative measurements of. I would recommend one end remain in the cabin and the other be moved at various points. Get your assisitant to take pics and log the positions while you drive at a steady speed that is the same for all measurements. To save time, build lots of parallel U-tubes and tape the measurement ends at the various points.
If you want to remove any measurement bias that may be caused by the direction that the end of the tube is pointing, then repeat each measurement a number of times with that end in various directions, documenting each time. If you want to measure relative to the free stream pressure instead of cabin pressure, you will need to put the end of the tube(s) parellel to the airflow far enough outside the body of the car that it is not affected by the boundary layer.
By comparing how high or low the water moves in the tube when measuring the different points you will build a relative pressure map that will confirm what is what. It will look remarkably like that picture from the MTN.
I have been here before, check out Ben's effort to work out the best plase to put vents on racing Soarers
http://soarercentral.com/sc-forum/messages/263854/341853.html.
Anyone want to take up the challenge?
I would also be interested if anyone has compared an engine bay pressure map with side mount radiator (with and without cowling, rubber shroud seal etc) to a front mounted radiator (with and without the rest of the grill blanked off), especially the pressure drop across the radiator in each case. If there is no pressure drop across the radiator, then air is not going to flow through it very efficiently, hence poor cooling.
If only i had the time . . .
cheers
michael
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It was a pleasure ausmini. I'll miss all you misfits and reprobates