@Z I did your water bottle experiment with a shop vac cleaner (a big one) - could pick up up to 0.8 lt of bottle without any gap .Using tooth picks i found (apx 2mm thk - not 1mm like in your experiment i couldnt lift it and went for 0.5 lt which i could not lift either -settled for apx 0.35lt which i lifted
Upon close inspection there is something important that happens to the bottle as the vac hose approaches - they deform making the leakage smaller so the suction stronger (try to approach the hose slowly to the bottle and see the bottle deforming (at least my 0,4-0,5 thk bottle did that
So the gap between the road and the skirt seems to be a super important factor
Curiosity led me to ask a friend to look at the back of his vaccum former/thermoforming machine where he found a radial flow snail type fan - as Z proposes but in this application we have no gaps. Try leaving a thermoforming polycarbonate sheet to stay a bit more over the oven of a vac former, during the upcoming forming process it is possible that due the extra sag from the extra unwanted heating that we introduced , the sheet will become so thin that upon vacuum over the mold a small hole will open up somewhere and suddenly all pressure is lost and we possibly have to bin the part...
So why leave ANY gap if it drops the vacuum performance so much , why did Chapparal 2J as well as the Cheapparal Vette leave apx 12mm distance from skirt to road? (the 2J went to great length to keep the movable lexan skirts at constant gap with the road with a specially designed mechanism) , why not just leave 2-3mm and form the front part of the skirt V shape as a ship (or put a V shaped rubber sweeper in front of the skirt ) as Z commented so that the debris is not stuck in the minimal gap ?
The answer (in my opinion) is to let the actual engine of the vehicle propel the thing forward and not stay stationary!! Remember the road & track competition mentioned on the "Build my own sucker car " thread ? Someone mentioned there the same thing happening to a modified vacuum kart - had difficulty moving! I guess since he had no suspension or adjustable height skirt he actually had to play with the vac engine throttle or openings in the vacuum floor to get the thing moving ....
Try to put the vacuum hose of your vac cleaner on the ground and moving the vertical hose across the ground and then putting some distance and moving it - it was much easier for me
I guess when introducing a gap the benefits from the radial fan evaporate as you obviously have to draw much volume of air to create the needed pressure difference - i dont know obviously the characteristics of a compounded radial fan set up but the gut feeling i am getting is that there is significant airflow taking place in the case of the 2J and BT46 so that their axial fans are not stalled
What do you people think?
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