90 degrees to airflow is what I was trying to tell you. I would not protrude them, try to make them level with the cowling if you can. If you protrude them, they will create turbulance and drag. You want the air to pass over the openings of the tubes smoothly and that will create the vacumn. Larry H.
from: Dan Heath Sucking air - Oil temp problem So, I decided to put two 2" aluminum tubes through the bottom of the cowl, sort of like very short exhaust pipes, to which I will run my air ducts from the plenum, behind the oil cooler. These will protrude somewhat from the bottom of the cowl, and I think that I should cut them at an angle to create that "sucking" effect. Now for the question. Does anyone have an EDUCATED opinion on the angle, to the air stream, at which I should cut these tubes to get the maximum "suck"?
