Tweet
Originally posted by bszopi
View Post
Without putting too fine a point on it... as an aviation mechanic who flew in every plane (helicopter) he worked on in the military for post-mechanical work Test Flights as well as a SAR Crewman... understanding the basic principles of flight and the actions of fluid air on lift surfaces was crucial during Aviation Machinist School and while flying in and repairing these complicated machines. The author of that article would have you believe that when constricting an airway for an engine... or as he puts it ..."Like putting your finger on a garden hose..." that air pressure would INCREASE as a result of the Venturi shaping the air column. This is completely wrong.
The whole idea of any Venturi shaped intake passage is that by narrowing the inlet with a curve...the velocity of the air moving in the column entering the gradually narrowing tube will increase...but Bernouilli's Principle posits that the AIR PRESSURE within that moving column of air will DECREASE when passing over any curved surfaces...simply because the molecules of gas making up the atmospheric stream separate and thereby cause a substantial drop in air pressure.
You can prove this right now... right where you sit. Just take a sheet of paper 8.5" X 11" and tear off about a 1" strip... Now ...while holding one end of the strip between your index finger and thumb...allow the strip to drape over the back of your hand...Gravity will fold the strip over into a curve that in this case emulates either the curved surface of a wing structure...or in this example...the curvature of the inner surface of a Venturi Tube on an intake manifold.
Now if you slowly blow air over the surface of that strip of paper, you will gradually see the paper rise straight out in front of you. If the air comes too fast...it will cause turbulence on the trailing edge of the paper and it will flap up and down...like the stall of a wing with too much of an angle of attack on an air column. This phenomena is caused by and called the Differential Pressure between the normal room PSI around you of approximately 14.7 PSI... versus the reduction in the air pressure you have created by blowing a small column of air over the curved paper "wing".
The results of this simple experiment will prove my point. The real reason for the shape of a Venturi intake is so that the placement of the fuel vacuum in-port where fuel is taken in on a carburetor style engine will flow best at the point where the vacuum is the highest possible...because the partial vacuum present inside the Venturi chamber allows the normal air pressure present inside the fuel float chamber to push down on the fuel and force it into the intake via... Differential Pressure.
When it comes to learning anything new...I'm like Fox Mulder on "The X-Files"..."I want to believe..." But if I see something this egregiously wrong... I might have to challenge the source of this information. I'd better be right about what I have just suggested... because the millions of people who will fly around America in airplanes for this Thanksgiving Holiday...are counting on it!
Please know that my criticism is with the author of that entire article and that everyone should know that you are without fault in this situation. I'm glad to look at any other source of information on the Runner Length vs. Torque Topic if you can recommend them. I really want to know why this is true from someone who gets it right.
Comment