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The question is very clear and requires no thought if there was a response resulting from experience and tell you again..........
why the center of pressure shifts forward when the angle of attack increases? |
The question is very clear and requires no thought if there was a response resulting from experience and tell you again.......... why the center of pressure shifts forward when the angle of attack increases? Why it shifts forward, starts to get a little complex. Pages can be written on it. And people smarter than I can offer technical explanations. Perhaps asking your lecturer is a better course of action. When you lift the plane's wing in the air to 16 of the angle of attack, as what happens when the point of pressure I mean, why step up when at high angle of attack? Please Explain to me And had many baffled and bemused.:\ |
Level 6 Engrish?
I want my $100 back :{ CMN :E |
The best explanation I can think of given I'm ironing and watching the tour de france and have had no sleep...is that the centre of pressure is the "average" of the pressure differential generated by the lifting surface. As the AOA is increased, the curvature of the surface effectively increases and the greater the curvature (if using basic Bernoulli's principle) the greater the lift. For the air to flow over this greater curvature it uses up more of the energy in the air and hence the transition and separation points move forward. That is assuming I've understood your question correctly. Frankly I wouldn't be surprised if I've not understood it at all as the standard of English is pathetic and not up to the standards I expect of a Generation Y member-must be a '90s Gen Y rather than an '80s one... Thank you very much for the answer, and sleep peacefully cynical pilot |
Thanks for rephrasing. The second time you asked, it made perfect sense. The first time, on the other hand....
One useful way to think about it is if we drew the pressure pattern on a diagram of the wing, the low pressure region on the upper surface would be deepest, or at its minimum pressure, near the centre of pressure. What this means is that as the air flows past the centre of pressure, it will encounter steadily increasing static pressure called the adverse pressure gradient. Because the low pressure region (the lift) is so deep at high angles of attack, the airflow would require more energy (which it doesn't have) to overcome this adverse pressure gradient. The result is that there isn't enough energy to overcome it, and the airflow detaches from the wing. So, as the angle of attack increases, the airflow separates closer and closer to the leading edge, and an increasingly smaller section of the wing is left to produce the lift. The centre of pressure is the average of that smaller area and therefore moves forward. |
Thanks for rephrasing. The second time you asked, it made perfect sense. The first time, on the other hand.... One useful way to think about it is if we drew the pressure pattern on a diagram of the wing, the low pressure region on the upper surface would be deepest, or at its minimum pressure, near the centre of pressure. What this means is that as the air flows past the centre of pressure, it will encounter steadily increasing static pressure called the adverse pressure gradient. Because the low pressure region (the lift) is so deep at high angles of attack, the airflow would require more energy (which it doesn't have) to overcome this adverse pressure gradient. The result is that there isn't enough energy to overcome it, and the airflow detaches from the wing. So, as the angle of attack increases, the airflow separates closer and closer to the leading edge, and an increasingly smaller section of the wing is left to produce the lift. The centre of pressure is the average of that smaller area and therefore moves forward This is the answer that I would have liked and I think you are really intelligent pilot |
or what about the Vortex, or Lifting line theory of lift,? would that help explain how the COP moves forward with increasing AOA? |
I didnt think the airflow actually 'detatched' from the wing as that would create a vacuum as far as I am aware. It is important to distinguish between the separation point (where the boundary layer detaches) and the transition point/line (where the boundary layer becomes turbulent). A turbulent boundary layer is not necessarily a bad thing - hence vortex generators, etc. |
Some light reading for you on this subject:
Noel Kruse's Book #1, Aerodynamics and Other Stuff, is a free download here. Lesson 2 on page 22 is a good place to start for this topic. |
I didnt think the airflow actually 'detatched' from the wing as that would create a vacuum as far as I am aware. |
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