At 06:56 AM 12/13/04 -0600, you wrote: >1. That sucking sound you here from the upper surface of the wing is the >plane pulling money from your wallet. >2. "Sucking up" is a force only when you are complimenting someone. >Here is a link to a scientific explanation of LIFT: >Dick Hartwig >_______________________________________
Larry's theory of lift: That "sucking sound" you hear is your "pucker" muscles giving out a muffled YEEEEE HAAAAAA !!! On a more technical note, Bernoulli's law, as stated in "Elements of Aeronautics" (Pope-Otis, dated 1941), as it applies to airfoils is this: "In a streamline flow, the greater the speed of the air the less the pressure of the air, and the less the speed of the air the greater the pressure." I don't think this theory has changed much since then. The wing on the KR is not divided into top only or bottom only but is acting as a single unit. As it slices through the air, the air that is directed over the top of the wing must accelerate in order to reach the trail edge at the same time as the air directed below the wing because the air over the top has a greater distance to travel. As the speed of the "over-the-top" air increases, it's pressure drops. Assuming the air on the bottom side of the wing maintains it's static pressure (29.92 in/2 at sea level, 59degrees F) , we now have a difference of pressure of X in/2 between the two surfaces. So, is it sucked up on the top side or pressured up from the bottom side, you decide. I conclude it has a "pulling force" on the top and a "pushing force" on the bottom acting on a single unit, the wing. The wing, as a single unit, is forced in the direction of the low pressure. There are of course too many other variables to cover here such a wing shape, cord to span ratio, , etc. but the basics remain the same. I won't go into "angle of attack" except to say that it has a direct effect on the location where the greatest "low pressure" or "difference of pressure" is generated on the top surface of the wing. The greater the angle of attack, the further forward the center of lift (greatest low pressure) is generated. The less the angle of attack, the further to the rear the center of lift is located. This directly affects the "balance" of the airplane in the air and requires the elevator forces to change to compensate for the changing center of lift. When flying my KR, as the speed picks up in cruise, the wing develops more and more lift. With the center of lift behind the C.G., the nose wants to pitch down as the speed increases and the amount of lift increases. Believe me, this change is considerable. I once demonstrated it to a friend by taking off with the trim set at neutral, accelerating to cruise, and as I passed him in the air I released the stick. I pulled negative G's and scared the s#%*t out of myself. I had been holding considerable back pressure on the stick to compensate for the increased lift being generated behind the C.of G. If I slow to say 120mph, the amount of lift ( behind the C.G. ) decreases and the nose of the airplane tends to rise and the amount of back pressure on the stick or trim required to hold the nose up is much less. This can also lead to a problem when the C.G. is too far to the rear. As the airplane slows in flight, you continue to increase the angle of attack to maintain altitude. The center of lift continues to move forward on the wing to a point forward of the C.G. and you could possibly run out of enough elevator authority to lower the nose and continue safe flight. Conclusion: The theory of lift is accurate regardless how you interpret it. I'd suggest that those of you that have not yet completed you project, get back to the shop and do so with complete assurance that if built to plans, or somewhere close, that it will actually fly when completed! You too will then be overwhelmed with the feeling that can only be expressed with a giant YEEEEEEE HAAAAAAAA . Larry Flesner 112.5 hours and still grinnin'
