Max Power From , joined Dec 1969, posts, RR: Posted (12 years 9 months 1 week 6 days 14 hours ago) and read 1859 times:
Ok I need some help with this one. All the books I read and folks I talk to say it's the low pressure over the top of the wing that gives lift. The air flowing over the top has to go faster than the air on the underside, there fore a low pressure area and lifting the wing up. There must be also a lot of pushing from the air on the bottom side also? I say this because for example, in a car at 50 mph and your hand outside the window, angle it up and the air pushes your hand up, just like under water. How much of lift is the upward push under the wing with a certain angle of attack. This has to play a big part in the aerodynamics of flying? No one ever talks about the underside of the wing. thanks
Ralgha From United States of America, joined Nov 1999, 1614 posts, RR: 6 Reply 1, posted (12 years 9 months 1 week 6 days 14 hours ago) and read 1655 times:
The pressure differential around a wing accounts for only a small part of the lift. There is high pressure below, which wants to get on top where there is low pressure, thus pushing the wing up. However, most of the lift comes from the angle of attack of the wing. The angle of attack (AoA) is the angle between the chord line (imaginary line from the tip of the trailing edge to the tip of the leading edge) and the relative wind. When you stick your hand out the window of a car, you are feeling lift due to AoA. You turn your hand up, it has a positive AoA and is pushed up, you turn your hand down, it has a negative AoA and is pushed down. Airplane wings, however, rarely have a negative AoA.
Spoiler From Spain, joined Apr 2007, 0 posts, RR: 0 Reply 5, posted (12 years 9 months 1 week 5 days 19 hours ago) and read 1580 times:
Yup, an argument. What Ralgha described is reffered to as 'dynamic lift.' But it doesn't account for that much of the total lift generated by wing. Most of the lift is, in fact, formed by the high and low pressure areas. Let's just pretend that it is angle of attack that determines the amount of lift produced. The higher angle of attack, the higher the amount of lift generated. Under those conditions, an airfoil could theoretically never stall, because the critical angle of attack could never be exceeded. Yes, dynamic lift does increas with angle of attack, but dynamic lift isn't a large producer of the total lift.
Max Power From , joined Dec 1969, posts, RR: Reply 6, posted (12 years 9 months 1 week 5 days 16 hours ago) and read 1567 times:
Ok, but to Spoiler. lets say I just had a wing or even a 4x8 sheet of plywood. standing in the bed of a small truck, as I increase the angle of attack it pulls me up harder. Should I be able to keep increasing the angle the more lift until, it gets to lets say the vertical or 90 deg. position then it's pushing me back. I would think somewhere there it would be stalled. Thanks.
IFF/7000 From , joined Dec 1969, posts, RR: Reply 7, posted (12 years 9 months 1 week 5 days 16 hours ago) and read 1564 times:
It's the underpressure that keeps the wing in the air. At a steady speed and an increasing AOA lift increases until just before the critical angle of attack.At this critical angel of attack the upper airflow starts to separate from the wing and you end up with a stalled wing. And like Spoiler says if you could still increase the AOA the high pressure would increase (but you would still stall).
IFF/7000 From , joined Dec 1969, posts, RR: Reply 8, posted (12 years 9 months 1 week 5 days 15 hours ago) and read 1563 times:
Maxpower at 90° you do not feel lift but drag. Drag is the only thing we can miss on a wing. Airflow produces lift and drag with the AOA you increase or decrease both until imax. Check the lift/drag curve (CL/CD with AOA).
Spoiler From Spain, joined Apr 2007, 0 posts, RR: 0 Reply 9, posted (12 years 9 months 1 week 4 days 12 hours ago) and read 1547 times:
Ok, so I got a little curious about this one, and I went to my flight manuals to research. It turns out that at a higher airspeed, and lower angle of attack, most of the lift is caused by the pressure differential. At higher angles of attack, dynamic lift increases with the angle of attack. But the majority of lift is created by pressure differential. Dynamic lift is great for lifting boards out of trucks, or hands stuck out car windows, but we are talking about lifting airplanes here. Dynamic lift is enough to lift the weight of the board, or the weight of your hand, given it's surface area, but with airplanes, a lot more weight is lifted per surface area. Could you strap a couple sheets of plywood with the same wing area it's normal wing on an airplane and expect it to fly? If dynamic lift were responsible for the majority of lift produced, yes.
JG From United States of America, joined Jun 2005, 0 posts, RR: 1 Reply 10, posted (12 years 9 months 1 week 4 days ago) and read 1538 times:
After all of this, I still favor newtonian over bernoullian for the bulk of lift production. Afterall, we are not all flying straight Clark-Y airfoils or some GA NACA number. I was always told, if you put enough power on a rock it will fly... that goes for plywood, Concorde, Burt Rutan creations, and space shuttles alike.
Spoiler From Spain, joined Apr 2007, 0 posts, RR: 0 Reply 11, posted (12 years 9 months 1 week 3 days 19 hours ago) and read 1525 times:
All you proponents of newtonian lift just keep proving my point for me. Sure, a rock will fly if you can get it moving fast enough, due to dynamic (newtonian) lift. Consider a small airplane such as a Cessna 172. There is no way that the airplane could stay aloft using dynamic lift as the major source of lift. It can't go fast enough. Why do you think we even have airfoils? What about flaps? I'm sure the next thing you are going to tell me is that flaps increase lift because the air flowing underneath the wing hits the flap and is forced down. How would you explain why almost all jet transports have leading edge devices (slats)? Have any of you newtonian guys ever even been to ground school? Come on! This is basic aerodynamics! I want you to do an experiment for me. Take a standard piece of 8-1/2" X 11" piece of paper, and hold it in front of you lengthwise, with two hands, so each hand is holding one of the corners. Ok? You with me? Next, I want to to bend the edge of the paper that's toward you slightly downward, so the paper resembles an airfoil. Next, I want you to blow over the top, not underneath, the top of the airfoil. The paper rises, and it isn't because of dynamic lift. And the newtonian theory still doesn't explain why an airplane can stay aloft with a low angle of attack, such as cruise flight (and I don't want to hear angle of incidence!) What about flight at minimum controllable airspeed (MCA)? The airspeed is low, so dynamic lift diminishes even though the angle of attack is large. How does the airplane maintain altitude? Have you considered induced drag? If airplanes have such a big drag penalty from induced drag, why even bother with airfoils if it is newtonian lift that is the major contributor? What about ground effect? It is the air coming over the wing, striking the ground that causes ground effect, not air deflected from the flaps (the air striking the ground is not newtonian lift the way that we've described it. It's ground effect - a newtonian phenomenon, but not dynamic lift). What about vortex generators? What about spanwise airfoil variations? I don't know how to make it any clearer. Why would any of this come in to play if bernoulian lift wasn't much of a factor.
JG From United States of America, joined Jun 2005, 0 posts, RR: 1 Reply 13, posted (12 years 9 months 1 week 3 days 12 hours ago) and read 1521 times:
Wow, touched a nerve, sorry. Thank you for your passionate response. Tried your experiment, loved it. Could we agree that it is a little of both. I do not possess the drive, passion, or inclination (incidence) to battle over this topic.
My son, needs a diaper change and I am still trying to answer the heredity vs. environment question as I assess his behavior. I feel that it may take a lifetime to answer.
JG From United States of America, joined Jun 2005, 0 posts, RR: 1 Reply 15, posted (12 years 9 months 1 week 3 days 7 hours ago) and read 1511 times:
I offer this simple article to amuse, entertain, enlighten, and present a different frame of reference. This article describes more of a system than a myopic belief in one or the other (Newton or Bernoulli).
Panman From Trinidad and Tobago, joined Aug 1999, 790 posts, RR: 0 Reply 16, posted (12 years 9 months 1 week 3 days 5 hours ago) and read 1507 times:
Bruce you just contradicted yourself. Where would the dynamic lift come from at a low angle of attack? Just put your hand (which is not an aerofoil) out of the window of any moving vehicle and keep it parallel to the direction of travel and you hardly feel anything but the air moving around it.
At low angle of attack it is most definately pressure differential that creates lift. In this instance speed is directly proportional to lift created and induced drag.
JG From United States of America, joined Jun 2005, 0 posts, RR: 1 Reply 17, posted (12 years 9 months 1 week 2 days 12 hours ago) and read 1491 times:
This site is for you... to peak you curiosity, round out your education and generally tame your passion. I have been to ground school, like you, been flying since my early teens (13) and have mucho experience under my belt... enough to realize that there is always someone who knows more than me.
Please read and enjoy this site with my compliments... there are many more available if you wish to pursue this further. There were so many questions in your post to address. Please do not treat a private pilot text on lift as gospel to fluid dynamics. I do appreciate your enthusiam, as misdirected as it may be. (observation not flame) http://www.allstar.fiu.edu/aero/airflylvl3.htm
Max Power From , joined Dec 1969, posts, RR: Reply 18, posted (12 years 9 months 1 week 1 day 19 hours ago) and read 1480 times:
Well, thanks for all the information, now I'm not so sure I want to fly. Thanks to JG and the NASA site. Wish I understood it all! I appreciate everyone's imput. Now then, let's see, if a apple falls from a 30 foot tree and strikes the ground, would the same apple strike the ground twice as hard if the tree was 60 feet? and twice as long in flight?
JG From United States of America, joined Jun 2005, 0 posts, RR: 1 Reply 23, posted (12 years 9 months 2 days 16 hours ago) and read 1452 times:
We had a term for your previous post this year during our US Presidential campaign and election... Fuzzy Math. Looking at your profile I can only assume that you are probably not a democrat and that you derived some entertainment from that recent event.
Be careful, in your equation 1/2 rho V^2 S Cd, whether for drag or Cl for Lift you may not cancel out the "2" in your doubling of the velocity discussion.
it is (2V)^2
it is not 2(V^2)
My long dead algebra teacher thrashed me for that, not to mention the occasional (+/-) error.
Proper handling of your expression should demonstrate to your that lift or drag (as appropriate) will increase by 4x when you double the velocity. Let us hope that the coefficient of lift is greater than the coefficient of drag for a given airfoil... my career depends on it. For your entertainment please enjoy the links to interesting sites that I have posted in previous replies.