Yes, but that's not even the issue with those lift discussions. People want to know "the cause". But physics often just states relationships between quantities measured at the same time, so cause-effect ordering is arbitrary.Aerodynamics is freaking complicated.
Passing trains (or passing anything) pulls air along. You will not get sucked into the side of a train. You might get sucked into the low-pressure wake behind a train, though, but that is a different concept. The water ski analogy is pretty rough. Both an airplane wing and a water ski deflect a fluid down in order to stay up, but that is about where the similarity stops.What? Oh yes, you talked about passing trains, and I'm not disagreeing. Passing train pulls air along it. But there has no been any previous mention about water skis :)
Airfoils have a special shape, particularly at their trailing edge. Most of them are "sharp", though it works with a flatback airfoil, too. The important thing is that the trailing edge of the airfoil fixes the separation point at a location that it otherwise would not have been. This combined with the conservation of mass and momentum results in the air over the top being greatly accelerated compared to that over the bottom. The results is a greater pressure differential and more downwash compared to a flat plate. A flat plate at angle of attack (or a ski) doesn't have this action, and so while it can generate lift, it doesn't generate nearly as much.What do airfoils do? Do they somehow push air at distance? At greater distance compared to a flat board? I think airfoils are just boards with a shape that allows a larger angle of attac than flat boards.
There's a scale factor involved. For small balsa type gliders, a flat or nearly flat plate wing is reasonably efficient. For gliders with wingspans somewhat less than a meter, a thin symmetrical wing with some tapering at the trailing edge is good enough. Thin airfoils with some camber show up at around 1 to 1.5 meter. At 2 meters or greater, more conventional airfoils are used.A flat plate at angle of attack (or a ski) doesn't have this action, and so while it can generate lift, it doesn't generate nearly as much.
That's not a strictly accurate statement. It has less to do with scale and more to do with the "mission requirements" of each of the objects you mentioned. A small balsa glider can get away with simple, flat wings because it is made of extremely light materials and has no requirements other than gliding. If it has propulsion, like a wind-up propellor, they are generally very large and provide a large thrust to weight ratio. In other words, it doesn't take much lift to keep them aloft, they don't have to haul anything, and they have plenty of thrust, so having an inefficient wing is no big deal. As you get larger, the weight goes up due to materials requirements, internal structure, propulsion requirements, etc. Generally the thrust to weight ratio is likely to go down and therefore, the efficiency of lift generation is more important.There's a scale factor involved. For small balsa type gliders, a flat or nearly flat plate wing is reasonably efficient. For gliders with wingspans somewhat less than a meter, a thin symmetrical wing with some tapering at the trailing edge is good enough. Thin airfoils with some camber show up at around 1 to 1.5 meter. At 2 meters or greater, more conventional airfoils are used.
I was making a reference to small gliders similar to this one.scale factor
The problem with using this site as a source is that, while he seems to have made a pretty neat balsa glider, his grasp of aerodynamics is at best incomplete. Sure he uses the term Reynolds number a lot (in quotes!), but it is pretty clear to me that he doesn't know what it is.I was making a reference to small gliders similar to this one.
The article mentions that a lighter model flying at slower speeds would do better with larger wing chord and/or "flatter" wings due to Reynolds issues (slow speed, small wing chord). I'm wondering if there is much to gain in lift to drag ratio by using a more cambered airfoil for this type of model glider.
All of which is in line with what I have been saying. Unless you go to an extremely tiny scale, an airfoil will outperform a flat plate at generating lift regardless of the size (assuming that neither is experiencing stall, of course). If you go small enough to change that, you are likely in the range where we are talking about insect wings, and I am not nearly as familiar with aerodynamics on such a small scale as that.In the case of 1.5 meter gliders, thin but otherwise conventional air foils are used as seen in the attachment. The wings have full length ailerons that can be moved in unison to increase / decrease camber to provide a wider speed range. There are issues related to scale, speed range, and wing span being limited to 1.5 meters by the rules. The wings use a relatively large wing chord to increase wing area, which decreases wing loading and sink rate.
That is not an issue with Bernoulli's equation itself, as Bernoulli says nothing about why air moves faster. It only provides a relationship. Further, there really isn't necessarily a cause and effect here between pressure and velocity. Really, the two are interrelated and it doesn't really matter which one you want to say comes first as far as I can see. As long as you don't fall victim to the equal transit time myth, then it doesn't really matter anyway.One issue related to Bernoulli are statements that imply faster moving air results in lower pressure, as opposed to air accelerates from higher pressure zones to lower pressure zones, and as it does, Bernoulli describes the relationship between the speed^2 of the affected air and it's pressure. What isn't explained is how wing produces low pressure zones above the wing. A simple explanation is that the upper surface of a wing curves and/or recedes away from the flow, which has to accelerate towards the surface of the wing to fill in what would otherwise be a void (or if stalled, vortices fill in what would otherwise be a void). A pressure gradient coexists with the acceleration towards the upper surface. The reduced pressure near the upper surface of the wing also causes the air to accelerate in the direction of the flow (the faster moving air from the wing's perspective).
Outperform is a good description..All of which is in line with what I have been saying. Unless you go to an extremely tiny scale, an airfoil will outperform a flat plate at generating lift regardless of the size (assuming that neither is experiencing stall, of course).
The Bernoulli principle describes pressures. Pressure x Area = Force, which is the lift force.No no. He is claiming the down wash of air is the only component needed to explain lift. He ignores the Bernoulli Principle.
If the Bernoulli Principle did not contribute to lift, then there would be no reason for a cambered wing, you would simply use a plank.