I am so very happy to finally have watched experimental effects in this series and I am in so much appreciation for the sharing of your work ......... Thanks for sharing ......... However I would have loved to watch all the experiments with the wind tunnel working in a vertical position yielding interesting results but then may have had nothing to do with the "secret" of flying as we know it ...... I would keep on the look out to achieve my wish of watching someday the same experiments not on a horizontal plane, not tangential to gravity.
@Synergy long ago, I assembled and flew RC gliders, airplanes, helicopters, gyros, and hydrofoils, but all of these work exponentially on horizontal fluid differentials called lift .... blowing on a side of a horizontal sheet of paper behaves deferrebtly than on a paper on a vertical plane related to gravity
The negative tangential force is an illusion. It gave rise to the concept of aspiration; that the wing would generate a forward force that would drive it through the air. This would allow a wing to fly horizontally through still air without any external power. It would permit a perpetual motion machine. The Wright brothers were aware of this error. The illusion derives from the convention of resolving the forces into a normal force perpendicular to the chord line and a tangential force parallel with the chord line. It was found that under certain conditions the resultant force pointed forward of the perpendicular. This was interpreted that this force would drive the wing forward through the air. This conclusion is false because the chord line in these conditions does not point into the oncoming wind, it is elevated above the wind direction at an attack angle. It happens that in the case in question the attack angle is always somewhat greater than the forward inclination of the normal force, such that the resultant force points backward relative to the wind direction. For example, the attack angle might be 5 degrees and the resultant force might incline 2 degrees forward of the normal. That would mean that the resultant would incline 3 degrees backward of the perpendicular to the directions of the airflow. A less confusing way to resolve the resultant force is into lift, the component of the resultant force perpendicular to the direction of flight, and drag, the component of the resultant force parallel to the direction of flight. When resolved in this way, it is seen that wind tunnel tests always show a positive drag force.
So it would seem. How, then, does one explain what we just saw in the video? Is it because the model is constrained by the rail, and its upward force of the wheels against the rail is translated to forward movement by resolving the lift into vertical and horizontal components?
@@aeromodeller1 But you know what, I have reconsidered. We know that boats can "tack" into the wind. If you draw the vectors, there is no component of the wind going against itself, so the generation of lift must have a component angled forward of the normal line, just like Herr Professor said. Similarly, in the Professor's illustration, if the wing's lift were at a normal angle to the wing, and hence the rail, there is no forward component, and the combination of lift and drag on the wing would slide it backward or would just lift the wing at 90° to the rail and not move either forward or backward. To get forward motion, there must be a vector component angled forward along the rail. I think this Very Famous Aerodynamicist knows what he's talking about.
@@jwills8606 No. The sailboat is not experiencing only aerodynamic forces, it is also experiencing hydrodynamic forces on its hull. Tacking does not go directly into the wind, it goes at some angle off the wind. The hull moves through the water at an attack angle to its direction of motion. The force on the hull is what moves the boat into the wind. It is analogous to the force from the rail. Look it up. I was surprised Lippisch said that. He should have known better. The phenomena implied here was known as aspiration. If aspiration was real, it would not be necessary for airplanes to have engines; the wing would pull itself forward through the air. This would also produce a perpetual motion machine. Several wings arranged around an axis like a windmill would pull themselves around, generating power in still air. It was known in the late 1800's that aspiration was an error. If you plot the force diagram of an airfoil, you will see that when the aerodynamic reaction points "forward" along the arbitrary wing chord, the attack angle makes it point backwards, as I described above. I went right to the source. Otto Lilienthal, Birdflight as the Basis of Aviation, s3-eu-west-1.amazonaws.com/bga-sg-archive/Books/BIRDFLIGHT%20AS%20THE%20BASIS%20OF%20AVIATION.pdf SS XXIV. - The Advantages of Curved Wings over Plane Surfaces. "Of still greater importance, however, is the more favorable direction of the resulting air pressure in the case of a curved surface. The retarding component of the plane surface is replaced by a pushing component so that the real obstacle to the attainment of power economy in forward flight is removed when using a curved surface, ..." SS XXIX. - Comparison of the Direction of the Air Pressures. "Under these conditions the characteristic difference of curved surfaces against planes appears more striking; not only does the direction of the air pressures closely approach that of the perpendicular to the surface, but for certain angles it actually passes beyond it to the other side, converting the usual restraining component into a propelling component. Curved Surfaces, when placed horizontally, and moved downward under certain angles have therefore the tendency to automatically increase the horizontal velocity." When we look at the plot of the data for the most favorable case, Plate IV, a 1/12 camber arc airfoil, Fig. 1. shows the usual polar diagram in which the resultant is drawn as a vector arrow from the origin with drag on the horizontal axis and lift on the vertical axis. This shows that in no case does the resultant point forwards into the direction of flight. Fig. 2. shows the resultant force vectors plotted on the fixed airfoil profile. This shows that at attack angle of 20 degrees, the resultant points 5 degrees forward of the perpendicular to the chord. This is misinterpreted as being a propelling force. It is not! When this diagram is rotated 20 degrees to put the airfoil chord at the 20 degree attack angle, the resultant points back 15 degrees from the perpendicular to the direction of flight. Relative to the direction of flight, it points backward, it is a restraining force. We can see this in Fig.1. where the 20 degree attack angle force vector points 15 degrees back from the vertical lift axis.
@@aeromodeller1 Very well explained analysis! I enjoyed reading and digesting this. The "aspiration" error, as I understand it from your explanation, is assuming that the lift force always points ahead of the perpendicular, regardless of the angle of attack (which it does not). While Lippisch fails to point out this faulty interpretation, it doesn't appear that he ever directly endorses it. Instead, it appears that his main point was to show that the actual drag experienced by a cambered wing in flight is much less than the original plate theory predicted. This is due to the lift force pointing ahead of the perpendicular to the chord when at positive angles of attack (as you pointed out). Thus, as Lippisch concludes, the Wright brothers were convinced that heavier-than-air flight was possible, since the propulsion requirements would be far less than originally expected.
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Great series! Thank you for posting!
This guy reminds me of my old teacher who could talk for hours about the fine details of dynamic tyre deformation.
I am so very happy to finally have watched experimental effects in this series and I am in so much appreciation for the sharing of your work ......... Thanks for sharing ......... However I would have loved to watch all the experiments with the wind tunnel working in a vertical position yielding interesting results but then may have had nothing to do with the "secret" of flying as we know it ...... I would keep on the look out to achieve my wish of watching someday the same experiments not on a horizontal plane, not tangential to gravity.
@Synergy long ago, I assembled and flew RC gliders, airplanes, helicopters, gyros, and hydrofoils, but all of these work exponentially on horizontal fluid differentials called lift .... blowing on a side of a horizontal sheet of paper behaves deferrebtly than on a paper on a vertical plane related to gravity
@Synergy thanks for recommending it
UNREAL EXPLANATION.
The negative tangential force is an illusion. It gave rise to the concept of aspiration; that the wing would generate a forward force that would drive it through the air. This would allow a wing to fly horizontally through still air without any external power. It would permit a perpetual motion machine.
The Wright brothers were aware of this error.
The illusion derives from the convention of resolving the forces into a normal force perpendicular to the chord line and a tangential force parallel with the chord line. It was found that under certain conditions the resultant force pointed forward of the perpendicular. This was interpreted that this force would drive the wing forward through the air. This conclusion is false because the chord line in these conditions does not point into the oncoming wind, it is elevated above the wind direction at an attack angle. It happens that in the case in question the attack angle is always somewhat greater than the forward inclination of the normal force, such that the resultant force points backward relative to the wind direction. For example, the attack angle might be 5 degrees and the resultant force might incline 2 degrees forward of the normal. That would mean that the resultant would incline 3 degrees backward of the perpendicular to the directions of the airflow.
A less confusing way to resolve the resultant force is into lift, the component of the resultant force perpendicular to the direction of flight, and drag, the component of the resultant force parallel to the direction of flight. When resolved in this way, it is seen that wind tunnel tests always show a positive drag force.
So it would seem. How, then, does one explain what we just saw in the video? Is it because the model is constrained by the rail, and its upward force of the wheels against the rail is translated to forward movement by resolving the lift into vertical and horizontal components?
@@jwills8606 Yes. If the rail had been horizontal, the wing would have gone backward.
@@aeromodeller1 But you know what, I have reconsidered. We know that boats can "tack" into the wind. If you draw the vectors, there is no component of the wind going against itself, so the generation of lift must have a component angled forward of the normal line, just like Herr Professor said. Similarly, in the Professor's illustration, if the wing's lift were at a normal angle to the wing, and hence the rail, there is no forward component, and the combination of lift and drag on the wing would slide it backward or would just lift the wing at 90° to the rail and not move either forward or backward. To get forward motion, there must be a vector component angled forward along the rail. I think this Very Famous Aerodynamicist knows what he's talking about.
@@jwills8606 No. The sailboat is not experiencing only aerodynamic forces, it is also experiencing hydrodynamic forces on its hull. Tacking does not go directly into the wind, it goes at some angle off the wind. The hull moves through the water at an attack angle to its direction of motion. The force on the hull is what moves the boat into the wind. It is analogous to the force from the rail. Look it up.
I was surprised Lippisch said that. He should have known better. The phenomena implied here was known as aspiration. If aspiration was real, it would not be necessary for airplanes to have engines; the wing would pull itself forward through the air. This would also produce a perpetual motion machine. Several wings arranged around an axis like a windmill would pull themselves around, generating power in still air. It was known in the late 1800's that aspiration was an error. If you plot the force diagram of an airfoil, you will see that when the aerodynamic reaction points "forward" along the arbitrary wing chord, the attack angle makes it point backwards, as I described above.
I went right to the source. Otto Lilienthal, Birdflight as the Basis of Aviation,
s3-eu-west-1.amazonaws.com/bga-sg-archive/Books/BIRDFLIGHT%20AS%20THE%20BASIS%20OF%20AVIATION.pdf
SS XXIV. - The Advantages of Curved Wings over Plane Surfaces.
"Of still greater importance, however, is the more favorable direction of the resulting air pressure in the case of a curved surface. The retarding component of the plane surface is replaced by a pushing component so that the real obstacle to the attainment of power economy in forward flight is removed when using a curved surface, ..."
SS XXIX. - Comparison of the Direction of the Air Pressures.
"Under these conditions the characteristic difference of curved surfaces against planes appears more striking; not only does the direction of the air pressures closely approach that of the perpendicular to the surface, but for certain angles it actually passes beyond it to the other side, converting the usual restraining component into a propelling component.
Curved Surfaces, when placed horizontally, and moved downward under certain angles have therefore the tendency to automatically increase the horizontal velocity."
When we look at the plot of the data for the most favorable case, Plate IV, a 1/12 camber arc airfoil, Fig. 1. shows the usual polar diagram in which the resultant is drawn as a vector arrow from the origin with drag on the horizontal axis and lift on the vertical axis. This shows that in no case does the resultant point forwards into the direction of flight. Fig. 2. shows the resultant force vectors plotted on the fixed airfoil profile. This shows that at attack angle of 20 degrees, the resultant points 5 degrees forward of the perpendicular to the chord. This is misinterpreted as being a propelling force. It is not! When this diagram is rotated 20 degrees to put the airfoil chord at the 20 degree attack angle, the resultant points back 15 degrees from the perpendicular to the direction of flight. Relative to the direction of flight, it points backward, it is a restraining force. We can see this in Fig.1. where the 20 degree attack angle force vector points 15 degrees back from the vertical lift axis.
@@aeromodeller1 Very well explained analysis! I enjoyed reading and digesting this. The "aspiration" error, as I understand it from your explanation, is assuming that the lift force always points ahead of the perpendicular, regardless of the angle of attack (which it does not). While Lippisch fails to point out this faulty interpretation, it doesn't appear that he ever directly endorses it. Instead, it appears that his main point was to show that the actual drag experienced by a cambered wing in flight is much less than the original plate theory predicted. This is due to the lift force pointing ahead of the perpendicular to the chord when at positive angles of attack (as you pointed out). Thus, as Lippisch concludes, the Wright brothers were convinced that heavier-than-air flight was possible, since the propulsion requirements would be far less than originally expected.