A wing creates lift by reflecting the vertical momentum of the approaching relative air flow to leave the wing with a downward change. That is, wings reverse the vertical component of the incoming flow. This is possible only by exerting a downward force on the flow stream. And, so the wing itself experiences an equal and opposite lift force that we call lift.
At any given airspeed, the lift varies with the angle-of-attack (AOA). The AOA is the angle between the approaching flow and the chord line (leading to trailing edge). The greater the AOA, the greater the lift and vice versa. Likewise, at constant AOA, the lift varies with airspeed. The greater the airspeed, the greater the lift force and vice versa.
This is known to everyone who has ever stuck a flattened hand out a car window into the air stream. Tilting the hand up increases the lift on the hand. Tilting it down reverses the direction of the lift. Likewise, the faster the car travels, the greater the lift and vice versa. These concepts are illustrated in Fig. 3.
The elevator is the AOA control for an aircraft. If the pilot pulls back slightly on the control stick and holds the new position, the AOA increases and the lift force increases with it. That, in turn, produces an unbalanced, upward force on the aircraft, causing it to accelerate upward. This upward acceleration may cause the aircraft to begin moving to a higher altitude or it may only reduce begin reducing the rate of descent (sink). For sake of discussion, let's assume the aircraft begins movint to a higher altitude. As the aircraft ascends, it's gravitatinal potential energy increases.
The equation for a change in gravitational potential energy is Ep = mgh, where m is the mass (or weight) of the aircraaft, g (9.8m/s2) is the gravitational constant and h is the change in altitude.
Ignoring the energy loss from aerodynamic drag, the increased potential energy must produce a corresponding decrease in the kinetic energy, the energy of motion. This is because physics demands the conservation of energy. Energy cannot be created or destroyed. So, the total energy (potential plus kinetic) must remain constant.
The equation for kinetic energy is Ek = (1/2)mv2, where m is the mass (or weight) and v is the magnitude of the velocity of the aircraaft.
Thus, as the aircraft rises it slows to a new equilibrium airspeed that is appropriate for greater AOA. As the aircraft slows down, the lift declines accordingly and eventually reaches the weight of the aircraft again. After that, the aircraft flies at a reduced, steady speed.
The reverse occurs when the control stick is moved forward.
The thing to remember is that when the aircraft slows down the AOA increases (nose up) and when it speeds up the AOA decreases (nose down). However, changes 1 and 3, noted above (increased altitude and downward pitch), violate normal behavior! It follows that this performance scenario indicates a change in wing aerodynamics that reverses the normal relationship between AOA, airspeed and altitude.
As you play the video, you will see the ASI needle move steadily from 60 kts to 52 kts (large blue hash mark below 3 o'clock position). As the glider slowed down the nose slowly pitch up and the glider gained 29 feet as kinetic energy converted into gravitational potential energy. This is normal. However, precisely at 52 kts the glider departed from normal behavior when the nose suddenly pitched sharply down. It did this while the airspeed was held virtually constant. Watch the ASI as the nose pitches down and holds the new attitude. As this continues, the variometer needle begins moving up from 4.5 to 1.7 kts. These actions violate the theory! The nose should have stopped rising at 52 kts and ahould have remained at that new angle as the airspeed held constant. Clearly, something changed suddenly to make the glider fly the same airspeed with a sharply reduced AOA.
As the airspeed slowed from 60 kts, the nose pitched up gently and the glilder climbed normally. But when the speed reached 52 kts, the deturbulators suddenly began working; i.e., a beneficial flow-surface interaction mode turned on and the boundary flow over the wind snapped to a modified state. I'll not say more about the modified flow state except that it attempted to increase the lift force. But, as the video shows, holding the airspeed constant at 52 kts caused the lift force to remain equal to the glider's weight, thereby causing a reduction in the AOA. Finally, in keeping with theory, the pitch remained at the new attitude as the airspeed remained constant.
Finally, as the glider held the new AOA, the sink rate decreased from 4.5 kts to 1.7 kts. This extreme performance boost is clearly due to the preceding event the suddenly occurred at the well documented performance airspeed of 52 kts. This occurred at 3700 feet, about 1000 feet above the atmospheric boundary layer where vertical mixing occurs. This can be verified by the steadiness of ground features relative to the airframe in the video clip. It follows that the event recorded is not due to a sudden encounter with rising air.
This sequence of occurrences is corroborated by Fig. 4. The arrow labeled Start shows how decreasing the airspeed from 60 to 52 kts moved the glider from a region of poor performance to a sharp peak of extremely good performance. The sudden performance boost at the precise moment of reaching this measured performance airspeed is not a coincidence. It is in fact a recurrence of the measured phenomenon.
The upward pitch momentum carried the attitude beyond the new equilibrium point and the glider began losing airspeed. This was corrected by the pilot and the nose again pitched down as the glider again reached the 52 kt performance peak. This was a second onset of performance. The arrows labeled Bobble in Fig. 4 show the speed changes as they relate to expected performance.
This episode illustrates the instability of the flow-surface (deturbulator surface) interaction mode(s) that enable(s) flow patterns favorable to extreme performance.
The suddeness and great momentum of the down pitch at 48 kts can be understood by noticing the extreme performance difference over an airspeed span of just 1 kt (48 to 49 kts) in Fig. 4.
This possibility appears to be supported by the overall performance, while cruising, after this performance event (Fig. 5). This pattern is shown in Fig. 6. The brown curve shows the glide ratios while cruising. The brown horizontal line is the baseline performance of the glider while flying 65 kts, an estimate of the averge cruising speed. The airspeeds are also labeled. The altitude vs. time profile is plotted in the background (red=pressure altitude, blue=GPS altitude). Regions highlighted in yellow show the data points that were used to calculate the performance peaks.
Notice that the performance valleys are at first rising and then take a downward slope. This suggests a long shear wave influencing the data taken while cruising at lower altitudes near the boundary layer.
The most obvious objection is that the glider encounteres rising air (convection) when performance speeds are being measured. The problem with that is the amazing correspondence of this "rising air" with performance measurements. It has been well documented that the "rising air" repeatedly arives at the beginning of performance measurements and leaves precisely at the end of them.
Furthermore, this performance scenario occurred at 3700 ft altitude which was about 1000 ft above the top of the boundary layer (where thermal mixing occurrs). The top of the boundary layer was observed on tow as all turbulence ceased at 2700 feet. Furthermore, one can see the stable motion of the airframe in the videos. "Kick in the seat of the pants" events do not normally occur in the smooth air above the inversion level. Shear waves my occur, as well as small scale turbulence, but not vertical convection that can kick a glider around as in this event. It is not reasonable to assume that this scenario was produced in smooth air, above the inversin level, by convection that just happened to arrive at precise moments when previously measured performance airspeeds were encountered.
A second objection might be that this event was not a case of extreme performance at all, but rather a momentary loss of extreme drag. Based on the enhanced performance measurements (Fig. 4) taken in the same flight at higher altitudes (Fig. 5), with the 52 kt point being measured twice, and also numerous prior measurements that corroborate them, I think that the low glide ratios of this event resulted from flying in the down side of a long shear wave.
This event is yet another piece of evidence supporting the reality of extreme performance from deturbulated boundary flow control. It's time for professioinal aerodynamicists to take this seriously and to initiate their own investigations. To date, I am aware of two who have made this commitment. Dr. Sinha and I stand ready to assist any legitimate investigation.
If you are interested, I suggest that you contact me for samples of deturbulator substrates. These are the only components that are not commerically available. Also, I suggest that you begin with bottom surface tests. Top surface deturbulation is very difficult to simulate in wind tunnels. Instead, try a panel on the pressure side of the wing just behind the reattachment point as illustrated in Fig. 8. No vent ports are needed and you should see consistent drag reductions.