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Side View of the target and tell tale strut

g. 5. Windscreen System, front view. The Perspective Grid pattern of very fine line markings is well known as having been used by Dutch Painters as a tool for perceiving the spot of converging vanishing point perspective. The painters would construct the grid out of wire in a frame and place it on a stand some distance in front to assist in perception of converging depth. It is difficult to look only for the spot of convergence, it is more easily located by seeing the larger distortions around the convergence and pointing to it. This point of convergence is important in landing an aircraft because the aircraft is moving, and the point of convergence that is not moving in the windscreen is the point where the airplane is likely to impact the ground. The grid would make it easier and more obvious to perceive this point of convergence continuously and accurately during the landing approach. There is also a technique of a constant angle with the horizon by seeing and constant distance on the windscreen with the horizon. The grid should help in these perceptions, although the detection of the vanishing point is believed to be the better method.
[Para 22] Fig. 6. Windscreen System, side view. This view shows the protruding holder for the target, and angle of attack and yaw vane. It is hoped that by testing and method it can be possible to calibrate the vane despite the variations in propeller slipstream problems in a single engine tractor aircraft. A very spiky or furry stick or yarn could have damping and Reynolds number effects which would limit vibration. The vibration and lack of exactitude that could result from placement in the propeller slipstream could have some benefit in solving one of the problems of simple angle of attack flying. When a pilot closely chases or targets a specific angle of attack he can cause a phugoid oscillation of the whole aircraft where it cyclically changes airspeed at the same angle of attack. Since this condition is prevalent some accommodation has to be made, in the pilots head or in the instrument. The pilot can use the angle of attack information as a gross guide to see where he is trending, and look at the airspeed and the pitch angle to dampen the oscillation. If the angle of attack and yaw vane in this application is vibrating about then it can only be used for gross interpretation and not for fine chasing so the two problems cancel each other a bit. The benefit is still there since accidents typically involve gross errors that begin some time before the accident occurs. Since the subject instrument is right in front of his face out of the window in the direction he is going then gross errors could be seen before they become irrecoverable. This type of instrument could still have utility and improved accuracy if placed in some location outside of the propeller where the pilot can get a decent look at it. A pith ball tube type windspeed indicator can be placed in concert with the angle of attack indicator. This is a clear tube with many holes drilled all along it and capped at the top, the air from below blows the ball upward. It is inexpensive but it requires calibration to the expected pitch angle of the plane since it is gravity dependant. Spring loaded airspeed indicators have been used in the biplane days and these are not gravity dependent, and may be a solution. The take off speed and the stall speeds and the pattern speeds are the important speeds for such an external indicator.
[Para 23] Fig. 7. Windscreen System, pilot's view. Placing a "push" label at the bottom of the windscreen and a "go around" could be correlated by the pilot with the non moving vanishing perspectives spot of vision to remind the pilot that corrective action should be taken at these extremes. If the Perspective Grid is very effective in showing the vanishing point this type of labeling might be effective. Testing is required.
[Para 24] With the perspective grid alone the point of non moving perspective that the pilot perceived could be marked on the screen from the bottom up as , Lite , Medium, and Heavy to reflect the differing angles power off Landing which vary with aircraft weight. This marking could also be placed on the larger triangular target detailed in Fig. 8 , although here there is a conflict between the best power off glide form of landing and a fixed angle of descent approach. The best power off glide form is handy for emergency landings, and some instructors advocate all landing being make in this way as practice. The fixed angle of approach may be needed for heavy airplanes needing power, windy and high crosswind landings, instrument landing practice etc. Each aircraft model would have to be tested and developed to determine if there is an effective combination with one labeling target system or if one or the other would have to be chosen. Tests of confusion or understanding by uninformed pilots would have to made to evaluate the effectiveness of potentially conflicting procedure and symbology. In a more elaborate installation the target could be adjustable for conditions, but mechanical simplicity would be preferable.
[Para 25] It is an established practice to place and half arc on the windscreen as this is supposed to help people maintain the concept of level horizon in a turn. While this could be beneficial it would have to be evaluated against the other visual devices for clutter. The angle of attack and yaw devices may be more important the horizon pitch references as it may be more important to avoid a stall than to maintain altitude.
[Para 26] The two circles at each upper side are labeled here for our purposes but would not be labeled in actual use. These open circle targets are placed in the approximate location of the entrances of the optic nerve in each eye when the pilot is straight looking forward. These circles are to lure the pilots eye into an effective minimum traffic scan than breaks away from staring straight ahead and checks these tempting holes.
[Para 27] The slip skid ball has been duplicated and removed from its unnecessary bulky housing way down on the instrument panel and placed directly on the wind screen suitably held by foot shaped bookends that instruct the pilot to "step on the ball" to keep it centered. Since uncoordinated flight is associated with stall spin accidents while the pilot is looking out the window, it seems best to bring this tiny and inexpensive and useful instrument into its easiest field of viewablity.
[Para 28] Fig. 8. Windscreen System, detail of Landing Target with Relative Air flow indicator. The indicating stick or yarn could be replaced by surface mounting a grid of tiny light emitting diodes on the windscreen in and around the triangle to electrically represent the yarn with signals form a sensor system that is remotely mounted outside of the propeller slipstream.
[Para 29] The triangular target would normally be calibrated to a normal flaps down landing as that stalls at a lower angle of attack and is the common landing scenario. The triangular shape is unique as it combines the angle of attack information with yaw information to show the convergence of risk of stall spin accident with combinations of yaw angle and angle of attack in the same instrument. target system shows the pilot the probable glide angle for landing in the specific aircraft, probably in a power idle condition. This targeting may only hold for a no wind condition and must be correlated with the moving vanishing point which is accentuated by the perspective grid.
[Para 30] As can be seen in the Fig. 11, marking the airspeed indicator with relevant speeds is difficult due to lack of space and the way indicated airspeed varies with weight. The wing angle of attack solves many of those problems but they are not available and or cheap. Some complain the angle of attack systems can cause a phugoid oscillation in susceptible planes at susceptible airspeed. The angle of attack indicator can be dampened by vertical airspeed to solve this, but it does not matter if angle of attack instrumented aircraft are not available for rent or purchase. For economy and expediency here, the solution is to integrate visual cues and information that allows the operator to subconsciously dampen the angle of attack information by balancing with exterior visual pitch information and airspeed information. Simple yarn or vane angle of attack instruments in the exterior field of view mimic the ancient telltales of the sailing boats. A angle of attack and yaw device can be created very simply on in front of the windscreen of the aircraft. Difficulties arise with propeller wash and flap settings which can complicate the accurate marking and calibration of such devices. It has been shown on paper that some places on aircrafts aerodynamically compensate for the flaps by the flaps own influence, thereby allowing a single stall indicator point for all flap positions. Compensation or accommodation of propeller wash effects may be possible.