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VISION FROM THE COCKPIT TO THE OUTSIDE AND TOWARD THE INSTRUMENT PANELS

 

PURPOSE

The purpose of these measurements is to determine selected visual angles through the windscreen, canopy, and side windows of the cockpit and visual access to controls and displays on the instrument panels.

DISCUSSION

We measured several aspects of vision from the cockpit, including vision over the nose, upward under the overhead or canopy bow, over the canopy bow and over the side of the cockpit.  We also measured vision out of side windows when appropriate.  Because of its obvious importance in approach and landing and the fact that it is in the direction of flight, the principal measure of vision out of the cockpit is the maximum depressed line-of-sight over the nose.  Since the over-the-nose and the under- and over-the-canopy bow measurements are within the vertical fore and aft (X-Z cardinal) plane of the aircraft, they are easily associated with pitch.  Vision directly over the side of the cockpit is usually within or close to the vertical side-to-side (Y-Z cardinal) plane and equally easy to associate with aircraft roll.  Other measures at intermediate angles between these two cardinal planes are more difficult to associate with aircraft attitude.

Since all measurements of vision are tied to aircraft attitude, they are easily altered, inadvertently or by intention, by changing aircraft attitude.  To make operational sense out of all the various measures of vision, therefore, aircraft pitch, roll and yaw attitudes must be known.  We used a carpenter's inclinometer to determine pitch.  Since the aircraft cockpits were examined on the ground, roll was always assumed to be zero.  Yaw is irrelevant to our examination of vision.

In the examination of vision inside the cockpit, special attention is given to those controls potentially obscured by the glare shield, control stick or wheel, throttle, and knees.  Using line drawings of the instrument panels, the outlines of visual obstruction are drawn as the subject sees them.  This procedure is described in detail further on.

The Design Eye Point is the basic reference around which the cockpit is designed.  It is the point on the Horizontal Vision Line to which the crew station designer specifies that the pilot should adjust his eyes.  The geometry of the cockpit is laid out around this point.  The amount of seat adjustability is dictated by the design range for Sitting Eye Height.  If seat location and adjustment range is appropriate then all pilots within the design range should be able to adjust the seat such that his or her eyes are at the Horizontal Vision Line.  They may or may not coincide with the Design Eye Point.  If it was always possible to adjust the eyes to the Design Eye Point, characteristics of vision would not vary among pilots.  In practice, however, pilots do not, or may not be able to, adjust their eyes to these design landmarks.  For that matter, there usually isn't a commonly known or convenient procedure for locating them.  While subjects throughout the range for Sitting Eye Height are used to examine vision outside the cockpit,  emphasis is given to the short Sitting Eye Heights for over-the-nose vision.  Larger subjects are emphasized for evaluations of vision under the overhead and canopy bow.  The larger subjects are also emphasized in examinations of potential obstructions by the glare shield toward the upper part of the main instrument panel, since they are the most likely to experience visual problems of this kind.  The smaller subjects tend to experience visual obstructions produced by the control wheel or stick, throttle and the knees.

PROCEDURE

Initially, we used a carpenterís inclinometer fitted with a sight tube to measure visual angle.  The sight tube is equipped with cross-hairs at each end.  Later we used an Abney Level.

The examination proceeds as follows:

The subject, dressed in full flight gear minus helmet, is installed into the seat.  Parachute and inertia reel harnesses are buckled and adjusted.

External Vision

            Forward Cockpit

Part of the examination of vision from the cockpit is conducted with the canopy open - part of it with the canopy closed.  We usually begin with the canopy open to permit the subject to gain experience using the measuring instruments before isolating him under a closed canopy.

            a. The subject adjusts the seat full-up, as illustrated in the figure below, with the head in the Frankfurt Plane. He/she sights straight ahead over the nose of the aircraft to the ground at the lowest attainable visual angle. Click on for a proposed data blank to use in recording vision data. 

            b. The subject then thrusts his/her head upward and aft to gain additional vision over the nose and the angle of the line of sight is measured again. 

            c. With the subjectís head again in the Frankfurt Plane, measure the angle of vision straight ahead upward under the windscreen bow. See an illustration of this measurement, see the the second figure below. 

            d. Lines of sight over the nose and upward under the canopy bow are repeated typically at one-inch intervals from full-up to full-down.  Care should be taken to ensure that intervals begin at the full-up seat position, even though the subject's head may strike the canopy when the seat is full-up with the canopy closed, or that the initial seat position studied may not be adjusted precisely to one of these intervals.

            e. The canopy is then closed.  The subject raises the seat to full-up or until appropriate head motion clearance is attained.  With the head oriented in the Frankfurt Plane, the subject sights through the sight tube or Abney Level straight ahead over the canopy bow (as appropriate).

            f. With the subject's head oriented level, measure and record the angles of vision out of the lowermost left corner of the windscreen, just forward of the root of the canopy bow as well as aft of the canopy bow at its junction with the side sill, as appropriate.

            g. A measurement is also taken of the maximum depressed line of sight over the side of the cockpit, perpendicular to the long axis of the fuselage.

            h. These measures of vision are modified as appropriate for flight decks and other side-by-side cockpits.

            i. The canopy is then opened.  Without disturbing the position of the seat, examine vision to display surfaces in the cockpit.

 

OVER-THE-NOSE VISION, HEAD IN FRANKFURT PLANE. With the head oriented in the Frankfurt Plane, the subject sights through a sight tube/inclinometer or other appropriate sighting device straight ahead over the nose of the aircraft.  The angle from horizontal is recorded. 

 

OVER-THE-NOSE VISION, HEAD TILTED UP AND AFT. The subject rotates his/her head upward and aft to gain additional vision over the nose. Using an appropriate sighting device, the angle from horizontal is measured and recorded. 

 



VISION UPWARD, UNDER THE CANOPY, HEAD IN FRANKFORT PLANE. With the head oriented in the Frankfurt Plane, the subject sights through a sight tube/inclinometer or other appropriate sighting device straight ahead and upward under the canopy frame. The angle from horizontal is recorded. 

            Aft Cockpit

            a. Measures of vision is taken in the forward cockpit are repeated, as appropriate, in the aft cockpit.

            b. To offer realistic visual field to the test subject, another subject or assistant, wearing a helmet, is seated in the forward cockpit and the seat adjusted, with the canopy closed, so that the helmet appropriately clears the underside of the canopy.  The subject in the aft seat, which has been similarly adjusted to obtain similar, but bare headed clearance, sights along the long axis of the aircraft, over the helmet of the forward occupant or the head box, whichever dominates in the obstruction to vision, in an attempt to sight over the nose of the aircraft.  In addition, the subject should move his/her head to the side to look beside the head box or helmet and above the shoulder of the forward occupant and attempt to obtain a view over the nose.  If and when the subject achieves this, it is important for the investigator to establish a visual reference point in the forward cockpit to ensure that all subjects establish a comparable line of sight.

Internal Vision

Visual access to internal displays potentially obscured by cockpit structures and body parts is evaluated with the seat adjusted upward until appropriate head clearance with the canopy is obtained, or full-up, whichever occurs first.  With the head oriented in the Frankfurt Plane, the subject visually examines the instrument panel to determine if any displays are obscured.  The glare shield, control column and wheel, as well as the knees, should receive special attention.  Using a line drawing of the instrument panel, the subject should diagram those portions of the panel, if any, that are obscured.  Seat position should also be recorded.

ANALYSIS AND RESULTS

When there are adequate numbers of subjects representing the specified minimum Sitting Eye Height, analysis can be as simple as averaging the line-of-sight values for each seat position.  For complete understanding of Sitting Eye Height and vision relationships, however, regression equations should be prepared and regression plots made.  Table 2 presents data regressed from such an equation for the T-37B.

Visual angles over the nose, especially, must be differentiated in terms of the aircraft structure over which the lowest visual angle is obtained.  For the higher seat positions and eye heights, this will likely be the actual nose of the aircraft.  For lower seat positions and shorter eye heights, it may be the glare shield, or some intermediate structure.  As the eye is lowered (for whatever reason) in the T-38A, for example, the "aircraft structure horizon" changes from the nose to the base of the windscreen and, immediately thereafter, to the glare shield. 


VISION FROM THE LEFT COCKPIT OF THE T-37B.

Sitting Eye Height = 28.9", the Small Generalized Female, Table 1.

                   L i n e s   o f   S i g h t   i n   D e g r e e s 

(Rounded off to the nearest whole degree)

 

SEAT POSITION

O'NOSE*

O'NOSE

OVER BOW*

UNDER BOW*

 

 

HEAD UP/AFT

 

 

 

 

 

 

 

FULL-UP

- 10 Degrees

- 12 Degrees

+23 Degrees

+11 Degrees

   - 5/8"

- 10

- 12

+24

+12

- 1 1/4"

  - 9

- 11

+26

+14

- 1 7/8"

  - 9

- 11

+27

+15

- 2 1/2"

  - 8

- 10

+29

+17

- 3 1/8"

  - 8

- 10

+30

+18

- 3 3/4"

  - 8

- 10

+31

+19

- 4 3/8"

  - 7

  - 9

+33

+21

FULL-DOWN

  - 7

  - 9

+34

+22

 * Head in Frankfurt Plane.

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