Abstract:
In a simulator for helicopters, the images seen are displayed through the bottom windows by means of a system collimated to infinity, including, for each side of the cockpit, a projector (15, 16), a spherical mirror (12, 13) and a screen (17, 18).

Description:
BACKGROUND OF THE INVENTION 
     In flight simulators, such as helicopter flight simulators, there is a known way of obtaining a wide horizontal field (of 180° or more) by means of projection systems collimated to infinity using a spherical mirror out of axis and a screen, that is also spherical, associated with a projector. By contrast, in the vertical direction, the size of the field attains hardly 40° because of the conformation of the optic system. To enable the display of the image seen through the bottom windows of a helicopter, it is generally the practice to use a cathode-ray tube monitor with a system of display at infinity but, in this case, the field obtained through the monitor is inadequate. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is a projection system for cockpit simulators, especially for helicopter simulators, having both a big horizontal field and a big vertical field, this goal being achieved without parallax errors. 
     In addition to the known collimated projection system with display at infinity using a spherical mirror for the display of the upper part of the vertical field, the system according to the present invention includes a projection system collimated to infinity using a spherical mirror out of axis and a lateral lower screen for the display of each of the two lower lateral parts of the vertical field. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention shall be understood more clearly from the following detailed description of an embodiment, taken as a non-restrictive example and illustrated by the appended drawings, wherein: 
     FIGS. 1 and 2 respectively show a top view and a sectional view of a known type of simulator; 
     FIG. 3 shows a side, sectional view of a system according to the invention, and 
     FIG. 4 shows a top view of the system of FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is described here below with reference to a helicopter simulator, wherein the bottom part of the cockpit has opaque zones at the center and windows on the sides, and the role of the simulator is to restore, in addition to the main wide-angle field, the image seen by the pilot as well as by the co-pilot through these bottom windows. Naturally, the invention is not restricted to the application to a helicopter simulator and may be implemented in a simulator wherein it is necessary to display images with wide horizontal and vertical fields, a substantially central part of these images being masked by the cockpit. 
     FIGS. 1 and 2 shows a schematic view of a prior art cockpit simulator with several (for example three) projectors. This simulator has a mirror 1 covering a horizontal field of about 180°. The mirror 1 is associated with a screen 2 also covering a horizontal field of about 180°. In the present example, the projection system has three projectors P1 to P3 that cooperate with the mirror 1 and the screen 2 and are located behind and on top of the observers seated in their usual places (pilot&#39;s seat SP and co-pilot&#39;s seat SC) in the cockpit 3. To display the images that have to be seen through the lateral bottom windows 4A, 4B of the cockpit, a complementary projection system is positioned in the vicinity of these bottom windows. This complementary system is referenced 5 for the left-hand bottom windows and 6 for the right-hand bottom windows. Each of these systems has a cathode-ray tube screen, a semi-transparent plate at 45° and a spherical mirror. For reasons of layout, the distance between the observer and the mirror of the corresponding complementary projection system is appreciably greater than the radius of this mirror. This means that the field of this complementary system is greatly reduced and can be used to cover only a small part of the bottom windows. 
     FIGS. 3 and 4 show the projection system according to the invention. This system has an upper mirror 7 similar to the prior art mirror 1. This mirror can advantageously be used to display a horizontal field of about 180° to 225° that can be seen through the upper windows FS of the cockpit. 
     The mirror 7 is associated with an upper screen 8 similar to the screen 2 of FIGS. 1 and 2, and with three projectors 9, 10, 11 making it possible to obtain a panoramic image of about 180° in the horizontal direction. The screen 8 is above the observers&#39; (pilot&#39;s and co-pilot&#39;s) eyes. 
     To display the images liable to be seen through the bottom windows of the cockpit, the invention provides for the positioning (cf. FIGS. 3 and 4), beneath the upper mirror 7, of two lateral lower mirrors 12, 13 that are symmetrical with respect to the longitudinal axis 14 of the cockpit 3 of the simulator. Each of these mirrors 12, 13 is associated with a lateral screen 17, 18 respectively and with a projector 15, 16. The mirrors 12, 13 are spherical mirrors and are positioned so that they can be seen by the pilot and co-pilot through their respective bottom windows. The edges of these mirrors 12, 13 and screens 17, 18 are at about the same horizontal level and slightly above the lower edge of the mirror 7. The mirrors 7, 12, 13 are advantageously rigid, made of glass or of a plastic/foam/plastic sandwich material, thus enabling them to be efficiently joined by means of the sharp edges of mirrors such as this. It will be noted that, for the mirrors 7, 12, 13 to be properly joined to one another, it is necessary, in particular, for the lower edge of the mirror 7 to be a sharp edge, for the mirror 7 masks the upper edge of the mirrors 12 and 13. This means that, with presently used technologies, at least this mirror 7 should be rigid. 
     The lateral projectors 15, 16 are positioned on either side of the cockpit 14, roughly at the level of the plane passing through the observers&#39; eyes. These projectors are of any appropriate type: based on light valves, liquid crystals or high brilliancy cathode-ray tubes.