Patent Publication Number: US-6658985-B2

Title: Site head with integrated laser designator for use in aircraft such as a rotorcraft

Description:
TECHNICAL BACKGROUND 
     This invention relates to a sight head equipping an aircraft such as a rotorcraft. More precisely, the object of the invention is a sight head fitted with an integrated laser designator for the illumination of a target using a laser beam radiating in the visible or near infra-red spectrum. 
     The invention applies in particular to a sight head of a helicopter weapon fire control system. 
     STATE OF THE TECHONLOGY 
     It is known to fit military helicopters with a weapon fire control system equipped with a sight head. More precisely, the sight head comprises a pod the major part of which is generally located above the roof of the helicopter fuselage. An eyepiece carrier arm extends the sight head to the inside of the fuselage. 
     Under certain conditions of use, it is necessary to illuminate the target with a laser beam. Depending on whether the operator observes the target with his naked eye or using night vision goggles, a laser beam transmitting in the visible or near infrared spectrum is used. 
     Currently, the illumination of the target is performed using a device known as a ‘laser designator’. More precisely, this device is hand held outside the helicopter. In effect, the fuselage of the helicopter creates a strong attenuation of the laser frequencies and would cause harmful internal reflections if the laser pointer were to be used inside the helicopter. 
     Because of their manual characteristics and the need for deployment outside the helicopter, the existing laser designators do not allow precise sighting. The usability is thus reduced. 
     FR-A-2 640 037 relates to a sight mast for a helicopter fitted with a telemeter or laser photoelectric shutter which looks through the blades of the rotor. This arrangement allows the motion of the blade during the alignment phase between the sight and the seeker head of a missile to be taken into account. 
     DESCRIPTION OF THE INVENTION 
     Precisely, the object of the invention is a sight head equipped with an integrated laser designator to allow an optical pointing accuracy and an optimum usability, without degrading the inherent characteristics of the sight head. 
     More precisely, the invention refers to a sight head for a rotorcraft, comprising a pod in which at least a part is available mounted externally to the rotorcraft fuselage, characterized by the integration of a laser designator in the said part of the pod. 
     Preferably, the part of the pod installed externally to the fuselage has the sight head covered by an existing aerodynamic fairing. Thus, the aerodynamic characteristics of the sight head are not modified by the installation of the laser designator. 
     Advantageously, the laser designator comprises a laser transmitter and a means of adjusting its alignment within the said pod, allowing the laser beam from the laser designator to be aligned parallel to a sight axis of the sight head. It is thus possible to accurately adjust the parallelism of the laser beam with the axis of the sight head. 
     In this case, the preferred alignment method consists of three adjustment screws equally spaced around the laser transmitter. 
     Furthermore, the laser designator also comprises its own power supply for the laser transmitter and a radio receiver, required to start and stop the laser emission. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     This document describes as an illustrative example, which is non-exhaustive, a preferred way of implementing the design of the invention, by reference to the drawings at annex in which: 
     FIG. 1 is a side view, which represents schematically the forward part of a helicopter fitted with a sight head and integrating a laser designator in accordance with the invention; 
     FIG. 2 shows a perspective schematic view of the sight head in FIG. 1; and 
     FIG. 3 is an exploded perspective view of the laser designator fitted to the site head of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     In FIG. 1, the front part of the helicopter has been shown schematically. This comprises a fuselage  10  where the roof supports a sight head  12  of a weapon fire control system (not shown). 
     The sight head  12  comprises a pod  14  of which a main assembly  16  is situated above the roof of the fuselage  10 , externally to the helicopter. Another part  18  of the pod  14  is located inside the cockpit  20  of the helicopter. An eyepiece carrier arm  22  fitted with an eyepiece  24  is fitted to the part  18  of the pod  14 , in order to allow an observer inside the cockpit  20  to utilise the sight head  12 . 
     The parts  16  and  18  of the pod  14  and the eyepiece carrier arm  22  are used to house different optical components (not shown) allowing an observer looking through the eyepiece  24  to view a scene along the sight axis  26 . Only the output lens  28  fitted on this axis  26  can be seen in FIG.  2 . 
     In the design configuration shown in FIG. 2, the main assembly  16  of the pod  14  also allows a camera  30  to be fitted. 
     In accordance with the invention, a laser designator is also fitted inside the main assembly  16  of the pod  14 . 
     More precisely and as illustrated in particular in FIG. 3, the laser designator  32  is installed in a zone within the main assembly  16  of the pod  14 , and the externally mounted portion covered by an existing aerodynamic fairing  34 . In the design configuration represented in the figures, the zone which houses the laser designator  32  is situated above the camera  30 . However, this zone can be sited in any other available appropriate location, depending upon the specific characteristics of the sight head installation arrangements. 
     Generally, the zone in which the laser designator  32  is fitted is chosen taking account of a certain number of criteria, such as the level of comfort for the operator, the availability of adequate installation space to accept the different assemblies of the laser designator, the existence of adequate mounting seats to ensure a rigid installation, the ease of maintenance access and the conformance with the external envelope geometry of the sight head. 
     The laser designator  32  essentially comprises a laser transmitter  36 , a stand-alone power supply  38  for the transmitter and a radio receiver  40 . 
     The laser transmitter  36  is, for example, a laser emitting diode able to produce a laser beam in the visible or near infra red spectrum, depending on whether the observer is viewing a scene with the naked eye or using night vision goggles. 
     The laser transmitter  36  is fitted to a reference support unit  42 , fitted inside the assembly  16  of the pod  14 , for example using a screw  43 . More precisely, the laser transmitter  36  is fitted to the support unit  42  using an angular adjustment arrangement  44 . The said adjustment arrangements are used to allow accurate adjustment of the parallelism of the laser beam emitted by the laser transmitter  36  with respect to the sight axis  26  of the sight head  12 . 
     In the preferred embodiment of the invention shown in FIG. 3, the angular adjustment arrangements  44  comprises three adjusting screws  46 , in line with the axis of the laser transmitter  36  and equally spaced around this axis. 
     More precisely, a forward part of the laser transmitter  36  is attached to a plate  48 , at the front of the support unit  42 , and passes through an opening  49  machined in the said support unit. Furthermore the screws  46  pass freely through the holes  50  and  52  formed respectively in the support unit  42  and the plate  48 , and they are screwed into the nuts  54 , at the front of the plate  48 . Helical compression springs  56 , fitted to each of the screws  46  between the support unit  42  and the plate  48 , ensure that the two parts remain permanently separated from each other. 
     When the aerodynamic fairing  34  is in place, i.e. when fitted to the main assembly  16  of the pod  14 , for example using a screw (not shown), the forward end of the laser transmitter  36  is opposite to an opening  58  made in the said fairing and each of the nuts  54  is then opposite a hole  60  drilled in the fairing  34 . 
     It is thus possible to adjust alignment of the beam emitted by the laser with respect to the sight axis  26 , by introducing a tool such as a spanner through the holes  60 , in order to access the nuts  54 . In fact, by rotating one of the screws  54  in one or other direction, using the appropriate tool, has the effect of compressing or lengthening the spring  56  held captive on the screw  46  by the nut. Thus it is possible to adjust the distance between the plate  48  and the support unit  42 , with respect to the screw  46  considered. 
     The power supply  38  is, for example, a dry cell or electrical supply battery. It is located beneath an opening in the fairing  34 , usually closed by a hatch  62 . The power supply  38  is used to supply the power to the laser transmitter  36  as well as the radio receiver  40 . 
     Finally, the radio receiver  40  is connected electrically to the laser transmitter  36  and the power supply  38  in order to allow the laser transmitter  36  to be switched on and off. 
     Of course, the invention is not limited to the design configuration, which has been described for example purposes. Hence, as has already been stated, the laser designator may be installed in a different design of sight head and in a different location to that described, and still remain within the framework of the invention.