Abstract:
In a method for operating an infrared countermeasure optical device on an aircraft, the improvement comprises the steps of positioning a deflector upstream from the optical device to allow said optical device to operate in high-speed freestream flows.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims rights under 35 U.S.C.§119(e) from U.S. Application Ser. No. 61/010,429 filed Jan. 7, 2008. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     This invention was made with United States Government support under Contract No. HSSCHQ-04-C-00342 awarded by the Department of Homeland Security. The United States Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to infrared countermeasures for use on aircraft and more particularly to means for limiting loads on optical devices used in such infrared countermeasures. 
     2. Brief Description of Prior Developments 
     Infrared countermeasure optical devices are conventionally positioned on aircraft. A need exists for a way to protect infrared countermeasure optical devices from high-speed airflow in order to maintain low torques on the rotating head of the device, lower drag load on the optical device, and limit foreign object damage to the optical device. This protection must not degrade performance of the optical device due to additional physical blockage of lines of sight. 
     SUMMARY OF INVENTION 
     According to the present invention, a deflector diverts airstream away from the infrared countermeasure optical device while minimizing drag increase to the airframe. This results in very low torques on the optical device, allowing it to operate in high-speed freestream flows without stalling motors. Also, the deflector provides significant FOD protection and does not add any additional blockage to the field of view beyond what is blocked by the aircraft fuselage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is further described with reference to the accompanying drawings wherein: 
         FIGS. 1 and 2  are various views of a preferred embodiment of the deflector of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Optic devices with rotating heads produce bluff bodies in the airstream that are sensitive to high-speed airflow due to high aerodynamic torques, FOD susceptibility, and high drag loads. To protect and shield these optic devices, a deflector was developed consisting of a contoured plate swept aft and mounted upstream of the optic device. The width, height, and sweep angle of the deflector were selected using advanced viscous computational fluid dynamics methods to assure the high-speed airstream was diverted from the optic device (jamhead) for all flight conditions. Designed for subsonic operation, the upstream airflow reacts to the deflector diverting flow outboard of the optical device, resulting in low torque on the optic device rotating azimuth and elevation heads. The deflector interface drawings are shown in  FIG. 2  outlining the profile and the mounting location relative to the optical device (PTH). The resulting design is a low cost method that shields the optic device from high aerodynamic torques and also provide FOD protection for sensitive optics. 
     The deflector profile and upstream location relative to the jamhead were derived to assure the high-speed flow that would normally impinge on the jamhead would be diverted over the jamhead. The height of deflector was limited to assure no additional blockage of the laser port beyond what was blocked by the aircraft fuselage. As a result, the jamhead is operating in the wake of the deflector and therefore has very low dynamic pressure and low torque and drag loads. 
     Wind tunnel testing of a production operational optical device was completed verifying operation and integrity at speeds up to 300 knots. This testing verified that the optical device with a deflector mounted upstream has the capability to accurately point and track over various required flight envelopes including speeds up to 300 KCAS. The point and track capability was derived by the Optical Device maintaining allowable motor current and temperature limits for safe operation. 
     Referring to  FIG. 1 , the deflector includes a base surface  10  and a plurality of vertical ribs as at  12 ,  14 ,  16  and  18 . There is also an angular front surface as at  20 . 
     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications or additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.