Cooling system for optical port

A system for eliminating distortion of optical ports during supersonic flight includes an electrohydraulic pump which is controlled by a potentiometer actuated by expansion and contraction of a gas that acts on a piston which is mounted in a cylinder. The cylinder is mounted in thermal contact with a frame which supports one or more layers of optical glass. The electrohydraulic pump operates to pump cooling fluid into the frame thereby cooling the frame and the optical glass when the gas expands as a result of heating during supersonic flight.

BACKGROUND OF INVENTION 
The present invention relates generally to the field of aerial photography 
and more particularly to a cooling system for an optical port. 
Supersonic aircraft typically incorporate optical ports for aerial 
photography. These ports incorporate one or more layers of optical glass 
mounted in a frame attached to a fuselage of the aircraft. During 
supersonic flight, there is heating of an outer skin of a fuselage and 
consequently heating and distortion of the frame and the optical glass. 
This heating causes distortion of the optical glass and a loss of quality 
in photographs taken therethrough. The heating problem is pronounced in 
pilotless aircraft which operate at extreme speeds, resulting in a high 
degree of heating and, consequently, substantial thermal distortion of the 
optical glass. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a cooling system for an 
optical port which is capable of preventing overheating of an aircraft 
optical port during supersonic flight. 
Another object of the present invention is to provide a cooling system for 
an optical port which prevents thermal distortion of the optical port. 
Another object of the present invention is to provide a cooling system for 
an optical port which is capable of high quality photography during 
supersonic flight. 
Yet another object of the present invention is to provide a cooling system 
for an optical port which comprises a small number of simple component 
parts resulting in long term reliable operation. 
The foregoing and other objects and advantages of the present invention 
will appear more clearly hereinafter. 
In accordance with the present invention there is provided a cooling system 
for an optical port for supersonic aircraft which comprises a frame 
connected to the aircraft's fuselage and which supports a plurality of 
layers of optical glass. 
An electro-hydraulic system includes an electro-hydraulic pump connected to 
a reservoir and to the frame via hydraulic lines. Operation of the pump is 
controlled by a potentiometer which is connected to a thermal sensing 
element. The thermal sensing element includes a piston which operates in a 
cylinder mounted in the frame and is at the same temperature as the frame. 
The space under the piston is filled with gas such as FREON.RTM. -12, 
which has a co-efficient of expansion that is linearly proportional to 
changes of temperature. When the frame is heated, the FREON.RTM. -12 gas 
expands and actuates the potentiometer to operate the electrohydraulic 
pump to deliver a suitable rate of flow of cooling hydraulic fluid to the 
frame. As the optical glass gets hotter, the FREON.RTM. -12 gas expands, 
moving the potentiometer to increase the operation of the pump, thereby 
increasing the cooling of the glass. 
The cooling system provides increased cooling flow during periods of 
increased heating of the glass, thereby maintaining acceptable temperature 
of the glass and preventing thermal distortion.

DETAILED DESCRIPTION OF THE INVENTION 
With reference to the drawings, wherein like reference numbers designate 
like or corresponding parts throughout, there is shown in FIG. 1 a cooling 
system for an optical port 10, made in accordance with the present 
invention, which includes a frame 12 which supports a plurality of plates 
or layers of optical glass 14, 16, an electro-hydraulic pump 18, a 
reservoir 20 and hydraulic lines 22, 24 which connect the reservoir 20 and 
frame 12. The frame 12 is connected to the fuselage 26 of an aircraft by 
conventional fasteners, such as bolts or screws, which are not shown. The 
electro-hydraulic pump 18 is connected in flow communication to reservoir 
20 via hydraulic lines 74, 76. The electro-hydraulic pump 18 is connected 
to a source of electrical power via electrical lines 28, 30 and to a 
potentiometer 32 via electrical lines 34, 36. 
Potentiometer 32 has a movable contact 38 which is connected via a rod 40 
to a piston 42 of a thermosensing element 44. 
The thermosensing element 44, which forms a key feature of the present 
invention, includes a cylinder 46 which is attached to the frame 12, as is 
shown in FIGS. 1 and 2 and thus the thermosensing element 44 is at the 
same temperature as the frame 12 and the optical glass 14, 16. The piston 
42 is slideably mounted in cylinder 46. A space 48 under the piston 42 is 
filled with gas which has a co-efficient of expansion which is 
proportional to changes in temperature and creates a generally linear 
volume to temperature relationship. 
A preferred gas for this application has been found to be FREON.RTM. -12 
(dichlorodifluoromethane), having the formula CCl.sub.2 F.sub.2, molecular 
weight 120.91, registry number 75-71-8. 
A preferred composition of the optical glass is: Aluminosilicate glass, 
glass code 1720, color-clear, form BT Class I, service temperature 490 
degree Centigrade, preferred thickness in the order of 3.2 mm. 
The layers of optical glass 14, 16 are supported by projecting portions 68, 
70, 72 which are integrally formed in the frame 12 as is shown in FIG. 2. 
The cross-sectional shape of the frame 12 preferably has the general 
configuration of a capital letter "E". The layers of optical glass 14, 16 
may be circular or, alternatively, rectangular in shape when viewed in 
plan view. 
Relatively thin walls 50, 52 of the cylinder 46 allow the gas in the space 
48 below the piston 42 to expand or contract in accordance with heating or 
cooling of the fuselage 26 and the frame 12. 
By way of example, a space 58 between the optical glass layers 14, 16 is 
typically in the order of 2 to 2.5 mm and a surface 60 of the optical 
glass layer 14 is typically recessed approximately 3 mm below outer 
surface 62 of fuselage 26. These dimensions are by way of example only and 
do not constitute limitations on the present invention. 
During operation, the temperature of the optical glass 14, 16, the frame 12 
and the gas interspace 48 are initially the same. When the temperature of 
the frame 12 increases, for example, due to supersonic aircraft speed, the 
temperature of the gas in the space 48 is similarly raised. The gas in the 
space 48 expands, thereby moving the piston 42 and the potentiometer 32 in 
the direction shown by an arrow 66 in FIG. 1, changing resistance of the 
potentiometer 32 and causing the electro-hydraulic pump 18 to turn on or 
to increase its pumping action and pump hydraulic fluid into the cavity 54 
of the frame 12 to cool the frame 12 and the optical glass 14, 16. 
The glass layers 14, 16 form an optical port 64 and the system 10 according 
to the present invention is used typically with a camera 56 which is shown 
in broken lines 56 in FIG. 1 for aerial photography. Cooling of the frame 
12 and the optical glasses 14, 16 prevents thermal distortion of the 
optical glasses 14, 16 and improves clarity and accuracy of photographs 
taken by the camera 56. 
The foregoing specific embodiments of the present invention as set forth in 
the specification herein are for illustrative purposes only. Various 
deviations and modifications may be made within a spirit and scope of this 
invention, without departing from a clearly discernable theme thereof.