Enclosure for position transmitter

The present invention relates to a enclosure for a control surface position transmitter used on aerospace vehicles. The enclosure has improved capability for protecting the components of the position transmitter from damage caused by moisture-induced corrosion. The enclosure is a can-shaped structure that includes separate compartments for its mechanical and electronic components. A series of channels and passageways allow air to circulate freely in and out of the mechanical component compartment, and the electronic component compartment includes a low power heater to keep the electronic components dry and moisture-free.

TECHNICAL FIELD 
This invention relates to position transmitters, and specifically to 
control surface position transmitters used on aerospace vehicles. Most 
specifically, this invention relates to control surface position 
transmitters that have improved capability for protecting their mechanical 
and electronic components from damage caused by moisture. 
BACKGROUND OF THE INVENTION 
Aircraft and other aerospace vehicles utilize a number of control surfaces, 
such as wing flaps, to achieve their aerodynamic performance. These 
surfaces are typically moveable by the pilot, and their proper use 
requires the pilot to have accurate information concerning the surface's 
actual position relative to the vehicle. Prior art position transmitters 
used in the aerospace field utilize a combination of mechanical and 
electronic components sealed within a suitable enclosure to determine the 
position of the control surface and to provide information to the pilot or 
the vehicle control systems concerning such position. 
As is well known, aerospace vehicles operate in a variety of precipitation, 
humidity, and altitude conditions. Precipitation and humidity often lead 
to corrosion, and therefore, prior art position transmitters have tried to 
seal their mechanical and electronic components inside a hermetic 
enclosure to prevent such damage. However, the hermetic seals in prior art 
devices have been observed to fail, and when they do, humid air that 
passes into the enclosure condenses, causes corrosion damage, and renders 
the position transmitter inaccurate and eventually unusable. Even minor 
breaks in the hermetic seal cause problems, especially when the 
transmitter and the aircraft it is attached to cycles between high and low 
altitudes characterized by low and high humidity levels, respectively. 
Because proper functioning of the position transmitter is crucial for safe 
operation of the flight vehicle, there has been a longstanding need within 
the aerospace industry for a enclosure with improved resistance to damage 
caused by the effects of moist air. The present invention satisfies that 
need. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a control surface position 
transmitter for use on an aerospace vehicle and having improved resistance 
to humid-air induced corrosion includes an enclosure that provides 
separate compartments for mechanical and electronic components, and has a 
combination of channels and passageways that allow air to circulate in and 
out of the mechanical compartment and also allow moisture that condenses 
within the mechanical compartment to be easily removed therefrom; the 
electronics component compartment is adjacent to the mechanical 
compartment within the enclosure, and includes a low power heater to 
insure dry, moisture-free operation of the electronic components. 
In one embodiment of this invention, the enclosure comprises: (a) a 
faceplate having a wall for attaching the enclosure to a support structure 
of the flight vehicle; (b) a bulkhead for attachment to the faceplate and 
for defining, in combination with the faceplate, a first compartment; and 
(c) a cover for attachment to the faceplate and for defining, in 
combination with the bulkhead, a second compartment; wherein the faceplate 
includes a cylindrical wall extending transversely and axially from the 
attachment wall, and adjacent first and second channels that extend 
circumferentially about the outer surface of the cylindrical wall; and 
wherein a passageway extends through the second channel and into the first 
compartment. In this preferred embodiment, the channels cooperate to shed 
water and other moisture from the surface of the enclosure, and the 
passageway allows for fluid communication between the first compartment 
and the environment exterior to the enclosure. 
In a preferred embodiment of this invention, mechanical components of a 
control surface position transmitter are located in the first compartment, 
and electronic components are located in the second compartment. The 
electronics compartment is kept dry by a low power electrical heater that 
provides sufficient energy to aid in evaporating any moisture in such 
compartment. 
Other features and advantages of the present invention will be understood 
with reference to the best mode for carrying out the invention, described 
below in combination with the drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
The invention is best understood by reference to FIG. 1 which shows a 
simplified, exploded view of the primary components of a enclosure 10 for 
a position transmitter in accordance with the present invention. The 
enclosure 10 is essentially a compartmentalized, can-shaped structure that 
comprises a faceplate 12, a bulkhead 14, and a cover 16. The faceplate 12 
includes an attachment wall 18 with mounting holes 20 for receiving bolts, 
screws, or other similar means for attaching the faceplate 12 to a 
structure of an aircraft or other aerospace vehicle. The faceplate 12 also 
includes spaced apart bosses 22a, 22b, 22c, 22d, each with a hole 24 for 
receiving screws, bolts or the like for attaching the bulkhead 14 and 
cover 16 thereto. The bulkhead 14 has holes 26 that correspond to the 
holes 24 in the faceplate 12, and the cover 16 has similar, corresponding 
holes 28. In the preferred embodiment of the invention, bolts (not shown) 
extend through holes 28 in the top surface 32 of the cover 16, thread into 
standoffs 27 that pass through corresponding holes 26 in the bulkhead 14; 
the standoffs 27 thread into the holes 24 in each boss 22a, 22b, 22c, 22d 
of the faceplate 12. 
The faceplate 12 includes a cylindrical wall 34 that extends axially from 
the attachment wall 18. The cylindrical wall 34 has an inner wall surface 
36 and an outer wall surface 38. As is also shown in FIG. 2, a first 
channel 40 extends radially inwardly and circumferentially about the outer 
surface 38 of the faceplate 12. A second channel 42 is axially adjacent to 
the first channel 40, and also extends radially inwardly and 
circumferentially about the outer surface 38 of the faceplate 12. The 
faceplate additionally includes a groove 44 in its outer surface 38 for 
receiving an o-ring or other similar seal 86, for sealing against the 
inner surface 46 of the cover 16 when the faceplate 12, bulkhead 14, and 
cover 16 are fully assembled. The faceplate 12 further includes a central 
bore 48 for carrying a bearing (not shown) that supports a shaft 96 (see 
FIG. 3). As is seen in FIG. 1, between the pair of bosses 22a and 22b, the 
cylindrical wall 34 of the faceplate 12 extends in the axial direction a 
greater distance than it does between the bosses 22c and 22d; between 
bosses 22a and 22b, the wall 34 forms a water collection surface 52. When 
the bulkhead 14 is attached to the faceplate 12, the surface 54 of the 
bulkhead 14 is in abutting relationship to the axial end 56 of the water 
collection surface 52. 
The bulkhead 14 is disk-shaped, and includes a groove 60 that extends 
circumferentially about its outer rim 62 for receiving an o-ring or other 
similar seal 88; the o-ring 88 abuts against the inner surface 46 of the 
cover 16 when the faceplate 12, bulkhead 14, and cover 16 are fully 
assembled. The bulkhead 14 also includes bore holes 63 for mounting 
position transducers 114 and 118 (see FIG. 3) as described in more detail 
below. 
The cover 16 includes an inner surface 46 and an outer surface 64; as 
indicated above, the inner diameter of the cover 16 is chosen so that when 
the cover 16 is assembled to the bulkhead 14 and faceplate 12, the cover 
inner surface 46 engages the seal 88 in the groove 60 of the bulkhead 14, 
and the seal 86 in the groove 44 of the faceplate 12. When fully 
assembled, the cover 16 and bulkhead 14 define a compartment 66 for 
electronic components (such as the transducers 114 and 118), and the 
faceplate 12 and bulkhead 14 define a compartment 68 for mechanical 
components (such as gears 108 and 110, described below.) The cover 16 also 
includes a conventional, environmentally sealed electrical connector 70 
(preferably of the pin-connection type) that allows for communication 
between electronics in the electronic components compartment 66 and an 
output transmitter (not shown). The connector 70 is secured to the cover 
16 by conventional means. 
A key feature of this invention is the manner that it prevents moisture 
from damaging the components in the mechanical compartment 68 and in the 
electronic compartment 66. Damage to such parts, caused by moisture, is 
believed to be a leading cause of failure of prior art position 
transmitters. The invention achieves its desirable water-protection 
capability by allowing air to readily enter and exit the mechanical 
compartment 68 of the enclosure 10. The manner that this is done is better 
appreciated with reference to FIG. 2, which is a sectional view along the 
lines 2--2 of the fully assembled enclosure 10 shown in FIG. 1. 
As seen in FIG. 2, the first channel 40 in the faceplate 12 is defined at 
one end by the attachment wall 18, and at the other end by an opposed, 
axially spaced apart first shoulder 72 that extends radially outwardly 
from the cylindrical wall 34 of the faceplate 12. The second channel 42 is 
defined by the first shoulder 72 and an opposed, axially spaced apart 
second shoulder 74 that extends radially outwardly from the cylindrical 
wall 34. As is seen in the Figure, the first shoulder 72 is axially 
intermediate the attachment wall 18 and the second shoulder 74. When the 
position transmitter 10 of this invention is installed for its intended 
use, e.g., on an aircraft, the axis A of the enclosure is preferably 
parallel to the horizontal plane. 
A slot 76 extends in the circumferential direction through the second 
shoulder 74 and provides fluid communication between the mechanical 
compartment 68 and the ambient atmosphere external to the enclosure 10. 
Accordingly, air freely passes into and out of the mechanical compartment 
68. Preferably, the circumferential length of the slot 76 is greater than 
its radial width to allow liquid condensate to drain easily from the 
mechanical compartment 68; slot widths in the range of about 0.5-0.7 
inches have been useful, with lengths somewhat greater, to allow water and 
other liquids to drain from the enclosure interior at a variety of 
aircraft attitude conditions. The axially extending centerline 78 of the 
slot 76 is radially inward of the outer end 80 of the first shoulder 72. 
Preferably the inner and outer surfaces 82 and 84, respectively, of the 
slot 76 are both inward of the shoulder end 80. As is seen in FIG. 2, the 
slot surface 82 is outwardly spaced from the portion 85 of the cylindrical 
wall 34 that lies between first and second shoulders 72 and 74. 
When fully assembled, the cover 16 is engaged against the outer surface 38 
of the faceplate 12 by the o-ring seal 86 in the groove 44. Additionally, 
the cover 16 is sealingly engaged against the rim 62 of the bulkhead 14 by 
the o-ring seal 88 in the groove 60. The use of o-rings is not critical to 
the invention; other types of sealing means will be useful, as is well 
known to those with ordinary skill in the art. The axial end 90 of the 
cover 16 is adjacent to the attachment wall 18 of the faceplate 12, and is 
between the wall 18 and the first shoulder 72. Because the cover end 90 
does not extend all the way to the attachment wall 18, air may readily 
flow between the wall 18 and cover end 90, past the first shoulder 72, 
through the slot 76, and into and out of the mechanical compartment 68, as 
indicated by the arrows 92. 
The outer surface 84 of the slot 76 is defined by the water collection 
surface 52. As a result, if moist air passes into the mechanical 
compartment 68 and then condenses, the condensate will, by the force of 
gravity, collect on the water collection surface 52, and flow through the 
slot 76 and out of the enclosure 10. Additionally, if the enclosure is 
exposed to fluid spray (e.g., rain, water washings, etc.) then in the 
unlikely event that water is able to follow the circuitous path shown by 
arrows 92 into the mechanical compartment 68, the liquid will also simply 
drain out of the slot 76 under the influence of gravitational forces. In 
the preferred embodiment of the invention, four slots 76 are spaced about 
a semicircular sector of the faceplate 12. When the enclosure 10 is 
installed on an airplane, the circumferential midpoint of one slot 76 is 
substantially aligned with the vertical direction when the airplane is at 
rest on the ground. 
The slot 76 through the second shoulder 74 therefore performs a dual role: 
allowing air to freely pass in and out of the mechanical compartment 68, 
and allowing any liquid, typically in the form of condensate, to easily 
drain from such compartment. This construction is contrasted with prior 
art designs, where air is excluded from the compartment by a hermetic 
seal; however once the seal breaks in these prior art designs, and air is 
able to leak into the compartment, it is trapped there by the still 
functioning (albeit not perfectly functioning) seal. If the trapped air 
contains any moisture, as it likely will, that trapped moisture will 
eventually cause any metal components in the prior art enclosure 
compartment to corrode. 
As shown in FIG. 2, components in the mechanical compartment 68 are 
physically isolated, by the bulkhead 14, from the components in the 
electronic compartment 66. The bulkhead 14 therefore keeps moisture in the 
mechanical compartment from passing into the electronic compartment. Any 
moisture that does, however, enter the electronic compartment 66 is 
evaporated by heater 126 attached to heat sink 124. The heat sink 124 is 
arc shaped and is attached to a stand-off 122 on the electronics side of 
the bulkhead 14, so that the heat sink 120 is separated from the bulkhead 
14 by a slight air gap 123. The air gap 124 thermally insulates the heat 
sink 120 from the bulkhead 14. A low wattage heater 126, which draws from 
the same voltage source (not shown) that powers the electronic components 
within the enclosure, is thermally coupled to the heat sink 124. During 
operation of the aircraft, the heater 126 constantly draws power and 
raises the temperature of the heat sink 120, The heat sink 120 radiates 
heat into the space within the electronics compartment 66, limiting the 
condensation of humid air that may find its way into the electronics 
compartment 66; the heat also vaporizes any moisture that does condense in 
the electronics compartment 66, which keeps the electronics compartment 66 
dry and corrosion free. Optionally, the bulkhead 14 may include a vent 
hole 94 that allows air to pass between the electronics compartment 66 and 
the mechanical compartment 68; any humid air in the electronics 
compartment 66 when the aircraft is on the ground will likely be drawn out 
of such compartment, through the vent hole 94, as the aircraft takes 
flight into higher altitudes and lower pressures. Thus, the vent hole 94 
assists the electronics compartment 66 in cleansing itself of humid air. 
While the enclosure of this invention may have a variety of different uses 
as a control surface position transmitter, a preferred application is that 
of a flap position transmitter for an aircraft such as a modem, turbine 
engine powered airplane. As is well known to those skilled in the art, a 
flap position transmitter of this sort informs the pilot of the 
aerodynamic position of the wing flaps, so that they may be adjusted as 
necessary, during flight. In the typical case, the flap position 
transmitter includes a rotating shaft that is attached by appropriate 
linkages to the underside surface of the flap; movement of the flap is 
either the up or down direction causes the shaft to rotate. Such rotation 
is then converted, through conventional electronic processing, into a 
signal indicative of the flap's position that is sent to the pilot in the 
cockpit. 
In applications as just described, and as shown in FIG. 3, the shaft 96 of 
the transmitter 100 extends in the axial direction from the enclosure 10; 
a first end 102 of the shaft 96 is secured to a flap linkage 104. A second 
end 106 of the shaft 96 is attached to a main gear 108 that is one of the 
mechanical components secured within the enclosure 10. The main gear 108 
drives additional gears coupled to transducers that convert the rotary 
motion of the gear to an output voltage signal in the typical fashion; the 
output voltage is proportional to the amount of rotation of the gear. The 
main gear 108 drives a pinion gear 110 coupled by shaft 112 to a linear 
transformer 114. Similarly, the main gear 108 drives another pinion gear 
(not shown) coupled by shaft 116 to a synchronization transmitter 118. 
Other pinion gears may also be driven by the main gear 108, depending on 
the particular function to be performed by the position transmitter. In 
the embodiment shown in the Figure, the output voltage from the linear 
transformer 114 is transmitted to the pin connector 70 and then to a 
computer in the cockpit. This signal informs the pilot of the position of 
the wing flaps. The signal may also be processed by appropriate electronic 
circuitry (not shown) within the electronics compartment 66 and sent to 
relays that are programmed to, e.g., turn on or off warning lights such as 
the "Fasten Seat Belt" light in the passenger portion of the airplane. The 
synchronization transmitter performs a similar function as the linear 
transformer, but instead provides a signal to, e.g., a flight control 
computer that controls other functions of the airplane that are affected 
by the position of the control surface. 
It should be apparent from the foregoing that the enclosure of this 
invention is not limited to application as a flap position transmitter. 
The particular mechanical and electronic components housed therein are not 
critical aspects of the invention. The enclosure will find numerous uses 
in operating environments where the components must be kept free of 
moisture that will invariable and eventually cause corrosion and failure. 
The enclosure of this invention achieves such desirable characteristics by 
its use of a cylindrically-shaped faceplate with a plurality of grooves 
extending about its outer diameter that allow the enclosure to efficiently 
shed water that collects on the enclosure outer surface; and at least one 
labyrinth passageway that is constructed and arranged to allow air to 
freely circulate through the enclosure's mechanical compartment and 
thereby continually cleanse the compartment of humid air that might 
otherwise stagnate and condense. If any humid air condenses within the 
mechanical compartment, the construction of the faceplate and preferred 
orientation of the enclosure when attached to the aircraft causes the 
condensate to collect on the water collection surface and flow through the 
slot and out of the mechanical compartment. The low wattage heater in the 
electronics compartment keeps the electronics dry and corrosion free. 
Although the present invention has been shown and described with respect to 
a preferred embodiment thereof, workers skilled in the art will recognize 
that changes can be made in form and detail without departing from the 
spirit and scope of the invention.