Thermally compensating insert fastener

A fastener assembly is shown including a cylindrical support structure with a bore provided partially therein, the bore having a wall surface with a slot, and a bushing, disposed within the bore of the cylindrical support structure, having an end and an outer surface with a slot therein. The bushing further includes a bore with a first portion having a first diameter and a second portion having a second different diameter, the bushing also having a pair of tangs extending from the end. The fastener assembly further includes a nut, partially disposed within the second portion of the bore of the bushing, the nut having an outer surface with a pair of lugs disposed on the outer surface to engage the pair of tangs of the bushing and a pin disposed juxtapositional the slot of the wall surface of the cylindrical support structure and juxtapositional the slot of the bushing. The fastener assembly still further includes a pin disposed juxtapositional the slot of the wall surface of the cylindrical support structure and juxtapositional the slot of the bushing. With such an arrangement, a fastener assembly is provided in which a forward shell section and an aft shell can be interconnected independent of the cylindrical support structure, thus maintaining circularity of airframe components and minimizing circular distortion.

BACKGROUND OF THE INVENTION 
This invention pertains generally to fasteners and particularly to a 
thermally compensating insert fastener for interconnecting two sections of 
a missile. 
It should be appreciated in an apparatus such as a missile it is often 
desirable to construct a missile in sections. Typically the missile 
includes a radome, a guidance section, a warhead section, a flight control 
section and a rocket motor section. In a missile, the guidance section can 
be pressurized to prevent high voltage arcing during operation at high 
altitudes. Numerous seals are employed to maintain guidance section 
pressure during passive captive carry flight and during active operational 
free flight. Loss of pressure during flight can cause the guidance section 
which houses a target seeker to operate incorrectly. 
One known cause of loss of pressure in the guidance section during flight 
is from an improper seal at an interconnection of two sections of the 
missile. One type of interconnection for connecting a forward titanium 
shell with an aft titanium shell includes an inner titanium support 
structure which is mutually interconnected with the forward and aft 
titanium shells with a set of eleven fasteners. Each of the fasteners 
include an external countersunk screw and a "Keensert", which is an 
externally threaded bushing having an internally mounted nut, affixed 
within the internal support structure. 
With such an arrangement, when the fasteners are tightened, deformation of 
the forward and aft shells will occur as the forward and aft shells are 
drawn toward the internal support structure. Since the inner diameter of 
the forward shell will not exactly match the outer diameter of the aft 
shell and the inner diameter of the aft shell will not exactly match the 
outer diameter of the internal support structure due to manufacturing 
tolerances, varying radial gaps will exist. As the fasteners are 
tightened, scalloping of the forward and aft shells will occur. Typically, 
visible measurable shell scalloping between fastener locations can be 
observed with the forward shell being the most deformed. The 
interconnection also includes two seals using butyl O-rings. One O-ring 
seals the forward shell to the support structure. The other O-ring seals 
the aft shell to the support structure. When the forward shell and the aft 
shell are interconnected with the support structure, the seals are 
uniformly compressed. As the fasteners are tightened, mechanical 
deformation is induced and the seals are no longer uniformly compressed. 
Cold temperatures inhibit the seal response to changes in compression 
which occur during rapid airframe heating. The latter can induce seal 
failure and pressure loss during flight. 
SUMMARY OF THE INVENTION 
With the foregoing background of this invention in mind, it is a primary 
object of this invention to provide a fastener assembly which minimizes 
airframe shell distortion and inner structure distortion of a missile. 
Still another object of this invention is to provide a fastener assembly 
having an uniform seal compression during storage and, in flight 
environments, having an increase performance at varying temperatures 
The foregoing and other objects of this invention are met generally by a 
fastener assembly including a cylindrical support structure with a bore 
provided partially therein, the bore having a wall surface with a slot, 
and a bushing, disposed within the bore of the cylindrical support 
structure, having an end and an outer surface with a slot therein. The 
bushing further includes a bore with a first portion having a first 
diameter and a second portion having a second different diameter, the 
bushing also having a pair of tangs extending from the end. The fastener 
assembly further includes a nut, partially disposed within the second 
portion of the bore of the bushing, the nut having an outer surface with a 
pair of lugs disposed on the outer surface to engage the pair of tangs of 
the bushing and a pin disposed juxtapositional the slot of the wall 
surface of the cylindrical support structure and juxtapositional the slot 
of the bushing. The fastener assembly still further includes a pin 
disposed juxtapositional the slot of the wall surface of the cylindrical 
support structure and juxpositional the slot of the bushing. With such an 
arrangement, a fastener assembly is provided in which a forward shell 
section and an aft shell can be interconnected independent of the 
cylindrical support structure, thus maintaining circularity of airframe 
components and minimizing circular distortion. The forward and aft shell 
are rigidly attached to each other and not to the cylindrical support 
structure, so that aero heating of the forward and aft shells will not 
induce more distortion. 
In accordance with a further aspect of the present invention, the bushing 
further includes an opposing end having a radially curved surface with a 
contour to match an inner surface of a missile shell when the missile 
shell is mated with the opposing end of the bushing. With such an 
arrangement, uniform compression is maintained between the opposing end of 
the bushing and the inner surface of the missile shell. 
In accordance with a further aspect of the present invention, the 
cylindrical support structure of the fastener assembly further includes a 
first seal gland disposed forward of the bore of the cylindrical support 
structure and a second seal gland disposed aft of the bore of the 
cylindrical support structure. The fastener assembly further includes a 
first and a second methyl-phenol-silicone O-ring, the first O-ring 
disposed adjacent the first seal gland and the second O-ring disposed 
adjacent the second seal gland. With such an arrangement, the fastener 
assembly provides uniform O-ring compression and uniform O-ring 
compression is maintained during varying changes in temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, a missile 100 is shown to include a radome 1, a 
forward missile shell 2, and an aft missile shell 4. The forward missile 
shell 2 is connected to the aft missile shell 4 using fastener assembly 
10. The fastener assembly 10 includes a cylindrical support structure 12 
which is described further hereinafter. A plurality of screws, including 
screw 6, are mated with a corresponding plurality of bushings, (not shown) 
and nuts (not shown). The plurality of screws, here numbering eleven, are 
spaced circumferentially about the periphery of the missile as required 
and when tightened connect forward missile shell 2 with aft missile shell 
4. With such an arrangement, an inner sealed missile compartment 11 is 
provided. Although not shown for sake of illustration, a missile seeker is 
disposed within the inner seal missile compartment 11 to provide the 
guidance section of the missile 100. The fastener assembly 10 when used 
with the plurality of screws, including screw 6, provides a technique for 
interconnecting forward missile 2 with aft missile shell 4 while 
maintaining minimal circular distortion about a missile center line 8. The 
inner seal missile compartment 11 is a sealed compartment which is 
pressurized requiring the interconnection 3 to be a pneumatically sealed 
interface. The fastener assembly 10 provides such an interface. 
Referring now to FIGS. 2, 3, and 4, a portion of fastener assembly 10 is 
shown to include the cylindrical support structure 12, a bushing 16 and a 
nut 14. With the aft missile shell 4 disposed about a portion of the 
fastener assembly 10 and the forward missile shell 2 is disposed about a 
portion of aft missile 4 and a portion of the fastener assembly 10, the 
screw 6 is mated with the bushing 16 and the nut 14 to provide the 
interconnection 3. Here the forward missile shell 2 and the aft missile 
shell 4 is fabricated from titanium, as well as the cylindrical support 
structure 12. 
The bushing 16, fabricated from stainless steel, includes a cylindrical 
shaped structure with a bore (not numbered) provided through the center of 
the structure. The bore includes a first portion 26 having a first 
diameter to accommodate the shaft of the screw 6 and a second portion 27 
having a second different diameter to accommodate the nut 14. A first end 
32 of the bushing 16 is disposed against an inner surface 33 of the aft 
missile shell 4. The first end 32 of the bushing 16 includes a radially 
curved surface with a contour to match the shape of the contour of the 
inner surface 33 of the aft missile shell 4. The latter provides uniform 
compression between the first end 32 of the bushing 16 and the inner 
surface 33 of the aft missile shell 4 when the screw 6 is tightened with 
the nut 14. A second opposing end includes a pair of tangs, including tang 
28 and tang 30, extending from the second opposing end. A slot 24 is 
provided within the outer surface as shown. 
The nut 14, here fabricated from stainless steel, includes an outer surface 
41 with a diameter such that the nut 14 will fit into the second portion 
27 of the bore within the bushing 16. A pair of lugs, including lug 38 and 
lug 40, extend from the outer surface 41 of nut 14, as shown, and engage 
tang 28 and tang 30 of the bushing 16 when the nut 14 is disposed within 
the bushing 16. The latter provides torsional coupling between the tangs 
28 and 30 of the bushing 16 and the lugs 38 and 40 of the nut 14. A radial 
face surface 36 of the nut 14 rests adjacent a radial face surface 34 of 
the bushing 16 when the nut 14 is mated with the bushing 16. Threads 43 
are provided within the nut 14 to mate with mating threads 15 of the screw 
6. 
The cylindrical support structure 12, here having a shape as shown, 
includes a plurality of bores, including a bore 44 and here numbering 
eleven, spaced circumferentially about the cylindrical support structure 
12. The bore 44 is sized to accommodate the bushing 16 and the nut 14 such 
that the bushing 16 is constrained to a slip fit within the bore 44. The 
bore 44 is limited in depth and does not breach the inner sealed missile 
compartment 11 (FIG. 1). The bore 44 includes a wall surface 45 with a 
slot 42 provided therein. With the bushing 16 mounted within the bore 44 
of the cylindrical support structure 12, the slot 24 of the bushing 16 is 
disposed adjacent the slot 42 within the bore 44 of the cylindrical 
support structure 12 and a pin 8 is disposed between the slots 24 and 42. 
With such an arrangement, the bushing 16 is prevented from rotating within 
the bore 44. Each one of the plurality of bores spaced circumferentially 
about the cylindrical support structure 12 are similar to the bore 44 with 
each bore accommodating a corresponding bushing similar to the bushing 16, 
a corresponding nut similar to the nut 14 and a corresponding pin similar 
to the pin 8. On either side of the plurality of bores, including bore 44, 
a seal gland, here seal gland 46 and seal gland 48 respectively, is 
provided circumferentially about the cylindrical support structure 12. 
Disposed within the seal glands 46 and 48 are a seal 20 and a seal 22, 
respectively. The seals 20 and 22 are a methyl-phenol-silicone O-ring and 
provide a proper seal over a varying temperature range. The seal 20 
provides a proper seal between the cylindrical support structure 12 and 
the forward missile shell 2. The seal 22 provides a proper seal between 
the cylindrical support structure 12 and the aft missile shell 4. 
With such an arrangement, a pneumatically sealed (pressurized) structural 
interconnection is provided. Since bushing 16 is freely slidable within 
the bore 44 of the cylindrical support structure 12, when the screw 6 is 
tightened with the nut 14, forward missile shell 12 is connected to aft 
missile shell 4 independently of cylindrical support structure 12. The 
latter provides a uniform peripheral squeeze of the seals 20 and 22 at 
changing environments and minimizes distortion of forward missile shell 2 
and aft missile shell 4. Such an arrangement also provides unrestrained 
thermal growth of the forward missile shell 2 and the aft missile shell 4 
during rapid temperature changes. The amount of thermal expansion for the 
cylindrical support structure 12 is different than the amount of thermal 
expansion of the forward missile shell 2 and the aft missile shell 4, 
since the cylindrical support structure 12 is exposed to less heat than 
the forward missile shell 2 and the aft missile shell 4. Since forward 
missile shell 2 and aft missile shell 4 are independent of the cylindrical 
support structure 12, unrestrained thermal growth of the forward missile 
shell 2 and the aft missile shell 4 can occur independent of the 
cylindrical support structure 12, thus reducing missile shell distortion. 
Having described this invention, it will now be apparent that the number 
and disposition cf various elements of the fastener assembly 10 may be 
changed without affecting this invention. It is felt, therefore, that this 
invention should not be restricted to its disclosed embodiment but rather 
should be limited only by the spirit and scope of the appended claims.