Latch system

A latch system is provided for an aircraft nacelle. In one embodiment, the nacelle (10) comprises first (24) and second (18) cowls that are hingedly mounted to the nacelle for pivotal movement between closed, operational positions and open, maintenance positions. The latch system comprises latch means (42) movable to and from a latched position in which the latch means holds the first cowl in its closed position and prevents it from moving to an open position. The latch means includes locking means (152, 168) associated with the second cowl for holding the latch means in its latched position when the second cowl is in its closed position. As a result, the first cowl is held in its closed position when the second cowl is in its closed position. In a second embodiment, a disengageable latch (40) is provided for latching the edge of a cowl remote from the cowl hinge point (132). The latch comprises a toggle linkage (70, 86) movable to and from a latched position in which the toggle linkage engages the cowl and holds the cowl in its closed position and prevents it from moving to an open position, and a locking member (100) pivotally mounted to the nacelle for rotation to and from a locking position in which the locking member abuts the toggle linkage and holds the toggle linkage in its latched position.

FIELD OF THE INVENTION 
This invention relates to latch systems for hinged structures, and in 
particular to latch systems for cowls of an aircraft nacelle. 
BACKGROUND OF THE INVENTION 
Modern jet engines commonly include a pair of thrust reverser ducts or 
cowls which, during aircraft operation, define the outer wall of the 
engine exhaust nozzle. Such thrust reverser ducts must be capable of 
withstanding considerable loads caused by the high pressure of the jet 
exhaust stream which it contains. The thrust reverser ducts are normally 
hingedly connected to the upper portion of the nacelle near the point 
where the nacelle is attached to the engine support strut. The ducts can 
be pivoted upwards about their hinge points to provide access to the 
engine for maintenance and repair. For aircraft operation, the ducts are 
pivoted downwards into closed positions in which their lower ends are 
adjacent to one another, or adjacent to an interposed strut, services 
channel or bifurcation. The closed ducts are then secured by latches to 
form a continuous circumferential load bearing structure. 
The design of latches for thrust reverser ducts is complicated by a number 
of factors. For example, thrust reverser ducts must have an appreciable 
thickness in order to accommodate flow reversing cascades, and the inner 
surfaces of the ducts must include a load bearing member or ring to 
withstand the aforementioned loads due to internal pressure. Furthermore, 
a large circumferential force must be applied during latching to ensure 
satisfactory flange seating. The hinge line of the ducts, however, must be 
adjacent their outer surfaces to avoid interference with adjacent 
structure when the ducts are opened. As a result, a latch system for such 
thrust reverser ducts must include upper latches for latching together the 
upper ends of the load bearing rings near the top of the nacelle, as well 
as lower latches for connecting the lower ends of the load bearing rings 
to form a continuous circumferential load bearing structure. The upper 
latches of such a system are quite inaccessible. They are not only located 
inboard of the outer surface of the nacelle, but in a typical airplane 
installation they are a considerable distance above the ground as well. In 
the past, complex mechanical linkages or electrical actuators have been 
required to permit such latches to be locked and unlocked from ground 
level. Furthermore, since the latches are not visible when the ducts have 
been closed, means have been required for enabling maintenance personnel 
to confirm that the latches are locked after the ducts have been closed. 
In practice it is desirable that the upper latch system be nondisengaging 
because of its inaccessibility but the lower latch system must disengage. 
SUMMARY OF THE INVENTION 
The present invention provides a latch system for an aircraft nacelle which 
avoids the aforementioned accessibility limitations. The latch system of 
the present invention is adapted for use with a nacelle comprising first 
and second cowls, each cowl being hingedly mounted to the nacelle for 
pivotal movement between a closed, operational position and one or more 
open, maintenance positions. The latch system comprises latch means 
movable to and from a latched position in which the latch means holds the 
first cowl in its closed position and prevents it from moving to an open 
position, the latch means including locking means associated with the 
second cowl for holding the latch means in the latched position when the 
second cowl is in its closed position. As a result, the first cowl is held 
in its closed position when the second cowl is in its closed position. 
In a preferred embodiment, the first cowl includes an edge along which the 
first cowl is mounted to the nacelle, and the latch means is connected to 
the first cowl adjacent such edge. The latch system may also include 
second latch means for selectively connecting an opposite edge of the 
first cowl to the nacelle. The first mentioned latch means may comprise a 
first link arm pivotally connected to the nacelle at a first pivot point, 
a second link arm pivotally connected to the first cowl at a second pivot 
point, and nondisengaging connecting means connecting the first link arm 
to the second link arm. Since the connecting means is nondisengaging, the 
first cowl remains connected through the latch means to the nacelle when 
the first cowl is moved to an open position, and separate means are not 
required for confirming that the latch means is engaged after the firs 
cowl has been closed. 
In a further aspect of the invention, the first cowl comprises a 
semicylindrical sheet having an edge, spaced-apart inner and outer 
surfaces, and a load bearing ring extending in a circumferential direction 
along the inner surface of the cowl. The first cowl is hingedly mounted to 
the nacelle along such edge adjacent the outer surface of the cowl, and 
the latch means engages one end of the ring. 
In a further aspect of the present invention, a latch system is provided 
for a nacelle comprising a pair of first cowls and a pair of second cowls, 
each cowl being hingedly mounted to the nacelle for pivotal movement 
between a closed position and one or more open positions. The pair of 
first cowls in their closed positions substantially define a cylindrical 
passage. The latch system comprises latch means associated with each first 
cowl, each latch means being movable to and from a latched position in 
which its associated first cowl is held in its closed position. Each latch 
means includes locking means associated with one of the second cowls for 
holding the latch means in its latched position when the associated second 
cowl is in its closed position. Each first cowl is thereby held in its 
closed position when the associated second cowl is in its closed position. 
In a further aspect of the invention, a latch is provided for an aircraft 
nacelle, the latch comprising toggle linkage means and locking means. The 
toggle linkage means is movable to and from a latched position in which 
the toggle linkage means engages the cowl and holds the cowl in its closed 
position and prevents it from moving to an open position. The locking 
means is adapted for holding the toggle linkage means in its latched 
position. The locking means includes a locking member pivotally mounted to 
the nacelle for rotation to and from a locking position in which the 
locking member abuts the toggle linkage means and holds it in its latched 
position. 
These and other features and aspects of the invention will become apparent 
in the detailed description and claims to follow, taken in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring initially to FIGS. 1 and 2, a jet engine nacelle 10 is shown 
comprising inlet assembly 12, thrust reverser assembly 22, core assembly 
30 and fan cowls 18 and 20. Fan 16 and fan case 28 (FIG. 2) are part of 
the jet engine and are shown for reference. Each fan cowl 18 and 20 is 
capable of being moved between an open, maintenance position, as 
illustrated by fan cowl 18, and a closed, operating position, as 
illustrated by fan cowl 20. Both fan cowls pivot about hinge points near 
the upper portion of nacelle 10, as hereinafter described in greater 
detail. 
Thrust reverser assembly 22 comprises thrust reverser ducts 24 and 26. Each 
thrust reverser duct is capable of being moved between an open, 
maintenance position, as illustrated by thrust reverser duct 24, and a 
closed, operating position, as illustrated by thrust reverser duct 26. 
During normal aircraft engine operation, fan 16 forces air through an 
exhaust nozzle formed between the closed thrust reverser ducts and core 
assembly 30. During reverse thrust operation, this airflow is interrupted, 
and the air is instead forced through a plurality of flow reversing 
cascades (not shown) in the thrust reverser ducts. In either instance, the 
thrust reverser ducts are subjected to substantial hoop loads caused by 
the high pressure air flowing therein, and the system for latching the 
thrust reverser ducts in their closed positions must be adapted to 
withstand and transmit such loads. 
Fan cowls 18 and 20 and thrust reverser ducts 24 and 26 each comprises a 
semicylindrical sheet member having generally linear edges. The rear 
portions of the fan cowls overlap slightly with the forward portions of 
the thrust reverser ducts, with the fan cowls being positioned radially 
outward with respect to the thrust reverser ducts. FIG. 2 shows a cross 
section of nacelle 10 through the area of overlap. The nacelle is 
supported at interface surface 33 by strut 34, and is generally 
symmetrical about vertical centerline 36. Fan cowls 18 and 20 and thrust 
reverser ducts 24 and 26 are hingedly mounted by supports 38 and 39. When 
thrust reverser ducts 24 and 26 are in their closed positions, the lower 
ends of the thrust reverser ducts are secured together by lower latch 
assembly 40, lower latch assembly 44, and crosstie fitting 58. Similarly, 
the upper ends of the thrust reverser ducts are fastened together by upper 
latch assembly 42, upper latch assembly 46, and crosstie fitting 140. 
Crosstie fittings 58 and 140 are secured to engine fan case 28. Thrust 
reverser duct 24 includes inner flange 50, forward bulkhead 52, and outer 
flange 54. Forward bulkhead 52 comprises a radial plate joining the inner 
flange to the outer flange near the forward end of thrust reverser duct 
24. Similarly, thrust reverser duct 26 comprises inner flange 51, forward 
bulkhead 53, and outer flange 55. When the thrust reverser ducts are in 
their closed and latched positions, a continuous circumferential load 
bearing circular structure is formed comprising inner flanges 50 and 51, 
crosstie fittings 58 and 140, lower latch assemblies 40 and 44, and upper 
latch assemblies 42 and 46. The inner edges of inner flanges 50 and 51 are 
V-shaped and are received within matching V-groove 31 (FIG. 3) in the 
outer surface of engine fan case 28, thus securing the closed thrust 
reverser ducts against fore-to-aft motion with respect to the fan case. 
The configuration shown in FIG. 2, wherein the lower ends of the thrust 
reverser ducts are connected by a crosstie fitting and two lower latch 
assemblies, is particularly adapted to those situations in which area 56 
outboard of the underside of the engine fan case near centerline 36 is 
required for equipment related to the engine installation. It is to be 
understood that if area 56 is not required for such equipment, then a 
single latch may be used to connect the lower ends of the thrust reverser 
ducts directly to one another. 
Lower latch assembly 40 is shown in greater detail in FIGS. 3 through 5. 
FIG. 3 shows the lower latch assembly in its fully latched and locked 
position with the thrust reverser duct 24 closed. FIG. 4 shows an 
intermediate stage in which the lock is released and the assembly is 
between latched and unlatched positions, and with the thrust reverser duct 
24 still closed. FIGURE 5 shows the unlatched configuration. Lower latch 
assembly 44 is the mirror image of lower latch assembly 40 about 
centerline 36. In FIGS. 3 through 5, fan cowl 18 is open and is therefore 
not shown. 
Referring initially to FIG. 3, the function of lower latch assembly 40 is 
to latch inner flange 50 to crosstie fitting 58, cross tie fitting 58 
being in turn attached to the engine fan case 28 by attachments 29. The 
tension bearing links of the latch assembly include clevis 60, latch arm 
70, latch engagement hook 86, and adapter plate 80. Clevis 60 is bolted to 
crosstie fitting 58 by means of adjusting nuts 62, such that the position 
of the clevis can be adjusted in a circumferential direction. Clevis 60 
includes depending shoulder 64 that includes an opening through which 
positioning bolt 66 extends. Positioning bolt 66 is adjustably secured to 
shoulder 64 by nuts 68. The purpose of positioning bolt 66 is described 
below. 
Latch arm 70 is pivotally secured to clevis 60 by pivot pin 72. Pivot pin 
72 includes a torsion spring (not shown) that biases latch arm 70 in a 
downward (clockwise) direction. Latch arm 70 includes depending lip 74 
adapted to abut positioning bolt 66 when the latch arm moves in a 
clockwise direction. The end of latch arm 70 remote from pivot pin 72 
includes latch pin 76 affixed to the latch arm. 
Adapter plate 80 is bolted to inner flange 50 by bolts 82. The adapter 
plate extends into a recess 84 formed by cutting away a portion of inner 
flange 50. Latch engagement hook 86 is connected to adapter plate 80 by 
pivot pin 88, pivot pin 88 including a torsion spring (not shown) that 
biases the latch engagement hook in a clockwise direction. Latch 
engagement hook 86 includes a depending trip member 92 whose function is 
described below. When the lower latch assembly is in the fully latched 
position shown in FIG. 3, latch engagement hook 86 engages latch pin 76 of 
latch arm 70, and the assembly is positioned such that latch pin 76 is 
slightly over center with respect to pivot pins 72 and 88. Therefore, hoop 
tension placed on lower latch assembly 40 by any opening force acting on 
thrust reverser duct 24 will tend to drive latch pin 76 upwards toward 
inner flange 50, tightening the latch and locking the thrust reverser duct 
in the closed position. 
In FIG. 3, latch arm 70 is locked into its latched position by locking 
handle 100 such that even when the lower latch assembly is not under 
tension, latch arm 70 and latch engagement hook 86 cannot drop downward to 
release the latch. Locking handle 100 includes an extended lever arm 101 
and is secured to forward bulkhead 52 by pivot pin 102. The locking handle 
also includes roller 104 that is adapted to abut latch arm 70 and prevent 
the latch arm from moving downward, thus securing it in the locked 
position. When locking handle 100 is in its fully locked position 
indicated in FIG. 3, roller 104 is slightly over center with respect to 
pivot pin 102, and any downward force exerted by latch arm 70 drives the 
locking handle clockwise to secure it in its locking position. Locking 
handle 100 is held in its locking position by means of locking pawl 110. 
Locking pawl 110 is connected to forward bulkhead 52 by pivot pin 112, and 
includes detent slot 111 which engages pin 108 extending rearwardly from 
locking handle 100. When locking pawl 110 so engages pin 108, the locking 
handle is prevented from rotating in either direction about pivot pin 102. 
Lower latch assembly 40 includes second locking pawl 114 and torsion 
spring 116 that are also connected to forward bulkhead 52 by pivot pin 
112. Torsion spring 116 biases both locking pawls in a downward direction. 
As described below, detent slot 115 in locking pawl 114 serves to engage 
pin 108 when the lower latch assembly has been unlatched. Torsion spring 
116 keeps locking pawl 110 or locking pawl 114, whichever one is active, 
engaged with pin 108 for securing locking handle in the locked or in the 
unlocked position. Torsion spring 116 also keeps locking pawl 110 or 
locking pawl 114, whichever one is inactive, in spring loaded position for 
automatic engagement with pin 108 when the locking handle is moved from 
one of its two secured positions to the other. In the latched 
configuration shown in FIG. 3, spring 116 holds inactive locking pawl 114 
against stop pin 118 that extends from forward bulkhead 52. 
Rod 120 is connected at one end to locking pawl 110 by pivot pin 122, the 
other end of rod 120 being slidingly received in guide 124. Guide 124 in 
turn is secured to the inner surface of outer flange 54. Rod 120 serves to 
visually indicate, to a person outside the thrust reverser duct, whether 
or not lower latch assembly 40 is locked. The nacelle may be constructed 
such that rod 120, when it protrudes from outer flange 54, also creates a 
physical interference that prevents the closing of fan cowl 18 until the 
thrust reverser duct is properly locked. 
The sequence of latching and unlatching lower latch assembly 40 is 
illustrated by the sequence shown in FIGS. 3 through 5. Referring 
initially to FIG. 3, the unlocking sequence commences when an upward, 
clockwise force is exerted on locking pawl 110, such that detent slot 111 
is released from pin 108. Locking handle 100 is then free to rotate in a 
counterclockwise direction. After a small amount of such counterclockwise 
rotation, roller 104 contacts trip member 92 depending from latch 
engagement hook 86. Continued counterclockwise rotation of locking handle 
100 causes roller 104 to rotate the latch engagement hook downward 
(clockwise) which in turn rotates latch arm 70 downward. Downward motion 
of the latch arm is possible because roller 104 has at this point dropped 
a sufficient distance below the original latch arm position due to the 
rotation of locking handle 100. After latch arm 70 has rotated a short 
distance downward, latch pin 76 passes over center with respect to pivot 
pins 72 and 88, effectively releasing the latch. This is the configuration 
shown in FIG. 4. Once free of pin 108, locking pawl 110 moves downward 
until it contacts stop pin 118. When locking pawl 110 is in this position, 
rod 120 extends a short distance outside of outer flange 54, providing the 
safety feature of a visual indication that the latch is unlocked. 
Continued counterclockwise rotation of locking handle 100 causes roller 
104 to drop beneath and out of contact with latch arm 70, and causes pin 
108 of locking handle 100 to be engaged by detent slot 115 of locking pawl 
114, such that the locking handle is now prevented from rotating in either 
direction and is thus secured in the unlocked position. 
As soon as lower latch assembly has been released (FIG. 4), the thrust 
reverser duct may be moved rightward to a position such as that indicated 
in solid lines in FIG. 5. As a result of such motion, latch engagement 
hook 86 rotates clockwise until trip member 92 contacts inner flange 50, 
and latch arm 70 rotates clockwise until lip 74 contacts positioning bolt 
66. Further clockwise rotation of both the latch arm and latch engagement 
hook is thereby prevented. Continued opening of thrust reverser duct 24 is 
illustrated by the phantom lines in FIG. 5. 
Gravity and the springs associated with pivot pins 72 and 88 ensure that 
latch arm 70 and latch engagement hook 86 will remain in the relative 
positions shown in FIG. 5 as long as the thrust reverser duct remains 
open. Therefore when the thrust reverser duct is again closed, pin 76 of 
latch arm 70 will be positioned to engage latch engagement hook 86, as 
indicated in solid lines in FIG. 5. Locking handle 100 can then be 
released from locking pawl 114, and the locking handle rotated clockwise 
such that roller 104 forces latch arm 70 and latch engagement hook 86 back 
through the position shown in FIG. 4 and finally into the locked and 
latched position of FIG. 3. The leverage provided by lever arm 101 of 
locking handle 100 and the gravity forces acting on the thrust reverser 
duct facilitate the locking of the lower latch assembly against the 
frictional resistance to closing of inner flange 50 in V-groove 31. The 
toggle action resulting from the geometrical relationship of the elements 
of this latch guarantees that a very large circumferential closing force 
will be applied to inner flange 50 and cross tie 58 and the intervening 
elements of lower latch assembly 40 for a relatively low manual force 
applied to lever arm 101 of locking handle 100. This arrangement is very 
useful for overcoming friction and ensuring acceptable seating of inner 
flange 50 in V-groove 31 of fan case 28. 
To minimize the weight of the lower latch assembly, lever arm 101 of 
locking handle 100 may be omitted, and the central portion of the locking 
handle near pivot pin 102 may instead be provided with a slot or analogous 
structure to securely receive a screwdriver or other tool that can serve 
the function of the lever arm. 
Upper latch assembly 42 is shown in detail in FIGS. 6-8. FIG. 6 shows the 
latch assembly in its fully latched and locked position. FIG. 7 shows the 
upper latch assembly in an unlocked and partially unlatched position with 
the fan cowl open and the thrust reverser duct still closed. FIG. 8 shows 
the upper latch assembly in the fully unlatched position, with both fan 
cowl 18 and thrust reverser duct 24 open. Fan cowl 18 is connected to 
support 39 at pivot point 130, and thrust reverser duct 24 is connected to 
support 39 at pivot point 132. Upper latch assembly 46 is a mirror image 
of upper latch assembly 42 about centerline 36. 
The function of upper latch assembly 42 is to latch inner flange 50 to 
crosstie fitting 140 in such a manner that the structure will transmit 
circumferential loads across the junction but will still allow the thrust 
reverser duct 24 to open by rotation around pivot point 132. The tension 
bearing links of the upper latch assembly include clevis 142, latch arm 
146, side link 150, and adapter plate 156. Cross tie fitting 140 is 
secured to engine fan case 28 by attachments 141. Clevis 142 is bolted to 
crosstie fitting 140 by means of adjusting nuts 144, such that the 
position of the clevis can be adjusted in a circumferential direction. 
Latch arm 146 is pivotally secured to clevis 142 by pivot pin 148. Latch 
arm 146 includes an upwardly projecting shoulder 164 whose function is 
described below. The end of latch arm 146 remote from pivot pin 148 is 
connected to side link 150 by pivot pin 154. 
Adapter plate 156 is bolted to inner flange 50 by bolts 158. The adapter 
plate extends into a recess 160 formed by cutting away a portion of inner 
flange 50. Side link 150 is connected to adapter plate 156 by pivot pin 
162. When the upper latch assembly is in the fully latched position shown 
in FIG. 6, pivot pin 154 is slightly over center with respet to pivot pins 
162 and 148. Circumferential force acting through upper latch assembly 42 
therefore drives pivot point 154 and latch arm 146 downward into inner 
flange 50, tightening the latch. 
FIG. 6 illustrates latch arm 146 locked into its latched position by fan 
cowl link 152. One end of fan cowl link 152 is connected to pivot pin 154. 
The other end of the fan cowl link includes guide pin 172 that is 
slidingly received in slot 170 of guide 168. Guide 168 is in turn 
connected to fan cowl 18, shims 174 being used to adjust the position of 
the guide with respect to the fan cowl. The position and orientation of 
guide 168 and slot 170 is such that when fan cowl 18 is closed, guide pin 
172 is in the radially outermost position in slot 170, such that fan cowl 
link 152 is not free to move upwards. Therefore when the upper latch 
assembly is in such a locked configuration (FIG. 6), latch arm 146 is not 
free to move upwards, and upper latch assembly 42 is locked. 
When fan cowl 18 begins to move from its closed position illustrated in 
FIG. 6 to an open position, guide 168 begins to rotate about pivot point 
130. Because of the orientation of slot 170 with respect to pivot point 
130, latch arm 146 and pivot point 154 can remain in their latched 
positions shown in FIG. 6 only if fan cowl link 152 can rotate 
counterclockwise such that guide pin 172 moves leftward in slot 170. 
Leftward motion of the guide pin, however, is prevented by stop pin 166 
that extends from fan cowl link 152 and abuts shoulder 164 on latch arm 
146. As a result, fan cowl link 152 is forced to move in an upward 
direction in response to the opening motion of fan cowl 18. Even if slot 
170 were oriented differently, continued opening of fan cowl 18 would 
eventually cause guide pin 172 to contact the bottom of the slot, causing 
the fan cowl link to move upward. The upward motion of fan cowl link 152 
rotates latch arm 146 and side link 150 upwards, pivoting about pivot pins 
148 and 154, respectively, such that pivot pin 154 passes over center with 
respect to pivot pins 148 and 162. At this point, upper latch assembly 42 
is unlocked and unlatched. FIG. 7 shows the configuration of upper latch 
assembly 42 with fan cowl 18 fully open. Since in this configuration fan 
cowl link 152 can move upwards without rotating leftward, and since pivot 
pin 154 has passed over center with respect to pivot pins 148 and 162, 
thrust reverser duct 24 is now free to open assuming that lower latch 
assembly 40 has been released. FIG. 8 shows the configuration of the upper 
latch assembly with both fan cowl 18 and thrust reverser duct 24 open. 
Side link 150 has pivoted through an angle of greater than 90.degree. in 
relation to inner flange 50 from its position in FIG. 7, and guide pin 172 
has moved to the upper end of slot 170. The closing of thrust reverser 
duct 24 and fan cowl 18 is the reverse of the above-described sequence. 
While the preferred embodiments of the invention have been illustrated and 
described, it should be understood that variations will be apparent to 
those skilled in the art. Accordingly, the invention is not to be limited 
to the specific embodiments illustrated and described herein, and the true 
scope and spirit of the invention are to be determined by reference to the 
following claims.