Retractable Ball Turret
Sperry Lower Retractable Ball mounted in the belly of the PB4Y-1, is the deadly
and efficient defender of the bomber's once soft underside. It was built especially
for the PB4Y-1 whose ground clearance calls for a ball turret that can be kept
out of the way on takeoffs and landings. Its guns sweep in a full circle and offer
protection from any fighter who dips below the bomber's level. Its sight, the
Sperry K-4, computes deflections automatically even when the gunner, swinging
around below the plane, is unable to tell exactly which way he is facing.
|Facts and Figure|
The retractable mechanism to pull the turret up into the belly of the bomber is simple. The big hydraulic cylinder is secured to a supporting beam in the top of the plane and the turret is suspended from a piston riding within the cylinder. A hand pump mounted on a fuselage wall supplies hydraulic pressure to force the piston up and raise the turret, which can be locked in place with safety hooks on the upper trunnion housing. A valve on the fuselage releases the hydraulic pressure and permits the piston and turret to slide down.
The stowing position for the turret and guns after they have been retracted is 180 degrees azimuth and 22 degrees elevation.
Getting InTo start getting acquainted with the Sperry Ball, get in. You will have to be careful—men have been injured and even killed because they did not know the right way to get in, or were careless about it. The turret ball is heavy and yet delicately balanced; unless it is locked in place, it may swivel and break a man's leg or snap him almost in two as he attempts to enter. Remember also, as you step into the turret for the first time, that on combat missions you will never get in until your bomber is in full flight, and will always get out before the landing. The ball turret, hanging down beneath the plane, is no place to be when the bomber is moving along the ground. As you get in, take these steps carefully and in proper order. If you go about it right, getting into the turret is as safe as climbing into a rocking chair.
Make sure that the turret is properly seated at its lowest position. Tapered bushings, mounted on the azimuth ring of the turret, should sit squarely in holes provided for them in the plane's floor ring. If they don't, jockey the turret until they do.
Make sure the master switch on the support beam is on.
Open the turret entrance door. Test the turret by grasping the supporting structure and putting your right foot on the seat. Try to work the turret with the pressure of your foot. There should be no movement. If there is movement, the elevation gearing is not engaged.
Lower yourself into the turret by grasping and swinging down on the support frame. Put your right heel on the right foot rest, then your left heel in the range pedalbeing careful not to throw your whole weight on the range pedal.
Fasten the safety belt. Close and fasten the entrance door. Make sure that the door latches are securely closed. Then you are ready to go.
OPERATING THE TURRET
Make sure the azimuth power clutch is engaged—the lever at the upper right
should be down.|
2 Flip on the main power switch—a toggle switch under a wire guard on the junction box beside your left knee.
3 Right beside the power switch are the two gun selector switches for firing the guns separately or together. Flip both of them on.
4 Turn on the sight switch directly in front of your nose on the sight. Turn the sight rheostat beside it to adjust the brightness of the light. Never operate the turret under power with the sight switch off.
5 Finally, grasp the two handgrips. Don't worry about safety switches—the turret has none. But, notice that in azimuth the controls work exactly opposite to all other turrets. To move the turret right, swing the handgrips to the left; to turn left, swing them to the right. Pull back on them to tilt the turret and guns up, and press forward to turn the turret and guns down. Don't jerk. Steady, smooth tracking is especially important in using the Sperry sight.
The other controls you will use in combat are right at hand. On the top of each handgrip, under your thumbs, are firing buttons, used instead of triggers on the Sperry Ball. The fuses which protect the Sperry's electrical circuits are in the junction box beside your left knee, where you found the main power switch. For charging the guns, you will find two handles next to your feet. Reach down to the floor, arms crossed, and pull the handles up carefully until the slack is out of the cables. Then pull them up sharply all the way. Don't ride the cables on the return action; allow them to go back under their own power, still keeping your hands on the handles.
. Where to Find the Controls
are seated, the controls and switches of the turret are spread before you. Check
clutches and turn on the switches in exactly the order shown here.
Using Auxiliary Equipment
will find a demand type regulator with a hose connection for your oxygen mask
right under your seat. Alongside your right ear is the flow and pressure gage.
The oxygen is drawn from the plane's central tanks in most models. The heated
suit plug-in is also under your seat. The interphone jacks for your headphone
and throat microphone lead out of the junction box. A trouble light is clamped
in a clip just under top rim of the ball to the left of your head. By your right
foot is a new azimuth turret position dial, in which a cutout of your guns rotates
change to manual operation:
To get out of the turret, drive it to90 degrees in elevation, so that the
guns point straight down; this will bring the doorway into place in the floor
of the bomber. At the same time, drive the turret to 180 degrees in azimuthsix
o'clock on your azimuth turret position dial.
to the upper curve on the ball, moves up as you turn the ball in elevation, and
presses against the elevation retraction position switch, throwing it on. This
switch flashes a light in the pilot's compartment to tell him when the ball turret
is retracted and the plane is ready to land.
1. Run the
guns to 180 degrees azimuth and 90 degrees elevation and get out of the
Preparing the Turret for Combat|
With the working information contained in the preceding pagesand sufficient practice tracking with the Sperry sightyou could easily take over the Sperry Ball in combat. If you specialize in this turret, however, that will be only part of your job.
The rest of your jobadjusting sight and guns and loading ammunition for a missionis explained in the following pages.
K-4 is an upside-down type of automatic computing sight built especially for the
Sperry Ball. Held by a single long mounting pin, it hangs down from the sight
cradle on a level with your head. Connected to the sight are three flexible shafts
which bring it the turret movement and range data needed for computing deflections.
The upper shaft entering the top rear of the sight revolves as the turret moves
in azimuth. The lower shaft at the top rear revolves as the turret moves in elevation.
The third shaft, on the left side, leads to the range pedal, which you move with
your left foot to frame the target in the sight reticles.|Restricted
The guns are mounted in the Sperry Ball to feed from the outside—the right gun feeds from the right and the left gun from the left. The guns are held in their cradles by a rear trunnion block and slide (A) and two front trunnion studs (B). The rear trunnion block, attached to the rear mounting holes of the gun, dovetails into the rear trunnion slide—merely check it to make sure that it rides snugly in the slide. The front trunnion studs, which screw into the front mounting yoke of the cradle and into threaded holes in both sides of the gun adapters, must be safely wired.
|Special charging units (C) are installed on the inside plates of the guns, with mounting bolts which must be safety wired. The cable connection to each unit must have a cotter pin (D). Special link ejection chutes (E) are installed on the inside of the guns, where they are held by the guns' belt feed pawl pins and cotter pins. The guns can be adjusted up, down, or sideways in their cradles by using an adjustment screw and bolt assembly provided on each rear trunnion.|
make the adjustments: |
Loosen the vertical lock nuts and adjustment nuts.
Loosen the lateral lock nuts. |
Turn the lateral adjustment screws on each side of the mount right or left to move the back of the gun from side to side.
Turn the vertical adjustment nuts right or left to raise or lower the back of the gun.
When the gun is in its proper position, tighten all lock nuts.
By means of these adjustments the guns can be centered in their mounts.
To center them you will have to move the adjustment screws and nuts back and forth until you find the approximate center of both the lateral and vertical adjustment movements. With practice, you will be able to center a gun quickly and with little error.
|There are a number of ways to harmonize the Sperry Ball's guns and sight. Because of the Ball's computing sight and compact construction, they are more complicated than the procedures for other turrets. In all cases the sight must be removed and reinstalled in the turret to do a good job. The handiest method for gunners is to boresight the guns and line up the sight on some small object, such as a tree or a chimney, at least 1,000 yards from your plane. This is known as the field, or distant object, method of harmonization.|
First move the guns to zero elevation.
Get out of the plane, remove both gun access plates from the ball, and the backplates
and bolts from both guns. (Or you can use a boresight reflector to enable you
to sight through the barrels without removing the parts.) Open the turret door.
Disengage the azimuth and elevation power clutches. Line up the centered gun on the object selected, using the hand cranks to move the turret until the object is exactly in the center of the gun bore. Then lock the turret in this position by re-engaging the azimuth and elevation power clutches.
Line up the other gun on the same object by turning its vertical and lateral adjustment screws and nuts. Don't move the turret as you do this. When you have the object exactly in the center of the gun bore, tighten all lock nuts.
Move the turret by hand crank to zero azimuth and zero elevation and lock by reengaging the azimuth and elevation power clutches.
Remove the sight from its mounting bracket by unlocking and withdrawing the long mounting pin. Handle the sight carefully.
|Flexible Shaft Connections|
Set the azimuth and elevation position dials to zero, using the azimuth shaft to rotate the azimuth dial and a piece of flexible shaft to turn the elevation dial.
Elevation gear unit |
B Elevation rate input shaft
D Range shaft to range pedal
F Azimuth rate input
G Azimuth gear unit
Connect the electric cable and install the sight in the turret.
Connect the elevation shaft to the elevation input on the sight and the azimuth shaft, which was left connected to the sight, to the turret. Make sure you do not move the azimuth and elevation dials off zero in doing this, and make certain all connections are secure.
Connect the range shaft to the sight's range input and disconnect it from the range pedal. Rotating the shaft with your fingers, turn the range dial as far past zero as it will go, then back it off a quarter turn of the flexible shaft. With the range pedal all the way up, connect the range shaft to the range pedal again
First remove the ammunition can covera plate in the turret surface held by four Dzus fasteners, or by two cover latch screws in later models.
|Note that the cans are equipped with baffle plates to insure positive feeding and to keep the ammunition from tumbling about.|Restricted
Start with the single-link end of the belt
first, so that the double-link end will feed up into the gun, and fold the belts
into the cans in the pattern shown in the diagram. Force the belts down through
the chutes to the guns. By putting pressure on the ammunition in the chute, the
first round will move into the feedway, over the belt holding pawl. Caution: Fasten
the ammunition can cover securely after loading.
|Pre-Flight Routine . . . follow it step by step|
|(The plane should
be over a testing pit to allow normal movement of guns.)|
1. Install the guns' barrel and oil buffer groups leaving out bolts and backplates.
2.. Check harmonization of sight and guns by boresighting on an object at least 1,000 yards from the plane, or a pattern stand.
3.. While harmonizing the guns, make sure the manual system is working properly.
4.. Make sure the gun bolts are assembled properly, to feed from the right in the right gun and from the left in the left gun. Then install bolts and backplates in both guns.
5. Try to rock the guns in their cradles to make sure their mounts are secure. Check to make sure the rear trunnion blocks fit securely in the rear trunnion slides, and that the front trunnion studs are safety wired.
|6. Make sure the bolts mounting the charging units
to the inside of the guns are safety wired and cable connections have cotter|
7. Inspect the electric cables. Make sure all cannon plug connections are tight. Report any frayed or damaged cables.
8. Make a visual check of the fuses in the junction box, using your trouble light. If any are burned out, have them replaced. (The spare fuses carried in the spare parts box should be saved for combat emergency.)
9. At the same time, check your trouble light. Turn on the switch and make sure the bulb is bright.
10. Check oxygen and interphone connections in the turret.
| 11. Inspect all hydraulic
lines. If you find excessive leakage, report it immediately.|
12. Check the round gage on the side of the oil breather tank. If oil is not level with the bottom of the gage window, report it.
13. Make sure the plexiglas and safety windows are clean.
14. Enter the turret correctly with care.
15. Make sure that the inside azimuth and elevation power clutches are engaged.
16. Turn on the main power switch.
17. Flip on the sight switch. The sight motor; should start, the sight bulb light up. Turn the sight rheostat to check operation. Make sure the optic head is clean.
18. Check all input shaft connections to the sight. Make sure they are tight.
19. Work the range pedal with your foot to make sure the reticle moves in response.
20. Make sure both gun chambers are empty. Then turn on both gun selector switches. Check the guns' headspace. Pull one trigger at a time, charging the guns each time, and check the Electric Triggers for proper adjustmentlisten for a "click" as the firing pins of the guns release.
21. Turn off right gun selector switch, and make sure either trigger operates the left gun's Electric Trigger. Then turn on right gun selector switch and turn off left gun selector switch. Make sure that each trigger sets off the right gun's Electric Trigger.
22. Run the turret under power in azimuth and elevation, to check on ease of operation. Run the guns up to the fuselage to make sure the limit stops are working. Then stop the turret and check for creep.
23. Check the fire cutoff system by swinging the guns on the propeller and antenna loop areas of the plane and attempting to fire. Make sure the guns cease firing
with the proper amount
of safety margin your crew chief will tell you how much.
The Bendix Upper Deck
The Bendix Upper Deck Turret is an all electric turret used exclusively in the PBJ Mitchell bomber where it protects the upper area of the plane. There are two basic models: the Bendix 250CE-3 and the Bendix 250CE-4. The Bendix 250CE-3, used only on early models of the PBJ, is mounted just back of midship. When waist guns were introduced to the PBJ, the Bendix 250CE-4 was designed for mounting just aft of the pilot's compartment. The two models are essentially alike. The description of the Bendix 250CE-4 in the following pages will also enable you to operate the Bendix 250CE-3.
Facts and Figures
The Bendix Upper operates electrically on power supplied by the bomber's central system.
The turret can move 360 degreesa full circle in azimuth.
The stowing position is 0 degrees elevation and 180 degrees azimuth-guns level and pointing straight back toward the tail.
To start getting acquainted with the Bendix Upper, step right in. You won't have any trouble this is one of the easiest of all turrets to enter and operate.
Adjust the footrests to fit your own height by moving them up or down in the notches on the foot slide.
you preferand a few trials will show you if this is the easiest method for
youyou can snap the seat up to its locked position before you get in. Then
stoop into the turret, throw one leg over the seat as if you were mounting a high
bicycle, and pull yourself up by the inner turret supports.
you can leave the seat down, step up on the footrests, pull yourself up by grasping
the inner turret supports, brace one elbow over one of the supports, and with
your free hand pull up the seat to its locked position beneath you. When you are
seated, your eye should be level with the sight. If not, adjust the height of
the seat by turning the small handle and swivel on the right side of the seat
support, loosening the band that holds the seat to the central column. Slide the
seat up or down on the column until you have it just where you want it. Then reverse
the handle, tightening the seat in place, and you are ready
|OPERATING THE TURRET|
. . where to find the controls
can get the turret into action about as quickly as you could start an automobile
on a warm summer day. First reach outside the turret to the left wall of the fuselage;
there you will find a long, narrow box with two switches mounted on it. One is
the main power switch; turn this one on first. Then flip on the heat-light
switch right beside it, which shoots power to the sight bulb, trouble light,
and heated suit unit. |
Use the sight rheostat (D), on the controller housing just above the left handle, to adjust the brightness of your sight bulb to outdoor lighting conditions.
Then grasp the control handles so that the bottom edges of your hands press down the two safety switches (C). As long as either one of these switches is held down, the turret is ready to operate. With the switches up, the turret won't move.
Turn the handles just as you would steer a bicycleto the right to go right, left to go left. Press down on the heels of the handles to raise the guns. Pull up on them to lower the guns. Move the controls smoothly and deliberately, and you will be able to track any target closely and with deadly aim.
The other controls you will need in combat are practically at your fingertips.
Right under your index fingers on both control handles are the triggers (B).
On top of each handle, by your thumbs, are the high speed buttons (A) that give you extra speed for changing quickly from one target to another.
In front of your hands at the back of the controller housing are two shiny metal disks that are your push-to-talk buttons (E). Pressure on either disk opens the interphone system for you to speak.
|The charging units are your footrests. To charge the guns, draw the foot rests up as far as they will go in their slides with the toe of your shoe, then step down on them sharply.|
|Using the Auxiliary Units|
Because the Bendix is used only in the PBJ, a low-level bomber, it has no oxygen system. But it has all the other standard auxiliary units. The heated suit plug-in (A) is mounted on the right side of the controller housing. The interphone jacks (B), for connecting your earphones and throat microphone, lead right out of the controller housing. The interphone selector switch is mounted on the fuselage near your turret. The trouble light (C) is on the front left-hand corner of the controller housing.
The Bendix Upper's manual system can be used only for
moving the turret to make repairs and adjustments: it is not designed for operating
the turret in combat emergencies. A single crank with a flexible shaft, stored
at the base of the turret, is used to move the turret in either azimuth or elevation.
To move the guns up or down, put the crank on the elevation shaft (D) in front
of the sight cradle. To rotate the turret, you will have to get down in the turret
and put the crank on the pinion shaft (E) in the azimuth gearing at the base of
the main support column.
Before leaving the turret, move it to stowing positionguns pointing straight back toward the tail. Turn off all the switches. Then slide down off the seat and back out of the turret. Once you are out, unlatch and stow the seat.
the Turret For Combat
If you specialize in the
Bendix, however, you will have to adjust the sight and guns for a mission, and
load ammunition. The method of getting the turret ready for action is explained
on the following pages.
Adjusting the SightThe Bendix Upper s N-8 or N-6A sight fits into a bracket in the sight cradle directly in front of you. To adjust the position of the sight, as may sometimes be necessary in harmonizing the guns, loosen the mounting bolts and turn the adjusting bolts you will find nearby. The two mounting bolts directly in front (A) hold the sight vertically in its bracket; the adjusting bolt(B) directly beneath them moves the sight up or down. The two mounting bolts at the top (C) hold the sight in place laterally; the adjusting bolt (D) in front of them moves the sight from side to side.
For full instructions on care and checking of the sight, see the Sights and Sighting section.
charging units (E) operated by your footrests, are mounted on the outside of the
guns' receivers; their mounting bolts must be safety wired. Special case ejection
chutes are installed on the outside of the guns to carry used links away from
the guns; the hollow pins holding the chutes in the guns must have cotter pins.
Special ammunition feed rollers (B) are mounted on top of each gun and held by
the gun cover pin, which must have a cotter key.
make the adjustment:
Harmonizing the Guns and Sight
There are a number of ways to harmonize the sight and guns in the Bendix Upper Deck Turret. The exact procedure will be defined by the Squadron Gunnery Officer. A handy method is to line up the sight and boresight the guns on some small object such as a tree or chimney, at least 1,000 yards away. You will need an assistant in the turret and a muzzle-type boresight tool to do this.
FIRST, have your assistant move the turret until the dot of the sight is centered on the object. Place the boresight tool in one gun, and have your assistant adjust its rear mount until the same object is exactly centered in the gun bore. Then do the same for the other gun. Sometimes there may not be enough adjustment in the gun mounts. In that case, center the guns in their mounts and boresight each gun on the object. Then move the sight by its adjustment bolts until the dot is on the same object. I
IMPORTANT: Check harmonization by swinging the turret on another small object off to one side, 1,000 yards away, and bore-sighting to make sure sight and guns all line up on the same object. Select another object and check again. If sight and guns are out of line on any object, call in turret maintenance.
method of harmonizing the Bendix Upper is to boresight on a pattern
stand, such as the one illustrated here. Set up the stand level with the guns
at least 50 yards away. Center the guns in their mounts. Then boresight the guns
on the pattern and line up the sight on the sight cross, using the standard technique
described in the Sights and Sighting section. Both methods described here are
|Two big ammunition cans, one marked for the hang down on either side of the center column, right gun and the other for the left, hold about Load them in the standard fold-in pattern, 400 rounds apiece. They hook on the inside of single-link end first, making sure the rounds will the big ring casting circling your head and point toward the center of the turret when the|Restricted
cans are hung up on the inner rim of the turret. Place the loaded cans
on the turret floor, right below where they will hang. Then lift each can straight
up, using one knee as a support under the can. On the top edge of each can is
a bar which must hook into the support hook on the front of the main turret casting.
Two spent round bags, to receive used brass ejected from the guns, hook to the mouth of the guns' case ejection chutes.
. . . FOLLOW STEP BY STEP
Make sure the gun bolts are properly assembled, one for left-hand feed in the
right gun, the other for right-hand feed in the left gun. Then install the bolt,
barrel, oil buffer, and backplate groups in both guns.|
2.. Try to rock the guns in their cradles to make sure they are securely mounted. Check the front and rear studs and mounting bolts to make sure that they are properly safety wired and tight.
3. Inspect the charging units to make sure that they are securely mounted and safety wired.
4. Inspect the ammunition rollers and case ejection chutes to make sure they are properly mounted and the pins holding them have cotter pins and keys.
5. Check harmonization with a boresight tool by boresighting the sight and guns on some small object at least 1,000 yards away, or on a pattern stand. Double-check by bore-sighting on two or three other objects.
6. Inspect the electric cables. Make sure all cannon plug connections are tight. Report any frayed or damaged cables. Take particular note of the interphone cable on the right side of the controller housing to make sure it is not loose or frayed.
7. Inspect your ammunition belts to make sure the rounds are in good condition and properly belted.
8. Load the ammunition cans and lift them into place in the turret. Make sure the cans are hooked up securely in front, and the
pins are locked at the bottom rear of the cans. Open the inspection doors in the
front of the cans to see that the ammunition is correctly placed in the cans,
with the cartridge points facing toward the center of the turret.
triggers. Listen for a "click" as the firing pins in the guns release.
Both guns should fire from either trigger.|
15. Run the turret under power in azimuth and elevation at normal speed and then with the high speed button held down, to check on ease of operation. Make sure the turret runs with either safety switch held down. Test the limit stops (called brakes on the Bendix) by attempting to bring the guns down on the fuselage forward and backward. Then stop the turret suddenly and check for creep.
15. Check the fire cutoff system by swinging the turret and guns on the tail and propeller areas of the plane, charging and attempting to fire the guns on each area. Make sure the guns stop firing with the proper amount of safety margin around all sides of the restricted areas—your crew chief will tell you how much.
Plug in your headphones and microphone to test whether your crew mates can hear
you and you can hear them.
Run the turret to its stowing positionguns level and pointing straight back
on the tail.|
2. Clear the guns by opening the gun covers and then charging them twice.
3. Shut off all switches.
4. Remove ammunition from the feedways and all ammunition from the turret.
5. Remove and empty the bags which receive spent rcunds and links from the case ejection chutes.
Field strip the guns.