Aircraft technical Basics: TM 1-409, Aircraft Armament and Pyrotechnics, 1941: XIII. - Bomb Racks, Bomb Hoists, and Tow Targets

Section XIII - BOMB RACKS, BOMB HOISTS, AND TOW TARGETS

86. Bomb racks.-a. General.-As it is impracticable to move about or handle aerial bombs while the airplane is in flight, a holder or rack is used, which has been built in the airplane as a part of its construction, and to this rack is connected a release having a dual control. While this release is ordinarily operated by the bombardier, it has been made dual so that it may be employed by the pilot in an emergency, such as the necessity of immediately dropping all bombs prior to the making of a forced landing of the aircraft. In cases where the pilot operates the emergency release, he releases the bombs according to the position of the arming lever which is operated by the bombardier, and which is normally in the "safe" position, unless a run is being made on the target. Thus for emergency release, the pilot will normally release the bombs "safe." When the bombardier operates the release, the bomb may be "armed" by the action of the arming lever, that is, made ready for explosion on impact or at a predetermined interval of time thereafter; or the bomb by means of the arming lever may be dropped "safe," that is, "unarmed," and therefore incapable of exploding on impact. Bomb racks are made principally of duraluminum, with the use of certain steel alloys in places where exceptional strength is desired. The weight of such racks is kept to the minimum consistent with necessary strength in order that the load of bombs carried will not have to be unnecessarily curtailed. The majority of bomb racks are multiple station racks; that is, each rack will carry more than one bomb.

b. Releasing.-The bomb release mechanism may be adjusted so as to drop a single bomb at a. time or to drop all bombs simultaneously. The device for arming the bomb, or, if not used, for allowing the bomb to remain "unarmed" or "safe" as referred to in a. above, is incorporated in the bomb rack and is controlled by either the release handle or a special arming handle.

c. Types.-Two general types of bomb racks are used on the various types of tactical airplanes, the internal and the external; so designated from the manner in which they are carried by the airplane. Racks which are attached to the outside of the fuselage, or to the underside of the wings of an airplane, are known as external bomb racks. Those that are attached to the inside of the fuselage, and which carry the bombs entirely within a compartment in the fuselage, are known as internal bomb racks.

d. Location.-In order that the operation of releasing a bomb, and the consequent sudden decrease in load may not disturb the steady horizonal flight of the airplane, the center of gravity of each bomb of the bomb load must be as close to the center of gravity of the airplane as possible. With an internal rack, this condition may be satisfactorily obtained, since the distance of the bombs from the center line of the fuselage is not great when compared with the distance to the control surfaces of the wings. The centers of gravity of the various sizes of bombs do not differ materially, and it is therefore possible to locate the bomb rack correctly in relation to the fore and aft center of gravity of the airplane. When some types of external racks are mounted on the wings, the balance of the aircraft is not always easy to retain.

87. Essential characteristics.-a. Safety factors.-All internal and external racks, when installed, have the following safety factors:

For vertical load, 7 to 1.

For fore and aft load, 3 to 1.

For transverse or lateral load, 2 to 1.

These factors are based upon the maximum bomb load which the rack is capable of carrying. These factors mean that the rack and installation are capable of carrying seven times the maximum load the rack is designed to carry in a vertical position, and is capable of withstanding three times the strain of the maximum load in the fore and aft position, and twice the maximum load in the transverse position. Such safety factors are necessary, due to jolts and jars usually experienced in the take-off and also in rough air that may be encountered in flight.

b. Security of attachment.-All bomb racks must be firmly and securely attached to the airplane and must provide a positive and secure means of carrying the bombs.

c. Positive and instantaneous release.-All bomb racks must be provided with a positive and instantaneous release mechanism.

d. Safety or arming mechanism.-All bomb racks must be provided with a safety or arming mechanism, so that the operator can release the bomb or bombs either "armed" or "safe" at will.

e. Positive lock-All bomb racks must have a positive lock to lock the racks against accidental release.

88. Inspection and maintenance.-In general, all inspection and care confines itself to keeping the rack clean and checking it for proper operation.

a. Inspection-Inspect in accordance with Air Corps Circular 15-43 and Technical Orders of the 11-5-, 11-25- and 11-30-series. In addition, the inspection and maintenance in b and c below should be performed.

b. Preflight.-All parts should be inspected as necessary, depending upon the service use. This inspection should include a thorough check of the bomb rack, bomb rack controls, and bomb rack indicating system to assure correct operation at all times. Operate the racks both mechanically and electrically.

c. Cleaning and lubricating.-Caution: Bomb rack and control system parts should not be greased or oiled at any time as this tends to collect an accumulation of dust and dirt which may cause a malfunction of the rack. However, all moving parts of the release mechanism should be given applications of dry graphite to reduce friction to a minimum. When necessary to clean the bomb rack, it should be accomplished by the use of kerosene, Spec. No. VV-K-211. The rack should always be thoroughly cleaned prior to loading bombs for bombing missions.

89. Bomb hoists-a. General-Bomb hoists are normally considered to be a system for the loading of heavier types of demolition bombs. Generally, hoists are intended to be used in loading of bombs from 300 pounds to 2,000 pounds in weight. In some instances, the bomb hoists can also be used to hoist loaded chemical tanks. However, they are generally limited to their primary purpose. The bomb hoist usually consists of a worm driven, hand powered, gear and pully arrangement. The hand crank, worm gear, and cable drum is mounted on one unit suitably braced. This unit may be permanently attached in position to the ship, or may be detachable and stored for carrying in other positions. Other components of the hoists are idler pulleys, spacer pulleys, hoist cables, and braces. To complete the hoisting equipment, a bomb sling consisting of two heavy canvas straps attached to hooks in such a manner that they may be in turn attached to hoisting cables.

b. Method of setting up hoist.-Information regarding the proper method of setting up the hoist will be found in the bomb bay of each  particular type of airplane. This information will normally consist of details regarding the positioning of idler pulleys and spacer pulleys. In addition, diagrams are usually included in the bomb bays to indicate the threading of the hoist cables to compensate for the different size or weight of bombs which may be used, or information may be found in Technical Orders of airplane concerned. The hoist drums may be located permanently in fuselage of airplane in such a manner that it can be used at once. Other types of hoists must. be assembled prior to use. This assembling may consist of removing the various hoisting components from their storage or carrying positions and forming a solid compact unit. It will be found necessary in some types of hoists to completely disassemble the hoist and set it up in a new position before it is possible to load bombs on a different rack. In general, one setting up of hoist will allow the loading of bombs on the two parallel racks. When the racks are so constructed that they are one behind the other or tandem, it will be necessary to disassemble the hoist and set it up again for loading bombs onto the second rack.

e. Precautions in Twisting.-(1) Do not release hoist and remove sling from bomb until the hoist cable has been slacked off approximately 2 inches from bomb, and security of shackle to bomb and to the rack has been determined.

(2) When hoisting bombs, it is necessary that the men operating the hoist drums must work evenly and smoothly to prevent uneven pulling of cable and bomb sling. This is necessary to prevent rolling of bomb from sling.

(3) The correct size of bomb sling must always be used.

(4) The bomb sling must be inspected for condition prior to hoisting (use). This will include frayed straps, loss of cable attaching ends, and general condition.

(5) The hoisting drums and worm drive will in some cases reverse under bomb weight if the hand crank is released.

(6) Bombs must be hoisted and loaded on the racks to match weight tabs at each station.

(7) After use in loading, the cables must have tension applied to them prior to and during rewinding upon hoist drum.

d. Maintenance.-(1) The hoist units will be inspected for such defects as frayed cables, loose bolts and nuts, lost or broken cotter pins or safetying, cracked or broken parts.

(2) Technical Orders sometimes prescribe periodic greasing of worm gear.

(3) It is sometimes necessary to periodically clean and grease hoist cables.

(4) It is necessary that hoist units when stowed be secured so as to prevent damage to airplane or hoist units.

90. Tow target equipment.-The purpose of tow targets is to give tactical units a moving target on which to fire, and which simulates the movement of aircraft. There are two general types of targets in use for this purpose; namely, the aerial gunnery target, which is towed approximately 600 feet in rear of the towing airplane and fired on by pilots and gunners in other airplanes, or by ground rifles and machine guns, and the antiaircraft gunnery target, which is towed with cable of sufficient length so that at no time will it be necessary for the gun battery to aim ahead of the towing airplane, and is fired on by antiaircraft batteries. A C4 or C4A wind-lass mounted in the rear cockpit of a two place towing airplane is necessary for paying out and reeling in the towing cable. In towing large targets for long range firing a C5 windlass is used. Extra flexible 1/8-inch steel cable, 7 by 19, Air Corps Spec. No. 48-35, in reels of 2,500 to 5,500 foot lengths are used as a towing line with these windlasses.

91. Description of tow targets.-a. A5 aerial gunnery tow target.-The A5 tow-target is made of grade A airplane cloth; it has one large sleeve, six small sleeves, and six bridle panels terminating at the front end to form a bridle loop. The six small sleeves are arranged in a circle, the outer circle nearly equal to the circumference of the large sleeve. The other end of each small sleeve is held open by means of a nonflexible steel ring and is attached to a bridle panel.

b. B12 antiaircraft gunnery tow target-The B12 target is constructed of the same material and is of the same design as the A5. The only difference being that the B12 is nearly twice as large to make it suitable for its purpose.

c. A6 tow target-(1) Purpose-The A6 tow target was developed to provide a flag type target for aerial gunnery, having a large effective area for high speed individual and group firing.

(2) Description-The A6 tow target consists of a cotton covered mesh wire fabric 9 by 40 feet, containing a steel tube spreader bar attached to the front edge of the flag material. The bridle ropes are attached to four points equally spaced along the spreader bar. A metal counterweight is provided for positioning the target in a vertical or horizontal position by attaching to the end of the spreader bar for vertical towing and to the center of the spreader bar for horizontal towing position.

92. Tow target windlasses.-Tow target windlasses are used to pay out and reel in the cable used for towing aerial targets. In order to perform the work for which they are designed, they must be capable of unwinding the desired length of cable and of rewinding the cable after the target has been released. The C4, C4A, and C5 windlasses are standard for use at present.

a. The C4 windlass mechanism consists of a reel with cable capacity of approximately 3,600 feet of 1/8-inch cable, a brake assembly which controls the rotation of the windlass reel, a wind driven rewind impeller geared to the clutch, a clutch which is a medium for engaging or disengaging the rewind impeller and windlass reel, a level wind mechanism, and a cable meter.

b. The C4A windlass is identical with the C4 windlass except that the type C4A has an electric rewind motor while the C4 has a wind driven impeller.

c. The C5 windlass is identical in design with the C4A, except that it has a larger cable capacity, 7,000 feet, and contains an air scoop for cooling the brake drum. The C5 windlass was primarily designed to be used with targets that are larger than the present A5 and B12 targets, and also for target missions where more than 3,600 feet of cable are required.

93. Installation.-a. Windlasses are usually installed inside the fuselage to the rear of the rear cockpit. Installation will be made in accordance with installation drawings for that particular type airplane.

b. Prior to installing the cable on a windlass, each end of the cable will be painted a bright red color for a distance of approximately 100 feet to enable the operator to determine when the end of the cable is approaching when paying out or reeling in, thus preventing possible damage to or loss of some part of the towing equipment. After the windlass assembly has been installed and the cable attached to the reel, the cable must be wound onto the windlass reel. This may be accomplished as follows :

c. On the C4 windlass

(1) By attaching the hand crank to the reduction gear shaft.

(2) By running up the airplane engine to provide air blast to turn the impeller.

(3) By using the motive power of an electric drill engaging the impeller retaining nut.

d. On the C4A or C5 windlass by operating the electric rewind motor. This will be accomplished with an auxiliary electric supply.

e. An exchange release will be attached to the cable in accordance with respective Technical Orders.

f. The quantity of lead ropes to be carried for each mission will be equal to the number of targets to be towed on that mission, plus one additional lead rope for carrying the drag release to release the last target. The steel ring of each lead rope will be threaded on the towing cable. The opposite ends of the lead ropes will be drawn into the operator's cockpit and separately secured in position for attachment to the bridle loops of the targets.

94. Launching targets.-a. After the first target has been attached to the first lead rope loop and the lead rope ring is drawn over the exchange release until it engages the latch, the target is ready to be launched. At no time while cable is paid out will the altitude of the towing airplane be less than one-half the number of feet of cable out. The pilot will then be signaled to reduce the flying speed to minimum safe flying speed. Release the brake on the windlass and launch the first target through the opening provided for that purpose. Immediately after launching the target, apply the brake gently until the unreeling of the cable is under control. After the desired length of cable has been unreeled, set the brake securely but watch it constantly. The flying speed can then be increased to any desired speed up to 200 m. p. h. for the A5 and B12 targets; for the A6 target there is no stated top towing speed. While the first target is being towed, the second one will be prepared to launch. When the second target is launched, the ring on the lead rope as it travels down the towing cable with the target strikes the exchange release trigger and automatically frees the target being towed. When exchanging targets, the speed of the airplane will be at its minimum.

b. To release the last target upon completion of the towing mission, attach a drag release to the remaining lead rope and launch in the same manner as when exchanging targets. The towing cable will be wound in (C4 windlass) by simultaneously releasing the brake and engaging the clutch. When the end of the cable is just beyond the tail surface of the airplane, the clutch must be released and the remainder of the cable reeled in slowly by carefully operating the clutch and brake alternately as required. After the cable has been rewound, the brake will be securely set and the end of the cable with the release and drag attached will be drawn into the cockpit preparatory to landing. Personnel operating a C4A or C5 windlass will comply with the operating instructions posted in a conspicuous place in the cockpit.

c. Before any towing missions are performed, the following warning will be posted in a conspicuous location in the operator's cockpit of the towing airplane :

DO NOT GRASP CABLE WITH HANDS UNDER ANY CIRCUMSTANCES. CUT CABLE IN CASE OF MALFUNCTIONS.

Inspection of towing equipment will be carried out in accordance with respective Technical Orders before the first towing mission each day.