TM 1-411, Airplane Hydraulic Systems and Miscellaneous Equipment: 11 - Aircraft Parachute Flare

SECTION XI: AIRCRAFT PARACHUTE FLARE

59. General.-a. The purpose of an aircraft parachute flare is to provide sufficient illumination over a sufficiently large area so that a landing can be made at night.

b. Flares are considered as flames having the same candlepower in all directions. The factors affecting the visibility from aircraft of ground objects lighted only by flares may be classified as follows:

Candlepower of the flare and number of flares used.

Height from which the flare is released.

Nature of the terrain reflecting the flare light.

Condition of the atmosphere.

The parachute is not considered as contributing to any of the illumination on the ground.

c. The altitude at which the flare is released affects considerably the ground illumination obtained from a given flare. The effective light area on the ground is circular in shape, with a diameter of approximately 6,000 feet at altitudes of from 1,000 to 3,000 feet. The area so lighted is approximately 1 square mile. Since objects on the ground are made visible by the light they reflect and by contrast with surrounding objects, landing fields being somewhat barren have a relatively higher reflection value so that other fields and wooded areas require a greater intensity of light and flares dropped over such areas must be at lower altitudes, or more than one flare must be in the air at the same time for good vision. The intensity of illumination necessary also depends on the condition of the atmosphere, that is, amount of haze, clouds, etc.

d. The maximum intensity of ground illumination will be obtained when a flare is released at between 1,000 and 2,000 feet altitude if the diameter of the circle of illumination on the ground and the average intensity of light are both considered; however, since the average time of burning is about 3 minutes and its rate of descent is about 600 feet per minute, to allow sufficient time for the flare to burn itself out while still suspended in the air, the minimum safe altitude is considered as 2,000 feet. This eliminates the fire hazard by allowing the flare to burn out before reaching the ground. The maximum speed at which it is safe to release flares is 135 miles per hour.

60. Description.-a. The aircraft parachute flare, shown in figure 58, is cylindrical in form and consists of the parachute case assembly and the illuminant assembly. The parachute case consists of a metal tube, closed at the upper end by a cover which is attached to the case by means of the tear strip assembly. The hangwire container assembly is located immediately beneath this cover and is held in position by a shoulder formed in the case and sealed by wires passing through the edge of the container and case. The ends of these wires are twisted together and secured by soldering.

FIGURE 58-Installation of suspension bands on flare.

b. The space in the parachute case immediately below the hangwire container is filled with the top cord, parachute, shroud assembly, and suspension wire in the order named. The remaining 2 inches of space below the second shoulder is occupied by the upper end of the illuminant assembly. This is inserted as far as the shoulder will permit and fastened in place by four wood screws.

c. The illuminant assembly consists of a cylinder 15 3/4 inches long entirely filled with illuminant with the exception of a recess in each end of the cylinder and a center tube in which the quick match is located. The large recess in the upper end of the cylinder contains the base block assembly. The recess in the lower end is empty and provides an air space around the lower end of the quick match. The lower end of the recess is closed by the body cover assembly.

d. Following are some descriptive data about the current type flare:

e. Racks.-(1) Flares may be carried on aircraft in either the horizontal or vertical position. Of the several type racks used to carry flares in the horizontal position the type most used is installed entirely within the wing of an airplane. The opening in the lower surface of the wing is closed by a spring retainer door. The door is opened by the flare release cable 20° ahead of the release of the flare to insure positive egress of the flare. The door is opened mechanically to break the sheath of ice which forms on the under surf ace of the wings under certain weather conditions. The rack consists of two carrying hooks pivoted in the frame, linked together, and released simultaneously by a releasing latch at the forward end. The arming wire swivel loop is attached to a snap hook fastened to the front end of the flare rack. When flares are to be carried in a horizontal position, the suspension bands are installed on the flare body, spaced 14 inches apart, as shown in figure 58, to support the flare on the racks. Black bands are painted around the flare cans at the locations for these suspension bands. There are also short, black lines painted parallel with the longitudinal axis of the flare for locating the loops on the suspension bands.

(2) The rack in most general use for carrying a. flare in the vertical position is cylindrical and closed at the bottom by a carrying and releasing door on which the flare rests when installed. The top of the rack is covered by a hinged lid in which the hangwire swivel loop of the flare is anchored. The lid is fastened by a spring latch and covers the rack to prevent the entrance, of water, etc. The rack may be loaded from either the top or bottom, depending upon the overhead and ground clearance available.

(3) A flare-release handle is used to release the various vertical and horizontal flare racks. One handle is used with each rack and the cables connecting them are provided with a return spring to retract the handle after release and to provide the 1/2-inch slack necessary to remove all tension on door release and rack-release mechanisms.

61. Operation.-The operation of the flare is the same whether carried horizontally or vertically. When the mechanism carrying the flare is released, the flare falls to the full length of the hangwire, pulling the hangwire container out of the parachute case, following which the top cord, the parachute (closed), the shrouds, and the suspension wire are withdrawn. As the entire weight of the illuminant assembly comes on the tear strip to which the top cord is attached, the strip is broken and the, parachute falls free and opens. At approximately the same time the weight of the illuminant assembly on the parachute and its suspension wire draw the pull wire to which the friction wire loops are attached out of the upper recess in the illuminant assembly. This withdrawal of the friction wire through the primer charge causes ignition of the quick match which projects into the space around the ignition block in the base of the base block assembly. The quick match burns down through the long center cardboard tube in the illuminant assembly and ignites the first fire charge carried in the base of the illuminant case. This burns out the lower disk and the lower rim of the illuminant case, freeing the body cover assembly from the case. The main body of the illuminant is ignited by the first fire charge and burns steadily upward as the flare descends.

62. Maintenance.-a. Flares installed on aircraft are always carried armed, that is, with the hangwire swivel loop properly anchored. This is to prevent the flare assembly being accidentally dropped without burning, which is extremely hazardous in populous areas. Although constructed so as to be practically waterproof under normal conditions of use, flares should not be exposed unnecessarily to dampness.

b. At the time of installation of flares in the flare racks, and at periodical inspections, the operation of the racks and release mechanism is checked by installing the flares without securing the hangwire swivel loops and then operating the release mechanism. When this check is being made, someone is stationed beneath the airplane to catch the flare before it strikes the ground. Where desired, this test may be accomplished by substituting a dummy flare of approximately the same weight, diameter, and length as the flare; however, the flares to be installed in vertical flare racks following this test are then tried in the rack to ascertain whether binding occurs at any point. If binding occurs, other flares will be tried to secure one that will slide freely in and out of the chute. Care is taken in handling flares that the carrying hooks are not bent and that the flare body is not dented or otherwise damaged.

c. The premature release of flares when taxiing over the ground may cause the flare to strike the ground without pulling of the hangwire container. In this case the bottom of the flare will be dragged over the ground until the bottom covering is torn off, exposing the ignition elements. As these elements are readily ignited by friction, ignition of the candle and subsequent burning of the airplane may result either before or after the airplane has left the ground. Under these conditions it is impossible to release the burning flare from the flare rack by operating the controls, since the flare is suspended by the hangwire, which in turn is secured to the rack. Only by exercising the utmost care and checking all parts of the flare rack and the flare installation can prevention of premature release and malfunction of flares be assured.