TM 1-411, Airplane Hydraulic Systems and Miscellaneous Equipment: 7 - Floatation Equipment

SECTION VII: FLOTATION EQUIPMENT

44. General.-a. The types of flotation equipment carried in aircraft are pneumatic rafts, pneumatic vests, and airplane flotation gear, of which only the first two will be discussed.

b. Because such large volumes can be conveniently stored in a small cylinder, CO₂ gas is used for the inflation of this equipment. The capacities of  the cylinders used in each case and the. weight of the CO₂ charge are given in table III.

45. Pneumatic rafts.-a. Types.-These rafts are designed to be carried in aircraft engaged in overwater flights. The pneumatic rafts in use at the present time are-

Type A (1,000 pound capacity).

Type B (400 pound capacity).

Type C (250 pound capacity).

Type D (2,000 pound capacity).

Early models of the rafts were constructed of rubberized fabric, with integral tubular gas cells or compartments, equipped with valves and rnanifolding for CO inflation. The later type rafts have an outer covering of rubberized fabric and removable latex-rubber tubular gas cells or compartments equipped with valves and manifolding for CO₂ inflation. A typical raft is shown in figure 45. Each raft is furnished with a waterproof carrying case, sufficient in size to store the deflated raft and the accessories.

b. Accessories-The following accessories are kept in each raft carried in aircraft; one carrying case, two oars, one hand pump, one repair kit, 40 feet of 75-pound lashing cord, and one emergency signal kit. The kit is filled each time the raft is placed on the airplane and contains one pyrotechnic pistol and six red parachute distress signals. When these items are placed in the signal kit container, the folds in the top of the container are cemented down with two coats of rubber cement. The sealing strip is then cemented down across the opening edge with two coats of rubber cement. In view of the danger involved in the storage of pyrotechnics the above items are returned to their proper stores when the raft is removed from aircraft and returned to stock.

 c.-Inflation.-Two types of release valves are employed: combination cutter and hand-shut-off type, and a combination hand-shutoff quick-release type. Operation of the first type is accomplished by raising the valve handle which breaks the safety wire, and turning the handle 180° clockwise or in the direction indicated by the arrow on the top of the valve.

FIGURE 45-Inflated pneumatic raft.

This movement sends a cutter through a safety disk releasing the CO₂ gas. The gas flow can be shut off from the raft at any time by turning the valve in the opposite direction as far as it will go. The second type valve is operated by simply pulling a toggle cord, which raises a handle and allows a spring loaded valve stem to rise. The gas flow can be shut off by screwing down the valve stem as far as it will go. The specified charge in cylinders for rafts is such as to inflate the rafts to 1 pound per square inch gage pressure at 70° F. Due to its low temperature, the initial pressure of the gas in the raft is less than this, but it will increase gradually until it reaches atmospheric temperature, usually in about 10 to 15 minutes. If at any time the gas cell appears to be inflated too tightly the pressure may be reduced by opening the topping off valve. As soon as the pressure is sufficiently reduced, these valves are securelyclosed. The amount of inflation should be just sufficient to maintain a well rounded contour of the gas cells. If the raft is under-inflated, either initially or because of gas-cell leakage, the hand pump is attached to the topping off valve, and each gas cell further inflated by hand. The repair kit furnished with each raft contains rubber cement and patch material

FIGURE 46.-Raft being deflated.

for repairing leaks whenever necessary. The pneumatic seats are generally provided with a valve on the side or the bottom side, of the seat for inflation with the hand pump.

d. Deflation.-Deflation of the raft is accomplished by unscrewing the topping off valves on each gas cell, opening each seat valve, and folding and rolling the raft to completely expel all gas. The raft is completely deflated, the discharged cylinder replaced with a charged one, and all valves secured before the raft is placed in the carrying case.

e. Folding.-The operations for proper folding are. shown in figures 46, 47, 48, and 49. Where practicable, the external surf aces of the rubberized f abric are thoroughly powdered with tale before folding.

FIGURE 47.-Deflated raft being folded.

FIGURE 48.-Final folding operation.

f. Repairs.-No repairs are made to the rubberized fabric or latex bladders other than the patching of small holes. Such repairs are made by patching the bladder with rubber cement and bladder material and the casing with rubber cement and rubberized fabric, all supplied in the repair kit. Rafts having large tears, rips, and severely chafed areas are condemned.

FIGURE 49.-Raft and accessories being placed in carrying bag.

When cylinder connections, manifold, and topping off valves are found defective they are repaired or replaced as required.

g. Impection.-The date of each 6 months' raft inspection is stenciled  in indelible ink to the right of the inspection patch as viewed from the end of the raft on which the CO₂ cylinder is mounted, using letters and figures approximately 1/2 inch high; for example, Tested 12-8-38.

h. Storage.-Rafts, when not in use on aircraft, are unfolded and stored away from light in a cool, dry location favorable to the storage of rubber articles.

i. Age.-The age limit of rafts is from 3 to 4 years depending upon the particular type and model. Consult Technical Orders for further information of this nature. The date of manufacture is stenciled on each raft.

FIGURE 50.-Life-preserver vest.

46. Pneumatic life-preserver vests.-a. Type.-The current type pneumatic vests, shown in figure 50, is designed primarily for use under climatic or other conditions that render the wearing of kapok filled or similar types of buoyant garments undesirable because of their discomforting bulk or heat-retaining qualities. However, if maximum safety is desired, regardless of these discomforts, the kapok filled life-preserver vest should be used instead of the pneumatic type. The pneumatic life-preserver vest consists of a double compartment cotton fabric outer casing, enclosing two separate latex rubber cells. Buoyancy for emergency use is obtained by inflation with CO₂ gas, two CO₂ cylinders (one for each compartment) being provided for this purpose. CO₂ cylinders for use with this life-preserver vest are not rechargeable. The vest is to be worn deflated under the parachute harness. At no time, however, is it worn under tight fitting clothing.

b. Inflation.-The vest is inflated by pulling downward on the cord attached to the two discharge levers. This actuates both plungers and punctures the sealing caps on the two CO₂ cylinders. If inflation of both compartments does not occur simultaneously, an additional pull on the cord may be required before both of the sealing disks are punctured. Additional inflation, if necessary, may be ef fected by opening the valves at the neck of the vest and blowing with the mouth. When placing the CO₂ cylinders in the containers, the ends of the cylinders containing the sealing caps must be inserted first, with the discharge levers in a vertical position and safetied with light safety wire against the side of the container to prevent premature discharge of the cylinder as the container cap is being secured in place. The, cap should always be tightened firmly by hand to prevent leakage.

c. Deflation.-Deflation is accomplished by opening the. mouth valves and slowly rolling up the vest.

d. Storage.-When not in use life-preserver vests are kept in their original container and stored in a cool, dry storage room.

e. Repair.-Repair of leaks or punctures in the latex rubber cells is made by first removing the stitching of the fabric outer casing near the leak and applying standard Air Corps cold patch. The rubber cell is then tested for leakage by inflating and submerging in water. If the leak has been satisfactorily repaired the outer casing is replaced and restitched. Snagged or chafed spots in the fabric outer casing may be repaired by sewing a patch of 6-ounce cotton fabric over the damaged area, provided the patch does not exceed 2 square inches in area.

f. Inspection.-The, date of each 6-months' inspection is stenciled in indelible ink on the vest; for example, Insp. 6-23-40.

g. Age.--Vests are considered unserviceable and disposed of 3 years after the date of manufacture stamped on each vest. CO₂ cylinders that are removed from unserviceable vests are returned to stock.