For almost a year, advertising messages of Consolidated-Vultee have been emphasizing the most unbelievable truism that airplanes can link every point on the face of the earth with sixty-hour schedules. A few months ago, the general theme was graphically demonstrated when Consolidated released a book containing several hundred airline maps as a preview of Moscow to Minneapolis, New Orleans to New Caledonia air service. The maps, and the entire advertising theme, may well be interpreted as a combat report on the performance of Consolidated's own B-24, for it is certain that few cities of the world have been without some contact with this mammoth battlewagon.
Pot-bellied and slab-sided, with the general beauty of a caboose, this venerable airplane has served every one of the Allies on every war front. Its versatility and importance will, undoubtedly, become more apparent as the tempo of offensive war increases during the coming months. In the meantime, at least one B-24 can, at this moment, strike at any target in any Axis or Axis-dominated nation in considerably less than sixty hours. Nor does the B-24's worth begin and end on strategic bombardment operations. A veteran of Ploesti and Port Moresby, no stranger to Rabaul or Reykjavik, the B-24 is carrying blood plasma and block busters, generators and generals, wounded troops and weary ferry pilots into all of the fourteen theaters of American air activity, serving as a one-man gang in the war for liberation of enslaved nations. As each new city or sector falls into Allied hands, other Liberators move in with food and clothing to free civilians from fear and want. There are, apparently, no jobs which the Liberator cannot perform, and on its record alone it must be rated as the most appropriately named of all warplanes a Liberator in every sense of the word.
Bigger in span than a prewar British hangar, higher than most of the factories producing its component parts, the Liberator is hardly a toy for those untrained in its operation or maintenance. But to regular B-24 pilots and crew chiefs, it is a docile machine, big in proportions but small in problems. More than one technician has expressed the sentiment that a B-24 will take care of itself to a large extent if it is flown by a thoughtful pilot and handled by conscientious ground crews. Care instead of elaborate servicing cures will keep B-24s in the air under all circumstances.Pilot Precautions
This importance of pilot foresight represents an unique aspect on the military aircraft maintenance problem, and might well be presented here through the instructions normally given to B-24 pilots but seldom conveyed to the men on the line. For example, the B-24 is one of the world's biggest aircraft supported on the ground by a tricycle landing gear. Successful use of this undercarriage belies the prewar thought that tricycle gear had been carried to its ultimate when North American added this equipment to the B-25 structure. In the light of the record, it seems that the three-way gear can serve any ship, no matter how large, if pilots land and take-off at speeds suited to load characteristics. In the case of the B-24, a lightly-loaded ship must take off at a speed of about 110 mph while a Liberator loaded to the gunwales must move at 130 mph before leaving the ground. Proper taxiing can eliminate more than a dozen service problems, all of which evolve from the tremendous size of the landing gear and its components. Tires, for instance, are difficult to change when their diameter approaches the height of a human being. But the pilot who moves forward slowly from the starting line, makes no sharp turns, and steers with the engines and not with the brakes, can keep his B-24 tires in good condition for many missions, while, at the same time, saving the nose wheel and main wheel aerols from undue stress leading to hydraulic system servicing.
The Pratt & Whitney Twin Wasp engines also demand care from the pilot if frequent engine overhaul is to be prevented. Liberator pilots usually idle their four engines at no less than 800 rpm, no more than 1,000 rpm, with cowl flaps opened about one-third for proper cooling on the ground. Headed into the wind on take-off, the skillful B-24 pilot will extend his flaps one-fourth or more, depending on takeoff run, before opening throttles slowly until full positions are reached. Brakes are applied until manifold pressure reaches proper level, then full power is supplied for the takeoff in order to reduce tire wear and landing gear strain. A straight course is maintained by rudder operation and not by use of the brakes.
Landing legs are raised and locked as soon as the plane clears the field to become completely airborne and sufficient power is used to give a speed of 130 mph as soon as possible, as a precaution against low-altitude engine failure. Flaps are not raised until the plane's speed exceeds 150 mph, When the plane reaches its best cruising altitude, it is leveled off and speed is increased for a few moments before being cut to the most economical operating speed. Too early decrease in speed will cause the plane to mush with nose up in a position which produces generally sluggish operation. Engine head temperatures are controlled at all times by use of the cowl flaps, with the range between one-third and two-thirds open avoided because of the buffeting tendency apparent when the plane flies at cruising speed. To any mechanic who has sweated over lock mechanisms, misaligned landing legs and flaps, fuel-consuming engines, clogged oil systems, and overheated engines, it should be obvious how much maintenance work can be eliminated from the B-24 routine when pilots observe all of these points when flying the Liberator.The Plane in Flight
Every service procedure, regardless of the plane under consideration, is aimed at maintenance of the entire ship in a condition of efficiency approaching the 100% of a new plane. Thus, any elimination of airframe abuses is certain to lessen the hangar time required between missions. This is particularly true with the Liberator, because of its size and variety of loadings. One of the most flyable heavy planes of the war, the B-24 can be banked at angles up to 60° with no difficulty or danger. Pilots must, however, remember that a bank this steep increases the load factor to 2, with any load doubled in severity when the bank is 60°. Similarly, load strains are increased when the plane operates in turbulent weather, so B-24 pilots normally cut their speed to 150 mph and drop their landing gear when flying on instruments, with the automatic pilot disengaged entirely whenever rough air is encountered. When weather conditions dictate maneuvering of the plane, the B-24 is properly trimmed by use of the trim tabs as a precaution against undue airframe strains likely to result if the pilot relaxes momentarily while attempting to carry the whole rudder load. Mechanics who have serviced Liberators in the various military theaters all agree that a great many of the rivet replacements, panel repairs, and structural reinforcements have resulted more from the actions of friendly but thoughtless pilots than from the combat activity of enemy pilots.
Returning from a mission, nervous, tired, hungry, and anxious for the safety of their crew, both the pilot and the co-pilot have mental loads which no ordinary man could assume. It is, therefore, a tribute to American pilots that their landings so closely follow the instructions outlined in their pre-combat training, contributing much to the endurance of B-24 Liberators. For instance, the plane is never swerved sharply despite the fact that ground-loops are rare with tricycle-geared airplanes. The nose wheel, which swivels perfectly over a 90° arc, may be seriously damaged when turned too sharply. The brakes, which include both an outboard and an inboard drum on each wheel so that at least one-half power is always available, are never applied for long periods of time and any application of the brakes is accompanied by coordinated application of engine power. When the brakes become overheated in the course of a short landing run, they are allowed to cool before parking brakes are set. When emergencies demand extremely short landing runs, the brakes must be applied immediately after the plane makes a full tricycle contact with the field. The resulting thrust of the nose wheel, with possible damage, is alleviated by pushing the elevator controls forward just before the brake pedals are activated.General Aspects To better understand succeeding comments on pilot attention to the B-24, it is well for the reader to know something of the general structure of the Liberator a structure which, though not basically different, is actually unique among large combat planes. Shorter than the Flying Fortress in fuselage length, measuring 66' 4" from Emerson nose turret to the matching tail turret, the generally bulbous structure is emphasized further by a Davis wing measuring 110' from tip to tip. The Liberator fuselage is 10' 5" high while the plane in normal hangar position requires clearance for an overall height of 17' 11". It is, obviously, one of the biggest American planes ever committed to production. That an airframe of this size demands plenty of routine care is apparent in a consideration of the maintenance charts concerning the lubrication system alone.
Starting at the gun socket mounts in the nose, servicemen must add lubricating compounds every twenty-five hours. A few stations back, the nose wheel door is greased every fifty hours, the pilot's seat rollers get grease every fifty hours, and the seat itself is lubricated after a hundred hours of operation. Chains are lubricated with special compounds at twenty-five hour intervals, while the tracks for pedals are cleaned, though not greased, before each mission. The nose wheel gear box and brake pedal linkage in this compartment are lubricated every fifty hours, while rudder chains are treated at twenty-five hour intervals. In the wing, first attention goes to sprockets, universal joints, tab hinges, and screw jacks which are oiled every twenty-five hours. At fifty-hour intervals, power plant cables and landing gear lock mechanism are treated with special lubricants, while the gear boxes, including the landing gear box, are oiled at three hundred-hour intervals. Bomb doors and cables in the mid-section are lubricated with oil and special compounds respectively at twenty-five hour intervals, while elevator and rudder tab hinges, screw jacks, and universal joints in the tail section are lubricated at the same time. Gear boxes in the tail are greased every three hundred hours while the locking mechanism receives new oil every 50 hours. The main landing gear calls for faring hinge lubricant and fairing link oil every twenty-five hours, grease on latches and pinions every twenty-five hours, special grease on wheel bearings at one hundred-hour intervals, and needle bearing lubricant every three hundred hours. Lubrication of the nose wheel follows a similar pattern with the addition of oil on lever shaft and latch assembly every fifty hours and grease on the locking mechanism every twenty-five hours of flight.Crew Cautions It would be impossible to tell the whole maintenance story of the Consolidated B-24 without revealing valuable tactical information to the enemy. Nor will space limitations permit even summarization of all servicing routines on hydraulic, electrical, power plant, and radio equipment. There are, however, several cautions which may be followed with success by technicians trained on any large American bomber. With these rules and common sense, the trained man can quickly adapt his talents to the special techniques of B-24 servicing.
First of all stay out of the B-24 tail area unless the plane is supported at the rear section. A tricycle landing gear naturally pivots the plane well forward and load must be concentrated accordingly. In towing the B-24, never attempt turns of greater than 30°. While it is true that the nose wheel will pivot on a 45° arc in take-off and landing, the tire wear of low speed towing is something more serious, while the tow bar strain on the nose wheel aerol is considerably greater than the thrust and surface friction built up when the plane moves forward at 110 mph. And, as a seemingly unnecessary precaution but one which has been found important too often, don't walk on hatches. The followup usually corresponds to the action of a trap sprung beneath a man being hanged.
This article was originally published in the March, 1944, issue of Air Tech magazine, vol 4, no 2, pp 19-25, 72-73.
The original article includes 12 diagrams.