The United States is today in the process of building the greatest air armada in history. For the last 20 years, though the quality of its pilots and planes has been excellent, its numbers were few. The US has lagged behind other world powers in military aviation. First Italy, then Russia, and most lately Germany and England have been the builders of mighty air fleets. But, with the outbreak of the war and the launching of our armament program, the situation has changed and the United States is getting under way.
Certain facts regarding the present US Air Corps program are of a secret nature and hence may not be discussed in this article. However, from facts that have been made available to the public, it is possible to make a brief survey of the proposed line-up of the new planes of the Army Air Corps; of its expanding personnel and changing policy.
The new Army Air Corps is to be built around two types of heavy bombardment planes, three medium bombers, three light bombers, three pursuit types, and one pursuit-interceptor. With swarms of trainers and observation craft, its total strength will, in time, approach 25,000. If Navy planes are counted as they must be America's air force will surpass even that of the incredible Nazi Luftwaffe.
The Boeing Flying Fortress, Consolidated B-24, Martin B-26, North American B-25, Douglas A-20A, Douglas A-24 (SBD-3), Curtiss XSB2C-1 (Army designation not yet known), Bell P-39 (Airacobra), Curtiss P-40 and P-46, Republic P-47 and Lockheed P-38 ships widely known as well as ships not so familiar, they're all there. All are on order, most by the hundreds. Production on all but a few is already under way. The total cost for planes and engines under this program comes to $1,500.000,000.
The geography of the United States its tremendous size and far-flung borders has dictated great range as a primary characteristic of its Air Corps bombers. American bombers must be capable of quick transfer from coast to coast. Speed was a secondary consideration for a time; it was expected that the most American planes would be called upon to face would be ship-based aircraft, which are not as fast as land-based types. Hence the development of such lumbering machines as the Douglas B-18. The B-18 and her somewhat more modern sister, the B-18A, are not very fast (220 mph top) but they can carry 4,400 pounds of bombs over a radius of nearly 1,000 miles.
In the new Air Corps the problem imposed by geography has been met in a somewhat different way because the European war has taught the increased importance of speed and the general advance in aeronautical science has made it possible to build speed and range into the same plane.
Extreme range, with adequate speed, are provided by the four-motored heavy bombardment craft. The heavy twin-engined type of familiar character (good range and load, but poor speed) is out. The need for greater speed is met in the medium series which is shorter-ranged and cannot carry the same load. One medium bomber, the Martin B-26, grosses nearly 13½ tons; the North American B-25 is the other and weighs about 11 tons fully loaded. The Douglas B-23 (13½ tons, Twin Cyclones, 295 mph) was an intermediate type along the line of development of the current medium bomber. Only 30 B-23s were built and no more have been ordered.
Air weapons of extreme mobility, capable of carrying out diving attacks, are provided in the light bomber class. The famous B-17 class will remain the backbone of the Air Corps' heavy-duty squadrons but it will not be the Flying Fortress familiar today. The four-motored Boeing giant has undergone half a dozen major modifications in its four- year history. Going into production in January is the latest of the series, the B-17E, which will have a top speed approaching 300 mph, a gross weight of 22 tons, a radius of action (distance of target a plane can reach, allowing for return to base; radius of action usually is about 45 per cent of maximum range) of 1,700 miles and bomb load, at shorter distances, of five tons. It will be the first Flying Fortress with power-driven turrets and heavy defensive armament which replace the single-gun blisters and sliding panels of earlier models. Installation of a rear turret necessitated complete redesign of the whole rear half of the fuselage. The new Boeing will also incorporate an exhaust-driven turbosupercharger which will give the plane high performance at 25,000 feet and enable it to operate successfully just above 30,000.
The Air Corps already has about six squadrons of earlier Flying Fortresses, including the original B-17, the B-17B (the first production plane with a turbosupercharger), and the B-17C. The "C" and "E" both are driven by the most powerful Wright Cyclone single-row engines, each rated at about 1,200 hp
The B-24 is a little smaller and faster 310 mph, full weight 20 tons, 1,500-mile radius, four-ton bomb load, tricycle landing gear, a high wing and four Pratt & Whitney 1,200 hp Twin Wasps. It, too, is power-turreted, the first Air Corps plane to be so equipped. This installation, as was to be expected of any new development, caused a little difficulty.
This Consolidated ship combines unusually low drag and easy handling with a high wing loading, something that is not found in every airplane and which is characteristic of the unorthodox Davis-Caltech thin section wing, around which the plane is built.
Both the Boeing and Consolidated, as well as other smaller bombers, will have one feature not previously found in US bombers quarter-inch armor shielding the combat stations of every man aboard ship, with the probable exception of the luckless tail gunner. He is difficult to shield because the tail turret is so heavy that the additional weight of armor would make the plane unflyably tail-heavy.
The Air Corps has virtually no B-24s on hand as the first 26 are being turned over to the British.
The Martin B-26, one of the medium bombers, has just reached the prototype flight-testing stage and information about it is, therefore, very much restricted. Suffice it to say that it is a semi-high-winged plane with a gross weight of 26,625 pounds, two Double Wasp engines, four-bladed Curtiss propellers and a tricycle landing gear. Top speed: about 340 mph. Maximum bomb load is believed to be about 3,000 pounds.
The best-known current Martin is the 167W, which was ordered originally by the French and is now being turned out in quantity for the English. The 167W is an eight-and-half-ton attack plane powered by Twin Wasps and should not be confused with the B-26. The B-26 is a completely new design.
The North American NA-40 the B-25 also is a medium bomber. It is a much modified version of the overgrown attack bomber North American first developed about two years ago. High-winged and tricycle-geared, its two Twin Cyclones drive it about 325 mph. Medium bombers will all have power turrets.
The three ships in the light bomber class are one attack and two dive bombers. The Douglas A-20A is the attack ship and is a plane with a long history indeed. It is descended from the first DB-7, the plane which Douglas intended to submit in the Army's first attack-bomber competition two years ago. It crashed on a test flight over Los Angeles, killing Pilot Johnny Cable and injuring the famous French aircraft inspector, Paul Chemidlin, whose presence aboard an allegedly secret American military plane precipitated a bitter debate in Washington. None of the actual entrants won the contest. Douglas did, although the company was unable to send a ship to Wright Field. Its engineers, instead of attempting to rebuild the DB-7, designed a vastly superior model which won Army approval. This is the A-20A. At the same time they turned out a couple of other modifications of the DB-7 to the orders of the French and British purchasing commissions, known as the DB-7A and B.
All are 8½-ton, tricycle-geared, high-winged, twin-engined monoplanes, with a span of about 60 feet. The DB-7 and 7A are fitted with engines in the 1,000 hp class; the 7B and the A-20A, which differ from each other in other respects, are powered with Twin Cyclones. The DB-7's top speed is just over 300 mph, the 7A about 315, the 7B and the A-20A about 350 just above 15,000 feet. Originally the A-20A was to have been equipped with turbosuperchargers which would have sent it through the air at 390 mph at 25,000 feet. But it is said that not enough of the new type blowers are available and that plans for their use in the A-20A have been abandoned. The whole series make acceptable reconnaissance craft and multi-engined fighters as well as the ground attack planes originally intended.
The radius and bomb load of these planes, when equipped for bombardment missions, are not great, as is to be expected: 500 miles and 1,000 pounds. The British versions of this series have been criticized by the British themselves because the fuselage is too narrow to permit side-by-side seating of the pilot and the bombardier-co-pilot. The fuselage was made as narrow as possible in the interest of speed.
The dive bombers the SBD-3 (A-24), and the XSB2C-1 both are Navy types to be adapted for Army use. Less than a hundred of the SBD-3s have been ordered. The order was placed by the Navy, from which the War Department will buy its dive bombers. The number of XSB2C-1s to be procured is not as yet known. Both are single-engined, low-winged monoplanes, the SBD by Douglas, the other by Curtiss. The Curtiss is the newer. The Douglas divers are actually the third in a series, the first two models of which were for the Navy exclusively. Production of the first of the series has already been completed. The Curtiss, successor to a long line of Curtiss biplane dive bombers (the famous Helldivers), is not yet in production.
They are both quite small as they were built originally for operation from aircraft carriers. The Douglas's top speed is about 275 mph and it is driven by a Wright Cyclone. The somewhat larger Curtiss is Twin Cyclone-engined and approaches 300 mph. Bomb loads: 1,000 and 1,500 pounds respectively. The differences between Army and Navy versions are relatively slight, the main ones being the elimination of deck-landing and emergency flotation gear from the Army models.
At first glance these speeds do not appear impressive. It must be remembered, however, that top speed has to be sacrificed in this class of ship to flaps and other essential diving brake equipment. Contrary to the general impression, high diving speeds are undesirable as an unnecessary strain would be placed on ship and crew and the pull-out would have to begin at too high an altitude. Diving speeds of around 300 mph are preferable. The Junkers Ju-87, Germany's famed Stuka, is a single-engined ship with a top speed of less than 250 mph.
Air Corps pursuit squadrons should provide not only ships with exceptional speed and heavy armament, but also some with range enough to accompany bombers on relatively close missions. Escorting bombers on long distance raids is theoretically desirable but at present is entirely out of the question. Without any intention of taking sides, it must be reported that a series of torrid disputes has been raging over whether all the new fighters measure up to these standards in every respect.
In service in the largest numbers so far is the Curtiss P-40. Coming into service now is the P-46, a slightly modified P-40. Most unorthodox is the Bell Airacobra (the P-39), and most spectacular is the twin-engined Lockheed P-38. The P-47, the Republic entry, is a newcomer and is still a fairly long way from quantity production. The P-47 is a low-wing monoplane, but, unlike the others, is powered by an air-cooled radial, the 18-cylinder Pratt & Whitney Double Wasp (1,850 hp for take-off). Its speed is over 400 mph at 30,000 feet (it has a turbo blower), but falls off rapidly to under 350 at 15,000 feet. Armament not released. All Air Corps pursuit types but the P-47 also are on order for the British.
The P-40 is the successor not only to the Curtiss P-36 but also to the YP-37, the first high performance American fighter designed for the installation of a liquid-cooled in-line engine the Allison, of course. The Allison's 1,000 hp at full throttle gives the P-40 a speed of about 365 mph and the cleaner P-46 perhaps 380.
The original armament of four rifle-caliber machine guns is believed undergoing change, as four guns are not now considered adequate. British Spitfires and Hurricanes have long had eight, the Hurricane III has 12 and the new British fighters with 2,000 hp motors (the Tornado and Typhoon) eight machine guns and four 20-mm cannon.
Larry Bell's nine-ton multi-engined Airacuda fighter, with its pusher propellers and other unusual features, four years ago led the aviation world to expect the unorthodox every time he produced a new ship. The P-39 is no disappointment on that score. It is a low-wing, monocoque monoplane, which is not at all unusual. It has a tricycle landing gear, which is no longer unique. But the Allison engine is in the rear and its tractor propeller is turned by a long drive shaft which passes beneath the pilot's feet. The pilot sits on the front end of the gearbox. By this strikingly different arrangement, several weighty advantages are gained. The British, however, who have roasted the Airacobra in their technical magazines, claim that a number of disadvantages also result.
Because the engine, the greatest mass of weight in the ship, is nearer the center of gravity and center of pressure, the P-39 is more maneuverable than might be expected of a ship of its speed or high wing-loading. Getting the engine out of the nose also permits the installation of more and bigger guns right in the nose, within reach of the pilot. Guns do not jam often today but, when they do, the pilot appreciates easy accessibility. Installation of a nose wheel for the tricycle landing gear would have been more difficult in a conventional machine.
The rear engine offers a certain amount of protection to the pilot from behind. The radiators for a liquid-cooled motor must be immediately adjacent to it. Placing the radiators aft of the cockpit, as in the Airacobra, reduces drag not only by making possible a cleaner nose but because obstructions near the tail of a ship offer less resistance in themselves.
The most serious criticism of the Airacobra, as charged by the British, is that its rear engine very simply means more dead pilots. It is feared that the engine will keep on going in the event of a crash and crush the man unlucky enough to be in the cockpit at the time. Fear of this sort of occurrence was one of the factors in the general abandonment of the pusher engine a generation ago.
In such ships as the Airacobra the engine itself is also more exposed to bullet damage. Most enemy bullets come from the rear because most dog fights are fought head-on-tail. Unfortunately the liquid-cooled engine's cooling system is vulnerable. Loss of coolant and consequent seizing of the engine is a leading cause of losses in the war. The only way to shield the rear engine is to provide special armor. A small pursuit ship, however, can ill afford all that extra weight.
Too, the front of the cockpit of the Airacobra must be plated to protect the pilot. The nose gun arrangement is not considered particularly advantageous in any case by armament experts, who prefer to locate the guns in the wings outside the propeller disk altogether. Higher rates of fire are thus possible. The last word in this dispute will not be had until British Airacobras go into action with the RAF and it is possible to compile a won-and-lost tally. The P-39's designed top speed is about 410 mph. Its original armament included four small-bore machine guns and a 37-mm cannon firing one pound shells. This also may be undergoing change.
The P-38, in whose prototype Lieut Ben Kelsey loafed across the continent two years ago at 356 mph on 60 per cent throttle, is powered by two Allisons and should be good for 420 mph. (Talk of this plane or any other ship in production approaching 500 mph speeds is, to say the least, slightly exaggerated.) The Lockheed is, of course, larger than any of the others, grossing five as against the others' three tons. Several widely differing armaments have been tried out on the P-38, which went into production only in December. One arrangement: two machine guns, two 20-mm cannon and one 37-mm cannon.
One of the most critical problems faced by the Air Corps is the fact that the Allison company still is not able to produce nearly enough of the engines powering all pursuits but the P-47. Production passed the 200-mark in September and is currently about 300. This is enough to equip only 50 to 60 each of the three Allison-powered fighter models. The problem is considered so serious that some are exploring the possibility of substituting another in-line engine possibly the Rolls Royce Merlin, which the Packard company will have in production in about half a year. Because of the Allison's unusual length 93 as against 75 inches for the Merlin, for example, this is flatly impossible in the P-38 and P-39, and difficult in the P-46.
These planes by no means complete the roll of types which will make up the Army Air Corps as it develops during the next few years. Military aviation is not standing still, particularly in time of war. In time, for example, fighters powered by 2,000 hp in-line engines will probably make their appearance. No such plane is under construction in the United States at present because no such engine is available, as in England and Germany. Over there Napier Sabre, Rolls Royce Vulture, doubled Jumo 211, and doubled Daimler-Benz 601-A engines are already powering super-speedy fighters, like the Hawker Typhoon and Tornado and Focke-Wulf FW-156, which will soon go into service. Similar equipment will be developed in the United States.
This article was originally published in the February, 1941, issue of Flying and Popular Aviation magazine, vol 28, no 2, pp 14-16, 67, 81.
The original article includes photos of B-17, P-39, P-40, SBD, B-24, B-25, B-26, P-38, SB2C.
Photos are not credited.
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