Boeing B 29 Superfortress

Introduction

The Boeing B-29 Superfortress is now mainly remembered for the disastrous missions against Germany in 1944 and 1945 during which an efficient and effective German defensive system inflicted prohibitive losses on the bomber formations. As a result of those raids, today many see the B-29 as a failure and a very poor second-best to the B-36. This does not do the aircraft justice; the B-29 was in many ways a more advanced and technologically-developed aircraft than the B-36. The Convair Peacemaker was innovative only in terms of its sheer size; nobody had ever attempted to build an aircraft that big before. However, the Consolidated designers had been conservative and had stuck to well known techniques and practices. Not so the Boeing engineers; in designing the B-29, they adopted radical and innovative solutions to the design problems they faced and their design benefitted as a result. If such a measure as performance per pound existed, the B-29 would have been significantly better than the B-36 in that regard. It is arguable that, had history gone differently and the U.S. had forward bases to deploy from, it would have been the B-29 that would be remembered by history, not the B-36.

Early History

The origin of the B-29 can be traced back to the Boeing Model 316 project, which had been derived directly from the XB-15 of 1934. It differed from the XB-15 primarily in the relocation of the wing from a low- to a high-mounted position on the fuselage and by the installation of a nosewheel undercarriage. Since the XB-15 had been seriously underpowered, the Model 316 was to have been powered by four 2000 hp Wright R-3350 Duplex Cyclone eighteen-cylinder air-cooled radials. The next step was the Boeing Model 322 project of March 1938. The Model 322 resembled the Stratoliner in some respects, combined a new, large-diameter fuselage with a standard B-17 wing and tail. The Model 322 featured a nosewheel undercarriage and was to be powered by four Pratt & Whitney R-2180 radials. A maximum speed of 307 mph at 25,000 feet was envisaged, and the maximum bomb load was to have been 9920 pounds. Further work resulted in the Model 333A of late 1938. It was to have been powered by four 1150 hp Allison V-1710 twelve-cylinder liquid-cooled engines, installed in tandem pairs. However, full pressurization of the cabin was considered impractical because of the need to open the bomb bays during high-altitude flight, and it was decided that only the crew areas in the nose and in the mid-fuselage sections were to be pressurized. The nose and mid-fuselage pressurized cabins were to be connected by a pressurized tunnel passing over the bomb bay that allowed the crew members to change positions during pressurized flight. This feature remained on all subsequent Boeing long range bomber design proposals.

Because of the poor high-altitude performance of the Allison liquid-cooled engine, variations of the project were proposed with the new flat-mounted Wright and Pratt & Whitney radial engines. This led to the Model 333B project of February 1939. It was powered by four Wright engines buried in the thick wing. With a gross weight of 52,180 pounds, the maximum speed was to have been 364 mph at 20,000 feet. The range was to have been 2500 miles with a 2000-pound bombload. In March 1939, the Model 334 was proposed. The wingspan was extended to 120 feet in order to provide enough fuel to reach a range of 4500 miles. The Pratt & Whitney radials were still buried in the wing. A twin fin-and-rudder was to have been used to facilitate the installation of tail armament. Gross weight was up to 66,000 pounds and maximum bomb load was 7830 pounds. In July of 1939, Boeing revised the design still further to produce the Model 334A. It eliminated the buried engine installation and the twin fin-and-rudder assembly of the Model 334 and replaced them with four conventionally-mounted Wright R-3350 radials and a single vertical tail. A high aspect ratio wing of 135 feet span was to be used. The Boeing proposal had finally begun to take the recognizable shape of what was eventually to emerge as the Superfortress.

In the meantime, General Henry H. (Hap) Arnold, the acting head of the Army Air Corps, had become alarmed by the growing war clouds in Europe and by the Japanese military campaign in China. He established a special committee, chaired by Brigadier General W. G. Kilner, to make recommendations for the long term needs of the Army Air Corps. No less a personage than the famous aviator Charles Lindbergh had been a member of the committee. Lindbergh had recently toured German aircraft factories and Luftwaffe bases, and had become convinced that Germany was well ahead of its potential European adversaries. In their June 1939 report, the Kilner committee recommended that several new long-range medium and heavy bombers be developed. Hastened by a new urgency caused by the outbreak of war in Europe on September 1, on November 10, 1939, General Arnold requested authorization to contract with major aircraft companies for studies of a Very Long-Range (VLR) bomber that would be capable of carrying any future war well beyond American shores. Approval was granted on December 2, and USAAC engineering officers under Captain Donald L. Putt of the Air Material Command at Wright Field began to prepare the official specification.

In January 1940, the Army issued the formal requirements for the VLR "superbomber". The requirements called for a speed of 400 mph, a range of 5333 miles, and a bomb load of 2000 pounds delivered at the halfway-point at that range. The official specification was revised in April to incorporate the lessons learned in early European wartime experience, and now included more defensive armament, armor, and self-sealing tanks. Boeing had already started work on the Model 341 project, which featured a new high-lift aerofoil for a high aspect-ratio wing of 124 feet 7 inches in span. The Model 341 offered a maximum speed of 405 mph at 25,000 feet. It was to have been powered by four 2000 hp Pratt & Whitney R-2800 radials. Weighing 85,672 pounds, the range was to have been 7000 miles with one ton of bombs. A maximum load of 10,000 pounds could be carried over shorter distances. In order to meet the new requirements, the Boeing Model 341 design was reworked into the Model 345. The Model 345 envisaged a pressurized aircraft, four Wright R-3350 engines replacing the R-2800s of the Model 341, a twelve-man crew, a double-wheeled tricycle undercarriage which retracted into the engine nacelles instead of sideways into the wing as on previous projects, four retractable turrets each carring a pair 0.5-inch machine guns, and a tail turret with two machine guns and a 20-mm cannon. The retractable Sperry power turrets were operated under remote control by gunners sighting through periscopes. The Model 345 was to be capable of carrying a ton of bombs over the stipulated 5333 miles at a cruising speed of 290 mph. The maximum bombload was to be 16,100 pounds. The maximum speed was estimated to be 382 mph at 25,000 feet. The weight was to be 97,700 pounds.

The Boeing Model 345 design was formally submitted to the Army on May 11, 1940. The Army was sufficiently interested that it awarded Boeing an appropriation for additional studies and wind-tunnel tests on June 17, and additional funds were obtained on June 27. On August 24, 1940, the Army ordered two prototypes and a static test model from Boeing under the designation XB-29. Full-scale mockups were ready for inspection by late November and the Army was so impressed by the Boeing submission that a third prototype was added to the contract on December 14. However, by this time the B-29 program was already being left behind by the developing world situation. The Halifax-Butler Coup in the U.K. had taken Great Britain out of the war and, with it, removed the possibility of forward bases from which to attack Germany. These factors were reflected in the U.S. warplan AWDP-1 that envisoned transatlantic bombing raids on Germany from bases in the Zone of the Interior. The B-29, remarkable as its performance was, could not achieve this. Convair's B-36 could and that aircraft had absolute priority over the B-29 as a result.

The B-29 also had a problem in that its technologies were mroe radical than those of the B-36. As President LeMay remarked, "There was nothing radical or innovative about the B-36. Just a lot of it." Those advanced technologies in the B-29 had problems all of their own that delayed the Superfortress while the B-36 powered ahead. Soon, the two aircraft were proceeding almost in parallel.

Another mockup of the B-29 was started in May of 1941 with 14 service-test examples were ordered under the designation YB-29. On May 17, 1941, the Army announced that an order would be placed for 250 B-29s. This order was confirmed in September 1941, the contract being increased to 500 in February 1942. Originally it was planned that the B-29 would be built ina government-owned assembly complex at Wichita, but this was assigned to the B-36 program and the B-29 was relegated to another Boeing plant, this one located at Renton in the state of Washington. The Boeing-Renton plant had originally been built by the Navy for the manufacture of the Boeing PBB-1 Sea Ranger twin-engined patrol bomber seaplane.

The Model 345 design that eventually emerged featured a high-aspect ratio wing that was mid-mounted on a circular-section fuselage. The wing loading of the B-29 was projected to be so high that special means would have to be taken to prevent the landing speed from being prohibitively high. This was done by using Fowler-type flaps to increase the lift coefficient of the wing. These flaps added 20 percent to the overall wing area when extended. The rear portions of the inner engine nacelles were extended aft of the wing trailing edges, which were modified to improve the flap characteristics. During design, the forward fuselage was extended, increasing overall length from 93 feet to 98 feet 2 inches, and the contours of the streamlined transparent nose were rounded off. A large dorsal forward extension was added to the vertical tail surfaces to improve asymmetric handling.

A remotely-controlled armament system had been adopted for the Model 345, since manned turrets were rejected as being impractical for the altitudes at which the B-29 would be operating. Four turrets were to be fitted, two on top and two underneath the fuselage, each with a pair of 0.5-inch machine guns. A fifth turret was in the tail and was under direct control of a tail gunner. It carried two 0.50-inch machine guns and one 20-mm cannon. Bombs were to be carried in two separate bomb bays, each with its own set of doors. The release of bombs was to be controlled through an intervalometer to preserve aircraft balance by alternating release between the bays. The engine for the B-29 was the completely new 2200 hp Wright R-3350 Duplex Cyclone eighteen-cylinder twin row air-cooled radial. In order to gain the utmost power at high altitude, the engine was fitted with two turbosuperchargers instead of the usual one. The superchargers were General Electric B-11 units, automatically regulated by a Minneapolis-Honeywell electronic system. It was anticipated that the crew would normally consist of 12. The crew consisted of two pilots, a navigator, a bombardier, a flight engineer, a radio operator, a radar operator, and five gunners.

The first XB-29 (41-0002) flew on September 21, 1942 at Boeing Field, Boeing's chief test pilot Edmund T. "Eddie" Allen being at the controls. No armament was initially fitted. The engines were four R-3350-12s with 17-foot diameter three-bladed propellers. Unfortunately, the early R-3350 engines were subject to chronic overheating and were specially prone to catching fire upon the slightest provocation. On December 28, one of the R-3350 engines of the prototype caught fire during a test flight, forcing Allen to return immediately to Boeing Field. Aside from the engine problems, the performance and handling qualities of the B-29 were found to be excellent. The second XB-29 (41-0003) flew for the first time on December 30, 1942, but this flight was cut short by another engine fire, which caused a suspension of further tests until the engines could be replaced. The engines from XB-29 number 1 were removed and put in No. 2. The second XB-29 flew again on February 18, 1943, but an inextinguishable engine fire broke out just eight minutes into the flight, forcing an emergency return to the field. While attempting to land at Boeing Field, the fire burned through the main wing spars and caused the wing to buckle. The burning XB-29 plunged into the nearby Frye Meat Packing Plant factory, killing test pilot Eddie Allen and everyone else aboard, plus about 20 workers on the ground.

This crash caused ripples up the chain of command all the way to President Franklin Roosevelt, who was already unhappy about the delays in the B-29 program. By this point, the B-29 program was actually running behind the rival B-36 and there were questions as to why the Boeing bomber was being built at all. Senator Harry Truman's Special Committee to Investigate the National Defense Program, which had been established to expose fraudulent overcharging and other violations in defense acquisitions, looked into the B-29 program and concluded that the problem lay with substandard or defective engines delivered by the Wright Aeronautical Company. The USAAF also came in for a share of the blame, by having put too much pressure on the Wright company to speed up engine delivery.

Security Problems

There were also suspicions that a major security leak existed within the Boeing Corporation. Details of the B-29's performance were already leaking out and it was apparent that these were being taken into account when the Germans laid down their specifications for their new interceptor, the Ta-152H. In addition, when the first examples of the German Me-264 long-range bomber were sighted, it became apaprent that these aircraftw ere almost identical (in dimensions, to within jhalf an inch) of the Boeing 334. It has long been asserted that the Me-264 was a copy of stolen plans of the Boeing 334 athough the matter has never been proved.

Variants

Boeing YB-29 Superfortress

Fourteen service test aircraft were built at the Boeing plant at Wichita, Kansas as YB-29. The first YB-29 (41-36954) left the production line at Wichita on April 15, 1943, flying for the first time on June 26, 1943. On June 1, 1943, the first B-29 combat unit, the 58th (Very Heavy) Bombardment Wing, was activated at Marietta, Georgia in advance of delivery of the first YB-29s. By July, seven YB-29s had been delivered to the USAF and were used to equip new training squadrons. The primary feature of the YB-29 was its defensive armament of four twin 0.5 machine gun turrets plus a fifth mount in the tail. The Sperry system on the XB-29 was scrapped and the solution offered by General Electrics was offered. The General Electric system featured stationary, non-retractable turrets operated by remotely-situated gunners using computerized gunsights. There were five turret positions: upper-forward, upper-aft, lower-forward, lower-aft, and tail. Each turret contained two 0.50-inch machine guns, with the tail position containing an additional 20-mm cannon M-2 Type B cannon with 100 rounds. All guns except the tail gun were aimed and fired remotely by a set of gunners. There were four gunner sighting positions, one in the extreme nose operated by the bombardier, and three at the position in the waist where the rear pressurized compartment was located.

Boeing B-29 Superfortress

The first production B-29s began to roll off the production lines at Boeing-Renton in September 1943. In the initial B-29 models, fuel was carried in fourteen outer-wing, eight inner-wing, and four bomb bay tanks, giving a maximum capacity of 8168 US gallons. An early modification added four tanks in the wing center section, bringing total fuel capacity to 9438 US gallons. The R-3350-41 engine was introduced by Boeing on the Block 50 B-29. The armament of the aircraft continued to offer problems. It was found that the trajectory of the shells fired from the 20-mm cannon in the tail was completely different from that of the bullets from the 0.50-inch machine guns, which made aiming difficult in combat conditions. Consequently, the 20-mm cannon was deleted from the tail position. Early combat experience indicated that the B-29 needed more protection against fighter attacks coming from the front. The forward dorsal turret armament was increased to four 0.50-inch machine guns as a result. This armament proved to be pathetically inadequate.

Specification of the Boeing B-29 Superfortress:

Engines: Four Wright R-3350-23 Duplex Cyclone eighteen-cylinder air-cooled radial engines each with two General Electric turbosuperchargers, delivering 2200 hp for takeoff and having a war emergency rating of 2300 hp at 25,000 feet. Performance: Maximum speed 357 mph at 30,000 feet, 306 mph at sea level. Maximum continuous cruising speed 342 mph at 30,000 feet. Economical cruising speed 220 mph at 25,000 feet. Initial climb rate 900 feet per minute at combat weight. An altitude of 20,000 feet could be attained in 38 minutes. Service ceiling 33,600 feet. Maximum range was 3250 miles at 25,000 feet with 5000 pound bomb load. Practical operational radius was 1600-1800 miles. Maximum ferry range was 5600 miles, rising to 6000 miles with the extra fuel. Weights: 74,500 pounds empty, Normal loaded 120,000 pounds, maximum overload 135,000 pounds. Dimensions: wingspan 141 feet 3 inches, length 99 feet 0 inches, height 27 feet 9 inches, wing area 1736 square feet. Armament: Twelve 0.50-inch machine guns in four remotely-controlled turrets (two above and two below the fuselage) and in the tail, each with 1000 rounds of ammunition. In addition, early production blocks had a single rearward-firing 20-mm M2 Type B cannon with 100 rounds in the tail position. Later, two more guns were provided for the forward top turret. Maximum internal short-range, low-altitude bomb load was 20,000 pounds. A load of 5000 pounds of bombs could be carried over a 1600-mile radius at high altitude. A load of 12,000 pounds of bombs could be carried over a 1600-mile radius at medium altitude.

Boeing B-29A Superfortress

The B-29A was essentially the same as the B-29, differing from the B-29 primarily in the wing center structure. The B-29 had employed a two-piece wing center section that was bolted together at the center line and which was installed as a single unit passing entirely through the fuselage and supporting the engine nacelles. The B-29A used a very short stub center section that did not project beyond the fuselage sides, being only 47.75 inches wide on either side of the center line or almost eight feet in total. Each pair of engine nacelles was fitted to a separate short section of wing. The outer wing panels were attached at the same point on B-29s and B-29As alike. These wing changes were internal only, and there were no external differences visible in the wing root area, except for the overwing panelling on the fuselage. The B-29A was powered by four R-3350-57 engines. 1119 B-29As were built, with block numbers reaching -75. Revised engine nacelles had the oil coolers and intercoolers moved further aft, which gave them a "chinless" appearance. Because of this chinless appearance, these nacelles became known by the nickname *Andy Gump*, who was a famous cartoon character of the period. The B-29As were fitted with pneumatically-operated bomb-bay doors which could be snapped shut in less than a second. The normal hydraulic doors took seven seconds to close. Perfomance of the B-29A was identical to that of the B-29.

Boeing B-29B Superfortress

The B-29B drew on the weight reduction program and was a lightened version on the Superfortress. It had all but the tail defensive armament removed, since experience had shown that by that stage in the war the only significant enemy fighter attacks were coming from the rear. The tail gun was aimed and fired automatically by the new AN/APG-15B radar fire control system that detected the approaching enemy plane and made all the necessary calculations. The elimination of the turrets and the associated General Electric computerized gun system increased the top speed of the Superfortress to 364 mph at 25,000 feet and made the B-29B suitable for fast, unescorted hit-and-run bombing raids and photographic missions. Most of the weight saved by stripping off the defensive armament was devoted to improved speed and agility. The plane could operate with a crew of seven to eight, since fewer gunners were now required. However it often carried up to ten (commander, pilot, navigator, radar operator, bombardier, radio opperator, flight engineer, tail gunner, and two scanners). The scanners were supposed to look out for other planes, both friendly and enemy. A total of 311 B-29Bs were built between January and September of 1945. Most of the B-29Bs were issued to the 315th Bombardment Wing operating from Iceland in 1945.

Specification of Boeing B-29B Superfortress:

Engines: Four Wright R-3350-41 Duplex Cyclone eighteen-cylinder air-cooled radial engines each with two General Electric turbosuperchargers, delivering 2200 hp for takeoff with a war emergency rating of 2300 hp at 25,000 feet. Performance: Maximum speed: 364 mph at 25,000 feet Normal cruising speed: 210-225 mph Maximum range: 4200 miles at 10,000 feet with full fuel load and 18,000-pound bombload. Practical operational radius 1800 miles. An altitude of 20,000 feet could be attained in 33 minutes at 110,000 pounds gross weight. Fuel capacity: 6988 US gallons, the bomb bay tanks were not standard fit. Weights: 69,000 pounds empty, 137,000 pounds loaded with 18,000 pounds of bombs. Dimensions: wingspan 141 feet 3 inches, length 99 feet 0 inches, height 27 feet 9 inches, wing area 1736 square feet. Armament: two 0.50-inch machine guns in the tail. Bombload was typically 20,000 pounds, although with a mix of high explosive and incendiaries, this could be increased to 22,800 pounds.

Boeing RB-29C Superfortress

All surviving B-29Bs were modified with SHORAN navigation radar and additional radar equipment for electronic reconnaissance. The RB-29C entered SAC service between June and October 1945. The RB-29C featured six electronic countermeasures stations, which required a number of internal structural changes. Some external modification had to be made to accommodate the radomes and antennae of the aircraft's new radar equipment. During the reconfiguration process, the 16-crew RB-29C was fitted with an improved nose that had a large molded plastic cone and an optically-flat bomb-aiming window in the lower portion instead of the seven-piece B-29 unit used throughout the B-29B production run. Ten cameras could be carried (4 K-38s with 36-inch lens, or 2 K-38s with 24-inch lens; 1 L-22A or K-17; 1 A-6 motion picture camera; 3 K-17cs; 1 T-11 with 6-inch lens). The primary mission of the RB-29C was to take radar pictures of key targets in Germany for the B-36s. The last RB-29C Superfortresses were delivered in May 1946, this concluding the B-19 production run. The aircraft remained in service until July 1949.

Specification of Boeing RB-29C Superfortress:

Engines: Four Four Wright R-3350-41 Duplex Cyclone eighteen-cylinder air-cooled radial engines each with two General Electric CH-7-B1 turbosuperchargers. Performance: Maximum speed 397 mph at 30,000 feet, 389 mph at 25,000 feet. Cruising speed 235 mph. Stalling speed 136 mph. Service ceiling 37,150 feet. Initial climb rate 1680 feet per minute. Combat radius 2440 miles. Takeoff ground run 6150 feet at sea level. Takeoff over 50-feet obstacle 7620 feet at sea level. Dimensions: Wingspan 141 feet 3 inches, length 99 feet 0 inches, height 32 feet 8 inches, wing area 1720 square feet. Weights: 88,438 pounds empty, 107,500 pounds combat, 173,000 pounds maximum takeoff. Armament: Two 0.50-inch machine guns in tail turret. No bomb load, the bomb bay being occupied by cameras and reconnaissance equipment.

B-29 Combat Experience

The first B-29 groups, the 58th and 73rd Bomb Groups arrived in Russia in May 1944 and were initially used against targets relatively close to the German front line. In this respect, they replaced the B-17s that were on their last legs. The new bombers proved a devastating weapon, delivering three times the bombload of a B-17E while their higher speed and operationa altitude caused the defenses severe problems. At first, losses were very low and this encouraged a switch to deeper penetration raids. This threw the new bombers directly against the German NIADS air defense system. Worse, the Germans were introducing new, higher performance fighters including the jet-engined Me-262 that were more than capable of dealing with the B-29. As the B-29s attempted to penetrate deeper into German controlled airspace, their losses soared with some raids experiencing 50 percent or more casualties. This culminated in the disastrous Ploesti Air Raid in which every one of the 195 B-29s taking part was shot down. After Ploesti, the B-29s either operated at night or flew the original relatively short-range missions against near-front line targets.

Although the B-29 raids were regarded as a failure - as indeed they were and a very expensive one - they proved an important point. The B-29 had been designed to fight its way through the enemy defenses and was weighed down with armor and defensive guns. These were virtually useless, so why carry them? This revalation was driven home when a USAF Strategic Air Command Pilot, Colonel Tibbets, took up a B-29 that had been stripped of all its guns and armor. The lightened aircraft proved faster than, and could actually outmanoeuver, P-47s sent up to intercept it. This was too late to help the B-29 program but the lessons proved invaluable for the B-36s.


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