The Ultimate Superfortress: The B/RB-54A

Concept art of the B/RB-54A in flight
(Boeing Historical Archives)

During the Second World War Boeing worked extensively on further improvements to the B-29 Superfortress. The most important of these improved variants was the B-29D that involved swapping out the Wright R-3350 radial engines with the more powerful Pratt & Whitney R-4360 Wasp Major radial engine. In July 1945 the USAAF signed a contract for 200 B-29Ds, but with the end of the war and the rapid postwar demobilization, the B-29D contract was canceled. With the creation of an independent United States Air Force in 1947, there was a need for interim bombers pending the arrival of more advanced jet bombers. The USAF was already getting the Convair B-36 which took on the mantle of the heavy bomber, but the USAF also wanted the B-29D which would be redesignated as a medium bomber. The USAF had the B-29D redesignated as the B-50 to avoid the appearance of ordering a "wartime" bomber. Making its maiden flight on 25 June 1947, the B-50 Superfortress would eventually result in 320 examples of all variants produced.

Boeing, however, was working on an even more powerful and longer-ranged development of the B-50. Designated the B-50C, this evolution into the ultimate Superfortress was designed to extract as much speed and performance as was possible using a new version of the Pratt & Whitney R-4360 Wasp Major engine that added what was called a "variable discharge turbine" (VDT) to the engine. The standard Wasp Major used on the B-50 developed approximately 3,500 horsepower and a Wasp Major with a VDT could easily produce 4,000 horsepower, making it one of the most powerful production piston engines in the world.

The Wasp Major VDT
(from the Engine History website)

The VDT consisted of two General Electric CHM-2 turbosuperchargers that collected the hot exhaust gases from the 28 cylinders of the Wasp Major. A portion of the hot gases were diverted through an intercooler to provide turbosupercharging at high altitudes. The bulk of the hot gases went through the CHM-2 turbines and were exhausted out a variable area nozzle that resembled a set of eyelids. By adjusting the size of the nozzle, jet thrust could be achieved that had the potential to add as much as 15% to the speed of the B-50C over the production standard B-50. The Wasp Major VDT was already flying at this point on the Republic XF-12/XR-12 Rainbow long range reconnaissance aircraft. 

The scope of the changes needed to for the B/RB-54 resulted in a redesignation to B-54 with the planned reconnaissance variant being the RB-54. The jump in power output from the use of the Wasp Major VDT resulted in a redesign of the wings that resulted in a wingspan that was over 20 feet longer than that of the B-50 with a chord increase as well- an additional six feet of chord at the wing root and an additional four feet of chord at the wing tip. This provided additional fuel capacity along with external fuel tanks which were three times the capacity of the external tanks used on the B-50A on the outboard wings. The wingspan increase was so much that outrigger gears were needed under the outermost engine nacelles. Wind tunnel testing had shown that the new wing and powerful engine output also required a longer fuselage and the B/RB-54's fuselage was stretched 10 feet. Instead of the plexiglass domes used by the gunners on the B-29/B-50, low drag hemispheric sights were used. These used a fish eye hemispheric optical element that the gunner sighted through. Glenn's Computer Museum has some great pictures of the R/RB-54 hemispheric gunsight. The tail gunner also had a hemispheric gunsight but also had a radar to direct the four-gun turret as well which was mounted in fairing above the gun turret but below the hemispheric gunsight. Fairings were also present on the nose and under the forward fuselage for bombing and navigation radars. 

As a comparison, the B-29 weighed 120,000 lbs fully loaded and the B/RB-54 would weighed in at 207,000 lbs at takeoff. The Wright R-3350 engines of the B-29 developed 2,200 horsepower and the bomber had a range of approximately 3,250 miles. The B/RB-54 would have been able to push 8,000 miles of range. The mockups were completed in 1948 and the contract was signed for 43 bombers as an initial production lot. While the Secretary of the Air Force Stuart Symington and the USAF Chief of Staff General Hoyt Vandenberg were supportive of the B/RB-54 project, General Curtis LeMay, the head of the Strategic Air Command, felt that the B/RB-54 was inferior to the Convair B-36 Peacemaker particularly the B-36D that added four J47 jet engines under the outer wings. Pending the arrival of the B-52 Stratofortress, LeMay felt deterrence was better served by the B-36 which could fly faster, farther, higher, and carry a significantly larger bomb load. In the postwar atmosphere of austerity, more B-36s couldn't be accommodated in the Air Force budget and Secretary Symington offered LeMay more B-50s instead of increased numbers of B-36s. This was even more unsatisfactory to the outspoken SAC commander who then argued that if he couldn't get more B-36s, then the funding set aside for the B/RB-54 should be shifted over to get more of the Boeing B-47 Stratojet which made its first flight in December 1947. This was agreeable to all involved, even for Boeing as it meant more funding for the Stratojet program. The B/RB-54 project was cancelled with the prototype approximately 75% complete (it was converted from a B-50A) at Boeing's Seattle facilities. In addition, the addition of the outrigger gears wasn't popular with SAC as many of its bases would need widened taxiways and runways to accommodate the B/RB-54. 

The B-29 lineage would live on, though, in the C/KC-97 Stratofreighter (the last examples being retired in 1978) and in the commercial Boeing 377 Stratocruiser. But neither would have matched the leap in performance of the B/RB-54, the "ultimate" Superfortress.

The Retromechanix page has a series of superb photos via the National Archives that show the B/RB-54A mockup in detail as well as some schematic drawings. It's well worth the time to browse them!

Source: Boeing B-29 Superfortress (Crowood Aviation Series) by Steve Pace. The Crowood Press Ltd, 2003, p166-168. Boeing B-50 (Air Force Legends Number 215 by Geoffrey Hays. Ginter Books, 2012, pp 118-121.

The Unconventional Genius of Carl Norden

Carl L. Norden

After the Manhattan Project to develop the atomic bomb, the next biggest top secret defense program in the United States at the time was the development and production of the Norden bombsight. The Norden sights were used in all of the United States Army Air Forces heavy bombers (the Boeing B-17 Flying Fortress, the Consolidated B-24 Liberator, and the Boeing B-29 Superfortress) primarily and it was a Norden sight that bombardiers used to drop the atomic bombs on Hiroshima and Nagasaki that brought the Second World War to a close. Despite its crucial role in strategic bombing campaigns in both the European and Pacific Theatres, the Norden bombsight was a Navy program and every Norden sight used by the US Army Air Force had passed through the hands of Navy inspectors. How this state of affairs came to be is the story of how an unconventional but brilliant Dutchman, Carl Norden, came to be employed by the Navy prior to the start of the Second World War. 

Carl Norden was born on 23 April 1880 in Semarang, Java, in what was the Dutch East Indies (modern day Indonesia), the middle child of five siblings in a household with absent father. From a young age, his mother considered him the most reliable and responsible of his siblings- in a sense, he became the "man of the family". He had wanted to become an artist, but when his older brother decided to pursue an artistic career, Carl decided to pursue a lucrative career in order provide for his mother and his siblings, enrolling in the Federal Polytechnic Institute in Zurich, Switzerland and graduating in 1904 as a mechanical engineer. Although Dutch by birth, Norden's father was a naturalized Dutch citizen from German and Norden's own wife was from Austria. Norden's German ties dovetailed into his natural engineering and mathematical prowess- it was said that Carl Norden viewed everything in life in mechanical terms governed by mathematical formulas, the universe being nothing more than a great mechanical timepiece. After his graduation in 1904, he emigrated to the United States where he had a wealthy uncle who had made his fortune in the cotton business. Norden worked for a series of companies as a mechanical design engineer, but it was painfully obvious that he was difficult to employ as he was very much a prima donna. But there was no question of Norden's brilliant mind and after a series of employers over six years, he finally came to work for Elmer Sperry Sr. and his sons, Elmer and Lawrence at the Sperry Gyroscope Company. Norden's mechanical aptitude fit well into the work the Sperrys were doing for the Navy in developing gyroscopes to improve the accuracy of naval gunnery from moving ships. Norden's work with Sperry was invaluable for the company and Norden made many contacts within the Navy as a result. Norden tolerated Sperry as the work was interesting, but the relationship soured when, after solving the problem of gyroscopic oscillation, Norden got what he thought was an insulting $25/week raise as a reward. Norden quit and became a consulting engineer to the Navy, but it was the start of a feud between Norden and Sperry for years. Norden often dismissively told people Sperry "would patent gravity if he could" and Sperry for years tried to legally dispute many of Norden's later patents. 

In 1913, Norden set up shop near the Brooklyn Navy Yard and continued to work on the ship stabilization project for the Navy much to Sperry's chagrin. The Navy was enamored with Norden's genius and that relationship in large part protected Norden from Sperry's multiple legal challenges. With the progress on the ship stabilization project slow in coming, the Navy astutely put Norden's mind to work on other projects, starting the aerial gyroscopes for the aerial torpedo project as well as designing catapults and arresting gear for aircraft carriers. The arresting gear of the USS Lexington and USS Saratoga were designed by Norden himself on his dining room table!

At the time, the Navy was pursing a bombsight program as it felt that the best way to sink ships from the air was via high altitude level bombing. General Billy Mitchell's ship-bombing tests in the summer of 1921 against captured German warships convinced the Navy that it had to find a way to sink ships at sea. The Navy's Bureau of Ordinance (BuOrd) was responsible for the bombsight program and many different types, including some from Sperry, were tested. Officers with the Aviation Section of BuOrd came to know Carl Norden from his work on the aerial torpedo project as he had been consulted as an outside expert to evaluate Sperry's work (something which truly irritated Sperry to no end). They were impressed with the comments made in the reports and not knowing who Carl Norden was, found a report signed "Norden". A quick check of the Brooklyn telephone book and a few calls got the officers from BuOrd in touch with Norden who agreed to review the Navy's bombsight program. The gyroscopic stabilization work he had done for the ship and aerial torpedo project dovetailed neatly into the bombsight problem as Norden recommended that the bombsights be not only gyroscopically stabilized, but also connected to either an autopilot or pilot director so that during the bomb run, the bombardier was the one "flying" the aircraft. Eventually modifying existing bombsights turned out to be a failure and the BuOrd and Norden decided to start from scratch and create a whole new bombsight that would launch the Norden bombsight into aviation history. 

That's not to say that Norden's genius resulted in success. For most of the 1920s, many of the literally handcrafted Norden sights had dismal performance. But Norden wasn't one to give up and the Navy was an incredibly accommodating employer. Well aware of Norden's personality- they nicknamed him "Old Man Dynamite", they gave him tremendous latitude as long as he kept delivering results in the form of progressive improvements to his bombsight designs. Unlike most engineers, Norden did his own drafting. He didn't have an extensive engineering library, he preferred to work with his slide rule, a set of engineering tables and a few select references. He often stayed at his mother's home in Zurich, Switzerland, to ponder mechanical problems and develop solutions. His drawings and correspondence were then delivered to the US Navy by diplomatic pouch from US embassy in Switzerland. The State Department wasn't keen on this but high level pressure from the US Navy encouraged diplomatic officials to be as accommodating to "Old Man Dynamite" as possible. Sometimes it was his family he sent to Switzerland so he could be alone to solve some problems back in New York. Also unique to the Navy's relationship with Norden was that any patents were held by the Navy and classified as top secret. In this way, not only was Norden shielded from Sperry's legal challenges, but it also meant that the Navy didn't have to follow the prescribed competitive bidding rules to pay Norden for his work. Many of Norden's patents sponsored by the Navy from the 1920s and 1930s weren't even declassified until 1947! In contrast to the US Army Air Corps (forerunner of the US Army Air Forces) who held open competitive bidding in its own bombsight program and trialled bombsights from several different manufacturers, the Navy only did business with Norden and Norden alone. In fact, the Navy was Norden's only client! 

Theodore Barth at a circus held for Norden employees

As work on the Norden sights continued in the 1920s, BuOrd recommended that Norden partner up with an engineer to start moving the bombsight project towards mass production. Knowing Norden well, the Navy partnered him up with a former Army colonel and engineer by the name of Theodore Barth and it was the start of a very close relationship between the two men for many years. Norden's own children regarded Barth as a secondary father figure in their lives, so close was Barth to Norden. It was Barth who was tasked by the Navy to take Norden's designs and put them into production. Compared to Norden, Barth was very personable and possessed quite a bit of business acumen as well- Norden may have been the brains of the operation but it was Barth who made everything work and kept everyone happy. During the Second World War, Barth took it as his job to take care of all of the employees that were building bombsights. He often gave away baseball tickets and even rented out Madison Square Garden for a circus just for Norden's employees. 

From the time Norden was contacted by the Aviation Section of the Bureau of Ordinance to the delivery of the first production bombsight to the fleet, the Norden Mark XI, nine years had elapsed. During those nine years Norden progressively refined the design of what was essentially a clocklike analog computer that was gyroscopically stabilized and linked to the autopilot. The Navy, though, did hedge its bets just a bit- during that time it had contracted with General Electric for a back up bombsight design called "Scheme B" or the Mark XIII. After three years, the Navy found the GE bombsight was woefully inferior to Norden's designs and canceled "Scheme B". 

Norden M-1 bombsight

By the early 1930s, the US Army Air Corps became aware of the Norden program and was keen to get its hands on the bombsights for its own testing. The head of the Army Air Corps, General Henry "Hap" Arnold (who would head the USAAF during the Second World War), was shocked to hear of the working arrangement between the Navy's BuOrd and Carl Norden, from Norden not even being a US citizen to the fact that Norden did a lot of his work abroad in Switzerland and then sent drawings back via diplomatic couriers to New York City for Theodore Barth and Navy officials to review. The Navy wasn't about to change the way it did business with Carl Norden to assuage General Arnold's concerns, though. It basically came down to something along the lines "If you want Norden bombsights for Army bombers, this is the arrangement you have to live with!". As a modest concession, though, the Navy had the FBI provide a security detail for Norden and agents were planted in Norden's production facilities in New York City to root out any foreign spies. At all times, at least two armed agents were with Norden at all times. There is an apocryphal story that when Norden wasn't getting his way with the Navy, he'd insinuate he'd leave the United States and go to work for the British. He would later remark it was empty threat "As no self-respecting Dutchman would ever work for the British!"

By 1928, Norden was at work at a massive improvement to the Mark XI sight called the Mark XV. He delivered the Mark XV prototype to BuOrd in 1930 and it was this sight that pretty much ended the GE alternate bombsight program. The bombsights that came from the Mark XV design were known as the Norden M-series sights and those would become standard on American heavy bombers.  By this point, however, the Navy was drifting away from relying on high altitude level bombing at sea as dive bombing was explored by units in the fleet. But the arrangements between the Navy and Carl Norden remained with his New York City factory essentially being a Navy factory! By 1934, Norden's bombsights became the standard for the Army Air Corps, first being installed on Martin B-10s. It's estimated that approximately $1.5 billion was spent on the development and production of Norden bombsights. 

Carl Norden was passed away in 1965 in his beloved Switzerland. His company lived on as Norden Systems to be acquired by Westinghouse which was in turn acquired by Northrop Grumman. Norden and Barth also set up a second company called Barden to manufacture bombsight components- Barden is still  around today, fabricating ball bearings for a variety of industries including aerospace. Carl Norden was inducted into the National Aviation Hall of Fame in 1994. 

Source: America's Pursuit of Precision Bombing, 1910-1945 by Stephen L. McFarland. Smithsonian Institution Press, 1995, pp 45-76. Photos: Norden Systems Division via Stephen L. McFarland's book, Wikipedia

The Development of the Boeing Flying Boom

World War II USAAF tests with B-24 tankers and B-17 receivers

Though the United States had explored using air refueling to extend the reach of strategic bombing missions during the Second World War, nothing operational had come of the work by the time the war ended in 1945. In the immediate post war years, the newly independent United States Air Force and its nuclear deterrent arm, the Strategic Air Command, had both the weapons and the aircraft to carry out nuclear strikes, but what was lacking given the technology and geopolitical climate of the day was overseas bases that would allow SAC's bombers to reach the Soviet Union. As it was, the Boeing B-29 Superfortresses that were the main strike force of SAC lacked the range to hit Soviet targets nonstop from bases in the United States. While the US government placed priority on securing overseas bases for SAC, the USAF made inquiries to the leading experts of air refueling of the day, Flight Refueling Limited in Great Britain. It was Flight Refueling that consulted with the US Army Air Forces during the Second World War and assisted with several trials using B-24 Liberators as tankers and B-17 Flying Fortresses as receivers. Several sets of air refueling equipment were procured from Flight Limited and installed on a very limited basis on several B-29 Superfortresses to get crews trained on the procedure. However, the USAF was dissatisfied with the system as it took time to rendezvous and get into the proper position, change positions, and then transfer fuel. Using Flight Refueling's method, the receiver trailed a hauling line with a weight and hook at the end. The tanker approached from the side and below and deployed a contact line that crossed over the hauling line of the receiver and engaged the hook. The tanker then moved above the receiver, pulling in the hauling line with the contact line. The refueling hose was then attached to the hauling line and it was then pulled down to the receiver which had a refueling receptacle in the tail gunner's position and refueling commenced. The lines and refueling hoses used created tremendous drag that imposed air speed restrictions that may have been acceptable for a piston-engined bomber but wholly impractical for a future jet-powered bomber. 

The USAF contacted Boeing in November 1947 if they would be willing to look at the air-refueling problem within the purview of the company's ongoing research programs. In the following month, the Preliminary Design Group and the Experimental Manufacturing Division at Boeing formally signed a contract with the Air Force to work on improving air refueling. Boeing's first step was to determine what formation can two Superfortresses operate most closely for an extended period of time safely to conduct air refueling. Boeing's engineers figured the refueling solution would be easier the closer the aircraft could fly to each other and not have to do the position changes that the Flight Refueling method entailed. To this end, in May 1948, the USAF ran a series of tests out of Wright-Patterson AFB in Dayton, Ohio, using B-29s flown in every possible formation and relationship to each other. Escorting aircraft photographed the formations from every angle and Boeing's team would then analyze the photographs to determine their three-dimensional relationship to each other. For every possible formation, the flight crews involved were also queried on things like workload and visibility in maintaining the formation. As a result of these test flights, it was determined the optimum position that provided a relatively low workload with good visibility was to put the aircraft in trail formation with the trailing aircraft vertically displaced 25 feet and longitudinally displaced 10 feet. This gave the flight crew in the trailing aircraft the best view of the lead aircraft with the closest possible distance. Pilots in the trailing aircraft found that if they flew less than 25 feet vertically displaced below the lead aircraft, they got buffeting from the wake of the lead aircraft which gave the formation an inherent safety feature. 

After determining the most optimal close formation, the next step for the Boeing team was to figure out the best fuel transfer method. Five different refueling systems were explored. The first three systems were probe-and-drogue applications with the tanker trailing a hose with a drogue at the end with the receiver flying a probe into the drogue to make the connection. Though this method is used today by the US Navy and US Marine Corps as well as a large number of air arms like the RAF, the Boeing team felt that the hose movement could be unpredictable in rough air and required too much maneuvering by the trailing aircraft to make hose contact. Such maneuvering might be fine for a smaller tactical aircraft, but Boeing was less than thrilled about the prospect of a large receiver aircraft having to maneuver frequently before contact so close to the tanker. 

The imaginative fourth proposed system involved a gun-turret like assembly on the tanker's forward dorsal fuselage. The tanker would take the trailing position and the turret would deploy a rigid boom up and forward to engage a receptacle on the underside of the tail of the receiver. The boom would be maneuvered like a gun turret by an operator aboard the tanker and when not in use, the boom would slew 180 degrees and stow atop the dorsal fuselage of the tanker. While imaginative, it was soon realized the aerodynamic loads on the boom would be significant. But what if their positions were reversed? What if the tanker lowered the boom aft and down to the receiver who had a receptacle on the top of the fuselage? This way the operator did all the work from the tanker and the receiver flight crew could focus on holding the prescribed position in trail behind the tanker. Flight test personnel with experience with the flight refueling systems of the day were consulted and all agreed that a boom lowered from the lower aft fuselage of the tanker to the top of the fuselage of the receiver would be the most ideal. A rigid boom would allow fuel transfer rates much higher than a hose system and small aerodynamic surfaces would be used on the end of the boom to maneuver it to the receptacle of the receiver- which is how Boeing came to call it the "flying boom". 

B-50 "Lucky Lady II" taking on fuel from a KB-29 hose tanker

While Boeing's engineers in Seattle worked on the flying boom concept, the Air Force's first secretary after its creation, Stuart Symington, had testified before the Senate Armed Services Committee in March 1948 that the latest air refueling systems would allow the new Boeing B-50 Superfortress to reach any part of the Soviet Union, but the reality of it was that all the USAF had were the first Flight Refueling hose units on a handful of B-29s and that the flying boom was still a paper project. Quite literally on the following day, the USAF instructed Boeing's Wichita division to get as many hose units onto KB-29 tankers as possible and get the new B-50s up to speed as receivers with an interim system until the flying boom was operational. The first operational installation was ready in less than 30 days and by the end of 1948. On 26 February 1949, the B-50 Superfortress "Lucky Lady II" took off from Carswell AFB in Fort Worth, Texas, and flew around the world nonstop in 94 hours, taking fuel from hose-equipped KB-29s four times during the record-breaking flight. 

The flying boom equipped KB-29P Superfortress tanker

Despite this very public success, Boeing continued to develop the flying boom and interestingly, had funded the development internally without outside USAF funds. Two dry booms were built for KB-29s as proof of concept. Though not able to transfer fuel (hence the term "dry booms"), the dry booms were actually installed on KB-29s in June 1948, a full seven months before the circumnavigation flight of "Lucky Lady II". Dry receptacles for the purposes of flight test were installed on a B-47 Stratojet and an F-86 Sabre. Flight tests using the dry boom were conducted through the summer of 1948 out of Seattle, Wichita, and Wright-Patterson AFB in Ohio. The tests were successful and the USAF requested Boeing transfer the flying boom work to Curtiss Aircraft. As the company had an absence of work postwar, the USAF wanted to keep Curtiss in business, but quite obviously, Boeing wasn't happy with that request, particularly since development had so far involved company funds without any USAF funding. By April 1949, Boeing was already constructing wet booms (flying booms able to transfer fuel) and was resisting USAF pressure to transfer the program to Curtiss Aircraft. Boeing won the dispute with the USAF by insisting its flying boom work was proprietary and would have commercial applications in refueling jet airliners. Since no USAF funds had been used in development so far, the USAF found it didn't exactly have financial clout to compel Boeing to transfer the program to Curtiss. Up to this point, the flying boom program was classified and the USAF had insinuated that the program's classified status meant that it couldn't be used for commercial applications. But the flight test program had already been publicly revealed by the USAF itself in an October 1949 press release! Boeing did finally get its contract for the flying boom. From 1950 to 1951, the Boeing Renton plant converted over 100 B-29 Superfortresses into KB-29P flying boom tankers with the first tanker delivered to SAC in March 1950. A fixed cradle structure supported the flying boom when it was raised. A hemispheric plexiglass dome replaced the tail turret and laying in a prone position, the boom operated "flew" the boom to the receiver. Boeing had always considered the KB-29P an interim tanker and soon enough was working on a tanker version of the C-97 Stratofreighter- not only did a tanker version of the C-97 offer more fuel carrying capability, it could also carry cargo when not being used for air refueling, offering mission flexibility for the USAF. The first flying boom-equipped C-97 was flight tested by Boeing in September 1950 and so impressed the USAF that all remaining orders for the C-97 were to be completed as KC-97s. In fact, the first KC-97 was delivered to the USAF only eight months after the KC-97 contract was signed with the first units operational in July 1951. Boeing then suggested a turboprop-powered KC-97 to the USAF, but the military was ambivalent to the idea, but by that point, Boeing was already working on a new breed of transport that would eclipse even the turboprop powered KC-97. But I'm pretty sure you know how that story ends! 

Source: Passing Gas: The History of Inflight Refueling by Vernon B. Byrd. Byrd Publishing, 1994, pp 123-136. Photos: National Museum of the United States Air Force.

The Boeing PBB Sea Ranger: The Best Flying Boat at the Worst Possible Time

The Boeing XPBB-1 Sea Ranger prototype

Despite being a dated pre-war design, the Consolidated PBY Catalina was already successful before America's entry into the Second World War. Martin Aircraft decided to go one step further than the Catalina realizing the potential of newer, more powerful engines with its 1937 offer to the US Navy for what became the PBM Mariner. With a bigger hull but the same speed and payload of the PBY Catalina, Martin's proposal was eagerly received by the US Navy and the Martin XPBM-1 prototype made its first flight in February 1939. Seeing what Martin had accomplished with the design, in the following month the Navy issued a new specification for an even more powerful twin engine flying boat using the new powerful Wright R-3350 Duplex Cyclone radial which had made its first bench run in May 1937. The Consolidated PBY Catalina used the Pratt and Whitney R-1830 Twin Wasp radials developing 900 hp each. The Martin PBM Mariner used Wright R-2600 engines developing 1600 hp each. The Wright R-3350 in development developed 2200 hp, so the potential for an even better twin engine flying boat was obvious to the Navy. With Martin and Consolidated busy with their respective flying boat designs, the Navy invited Boeing and Vought-Sikorsky to submit designs that used two R-3350 engines. Vought-Sikorsky had extensive flying boat expertise with pre-war designs used by both the Navy and civilian airlines. Boeing had just flown what many considered the pinnacle of commercial flying boats, the Boeing 314. 

Note the long tapered wings that were based on the B-29's 

Boeing's initial submission featured a tapered straight wing using the Davis airfoil with retractable outboard floats and a bomb bay within the hull. The flying boat was also pressurized to allow high altitude transit to patrol areas. The Navy preferred the Vought-Sikorsky design but the company had little resources to spare was it was busy with other priority projects. The Navy then asked Boeing if they would be willing to build the Vought design on 24 February 1940, but Boeing expeditiously redesigned their submission and the following month responded the US Navy's request with a presentation of an improved design that had a narrow, low drag hull, fixed outboard floats, bomb bays moved into the inner wings and deletion of the cabin pressurization. The new design was larger and more capable and dispensed with the Davis airfoil with a new Boeing in-house design that was also used on the B-29 Superfortress project. The Navy was suitably impressed and ordered one prototype for evaluation as the XPBB-1 on 29 June 1940. The mockup review went quickly in January 1941 with the XPBB prototype starting construction in June 1941. With the potential of the new design to be superior to both the PBY and PBM, the Navy went ahead and ordered 57 PBB-1s on 8 October 1941 despite the XPBB prototype not having made its first flight yet. To accommodate production for the PBB Sea Ranger as it was called, a new Boeing plant was built on the southern shores of Lake Washington at Renton. With the clouds of war on the horizon that fall, the Navy indicated to Boeing that as many as 500 Sea Rangers would be needed before 1943. 

Note the bomb bay doors on the underside of the inner wings

The PBB Sea Ranger was a remarkable clean aerodynamic design for a flying boat. The outer wing and horizontal stabilizers were near-identical to that used on the B-29 Superfortress (which would make its first flight in September 1942). The Wright R-3350 engines developed 2300 hp and drove a 16.5-foot diameter three bladed prop. The original proposal was for counter rotating props, but designing the gearing for a contraprop proved to difficult at the time. Instead of fuel bladders, the wing was wet with integral tankage which not only saved weight, but gave the Sea Ranger an enormous fuel capacity that would make 72-hour patrols possible. As the tanks were emptied, carbon dioxide gas under pressurization would purge and inert each tank. Each wing had five bomb bays that were between the wing ribs with a roller door covering each bay. The payload of the ten bays would have been 20,000 lbs of bombs (identical to the B-29 bomb load). Pylons could be fitted between the bays to carry torpedoes or other weapons too larger for the wing bomb bays. The defensive guns were eight 50-caliber guns with a twin dorsal turret and twin tail and nose ERCO turrets that were similar to the nose turret of the Consolidated PB4Y Privateer. A single 50-caliber gun was used on two waist mounts which were teardrop shaped also like the waist mounts on the Privateer. Below the nose turret sat the bombardier whose front window could be protected by doors when the Sea Ranger was landing or taking off. In addition to the bombardier, two pilots, the flight engineer, navigator and radio operator sat in the flight deck with the remainder of the crew rounded out by five gunners. 

The Sea Ranger's wings were its key to long endurance patrols

On 9 July 1942 the XPBB-1 Sea Ranger prototype made its first flight from Lake Washington. There were remarkably few issues that arose during the flight test program. The aircraft was formally delivered to the Navy on 12 January 1943 but the prototype remained in the Puget Sound area for the Navy's trials. The production Sea Ranger would have differed only in details from the XPBB-1 prototype. It was during the flight test program that the fortunes of the Sea Ranger began to wane. It was clear by that point that the B-29 Superfortress program was a national priority for the war effort. This was taking on more and more of Boeing's resources and worse yet for the Sea Ranger, it used the same engines as the Superfortress and production priority for the R-3350 was earmarked for the B-29. This was also the same time that the Navy began shifting patrol missions to land-based aircraft like the PB4Y-2 Privateer. The same year that the Sea Ranger made its first flight, the Navy had also asked Consolidated about a variant of the B-24 Liberator that was more dedicated to the patrol bomber mission than the first PB4Y-1s which were Liberators with modest changes for the naval mission. The PB4Y-2 was the definitive patrol bomber version and it made its first flight in the same year as the Sea Ranger. As the Privateer didn't use the same engines as the B-29, it didn't have to compete for R-3350 production like the Sea Ranger. As a result, the Sea Ranger was canceled with only a single aircraft built. 

The Sea Ranger prototype was flown anyway further by the Navy to its flight test center at Patuxent River, Maryland, on 5 October 1943 and given a formal evaluation despite the cancellation. The Navy was immensely impressed with the Sea Ranger, believing it to be the best flying boat ever developed. Even though the Renton plant where the Sea Ranger was to be built was turned over to B-29 production, the Navy reconsidered its cancellation and approached Martin Aircraft about producing the Sea Ranger for Boeing. The R-3350 engines would have been swapped out with Pratt & Whitney R-4360 Wasp Major engines for a power boost along with two booster jet engines for added performance. The Wasp Major was even more powerful than the R-3350 and production was to begin on that engine in 1944. The Sea Ranger, even though a Boeing design, would have had the Navy designation P4M in recognition of Martin's production of the type. For obvious reasons, Martin wasn't enthused about building someone else's design and at the time of the Navy's proposal, work had already started at Martin on a land-based patrol bomber with two R-4360 Wasp Major engines and two Allison J33 booster jet engines. That design was what became the P4M Mercator which made its first flight in October 1946. 

News reel footage of the Sea Ranger's maiden flight

While the Sea Ranger presented a promising opportunity for Boeing, it ended up being a dead end that arrived at the twilight of the flying boat as a maritime patrol aircraft. Stuck competing with resources with the much more important B-29 Superfortress, the Sea Ranger's historical legacy is not so much its design but rather the Renton facility that was built in anticipation of production. The Renton facility became home to the B-29 program but in the post-war era was where Boeing was launched into the jet age with production of the KC-135, 707, 727 and 737 taking place at Renton. In fact, the Navy's newest maritime patrol aircraft, the Boeing P-8A Poseidon, is built at the Renton alongside commercial 737s.

Source: American Bomber Aircraft Development in World War 2 by Bill Norton. Midland Publishing, 2012, pp 117-120. Photos: Boeing, San Diego Aerospace Museum.

Master Sgt Red Erwin, One of Many Heroes

In coming up with a suitable blog post for Memorial Day, I had scoured my aviation library for a historical event- given that I've long been interested in military aviation history, there's no shortage of material in that department, believe me. However, I'm currently reading Barrett Tillman's outstanding book Whirlwind: The Air War Against Japan 1942-1945 and came across the story of a red-headed Alabaman, Master Sgt. Henry "Red" Erwin. In April 1945, the massive arsenal of democracy that was American industry had already started the systematic destruction of the Japanese war machine the previous month as Boeing B-29 Superfortresses of the XXI Bomber Command based in the Marianas Islands under the command of General Curtis LeMay began to deliver destruction to the cities of Japan. The first fire-bombing raids had already visited untold disaster on Tokyo and other urban areas of the Home Islands. Superfortress attacks on the kamikaze bases on Kyushu had helped ensure victory on Okinawa. And by this month, the XXI Bomber Command finally had enough Superfortresses to wage a round-the-clock strategic bombing campaign on the Japanese homeland. On 12 April 1945 news reached the bases in the Marianas about the death of President Franklin D. Roosevelt- for many of the fighting men in the Pacific, Roosevelt was the only leader they had known. But there was war to fight, and every bomb dropped meant getting home sooner. 

Erwin is 2nd from the right, front row, with his B-29 crewmates

On that day, 250 Superfortresses set out in three airborne task forces to attack industrial centers near Tokyo. Half of the force belonged to the 29th Bomb Group and were tasked to hit the Koriyama chemical complex north of Tokyo. Off the coast of Japan, the lead pilot of the Koriyama-bound force was Captain George Simeral flying The City of Los Angeles. His crew excelled at their jobs and earned The City of Los Angeles the lead position of the task force. His crew had been together since June 1944 and had already flown ten missions over Japan. As Simeral neared the coast. he ordered his radioman, Master Sgt. Red Erwin, to drop a phosphorous flare to mark the assembly point for his own squadron. Erwin left his station in the forward compartment, picked up the large flare canister and pulled the arming pin before dropping it as was the standard procedure- only this time the flare prematurely fired and a 1,300-degree Fahrenheit blast hit him in the face, blinding him and instantly burning off his nose and one ear. The forward compartment of the B-29 filled with white smoke and Simeral and his co-pilot quickly lost view of their instruments and the outside world. 

Erwin realized that the hot burning flare could burn through the compartment like a big blowtorch into the bomb bay and set off the bomb load. Griping around the compartment, he somehow managed to find the flare and pick it up. He stumbled his way forward, planning to throw it out the co-pilot's window but found his way obstructed by the navigator's table- the navigator at the time was in the astrodome taking a sighting when the flare fired. As the table could be unlocked and hinged downward, Erwin tucked the hot flare between one arm and his side and managed to fold the table so he could continue his way forward through the compartment. Though blinded, he somehow managed to get to the co-pilot's window, open it, and throw the burning flare overboard. He immediately collapsed on the bomber's throttle console. 

In the short time it took for Red Erwin to throw the flare overboard, the crew had lost control of the B-29 and Simeral managed to regain control with the bomber only 300 feet above the sea as the crew opened every hatch and window possible to vent the forward compartment. Everyone else did what they could to easy Erwin's suffering and Captain Simeral set course for Iwo Jima. The doctors there could do little for him and he was flown to Guam where a fleet hospital was located. General LeMay had been informed of the situation and when doctors advised him that Erwin would likely die from his burns, LeMay was determined to get him the Medal of Honor irrespective of the regulations. 

To understand what happened next, you have to realize that LeMay was already well-known in the USAAF as being very results-oriented. When he was tapped by the head of the USAAF, General Henry "Hap" Arnold, to head the XXI Bomber Command, the B-29 was not performing well as a combat machine, being constantly plagued by rushed training and poor maintenance practices. Arnold wanted results as he was one of the most staunch defenders of the B-29 program and the massive funding it required- not to mention a successful air campaign over Japan strengthened his case for an independent United States Air Force. LeMay was given his orders- and unusually for a combat command, the XXI Bomber Command was run right out of Arnold's office at the Pentagon so theater commanders couldn't appropriate the prized Superfortress for tactical missions. It was LeMay who had to deliver and the way Arnold entrusted LeMay, so did LeMay entrust his subordinates- "Get me the results I want and I won't ask questions." As a result, his subordinates became well-known in the Pacific Theater for circumventing rules and red tape to get their boss results. 

It usually took several months to get a Medal of Honor awarded as it passed via several levels of review. That didn't suit LeMay. His first act was to order an aircraft and its crew to Hawaii to get a Medal of Honor that could be presented to Erwin before he died. The crew took this task to heart and having found one in a display case, were unable to locate who had the keys to open the case. So they broke into the case and returned to Guam with the medal in hand. With the medal secured, LeMay then cabled General Arnold at the Pentagon and insisted that Erwin's award be approved immediately as he was on his deathbed. Luckily for LeMay, Arnold agreed with him and quickly got the orders and citation approved and the papers were on President Harry S Truman's desk in just days. In fact, one of Truman's first acts as President after FDR died was to sign the papers for the awarding of the Medal of Honor to Red Erwin!

Red Erwin's widow with the painting of him at Maxwell AFB

At a hastily arranged ceremony at Erwin's bedside at the fleet hospital in Guam, LeMay presented him with the Medal of Honor six days after the mission took place. The general order that announced the award took three months to be processed and formally announced! But the tough Alabaman surprised everyone by surviving his wounds. Over the next two and a half years he underwent over 40 reconstructive surgeries and managed to regain his vision. Discharged from the now-independent United States Air Force in 1947, he went to work for the Veterans' Administration hospital in Birmingham, Alabama, working closely with burn patients for the next forty years. Master Sgt. Henry "Red" Erwin passed away in 2002 at the age of eighty. 

After his death, the U.S. Air Force established the Red Erwin award for the outstanding enlisted airman of the year in the Air National Guard and Reserves. More recently, the library at the Air University at Maxwell AFB in Alabama was named the Red Erwin Library in his honor with a specially-commissioned painting of him and the B-29 Superfortress. Always the modest man, Erwin told everyone that he didn't wear the Medal of Honor for what he did on that fateful mission in 1945- he wore the medal for everyone who served.

Source: Whirlwind: The Air War Against Japan, 1942-1945 by Barrett Tillman. Simon and Schuster, 2010, p164-167. Photos: United States Air Force.

The Bell RP-63 Pinball

As the strategic bombing campaign over Germany built up in the spring of 1943, losses over the skies of the Reich began to mount as mission momentum increased over the course of that summer. While the ever-present flak was a significant threat to the B-17 Flying Fortresses and B-24 Liberators of the US Eighth Air Force based in the UK, it was the fighters of the Luftwaffe that were mauling the formations. From June into the autumn, losses were mounting and doubts were starting to be raised on the operational wisdom of daylight strategic bombing. The breaking point came on 14 October 1943 with the second attack on the ball-bearing plants at Schweinfurt, Germany. Already bruised from a vicious mauling at the hands of the Luftwaffe on the first raid on the Scweinfurt (which was attacked along with Regensburg on 17 August 1943 with the loss of 60 bombers), of the 291 B-17s sent on the mission, 77 bombers were lost and 122 were damaged. The day was named "Black Thursday" for having the highest number of crewmen lost on a single USAAF mission- 590 killed, 65 taken prisoner. Deep penetration missions of Germany were suspended until February 1944 when the long-range P-51 Mustangs arrived. 

But warnings were raised as early as 1942 stateside when Major Cameron Fairchild of the USAAF sought ways to improve the aerial gunnery skills of the men who manned the defensive positions on the heavy bombers. The techniques of training at the time were fairly basic, ranging from skeet shooting to firing at towed targets. Fairchild surmised the best aerial gunnery training would consist of being able to fire live ammunition at an actual fighter aircraft. His first task was to develop a bullet that had the same characteristics as a 30- or 50-caliber round but would splinter harmlessly on impact. Working with researchers at Duke University, the University of Michigan, and the Bakelite Corporation (one of the pioneering manufacturers of plastics), Fairchild and his team came up with a frangible bullet that was weighted with powdered lead to give it the proper weight and density. 

Fairchild proved to be willing to circumvent the usual Army bureaucracy to promote his ideas. Instead of working through the usual Army weapons development channels, he teamed up with academics to validate his ideas. Fortunately, the heavy losses of 1943 showed that aerial gunnery skills were lacking and Fairchild's frangible training bullets gained traction with the USAAF. He then selected the Bell P-63 Kingcobra as the target aircraft. As it was a type not used by front-line USAAF units, it was easily available. The P-63, designated RP-63, was given 1-inch thick armored glass with special armor in vulnerable areas. Sensors underneath the RP-63 registered hits and lights on the spinner and on the fuselage would light up, giving rise to the name "Pinball". 

Beginning in early 1945 RP-63 Pinballs would fly attack profiles against bombers with student gunners before they were assigned to a combat unit. A training B-17 might have 12 student gunners each having 2,000 rounds of Fairchild's special frangible ammunition to fire at the Pinballs. The Pinball pilots, flying RP-63s that were painted either dayglo orange or yellow, flew 2-3 missions a day from bases throughout the United States. Minor damage was easily repaired on the flightline but the Achilles heel of the Pinball was the wingroot air ducts that provided cooling air to the mid-fuselage mounted Allison V-1710 liquid-cooled engine. If a frangible bullet got into the duct, the fragments could damage the cooling system, resulting in an overheating engine and a mandatory deadstick landing or a bailout by the RP-63 pilot. 

A total of 300 P-63s were converted to the RP-63 Pinball configuration. Some aircraft also trained B-29 Superfortress gunners, but by 1947, the Pinball program was wound down and the last aircraft retired. Much of the early demise of the program came with the introduction of the centralized gunner control system in the Boeing B-29 Superfortress where analog systems provided the necessary lead and tracking for the gunners which used sights that remotely operated the turrets. Targets could be handed off from one gunner's sight to another and it made aerial gunnery training obsolete. The second factor in the demise of the Pinball program came with the gun-laying radar that was first introduced on the tail cannons of the Convair B-36 Peacemaker. Radar simplified tracking and accurately shooting at target aircraft. But the Pinball program lives on as an unique wartime solution that undoubtedly did its part to hasten the demise of the Axis in the Second World War.

Source: Air & Space Smithsonian, November 2010, Vol. 25, No. 5. "Just Shoot Me: In World War II, P-63 pilots had to learn to take it- and not take it personally" by James Dunaway, p50-53. RP-63 model by Scott Van Aken.

The Battle of Kansas Saves the B-29

By any measure of the day, the Boeing B-29 Superfortress was a quantum leap in aviation technology which unfortunately came with a lion's share of problems to be resolved before it was committed to combat operations. Keep in mind that when the B-29 was ordered into production, Pearl Harbor hadn't even happened yet and the first flight of the XB-29 prototype was still over a year away. On 6 September 1941 the US Army Air Corps (soon to be the US Army Air Forces) placed its initial production contract for 250 B-29s- and not only were these B-29s to be built not in Seattle but in Wichita, but the USAAC wisely ordered some of the B-29s to be license built from other manufacturers- Bell (at their Atlanta plant) and Martin (at their Omaha plant). Without the United States yet involved in war, the initial B-29 contract caused a firestorm with Congress that went away quickly as the first bombs fell on Pearl Harbor.

As Boeing lacked production space at its Renton, Washington, plant, the USAAC wanted production at Boeing Wichita which at the time was building biplane trainers and B-17 control surfaces. This caused a furor in Seattle, but the USAAC insisted on the security of a plant deep inland given that the B-29 would be a game changer once it entered service. Only the first three B-29s were built in Seattle.

The need for expansion at Boeing Wichita resulted in one of the largest population booms of the once quiet Kansas town. But as the flight test program of the B-29 progressed and the war widened in scope, more B-29s got added to the production order. By January 1944 Boeing Wichita alone had orders for 1,630 Superfortresses. But in that month, the production line was in chaos. Fewer than 100 production-standard B-29s had been completed and worse yet, an assessment by the 20th Air Force found not a single B-29 was ready for combat for a variety of technical reasons. Of those 100 Superfortesses completed and still in Wichita, less than 16 were flyable due to a lack of various components.

The legendary commander of the US Army Air Forces, General Henry "Hap" Arnold was surprisingly unaware of the situation when he arrived at Smoky Hill AAF in Salina, Kansas that January expecting to see off the first B-29 unit to be deployed to the Pacific, the 58th Bomb Wing. To say that General Arnold went ballistic would be understatement! All the available flying B-29s were being used for crew training and as such, many of them weren't even fitted with the defensive gun system let alone any of the other systems necessary for combat. Even worse, there was a shortage of qualified B-29 mechanics to get any aircraft combat ready.

If there was one man who had every right to be upset, it was General Arnold. Long passionate about the need for strategic bombing in any future war, in the face of criticism and doubt he championed the need for the B-29. He immediately placed his deputy, General B.E. Meyer in charge of a crash, round-the-clock program to get the B-29s combat ready. It started in early March 1944 and is known as the "Battle of Kansas", probably one of the most important battles the B-29 has ever had to fight. And it didn't help matters any that back in January General Arnold himself selected the still-under construction 175th Superfortress to be his aircraft and he wanted it ready by March 1st. That aircraft was named "The General H.H. Arnold Special" and it was th last of the first 175 B-29s involved in the Battle of Kansas.

Boeing brought in additional personnel to assist the USAAF mechanics in getting the B-29s combat ready. As these aircraft were already parked outdoors, much of the work had to be done in the bitter Kansas winter with personnel wearing warm high altitude flight suits and gloves which further slowed the work. Assembly line workers were diverted to assist as well as three eight-hour shifts were set up on the Boeing Wichita ramps to get those B-29s ready. Heated tents were set up near the flightlines so workers could take heated breaks from the cold weather. Twenty-four hours a day, seven days a week, for 35 straight days that first group of B-29s were readied for combat in some of the most atrocious winters in Kansas history. By the end of the month, the Battle of Kansas was won. With the coming of spring and the warmer weather, the first groups of combat-ready Superfortresses departed Wichita for the main B-29 training base, Smoky Hill AAF about 120 miles to the north of Wichita. The last of those 175 B-29s left for Salina on 15 April 1944.

In fact, the first of the 58th Bomb Wing's combat-ready B-29s were already heading out to the Pacific on 10 March 1944, their aircraft being some of the first to have been through the Battle of Kansas.

Source: Boeing B-29 Superfortress (Crowood Aviation Series) by Steve Pace. The Crowood Press Ltd, 2003, p39-40.

Less than six months separated the first flight of the Boeing 377 Stratocruiser and the first flight of the Boeing B-47 Stratojet in December of 1947. While the Stratocruiser represented in many ways the ultimate development of the B-29 Superfortress, there was a design evolution that connects the B-29 and the B-47 as well.

The genesis of the B-47 came in the midst of the Second World War when the US Army Air Forces (the USAF wasn't an independent branch until 1947) looked to the future and knew that jets were the way to go and decided a jet-powered bomber based on their top of the line aircraft, the B-29 Superfortress was what was needed next. Boeing's design team began with what was essentially a jet-powered development of the B-29 but ran into difficulties meeting the range and performance levels that the USAF desired. When the war ended in August 1945, Boeing's chief aerodynamicist, George Schairer, was already in Germany with a USAAF technical team that was evaluating captured German aeronautical research.

At the Luftwaffe research center at Volkenrode, the technical team was reviewing wind-tunnel research into swept wings. In a dry well Schairer and the team found hastily-dumped papers that showed the performance leap possible by combining jet engines and swept wings.

Schairer wrote a seven page later to the engineering team at Boeing working on what would become the B-47 Stratojet. The design process at the time had a design that had fuselage mounted engines and a straight tapered wing and Schairer detailed in his letter what he had found at Volkenrode and his thoughts at how it might benefit the jet bomber design. As a result, the design was reworked to feature a 35-degress swept wing- at the time designated the Boeing Model 448, it was the first of two major technological breakthroughs in the design of the B-47. At this point the design still had its engines mounted in the fuselage and team found that the thin, swept wing could bend excessively in some flight regimes.

The second technological breakthrough was to relocate the jet engines in pods in the wings. The weight of the engines offset bending in the wings and resulted in a more aerodynamic fuselage. It would set the pattern for all large jet aircraft from then onward.

When the XB-47 made its first flight in December 1947, it was only 44 years to the day of the Wright Brothers' first flight at Kitty Hawk. But there was one other aircraft that beat the XB-47 into the air as the first with swept wings, and that was the XP-86 Sabre from North American Aviation (later redesignated F-86). North American also had representatives on the same technical team in Germany with George Schairer.

Source: 747: Creating the World's First Jumbo Jet and Other Adventures from a Life in Aviation by Joe Sutter with Jay Spenser. Smithsonian Books, 2006, p53-57.