Extreme Punchout: The Ejection Seat of the X-15

The hypersonic speed and extreme altitude performance of the North American X-15 demanded one of the most complex ejection seats ever put into service. Earlier NASA research rocket aircraft like the Douglas D-558-2 Skyrocket and the Bell X-2 featured ejectable nose sections that the pilot would then bail out of conventionally once it had separated from the aircraft and stabilized. However, the weight and volume restrictions on the X-15 made such a system impractical and North American in conjunction with engineer/test pilot A. Scott Crossfield, North American Aviation designer Jerry Madden and the David Clark Co. (who had long made pressure suits for the military and NASA) designed an integrated system that combined the pressure suit design along with an advanced ejection seat.

The X-15 ejection seat in the aircraft
(USAF Museum)

David Clark's MC-2 pressure suit was the key to making an open-faced ejection at high Mach and high altitudes possible. It not only protected the pilot from the extreme windblast of hitting the airstream at Mach 3+, it also functioned as a pressure suit to protect the X-15 pilot at altitudes in excess of 250,000 feet. Despite the advanced nature of the pressure suit, it was understood that kinetic heating during a high-Mach ejection would probably result in mild burns to the head, knees, and toes which in effect projected into the airstream.

Because the rocket motor of the X-15 ejection seat had to be powerful to propel the pilot clear of the X-15's hypersonic shockwave, a novel means was used to transfer loads from the pilot's rear end to the seat pan. Each X-15 program pilot sat on a weather balloon filled with plastic beads and wiggled into it like a bean bag. A vacuum was applied which held the shape of the balloon. Once the pilot stood up, plaster of Paris was poured into the depression, creating an exact copy of the pilot's rear end. A block of Balsa wood was then carved to precisely fit the mould and this became the seat cushion of the X-15's ejection seat- not only was it custom fit which allowed the optimum transfer of shock loads from the pilot's body to the seat pan, it also made for a very comfortable seat!

Scott Crossfield in the MC-2 pressure suit
(NASA/Dryden Flight Research Center)

To prevent the flailing of the arms and legs during a high-Mach ejection, special articulated restraints would protect the pilot's legs and feet (also acting as a windblast deflector to minimize heat burns on the feet) as well as to the arms and hands. The articulated arms deployed gauntlets to protect the pilot's hands from aerodynamic heating as well.

Once the articulated arms deployed into place, the emergency oxygen supply took over pressurization of the suit and a heating unit activated to keep the pilot's helmet visor clear of ice. Once the canopy was blown off and the seat traveled up the rails, special wings on the sides of the seat deployed to stabilize the seat in the high-Mach airstream. In a conventional ejection seat, a drogue chute would be deployed to slow the seat down but at the X-15's speeds, such a chute would have melted instantly, so the X-15's seat deployed a pair of telescopic booms that projected aft and outward from the bottom of the seat to provide aerodynamic braking and helped the wings stabilize the seat.

Rocket sled test of the X-15 seat- note the deployed booms
(Boeing)

If ejection took place over 15,000 feet, a built-in barostat kept the pilot attached to the seat which allowed use of the seat's emergency oxygen supply. Once 15,000 feet was reached, the seat automatically released the pilot and activated his parachute. If ejection took place below 15,000 feet, a three second timer allowed the wings and drogue booms to deploy and stabilized the seat before separating from the pilot.

One little-known fact was that the X-15 cockpit was pressurized with nitrogen instead of oxygen as was used in the Mercury and Gemini spacecraft. The pilot breathed oxygen from the his suit which was only pressurized upon ejection. This meant the cockpit was fireproof, something that NASA tragically learned with the launch pad fire on Apollo 1.

The X-15s set an absolute speed record of Mach 6.7 and an absolute altitude record of 354,000 feet which qualified several of its program pilots for astronaut wings. Fortunately the ejection system was never needed and the one fatality, Michael Adams, occurred when his X-15 lost control and broke up on re-entry into the thicker levels of the atmosphere and the X-15's complex ejection system might not have saved him.

Interestingly, the David Clark MC-2 pressure suit served as the basis for the space suits for the Mercury and Gemini programs. The aluminized fabric exterior of the MC-2 suit carried over to the space programs and heavily influenced Hollywood cinematic depictions of space suits well into the 1970s.

Related reading: 

Lockheed's Contribution to the Space Shuttle Program
The Boeing 747 SCA Shuttle Carrier Aircraft
Flight Testing on the Cheap: The Groundbreaking M2F1 Lifting Body
How the Shuttle Orbiter Lost Its Jet Engines

Source: Eject!: The Complete History of U.S. Aircraft Escape Systems by Jim Tuttle. MBI Publishing, 2002, p136-143.

The Atomic Neptunes: The Navy's Interim Nuclear Bombers

P2V-3C JATO takeoff from the USS Midway

Not often realized in aviation history is the key role naval personnel played in the development and the deployment of the first atomic bombs that closed out the Second World War. In March 1943, Navy captain William Parsons was assigned to the Manhattan Project's Ordnance Division as he had had prior experience in the development of the proximity fuse for anti-aircraft shells. While he also contributed to the design of the atomic bomb's proximity fuse, he ultimately became responsible for the planning and execution of the US Army Air Force's use of the bombs against Japan. At Titian Island in the Marianas, it was Captain Parsons who was in charge of the bomb assembly and check out. The early bombs of those days had a core that was separate from the main core, this way the two parts were each of subcritical mass and unlikely to detonate as a safety measure. Once airborne, the "weaponeer" was responsible for inserting the core into the atomic bomb to arm it. The weaponeer also acted as the mission's tactical commander as they had the final authority on the bomb's use. On the Enola Gay's mission against Hiroshima, Captain Parsons was aboard as the weaponeer and armed "Little Boy" prior to its use. Parson's director of operations in the Manhattan Project was another naval officer, Commander Frederick Ashworth, a former Grumman TBF pilot. On the second mission against Nagasaki, Commander Ashworth was the weaponeer aboard Bock's Car. Though delivered to their targets by USAAF Boeing B-29 Superfortresses, both atomic bombs were armed by naval officers in flight and in essence, naval officers acted as the mission commanders. Despite the primacy of the Navy's carrier battle groups in the Pacific War, the Navy was well aware of the potential power of nuclear weapons in the postwar period. In September 1945 right after the Japanese surrender, the Chief of Naval Operations (CNO) established the Navy's "Special Weapons Division" which was headed by a vice-admiral. Planning immediately began for a new, much larger aircraft carrier that would carry the Navy's planned nuclear strike force. Until this supercarrier was launched, the three biggest aircraft carriers of the US Navy would be responsible for deploying nuclear weapons- these three ships were the Midway-class carriers- the USS Midway, USS Franklin D. Roosevelt, and the USS Coral Sea. In December 1945, the Navy laid out a three-phase carrier-based strategic bomber plan- Phase 1 called for modest capability bomber to speed its introduction and deployment to the fleet. That aircraft became the North American AJ Savage. Phase 2 was eventually dropped as it was decided to adopt the Allison T40 turboprop engine for an improved version of the AJ Savage- that aircraft was the failed XA2J Super Savage. Phase 3 was for the definitive jet-powered nuclear strike bomber that the Navy really wanted, and that aircraft would eventually become the Douglas A3D Skywarrior. 

North American Aviation received the contract to start work on the AJ Savage in June 1946. With the creation of an independent United States Air Force with the passage of the National Security Act of 1947, the assertive leadership of the USAF moved to become to sole user of nuclear delivery in the US military and pushed to relieve the Navy of its strategic ambitions. A rancorous conference chaired by Secretary of Defense James Forrestal in March 1948 in Key West, Florida, resulted in an agreement that the Navy could not only keep its land-based patrol bomber force but could continue development of its strategic air arm as it was consistent with the aims "to conduct air operations as necessary for the accomplishment of objectives in a naval campaign". Since the Navy's planned nuclear targets were all Soviet naval bases, it was given that the USAF's Strategic Air Command would be responsible for the targeting of Soviet urban and industrial centers while the Navy targeted naval bases and other military installations that threatened operations at sea. This didn't sit well with the USAF, but Forrestal's decision was further cemented at a second meeting held at the Naval War College in Newport, Rhode Island, in August 1948. As an interesting historical note to those meetings, the Navy had its own nuclear war plan independent of the USAF's plans until 1960, when both services' plans were integrated into what was called the Single Integrated Operations Plan, or SIOP. 

North American AJ-1 Savage, the Neptune's replacement.

With the prototype North American XAJ Savage making its first flight in May 1949, it was imperative during the development of the Savage that the Navy establish some sort of nuclear delivery capability from its aircraft carriers as soon as possible. The most ideal candidate aircraft to get some sort of interim capability fielded was the Lockheed P2V Neptune. In 1946, a modified Neptune named "Truculent Turtle" made a record-breaking long distance flight from Australia to Ohio, over 11,000 nautical miles without refueling. With the plans for the Midway-class carriers to operate in the Mediterranean with the nuclear-armed Neptunes, a flight from the eastern Med to Moscow was significantly less than that of the Truculent Turtle's flight and if the targets were coastal naval bases, the range required was even less. With a gross weight well in excess of the catapults of the Midway-class ships, the modified Neptunes would use eight 1,000 lb-thrust JATO rockets with a near-full length deck run of 900 feet and the starboard wingtip clearing the island by only 10 feet. The modified Neptunes were designated P2V-3C and only twelve such aircraft were ordered- since there were only three Midway-class ships and a small number of the Mk 1 bomb (based on the Little Boy design) available, the interim strike force would be very small until the AJ Savage became operational. The more advanced Mk 4 bomb which was based on the Fat Man design used on Nagasaki was too large for the Neptune's bomb bay- but the AJ Savage was designed from the outset to be able to carry the larger Mk 4 bomb. 

At first it was planned to give the P2V-3Cs the ability to return to the carrier after their missions. One of the twelve aircraft modified got a tail hook and around 128 field arrested landings were practiced both at Lockheed's facility at Burbank Airport and at the Navy's flight test center at NAS Patuxent River in Maryland. These flights were flown by another naval aviator who was a veteran of the Manhattan Project, Commander John Hayward. During the war he was assigned to China Lake where he worked on the implosion device used on Fat Man to start the nuclear chain reaction that resulted in detonation. Commander Hayward even flew the P2V-3C on touch and goes off the USS Franklin D. Roosevelt, but no arrested landings at sea were made. It was found that the Neptune's structure wasn't strong enough for carrier landings and the aircraft that Hayward flew on land-based arrested landings had numerous structural deformities as a result. Since there wasn't time to beef up the structure of the Neptune, the P2V-3Cs would have be craned aboard the Midway-class ships dockside and then, after completion of the mission, either ditch alongside the carrier or land at a friendly airfield. This made the P2V-3C aircraft pretty much a single-use weapon. 

Internal layout of the P2V-3C. Note the fuel tanks in the nose and aft fuselage.

Additional fuel tanks were added in the wings and fuselage of the Neptune to create the P2V-3C. Total internal fuel over a standard P2V patrol bomber was increased by an astounding 75%! The P2V-3C carried 4,120 gallons of fuel over the standard P2V's 2,350 gallons. Anything unnecessary to the nuclear delivery mission was deleted, especially if it caused drag- so the dorsal gun turret, nose turret, rocket launcher provisions on the wings and multiple antennas were removed. An AN/APS-31 search and navigation radar replaced the nose turret and it worked with a radar bomb sight. Even the astrodome was removed to reduce drag, sextant shots for navigation would be done via a periscope. Since the mission endurance of the P2V-3C would outlast the oil capacity of the Wright R-3350 radial engines, a 38-gallon oil tank was installed (in fact, the navigator sat on it) with plumbing to keep the engines replenished with oil during the mission. To further save on weight, even the emergency hydraulic system was removed from the P2V-3C. A pair of 20mm tail guns were kept for self defense along with radar detection equipment (but no countermeasures or jamming capability was installed) and the crew was reduced to just four: pilot, copilot/weaponeer, bombardier/navigator, and radioman/tail gunner. 

The first P2V-3C takeoff from a carrier took place in April 1948 fro the USS Coral Sea and a rapid series of demonstrations were made at increasing weights to show that a fully-fueled and loaded Neptune could make it off the carrier with a JATO-assist deck run. On one demonstration flight, Captain Hayward had the second Secretary of Defense, Louis Johnson, in the right seat. It was Johnson who succeeded Forrestal as SecDef and interestingly, just months before his flight on a P2V-3C demonstration takeoff, he had canceled the Navy's first supercarrier, the USS United States. Through 1948, the Navy conducted a series of long range missions from a Midway-class carrier to demonstrate the concept, a simulated weapon delivery and recovery to a friendly air base. Should the Neptune crew elect to ditch along side the carrier, a special flap was added to the underside of the P2V-3C called a "hydroflap" that helped keep the nose of the aircraft from boring into the water during ditching. 

With the deployment of the P2V-3C nearing, the Navy formed three Special Weapons Units- one each for each of the Midway-class aircraft carriers. Based and trained at Kirkland AFB in Albuquerque, New Mexico, where the Department of Energy in cooperation with the USAF had a nuclear technical facility, each unit would be responsible for the assembly, maintenance, and check out of each weapon. The technology of the day meant it took about 50 men and 80 hours to carry out a bomb aseembly and disassembly for maintenance checks. Modifications to each Midway-class carrier provided for facilities for bomb handling, storage, and maintenance with a special Marine Corps detachment for security. The first Navy heavy attack squadron was Composite Squadron 5 (VC-5), established at Moffett Field, California on 9 September 1948. VC-5's commanding officer was Commander Frederick Ashworth, the weaponeer on Bock's Car. In the following January, Captain John Hayward assumed command with Ashworth as his XO. The first P2V-3Cs were delivered to the squadron in November 1948. JATO training at NAS Patuxent River began in February 1949 and by March, three aircraft were craned aboard the USS Coral Sea for its first exercises. By April 1949, all three Midway-class carriers were ready for deployment- all three would be homeported at Norfolk, Virginia, on the East Coast since their deterrent patrols would be in either the Mediterranean or North Seas. 

JATO launch from the USS Franklin D. Roosevelt

It was by this time that the wisdom of using the Neptune as an interim aircraft proved wise- North American was running into development issues with the AJ Savage. Even though the deployment of the P2V-3C coincided with the arrival of the first AJ Savage aircraft, the early AJs were so unreliable and trouble-prone, most training had to be done with the Neptunes. By April 1950, VC-5 was sending detachments to the carriers that had both the AJ Savage and the P2V-3C Neptune. The AJs were used for carrier landing qualifications since the Neptunes lacked return provisions. The first operational deployment took place in January 1951 when VC-5 went aboard the USS Franklin D. Roosevelt. The aircraft weren't on the ship, though- the FDR left Norfolk for the Mediterranean with its complement of bombs and its attendant Special Weapons Unit. Six AJ Savages and three P2V-3C Neptunes departed Norfolk later for Port Lyautey, Morocco, to catch up with the carrier. Continued problems with the AJ kept them shore based. Since the Neptunes couldn't return to the ship, they were also shore-based in Morocco as well and would be craned aboard the carrier had tensions increased. It wasn't a practical arrangement but it was the only arrangement. So as to not alert the Soviets, Neptunes were craned aboard which ever Midway-class carrier was in the Mediterranean and practice launches carried out on a routine basis. Depending on the planned mission range, no more than three to four P2V-3C Neptunes could operate from the carrier- few of the carrier's air wing could be on deck as the Neptunes lacked wing folding and took up a lot of space. When not spotted for takeoff at the rear of the deck (the angled deck had yet to be retrofitted to the Midway-class), the Neptunes were parked on the forward deck but their size meant that only the port catapult could be used the carrier air wing. Needless to say, many carrier captains and CAGs despised the Neptunes! 

By 1952, the problems with the AJ Savage had been ironed out enough that they could assume the nuclear delivery role from the Neptunes. While the Savage was smaller with wing folding and could return to the ship, their large size still had them universally disliked as they got in the way of flight deck operations. The Savages, though, could operated off the smaller Essex class ships, which expanded the number of available carriers for nuclear deterrent patrol. One of the reasons the Midway-class ships didn't participate in the Korean War was that they were needed in the Mediterranean for deterrent patrols. The P2V-3Cs were reconfigured to P2V-3Bs and sent ashore to act as training aircraft for the crews bound for the AJ Savage. The Neptune's role as an interim nuclear bomber was brief, less than two years, but it gave the Navy valuable experience in not just operating large aircraft from carriers but also with nuclear weapons handling. 

Source: Strike From the Sea: US Navy Attack Aircraft From Skyraider to Super Hornet 1948-Present by Tommy H. Thompson. Specialty Press, 2009, pp42-56. "Naval Aviation Centennial: Neptune's Atomic Trident (1950)" US Naval Institute Blog, 6 February 2011. Photos: 

The North American XB-28: Too Much, Too Late

The sole XB-28 prototype. Note the remotely operated turrets.

With the North American B-25 Mitchell prototype (internal company designation NA-40B) already in the hands of the US Army Air Corps for flight testing in 1939, the promise of cabin pressurization offered a leap in bomber performance by being able to fly higher and faster. Accordingly, in August 1939, the Army issued the XC-214 specification which called for a pressurized medium bomber to supplant the medium bomber types that were soon to become operational. Only Martin and North American responded to XC-214. Martin's submission was for the XB-27 but the USAAC felt Martin didn't have a full grasp of the challenges of high altitude pressurization in their design and North American's submission, the XB-28 won the development contract. This took place on 15 November 1939 just three months after the Army issued its specification with North American inking a contract to begin formal design work on the XB-28. To give you an idea of the pace of development and the pressure of the looming clouds of war, the contract for the development of the XB-28 was signed around the same time that the Army ordered the B-25 Mitchell into production! The XB-28 had started out as a pressurized version of the B-25 Mitchell with a circular fuselage and Pratt & Whitney R-2800 Double Wasp engines with GE Type-C turbosuperchargers replacing the Wright R-2600 Twin Cyclone radials used on the B-25. Design work proceeded rapidly since the company was already at work on a pressurized successor to the B-25 at the time of the release of the XC-214 specification in August 1939. As design work progressed, changes were made stating with abandoning the Mitchell's twin fins for a single fin. Eventually the XB-28 as designed bore little resemblance to the Mitchell. The contract for three prototypes was signed on 13 February 1940. 

The five crew all sat in a pressurized compartment in the forward fuselage. 

Besides the change to more powerful R-2800 Double Wasp engines with GE turbosuperchargers, a third supercharger was also fitted to provide cabin pressurization. Heaters powered by gasoline warmed the air in the pressurization ducting for the pressure cabin located in the the forward fuselage. The elongated nacelles had an opening in the rear for the turbo-supercharger exhaust which added some forward propulsive power. The four bladed propellers were counter-rotating to cancel each other's torque to ease handling. Integral self-sealing fuel tanks took up most of the wings. Relatively unique for the day nose wheel steering was fitted and controlled by a lever in the cockpit similar to modern nose wheel tillers. Another unique feature was the use of fluorescent paint on the instrument panel and instruments that would glow at night from overhead UV lamps as an aid to night flying.

Overall configuration of the XB-28.

To simply the structure of a pressurized aircraft, the pressure cabin only occupied the forward fuselage. All the joints were sealed during assembly and the interior sprayed with a plastic sealant before installation of the cabin items. The cabin atmosphere was maintained at the equivalent of 8,000 feet up to an operating altitude of 33,000 feet. The crew of five was crammed into this space- with the pilot and co-pilot sitting side by side, behind them sat the primary gunner and the radio operator/secondary gunner. The bombardier/navigator sat in the nose compartment but could access the cramped flight deck via a floor panel by the co-pilot's feet. The bomb bay could carry up to 4,000 lbs of bombs and the three defensive turrets consisted of twin 50-caliber guns in dorsal, ventral and tail turrets that were operated remotely by the primary gunner and the radio operator/secondary gunner. Each gunner had a hemispheric observation window next to them and sighted the guns via a periscope system that protruded from streamlined twin fairings above and below the fuselage just aft of the flight deck. Initial plans for were for North American-designed turrets tied to a Sperry fire control system, but Sperry's resources were tied up with current production aircraft. It was decided to switch to General Electric for the remote fire control system and to have them be responsible for the turrets as well well. This imposed delays in the development as changes needed to be made to accommodate GE's equipment and systems. There was also a prevailing opinion at North American that Sperry's system was more advanced. A compromise was reached with the XB-28 defensive systems to use GE turrets and the Sperry sighting system. It's worth noting at this point that when the work on the remote turret fire control system on the XB-28 was under development, both Sperry and GE were working on getting the contract for the remote turret fire control system on the Boeing B-29 Superfortress- ironing out the kinks in the XB-28 gave GE valuable experience that helped the B-29 and made its system the production standard on the Superfortress.

Engine run up test at Mines Field in the summer of 1942.

The US entry into the Second World War slowed development of the XB-28 as priority shifted to production types and much of North American's resources were devoted to the production of the B-25 Mitchell and the P-51 Mustang. The maiden flight of the first prototype took place on 24 April 1942 at Mines Field (the site of today's Los Angeles International Airport/LAX) and the flight test program showed the XB-28 to be quite fast at high altitude, capable of 372 mph at 25,000 feet. Following the conclusion of North American's flight test program, the USAAF portion of the flight test program took place with the XB-28 operating out of Wright Field outside of Dayton, Ohio, for service trials. It was decided during the service trials that the third XB-28 prototype would be completed as a reconnaissance and photo-mapping aircraft designated XB-28A. North American was instructed to set aside work on the second XB-28 to get the XB-28A variant flying. The speed and altitude performance of the XB-28A was increased by reducing weight as well as installing more powerful versions of the R-2800 engines. The XB-28A made its maiden flight on 24 April 1943 (exactly one year after the first XB-28) but was unfortunately lost in flutter incident during dive testing on 4 August 1943 with the crew able to parachute to safety. At the time of the accident, design work on the production B-28 was underway with the most significant change being some extra scanning windows on the nose compartment for the bombardier/navigator.

By this point, however, it was realized that despite the outstanding performance of the XB-28, the realities of war showed that medium bombers already in service like the B-25 Mitchell and the Martin B-26 Marauder were most effective at low to medium altitudes flying interdiction missions where pressurization wasn't necessary. In the Pacific, B-25s equipped with extra forward firing machine guns were becoming very effective low level anti-shipping weapons while in the European theater, B-25s and B-26s operated most effectively at medium altitude (though some low level anti-shipping missions were flown in the Mediterranean against Axis vessels along the French and Italian coasts). The final nail in the XB-28's coffin was the Douglas product that was also first flown at Mines Field just a few months after the XB-28's maiden flight. The prototype Douglas XA-26 Invader first flew on 10 July 1942. It used the same engines as the XB-28, carried the same bomb load, but lacked pressurization which made it simpler to build and it only had a crew of three versus the crew of five on the XB-28. The sole XB-28 prototype was still at Wright Field at the time of the program's cancellation- it had its outer wings removed and sat out the war as a ground test article for pressurization tests before being scrapped.

Anigrand released a 1/72 resin kit of the XB-28 and this page has a great series of photos of a completed model that show the overall configuration of the XB-28. Take note of the hemispheric scanning bubbles on the upper lateral fuselage ahead of the wing for the gunners as well as the streamlined twin fairings above and below the forward fuselage for the sighting system to control the remote turrets.

Source: American Bomber Aircraft Development in World War 2 by Bill Norton. Midland Publishing, 2012, pp 66-69. Photos: USAF Museum, Anigrand

The Corvus Missile- Laying the Foundation for US Anti-Radiation Missiles

Wind tunnel model of the Corvus missile

In the Second World War, the Radioplane Company had built thousands of remote controlled drones for target practice. In the late 1940s, Radioplane was asked by the USAF for a jet-powered drone for target practice and in 1950 first flew the YQ-1 which was powered by a pulse jet. The drone only had a flight time of about 60 minutes which wasn't terribly useful for the USAF's needs. One drone was converted to use a small Continental J69 turbojet but by the time this version had flown in 1953, the USAF had settled on the Ryan Firebee series of drones for its needs. Radioplane's work transferred over to GAM-67 Crossbow missile program that started in 1953 to meet a USAF need for an anti-radiation missile for the Boeing B-50 Superfortress and B-47 Stratojet bombers. The Crossbow would have been the world's first missile designed to kill radars and was to have had a lightweight 10-kiloton nuclear warhead. A Stratojet could carry four Crossbows under its wings. The first successful guided flight took place in 1957 but the program was soon canceled due to technical difficulties. At the same time the Crossbow flight test program was gearing up, the Navy decided they wanted their own anti-radiation missile and in 1955 issued a requirement for a rocket-powered stand-off missile for its carrier attack aircraft. That missile was designated the ASM-N-8 Raven, but a parallel project going on at the time with the Navy duplicated the Raven's role, so the Raven program was canceled early on and efforts shifted (along with the ASM-N-8 designation) to what was called the Corvus missile. 

In January 1957, development of the Corvus missile was awarded to Dallas-based Temco Aircraft. Temco (Texas Engineering and Manufacturing) was founded in 1952 by Robert McCullough who was the plant manager of North American Aviation's plant in Grand Prairie next to NAS Dallas. McCullough and his group took over the plant from North American under the Temco name and kept it open doing subcontracting work for other aircraft manufacturers. Soon Temco got into electronics and missile guidance systems and by the time of the Corvus contract, nearly half of Temco's revenue came from their missile guidance work. The Corvus award was a boost to the company that they were experienced enough to take on a complete weapons system like the Corvus on their own.

XLR-48 engine on display at the Smithsonian

The Corvus was a big missile. It was 16 feet in length and weighed about 1750 lbs. It had delta wings to extend its range and cruciform tail surfaces set at 45 degrees from the delta wing. Instead of a jet engine as was used on the Crossbow, the Reaction Motors subsidiary of the Thiokol Corporation developed the XLR-48 Patriot pre-packaged liquid fuel rocket motor. Reaction Motors was already well established making rocket engines for the X-plane programs and to overcome the Navy's hesitation about having to store liquid rocket fuels aboard the carrier, the XLR-48 was pre-packaged with storable propellants so the missiles would never have to be fueled. This was a Reaction Motors innovation and for the Corvus, the XLR-48 offered greater thrust over a longer period of time than a solid rocket motor sized for the Corvus airframe. The propellants were hypergolic, meaning they ignited on contact which resulted in a surprisingly simple rocket motor. 

Drawing of an A4D Skyhawk with two Corvus missiles

The Corvus could be armed with either a conventional warhead or a 10-kiloton nuclear warhead very similar to what was planned for the Crossbow missile. Being rocket-powered, the Corvus was a lot faster than the jet-powered Crossbow, flying out at Mach 3 on a ballistic trajectory to 85,000 feet. The seeker head was designed by another Dallas-based electronics firm that would itself soon become famous in electronics, Texas Instruments. The seeker would lock onto an enemy radar emitter. In this mode, the Corvus had a range of 170 miles. It also could lock onto a target that was illuminated by the launch aircraft in a semi-active homing mode against non-emitting targets, but in this attack mode the range was shorter at around 100 miles. A data link would have been used to guide the Corvus in semi-active homing mode until it picked up the radar returns from the target. 

Corvus missile being launched from an A3D Skywarrior

The first airborne launches of the Corvus took place from a Douglas A4D Skyhawk in July 1959 from NAS Point Mugu in California. About twenty missiles were built and the program had progressed to fully guided flights when it was abruptly canceled in August 1960. The Navy had decided that nuclear-tipped air-to-surface missiles didn't quite fit with its operational doctrines and the program was transferred to the USAF. Finding the Corvus redundant to its own AGM-28 Hound Dog missile program that had been awarded already to North American Aviation in 1957, the program was canceled in late 1960 despite the Corvus being significantly lighter than the Hound Dog.

The work wasn't all for naught, though. Texas Instruments, who designed and was tapped to produce the Corvus radar seeker guidance head, gained significant experience from the program and would go on to work with the US Navy on the AGM-45 Shrike became the first American anti-radiation missile to be fielded and was used in combat for the first time in the skies over Vietnam against SAM sites. Texas Instruments would then go on in 1974 to develop the successor to the Shrike that is still in use to day, the AGM-88 HARM (High Speed Anti-Radiation Missile). 

As for Temco, their work on the Corvus made them an attractive merger target. Just prior to the Corvus cancellation in 1960, Dallas businessman Richard Ling, head of Ling-Altec Electronics acquired Temco to form Ling-Temco and shortly thereafter gained controlling interest in Chance Vought Aircraft, the new company becoming Ling-Temco-Vought, or LTV. 

Source: Scooter: The Douglas A-4 Skyhawk Story by Tommy Thomason. Crecy Publishing, 2011, p79. Pushing the Envelope: The American Aircraft Industry by Donald M. Pattillo. University of Michigan Press, 2001, pp 241-242. Detecting and Classifying Low-Probability of Intercept Radar by Phillip E. Pace. Artech House, 2008, pp 554-555. DesignationSystems.Net. Photos: Wikipedia, National Air & Space Museum, NASA.

The First B-25 Mitchell Executive Transports

General Eisenhower's personal B-25 transport in its later years.

Until the arrival of the Grumman Gulfstream I in 1958, the Lockheed Jetstar in 1960 and the Hawker Siddeley HS.125 in 1962, there weren't any aircraft that were designed specifically as business transports. From the end of the Second World War until the 1960s, most companies had the option of buying up surplus Douglas DC-3 or C-47 aircraft, getting a small piston-engined aircraft from the likes of Cessna, Beech, or Piper, or a refitted surplus bomber- this latter option was clearly the high end as ex-bomber aircraft usually had a speed and range advantage over both the DC-3 and smaller piston aircraft. These executive conversions were the cream of the crop of business aviation in those days, the 1950s and 1950s counterpart to today's Gulfstreams and Global Express bizjets. A whole new industry developed in the postwar era to cater to this high-end market. 

One of the more common executive conversions from any several companies in those days used the North American B-25 Mitchell as the base aircraft- they were inexpensive to acquire, readily amenable to modification, and had a reputation as good-handling aircraft (which was why there were so few B-26 executive conversions after the Second World War). But years before the 1950s boom in the market, North American Aviation itself pioneered the concept of using the B-25 as an executive transport. 

The very first B-25 Mitchell to be converted just so happened to be the very first B-25 Mitchell with the serial number 40-2165. That's right. The prototype production B-25 that made its maiden flight in 1940. It had been modified in several ways as the flight test program proceeded and by 1942 it was deemed to have cost too much to have had it modified to the standard that was being delivered to the USAAF in those days, so it sat in a corner of the North American Aviation's facility at Mines Field (today's LAX). At this point in the B-25 program, North American now had two plants running at full capacity turning out Mitchells- the Fairfax plant in Kansas City, Kansas, and one at Hensley Field in Dallas (which later became NAS Dallas). In addition, North American executives and engineers were regularly moving amongst the suppliers nationwide as well as Washington DC and Wright Field in Dayton, Ohio, where the USAAF's technical division was located. During the war, airline service wasn't dependable as most of the air capacity was used by the military to support the war effort and travel by train was too slow. Dutch Kindelberger, president of North American Aviation, ordered the stored prototype to be converted into an executive transport. Seven passengers seats were installed, two ahead of the bomb bar and five  in the aft fuselage. The bomb bay became a baggage compartment and bunks were installed above it. Four windows were installed in the aft fuselage for the passenger cabin and the glass nose was made solid with a smooth aluminum skin. Carpeting, upholstery and extensive soundproofing were also added as well as a small bar- something not highlighted or admitted to by North American- which got the aircraft the nickname "Whiskey Express". It was used extensively by the North American corporate brass until January 1945 when it had to be scrapped after a runway overrun at Mines Field. 

The second B-25 modified by North American belonged to USAAF General Henry "Hap" Arnold- visiting the Inglewood facility at Mines Field one day, Arnold got to see the Whiskey Express and as the Chief of Staff, he decided he needed one, too. This was 1943 and production was rapidly accelerating in the B-25 program, so it was easy to divert a B-25C from production to be fitted out by North American to a similar standard as Whiskey Express. After the war, General Arnold's personal transport was purchased by Howard Hughes who used for another twenty years before it was retired. 

The same year Arnold got his own B-25, a B-25J was taken off the production line in Kansas City and flown to Inglewood on a "secret" mission. Tail number 43-4030 was fitted out to become the personal transport for General Dwight Eisenhower. Unlike Arnold's B-25 which had olive drab upholstery, Ike's Mitchell had a more stylish blue interior. Clamshell doors were fitted to the nose for easy access to the extra communications and navigation equipment and more floor space in the aft fuselage was created by moving the gunner's aft hatch further back, giving the rear cabin more seating and a drop leaf table. Overhead luggage racks were also fitted and extra fuel tanks were fitted to the bomb bay to give it more range. Officially it was designated an RB-25J to hide its true nature as Ike's personal transport, but as the war in Europe progressed, it was redesignated CB-25J and when Eisenhower moved up to larger aircraft as the Supreme Allied Commander, the CB-25J was passed on for use by lower ranking generals and was used by the USAF postwar until it ended up in the possession of the South Dakota Air and Space Museum where it can be seen today. 

In 1944, General Arnold traded up to a newer Mitchell transport. Maybe it was knowing Ike had a nicer one than him, who really knows, but tail number 44-28945 was taken from the production line and fitted out identically to the Eisenhower's aircraft. Arnold used it until 1946, but it remained in USAF use for a number of years flying colonels around well into the 1960s. 

When the Whiskey Express got scrapped, the North American brass decided a replacement was needed. The same month that the Whiskey Express had its accident, a B-25J was pulled from the production line and fitted out to nearly the same standards as Eisenhower's aircraft and Arnold's second aircraft. But knowing the war was soon over, North American decided to go the extra mile thinking there might be a postwar market for the company in such a conversion (years before any such companies specializing in such conversions were in that business!). Extra navigational equipment as well as a cabin heater were added and it entered service in March 1945. Between flying for North American executives, it was flying a test program to get certification as an executive transport. But on 27 February 1946 during a test flight out of Mines Field over the Pacific, the flight crew radioed a mayday that a wing was on fire before the aircraft tragically exploded. 

N5126N, North American's last shot at a business transport

North American decided it had had enough of the conversion market after that tragic loss, but in 1950 with the rise of aftermarket companies that were doing the very same thing North American had done during the Second World War, they decided to take a second shot at the executive transport market. A surplus B-25J was used and this time a new nose that was 14 inches wider was added which allowed room for four passenger seats ahead of the bomb bay but behind the flight deck in addition to the aft fuselage cabin. The bomb bay was permanently closed and replaced with an baggage door and an electric lift at the front of the former bomb bay. Because of the wider nose, a new windshield was needed and the windshield from the Convair 240 worked perfectly. To reduce noise, a circular exhaust collector was used on the engines instead of having several separate exhaust stacks. Nicknamed the "Bulbous Nose B-25", it had the tail number N5126N. Flight testing began, but ended tragically a second time on 25 March 1950 when N5126N broke up in a thunderstorm over Arizona, killing seven North American flight crew and engineers. With that loss, North American decided to abandon the project. 

Through the 1950s, though, the USAF still had quite a few B-25s flying as transports on strength and contracted the Hayes Aircraft Company in Birmingham, Alabama, and the Tucson, Arizona, branch of Hughes Tool Company to carry out conversion work on the B-25s. While not as extensive as the Bulbous Nose B-25 aircraft, they definitely drew upon North American's work. Many of these converted B-25s became trainer aircraft with the military through the 1960s, not just with the USAF but also the Royal Canadian Air Force. 

Source/Photos: Deadly Duo- The B-25 and B-26 in World War II by Charles A. Mendenhall. Specialty Press, 1981, p101-111.

The Genesis of the B-25 Mitchell Strafer-Bomber

The first strafer package installed on a B-25 Mitchell.

The first half of 1942 in the Pacific were dark days for the Allies. With the loss of the Philippines and the Dutch East Indies and the fall of Singapore in February, Allied forces fell back in the face of the Japanese, seeking refuge in Australia to regroup for the offensive. Australia would soon become the base of operations for General Douglas MacArthur's South Pacific offensive as war materiel from the United States along with personnel began to flow in via a logistical supply line stretching from California via Hawaii and Fiji. It was via this route that the first North American B-25 Mitchell medium bombers began to arrive in Australia- rather unusually, though, the first B-25s to arrive were earmarked for the Dutch and were accompanied by Jack Fox, North American's field service representative. With ten brand-new B-25s present, it wasn't long before some back room dealings resulted in the B-25s along with Jack Fox being transferred to the US Army Air Forces at their new base in Charters Towers which was built in only six weeks by the Australians. Arriving at Charters Towers, Fox saw "his" B-25s arriving with American crews which was unusual as few pilots had been checked out in the new bomber. Fox queried one of the arriving pilots who gruffly responded "Who needs checking out? The damn thing has a stick and throttle, doesn't it?"

That was the legendary Captain Paul "Pappy" Gunn that Fox had just met. A retired Navy flight instructor, Gunn was living in the Philippines working for Philippine Air Lines when the Japanese invaded. Managing to assist the ultimately futile battle against the Japanese, Gunn managed to fall back to Australia where his intimate knowledge of the Philippines was put to use with an immediate commission in the USAAF. Gunn's initial meeting with Fox would be the start of the development of some of the most lethal aircraft fielded against Japanese forces in the South Pacific, the "strafer-bombers". But before we move on, we have to back track a little bit to January 1942 and back to the United States when the tactics of a minimum altitude bombing attack on ships and troops were being discussed within the USAAF. Soon tests were underway at Eglin Army Air Field in the Florida panhandle to develop the technique. By this time the USAAF in the South Pacific under General George Kenney, head of the Thirteenth Air Force, recognized the low-level attack virtues of the Douglas A-20 Havoc and North American B-25 Mitchells, roles they were not originally designed to perform. But Kenney was dissatisfied with the armament and bombs of the two attack aircraft as they weren't completely suited to how he wanted to employ them. 

With flight tests at Eglin AAF and with Kenney's own aircraft in Australia, skip bombing was developed which involved a low level approach against the heavy defensive fire of the Japanese ships. Lacking proper American fuses to perform skip bombing, Kenney had Australian fuses which were longer substituted on the bombs. With A-20 and B-25 crews training locally on skip bombing, the first attacks were found to be more successful if combined with Australian Beaufighters which strafed the ships to kept the defensive fire to a minimum. It was at this juncture that Pappy Gunn enters the picture. He had come up with a field modification for the A-20 that put a battery of four fifty-caliber guns in the nose since a bombardier wasn't needed on low level attack runs. This way skip bombing and strafing could be combined in a single aircraft. The results were better, but extra fuel tanks had to be installed in the Havoc's bomb bay to increase its range, which in turn reduced its bomb load. By by the summer of 1942 A-20s were in short supply as A-20 deliveries to the Russians were increasing.

"Pappy's Folly" with Pappy Gunn at the helm.

And that's when the B-25 entered the picture. It had longer "legs" than the Havoc and could carry a heavier load. Early skip bombing missions had already shown the B-25 eminently suitable for the role. Gunn and Fox come up with a field modification with General Kenney's blessing that put four fifty-caliber guns in the nose section with plenty of ammunition as well as an additional two pairs of fifty-caliber guns on external blisters on each side of the forward fuselage. By the summer 1942 Jack Fox issued a memo to all the other North American field reps in the South Pacific on how to modify the B-25 into a strafer-bomber. North American dispatched an engineering team to the field depot which was located at Eagle Farms in Brisbane to further assist Pappy Gunn and Jack Fox in their development work. The first B-25 Mitchell modified as a strafer-bomber was aptly named "Pappy's Folly" and personally flight tested by Gunn himself as well as Jack Fox. Working out the bugs, General Kenney then sent the two men and "Pappy's Folly" up to Port Moresby closer to the front lines for more testing. By February 1943 the North American team at Eagle Farms converted twelve more B-25s which were then assigned to crews with the 90th Bombardment Squadron in Port Moresby. Tactics were worked out and crews trained on a wrecked ship off the coast of Port Moresby- a pair of B-25s would approach enemy ships at 1,000-1,500 feet and then drop to 500 feet or lower on the final run in to the target. One Mitchell would open up with its gun battery to suppress the defensive fire while the other Mitchell would drop a string of three 250-lb bombs in a skip bomb attack. After the first pass, the pair returned for a second run, this time switching roles. 

During the first half of 1943 General Kenney's "commerce destroyers" wreaked havoc on Japanese shipping in the Bismarck Sea that supported the Imperial war machine. Soon airfields also came under attack by the strafer-bombers dropping 23-lb fragmentation bombs slowed by parachutes- "parafrag" bombs. They would soon be a decisive force in the campaign in the Southwest Pacific on the road back to the Philippines. 

Source/Photos: B-25 Mitchell: The Magnificent Medium by Norm L. Avery.  Phalanx Publishing, 1992, p95-103.

The Rocket-Boosted P-51 Mustang

In September 1944 the first operational unit of Messerschmitt Me 262 jet fighters was established under the command of the celebrated ace Major Walter Nowotny of the Luftwaffe, his unit being tasked with the operational development of tactics for the fighter and being named "Komando Nowotny" in honor of that significance. USAAF heavy bomber crews had ready been encountering the Me 163 Komet rocket interceptor for several months but the persistence of the jet over the point-defense nature of the Komet made the 262 a more significant threat in the eyes of the Allies. After Nowotny was killed in combat in November 1944, the unit became Jagdgeschwader 7 (JG 7), the first operational jet fighter unit in history. However a threat that the Me 262 posed in the threat, it was quickly realized that it was most vulnerable during its landing and takeoff phases of flight as early jet engines of the day suffered from long spool up times. If American fighter pilots could get at the 262 at its home bases, then its speed advantage was negated. 

The distinctively marked Fw 190 D-9s of JV 44

In response, not only did the Luftwaffe bases of the 262 boast more robust air defenses in the form of anti-aircraft artillery, German fighter pilot Adolf Galland's fighter unit, Jadverband 44 (JV 44) had also come up with another tactic to defend the 262s. At the time, Galland had become a very vocal critic of the Luftwaffe's tactics and operational decisions to the point of becoming quite the thorn in the side of Hermann Goering, the head of the Luftwaffe. It was thought by Goering and his command staff that if Galland were given front line command of a unit, he might be killed in action which would get him out of their hair. Galland was tasked to gather the best fighter pilots he could find to operate the 262 as JV 44 was formed in February 1945. To deal with marauding American fighters over their bases, one of Galland's men formed what was called the Platzschutzstaffel (airfield protection squadron). Equipped with Focke Wulf Fw 190 "Dora 9s" which had excellent performance at low to medium altitudes, the Dora 9s were painted with a distinctive red/white stripped pattern on the underside of the fuselage so they could be recognized and not fired up on by the anti-aircraft artillery of JV 44's base. Each time Galland sent up 262s on an intercept mission or 262s were recovering at the base, the distinctively-marked Dora 9s were airborne. 

Ground testing the Aerojet rocket-equipped P-51D

Fighting past the the Platzschutzstaffel's combat air patrols wasn't the most ideal situation as American fighter pilots also had to deal with the AAA. With the first American jet fighters still a ways from operational employment, various methods were considered to deal with the Me 262 jet menace. One of the few concepts that did make it to the flight test stage was a rocket-boosed North American P-51D Mustang. With an approximately 100mph speed advantage over the Mustang, it was felt that a rocket booster of some sort could bring the P-51D a burst of speed that would allow it to battle the Me 262 at altitude instead of over the Luftwaffe's home fields. Tail number 44-73099 was pulled from the production line for modification with an Aerojet liquid rocket engine installed in the lower aft fuselage just behind the radiator and ahead of the tailwheel. The rocket engine used two hypergolic fuels- red fumaric acid and aniline with the fumaric acid acting as the oxidizer. Both were extremely toxic and corrosive and each was housed in a pressurized, 75-gallon tank, one under each wing and much smaller than the standard Mustang drop tank. 

With the lower aft fuselage painted with a reflective material to prevent heat damage from the rocket engine, all the pilot had to do was flip a simple off/on switch on the left side of the cockpit to activate the rocket engine. North American test pilot Bob Chilton took the modified Mustang to the air for the first time on 23 April 1945 and at 21,000 feet, he fired the rocket engine and the Mustang surged forward another 100mph. The two 75-gallon tanks were sufficient for one minute of operation. Several test flight were made, but the underwing tanks, even though smaller than the standard fuel drop tank, induced a considerable amount of drag that prevented the rocket-boosted Mustang from really getting the most out of that one minute of rocket-boosted flight. By the time the USAAF took delivery of the 44-73099, the Germans had surrendered unconditionally and the operational need for the rocket boosted Mustang faded into aviation history. 

Source: Building the P-51 Mustang: The Story of Manufacturing North American's Legendary World War II Fighter in Original Photos by Michael O'Leary. Specialty Press, 2010, p166-167. 

Boron-based High Energy Jet Fuels

In 1910, German chemist Alfred Stock began to experiment with taking hydrocarbon-based compounds (all fossil-fuels are hydrocarbon-based) and using boron as a substitute for carbon. Given that boron's nearest neighbor on the periodic table of the elements is carbon, Stock was intrigued by the possibility of using boron-based compounds. While successful in making small quantities of boron-based compounds, the process needed was tremendously expensive and yielded little product which at the time had no practical applications. However, in the 1930s, boron's potential began to emerge when it was found that boron-based materials produced a very high heat than the corresponding carbon-based compounds, making boron-based fuel worth studying. Prior to the Second World War, pentaborane and other boron-based compounds were synthesized, but again, practical applications were still lacking despite the promise as a high-energy fuel. At the end of the war, the U.S. Army organized a pilot program to produce boron hydrides (the boron counterpart to hydrocarbon compounds) in more significant quantities as a possible rocket fuel. The boron hydrides created could produce up to 30,000 BTUs/lb, compared to 18,000 BTUs/lb for comparable hydrocarbon fuel. 

General Electric opened a boron hydride research facility in Malta, New York in the early 1950s to continue the work started by Alfred Stock forty years earlier and managed to several hundred pounds of boron hydride compounds for research use. A plant in Muskogee, Oklahoma, also operated under a government contract to synthesize more boron hydride compounds and managed to produce 300,000 lbs of boron fuel. By the early 1950s the possibilities of boron fuels got the attention of jet engine manufacturers. Various high-energy fuels (HEFs) were studied like liquid hydrogen, for example, but boron fuels offered the most promise as they weighed the same and occupied the same volume as conventional jet fuels. For a given quantity of boron fuel versus conventional jet fuels, as much as 40% more energy could be produced. Because boron HEFs had such similar properties to jet fuels, they could be handled and used similarly, unlike liquid hydrogen fuels. 

GE led the way in boron HEF research in jet engines, operating a modified J79 turbojet engine at NASA's Lewis Flight Propulsion Laboratory to run on boron HEF. Calculations showed that if boron HEF were used only in the afterburners along with regular JP-class fuels, a range increase of 16% was possible. If the same aircraft were to use boron HEF exclusively, an range increase of 30% was possible. From the viewpoint of the United States Air Force, aircraft using boron HEF would have longer range and be less reliant on air refueling. In addition, 95% of the world's boron oxide was located outside of Soviet-controlled areas, with the vast majority of those boron deposits in the desert regions of California and Utah. Despite the promise it held, by 1955 the USAF had still to set up any organized study of boron HEF. 

Despite official disinterest, the US Navy's Bureau of Aeronautics did fund boron HEF studies starting in 1952 under Project ZIP in which two chemical companies were contracted to produce boron HEFs. As a result of the Navy's funding, boron HEFs began to be known as "zip fuels". One of the contractors produced a 10-boron compound called decaborane which showed the most promise. The Navy's work got the USAF's attention and decaborane would be designated HEF-3 and all research efforts focused on the use of HEF-3 with the USAF taking over direction of GE's boron fuel work. By 1957, GE reported to the USAF that HEF-3 was a feasible, but that significant technical hurdles remained given the high toxic nature of HEF-3 and the fact that boron oxide deposits were left on engine components which accelerated wear and tear of the powerplants. 

About this time both Boeing and North American were working on the WS-110A (Weapons System 110A) project which would ultimately result in the North American XB-70 Valkyrie. The stringent specifications of WS-110A called for Mach 3 speed but intercontinental range for a new supersonic bomber to replace the Boeing B-52 Stratofortress. HEF-3 became an attractive fuel option for both companies even though the USAF and the Strategic Air Command never specifically directed the use of HEF-3 as a requirement. In December 1957, North American was selected by the USAF's B-70 Program Office as the winning contractor in the WS-110A competition. The Program Office suggested that use of HEF-3 on the XB-70 would be the most economical means of getting the required 6,500 mile range. While still not requiring HEF-3 for the design, funding was made available for the modification of the intended powerplant of the XB-70 Valkyrie, the GE J93 engine, to run on HEF-3. Design work on the XB-70 at North American proceeded on the assumption that the aircraft be able to operate on both conventional JP-class fuels and HEF-3. 

Requiring the use of HEF-3 on the XB-70, however, was withheld by the Pentagon pending further evaluation of the operational advantages and disadvantages of HEF-3. While the refining of JP-class fuels was relatively simple, the production of HEF-3 required several extra steps beginning with simpler boron compounds. These extra steps added considerable cost to the price per gallon of HEF-3. Estimated of an HEF-3 facility built and operated to support one combat wing of operational B-70As resulted in a $10/gallon of HEF-3; adjusting for inflation, a gallon of HEF-3 today would cost just over $75!

Compared to the JP-4 fuel that was to be used on the XB-70 prototypes, HEF-3 produced 25,000 BTUs/lb compared to 18,000 BTUs/lb for JP-4. The spontaneous ignition temperature for HEF-3 was 2,600 degrees Fahrenheit compared to 4,550 degrees F for JP-4. While HEF-3 presented on issues when in contact with metals, there were considerable concerns about it coming into contact with non-metal parts of the Valkyrie's fuel system. In addition, HEF-3 was more toxic than cyanide, which complicated storage and handling at SAC bases. The lower flashpoint of HEF-3 meant that nitrogen inerting of the fuel tanks was a required necessity and even the smallest leaks were unacceptable. In 1958, NASA, North American, the USAF and several chemical contractors formed an HEF Guidance Committee to provide more direction to research efforts and to keep those efforts in line with the development of the B-70. At this point, the intent at North American was to create a dual-fuel bomber that used JP-4 and HEF-3, but it began to add a significant cost to the unit cost of the Valkyrie, particularly when GE's own work on the HEF-3-powered J93 engine began to fall behind schedule. Despite this, in the summer of 1959 the Strategic Air Command began making its initial budget outlays for FY1960 for HEF-3 production to support the production Valkyrie bomber. 

Dissatisfied with the progress, though, just weeks later the Pentagon canceled the HEF-3-powered J93 engine program and limited the Valkyrie program to the use of JP-4 fuel only. Testimony by USAF scientists before Congressional committees revealed that the technical hurdles and the operating cost of using HEF-3 as a jet fuel were prohibitive given the defense budget of the day. With the winding down of the HEF-3 program, the only research that remained on boron fuels lasted in the early 1960s at Edwards AFB as an additive to rocket propellant. There was, however, small consolation to the engineers and scientists involved that Soviet research efforts proved to be equally frustrating in making boron-based fuels practical. The hazardous nature of boron fuels for the most part proved to the final nail in the coffin of the research work. 

Source: Valkyrie: North American's Mach 3 Superbomber by Dennis R. Jenkins and Tony R. Landis. Specialty Press, 2008, p77-82.

Lockheed's Contribution to the Space Shuttle Program

In the 1960s as preliminary design work began on what would become the Space Shuttle, thoughts turned to ways of protecting the vehicle on its fiery re-entry into the atmosphere. The thermal protection issue was closely intertwined with what structural material to use for the spacecraft. One school of thought was based on what was used on the X-15 program- a "hot structure" that was tolerant to high temperatures. Unfortunately this meant the use of expensive and possibly rare alloys. Since the X-15 was a smaller vehicle than what was planned for what would become the Shuttle, a hot structure made more sense. But a vehicle that was much bigger in size presented cost and materials challenges with the hot structure approach. Most of the design groups involved in the early planning preferred to use a conventional-alloy structure protected by a series of metallic shingles at first, but the weight of a reusable metallic thermal protection system was daunting, to say the least.

Lockheed had the necessary breakthrough that would allow the Shuttle to have a conventional-alloy structure but have a lightweight thermal protection system. Since the late 1950s Lockheed had been working on what it called a "reusable surface insulator" (RSI) made of ceramic compounds. By 1960 the company had applied for a patent on a material made of ceramic fibers. In 1962 Lockheed had created a ceramic electro-magnetically transparent radome 32 inches in diameter for the Apollo program, but the design changed and Lockheed's radome was never used in flight. However, the experience proved valuable for Lockheed which developed a special insulator that was made of a fibrous structure filled with the spaces filled with Plexiglass compound. They called it "Lockheat" and unlike the heatshields used on spacecraft of the day which were ablative (they charred to provide protection), Lockheat's material was called evaporative- the materials slowly evaporated, creating a protective gas layer. Different types of fibers were tested such as aluminum, silica, and born. Eventually by 1965 the company's Lockheat LI-1500 settled on silica fibers. It was light at only 15 lbs per cubic foot and was completely reusuable, being able to survive repeated heating past 2,500 degrees Fahrenheit. The Air Force flew a test sample in 1968 on a re-entry test vehicle and it passed with flying colors. LI-1500 is considered the progenitor of the Space Shuttle's current thermal protection tiles.

Lockheed continued to develop the silica-based RSI but they couldn't overcome the fact that it was very brittle. It couldn't cover an entire spacecraft, it had to be applied in small tiles calculated to be about 6 x 6 inches in size. With a small gap around each tile, the vehicle structure could deform slightly without compromising the integrity of thermal protection. Since the structure under tile even the small size of 36 square inches could still deform and crack it, the tile was bonded to a felt pad which in turn was bonded to the vehicle structure. A room-temperature vulcanizing adhesive was developed to affix the pad to the tile and the tile and pad to the spacecraft.

The silica-RSI tiles, though, weren't enough protection for the nose and wing leading edges for the proposed Shuttle Orbiter as those areas got even hotter than the tiles could tolerate. To solve this problem, the prime contractor of the Shuttle, North American Rockwell, turned to LTV (Ling-Temco-Vought) which had developed a reinforced carbon-carbon (RCC) material that was to be used on the cancelled X-20 Dyna Soar program. The RCC could easily heat up to 2,700 degrees F yet keep the spacecraft structure well below the 350 degrees F limit for aluminum. The black tiles were designed to protect up to 2,300 degrees F and white tiles were used to protect areas up to 1,200 degrees F. Those areas of the Orbiter that did not heat up past 750 degrees F were protected by a special blanket material called flexible reusable surface insulation, or FRSI.

As work continued on the Shuttle Orbiters in the mid-1970s, analysis found that stiff spots in the felt pads caused by gaps between the adhesive and the tiles and/or Orbiter structure could weaken the integrity of the tiles. NASA decided on what was called a "densification" process to strengthen the felt pads and a special silica slurry was created by DuPont that was applied to the back of the tile, baked for 2 hours, then waterproofed before being bonded to the felt pad.

But there was a problem. Columbia was nearing completion when the stiff spots in the felt pads were discovered and Columbia was due to be flown from Palmdale, California, to the Kennedy Space Center. Feeling that moving the Shuttle to the KSC was symbolic and important for program morale, Columbia was moved to KSC with 6,000 tiles missing and 24,000 already-installed tiles to be removed and modified. Not all the tiles had to be removed as it turned out, but each one already installed had to be tested for weakness. For 20 months, three shifts a day, six days per week, each tile was tested, removed and modified if necessary. The remaining 6,000 tiles still had to applied. This was March 1979 and by the end of November 1980 the tedious work was completed and further preparations could continue for Columbia's maiden flight on 12 April 1981.

Source: To Reach the High Frontier- A History of US Launch Vehicles, edited by Roger D. Launius and Dennis Jenkins. The University Press of Kentucky, 2002, p382-388.

Convair's Lenticular Defense Missile: Pye Wacket

Pye Wacket high speed wind tunnel model

In 1947 researchers at Wright-Patterson AFB in Dayton began investigations into the possibility of using missiles for bomber defense as the speed of jets and the weight of gun turrets made existing systems for bomber defense impractical. General Electric was the first to receive a USAF contract to pursue such studies, but soon transferred the work to Hughes where the missile developed didn't end up on bombers but on interceptors as the Falcon missile. McDonnell was next in 1952 to try and develop a jet-vane controlled defensive missile for the Convair B-58 Hustler, but the work was canceled in 1956. By that time, however, work began on the WS-110A project that would result in the North American XB-70 Valkyrie and more contracts were issued to study what the Air Force was calling DAMS- Defense Anti-Missile Subsystem, a system that fired a stream of pellets at inbound missiles. Again, those studies ended in 1959 despite some encouraging tests.

The USAF wasn't deterred, though, starting a program in 1958 in cooperation with North American and Convair called Pye Wacket for a defensive missile for the XB-70 Valkyrie. Three basic shapes were first evaluated by North American and Convair- a standard but modified version of the AIM-47 designed for the F-108 Rapier, a cylindrical missile using jet vane directional control, and an unusual saucer-shaped missile called a "lenticular defense missile". Studies showed the lenticular design the most promising as its shape allowed it to be pointed in any direction and fired, not wasting kinetic energy on turning towards the incoming threat.

By 1959 the USAF did a considerable amount of wind tunnel work at the Arnold Engineering Development Center in Tennessee of the lenticular Pye Wacket design. It was stable all the way to Mach 6. It had a diameter of 70 inches, was 9 inches deep at its thickest portion and weighed only 510 lbs. One end of the saucer shape housed the infrared seeker and two rocket motors were on the opposite end to give the Pye Wacket a range of approximately 72 nautical miles. A set of spoilers built into the curved surfaces of the missile provide directional control.

North American began to seriously consider the Pye Wacket missile for the XB-70 Valkyrie- posts were mounted vertically in the forward section of the weapons bay and the missiles were mounted on the posts via a screw thread that ran through the center of the missile. This way the saucer-shaped missiles could be threaded on the post and stacked. Two stacks of five missiles each would fit in the Valkyrie's weapons bay. When needed, the post rotated to point the lowest missile in the stack in the direction of the inbound target. The missile was then dropped out of the bay already pointed at the target at which point the rocket motors fired.

In the summer of 1959 Convair was awarded a design contract to further study the lenticular Pye Wacket design and modified the saucer shape to incorporate a blunt trailing end where the rocket exhaust was located. This improved the supersonic drag as well as the controllability of the missile. Roll reaction thrusters were added along with small lateral vanes as well as the original spoilers used on the original design. With over 80 hours of wind tunnel testing from speeds as low as Mach 0.6 to Mach 5, sled tests then took place at Edwards AFB on a full-scale article powered by three Thiokol solid rocket motors, the same type used singly on the AIM-4 Falcon air-to-air missile.

The tests reported accelerations on the order of 60G with the ability to make sharp high-G turns at supersonic speed without loss of control. An operational version of the Pye Wacket arming the Valkyrie would be 48 inches in diameter, carry a 50 lb warhead and be capable of extreme maneuvers up to Mach 6. Convair recommended that the Air Force procure 12 missiles for continued testing, but no documentation has been found that further details work done from that point on on the lenticular defense missile.

Convair also had proposed a strike version of the Pye Wacket that would allow a bomber to easily strike targets on each side of its flight path without having to overfly enemy defenses. A version was also suggested by the company to use as a highly maneuverable re-entry warhead for ballistic missiles.

It's always been a point of curiosity to me as an aviation geek why a weapon as promising as the Pye Wacket never got developed further. Or did it? Conspiracy theorists might think the Pye Wacket was classified and modern versions of the lenticular defense missile moving at speeds unattainable by manned aircraft might account for a good portion of the UFO sightings pointing to a super-maneuverable vehicle. Considering that the basic layout was stable at hypersonic speeds, it certainly would make a very capable rapid-strike weapon.

Now if you'll excuse me, I have to go fetch my tinfoil hat.

Source: Valkyrie: North American's Mach 3 Superbomber by Dennis Jenkins and Tony Landis. Specialty Press, 2005, p220-226. Photo: NASA