The X-28A Osprey, the Most Unlikely X-Plane

In 1969 homebuilt aircraft builder and boat designer George Pereira of Sacramento, California, started work on the Osprey I homebuilt flying boat. Using his technical background in powerboat design and construction, Pereira designed the Osprey I as a high-performance STOL sea plane intended for the growing homebuilt aircraft market. With folding wings, a single-seat open cockpit and able to be transported by a boat trailer, the Osprey I was made of wood, fiberglass, and styrofoam with a Continental C90 four-cylinder 90-hp piston engine mounted on a dorsal pylon driving a fixed-pitch two-bladed propeller. With one pilot and a full load of fuel, the aircraft weighed only 900 lbs and had a top speed of 135 mph. After finishing the design and construction, Pereira had to demonstrate that the Osprey I could safely be flown during an FAA mandatory 50-flight hour restricted flying period to be completed in less than six months.

Having duly met the FAA's requirements for a kitbuilt aircraft, Pereira was approached in 1971 by three Navy officials about seeing a demonstration of the Osprey and having one of their pilots checked out in the sole prototype. Pereira and later the Navy pilot operated the aircraft successfully over a three day period from the Sacramento River at which point the Naval Air Development Center informed Pereira that they were interested in the Osprey for Project Air Skimmer, a plan to deploy a simple single engine seaplane to Southeast Asia for air policing duties. The NADC's requirement called for not just an easy to build and fly aircraft but it also had to have a reasonable performance over existing kitplanes and be able to operate from the many rivers and lakes in South Vietnam's Mekong Delta region. Plans were for local manufacturer of the Air Skimmer aircraft by the South Vietnamese and that it be easy to train pilots to fly the aircraft in VFR conditions, operate from canals as little as 25 feet wide and be transportable by trailer with a maximum weight under 1,000 lbs.

Funded as the X-28A Osprey, the single prototype and its trailer were purchased by the US Navy on 27 July 1971 to be test flown from the Delaware River at the NADC's Philadelphia Naval Base. Since the test site sat under the Class B airspace of Philadelphia International Airport and the X-28A had only minimal instrumentation, it was restricted to 300 feet maximum altitude but it was felt that this wouldn't adversely affect the evaluation process. Flight tests took place between 16 September 1971 to 22 October 1971 and the X-28A was found to be easy to fly and easy to master by pilots of limited experience.

However, with the winding down of the Vietnam War, Project Air Skimmer quietly ended with no further plans for use in Southeast Asia. Pereira, however, refined the design with a two-seat enclosed cockpit and retractable landing gear as the Osprey II. First offered in kit form in 1974, nearly 600 have been built and flown. Not only will the X-plane be one of the smallest of the X-planes, it's the only homebuilt one, not to mention the only one that can still be built today by any homebuilt enthusiast of reasonable skill.

Source: The X-Planes- X-1 to X-45 by Jay Miller. Midland Publishing, 2001, p291-293.

The VDRK Motor Compressor Engine: The Sort-of-a-Jet

As 1944 began, Soviet aeronautical experts were already filtering through information of successful flight tests of British and American jet aircraft and the impending service introduction of rocket- and jet-powered aircraft in the Luftwaffe. The Soviet GKO (State Defense Committee- a wartime organization that ran the Soviet Union during the Second World War), headed by Stalin, quickly concluded that the different efforts by engineers doing research on jet propulsion at the time needed to be consolidated under one organization, the NKAP (People's Commissariat for Aviation Industry). By March of 1944 officials of the NKAP were ready to present Stalin proposals to accelerate Soviet aeronautical technology to match that of the Luftwaffe, but most importantly to keep up with the British and the Americans. Semyon Lavochkin, Artyom Mikoyan, and Pavel Sukhoi of their respective design bureaus (called OKBs) were instructed to develop jet fighters as a matter of national security. At the time, though, jet engine technology in the Soviet Union wasn't as far advanced as that of either the Germans or the British and American teams. Both Sukhoi and Mikoyan went looking for an alternative with more technical maturity to speed the development process of their candidate designs. 

If we roll back the clock a bit to 1942, a special section within the famous aeronautical and hydrodynamics institute, TsAGI, in Moscow, was set up to explore jet propulsion. One TsAGI engineer, Ghenrikh Abramovich, had devoted time to study the use of a piston engine to drive a separate compressor that would force air into a combustion chamber like a jet engine, only the thrust from the combustion chamber was used purely for propulsion and would not be used to drive a turbine as was the case with a jet engine. Piston engine supercharger technology at the time was mature enough that work on what was called a "motor compressor engine" was simply a derivation of that work as many Allied engines used exhaust driven turbines to compress air for the supercharger to allow piston engines to operate at high power levels at higher altitudes. A motor compressor engine simply used a drive shaft to drive the compressor instead of exhaust gases. 

(I should note here that some versions of the Pratt & Whitney R-4360 Wasp Major radial engine actually had a shaft-driven supercharger inside the engine. This would later lead to the VDT (Variable Discharge Turbine) which will be the subject of a future entry on this blog.)

The intended production version of the motor compressor engine was designated the VDRK. The piston engine drove an axial compressor in the VDRK with then not only drove compressed air like a supercharger to the engine, but also served the radiators. But the air was then passed into a combustion chamber mixed with fuel and ignited, allowing the VDRK's exhaust to act as a rudimentary jet booster. Both Sukhoi and MiG design bureaus selected the Klimov VK-107 liquid-cooled inline engine which via an auxiliary gearbox, drove the VDRK booster. At 23,000 feet the VDRK not only boosted the speed of the aircraft, it also boosted the power of the Klimov engine from 1,650 hp to 2,500 hp, making it an effective supercharger as well. An air inlet below the Klimov inline engine fed the VDRK. On takeoff, 95% of the piston engine's power drive the propeller. But once at altitude, a clutch was engaged which shifted some of the power to a step-up gearbox to drive the VDRK. The main engine's radiator was directly behind the axial compressor with a small diverter duct to feed compressed air to the engine like a conventional supercharger. The air that wasn't fed into the diverter was then mixed with fuel sprayed from seven nozzles and ignited by sparkplugs. At this point in the engine, the duct expanded to form a combustion chamber made of stainless steel to withstand the heat. At the very end of the fuselage a two part eyelid-like nozzle modulated the exhaust flow like a rudimentary adjustable engine nozzle. 

In May 1944 the MiG bureau began work on their design using the Klimov/VDRK engine, the aircraft being designated I-250. The NKAP instructed MiG to have two prototypes ready for testing as high-altitude interceptors by late winter 1945. The specification called for the I-250 to be able to reach 16,400 feet in 4.5 minutes (less if not using the VDRK), a maximum speed of 502 mph (again, less if the VDRK was not engaged) and a service ceiling of 39,000 feet with the VDRK engaged. The armament was one 23mm cannon and two 12.7mm machine guns. By October the mockups were being reviewed by the NKAP and engine testing at TsAGI showed that the combustion chamber of the VDRK needed to strengthened. Given the urgencies of war, prototype construction had already started with the first flight of the I-250 on 4 April 1945 and on its third test flight, the VDRK was engaged for the first time. The second I-250 prototype was completed the following month, flying for the first time on 25 May 1945. 

However, technical issues with the VDRK booster kept popping up and in July 1945 the first I-250 was lost with its test pilot when G-limits were exceeded and the tailplane failed. By this point the NKAP had concluded that the future of fighter aircraft lay with pure jet engines, but that the I-250 project was to continue to provide an aircraft that would give pilots experience in high speed flight. Sukhoi's Su-5 design was canceled as inferior to the MiG I-250 and a pre-production batch was ordered at the end of July for ten aircraft to be delivered at end of December. Power failures, winter fuel rationing and mounting technical challenges with the construction of both the aircraft (sometimes designated MiG-13) and the Klimov/VDRK engine meant that only one aircraft was built by the deadline. As a result, Stalin had the head of the NKAP arrested and a committee formed to investigate the reasons for the delays. Numerous directors, from the aircraft factory to the engine factories involved, were severely reprimanded (I cringe to think what a Stalinist reprimand involved) and the plant manager where the VDRK was built and his quality control manager were arrested and charged with industrial sabotage. 

Despite this, another FIFTY aircraft were ordered in February 1946 and the first pre-production batch had yet to be completed let alone start State certification trials! A new deadline for July 1946 was set and when this deadline failed to be met, 24-hour shifts were imposed on all the manufacturing facilities involved in MiG-13 production. Seven airframes were completed, but the VDRK engines continued to be source of technical obstacles. It was already August 1946 when the eighth aircraft from the original ten-aircraft order first flew and it promptly suffered an engine fire. It wasn't until September of that year that the first aircraft were delivered to the Air Force for acceptance trials. 

Oddly enough, at a meeting on 29 November 1946 chaired by Stalin himself, the pure jet MiG-9 and Yak-15 would be the main jet fighters of the Soviet Air Force and with the astounding prospect of getting superior jet engines and technical assistance from Britain, there would be no future for motor compressor engines. Despite this, Stalin instructed that acceptance trials for the I-250/MiG-13 continue and that production capacity be retained. By May 1947 the acceptance trials were in full swing and the Klimov/VDRK combination was FINALLY operating at specification. Since the Soviet Air Force was no longer interested in the aircraft, the naval air arm, AVMF, was convinced to accept the aircraft as an escort fighter for torpedo bombers. State acceptance trials were to continue under AVMF auspices at Riga on the Baltic coast, but continuing reliability problems and bad weather meant that only six flights had been completed by January 1948 and the VDRK had only been engaged once, and that one time was only 1.5 minute ground run. On 3 April 1948 the I-250/MiG-13 was declared as having failed its State acceptance trials and the aircraft faded into historical obscurity. By that time, the prototype of the MiG-15 jet fighter had already taken place in December 1947, powered by a license-produced Klimov version of the Rolls-Royce Nene engine obtained openly and with the approval of the British government!

Source: OKB Mikoyan: A History of the Design Bureau and its Aircraft by Yefim Gordon and Dmitriy Komissarov. Midland Publishing, 2009, p35-39.

The Barnes Wallis Swallow

As the Second World War began to wind down, renowed British aircraft designer Barnes Wallis started investigating the challenges of supersonic flight and concluded early on that a variable geometry swing wing was the best way to accommodate the center of gravity changes in moving between the subsonic and supersonic regimes. In 1946 he wrote an engineering paper entitled "The Application of the Aerodynamic Properties to the Stabilisation and Control of Aerodynes" (quite a mouthful) in which he combined his ideas on swing wings with laminar flow studies. Starting out with small hand launched models, Barnes Wallis gradually moved up to larger versions that were launched for a catapult at 100mph. His models had slender, ovoid fuselages with swing wings mounted far to the aft and a single highly swept fin. With the end of the war, the British government was eager to regain research ground lost to the Americans and Vickers was awarded a contract of a half-million pounds to study supersonic flight. With the cancellation of the Miles M.52 supersonic research aircraft, some of Vickers' money was reallocated to Barnes Wallis' project which was given the code name Wild Goose.

The Wild Goose project ran to 1954 and it used progressively larger radio controlled models based on Barnes Wallis' designs. The later models had provisions for rocket engines in the fuselage and the RAF took notice, considering the Wild Goose design as the basis of a long range surface-to-air missile to intercept Soviet bombers before they reached UK airspace. Wild Goose ended in 1954 but the research data acquired went over to a classified project known as Green Lizard. This project called for a compact missile fired from a storable tube with flip out wings for which Barnes Wallis supersonic design work was applicable. Green Lizard was envisioned as both a surface-to-surface missile that could dispense submunitions or a surface-to-air missile powered by turbojet engines for the long range interception of Soviet bombers. It's not known exactly when the Green Lizard project was terminated, but it may have run in parallel to the Wild Goose project.

As the database on his designs grew, Barnes Wallis then moved into a manned aircraft applications of his swing-wing designs. Small aircraft builder Heston Aircraft was a subcontractor on the Wild Goose project and Wallis worked with Heston to build a small flying demonstrator designated JC.9. With a single seat, retractable tricycle undercarriage and 46 feet in length, the JC.9 was planned to fly first as a glider, then have an turbojet engine installed for powered trials. The JC.9 was then shipped in sections to the Vickers Weybridge facility for final assembly, but for reasons unknown, it remained disassembled until scrapped.

By 1954 Barnes Wallis began thinking even bigger, adapting his unique swing wing design to a supersonic intercontinental range aircraft. The RAF had issued OR.330 (Operational Requirement 330) that called for high flying supersonic bomber/reconnaissance aircraft. Although not responsible for Vickers' submission for OR.330, Wallis adapted his design to meet the stringent requirements, coming up with a sleek arrowhead shaped tailless aircraft with slender swing wings pivoted at the aft end of the fuselage. Pod-mounted engines pivoted on the tips of the swing wings and also provided some directional control. Calling his revolutionary design the Swallow, small scale models were tested in Vickers' wind tunnels with encouraging results. Scale flying models of the Swallow powered by rocket engines easily attained Mach 2.5 in flight tests. While the Swallow wasn't selected for OR.330, the RAF was sufficiently interested to continue funding Wallis' work towards a scaled-down flying demonstrator called the Research Swallow that could be readily adapted for military roles. Versions of the Research Swallow were submitted to the RAF and Royal Navy as a supersonic strike fighter.

The most impressive would have been the bomber version of the Swallow and a supersonic military transport. The Swallow bomber would have been approximately the size of the B-1 bomber with 4-5 crew, a cruising speed of Mach 2 and a range of 5,000 miles carrying a single Red Beard nuclear bomb. The military transport was even larger with a civilian airliner version that could have carried 60 passengers between the UK and Australia nonstop. Development work on the bomber and transport versions of the Swallow was estimated at 10 years, but the infamous 1957 Defence White Paper of Duncan Sandys that stated the era of manned military aircraft was being eclipsed by missiles ended funding for the Swallow.

As consolation, Barnes Wallis was allowed to meet with the American Mutual Weapons Development Program to see if the United States was interested in his extensive work. Exchange visits were conducted between Wallis' facility at Vickers and Wallis himself led several teams to the United States to meet with NASA's Langley research facility. A six month joint UK-US development program was conducted at NASA Langley to further refine Wallis' work. By June 1959, NASA's extensive testing uncovered pitch up problems in certain flight regimes as well as higher than expected drag. This effectively killed off the Swallow as an aircraft design, but NASA found the body of work still applicable to a more conventional tailed swing design. This design would eventually evolve into the world's first production swing-wing combat aircraft, the General Dynamics F-111 Aardvark.

Source: Secret Projects: Flying Wings and Tailless Aircraft by Bill Rose. Midland Publishing/Ian Allan, 2010, p27-31.

ACE- The Aviation Combat Element, the Air Wing of the Amphibious Assault Carrier

The helicopter amphibious assault ships of the US Navy that transport Marine Expeditionary Units (MEUs) are often called the "big deck amphibs" as their size approaches that of the the aircraft carriers of previous generations. In fact, the latest class of assault carriers, the Wasp-class LHDs, are much larger than the Royal Navy's Invincible-class Harrier carriers and closer in size to ships like the old French aircraft carriers FNS Clemenceau and FNS Foch (size comparison here) Like a supercarrier, the assault carriers have their own air wing embarked with the Marine Corps calls an Air Combat Element or Aviation Combat Element (ACE). But there the difference ends. But let's back up a bit and talk about the MEU and how the ACE fits into the MEU.

Think of an MEU as miniature Marine Corps composed of approximately 2,300 personnel. The MEU is the basic deployable unit of a Marine Air Ground Task Force that integrates the soldiers, artillery, tanks, aircraft and logistcal support to conduct anything from combat operations to humanitarian relief efforts worldwide. There are four "elements" in an MEU- the Aviation Combat Element, the Ground Combat Element, the Command Element, and the Logistics Combat Element. The Ground Combat Element or GCE is centered around an 800-man infantry battalion to which are attached armor, artillery and transport to become a Battalion Landing Team. The Logistics Combat Element or LCE is in charge of keeping the MEU supplied while the Command Element or CE is obviously to run the whole show. The USMC has seven MEUs- three on the US East Coast, three on the US West Coast and one forward-deployed in Japan.

Back to the Aviation Combat Element, or ACE. The ACE is the MEU's air wing. The nucleus of the ACE is either a medium helicopter squadron (HMM) operating Boeing Vertol CH-46 Sea Knights or medium tilt-rotor squadron (VMM) operating the Bell/Boeing MV-22 Osprey. The VMM and HMM squadrons are set up so that other units can be attached to them to form the ACE. The VMM and HMM squadrons form the nucleus as they are the largest squadron in the ACE and have the most personnel and equipment. A normal VMM or HMM squadron might have 200 personnel, but when other units are attached to it like AV-8B Harrier IIs or other helicopter assets, it grows to over 500 personnel and becomes a "reinforced squadron". So for example, VMM-263 is a tilt-rotor squadron flying Ospreys. When the squadron goes to sea as part of an ACE, it becomes "reinforced" and is designated VMM-263 (REIN).

But what is unique about a Marine Corps ACE is that the attached units, whether they're fixed wing Harrier IIs, Super Cobra gunships or heavy lift CH-53Es, all take on the VMM or HMM's squadron identity and tail codes when deployed. So you might have six AV-8B Harrier IIs from VMA-223 that take on the identiy of VMM-263 if that's the squadron they get attached to in an ACE.

Unlike a US Navy supercarrier, the ACE units all have one ready room. The diverse units attached to the nucleus VMM or HMM squadron all brief and train together as a team. Everyone even wears the squadron patches of the VMM or HMM squadron they're attached to. And if necessary, an ACE can even have land-based KC-130 Hercules tankers attached to it, but the tankers operate from nearby land bases. This gives the MEU its own mini-air force that can conduct assault support, offensive air support, aerial reconnaissance, command and control, anti-air warfare, and electronic warfare (the six functions of Marine Corps aviation).

Every six to seven months an MEU goes out on deployment approximately one month after another MEU returns. Prior to entering the area of responsibility, the entire MEU, and in particular the ACE, have to train together to prepare for deployment. The first step is to get all the pilots of the ACE up to speed on shipboard operations as part of the reinforced VMM/HMM squadron. Then RUT, Realistic Urban Training, is carried out at the Indiana National Guard's Muscatatuck Urban Center. From there, the MEU goes back to sea for what is called a COMPTUEX, Composite Training Exercise that irons out any kinks between the Marine Corps units and the US Navy vessels of the fleet. The final exercise before deployment is the CERTEX, Certification Exercise which is the culmination of a 6-month long work up period. Once the CERTEX has been passed, the MEU and its associated ACE can go to sea as part of an Amphibious Ready Group composed of three amphibious assault ships, with the ACE based on the big deck amphib.

Source: Combat Aircraft Monthly, June 2010, Vol. 11, No. 6. "USS Nassau Air Combat Element" by Gert Kromhout, p56-59.

The Convair Model 6: A Jumbo Before Its Time

People sometimes ask me how I decide what to feature on Aviation Trivia of the Day. I'd say that the majority of the time it's something I've come across as I'm reading one of my aviation-related books. I'm one of those sub-clinical attention-deficit types who can't finish one book before starting another. I'll quite literally have quite a handful of books that I'm rotating through at any given moment. If I run across an interesting bit that I want to feature sometime in this blog, I'll make a small dog ear at the bottom corner of the page. So yeah, I have lots of books with lots of those little lower corner dog ears. But sometimes it can come from more unconventional directions.

I'm on Twitter as @SentinelChicken and the other day I was exchanging tweets with a fellow avgeek, @flyingwithfish who has a great blog here (Flying With Fish: The Blog for Those Who Fly & Those Who Want to Fly Smarter) about an entry he had on his blog regarding double-deck jets that came before the Airbus A380. His blog entry discusses the McDonnell Douglas MD-12 and I had tweeted to him about the Convair design that combined the fuselage of the production version of the XC-99 transport with the wings, jet engines and empennage of the YB-60 which was designated the Convair Model 6. He's going to be doing a write up in his blog on my artwork, so it wanted to return the favor the best I could be crediting him with giving me the idea for today's entry.

But before I can talk about the Convair Model 6, I have to jump back a bit and talk about both the XC-99 and the YB-60 as they're both derivatives of the B-36 Peacemaker. Convair's work on the B-36 began in the midst of the Second World War as there was a concern that Great Britain would fall to the Reich and we would need strategic bombers that could reach Europe from the United States. But in parallel to the development of the B-36 there were design efforts that looked at passenger versions of the B-36. As early as May 1942 Convair had been looking at a transport version of the B-36 called the Model 37 that combined the wing, six pusher piston engines and empennage of the B-36 to a new fuselage unit. In December 1942 the USAAF signed a contract with Convair to build a single example of what was designated the XC-99 on the stipulation that the XC-99 would not divert resources from the B-36 project. Convair saw the XC-99 as a way to validate some of the design concepts of the B-36 quickly as it would not need military equipment (what's called government-furnished equipment) for the transport role.

Despite the ongoing war, Convair pitched the XC-99 as a passenger transport to the airlines, even succeeding in getting 15 orders from Pan American World Airways for what the airline was calling the "Super Clipper". Production was to begin at the end of the war and the Convair Super Clipper would have carried 204 passengers in luxury across the Atlantic.

As the B-36 was built in Fort Worth, the XC-99 would have to be built at Convair's San Diego Lindbergh Field facility. The wings and empennage were shipped to San Diego from Fort Worth and on 23 November 1947 the XC-99 made its first flight. The XB-36, by comparison, made its first flight in Fort Worth on 8 August 1945. By January 1949 the XC-99 was retrofitted with four-wheel main bogies that allowed it to use any airfield in the United States and abroad that could accommodate the production B-36. The following year it got fitted with production standard Pratt & Whitney R-4360 radial engines that were more powerful than the earlier version installed.

In its 1950 incarnation, the XC-99 could carry over 100,000 lbs of cargo or 400 fully-equipped troops, or 300 litter patients on a double deck layout. Based at Kelly AFB and operated by the San Antonio Air Materiel Depot, the XC-99 flew on operational transport missions in the United States for several years before being retired. A production version of the XC-99 proposed by Convair would have moved the flight deck to a B-36 "bubble" atop the fuselage with the nose gear installed in a bulge under the nose (similar to what you see on the Lockheed C-5 Galaxy). Moving the flight deck upward to the top deck allowed straight through loading via aft clamshell doors and a ramp and nose doors and a ramp, a feature that the USAF didn't have at the time in its transport aircraft. This production version would have had a range of 3,800 miles with a full payload. The USAF, however, decided on the Boeing C-97/KC-97 Stratofreighter and the Douglas C-124 Globemaster II for its long distance heavy airlift needs, both aircraft that paled in performance of the proposed production version of the XC-99.

Now the YB-60 is often seen as the competitor to the Boeing B-52 Stratofortress on account of having the same eight engines in the same four paired nacelles, but the USAF never conducted a true competition for the role filled by the Boeing B-52, though Douglas and Convair did work on designs to fill that role even though Boeing was set to build the replacement for the Convair B-36. In August 1950, Convair submitted an unsolicited proposal for a jet-powered, swept-wing version of the B-36 Peacemaker. As Convair intended to use many B-36 components, the USAF was sufficiently interested to order two YB-60s (the original designation being B-36G). Using many of the structural components of the B-36F, construction of the first YB-60 began in Fort Worth in the spring of 1951 and it made its first flight on 18 April 1952, only three days after the first flight of the Boeing YB-52 Stratofortress.

Although there was no formal competition between the YB-60 and the YB-52, it was quite obvious that by using B-36 components, the YB-60 was significantly cheaper than the Stratofortress. But as the Stratofortress was designed from the outset as high-speed jet intercontinental jet bomber, its performance blew the YB-60 away. The YB-52 was 100mph faster (the thick B-36-based wing of the YB-60 was one of its biggest liabilities) and it had more refined aerodynamics as the YB-60 flight test program turned up multiple stability and control deficiencies. As a result, after only 66 flight hours the USAF canceled the YB-60 program with the second YB-60 being 95% complete.

So here's where the XC-99 and the YB-60 meet. Given the parallel design efforts taking place with several key personnel in common, it was inevitable that Convair would propose an all-jet version of the C-99 production version transport. First proposed in 1950, the jet-powered C-99 combined the swept-wings and eight jet engines in paired nacelles and swept empennage of the YB-60 with the production version fuselage of the C-99. It would have been an impressive transport with both nose and aft loading cargo doors, a double deck with the upper deck being pressurized and it jet form. And this was in the early 1950s- the USAF didn't have intercontinental jet cargo capability until the first flight of the Lockheed C-141A in December 1963 and while the Starlifter would have been faster than the Convair Model 6 jet transport, it didn't have the immense load capacity, being only able to carry about 70,000 lbs compared to 100,000 lbs of the Convair Model 6. And it wouldn't be until the first flight of the Lockheed C-5A Galaxy in June 1968 that the USAF had a double deck jet transport with straight through loading via the nose and tail! The Galaxy showed the march of technological progress by being able to carry over two and a half times the payload of the Convair Model 6 at higher speeds and farther distances.

But considering the technology of the day, the Convair Model 6 wasn't out of reach as it used components from both the XC-99 and the YB-60 that were already flight proven.

Source: Cold War Peacemaker: The Story of Cowtown and the Convair B-36 by Don Pyeatt and Dennis R. Jenkins. Specialty Press, 2010, p176-191.

The Turboprop B-17 Flying Fortress

In the late-1950s, many of the surplus Boeing B-17 Flying Fortresses that were used by the Navy, Air Force, and Coast Guard in the air-sea rescue role found their way into the hands of several civilian fire bomber operations that for the first time along with surplus Consolidated PB4Y-2 Privateers, offered a quantum leap in performance with the ability to carry significant loads of fire retardant. In fact, prior to the arrival of the B-17s and PB4Y-2s, no other civilian fire bomber then in use even remotely approached the fire retardant capacity of the converted four-engined bombers. In 1960, the first of about two dozen B-17s were converted with bomb bay tanks for aerial delivery of fire retardants.

The bomb bays were fitted with tanks that could carry 2,000 lbs of retardant. The tank was then subdivided into four compartments, each compartment having its own quick-opening door to empty that tank on a forest fire target. The converted B-17s were based on the -F and -G variants primarily (the USAF's air-sea rescue SB-17G, for example). Stripped of all non-essential equipment, the B-17 offered a significant increase in power in the typical-high altitude areas that most forest fires were found. Most of the conversions flew on contracts with the US Forest Service.

However, by the late-1960s many of the fire bomber B-17s were retired from service as aircraft like the Douglas DC-6 and ex-military Douglas C-54s were converted for the role. In addition, the Wright R-1820 Cyclone radial engines of the B-17s were becoming increasingly difficult to support with spare parts. One enterprising outfit got around this issue by re-engining their B-17 fire bomber with four Rolls-Royce Dart turboprops that once belonged to Vickers Viscount. As the Dart engines were much lighter than the Wright Cyclone radials, the nacelles had to be extended far forward to maintain the center of gravity with the propeller spinners being nearly in line with the nose of the B-17. Only one B-17, N1304N, was converted in 1970. Some sources indicate that the aircraft had the nickname "Batmobile" and she was so overpowered, that with both outboard engines shut down and feathered, she was still faster than a stock B-17 and this was while carrying a full load of fire retardant. When the pilots made their drop, they had to shut down and feather the outboard engines to keep from overspeeding the airframe.

This unique and one-of-a-kind B-17 Flying Fortress was unfortunately lost in the same year it was converted. While fighting a forest fire near Dubois, Wyoming, the engines lost power due to excessive ingestion of heated air and smoke from the fire and the aircraft failed to pull out of a retardant drop.

Source: Boeing B-17 Flying Fortress (Warbird Tech No. 7) by Frederick A. Johnsen. Specialty Press, 2002, p97-99.

The L-1000: Lockheed's Own Jet Engine

Probably one of the most obscure yet fascinating episodes in the history of jet engine development stemmed from Lockheed's innovative jet-powered L-133 fighter design that was submitted to the USAAF in March 1942. While the fighter design boasted advanced features like a canard and a blended wing-body, the Army Air Forces were more interested in the proposed engines of the L-133 which were to be two axial-flow jet engines designed by Lockheed itself designated L-1000. The engine had a multi-stage turbine to increase compression which translated into a greater thrust output. At a meeting at Wright Field in Dayton (where the USAAF's Power Plant Laboratory was located) in August 1942, military researchers and Lockheed engineers reviewed the L-1000's design- it was only 24 inches in diameter, 139 inches long, and weighed 1,235 lbs. Lockheed estimated that at full takeoff thrust, the L-1000 could develop 6,700 lbs of thrust. Despite the reservations of the Power Plant Laboratory, they felt there were enough features in Lockheed's jet engine that had potential that made it worth funding further development.

By comparison, that same year General Electric was working on their version of Frank Whittle's British W.1X centrifugal flow engine. GE first ran their I-A (which would later be designated the J31) on 18 April 1942, making it the first jet engine to operate in the US. It was 41.5 inches in diameter, 72 inches long, and weighed 865 lbs. At full thrust it developed only 1,250 lbs of thrust. At the time, Allied jet development had been focused primarily on centrifugal flow jets as that was the what was furthest along in terms of engineering and development compared to axial flow jets. The only other axial flow jet in development in 1942 was the Junkers Jumo 004 in Germany. It was already at the flight hardware stage that year and it was 152 inches long, 32 inches in diameter, weighed approximately 1,600 lbs and the early versions then being tested developed just under 2,000 lbs of thrust.

By comparison to the working jet engines of the day, the Lockheed L-1000 engine would have been quite a leap in performance in an axial flow engine that was smaller than the Jumo 004. Despite the potential, some officials in the USAAF were less than pleased with the idea of an airframe manufacturer developing its own jet engine, even though Northrop at the time was working on its own Turbodyne turboprop engine for its flying wing bomber designs. It was felt that airframe manufacturers lacked the expertise and facilities for the development, testing and production of jet engines.

Regardless of the objections of some officials in the USAAF, a contract was finally signed with Lockheed for good (there had been some dispute over intellectual property rights) on 31 July 1944 for approximately $1.2 million. A year later, Lockheed requested a one year extension as the pressures of wartime production had left it without sufficient engineering resources to devote to the L-1000, just as some in the military had predicted a few years earlier. As a result, Lockheed subcontracted 60% of the project to the Menasco Manufacturing Company. The Army acquiesced to this arrangement as long as Lockheed remained ultimately responsible for the engine. Menasco was allowed to manufacture the engine but under Lockheed's own engine patents. In the summer of 1946, the USAAF appropriated an additional $1.9 million to the L-1000 project by which time it would receive the designation J37. Lockheed assured the USAAF that production could begin as early as 1947.

Initial delays were due to manufacturing pressures at Menasco which was providing high-precision parts to the aircraft manufacturers of Southern California including Douglas, Convair, as well as Lockheed for the war effort. But with the cancellation of a good number of military production contracts with the Japanese surrender, Menasco was able to devote additional resources to the J37 project. Despite this, however, progress remained slow with the USAAF steadily losing patience with Lockheed. In late 1946, the J37 project was handed off to Wright Aeronautical Corporation, but by that time, Wright was more interested in its own developments and the GE/Allison J33 engine that was developed from Whittle's designs was a proven and mature powerplant already powering the Lockheed P-80 (later redesignated F-80) Shooting Star fighter.

The GE/Allison J35 engine would be the first axial-flow jet engine for the USAF and it had already made its first flight powering the Republic P-84/F-84 Thunderjet in February 1946 and would eclipse the centrifugal flow J33 engine in its performance. And even more powerful and successful development of the J35 was already being tested that year, the J47 engine. Lockheed quietly abandoned its efforts in developing a powerplant and all that exists of the L-1000 today is a mockup at the Planes of Fame Museum in Chino, California.

Source: Experimental & Prototype U.S. Air Force Jet Fighters by Dennis R. Jenkins and Tony R. Landis. Specialty Press, 2008, pXI, 21-23.

Trans World Airlines' Executive Transport B-17 Flying Fortress

Although in excess of 25 different versions of the Boeing B-17 Flying Fortress had flown since its first flight prior to the start of the Second World War, one of the most unique versions would have to be the only B-17 to be operated by US major airline after the war ended. During the war, many US airlines contributed to the war effort by training pilots, carrying priority passengers and delivering cargo to far-flung destinations well beyond their traditional domestic route networks. Immediately following the Japanese surrender in 1945, the airlines began the process of gearing up for normal civilian operations as rapid demobilization was the order of the day. One of those airlines was TWA, at the time was still known as Transcontinental & Western Airlines but would soon rename itself as Trans World Airlines.

During the war, TWA's five Boeing 307 Stratoliners were put into military service as transports starting in 1942. When they were returned to the airline in 1945, however, they had been heavily used with an untold number of flight hours and for what TWA wanted to do next, the "used" Stratoliners weren't up to the job. In 1946 TWA president Jack Frye and several of his deputies visited one of the RFC (Reconstruction Finance Corporation) depots at Altus AAF in Oklahoma to buy a low-time B-17G Flying Fortress. Several hundred stored B-17Gs were reviewed and their log books inspected. A Vega-built B-17G, 44-85728, was selected as it had very few flight hours on it. In fact, after it was built by Lockheed Vega and delivered to the US Army Air Forces in Burbank, California, it was flown directly into storage.

The sale was finalized on 26 June 1946 and the B-17G was assigned a civilian ferry registration of NX4600 for the flight to Boeing Field in Seattle where it would get conversion work for the role for TWA's mission. Jack Frye also made sure to make the arrangements for TWA to be the owner of a Limited Type Certificate for the B-17. In late 1946 the US Civil Aeronautics Board made these special LTCs available for certain surplus military aircraft that could be sold to civilian owners with the provisions that they not be used for carrying fare-paying passengers or revenue cargo- this restriction was a concession to the aircraft industry which feared that large numbers of surplus aircraft would hurt postwar sales of civilian designs. Most of the LTCs used in the postwar period were used to convert medium bombers into either forest fire-fighting water bombers or executive conversions that were common with the Douglas A-26 Invader and North American B-25 Mitchell.

At Boeing Field, TWA's B-17G was quite literally taken apart as all the military items were removed and extensive soundproofing and comfortable cabin appointments were installed. Additional windows were installed in the fuselage and upgraded avionics, engines, and propellers were installed. Boeing's designation for the B-17 was Model 299 and all the variants had a letter suffix. Since Boeing had already reached the designation Model 299Z, TWA's custom converted B-17G became the Model 299AB. With basic TWA markings and the tail number NL1B, the airline's B-17 would be used for long-range proving flights on prospective routes.

On 11 February 1946 the United States and the United Kingdom signed the Bermuda agreement that governed bilateral air services between the two nations (this would subsequently be reinforced with the Bermuda II agreement in 1977 which was only recently superseded by the Open Skies agreement with the EU just a few years ago). The British were well aware that the United States was on the cusp of domination in of the world's airline industry and the Bermuda agreement restricted US competition in the trans-Atlantic market between the two nations. While TWA and its rival Pan American came out ahead of other US airlines in the Bermuda agreement, Jack Frye wanted to use the B-17 for route proving to find ways of circumventing the Bermuda treaty.

TWA's officials set out on the flights in the newly-converted B-17 and brokered technical and financial agreements with airlines worldwide such as Saudia, Linee Aeree Italiane, Trans-Mediterranian Airways, Ethiopian Airways, and Iran Air. TWA would invest in these airlines and others in exchange for the airlines getting training and maintenance agreements with TWA. In the case of Iran Air, the airline invested in 10% of the Iranian airline and also got a five-year contract to manage Iran Air. On April 1947, TWA's luxuriously appointed B-17 was presented to the Shah of Iran as "deal sweetener" and re-registered as EP-HIM and flown by TWA crews.

Two years later a restructuring of Iran Air led to the TWA contact being nullified and in 1952 the B-17 was sold to the IGN (Institute Geographique National) as F-BGOE for scientific and global mapping survey flights. The IGN used the B-17 until about 1967 and it was scrapped 1972, ending the story of one of the most unique of B-17 Flying Fortresses.

Source: Aeroplane Monthly, June 2010, Volume 38, Number 6. "The Flying Fortress Airliner: The Original Stratofortress?" by Marshall Wainwright, p56-59.

The Story of "5 Grand", the 5,000th B-17 Flying Fortress Built

To boost morale on the home front during the Second World War, aircraft manufacturers celebrated production aircraft milestones. Lockheed, for example, painted the 5,000th P-38 Lightning red and named it "YIPEE". But Boeing wanted to do something different as it approached the 5,000 B-17 Flying Fortress to be built since the attack on Pearl Harbor when the US entered the war against the Axis. Aircraft number 40-37716, a B-17G, was that aircraft and early on it was marked with a notice on the fuselage that it was the 5,000th Flying Fortress to be built since the US entry into the war. Every worker who played a part in the construction of this particular aircraft was invited to sign the aircraft as it advanced down the production line in Seattle.

It celebrated the efforts of the thousands of workers who emigrated to Seattle to escape the effects of the Great Depression and work on Boeing's massive production facilities. The enthusiasm that workers applied their signatures even surprised the Boeing management as even parts from the subcontractors bound for 40-37716 were even signed, even though they'd be hidden away deep inside the aircraft. Appropriately, the B-17G was named "5 Grand" and before leaving the Renton plant was already being celebrated in newsreels and war bond drives. Instead of towing the B-17G out as had always been the protocol of the day upon completion, the workers themselves pushed 5 Grand out the factory doors to great fanfare.

In May 1944 5 Grand was officially delivered to the US Army Air Forces at Boeing Field and a bottle of champagne was ceremonially broken over the aircraft's nose. The USAAF even made sure that the crew assigned to 5 Grand were made up of locals from the Puget Sound area with Edward C. Unger of Seattle selected as the aircraft commander/pilot. 5 Grand was then flown to Kearney AAF depot in Nebraska for further modifications to make her combat ready. When she left the United States for the Eighth Air Force's bomber bases in Britain, over 35,000 signatures adorned the baremetal finish of 5 Grand. Some thought that the plane should be stripped as the Luftwaffe might make special effort to shoot down 5 Grand, but it was decided the signatures would stay in place. On the trans-Atlantic flight, the crew found the B-17G was about 7 mph slower than a stock B-17G due to the weight of the ink and paint used on the signatures and the surface roughness from some of the more colorful applications! The fuel consumption was higher and stronger-than-forecast winds aloft resulted in one of 5 Grand's engines cutting out on landing in the UK due to fuel starvation.

Assigned to the 333rd Bomber Squadron of the 96th Bomber Group at Snetterton Heath in Norfolk, one of its first local flights before combat missions were flown ended in near disaster when the electrical system failed and 5 Grand made a crash landing after ejecting its ball turret. She was repaired and reassigned to the 388th Bomber Group and would fly 78 missions over the Reich adorned with her signatures with her gunners claiming two Luftwaffe fighters destroyed.

On 14 June 1945 5 Grand returned home to the United States, first landing at Bradley Field in Connecticut before continuing on to Boeing Field in Seattle for refurbishment to go on a war bond tour. While in Seattle, many employees found their signatures still in place. Local officials wanted to preserve 5 Grand as a memorial to the city's home front war effort, but while the Seattle politicians debated the cost, 5 Grand was flown to Lubbock AAF in Texas for further repairs and refurbishment before being flown into storage at Kingman AAF in Arizona to be held in storage while Seattle officials decided how to proceed on the planned memorial incorporating 5 Grand. The US Army Air Forces were willing to donate 5 Grand to Seattle for the memorial planned by the Seattle Historical Society, but on 3 January 1946, Seattle city officials declined the donation of 5 Grand on the grounds that building a memorial with the aircraft represented too costly an endeavor.

Despite the efforts of Boeing employees who had signed 5 Grand, no one in the local government wished to take responsibility and the aircraft, still resplendent with its signatures, was sold off by the Reconstruction Finance Corporation to the scrapper where 5 Grand was unceremoniously broken up and molten down, forever lost to history.

Source: Aeroplane Monthly, June 2010, Volume 38, Number 6. "A Fort Named 5 Grand" by Howard Carter, p40-45.

The Tupolev Tu-114's First Visit to America

At the 1955 superpower summit in Geneva, Soviet premier Khrushchev found himself embarrassed when President Eisenhower and the American delegation arrived in four-engined propliners and he arrived in a small twin-engine Ilyushin Il-14 transport. Always the showman on the international stage and determined not to be shown up again by the Americans, Khrushchev decided to fly to the United States for his historic 1959 visit in the large Tupolev Tu-114.

Soviet planners, however, were not thrilled at the prospect as 80% of the trip between Moscow and Washington would be overwater and as Aeroflot, the operator of the Tu-114, had rarely conducted trans-oceanic flights at the time, lacked training with ditching techniques, survival at sea and use of life rafts and life jackets. The politburo of the Communist Party as well as the KGB urged Khrushchev to reconsider but he was resolute in making a "grand entrance" on the first visit of a Soviet leader to the United States. The Soviet Navy stationed ships every 200 miles along the route should the airliner have to ditch and the KGB even built a mockup fuselage and tested it in a large swimming pool in Moscow to test out water evacuation scenarios.

The flight went off without a hitch and the aircraft itself was quite the superstar when it landed at Andrews AFB. Eisenhower had offered Khrushchev a helicopter tour of the capital, but he refused as he feared a plot to throw him to his death from the helicopter. It was only after Eisenhower assured him he would be on the same helicopter than he agreed.

After his landmark tour of the United States, on the return flight to Moscow, the Aeroflot Tu-114 encountered a storm near Greenland and St. Elmo's fire danced all over the airframe as the plane temporarily lost contact with Moscow. Khrushchev was sleeping and not awoken during the storm, but the crew feared that loss of contact might cause anxiety in Moscow and fears of a US plot. Fortunately, the large airliner landed safely in Moscow and another unreported tense moment in the Cold War passed into history.


Source: Air Force One: The Aircraft that Shaped the Modern Presidency by Von Hardesty. Northwood/Tehabi, 2005, p60-65.

Selling the Skyhawk to Israel and a Watershed Change in American Foreign Policy

For a better part of the 1950s and 1960s Israel relied on France as its main combat aircraft supplier with the IDF/AF having flown the Dassault Ouragan, Mystere, Super Mystere and Mirage III as well as the Sud-Aviation Vautour in the strike role. But reliance on a single nation for arms worried Israel's government and by the late-1950s increasingly advanced Soviet designs were being purchased by Arab client states and the general perception in the world market was that French designs were falling behind the designs coming from the Americans and Russians. American concerns about growing Soviet influence in the Middle East created an opportunity for Israel to finally get access to American combat aircraft that had previous proven elusive due to diplomatic concerns.

In 1965 Jordan began to finalize purchase of MiG-21s from the Soviet Union, and as a moderate Arab state that had enjoyed decent relations with the United States, found that the Royal Jordanian Air Force would have access to US fighters in an effort to swing Jordan out of the Soviet sphere of influence. The United States offered to sell Jordan the Lockheed F-104 Starfighter and the administration of Lyndon B. Johnson asked the Israelis to not oppose the sale. Israel, sensing a chance to modernize the IDF/AF, stipulated that it would not oppose the sale as long as a similar class of aircraft were sold to Israel.

Throughout the spring of 1965 diplomats from both the United States and Israel met to negotiate a formula that would allow the sale of American arms to Israel provided that the Jordanian deal be allowed to proceed without objections. President Johnson, however, attached the condition that American aircraft would only be sold if comparable types were not available from European nations. The Israelis touched upon their operational requirements during negotiations and insisted upon 75 aircraft as part of the US commitment. Initially the Douglas B-66 Destroyer was offered, but it was quickly agreed to let the IDF/AF experts handle the specifics. Israel's military requirement was for two classes of aircraft, one in the heavy attack class to replace the Vautour and Super Mystere and a light attack class for a replacement of the Mystere and Ouragan. The French duly offered a proposed new version of the Vautour called the Super Vautour and the proposed Mirage F2, but both would not be available by 1970 at the earliest which wasn't acceptable to the IDF/AF. The Dassault Mirage IV was also mooted for an associated reconnaissance requirement, but it didn't fit the scope of the Israeli need. That left primarily American designs in the running.

At the 1965 Paris Air Show, the IDF/AF Chief of Staff, Ezer Weizman, and Yossi Sarig, a former Vautour squadron commander and head of the IDF/AF's operational planning, visited the Dassault chalet for a presentation on the Jaguar as a possible candidate for the light attack requirement. Halfway in the presentation, Sarig whispered to Weizman that the Jaguar would not meet the baseline mission profiles the IDF requested, so Weizman ended the presentation prematurely and walked out with the Dassault delegation angry. He went straight to the chalet of Douglas Aircraft and made arrangements for presentation later that day on the A-4 Skyhawk.

The IDF/AF (Heyl Ha'Avir) called its procurement program Plan Samuel, which called for 30 heavy attack aircraft and 120 light attack aircraft. The aforementioned Douglas B-66 Destroyer was rejected for the heavy attack requirement and the McDonnell F-4 Phantom II, Grumman A-6 Intruder and Vought A-7 Corsair were settled upon as the candidates. The light attack candidates were the Douglas A-4 Skyhawk, the Northrop F-5 Freedom Fighter, and the North American F-100 Super Sabre. Plan Samuel was presented to a joint State Department and Defense Department group in Washington in October 1965 and the reaction by the Americans was quite negative. Too many aircraft were being asked for and it was felt that the Israelis hadn't exhausted their European options yet. Believing that the American option was out, Israel nonetheless found itself engaged in backroom diplomacy as President Johnson wished to honor its commitment to supply Israel with arms given that they had not blocked the F-104 sale to Jordan.

As a result in February 1966 US officials gave Israel their best possible offer which was for 48 aircraft that had to be the least capable of the types that had been short-listed for Plan Samuel. The contracts for the purchase of the Douglas A-4 Skyhawk was signed on 18 March 1966 but was kept secret with the code name Operation Rugby in order to allow arms sales to both Jordan and Saudi Arabia to proceed. Israel had stipulated its own modifications for the A-4 Skyhawk while the United States insisted upon the deletion of specific advanced features like the bombing computers, radar warning systems and AGM-45 Shrike anti-radar missile launch capability. The combination of Israeli requirements and American conditions for a downgraded Skyhawk resulted in a new variant, the A-4H Skyhawk, the last of which was delivered in late 1968.

The purchase of the A-4 Skyhawk represented not just a fundamental change in Israeli defense policy, but it also represented a significant change US defense and foreign policy in the Middle East which up to that point had been one of primarily non-engagement. Spurred on by Soviet inroads and the creation of client states in Syria, Egypt, and Iraq, American foreign policy forever changed in the Mideast with the sale of those Skyhawks to the IDF/AF in the late 1960s.


Source: Israeil A-4 Skyhawk Units in Combat (Combat Aircraft series, No. 81) by Shlomo Aloni. Osprey Publishing, 2009, p-6-16.

The Lockheed CL-1201 Flying Aircraft Carrier

In aviation, those who dare to dream are either visionaries or insane. The long road of aviation history is filled with dead-end side roads of designs that simply boggle the mind. Those designs aren't just limited to fanciful thinking by eccentrics, either. Lockheed in the late 1960s devoted a surprising amount of effort to one of my favorite designs that most certainly falls into the "YGBSM" category ("You Gotta Be Sh*tting Me"- the unofficial motto of the USAF Wild Weasels, allegedly what was said by the pilots and WSOs who attended the first briefing on what was then a secret project). At the time Lockheed's Skunk Works had been looking at the feasibility of building an ultra-large transport for the US military and heading into the early 1970s the design evovled into the CL-1201 tailless aircraft that would have been for lack of a better description, a flying aircraft carrier.

The CL-1201 would have weighed in at a massive 5,265 tons with a wingspan of 1,120 feet and a fuselage length of 560 feet (about 2.5 times the length of a Boeing 747) and would have stood 153 feet high. Four massive turbofans would have provided a total thrust of 500,000 lbs. At altitudes below 16,000 feet, the engines would run on standard JP-5 fuel but once at cruise altitude, the engines would switch over to nuclear power, a single nuclear reactor aboard using liquid sodium metal as a cooling medium would transfer energy via heat exchangers to a non-radioactive secondary loop (what's called a closed-cycle nuclear engine). The heat transfer would be used to superheat the incoming area and expel it as jet exhaust. The reactor core would have been 30 feet in diameter with an output of just below 2,000 megawatts. This would have allowed the CL-1201 to cruise at over 30,000 feet at Mach 0.8 for as long as 41 days.

But that was only just part of the utter insanity of this design. It's immense size makes it likely it was probably a flying boat though schematics do show a fairly robust landing gear that may have been for ground handling. In addition to the four giant dual-propulsion turbofans, it also had 182 lift jets- that's right, lift jets. Possibly to shorten the takeoff run, but imagine something this size being VTOL! Two retractable banks of 24 lift jets were in the forward fuselage with the rest of the lift engines distributed along the wings aft of the rear wing spar, giving a total thrust of 15 million pounds!

Two versions of the CL-1201 were proposed- the first one would have been the LSA (Logistics Support Aircraft) which would have been a transport capable of carrying several hundred combat troops and their equipment directly to crisis points worldwide. One substudy even suggested using a 707-type transport to dock with the CL-1201 LSA to shuttle troops and personnel to and from the ground.

The other even more fanciful version was the AAC (Attack Aircraft Carrier). With 845 crewmembers, the AAC could carry 22 multirole fighter aircraft on special docking pylons under the wings. The pylons were large enough to allow fuel, rearmament, and maintenance access to the aircraft. A small internal hangar bay would have carried two small transport aircraft for shuttling personnel to and from the AAC. The defensive armament of the AAC is unclear, but there was suggestion of using AIM-54 Phoenix missiles for self defense as well as the defense provided by its own air wing. There were substudies as well for versions that could have launched battlefield ballistic missiles or function as airborne control centers.

At what point the CL-1201 design faded into obscurity isn't quite clear and there are suggestions that such design work was probably conducted more as an engineering exercise than a serious aircraft proposal. Regardless, the Lockheed CL-1201 flying aircraft carrier remains as one of the most outlandish designs ever worked on by a major aerospace company.

Source: Secret Projects: Flying Wings and Tailless Aircraft by Bill Rose. Midland Publishing, 2010, p96-98.

The 1952 Carswell AFB Tornado

Prior to the arrival of the Boeing B-52 Stratofortress, the responsibility for the long-range strategic deterrent of the United States rested with the Convair B-36 Peacemaker in the 1950s. The Atlas ICBMs were still years away from becoming operations and the first Polaris submarine-launched ballistic missiles were still on the drawing boards. The other bombers of the USAF's Strategic Air Command, the Boeing B-50 Superfortress and the Boeing B-47 Stratojet, were medium range bombers that could not strike Soviet targets from the United States. Only the B-36 had the range to reach the Soviet Union and the capacity to carry any of the nuclear bombs in the US stockpile.

As the B-36 was built and flight tested in Fort Worth at Convair's mile-long plant at Carswell AFB, the first of SAC's bomb wings to receive the Peacemaker were based at Carswell. The 7th Bomb Wing was the first to put the Convair's "big stick" into service, followed by the co-located 11th Bomb Wing. With Convair right across the runway at the base, any technical problems could be readily addressed. As a result, the majority of the United States' long range striking power was concentrated in Fort Worth.

On Labor Day, 1 September 1952, many of the base personnel and flight crews had the long weekend off. Weather forecasters had predicted severe thunderstorms for North Central Texas that afternoon with estimated winds of 60mph. As few personnel were on duty, few precautions were taken other than securing the B-36 aircraft with 3/8 inch steel cables. At 6:42pm, a tornado touched down on the base perimeter and struck the B-36 flightline directly. Maintenance docks used to work on the large bombers outdoors were thrown about and the steel cables tying down the bombers snapped as the planes were thrown about by the tornado like toys. Ruptured fuel tanks spilled thousands of gallons of high octane avgas all over the ramps. The anemometer on the Carswell control tower registered sustained winds over 90mph before being torn away by the storm. As the storm subsided, operations had to be transferred to nearby Meacham Field and other bases in the Southwest.

Two-thirds of the entire B-36 Peacemaker force was either damaged or destroyed in the tornado. One aircraft was completely shattered and would have to be written off while 72 bombers on the flightline and adjoining aprons were damaged and unflyable. Fortunately there were no fatalities given the long holiday weekend. Another 10 B-36s parked at the Convair plant were also damaged. Some of the bombers were shoved on top of each other and many had lost wings, empannages, or large fuselage sections. Because of the national priority placed on the B-36 fleet, by 5:30 the next morning a repair plan was underway with 1/3 of the repairs to be carried out by SAC, 1/3 of the repair work to be done by repair teams dispatched from Kelly AFB in San Antonio (the site of one of the USAF's heavy logistics centers), and remaining 1/3 would be carried out by Convair. So urgent was the matter than a 1-page typed letter was the basis of a multi-million dollar contract for Convair for its share of the repair work. Project FIXIT returned one bomber to operational service the first week, and nine more B-36s in the second week after the tornado. In less than a month, the 7th Bomb Wing was back at full operational strength of only one B-36 had to be written off out of the 83 damaged. By the end of the month, the round-the-clock effort had the 11th Bomb Wing operational and by the first week of October, 51 more aircraft were returned to service. The last repaired B-36 returned to duty on 11 May 1953.

Having 2/3 of the B-36 force knocked out in less than 30 minutes taught SAC a lesson. Each time severe weather threatened Carswell AFB, as many B-36s as possible were flown out to other bases and would return the next day. 

Senator Lyndon B. Johnson of Texas and his Military Preparedness Committee conducted an investigation that concluded the base commanders had taken all the adequate measures proscribed at the time with an approaching storm. The investigations called for improved weather forecasting and an increase in the research of tornadic thunderstorms which over the years would not only benefit the USAF, but the general public as well.

Source: Cold War Peacemaker: The Story of Cowtown and the Convair B-36 by Dennis R. Jenkins and Don Pyeatt. Speciality Press, 2010, p149-151.

The Martin B-26 Marauder medium bomber was built in two locations in the United States during the Second World War- at the main Martin plant at Middle River outside of Baltimore, Maryland, built 3,681 B-26s and the Omaha, Nebraska, plant, built 1,585 Marauders. Designed by Peyton Magruder, who at the time he was placed in charge of the B-26 program by Glenn Martin he was only 26, the B-26 Marauder started once it won the Army competition for a medium bomber in July 1939. The prototype rolled out at the Middle River plant on 25 November 1940 and made its first flight that day. The first production Marauders were already flowing to USAAF combat units in February 1941.

Marauders were blighted early on by numerous crashes caused by pilot inexperience but would go on to fly over 110,000 missions in the Second World War with a combat loss rate of only 0.5%, the lowest of any Allied bomber of the war.

But there were a lot more things that made the B-26 Marauder a milestone in aviation history that aren't as well known to the annals of history:

-It was the first Allied bomber type in Europe to complete 100 missions, a B-26 named "Mild and Bitter" with a mission against the Luftwaffe airfield at Evreaux, France on 9 May 1944.

-It was also the first Allied bomber type to complete 200 missions, a famous B-26 named "Flak Bait" that completed its 202nd mission in May 1945 before the German surrender.

-It was the first US Army Air Forces bomber to use aerial torpedoes during the war- a two-thousand pound naval torpedo could be slung under the fuselage from an external rack (most torpedo missions were flown in the Pacific).

-It was the first twin engine medium bomber to be able to carry a greater bomb payload than the Boeing B-17 Flying Fortress, the heavyweight of the day.

-It was the first US Army Air Forces aircraft to use external gun pods- two self-contained 50-caliber machine guns were mounted two to each side of the forward fuselage for ground strafing.

-It was the first bomber to have an all-plexiglass nose which happened to be a Martin innovation in shaping plexiglass into the necessary aerodynamic curves.

-It was the first combat aircraft to use butt seams for the skin rather than overlapping seams. This improved the aerodynamics of the bomber by reducing drag.

-It was the fist bomber to use an all-electric bomb release mechanism.

-It was the first US combat aircraft with self-sealing fuel tanks, another Martin innovation which was called "Mareng Cells"- short for Martin Engineering.

-It was the first bomber to use flexible tracks to bring ammunition from its storage boxes in the mid-fuselage bomb bay to the tail gunner's position. And the maker of those flexible tracks? Lionel. Of Lionel trains fame.

-It was the first combat aircraft to substitute plastic for metal in over 400 components for weight savings.

Source: Raise Heaven and Earth: The Story of Martin Marietta People and Their Pioneering Achievements by William Harwood. Simon & Schuster, 1993, p193-212.

Extending the Range of Escort Fighters: Wingtip Coupling

In the immediate postwar period the performance of jet engines was such that they weren't economical and for the nascent USAF needing high performance escort fighters for its bomber fleet, they simply didn't have the range to accompany bombers like the Convair B-36 Peacemaker and the Boeing B-50 Superfortress on their projected missions. While the idea of a parasite fighter like the McDonnell XF-85 Goblin represented one approach, it represented a loss of bombload as the parasite fighter had to be carried under the fuselage, the most ideal location being where the bomb bay was located, near the bomber's center of gravity.

Dr. Richard Vogt, a German engineer who had headed the design work at Blohm und Voss during the Second World War, was brought the United States under Operation Paperclip (which also resulted in Werner von Braun coming to America) and his first posting was with the Air Force Research Laboratory at Wright-Patterson AFB in Dayton, Ohio. While continuing his research on unorthodox aerodynamic concepts there (he had designed the asymmetrical BV 141 while at Blohm und Voss), he developed the idea of increasing the range of an aircraft by attaching free-floating wings to the wingtips of the existing aircraft. Extra fuel tanks formed the body of the wing extensions and the aerodynamic lift from the extensions supported their weight in flight without significant structural penalty to the main aircraft. In addition, these extensions increased the wing aspect ratio, thereby reducing drag and improving the range.

While this idea was first applied to the early candidate designs for the USAF WS-110A program that resulted in the North American XB-70 Valkyrie bomber, the concept also got the Air Force's attention as a means of extending the range of its new jet fighters by substituting escorting jet fighters for Vogt's free-floating wing extensions. In 1949 the first flight trials took place using a Douglas C-47A and manned Culver PQ-14B drones. A simple coupling device allowed three degrees of freedom for the attached PQ-14B- a small ring on a short boom was attached to the wingtip of the C-47 and the PQ-14B had a rear-facing lance that engaged the ring and the drag of the PQ-14B kept it locked on the wing of the larger C-47. To disengage, the PQ-14B pilot simply throttled up and moved forward, sliding the lance out of the ring on the coupler. Since the PQ-14B was supported by its own lift, no structural reinforcements were needed on the PQ-14B or to the C-47 for that matter.

Flight tests began on 19 August 1949 and the first successful coupling was made by Second World War ace Clarence "Bud" Anderson at the controls of the PQ-14B on 7 October 1949. Problems were encountered with the wing tip vortex from the C-47 and the solution was to move the coupler outboard of the wingtip.

The USAF then initiated Project TIP TOW using a Boeing B-29 Superfortress and two Republic F-84 Thunderjets with development assigned to Republic Aviation. Two F-84Ds were modified into EF-84Ds with special wingtips that could attach to a coupling on the modified B-29 which was designated EB-29A. The wingtip vortex from the larger Superfortress made the coupling process hazardous and there were doubts as to whether service pilots with less experience than test pilots could accomplish the process. Despite 15 hours of coupled flying time with both EF-84Ds attached, on 24 April 1953 during the test of autopilot system to lessen the fighter pilot's workload one of the EF-84Ds rolled over onto the wing of the EB-29, causing a structural failure of the left wing and the loss of both aircraft in the process. The pilot of the EF-84D was killed instantly and only one of the five crew on the EB-29 survived.

Despite the loss the USAF persevered and proceeded with Project Tom-Tom- as the design was the brainchild of Major General Thomas Gerrity and Convair manager Tom Sullivan, it was spelled without all caps as was the standard USAF custom for project names. A Convair B-36 was assigned to Project Tom-Tom in May 1954. The coupling provision not only would grapple and hold onto the Republic RF-84F Thunderflashes used in the tests, but they could also provide fuel, power, pressurization and heat to the coupled jets. The first hookup was made on 2 November 1955 but again, the wingtip vortex from the significantly larger B-36 made it a dangerous affair for the pilot of the smaller aircraft. On what ended up being the final Tom-Tom flight in September 1956, Convair test pilot Beryl Erickson found his RF-84F oscillating violently but fortunately for the flight crews involved the coupling broke off and Erickson was able to land safely.

By this point the USAF's parallel experiments in inflight refueling were proving to be more practical and much easier to accomplish with much less risk to the flight crews and the Project Tom-Tom was canceled, ending work on tip-coupling.

Source: Cold War Peacemaker: The Story of Cowtown and the Convair B-36 by Don Pyeatt and Dennis R. Jenkins. Specialty Press, 2010, p224-226.

As the Vietnam War escalated in the 1960s and air crew losses began to mount to increasingly sophisticated air defenses, thoughts began to circulate in the USAF if there was a way to provide downed air crew with a better means of descent than just the winds and parachute. What if downed aircrew could have a better choice in where to land? And better yet, what if they could fly away to friendly territory? The USAF began to discuss with aircraft manufacturers and designers if there wasn't a way to package an ultralight aircraft or glider into part of the ejection seat and cockpit that would give shot-down air crew more options on bail out. Proposals were issued to the industry in 1967 and Bensen Aircraft Corporation, a well-known builder of homebuilt autogyro aircraft, submitted an unpowered version of one of their autogyros to be used as an autogyro glider. Bensen's proposals easily won the USAF over and contracts were issued in 1968 and the program received the X-plane designation of X-25A (a powered version) and X-25B (unpowered glider version). A third version called the DDV (Discretionary Descent Vehicle) was an even lighter and simpler version of the X-25B designed for one time use with automatic blade deployment to become a rotor chute even from a supersonic ejection.

The USAF took delivery of the X-25A and X-25B on 16 February 1968 and immediately embarked on a series of flights to determine the length of a pilot training cycle necessary to master the autogyro controls. The X-25A was used to power itself to an assigned altitude and then shut down its engine and autorotate. This was to determine the glide performance of the aircraft. Twenty pilots all with fixed wing experience and no rotary wing time were then checked out in the X-25B to see how easy it was to operate. All 20 pilots were able to master the X-25B within 30 minutes. The DDV was then used with anthropomorphic test dummies to measure G-loads and glide performance with an incapacitated pilot.

The winding down of the Vietnam War ended interest in the autogyro solution and it was felt that such an aircraft could be packaged to be accommodated in most combat aircraft cockpits with the current technology of the day. The X-25A is currently on display at the National Museum of the US Air Force in Dayton, Ohio, while the X-25B is at the Museum of Aviation at Warner Robbins, Georgia. The final disposition of the DDV is unknown but the X-25 will always be known as the smallest of the X-planes if not one of the most obscure.

Source: The X-Planes- X-1 to X-45 by Jay Miller. Midland Publishing, 2001, p272-275.

Although progressively improved and more powerful versions of the Bristol Olympus jet engine powered the Avro Vulcan bomber, there were also other versions of the Olympus destined for other aircraft that made their initial flights on specially-converted Vulcan testbed aircraft. In addition, other similarly-equipped Vulcans served to flight test other engines during their development cycles as well.

The first engine to be flight tested on the Vulcan wasn't an Olympus variant, though. That honor goes to the Rolls-Royce Conway low-bypass turbofan. The first prototype Vulcan, tail number VX770, was retrofitted with four Conway engines in 1956 and delivered to Rolls-Royce for the start of the Conway flight test program in August 1957. Unfortunately, VX770 was lost during a Battle of Britain flying display at RAF Syterston in September 1958 when the maneuvers it was performing overstressed the airframe, resulting in the loss of the crew. A second Vulcan bomber, XA902, was then selected to undergo conversion with the Conway engines to replace VX770. The conversion work began at Avro's facilities in December 1958 and was completed in July 1959. The Conway engines used were the Conway 11 engines (RAF designation Conway Mk.102 and 103) which were destined for use on the Handley Page Victor B.2, an upgraded version of the original Victor B.1 model.

The Conway test program called for the engines to be run at cruise power at 40,000 feet- however, at that power setting, the Conway 11s were more powerful than the Olympus engines of the Vulcan and the testbed would have easily exceeded the Vulcan's maximum speed and overstressed the airframe! As a result, the Conway 11 engines had to be operated at lower thrust settings similar to what was used on BOAC's Boeing 707-430 jetliners. It was found that two Conways could be operated at cruise settings as long as the other two engines were run at lower settings. Given that the prototype Vulcan VX770 that was lost wasn't as structurally strong as XA902, it became possible to complete the Conway flight test program.

With the Conway test program complete in 1961, XA902 was then converted to take Rolls-Royce Spey engines on the inboard positions while retaining the Conway 11 engines on the outboard positions. It made its first flight in this configuration in October 1961 to support the Spey development for its use on De Havilland DH.121 Trident, the BAC One-Eleven, the Blackburn Buccaneer S.2 and the Hawker Siddley Nimrod. XA902 would be retired from service in 1963.

In 1962, another early-mark Vulcan B.1 was taken from service to test the Olympus 22R engine that was destined for the BAC TSR.2. Vulcan XA894 was modified with a large ventral nacelle with bifurcated intake on each side of the nose landing gear. Conversion work on XA894 began at Filton in 1960 and it made its first flight with the much more powerful Olympus 22R in February 1962 in support of the TSR.2 development program. In December of that year during a ground run test, an uncontained turbine blade failure resulted in a fire that destroyed XA894. No replacement was needed, though, as the Olympus 22R had completed enough of the needed test points for the TSR.2 program.

In 1964, another Vulcan was pulled from service to serve as an engine testbed, this time it was tail number XA903 which arrived at Filton in January of that year for conversion work to flight test the Olympus 593 in support of the development of the BAC/Aerospatiale Concorde. Using a similar ventral nacelle as had been used on XA894 in the Olympus 22R flight test program, this time instead of a bifurcated intake a straight-through intake was used that resembled a single-engine Concorde engine nacelle. A retractable spray bar was also fitted ahead of the intake and water from a bomb bay water tank was used to test water ingestion and icing conditions on the Olympus 593 engine. The first flight was made with the Concorde engine in September 1966 and the test program finally ended in 1971 with over 400 hours of flight time. With the Olympus 593 at full power, the Vulcan testbed could still fly and maneuver with its own four engines at idle!

Testbed work would continue for XA903, though. In August of 1971 XA903 was flown to Marshalls of Cambridge for conversion work to support the development of the Rolls-Royce/Turbo Union RB.199 engine for the Panavia Tornado program. The ventral nacelle used for the Olympus 593 program was modified by Marshalls to not only accommodate the RB.199 engine, but to replicate the starboard side of the Tornado's fuselage. The first flight with the RB.199 was made in April 1973 and one of the most unusual aspects of the RB.199 flight test program was that the ventral nacelle was even equipped with a Mauser 27mm cannon that would be used on the Tornado. The cannon's location in relation to the intake replicated its location on the Tornado so that gun gas ingestion trials could be carried out. The firing trials were carried out at Boscombe Down but weren't done while airborne- XA903 remained on the ground and firing butts were used while Rolls-Royce and Turbo Union engineers analyzed the engine's performance as gun gas was drawn into the intake. A total of 285 flight hours were accumulated with the RB.199 on XA903 when the Vulcan was finally retired in February 1979, the last early-mark Vulcan B.1 to have flown.

Source: Avro Vulcan- Britain's Famous Delta-Wing V-Bomber by Phil Butler and Tony Buttler. Midland Publishing/Aerofax, 2007, p70-73.