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.