The First Steps to a Turboprop Transport, Part Two

A week and a half ago I had blogged about how the USAF was getting turboprop transport experience by setting up a test squadron at Kelly AFB to operated transport aircraft that had been converted to turbine power: 

52-2693 and 52-2672 in flight together.

On 15 June 1954, the headquarters of the Military Air Transport Service (MATS) activated the 1700th Test Squadron (Turboprop) at Kelly AFB, Texas, with the task of developing maintenance procedures and techniques for the employment of turboprop transport aircraft pending the arrival of the C-130 and C-133 into the USAF service. The squadron had three flights with each flight dedicated to a single type for the testing of standard transport aircraft that had been converted to turboprop power. The first of the three flights to be activated would operate the Convair YC-131C. Two aircraft were converted from standard C-131 Samaritan transports (the USAF version of the CV-340 airliner) to use early test versions of the venerable Allison T56 turboprop.

Back in January 2010 I had written a short posting about the second of the demonstrator aircraft that were operated by the 1700th Test Squadron and operated in the second flight of the unit- the Boeing YC-97J, a Pratt & Whitney T34-powered version of the C-97 Stratofreighter. I had recently picked up Cal Taylor's voluminous tome on the Douglas C-133 Cargomaster and he devotes considerable space to the YC-97J and its operational use by the 1700th TS. The YC-97J made its first flight at Edwards AFB on 19 April 1955 and given that it used the same T34 engines as the upcoming C-133, the USAF was keenly interested in flight testing the engine in an operational environment with the YC-97J. From my previous posting about the YC-97J: 

Boeing converted two aircraft (52-2693 and 52-2672, both KC-97Gs) to turboprop power. Pratt & Whitney YT34 turoprop engines (which would later be used on the Douglas C-133 Cargomaster) delivering 5,700 horsepower were substituted for the four R-4360 radial engines. For a brief time the USAF considered redesignating these two Stratofreighters as C-137, but ended up assigning them the designation YC-97J (ironically the C-137 got used for the Boeing 707s used by the military, itself a development of the Model 367-80 prototype).

The conversion to turboprop power shaved nearly 5,0000 lbs off the aircraft's weight as the YT34s were much lighter but more powerful. The first flight was made on 19 April 1955 and the YC-97J demonstrated significant improvements in overall performance. The top speed was 417 mph compared to 375 mph for a regular Stratofreighter and the YC-97J took only 14 minutes to reach 20,000 feet whereas the regular Stratofreighter took 50 minutes!

Inflight study of the YC-97J during its Edwards flight test program.

In addition to using the same T34 engines as the C-133, the YC-97Js also used an early version of the same Curtiss turboelectric three-bladed propellers planned for the C-133. The first YC-97J completed its flight testing at Edwards and was delivered to Kelly AFB on 14 September 1955, nine months after the YC-131Cs had arrived. The second YC-97J arrived at the end of the month. After a short series of flights operating within the continental United States, the USAF authorized the aircraft to begin overwater missions with the first overwater flight being to Kindley Field in Bermuda- the aircraft covered the 1,700 mile route from San Antonio to Bermuda in 4 hours 42 minutes, the fastest time at that point by a prop-driven aircraft. On 26 January 1956, the YC-97J departed for Rhein-Main AB in West Germany staging through Dover AFB in Delaware, then Newfoundland and Scotland. Despite record breaking cold weather on the trip, the YC-97J performed flawlessly without any of the usual maintenance headaches that were commonplace for the piston-driven C-97s. On the leg between Newfoundland and Scotland, four hours were shaved off the usual flight time when using C-124s or C-118s, the run being made in only 6 hours 30 minutes. It was clear that the time savings was tremendous on long distance missions. The international aviation press covered the flight with interest. On an outbound stop in London, the YC-97J was climbing out of Heathrow at 2,500 feet per minute and London ATC asked the pilots to slow the rate of climb as the radar dish was too slow to keep up! The return flight from Frankfurt stopped in Paris, London, the Scotland (Prestwick), Newfoundland (Goose Bay) then Selfridge AFB in Michigan before returning to Kelly AFB. It was the first round-trip trans-Atlantic crossing by an American turboprop aircraft. During the mission to West Germany and back, no engine or prop maintenance was needed and the aircraft's four engines used a mere four quarts of oil for the entire trip. Needless to say, the USAF was very enthusiastic about the aircraft!

In March 1956 the two YC-97Js were put on a scheduled cargo run between Kelly AFB to Ramey AFB in Puerto Rico via Charleston AFB in South Carolina and the return routing stopped over at Brookley AFB in Alabama (now Mobile Downtown Airport). Average flying time between San Antonio and Puerto Rico was 16 hours and despite the stopovers, it was still nine hours faster than what piston-driven USAF transports took to cover the distance. But it didn't stop there- that same month the first YC-97J made the first trans-Pacific crossing by a turboprop aircraft, averaging 360 mph over the 18,000 mile round trip. The longest leg of the route to Tokyo was between Midway Island and Yokota AB outside of Tokyo- on this leg the YC-97J flew at 30,000 feet and averaged 400 mph. 

In preparation for the arrival of the Douglas C-133 Cargomaster, the first group of air crew and mechanics arrived at Kelly AFB from Dover AFB for familiarization training with the T34 engine and its Curtiss propellers. The three-week course had pilots flying an average of 38 hours on the YC-97Js to build turbine experience while the Dover mechanics worked side by side with the Kelly AFB maintenance team to keep the YC-97Js flying. The reliability of the turboprop over the piston engine was now unquestionable and in the summer of 1956, both YC-97Js would fly a total of 46 hours 35 minutes together in a single calendar day as proof of the reliability of the turboprop. The engine overhaul time (TBO) over the course of the test program with the 1700th started out at 150 hours and ended up at 1,000 hours. 

The YC-97J departs San Diego Lindbergh Field.

In addition to its scheduled cargo flights, the YC-97Js were also flown on demonstration flights for interested groups ranging form the US Navy to other defense contractors like Pratt & Whitney and North American Aviation. On a three day demonstration in Connecticut for Pratt & Whitney, the YC-97J made 78 engine starts, 19 takeoffs and landings, 7 air starts and 15 flights without any malfunctions of the engine or propellers. By October, one of the T34 engines became the first American turboprop engine to reach 1,000 flight hours since its last overhaul. It was removed from the YC-97J with 1,001 hours and 20 minutes flight time and in that time, it only needed 44 hours of unscheduled maintenance and used a miserly 392 quarts of oil in that time frame, a fraction of what the regular C-97's piston engines would have used in 1,000 flight hours. The propellers also proved to be extremely reliable and when the first C-133 Cargomasters were delivered to Dover AFB, the engines and propellers were already rated at 1,000 hours TBO, a significant feat in that day. 

The 1700th TS's flight test program with the YC-97Js concluded on 15 November 1956, six weeks ahead of schedule. However, the aircraft were kept operational until 17 January 1957 as they were used in Operation Safe Haven to fly refugees from the 1956 Hungarian Revolution from Europe to new homes in the United States. The first YC-97J, would go on to create more aviation history, though- it was modified to become a Super Guppy transport. Aero Spacelines president Jack Conroy had already flown a piston driven Super Guppy, and aware of the pending retirement of the YC-97Js, acquired one as the turboprop engines made his conversion not only faster, but more efficient. The new turbine Super Guppy used a swing nose instead of a tail break as was the case with the original design and it was put into service with NASA in 1966, its first job transporting the second stage of the Saturn IB rocket from Huntsville, Alabama, where it was built to the Kennedy Space Center in Florida. It was subsequently retired to the Pima Air and Space Museum in Tucson, Arizona. 

Stay tuned for the final installment in this series which will look at the turboprop-powered YC-121F Super Constellation!

Source: Remembering an Unsung Giant: The Douglas C-133 Cargomaster and Its People by Cal Taylor. Firstfleet Publishers, 2005, p29-43. Photos: Smithsonian Institution, SDASM.

How a Tax Issue Launched the Boeing 707

Boeing chairman Bill Allen

In a past blog post I had mentioned that while most of aviation history is a study in technological progress, it as much shaped by the individuals and their personality traits as it is any development in aeronautics. That past posting back in March 2010 dealt with C. Edward Acker's personality and how it shaped Air Florida and impacted the newly-deregulated market in the United States in the 1980s. While someone like Acker brimmed with swagger and bravado, there as many individuals in the history of aviation who, by nature of their quiet reserve, are often overlooked as movers and shakers. I recently have been reading Sam Howe Verhovek's book Jet Age: The Comet, the 707, and the Race to Shrink the World and he places Boeing's chairman at the time of the launch of the 707, Bill Allen, as one of the true visionaries and business leaders in the industry. I have to admit my own understanding of Bill Allen up to this point was that while he shaped Boeing tremendously into what it is today in the commercial airliner market, he hardly filled the role of visionary, looking very much like many of the management types that you could have pulled from central casting for a 1950s-era movie. But what was it about Bill Allen that makes him a central figure in Verhovek's book? When he assumed the leadership role in Boeing in 1950, Boeing held less than 1% of the commercial airliner business that was dominated by Douglas and Lockheed. Though stunningly successful in the Second World War with its bomber designs, Bill Allen rightly saw that the growing air travel market represented a bigger prize than any military contract. But with a fraction of the commercial market, Boeing was already seen as a three-time loser in the race- the Boeing 247 was too small compared to the Douglas DC-3, the Boeing 314s were only built in small numbers primarily for Pan Am, and the landmark Boeing 307 Stratoliner was a flop that hardly made a dent in the marketplace. 

Bill Allen wasn't a pilot and he wasn't even an engineer. He would have readily admitted to not knowing much about either when it came to aviation. But he had his start as the company lawyer who handled the legal paperwork for Bill Boeing's timber business and then his aircraft company. Before long, Allen was one of those quiet in-the-background individuals that everyone saw Boeing himself often sought out for advice. When Boeing quit the company in 1934, Philip Johnson took his place and led the company through a dramatic expansion during the Second World War- and again, Johnson came to rely on Allen for advice and counsel on company decisions. When Johnson died of a stroke in his fifties, there was only one person the rank and file at Boeing would trust- and that was Bill Allen. But he found himself a single parent to two young girls after losing his wife to cancer when the offer from the board came to him. 

Maybe it was loyalty and maybe it was that he was part of Boeing since its early days as a timber company, but he took the job- but at the time, the airline industry was content with its Douglas and Lockheed piston propliners and Allen had a tough time selling the airlines on the idea of a jet. For many airlines, the jet was an unknown. Well, it was- until the De Havilland Comet took flight and electrified the world with its speed and grace. By 1952 the British aeronautical industry was the talk of the world with Eastern's Eddie Rickenbacker and Pan Am's Juan Trippe openly discussing orders of the Comet. It was an about face by the world's airlines and the US airline industry in particular that just a year earlier thought jet technology too immature for the traveling public.

Bill Allen on the right shows the Dash 80 to Bill Boeing.

Many companies wanted government subsidy to develop a jet airliner- Boeing's own engineers had been applying their experience in developing the B-47 Stratojet and the B-52 Stratofortress towards the company's own project which was designated Model 367-80 (the Model 367 was the C-97 Stratofreighter- the Dash 80 was designated such for secrecy, leading competitors to think it was just an improved version of the C-97). The costs of developing the Dash 80 amounted to a quarter of the company's value and to go it alone without government development aid represented a tremendous financial risk. There was many pros as there were cons in Allen's mind when it came to launching a jetliner.

But, Allen's own legal background was in tax law. During the Korean War, the Congress put what was called an "excess profits" tax in place to prevent companies from profiteering from the war effort. A company's baseline was set at its profilts made during the peacetime period of 1946 to 1949. Anything above that level in profits was subject to the tax. That period was a hard time on Boeing with the cancellation of numerous wartime contracts and profits during those years were slim at best. But with the ramp up in defense spending during the Korean War, Boeing's fortunes improved dramatically and that meant that the company was fully exposed to the excess profits tax while Douglas and Lockheed's profits during that time were higher thanks to their own commercial airliner production. That meant that Boeing would owe 82 cents on every dollar of profit while Douglas only would owe 68 cents and Lockheed only 48 cents on each dollar of profit.

Having a flying prototype gave Boeing an advantage.

Under most circumstances, Bill Allen might have gone to the state of Washington Congressional delegation for a political fix. But being the tax lawyer, he saw an opportunity- Take Boeing's profits and invest them heavily into the Boeing 707 project- that amount would be deducted from the profits and written off as a business expense. Boeing wouldn't need government aid to develop a new jetliner and it reduced the company's tax exposure. Allen pitched the idea to the Boeing board as an investment in the company's future that would put it at the forefront of jetliner development. In addition, company funding of a demonstrator aircraft would not only give the airlines something to see and ride as a flying design, it would also put Boeing in the lead for the USAF's plans for a new jet tanker to support its growing B-52 Stratofortress fleet. In a stroke of what some might call genius, Bill Allen could kill three birds with one stone- reduce Boeing's tax exposure, get a flying jetliner demonstrator, and use that demonstrator to get the jet tanker contract. That was the engineering genius of the Dash 80- it appealed to both airlines and the USAF for disparate roles. Boeing's competition for the jet tanker hadn't optimized their designs as transports as fully as Boeing had with the Dash 80.

It only took a month to get the go-ahead from the board of directors. In the summer of 1952, Bill Allen issued short statement to the press:

"The Boeing Company has for some time been engaged in a company-financed project which will enable it to demonstrate a prototype jet airplane of a new design to the armed services and the commercial airlines in the summer of 1954."

The rest, as they say, is history!

Source: Jet Age: The Comet, the 707, and the Race to Shrink the World by Sam Howe Verhovek. Penguin Group, 2010, p84-110. Photos: Smithsonian, Boeing.

The First Steps to a Turboprop Transport, Part One

The YC-131C in flight. Note the 3-bladed propellers.

By the time of the Korean Armistice in 1953, the US Air Force was busy absorbing the lessons of airlift accrued over a less-than-ten-year span from the logistics flights to support World War II to the Berlin Airlift to the strategic airlift partnership forged with the commercial airlines in the Korean War. In pace with advances in aerodynamics and propulsion, the USAF began a four-step process in exploring the possibilities of turboprop propulsion given that pure jet engines of the day were still incredibly fuel-thirsty. The first steps were taken in 1945 with the test program of the Convair XP-81 turboprop fighter that also had an Allison J33 jet engine for additional power. The next steps were the testing of turboprop engines on existing high-speed jet designs that would result in the XF-84H "Thunderscreech and test versions of the Boeing B-47 Stratojet and the McDonnell XF-88 that flew with turboprop engines. The third step was the installation of turboprops on existing transport designs to evaluate their performance on large transports. And the final step was the introduction of production-standard turboprop transports which would result in the Lockheed C-130 Hercules and the Douglas C-133 Cargomaster. 

On 15 June 1954, the headquarters of the Military Air Transport Service (MATS) activated the 1700th Test Squadron (Turboprop) at Kelly AFB, Texas, with the task of developing maintenance procedures and techniques for the employment of turboprop transport aircraft pending the arrival of the C-130 and C-133 into the USAF service. The squadron had three flights with each flight dedicated to a single type for the testing of standard transport aircraft that had been converted to turboprop power. The first of the three flights to be activated would operate the Convair YC-131C. Two aircraft were converted from standard C-131 Samaritan transports (the USAF version of the CV-340 airliner) to use early test versions of the venerable Allison T56 turboprop. The YT56 turboprops replaced the piston engines of the C-131 and drove three-bladed Aeroproducts propellers. As this was the combination planned for the Lockheed C-130A, Allison was, needless to say, keen on being involved in getting flight time for the new engine. Tail numbers 53-7886 and 53-7887 were pulled from USAF service and modified by Convair at their Fort Worth facility at Carswell AFB. After initial flight testing at Edwards AFB, the first YC-131C was flown to Kelly AFB on 20 January 1955 with the second aircraft arriving three days later. 

Ground run of the YT56 engines at Convair Fort Worth.

As the goal of the test program set up by the 1700th TS was to fly the turboprop aircraft assigned to it as much as possible, the YC-131Cs were assigned to a scheduled military passenger service that operated between Kelly AFB in San Antonio and Andrews AFB outside of Washington, DC. The first services began on 14 March 1955 as the first scheduled turboprop passenger services in the United States. Covering a distance of just over 1,200 miles, the YC-131Cs took 4 hours 20 minutes on the first flight, approximately 20 minutes faster than a piston C-131 on the same route. By May of that year a regular flying schedule was established that would have the 1700th TS flying the two YC-131Cs 3,000 flight hours in nine months. As maintenance at destination stations was not expected to be adequate, each scheduled route flown by the YC-131C always returned back to Kelly AFB where the squadron had proper maintenance facilities. By July the Civil Aeronautics Administration (the CAA, the predecessor agency to the FAA) assigned four pilots to the 1700th TS to gain knowledge and experience in scheduled turboprop transport operations. That particular month, the second YC-131C became the first American-built turboprop aircraft to exceed 1,000 flight hours. 

The second YC-131C being handed over the USAF.

In the first six months the YC-131Cs were flown intensively, sometimes over 30 hours per day between the two aircraft. The initial time between overhaul (TBO) on the Allison YT56 engines was set at 100 flight hours at the start of the program but the engine proved to be highly reliable and as the program progressed, the TBO was increased progressively up to 200 flight hours. Though the engines could have safely flown with a longer TBO than 200 hours, Allison engineers were anxious to teardown and study the engines to improve the planned production T56 that would be used on not just the Lockheed C-130 but also on the same company's L-188 Electra airliner. During the nine month test program, 55 engines were changed out and sent back to Allison for analysis. The three-bladed Aeroproducts propellers also had TBO limits, starting at 300 hours and then extended out to 1,000 hours by the end of the test program. With a reliability well in excess of what was possible with piston engines, the two YC-131Cs also became the first USAF turboprops to exceed 1,000 flight hours with one day a record being set with an astounding 46 hours and 20 minutes flown in a 24-hour period, evenly split between the two aircraft. 

On 15 December 1955 the test program with the YC-131C ended, 45 days early thanks to the reliability of the YT56 engine. The USAF gained important data on fuel planning for turboprops, ATC procedures, holding patterns and ground operations that was also shared with the airline industry. In addition, the first squadrons that would be receiving the first C-130A Hercules aircraft at Sewart AFB, Tennessee, Ardmore AFB in Oklahoma, and Eglin AFB in Florida, sent their initial cadre of maintenance personnel to the 1700th TS in San Antonio for familiarization with the T56 engine. Both aircraft were eventually declared surplus and passed on to civilian owners before being scrapped. 

The next blog post will look at the second of the three turboprop conversions operated by the 1700th TS. Stay tuned!

Source: Remembering an Unsung Giant: The Douglas C-133 Cargomaster and Its People by Cal Taylor. Firstfleet Publishers, 2005, p29-43. Photos: Smithsonian Institution, SDASM.

The Fighter That Shot Itself Down

The F11F-1, the first production Tiger version

In the mid-1950s the US Navy was hard at work with Grumman in getting the new F11F Tiger into service. Originally developed as a supersonic development of the F9F-6/7 Cougar, the program eventually resulted in an all-new aircraft for the day fighter role powered by the Wright J65 turbojet, a license-built version of the British Sapphire engine that also powered the Hawker Hunter and Gloster Javelin. Part of the flight test program to get the Tiger operational involved clearing the performance envelope for the firing of its four 20-millimeter Colt cannons which were mounted under and aft of the air intakes. As the Tiger was designed to be as light as possible so to attain the highest performance with its J65 engine, the expended cases and links from the Colt cannons were ejected overboard rather than be retained onboard the aircraft. During the cannon firing portion of the flight test program, it was immediately found that the airflow patterns around the aircraft allowed the spent cases and links to hug the fuselage, causing multiple dents and scratches. At one point in the program the Tiger test aircraft had to be fitted with an armored leading edge to the horizontal stabilizer as the damage from the links in particular could be significant. 

The solution was to change the ejection mechnism and associated chutes so that the shells were forcibly ejected out longer chutes that projected out into the airstream and away from the turbulent air along the sides of the Tiger. A complex internal mechanism recycled the links to a special compartment just ahead of the cannon ammunition boxes as the links tended to cause more surface damage than the spent casings.

On 21 September 1956, Grumman test pilot Tom Attridge sortied out of the company airfield at Calverton, Long Island in aircraft BuNo 138620 to conduct high speed firing tests of the cannons. It was the 41st flight for this particular F11F-1 Tiger and it was Attridge's second test flight of the day. His flight profile for this test was to start out at 22,000 feet and accelerate in afterburner at a 20 degree angle past Mach 1. Passing through 13,000 feet he would fire a four second burst of the cannon, wait three seconds to allow the guns to cool, and then fire a second burst, ending the profile at 7,000 feet when the ammunition load would be expended. 

How to shoot yourself down....

Attridge flew the prescribed profile and upon expending the ammunition, was suddenly confronted by the shattering of the forward armored windscreen caused by some sort of object. He immediately throttle back and pulled up to reduce speed to prevent the windscreen from caving in and at 13,000 and 200 KIAS he turned back towards Calverton. The only damage he could ascertain was a gash to the right intake lip and that everytime he took the engine up above 78% power, it began to run rough. Two miles from the end of the Calverton runway and at 1,200 feet with his wheels down and flaps lowered, Attridge found that 78% engine power was insufficient to maintain his glide path as the sink rate began to increase. He advanced to full throttle only to be greeted by what he described as "the engine sounded as if it was tearing up" and he immediately lost power. Three-quarters of a mile short of the runway, the Tiger settled into the trees and the aircraft traveled for 300 feet before coming to a stop. Though the aircraft was on fire, Attridge managed to escape quickly without injury and the Grumman crash crew and rescue helicopter were on scene in less than three minutes. Eleven minutes after landing, the company helicopter landed a local hospital to have Attridge evaluated. 

Examination of the aircraft showed it had been hit by at least three 20-millimeter rounds- one in the windshield, one in the right intake lip and one in the nose cone. In addition, projectile fragments were found in the first compressor stage of the engine along with fan blade damage- engineers suspected that perhaps the round that hit the right intake ricocheted into the engine. It was determined that Attridge had inadvertently shot himself down. At the first cannon burst, he was in 0.5G supersonic descent and had actually flown underneath the trajectory of the cannon projectiles from the first cannon burst. Eleven second later, as he began to pull out of the descent, he flew into the stream of projectiles from the first burst. 

Subsequent examination of the aircraft showed that Attridge had flown the same test profile earlier that day and what was thought to be large ding from an ejected casing on the vertical fin actually turned out to be a projectile hit- apparently Attridge had grazed himself on the first test flight of the day and gotten away with not shooting himself down!

Source: Aero Album, Spring 1968, Volume One. "The Tiger That Clawed Itself" by Robert Munro, p12-14.