19 December 2011

The Bell L-39 Swept-Wing Demonstrator

The Bell L-39 making a simulated carrier approach.
Following the end of the Second World War, captured German aerodynamic research had indicated the high-speed benefits of swept wings and many designs under development in the mid to late 1940s were revised to incorporate swept wings- two such examples being the North American F-86 Sabre and the Boeing B-47 Stratojet. While the USAF might have been enthusiastic about the benefits of swept wings, the US Navy still had its reservations- the Bureau of Aeronautics (BuAer), the Navy organization tasked with the development and support of naval aircraft, had concerns about the low-speed handling characteristics of swept wings as it was this particular flight regime that was critical in flight operations aboard aircraft carriers. While there was no questioning the high-speed benefits, the Navy didn't have the luxury of long runways to land at high speeds. To determine the scope of the problem, BuAer solicited bids from industry for a swept-wing flying demonstrator to explore the low-speed handling qualities of swept wings. Grumman tendered two proposals, one based on a modified F4F Wildcat as well as an all new aircraft that would have allowed wings of differing sweep to attached to the fuselage. Bell submitted a modification of its P-63 Kingcobra which won the contract as it offered lower development costs using two P-63 aircraft. The aircraft would be designated L-39. In those days, the Navy designated its research aircraft with a letter denoting the manufacturer followed by the manufacturer's model number- as exemplified by the more well-known D-558 Skystreak and later Skyrocket- "D" for Douglas, Model 558. In the case of the L-39, "L" was Bell Aircraft's letter designation and the swept wing demonstrator had the company designation Model 39. The design had really only a tangential relationship to the P-39 Airacobra (more on this in a bit). 

The wings were basically P-63 Kingcobra outer wing panels that were modified to be swept to 35 degrees and attached to an unswept center stub section. This was done for aerodynamic balance purposes. The wings were further modified with slats which could be positioned before flight either open or closed. Because of the wing modifications, the landing gear was non-retractable, but since BuAer was more interested in low speed landing, this was of no consequence. Two L-39s were built, differing only in the size of the slats.

The swept outer panels attached to an unswept center section.
The first L-39 was ready to fly only 10 weeks after the go-ahead from the Navy and made its first flight on 23 April 1946. The initial set of flight tests showed some handling issues that were easily resolved with further modification to the first aircraft- namely a fuselage extension aft of the wing to increase the moment arm of the tailplane to provide more pitch authority, a ventral fin for stability, and to shift the center of gravity rearward more, the original four-bladed P-63 propeller was replaced with a lighter three-bladed unit from a P-39 Airacobra (and thus the only real link between the P-39 and the L-39). The second L-39 demonstrator was completed with the additional modifications and joined the flight test program.

It was quickly determined that the swept wing with the slats closed possessed entirely unacceptable stall characteristics- namely it was abrupt and caused the aircraft to roll to one side. However, if the wing were slatted, then the stall characteristics become acceptable. Simulated carrier approaches and landings were made by both BuAer test pilots and even Corky Meyer, Grumman's chief test pilot (as Grumman was in the process of designing swept wing aircraft for the Navy). Handling and stall characteristics in the low speed regime around the carrier were quickly determined to not be an issue as long as the swept wing were slatted and the L-39 flight test program concluded in August 1946.

Close up of the L-39's wing slats.
One issue that did come up during the L-39 test program was that swept wings needed a responsive power source in the carrier landing pattern. On aircraft there is a relationship between power required for flight and airspeed. As the airspeed decreases, the power needed also decreases, but it then reaches a point due to drag that the power needed starts to go up even as the airspeed decreases. This is called the "back side" of the curve. In carrier aircraft, they are flown on this backside because the approach to the deck must be at as low as a speed is possible. On a propeller-driven aircraft, power can be immediately applied to halt the aircraft from settling in the approach and striking the ramp. But swept wings had a steeper "back side" and early jet engines took time to spool up. And it would be jet engine development that would later dog the Navy's aircraft programs in the 1950s. But more on that in a later post!

Source: U.S. Naval Air Superiority- Development of Shipborne Jet Fighters 1943-1962 by Tommy H. Thompson. Specialty Press, 2008, p69-73.

16 December 2011

The Massive Curtiss XP-71 Fighter

Early windtunnel model of the XP-71 with its wider twin-seat cockpit.
Before the entry of the United States into the Second World War, news stories were splashing headlines about the massed bomber attacks the Luftwaffe was conducting against British cities during the Blitz and in the run up to 1941, a concern about the potential of bomber attacks on the United States took root (despite the obvious shortcomings of any enemy bomber attack on US targets protected on each side by large oceans). A number of designs and studies were undertaken to evaluate the problem of intercepting enemy bombers and one of these resulted in a design specification for a large high-altitude fighter to carry a heavy cannon armament to attack bomber formations from ranges that would place it beyond a bomber's defensive guns. In April 1941, the Curtiss Aeroplane Company submitted six proposals with two, more refined, proposals the following November. One configuration met the proscribed needs of the military for a bomber destroyer and this aircraft was assigned the designation XP-71 with a $3.2 million contract for two prototypes which was signed on 28 October 1941. 

The Curtiss design had the internal company designation CW-29 and had it been built, it would have been the largest fighter aircraft ever developed in the United States- with a wingspan of 82.3 feet, a gross weight of 39,950 lbs and a fuel load up to 1,940 gallons, it was to be able to climb to 25,000 feet in just 12.5 minutes with a cruising speed of 428 mph. With an operating ceiling of 40,000 feet and a range of 3,000 miles, the XP-71 would attack enemy bomber formations well before they reached their targets. A heavy armament of two 37mm cannons with 60 rounds each and a 75mm cannon with 20 rounds was located in the nose and equipped with automatic feed systems so the aircraft only needed a minimal crew of just two. Two large Pratt & Whitney R-4360 Wasp Major 28-cylinder radial engines drove a total of nearly 7,000 horsepower to wing-mounted contra-rotating pusher props with a total of eight blades each and a diameter of 13.5 feet. General Electric turbosuperchargers would give the XP-71 the necessary high altitude performance along with a pressurized cockpit.
To put the massive size of the XP-71 into context, let's compare it with one of the larger production American fighters of the war, the Republic P-47 Thunderbolt. The XP-71 would have twice the wingspan, four times the gross weight, nearly four times the combat range, and nearly three times the engine horsepower of the Thunderbolt. In fact, the XP-71 had it been built would have been larger, heavier, faster, and longer ranged than even a late-model North American B-25 Mitchell medium bomber. 

This schematic hints at the immense complexity of the XP-71.
The mockup was inspected at Curtiss' St. Louis facility on 16 November 1942, at which time the design was revised from having two crew to just a single pilot. The original proposal had the two pilots sitting side-by-side. Following the mockup review, detailed design work took place well into 1943, by which time it was becoming clear to both the US Army Air Forces and Curtiss that the XP-71 might well be the most complex aircraft yet built. During ground firing trials of the nose cannon installation in February 1943, the nose structure failed in spectacular fashion, necessitating a redesign. Curtiss also had problems finding a suitable rangefinder for the fire control system and eventually settled on a radio-based model. Cooling of the R-4360 engines in the wing nacelles also required considerable attention with an annular intake with a gearbox-driven cooling fan being developed to insure adequate cooling airflow to the massive radial engines.

By the latter half of 1943 it was becoming apparent that the XP-71 was a plane without a mission as the strategic bombing campaign of Germany got underway. The likelihood of German bomber formations, let alone Japanese bomber formations, approaching US cities was almost nil. The USAAF considered re-roling the XP-71 as a photorecon aircraft, but no solid commitments were forthcoming. On 23 October 1943, the XP-71 program was terminated after the expenditure of $2.3 million with the first flight planned for June 1944. Curtiss attempted to salvage the program by pitching the XP-71 as an antishipping aircraft with its heavy nose cannons, but this role was already being filled by the proven B-25 Mitchell in the Pacific and Curtiss's engineering resources were needed on other projects.

Source: U.S. Experimental and Prototype Aircraft Projects: Fighters 1939-1945 by Bill Norton. Specialty Press, 2008, p138-139. Photos: National Museum of the United States Air Force.

13 December 2011

Violet Club: Quite Possibly the Worst Nuclear Bomb Ever Fielded

The warhead, or physics package, of the Violet Club bomb
When taking a look at the development of British nuclear weapons following the Second World War, it has to be viewed in the context of a piece of legislation in the United States that was passed in 1946- the McMahon Act or the Atomic Energy Act. Sponsored by Senator Brien McMahon of Connecticut who chaired the Senate Special Committee on Atomic Energy, this legislation is better known for its creation of the Atomic Energy Commission and the placement of nuclear weapons development and nuclear applications under civilian rather than military control. However, one consequence of the McMahon Act was the stipulation that nuclear weapons development be restricted from US allies- this affect the United Kingdom and Canada who had provided scientists and support to the wartime Manhattan Project. As a result of being shut out of American nuclear weapons development, the British set about to create their own air-dropped weapon which would be fielded in 1953 at RAF Witttering- though somewhat amusingly the first aircraft that could carry the bomb, designated Blue Danube, the Vickers Valiant, didn't become operational until a year later. The purpose of this wasn't just a message to the Soviets, but also to the United States that Britain was more than capable of fielding its own nuclear deterrent despite the McMahon Act. 

On 1 November 1952 the United States detonated its first fusion bomb (H-bomb) in the Ivy Mike test at Eniwetok Atoll in the Pacific. Given that the British were still shut out of US nuclear development by the McMahon Act, despite the fact that the Blue Danube fission bomb (A-bomb) was still a year out from being operational, strategic imperatives meant that Britain had to develop it's own H-bomb and the program was launched in 1954. In the UK, many military systems were assigned code names under the Ministry of Supply's "rainbow codes"- hence, "Blue Danube". In the development of an H-bomb, the casing had its own code name and the actual warhead, called the physics package, had another code name. The casing of the H-bomb was based on the Blue Danube casing and was designated Violet Club while the physics package was designated Green Grass. 

But before the code names had been settled upon, the British H-bomb had a different name- "Interim Megaton Weapon"- implying that it was a high-yield weapon but not a true thermonuclear or H-bomb/fusion weapon. And this is really at the heart of the history of the Violet Club and its historical legacy. First, it indicates that Violet Club was intended to be a temporary weapon and secondly, it wasn't a fusion bomb as was commonly believed by *both* the Soviet Union and the United States. 

The warhead or physics package of the bomb was based on earlier warhead designs that were named Orange Herald and Green Bamboo. Orange Herald was a lighter version of Green Bamboo and the designs were projected to be the new fusion warheads for the Royal Air Force's V-force, the Blue Steel stand-off missile, and the planned Blue Streak intermediate-range ballistic missile. Testing of Orange Herald showed that it had failed to boost the fission reaction to create a fusion reaction. The failure of the warhead designs left the British scrambling for a high-yield weapon and this became the Green Grass warhead of the Interim Megaton Weapon that was based on design elements of the earlier Green Bamboo and Orange Herald designs. As was the case in the United States, interservice rivalries in Great Britain meant that the Army wanted highly enriched uranium (HEU) for nuclear landmines in Europe and the Royal Navy wanted HEU for the reactors for its planned nuclear-powered submarine fleet. The Royal Air Force was of the feeling that the HEU that had so far been produced in British reactors had to be used or it would be lost to rival services, so that was one of several motivations to rush the Interim Megaton Weapon into service as it would use a significant amount of HEU.

Schematic of the Green Grass warhead showing how the ball bearings were used.
It was the design of the Green Grass warhead that went into the Violet Club that made it for all practical purposes a useless weapon. A hollow sphere of HEU was surrounded by a system of 72 explosive lenses that compressed the HEU to critical mass and detonation. But here was the problem. In the Green Grass warhead, the mass of HEU was in *excess* of the critical mass once compressed by the explosive lenses. That meant if the warhead were crushed or damaged during handling, it could partially detonate. American designs avoided this by having an HEU core that was inserted into the physics package usually by the bombardier once the bomber was in flight, thereby "arming" the bomb once the core was inserted. Without the core inserted, the HEU mass in the American designs was below the critical mass. The solution by British designers was to fill the center of the HEU sphere with 20,000 steel ball bearings to prevent the sphere from being crushed and reaching critical mass. To arm the bomb, a plastic plug was removed from the bottom of the warhead (accessible via a hatch on the underside of the Violet Club casing) that allowed the bearings to flow out, thereby arming the bomb. 

While it may sound like a creative solution, there were several issues: 
  • The weight of the ball-bearings increased the bomb's weight to 11,250 lbs which was greater than the capacity of not only the bomb release mechanisms of the V-bombers but also the ground-transport equipment of the bomb. 
  • The outflow of bearings took at least half an hour under ideal conditions- in cold weather, the bearings could freeze together, making arming the weapon near-impossible. 
  • Once the bomb was armed by allowing the ball-bearings to flow out of the center of the warhead, there was on way of making the weapon safe again. In fact, engine running was prohibited even with Violet Club "safed" as it was feared vibration would cause the plastic plug to fall out and inadvertantly arm the weapon. 
  • Because the bomb was armed irreversibly, airborne alerts were impossible because take off and landing were too hazardous to attempt with an armed Violet Club. 
  • Dispersal of the V-force to outlying fields was impossible as the bomb couldn't be flown to the dispersal airfield and the bomb transport equipment couldn't handle the Violet Club when it had its ball-bearings in place. 
The Blue Danube- the Violet Club looked similar externally.
While the Air Staff of the RAF ordered twelve Violet Club bombs, only five were made and as British author Chris Gibson put it in his book Vulcan's Hammer "From the RAF's point of view, that was five too many." With such an unwieldly weapon, why was it even fielded? First of all, remember that the British were classifying the Violet Club as megaton-class weapon by calling it the Interim Megaton Weapon. It definitely wasn't a megaton weapon, perhaps more 400 kilotons at best, but certainly the Operation Grapple tests at Christmas Island in 1957 did indicate to the Americans the British were succeeding at fielding their own H-bombs- even if those test detonations failed to created the desired thermonuclear reaction. So who was the target of the Violet Club? While serving notice to the Soviet Union that Britain was still a force to be reckoned with, it seems that perhaps the Americans were the target, so to speak- with a weapon in their inventory called Interim Megaton Weapon implying that newer designs forthcoming and the Grapple series of tests in 1957 making a good show of things despite failing to work as planned, in 1958 the United States repealed the McMahon Act and resumed full nuclear cooperation with the United Kingdom. The Green Grass warhead used in Violet Club would be the last all-British nuclear weapon as a new Mutual Defense Agreement signed as part of the repeal of the McMahon Act meant British designers now had access to more advanced and compact American designs. In fact, the successor to the much-despised Violet Club, the Yellow Sun Mk.2, used an Anglicized American Mk.28 thermonuclear warhead. But no other fission weapon ever fielded by any other nation approached the explosive yield of the Violet Club.
Source: Vulcan's Hammer: V-Force Projects and Weapons Since 1945 by Chris Gibson. Hikoki Publications, 2011, p47-51. http://www.nuclear-weapons.info/vw.htm, by Brian Burnell.

10 December 2011

How the US Coast Guard Ended up with the Dassault Falcon

HU-25 Guardian on short final into KDAL.
When the United States Coast Guard announced in January 1977 that a maritime patrol version of the Dassault Falcon 20 business jet was selected to replace the Grumman HU-16 Albatross and Convair HC-131As in the medium-range search and rescue role, it was the first time in the Coast Guard's 65-year history at that point that it had selected a non-American aircraft for its purposes. The road that led up to this landbreaking decision actually began in 1971 when the Coast Guard issued it's Medium Range Surveillance (MRS) requirement. At the time, the Coast Guard had selected what would have been a specially-developed version of the North American Rockwell Sabreliner 75 that would have been powered by Avco Lycoming ALF-502 turbofan engines- at the time, production standard Sabreliner 75s were powered by General Electric CF700 engines. However, the USCG came under intense criticism for the first incarnation of the MRS contract as it had not held an open competition for other aircraft manufacturers to submit proposals. Yielding to Congressional pressure, the Coast Guard canceled the contract with North American Rockwell and re-opened the MRS requirement as an open competition in 1975. 

The new MRS requirements stipulated that the aircraft be turbofan-powered to allow a high dash speed and high-altitude performance to fly over weather when enroute to a search area. The cabin had to be at least 600 cubic feet to allow all the equipment needed for fly several missions without having to return to base for a changeout of mission-specific equipment. Basic mission parameters were set at a 700 nm loiter at 2,000 feet at a distance of 150 nm from the base. A speed of at least 350 knots was required during the transit to and from search areas and the aircraft had to be capable of an airspeed of no more than 220 knots at 2,000 feet when in the search area. In March 1976, the USCG had received several submissions for consideration: 
  • North American Rockwell submitted it's previous proposed Sabreliner 75 development;
  • Gulfstream submitted two versions of the GII business jet, one powered by Rolls-Royce Spey turbofans and one powered by GE CF34 turbofans;
  • A highly unconventional submission came from ICX Aviation which had plans to license build the Yakovlev Yak-40 jetliner in Youngstown, Ohio. Their proposal was based on a Yak-40 powered by three Garrett AiResearch TFE731 turbofans;
  • Lockheed proposed a version of the Jetstar powered by two GE CF34 engines;
  • VFW-Fokker submitted two versions of the VFW 614 jetliner, one with Bendix cockpit avionics and one with Collins cockpit avionics- both versions would have used GE CF34 engines;
  • And finally Dassault through the Falcon Jet Corporation (a joint venture between Dassault and Pan Am to market the Falcon 20 in the United States) submitted a version powered by Garrett ATF3 engines called the Falcon HX-XX. 
The HU-25s are being replaced and serve at only 3 air stations.
By the fall of 1976, the field of submissions had been narrowed down to just three- Lockheed's CF34-powered Jetstar, VFW-Fokker's VFW 614 jetliner, and the Falcon HX-XX. Contractor bids were submitted to the Coast Guard on 28 October 1976 based on a 41-aircraft purchase and the Falcon HX-XX came out the cheapest at $4.9 million per aircraft. The VFW 614 was nearly 20% higher in unit price to the Falcon proposal and the Lockheed Jetstar proposal was a surprising 25% higher than the Falcon, coming in as the most expensive option. At the time, the Buy American Act of 1933 was applied to the bids which meant that the VFW-Fokker proposal was increased by an additional 12% in accordance with provisions of the act as it lacked significant American parts. The Falcon HX-XX, however, was exempted from this provision of the Buy American Act as the Falcon Jet Corporation in their proposal would import green airframes from Dassault and finish them out in the United States with American parts to equal 68.1% of the aircraft's value being sourced from US contractors- by the provisions of the law at the time, 50% was considered the minimum to qualify as a domestic product. Knowing the political winds in Washington when it came to a "foreign" aircraft purchase, the Falcon Jet Corporation even showed how over a 10 year service lift the value of American parts in the HX-XX increased to nearly 75%.

As a result, on 5 January 1977, Secretary of Transportation William T. Coleman, Jr, announced that the Falcon HX-XX was the winning submission and the aircraft would be designated the HU-25 Guardian in Coast Guard service. It set a precedent for the Coast Guard and two years later the service selected the Aerospatiale (today American Eurocopter) Dauphin helicopter to become the HH-65 Dolphin in the short-range recovery role. History repeated itself again several years ago when the EADS/CASA CN235MP was selected to replace the HU-25 Guardian in the medium range surveillance role- designated HC-144 Ocean Sentry, the first ones were delivered to the USCG in 2006.

Source: Air International, Volume 20, Number 4. "Uncle Sam's Gallic Guardian", p173-179. Photos: JPSantiago, United States Coast Guard

17 October 2011

The Ad Hoc Lashup That Resulted in Japan's Best Fighter of WW2

Japan's finest fighter of World War 2.
Unlike Germany and the Allies during the Second World War, the vast majority of Japanese fighter aircraft were powered by radial engines while other nations had a mix of both radial and inline engines for their fighter units. Only one production-standard Japanese fighter entered service with an inline engine, the Kawasaki Ki-61 "Hien" (Allied code name Tony). Over 2,500 Ki-61s were produced and saw service with the Imperial Japanese Army Air Force (IJAAF) from 1943 to the end of hostilities in 1945. The Hien was designed by Kawasaki's chief designer, Takeo Doi and his deputy, Shin Owada (Doi would later go on to design the postwar YS-11 airliner) in response to an IJAAF requirement for a multirole fighter that would use a license-produced version of the German Daimler-Benz DB601 liquid-cooled inline engine that also powered the Messerschmitt Bf 109. Proving itself to be a promising design, the Ki-61 turned out to have a major Achilles heel in its Kawasaki-built engine which was designated the Ha-140. Though the DB601 would be one of the Second World War's finest engines, by the time the Ki-61 entered service it was an old design that was already being outclassed by more powerful engines of both radial and inline design. Worse yet, the DB601 had very tight manufacturing tolerances and in Japanese license production, getting Ha-140 engines built as well as the DB601 proved elusive given the increasing toll being taken on Japanese industry which found itself constantly short of quality metals and lubricants given the tightening US Navy submarine blockade of the home islands. 

Ki-61 to Ki-100.
Worse would come as the war progressed into 1944 with Kawasaki's Akashi factory constantly being plagued by supplier shortages and properly manufactured crankcases and cylinder blocks. By the spring of 1944, more than half of the Ha-140 engines produced at Akashi that did leave the assembly line failed to pass acceptance testing! As a result, at Kawasaki's facility in Kagamigahara that produced the Ki-61 fighter found itself with increasing numbers of finished fighters sitting in open storage waiting for their Ha-140 engines. Matters worsened on 19 January 1945 when B-29 Superfortresses completely destroyed the Akashi engine plant, leaving 275 Ki-61 fighters without any engines. With the B-29s ranging with near impunity over the home islands, the IJAAF headquarters, the Koko Hombu, suggested that the engineless Ki-61s be adapted to take the most readily available and reliable engine- IJAAF engineers suggested that Kawasaki find a way to fit the engineless fighters with the Mitsubishi Ha-112 radial engine, a 14-cylinder twin row radial engine comparable in power to the Pratt & Whitney R-1830 radial used on the Consolidated B-24 Liberator and the Douglas C-47 Skytrain/Dakota. 

Takeo Doi was initially not pleased with the Koku Hombu's directive to fit the Ha-112 to the Ki-61. The radial engine was 48 inches in diameter and the fuselage of the Ki-61 was only 36 inches in diameter. But seeing as to how there was little alternatives and the need for fighters great, Doi had his engineering staff work around the clock to make the Ha-112 work with the Ki-61 Hien. Fortunately Kawasaki was in possession of a Focke Wulf Fw 190 which had been delivered to the Japanese several years earlier for engineering study. Using the cowl and engine mount of the Fw 190 as a starting point, Doi and his team even replicated the horizontal alignment and collection of the exhaust pipes of the Fw 190 which in the Kawasaki design actually added between 6 to 9 mph of thrust augmentation to the aircraft's speed. Designated the Ki-100, the prototype aircraft made its first flight a mere three months after start of design work- a figure all the more incredible in light of the tremendous toll the B-29 attacks were taking on Japanese industry. By the time the third Ki-100 prototype took flight, the Koko Hombu was sufficiently impressed that all the engineless Ki-61s were ordered to be converted to Ki-100 standard. 

On many occasions, Ki-100s bested Hellcats and Corsairs.
"Sufficiently impressed" would be an understatement- the Ha-112 radial engine actually made the Ki-100 superior in every performance parameter to the Ki-61, much to the surprise of Takeo Doi. Although just slightly slower in cruise than the Hien, the Ki-100 was more maneuverable and had a faster climb rate. The IJAAF even took the Ki-100 prototypes into mock air combat against a captured P-51C Mustang. With the flight test program only lasting three weeks, the first Ki-100s went into combat with the 18th Sentai in Chiba on the same night in March that B-29s had laid waste to sixteen square miles of Tokyo in a firebombing attack. Less than six weeks elapsed since first flight to first combat! Production of the Ki-61 was terminated immediately and in less than three months all 275 engineless Ki-61s were rebuilt as Ki-100s AND the Kagamigahara factory also managed to build nearly 75 new-build Ki-100s that featured a cut back rear fuselage to improve aft vision for the pilot. As fast as Ki-100s could be built they were funneled straight to home defense units who found the Ki-100 a formidable fighter. Numerous large dogfights against Grumman F6F Hellcats and Vought F4U Corsairs found the Ki-100 on the winning side with more American fighters shot down than Ki-100s. By May 1945 the Ki-100 finally had met its match as long range P-51D Mustangs from Iwo Jima were now escorting the B-29s all the way to Japan and back. Dogfights with P-51Ds ended up swinging in favor of pilot skill and numerical advantage rather than any deficiency on the part of either aircraft. 

The one weakness of the Ki-100 was its high altitude performance as it lacked a turbocharger and as a result, few B-29s fell to the Ki-100. Work was underway for a supercharged high altitude Ki-100 when the war came to an abrupt end with the atomic bombing of Hiroshima and Nagasaki. Unfortunately for Japan, only about 500 Ki-100s were built before the war ended, but compared to other Japanese fighter designs, the Ki-100 proved to be Japan's finest fighter aircraft as a swansong for the once-feared IJAAF. From inception to the end of the war, the lifespan of the Ki-100 was barely ten months with an ad hoc marriage of engine and airframe out of necessity! The only surviving Ki-100 can be seen today at the RAF Museum. 

Source: Air International, October 1976, Volume 11, Number 4. "The Last Swallow of Summer: The Extraordinary Story of the Ki-100", p185-191.

01 October 2011

Rivet Haste: Rebirth of the USAF at the end of Vietnam

Heritage Flight F-4E Phantom painted in Vietnam-era colors.
In several prior postings I had talked about how the United States set about improving the performance of its fighter pilots over the skies of Vietnam. The first one dealt with the testing and analysis of MiG fighters that had been obtained secretly by the United States and the second posting covered the origins of Red Flag, the exercises in Nevada that gave pilots valuable experience under simulated combat conditions. The Navy also instituted measures to improve its fighter pilots' performance after the Ault Report was commissioned by the Chief of Naval Operations to review naval air-to-air tactics. One thing to keep in mind is that there were numerous parallel measures being undertaken in the late 1960s and early 1970s to improve the dogfighting skills of American pilots. The main American fighter of the day that was in service with both the US Navy and USAF was the McDonnell Douglas F-4 Phantom II. The Air Force in particular, also looked at ways of improving the performance of the Phantom, a design that was originally intended for fleet air defense but found itself in swirling low speed dogfights over Vietnam for which it was never designed. 

The Phantom had two idiosyncrasies that proved to be a liability in a dogfight. Being a big hulking fighter with two J79 engines that left a nice smoke trail for the enemy to spot were one of just many faults of the aircraft. As the engines of the Phantom were optimized for high speed, so to were the aircraft's aerodynamics. In the low-speed regime during a dogfight, the F-4 was prone to what was called adverse yaw- normally when the pilot wanted to turn one direction, he only had to move the stick in that direction. At low speeds and high angles of attack that were commonplace in a dogfight, however, if a pilot pushed the stick to the left, the downward-deflected aileron on the right wing would produce more drag than lift, causing the Phantom to yaw back to the right even though the pilot wanted to turn left. As the yaw increases, the effective sweep on the left wing decreases and it starts to produce more left and the F-4 snaps to the right and then into a spin. All this happened nearly instantly and pilots had to compensate for the adverse yaw when rolling left or right by using the rudder aggressively during close air combat- instead of moving the stick into the direction of the turn, the rudder was deflected. So a left turn meant keeping the stick centered and pushing the left rudder pedal down. This causes the Phantom to yaw to the left and this decreases the effective sweep on the right wing- it therefore creates more lift and the plane now snap rolls into the direction of the turn. This took a lot of practice and it was suspected that a significant number of Phantom combat losses were due to adverse yaw conditions. 

The ergonomics of the Phantom cockpit weren't exactly great, either, with a mass of switches and dials that most Phantom drivers felt were scattered randomly over the instrument panel and side consoles. Most derided by the pilots were the switches on the panel by the pilot's left knee that controlled the Sidewinder and Sparrow missiles- one of the switches was a three-position switch that cycled through the Sidewinders and Sparrows. It felt identical to the other control switches on the missile panel and the last thing pilots wanted to do was look at the switch to make sure they flipped the right one in the middle of a dogfight. Resourceful pilots in Vietnam got hold a piece of plastic tubing that was used to sample oil from the engines. Cutting it into a two-inch length, it was slipped over the end of the switch so it stuck out from other switches. All a pilot had to do during combat was swat the tubing by his left knee to cycle through his missiles. 

South Korean F-4E shows off its leading edge slats.
When the F-4E entered service, its most obvious advantage was that it had an internal cannon in the nose, rectifying a situation often encountered in Vietnam when the MiGs were inside of the minimum launch parameters for either the Sidewinder or the Sparrow missiles. But the F-4Es had another advantage and that was what was called a "soft wing"- the wing now had leading edge slats that were controlled automatically by the flight control system whenever the angle of attack would reach a certain level. When the AoA hit this preset level, the slats would automatically pop out and it increased the lift across the wing- this had a dual effect on the Phantom- it eliminated the adverse yaw condition, even at high angles of attack. And secondly, the Phantom became practically spin proof as adverse yaw got eliminated- accidents from spins dropped dramatically and pilots could now haul around the beast in the sky without worrying about loss of control. In fact, some pilots felt that the soft wing F-4E flew just like the Northrop T-38 Talons used in advanced flight training. 

When the USAF brass got word of the improvised plastic tubing modification used in Vietnam, it became apparent after some analysis that many MiG kills were missed due to the missile switches being configured incorrectly. And truth be told, it was pretty embarrassing to know that to make a multimillion dollar fighter more effective in combat needed a cheap piece of tubing. The Air Force came out with a modification to the F-4E that was numbered 556. Pilots called it the "five-five-six mod" and what it did was add a switch on the outside of the left throttle. Operated by the pilot's left pinkie finger (hence it was called the "pinkie switch"), it if was pushed forward, the Sparrow missile was selected. If it was in the middle setting, a Sidewinder was selected. And if it was pulled all the way back, the F-4E's gun was selected. Since the pilot's hand was always on the throttles, the switch was readily accessible. The second part of the 556 mod was another switch added to the front of the left throttle that allowed the pilot to instantly reconfigure the weapons systems from air-to-ground to air-to-air. No longer was there a switch sequence to follow. Push one button, that was it. Other changes consolidated the bomb dropping switches into a single small panel. 

TISEO unit on the F-4E.
While the soft wing and the pinkie switch did much to ease the pilot's workload in air combat, there was still the issue of the rules of engagement requiring visual identification of a MiG before shooting. This restriction pretty much rendered the Sparrow useless as a beyond-visual range (BVR) weapon that could swat MiGs down from unseen distances. The biggest problem with the Sparrow with the RoE in use over Vietnam was that most engagements began head-on. At that distance, the Sparrow could be fired at a maximum of ten miles and a minimum of three miles. But head-on, the MiGs were much smaller and harder to see even if with a radar lock. With closure rates approaching one mile every three seconds, by the time the Phantom crew had a positive visual on the MiG, it was already too late to fire a Sparrow. The solution was called TISEO- Target Identification System Electro-Optical. Some F-4Es had an electro-optical telescope mounted on the leading edge of the left wing above the inboard pylon. The telescope had 4x and 10x magnification and displayed the image on the WSO's radar display. Now when the backseater had a radar lock, he could command the TISEO to track the target and then switch to 10x magnification for visual identification while the MiG was still in the firing envelope of the Sparrow missile.

With the soft wing, the pinkie switch, and the TISEO, the USAF realized it had the tools to make its fighter pilots more lethal. In the late summer of 1972, the Rivet Haste program was established. Rivet Haste would be the Air Force's acknowledgement that years of substandard training and poor doctrine had to be reversed. Rivet Haste combined the slatted wing, TISEO, and 556 mod of the F-4E and teamed them up with handpicked crews with combat experience over Vietnam. They were assembled at Nellis AFB and here the key of Rivet Haste would take place- intensive training with the new F-4Es against the secret MiG force that Air Force flew out of Tonopah north of Las Vegas. Each Rivet Haste crew were paired up to stay together through training to deployment for combat- this allowed the pilot and his WSO to develop their own system of coordination in the cockpit and carry that to combat. Six pilots and six WSOs were in each Rivet Haste group and each pilot/WSO would fly at least three missions against the MiGs at Tonopah. Each month, a new group of six pilots and six WSOs were assigned to Rivet Haste. Crews assigned to Rivet Haste saw it as a quantum leap in air combat training that the USAF had never had before, but the war in Vietnam ended less than two weeks after the first Rivet Haste crews arrived in Southeast Asia. 

It wasn't all for naught, though. The 556 mod spawned a cockpit design philosophy called HOTAS- Hands On Throttle And Stick- this meant that every function that a pilot needed in air combat (and even in air to ground combat) would be instantly accessible either on the throttle or stick. Many of the crews that were part of Rivet Haste would go on into important leadership positions in the post-Vietnam USAF that would result in a greater emphasis on realistic training. The realistic training provided to Rivet Haste crews would be one of several foundations that would result in the Red Flag exercises. 

As the saying today goes "Fight like you train, train like you fight". 

Source: Sierra Hotel: Flying Air Force Fighters in the Decade After Vietnam by C.R. Anderegg. Air Force History and Museums Program, 2001, p11-13, 32-35.

19 September 2011

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.

13 September 2011

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.

10 September 2011

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.

06 September 2011

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.

17 August 2011

Oliver Rasmussen Evades the Japanese for Ten Weeks- *in* Japan

Oliver Rasmussen in the back seat of the Helldiver
The run up for the Allied invasion of the Japanese home islands began on 1 July 1945 when Task Force 38, a powerful US Navy fast carrier armada, weighed anchor and headed out from its forward anchorage in the Philippines. Under the command of Vice Admiral John McCain aboard the Essex-class carrier USS Shangri-La, TF38 was tasked with Phase One of Operation Olympic, the preparatory phase of the invasion of Kyushu planned for November 1945. The aircraft of the task force would establish air superiority by mid-August over Kyushu which would in turn set the stage for Operation Coronet, the invasion of Honshu in 1946. The first strikes would begin on northern Japan on 13 July before moving south to Kyushu. In poor weather than grounded most of the Japanese fighter forces, the aircraft of TF38 struck coastal targets and shipping on Hokkaido, the northernmost of the home islands. Despite the weather, the Japanese managed to put up a spirited defense in the two-day strikes, with the Navy losing 44 aircraft and 26 pilots in crew. 

On the first day over Hokkaido, the Shangri-La's air wing would lose eight Curtiss SB2C Helldivers. One of the Helldivers lost was flown by Lt.(jg) Howard Eagleston, who descended too low under the overcast and struck a mountain in rural Hokkaido. He was killed on impact, but his gunner, 23-year old radioman Oliver Rasmussen, survived. With only the clothes he wore and an empty backpack, Rasmussen knew all too well what the Japanese did to their prisoners and decided he'd chance it in the Hokkaido wilderness. Being part Chippewa Indian from Minnesota, Rasmussen had come from an impoverished family (he referred to them as "the second generation right out of the teepee") but had spent his youth in the great outdoors. Having only a vague idea of his general location, Rasmussen spent seventeen days trekking to the coast, living off the land and avoiding any Japanese residents he came across. On 31 July upon reaching the coast, Rasmussen found his first source of significant food- a farmer's cow near his hideout would provide the sailor fresh milk for nine straight nights- each night he'd creep out to the cow and help himself to the milk and return to his hideout. The farmer never figured out what was going on, eventually turning to cow lose figuring she was longer able to produce any milk. 

Rasmussen then built a small boat and tried to head out to sea, but the breakers on that particular stretch of coastline proved hazardous. He retreated back up into the mountains of Hokkaido and set up quarters in an abandoned railroad shack where he kept himself fed with raw onions, birds' eggs, uncooked rice and frog legs. On 16 August, the day after the Japanese surrender, he was spotting by a Japanese civilian, but not aware the Japan had surrendered, Rasmussen abandoned his hideout and sought new refuge. After several days of exploring, he found a site well-hidden that was within easy reach of five farms. He scavenged some scrap lumber to build a small shelter and helped himself to the produce and milk from the five farms each night. As he hadn't bathed in weeks, one of the farms' dogs got his scent on 5 September and the owners went to investigate. He managed to knock over some of the farmers as he made a narrow escape back into the wilderness. Each day he noted more and more American aircraft flying overhead, but he was unable to get their attention. He did find it odd, though, that they attracted no defensive fire and it didn't appear that they were conducting any offensive strikes.

Frustrated that he wasn't able to attract any passing aircraft and growing weary of being in the wilderness, he opted for the direct approach on 19 September and walked into the port city of Tomakomai and presented himself to the local police station to surrender. To Rasmussen's surprise, the police chief treated him as a guest with his first real meal in ten weeks and a bath. It was then that he found out about Japan's unconditional surrender on 15 August. Rather amusingly, the police chief asked Rasmussen if he knew anything about the rash of milk and produce thefts from local farms over the past several weeks- to which Rasmussen denied any knowledge. After an astonishing sixty-eight days in the Japanese wilderness, he was returned to the USS Shangri-La to a hero's welcome. While the end of the war dominated news headlines in the United States, upon his return stateside some news articles did cover his story and regrettably most were condescending about Rasmussen's experience given his native American heritage. As a result, he told no one else about his story despite remaining with the Navy. 

Donald Norton's book on Oliver Rasmussen's experiences

Postwar, he made a career in the Navy working the Berlin Airlift and flying combat missions over Korea. He retired a chief petty officer in 1962 and settled in California where he got a technical job at the Lawrence Livermore National Lab. He passed away in his sleep in 1980 after a year-long battle with cancer with only a few people aware of his story. In the 1960s, though, a family friend made numerous recordings of Rasmussen's ten-week experience in Japan for a planned book. That family friend, however, died a year after interviewing Rasmussen and Rasmussen's wife put the tapes into storage. There they remained until nearly 20 years later, when one of Rasmussen's subordinates in the Navy from the 1950s, Donald Norton, set out to document Rasmussen's story for his own book project. Finding out that Rasmussen had died in 1980, his widow passed on the recordings to Norton, which became the basis for the book Chippewa Chief in World War II: The Survival Story of Oliver Rasmussen in Japan which was published in 2001.

Source: Whirlwind: The Air War Against Japan, 1942-1945 by Barrett Tilman. Simon and Schuster, 2011, p199-204.