29 October 2015

The Douglas F6D Missileer

The F6D Missileer's resemblance to the F3D Skyknight is apparent
In 1957 the US Navy issued a specification for carrier-based fleet defense fighter that could loiter for long periods of time at long distances from the carrier. In addition, the aircraft had to be able to engage enemy aircraft at 100 nautical miles with a powerful onboard radar and long-range air-to-air missiles. Under the assumption that enemy aircraft were to be destroyed at well beyond visual range, dogfighting capability was not necessary and the need for long endurance dictated a subsonic design. Six hours was the specified endurance for this fighter and in turn this meant a large fuel load. The complex radar systems planned called for a three-man crew, with the pilot and co-pilot on each side of the radar intercept officer, this way both of the flying crew man could share some of the same displays with the radar intercept officer (RIO). 

There were four components to 1957 concept for fleet air defense that would be issued to industry for submissions. The first, of course, was for the aircraft itself, which was awarded to Douglas Aircraft Company in 1959 for what was designated the F6D Missileer. But in addition, a contract was awarded to Westinghouse for the AN/APQ-81 radar that would be used by the F6D to track and engage enemy aircraft. The third component was a contract awarded to the Bendix Corporation for the large AAM-N-10 Eagle missile. What is little-known about the F6D program was the fourth component, for an advanced airborne early warning aircraft to search out targets for patrolling Missileers. This contract would go to Grumman Aircraft which resulted in the W2F Hawkeye (later redesignated E-2 Hawkeye) with its advanced AN/APS-125 radar which could scan an area 400 miles in diameter and cue several F6D Missileers. 

Overall configuration of the F6D Missileer
The F6D itself resembled a scaled-up version of the Douglas F3D Skyknight twin-seat all-weather/night fighter. The nose section was quite bulbous to house the Westinghouse AN/APQ-81 radar and the three man crew were seated side-by-side in a cockpit that resembled that of the Grumman A-6 Intruder. Two non-afterburning Pratt & Whitney TF30 turbofans were mounted on each side of the fuselage just under the unswept wings. At the time, the use of a turbofan engine in a combat aircraft was a new concept and the TF30 was selected for its fuel economy. Since the Missileer didn't have to be supersonic, there was no need for a heavy and fuel-hungry afterburner. 

The Westinghouse AN/APQ-81 radar would have been the most advanced radar of its day using pulsed-Doppler technology years before the first production pulse-Doppler radars would enter service. The radar had a maximum range against large aircraft of 120 miles and could track as many as eight targets at once. The radar could also send mid-course corrections to the Eagle missiles. 

Overall configuration of the AAM-N-10 Eagle missile
The Bendix AAM-N-10 Eagle was the first of the four components from the 1957 fleet defense concept to be awarded. A large solid rocket booster would boost the Eagle to Mach 3.5 after launch on a loft trajectory for maximum range. After the booster was jettisoned, the Eagle's own sustainer motor ignited and further accelerated the missile to Mach 4.5. The use of a loft trajectory gave the Eagle missile a range of 160 miles and on final approach to the target, the missile's own onboard radar system (based on the radar used on the Bomarc surface-to-air missile) switched on. The Eagle could be armed with either a conventional or nuclear warhead.

Despite the advanced nature of the technology used in the F6D Missileer program, many quarters in the Navy fundamentally opposed the concept, arguing that once the Missileer had fired its six Eagle missiles, it was left vulnerable and unable to defend itself as it lacked any other armament and its large subsonic size precluded any evasive maneuvers. Once firing its missiles, the Missileer faced a long return flight to the carrier to refuel and re-arm. In 1960, the building opposition within the US Navy won out and the F6D Missileer program was canceled along with the Westinghouse AN/APQ-81 radar and what was becoming an enormously complex AAM-N-10 Eagle missile. The cost of developing the missile itself was estimated to be more than the aircraft development cost. 

However, the development of the Grumman W2F/E-2 Hawkeye continued and the aircraft is still in production today, albeit with more advanced radar systems, and is perhaps sole remaining legacy of the ambitious, but flawed, F6D Missileer program. 

Source: American X & Y Planes: Volume 2; Experimental Aircraft Since 1945 (Crowood Aviation Series) by Kev Darling. The Crowood Press, 2010, p60-61. Photos: Wikipedia, various internet forums.

24 October 2015

Fox Two! The Birth of the AIM-9 Sidewinder Missile

An early Sidewinder test round- note the early constant chord fins
At the end of the Second World War, the Navy had been focusing its weapons development work at the remote Naval Ordnance Test Station Inyokern, California (today known as China Lake). Three hours northeast of Los Angeles in the high Mojave Desert and with 1,200 square miles of land to blow things up, the site tended to attract some of the more innovative if not unconventional minds in weapons design. A CalTech graduated named Bill McLean was working on a few ideas to improve the lethality of unguided air-to-air rockets. At the time, outside of guns, the only other air-to-air option in widespread use were rockets which were notoriously difficult to employ even against ground targets. One USAF Air Defense Command pilot once remarked that "the only thing you were sure to hit with air-to-air rockets was the ground."(In 1956 two USAF F-89 Scorpions tried to down an errant drone, firing over 200 rockets and failing to score a single hit.) The best options of the day were radar guidance, but the technology of the late 1940s and early 1950s meant a radar-guided missile would be heavy. McLean wanted something lightweight and simple that could be bought by the thousands. He reasoned that a self-contained guidance system would simplify the use of such a missile and he and a group of volunteers in their free time worked on infrared guidance- the missile could home in on the hot jet exhaust. 

At the time the Navy had been using 5-inch rockets since the Second World War in the air-to-ground role. Work on refining the 5-inch rocket had continued at China Lake (one result was the Zuni air-to-ground rocket still in use today). McLean wanted to combine the simplicity of a 5-inch rocket with infrared guidance. A rotating, gyroscopically-stabilized mirror looking through a transparent nose dome would reflect heat energy to a lead-sulfide photocell. Rather than focus on the target, the detector looked at the target's change in position and this way it automatically "led" the target and could hit from angle instead of just a tail chase which would require a significant speed advantage. This sort of guidance is called "proportional pursuit". Using his free time and the volunteer help of his fellow engineers, McLean developed a way to translate the seeker's findings to control inputs to the missile's fins. Another one of the team's ingenious solutions for the missile was a simple way to stabilize the missile so it didn't rotate about its long axis and complicate the work of the infrared seeker. Discs with spurs to catch the airstream to spin like roller wheels were installed on the edges of the main fins and were called "rollerons". By spinning up in the air stream, the rollerons acted like gyroscopes, keeping the missile from rotating on its long axis. It was an elegantly simple solution to a complex flight control problem. 

In 1950, the name for the missile was adopted, Sidewinder- after the predatory snake common in the Mojave Desert that used heat to sense its prey. Other names had been mooted, one of which was "Low IQ Homing Head" in reference to the missile's simplicity. By August 1952, the first aerial test shot was ready to take place. Future astronaut and Navy test pilot Wally Schirra fired the Sidewinder prototype from a Douglas AD-4 Skyraider at a Grumman F6F Hellcat drone. And it missed. And so did the next eleven test shots. Finally on 11 September 1953 after many fixes and revisions, the Sidewinder finally scored a proximity hit on its thirteenth test shot against a Hellcat drone. Four months later it scored a direct hit on a QB-17 drone square in its No. 1 engine. On 17 February 1954 McLean's small cadre scored another victory when another Sidewinder prototype destroyed another QB-17 that was thought to be indestructible because it had survived so many missile hits. 

The early test Sidewinder shots required the test pilot to monitor a small voltmeter in the cockpit to determine if the missile seeker was properly sensing the target's heat source. Realizing this was an unnecessary distraction in combat, McLean's small team came up with another simple solution- with just one additional wire from the missile, they could generate a tone that could be heard in the pilot's headset to let them know the seeker had the target- the famous "Sidewinder growl". The Navy was enamored with the Sidewinder's simplicity- at the time the US Air Force was bringing the Hughes AIM-4 Falcon into operational use. Developed by a vast engineering team at Hughes' southern California facilites, it was a much more complex weapon despite also being infrared guided. In fact, in 1956, a Navy team came to Holloman AFB in New Mexico (which sits astride the White Sands Missile Range) to prove to the USAF that an Air Force pilot who had never fired a Sidewinder before could destroy a target drone. It was an official shoot-out between the Navy's Sidewinder and the Air Force's Falcon missile and it was wildly successful for the Navy team- the story goes that the Navy test pilot on the team bet everyone in the test teams that the Sidewinder would work as advertised. Despite this, the USAF deployed the Falcon anyway and it proved to be dismal failure in the skies of Vietnam, quickly getting replaced by the Sidewinder in what was called the "Falcon Fiasco".

Evolution of the Sidewinder family
The first production Sidewinders (AIM-9A and AIM-9B) refined the aerodynamics from the straight, constant-chord fins of the prototypes. Still retaining the 5-inch diameter body, the seeker would feed commands to the forward set of fins while the larger aft set of fixed fins housed the rollerons, a layout that would be retained to this day until the debut in 2001 of the AIM-9X variant. The Sidewinder would have its combat debut in the 1958 Taiwan Straits Crisis when PLAAF MiG-17s used their high altitude advantage and cannon weaponry against the Taiwanese F-86 Sabres. In a secret program, several Taiwanese Sabres were quickly modified to fire the Sidewinder (again, reflecting the simplicity of the missile) and were used 24 September 1958 to ambush the Chinese MiGs. 

The Sidewinder missile so significantly changed the nature of aerial combat that it was even copied by the Soviet Union as the Vympel K-13 (NATO designation AA-2 "Atoll". It wasn't until the end of the Cold War that Russian designers admitted to what had been widely suspected for years. Even the parts numbers of the Sidewinder were replicated on the K-13! Hundreds of thousands of missiles have been built for United States military but also under license in Europe. China even copied the K-13 for its own use. The US Army fielded a surface-launched version that mounted four AIM-9D missiles on a tracked vehicle and was called the Chaparral. Older AIM-9C missiles pulled from service were converted in the 1990s into lightweight anti-radar missiles designated AGM-122 Sidearm. And the basic principles of the Sidewinder have influenced a large number of other infrared-guided missiles from around the world, from Israel's Python family to the French Magic family.

Navy deck crew lift a Sidewinder onto a Hornet's missile rail
The first Sidewinder missile's electronics consisted of only seven vacuum tubes and five moving parts. Over the years since then, the missile has retained the 5-inch diameter but has gotten longer from 109 inches to 119 inches as well as lighter, from 155 lbs to 118 lbs. The latest production model of the Sidewinder is the AIM-9X, the first missile to change the basic layout and seeker function completely. Instead of the rotating mirror, the seeker has a staring focal plane array using a pixel-based sensor derived from digital camera technology. The rollerons are gone and the fins are considerably smaller, now only making the -9X lighter but also making internal carriage easier. Jet vanes are now in the motor exhaust at the tail end to give it thrust vectoring which makes the rollerons unnecessary, makes the fins smaller and lighter, and gives the missile tremendous maneuverability. 

Not bad for missile that started out as a free time project with less than 25 engineers!

Source: Air & Space Smithsonian, November 2010, Volume 25, Number 5. "Sidewinder: The Missile That Has Rattled Enemy Pilots Since 1958" by Preston Lerner, p54-61. Photos: Wikipedia

19 October 2015

Mike Grimm, Father of the Night Stalkers

Michael Grimm, Father of the Night Stalkers
Conventional wisdom in aviation history points to the tragic debacle at Desert One in Iran during the hostage rescue mission as the watershed moment that culminated in the formation of the US Special Forces Command (SOCOM). While I do think that the story of the failed 1980 Iranian hostage rescue mission should be held near and dear to every military leader of this nation, there was actually someone else who sounded the warning bells three years before that fateful day in 1980. His name is legendary amongst US special forces personnel to this day, but I'd bet hardly any of us enthusiasts had ever heard of his name- Mike Grimm.

Long before he would make his mark on the history of US special forces, Mike Grimm was already a decorated hero of the Vietnam War when as a second lieutenant in 1968, assumed command of his platoon and managed to fight off through the night two entire companies of Vietcong before they could be extracted by helicopter from the battle zone. He stayed on with the US Army after the end of US participation in the war in 1973, eventually becoming a helicopter pilot and stationed in Hawaii in 1975. But serving in Hawaii was boring for Grimm, when the most serious decision they ever had to make was whether he would fly clockwise or counter-clockwise around Oahu. In 1976, the world was electrified with the stunning Israeli raid at Entebbe, Uganda, to rescue the passengers of a hijacked Air France flight. In less than one hour, Israeli commandos stormed the Entebbe Airport, killed nearly all the terrorists, rescued nearly all the hostages and only losing one commando. And they also manged to destroy most of the MiGs of the Ugandan Air Force in the process.

Mike Grimm realized that the United States lacked the capability to do what the Israelis managed to do- project power over 2,000 miles into hostile territory and effect a hostage rescue with minimal losses. Austerity was the key word in the post-Vietnam defense budget and even training exercises were canceled to save money. Once he had become the Divisional operations officer in 1977, he decided to use the Division's entire budget for training on a single exercise. He called it an Emergency Deployment Readiness Exercise (EDRE) and in the training scenario, his men and pilots would have to fly 200 miles to the island of Hawaii where a select group of soldiers playing terrorists were holding hostages. Grimm's men would have rescue those hostages with minimal losses. The tactics he developed for the exercise would be the blueprint for all future missions to come, even to this day.

Men from the First and Fifth Infantry Battalions at Schoefield Barracks on Oahu were selected to be the "raiders." Their helicopter element consisted of 10 Bell UH-1H Hueys and two Bell AH-1G Cobra gunships from A Company of the 25th Aviation Battalion. After an alert and planning period, the men and their helicopters flew from Schoefield Barracks to Hickam AFB to be loaded aboard USAF Lockheed C-141A Starlifters to simulate strategic deployment. The men were flown to Hilo Airport which would function as the "intermediate staging base" for the exercise. On 14 November they arrived in Hilo where the helicopters were readied for flight and they flew onward to Bradshaw AAF in the Pohaku Trainng Area in the center of Hawaii. This would be their "forward operating base" for the mission exercise.

The "hostages" were being held in the fire station of Waimea-Kohala Airport just 30 miles north of their forward operating base. The raid would be carried out at dawn as no night vision equipment was available. At ten miles from the target, the "terrorists" heard the team coming and "executed" the hostages. When Grimm's raiding force landed, they were wiped out to the last man.

The next day at Bradshaw AAF the After Action Review took place and everyone but Mike Grimm thought their Army careers were over when the Division commander, Lieutenant General Willard Scott arrived. He began the debriefing with the statement "This exercise was a really bad idea." As he continued for several minutes on the inappropriateness of using helicopter-borne infantry on anti-terror operations. "Our Army will never enter into this area. This is NOT our role."

At that moment, Mike Grimm stood up and interrupted his commander.

"Respectfully, sir, that is NOT correct." Here he was, a newly minted major, holding a two-star general to task. "Not only do we need to create this capability, sir, but if we don't, we are going to find ourselves at some point in our history embarrassed as a nation!"
Emblem of the 160th SOAR

Three years later, on the morning of 25 April 1980, in the Iranian desert, that embarrassment took place. The wrecks of five Marine RH-53D Sea Stallions and one USAF C-130 Hercules lay smoldering in the desert with the bodies of eight American servicemen. That year Mike Grimm was the commander of A Company of the 229th Aviation Battalion of the 101st Airborne Division where he was working with a handpicked group of men to transform the Hughes OH-6 "Loach" into what would become the MH-6/AH-6 "Little Bird" for night time special forces missions. On the night of 7 October 1981, Mike Grimm was flying one of the unit's MH-6s at low level over the Cumberland River when he hit the side of a power line tower and was killed instantly. One week later, in memorial to Mike Grimm, the new 160th Aviation Battalion uncased its colors. It was the birth of the Army Special Force's aviation element (Special Operations Aviation Regiment, or SOAR), the "Night Stalkers".

Source: The Night Stalkers: Top Secret Missions of the US Army's Special Operations Aviation Regiment by Michael J. Durant and Steven Hartov. GP Putnam and Sons, 2006, p33-64. Photos: US Army, Wikipedia

14 October 2015

The Spyplane Codenamed "Pie Face": The Birth of the Big Safari Program

The Big Safari emblem
(Big Safari Association)
At the end of the Second World War, Germany was divided into four occupation zones administered by the victorious Allied powers. The capital, Berlin, was in turn also divided into four zones. When The Soviet Union established East Germany from its occupation zone, West Germany was formed from the American, British and French occupation zones. Berlin was also divided into East Berlin and West Berlin with the western part of the capital surrounded on all sides by East Germany. By agreement, there were travel corridors to allow surface and air connections to West Berlin from West Germany. The air corridors were only 20 miles wide at a maximum altitude of 10,000 feet. The northern air corridor followed a Hamburg-West Berlin line, the central air corridor followed a Hannover-West Berlin line and the southern air corridor followed a Frankfurt-West Berlin air corridor. In the summer of 1952, the head of United States Air Forces Europe, General Lauris Norstad, made a special request to the USAF Chief of Staff, General Hoyt Vandenberg, for reconnaissance aircraft to use in Europe that in particular, could fly unnoticed in the West Berlin air corridors as a routine courier flight. Vandenberg convened a group of specially selected officers and civilians who would develop not just the aircraft needed for the requested USAFE mission but also a set of rule and procedures in order to field such an aircraft quickly and in secrecy. Lieutenant General Thomas Rhodes worked with a reconnaissance systems specialist, Furman E. O'Rear, to develop the procedures that would get the specialized aircraft into service. 

Rhodes and O'Rear laid down the "ground rules" for the project: 
  1. Only the minimum amount of documentation was needed. Personal contact and direct communication was preferred. 
  2. Strict security clearances would be issued on a need to know basis with a minimum of personnel. 
  3. No limit on funds for the project. Special capabilities needed in the field shouldn't worry about funding. 
  4. Primary responsibility for the program lay with the Director of Air Force Maintenance and Engineering (this later became Air Force Systems Command) who would direct the Air Force Materiel Command (this later become the Air Force Logistics Command in 1961).
  5. Coordination was the utmost importance between the different commands of the USAF and the intelligence community. A single project head would act as the point of contact for all the diverse interests involved. 
  6. Aircraft contractors selected would also issue strict security clearances to a closed off work area for any aircraft modifications. 
  7. The contractor selected would be responsible for yearly upgrades to any aircraft system. 
  8. It was agreed upon ahead of time that any modifications or changes needed to the aircraft systems would be approved to expedite the fielding and subsequent upgrades to any special capability aircraft. 
In addition to these ground rules, it was also agreed that any project would make use of an existing aircraft rather than develop a new aircraft. The project office was authorized initially with a five year commitment on the reconnaissance aircraft that would be fielded by the USAFE for use in the Berlin air corridors. When it was realized in 1953 that the program's set up lent itself well to other special projects, it was given its own code name by which it is still known today: BIG SAFARI.

The Boston Camera the USAF Museum
(USAF Museum)
The year before General Norstad's 1952 special request for a reconnaissance aircraft, a very large special optical camera had been flight tested on a Convair B-36. The camera, developed by optical scientists and engineers at Boston University in 1947-1949, was designated the K-42 but was known as the Boston Camera as well as the code names BIG BERTHA and DAISY MAE. With a 240 inch focal length (6096mm), it weighed nearly three tons and used very large 18x36 inch frame film. It would be the largest aerial camera ever built. The lens was fixed at f/8 with an electrically tripped shutter speed of 1/400 second. Allegedly it had the resolution to image a golf ball on the ground from 45,000 feet. During the flight test program it was decided that a bomber carrying the Boston Camera would have been conspicuous if not downright provocative and it would be better used mounted in a transport aircraft. The aircraft had to be large so as not to have any external modifications that would give away its carriage of the large camera. PIE FACE was the code name assigned to the effort to mount the camera in a transport aircraft. The first PIE FACE contractor was actually Boeing who had offered a YC-97 Stratofreighter- one YC-97 in fact had flown a handful of Berlin Airlift missions. Boeing at the time was preoccupied with other programs and afforded the PIE FACE program little attention to the point that security was constantly being compromised with the aircraft frequently parked in the open at the property perimeter fence line in Seattle. 

As a result, the PIE FACE contractor was changed from Boeing to Convair Fort Worth. This would become Detachment 1 of the Big Safari program. The general manager of Convair, August Esenwein, took a personal stake in the project and made sure the USAF had the necessary secure hangar space as well as any engineering personnel needed make sure PIE FACE was fielded quickly. Esenwein's personal involvement pleased the USAF and the working relationship between the USAF and Convair at Detachment 1 set the standard for future contractor relationships in the Big Safari program. In fact, Detachment 1 would run for twenty years with 87 different aircraft passing through Convair Fort Worth over that time span. 

PIE FACE would have looked just like this KC-97
While the Boston Camera did fly in Europe for six weeks on the YC-97, it was clear that as an early variant of the Stratofreighter it was less capable than the later KC-97 variants already in service. With less powerful engines, the YC-97 with the Boston Camera onboard was significantly altitude restricted. Given that the camera was used for stand-off oblique photography, a higher altitude meant that more of East Germany could be photographed from the air corridors. From 19 December 1952 to 23 February 1953, the Boston Camera was moved from the YC-97 to a KC-97 that had its boom removed, 49-2592. Both aircraft were literally cut in half behind the cockpit to move the camera from one aircraft to the other. The manual controls of the camera were upgraded with electrical and electromechanical controls as it was installed on the KC-97. Covert sliding doors were used to cover the camera ports when it wasn't in use. In addition to the installation of the Boston Camera, a 100-inch K-30 camera and a trimetrogon system of three K-17 cameras were also installed, all synchronized with the Boston Camera to give wider angle photographic coverage of the target areas and assist with mapping. A camera operator's station was installed in the cockpit with a special slaved sight to trigger the camera system. 

West Berlin air corridors
(German History in Documents and Images,
After flight testing with specially selected USAF crews, the PIE FACE KC-97 was assigned to 7499th Support Squadron (later renumbered to the 7405th) at Rhein-Main AB, the main USAFE transport hub in Europe. With each of the three air corridors to West Berlin being 20 miles wide, that was already 1/6th of East Germany that lay underneath any aircraft within the corridors. The addition of oblique photography added tremendously to the area surveilled- at the 10,000 foot maximum imposed by the Soviets, the majority of East Germany could be photographed by the PIE FACE aircraft. In addition to flying in the air corridors, perimeter flights along the border were also flown at altitudes as high at 32,000 feet. Just in the last six months of 1953 when it was first fielded, the specially-equipped aircraft had flown 13 missions (quite remarkable given the complexity of maintaining the camera system). The aircraft also stood alert for short notice missions and flew as far as the Arctic and the Middle East. Intelligence requirements soon outpaced the abilities of the aircraft and eleven other aircraft were added to supplement PIE FACE starting in 1954. Those aircraft will be the subject of a future article here at Tails Through Time, so stay tuned!

PIE FACE was scheduled to end in 1962 and 49-2592 was flown back to Convair Fort Worth for demodification. By that point the aircraft had already rotated through Fort Worth eight times for upgrades and further modifications. Engineers there had developed a pneumatic shutter system for the cameras in only 28 days that became the standard for any Big Safari photoreconnaissance system. But PIE FACE wasn't over just yet as the Cuban Missile Crisis erupted just as the aircraft was about to be demodified. Approximately 17 missions were flown from MacDill AFB in Tampa around the periphery of Cuba, PIE FACE's imagery supplementing that taken by the Lockheed U-2 overflight missions. In March 1965, 49-2592 returned to Convair Fort Worth for good as the airframe was worn out and given over for salvage. The Boston Camera ended up at the National Museum of the United States Air Force in Dayton, Ohio, where it can be seen today displayed with a Convair B-36 Peacemaker. 

Source: The History of Big Safari by Col. Bill Grimes, USAF (Ret). Archway Publishing in cooperation with the Big Safari Association, 2014, pp 1-16. 

09 October 2015

General Giulio Douhet, the First Air Power Visionary

Giulio Douhet, air power visionary
Those of us interested in aviation take it almost for granted the unyielding pace of technological development that has driven aviation forward through time. But even less heralded are those in aviation history who have shaped the thinking of aviation- it's easy for us to lay eyes on an aircraft or even to put our hands on one. They're very tactile and sensory experiences in aviation- to see one, hear one, feel one, even ride an aircraft. But how do you experience aviation doctrine? How do you grasp the thought processes that have shaped aeronautical progress? They're very abstract and not prone to enjoyment and appreciation by most of us. However, technological progress is a rudderless boat in chaotic waters without visionaries and thinkers to provide steering and direction. Of course we can name designers like Jack Northrop or Andrei Tupolev. Or pilots like Charles Lindbergh or Chuck Yeager. But the subject of today's blog posting is none of those- he didn't design any aircraft, he didn't even fly aircraft. But his writings on air power have left an indelible mark on aviation, if not history itself. 

Born in 1869, Giulio Douhet was a rare breed of Italian army officer who was both an infantry and artillery officer and what we might call a technocrat, having studied science and engineering as well. His earliest writings as part of the General Staff of the Italian Army covered mechanization and the incorporation of what would be come tanks in military doctrine. But with the arrival of lighter-than-air aircraft like dirigibles and the first practical biplanes prior to the First World War, Douhet quickly appreciated the advantages of aviation in war- aircraft could move in three dimensions and operate above and out of the reach of ground and naval forces with relative impunity. In 1912 when the Italians first used aircraft in combat in Libya, he wrote Rules for the Use of Airplanes in War, one of the first efforts to create a doctrine for military aviation- despite his own background as an artillery and infantry officer, Douhet felt that the current military leadership lacked an understanding of the inherent advantages of air power and an almost zealous desire to educate the establishment on air power would be Douhet's mission in his life. 

When the First World War broke out in Europe in August of 1914, Douhet was forty-five years old and no less energetic than officers half his age. With a near-insatiable appetite for the latest developments in aviation, he advocated the building of a force of 500 bombers that could bomb enemy forces from above without having to engage in prolonged combat. He worked closely with the Italian engineer Gianni Caproni in advising him on his own Caproni line of bomber aircraft. But Douhet would find the Italian military leadership incompetent as defeat after defeat was suffered by Italian forces. Convinced that aviation technology could reverse the lagging fortunes of the Italian military, Douhet wrote and spoke frequently to anyone and everyone in the military and government establishment. By 1916 his superiors had had enough when he had ordered construction of Caproni bombers without authorization. He was stripped of his rank and imprisoned on charges of "issuing false news" and "disturbing the public tranquility". It didn't stop him, though. He continued to write and refine his theories from his cell. 

In the fall of 1917, the Italian Second Army was completely routed at the Battle of Caporetto (in modern day Slovenia), suffering over 300,000 casualties. The Italian government in desperation released Douhet from prison and commissioned him as a general in charge of coordinating the nation's aviation strategy and doctrine. It would be too little too late as the entrenched Italian bureaucracy was unwilling to enact his plans and he resigned in protest in June 1918. With the Armistice in November of that year ending the First World War, Douhet's trial verdict was reversed and he was promoted, but by this point in his life he had lost faith in the Italian government and refused to return to duty. During the interwar period he traveled Europe visiting other nation's air arms, consulting with air officers and meeting with aircraft designers. In 1921 he wrote his landmark work Command of the Air which advocated an relentless air campaign of bombing an enemy's population and production centers, reducing their moral and material means of resistance. Properly conducted, he reasoned, such an air assault could force a quick decision and save millions of lives in the long run by avoiding a costly ground war. Douhet also pointed out that the efficient and proper means of carrying out such an air campaign would require an independent air arm led by an aviation-minded general staff. At the time, this was a revolutionary concept and only in Great Britain was the nascent Royal Air Force an independent air arm. For other industrialized nations of the 1920s, their air arms were subordinated to the army. 

Billy Mitchell, USAAC
Reception of Douhet's work outside of Italy was mixed. It wasn't even required reading at the RAF Staff College. But his work would find converts primarily in the United States- at the time the Air Force was part of the Army as the US Army Air Corps. One officer in particular would even meet with Douhet- Brigadier General Billy Mitchell. It was the year after Mitchell had demonstrated the vulnerability of warships to bombers by sinking several captured German warships off the Virginia coast. Mitchell had copies of Command of the Air sent to his superiors and he got banished to Hawaii and then Asia as a result. In 1925 Mitchell wrote a book of his own, Winged Defense, in which he refined Douhet's ideas of a strategic air campaign further and even declared the battleship obsolete as aviation technology matured. As a result, Mitchell was demoted in rank back to colonel. He would later be court-martialed for publicly criticizing the US military following the crash of the airship USS Shenendoah in a storm. But his six week court martial provided Mitchell the perfect forum for advocating views shaped by his mentor, Giulio Douhet. 
Sir Hugh Trenchard, RAF

Douhet died of a heart attack in 1930 and Mitchell himself would die in 1936, neither man living to see how their views of air power would come to fruition in the Second World War. While Command of the Air got little attention in the Royal Air Force, the most influential individual in the RAF at the time fortunately was a proponent of Douhet's theories- Sir Hugh Trenchard, Chief of Staff of the RAF and the man known as the "Father of the RAF". Trenchard, like Mitchell, would refine Douhet's ideas. By the time of the Second World War, Trenchard was every bit the irritant to the establishment as Douhet and Mitchell were, but had enough influence to avoid their fate. Following the disastrous loss of Norway to the Germans in 1940, Trenchard used his position in the House of Lords to criticize Prime Minster Neville Chamberlain's prosecution of the war which contributed to his replacement by Winston Churchill. Trenchard used in influence to put like minded officers in key positions in the Royal Air Force. After the war, Trenchard advised General Henry "Hap" Arnold in his own push for an independent United States Air Force.

The same year Mitchell died in 1936, contracts were issued to both Boeing and Douglas for a large four-engined bomber- while both companies' designs, the XB-15 and the XB-19, respectively, remained experimental, the engineering and design work on such a unprecedentedly large bomber would shape aviation technology throughout the Second World War. 

Source:  Whirlwind: The Air War Against Japan, 1942-1945 by Barrett Tillman. Simon and Schuster, 2010, p9-16.

04 October 2015

Birth of a Breed: The Development of the Douglas DC-1

The Douglas DC-1 at its 1933 handover to TWA
(San Diego Air and Space Museum Archives)
The crash of a TWA (Transcontinental & Western Air) Flight 599 on 31 March 1931 served as a major catalyst in the airline industry for adoption of all-metal aircraft. The Fokker F.10 was on a scheduled flight from Kansas City to Los Angeles when it encountered turbulence on its first leg between Kansas City and Wichita. As the Fokker F.10 airline had wings of wood laminate, accumulated moisture had caused a weakening of the glue used which led to delamination and structural failure. Aboard Flight 599 was the famed Notre Dame head football coach Knute Rockne, who along with five other passengers and two crew, were lost in the crash when the aircraft went down between the rural Kansas towns of Bazaar and Matfield Green. As a result of the crash, the Bureau of Air Commerce required operators of aircraft with wood wing structures to undergo frequent inspections- as this was economically unfeasible for most operators, all-metal designs were procured as soon as possible. TWA nearly shut down for good while its Fokker fleet was grounded for  inspections. Most of the types that were procured were interim types- but in 8 February 1933, a new airliner made its first flight that was a quantum leap over anything that had proceeded it, and that was the Boeing 247 which entered service with United Air Lines just fifty days later. All metal with a retractable undercarriage, the Boeing 247 was sleek and much faster than anything that had flown passenger services up to that point. Even the most current designs were instantly obsolete- for example, the Curtiss Condor biplane airliner had entered service with Eastern Air Lines and American Airlines just five weeks before United put its Boeing 247s into service. 

United's main rival on the transcontinental market was TWA- the Boeing 247 could now make the east to west transcontinental run in only 21 hours 30 minutes including technical stops. By comparison, TWA's Fokkers took 28 hours 43 minutes to fly from New York to Los Angeles. When TWA learned of United's order for the Boeing 247, he contacted Boeing about ordering the aircraft for TWA, but at the time, United and Boeing were part of the same holding company, United Aircraft and Transport Corporation and Boeing was contractually bound to deliver 60 Boeing 247s to United before it could supply airframes to other customers. TWA's vice president for operations, Jack Frye, wasted little time in sending a letter to other aircraft manufacturers soliciting interest in building at least 60 three-engined airliners for the airline. That letter went to Consolidated Aircraft, Curtiss-Wright, Douglas Aircraft, General Aviation Manufacturing, Stout (Ford) Aircraft, and Glenn Martin Aircraft. The letter included general performance specifications that any design had to meet: 

Jack Frye of TWA

1. All metal, trimotor preferred, combination structures and biplane would be considered, but the internal structure had to be metal. 
2. Thee engines of 500-550 hp. 
3. Maximum gross weight of 14,200 lbs. 
4. Weight allowance for radio and mail carriage of 350 lbs. 
5. Weight allowance for full instrumentation, including night flying, fuel to fly 1,080 miles at 150 mph, crew of two, at least 12 passengers in comfort. Payload had to be at least 2,500 lbs with full equipment and fuel for maximum range. 
6. Minimum top speed of 185 mph, cruising speed at least 146 mph. Landing speed not to exceed 65 mph, rate of climb at least 1,200 feet/min, minimum service ceiling of 21,000 feet and a minimum service ceiling with one engine out of 10,000 feet. 

The specifications page also emphasized that any design, fully loaded, "must make satisfactory take-offs under good control at any TWA airport on any combination of two engines." This landmark letter from Jack Frye is considered the "birth certificate" of the DC-1. When Donald Douglas received the letter in Santa Monica, he immediately convened a meeting with his top heads- James "Dutch" Kindelberger (of P-51 Mustang fame) who was his chief engineer, Arthur Raymond who was the deputy to Kindelberger, and Harry Wetzel, the Douglas Santa Monica plant director. With the United States in the midst of the Great Depression, it didn't take long for them to decide this was a tremendous business opportunity for the company. Just ten days after Jack Frye sent his letter of proposal, Douglas dispatched Arthur Raymond and Harry Wetzel with a ten-person team by transcontinental train to New York to meet with TWA. The Douglas team by this point had moved quickly and concluded that even though TWA was leaning towards a three engined design, they would offer a twin engined design that would be equal if not superior to TWA's specifications. The design would be an all-metal monoplane with a retractable undercarriage that would have passenger comfort as a priority. With Kindelberger supervising the design work in California and telephoning design details to Raymond and Wetzel as they were enroute to New York, the design was refined as the team prepared for its presentation to the TWA evaluation team which consisted of Jack Frye, Richard Robbins, president of TWA, and Charles Lindbergh, the airline's technical consultant. Also present were the teams from four other aircraft manufacturers, all of whom tendered three-engined designs. 

Having prior flying experience with other Douglas designs, Frye was favorable to the Douglas proposal, but Lindbergh had his doubts that a twin engined design could meet the airline's stringent specifications. Lindbergh in particular was concerned about single-engined performance at TWA's hot and high airports in the southwestern United States. The Douglas team in consultation with the engineerings staff in California rechecked their calculations repeatedly to be sure that their design could take off with a single engine from any of TWA's airports. With considerable trepidation, Douglas instructed his team meeting with TWA that he would agree to a contract provision guaranteeing this particular specification to satisfy Lindbergh's concerns. On 20 September 1932, TWA signed a contract for the first Douglas DC-1 for $125,000 (about $2 million of today's dollars) with options for 60 more aircraft based on the flight tests and performance of the DC-1. As an insurance policy against a possible failure of the DC-1, General Motors, which owned TWA, had its General Aviation Manufacturing subsidiary work on the GA-38X which was a three-engined larger derivative of the smaller single engined GA-43 airliner. Construction had started on the prototype, but work ceased early on when it became clear the DC-1 would be successful. 

Arthur E. Raymond, chief designer for the Douglas DC-1
(General Aviation News)
With a signed contract in hand, Donald Douglas assigned Arthur Raymond as the DC-1 project manager. Assisting him would be the legendary Jack Northrop, who was at the time managing the Douglas El Segundo division and would be managing the structural design of the DC-1. Other able Douglas engineers were put in charge of various systems and components for the DC-1. In addition and a first for a transport aircraft, extensive wind tunnel testing at Cal Tech's facilities in Pasadena, California, would be an integral part of the design and development process. Cal Tech's aeronautical faculty would head this effort to uncover as many issues as possible before any metal got cut for the prototype- it was wind tunnel testing that found the planned wing design was unstable and further wind tunnel testing at Cal Tech showed that sweeping the wing leading edge back addressed the stability issue. This was how the DC-1 and later DC-2 and DC-3 got their unique wing shape. 

With passenger comfort a priority, it was decided that the benchmark would be the interior noise of a Pullman rail car. The DC-1 cabin had to have the same level of noise or less. As the design effort proceeded, the early specifications for the Boeing 247 were published in Popular Mechanics and Arthur Raymond had copies of the article posted everywhere with the admonition "Do Better than Boeing!" It was vital at every step of the design process that the DC-1 be more comfortable than the Boeing 247 and an important design step was Northrop's wing design that would fit at the bottom of the fuselage without intruding into the cabin as was the case with the Boeing 247. Northrop's wing center section was relatively flat with the engine nacelles at the ends, outboard of which the outer wing panels were attached with the needed dihedral for stability. In a unique feature of the day, the passenger seats could also be reclined. Heating, ventilation, and the aforementioned soundproofing efforts were as considerable as any aircraft system to meet Douglas's desire for the DC-1 to be comfortable. The aisle width was a then-generous 16 inches (Americans in those days were nowhere near as obese as they are now) with a cabin height of 6 feet 4 inches. This would lay down the reputation of Douglas aircraft for years to come to be considered passenger-friendly.

Note the faired struts ahead of the wings on the DC-1
(San Diego Air and Space Museum Archives)
Both the Pratt and Whitney 9-cylinder R-1690 Hornet radial engine and the Wright 9-cylinder R-1820 Cyclone radial engine were evaluated with the Douglas team selecting the Hornet as the DC-1's power plant. Fixed pitch metal propellers were to be used for the prototype. Developments of both engines would figure prominently in American aircraft of the Second World War- the Cyclone would be progressively developed into larger versions that would power the B-17 Flying Fortress, the TBF Avenger, the B-25 Mitchell and in its ultimate development, the B-29 Superfortress and Lockheed Constellation. The Pratt and Whitney Hornet radial engine was a modest success but was developed into a twin row radial as the Twin Wasp which would be used on the DC-3 which in turn was developed into the outstanding Double Wasp and Wasp Major engines. The engine development is of course a future topic here at Tails Through Time! The engines of the DC-1 were one of the first transport aircraft to use the NACA cowling which streamlined radial engines by as much as 60%. When the prototype was rolled out in the summer of 1933, there were also faired struts that connected the forward fuselage with the engine nacelles ahead of the wings- in the prototype these carried sensor cables from the engines for test instrumentation but were later removed. 

On 9 April 1934, Dutch Kingleberger and Arthur Raymond filed for Patent No. 94,427 "Design for an Airplane" which described the layout and configuration of the DC-1 and later DC-2 development. Despite the patent's rather sparse documentation, it was issued by the US Patent Office in the following year. 

On 1 July 1933, the DC-1 would make its first flight as the birth of the Douglas breed of airliners. The story of the flight test program and service history of the DC-1 will be the subject of a subsequent article here, but it should be noted that in 1918, a very young Donald Douglas was working for Glenn L. Martin where he designed bombers for Martin but it was a transport derivative of his bomber designs that fascinated Douglas- the GMT or Glenn Martin Transport was a 15 seat aircraft that had a fully enclosed cockpit. Only one was built and it was destroyed in an accident in March 1920. The GMT was the first Douglas-designed transport and it was where Donald Douglas resolved that his dream was to design and build an aircraft that whose sole purpose was to carry passengers in comfort. That was in 1919-1920, the DC-1 when it made its maiden flight in 1933 was just the start of Donald Douglas's dreams coming true. 

Source: Douglas Propliners: Skyleaders, DC-1 to DC-7 by Rene J. Francillon. Haynes Publishing, 2011, pp 9-11, 46-53.