31 January 2010

When Israeli Aircraft Industries created the Kfir fighter-bomber by replacing the SNECMA Atar turbojet with a more powerful GE J79 engine, the additional modifications required to accommodate the American engine (which was shorter but heavier) along with the avionics needed for the strike role and the heavier undercarriage to increased takeoff weights with heavy bombloads degraded the performance and maneuverability of the the first generation Kfirs. Rather than try increasing the thrust of the J79 engine, IAI engineers decided the solution would have to be an aerodynamic one.

The addition of canards was favored early on and Dassault cautioned IAI about adding canards to the aircraft based on the French experience with the Mirage Milan canard test aircraft. Despite the warnings, no other solution was seen as being viable, so flight testing of the canard proceeded on the Technolog, a two-seat Mirage III that first tested the installation of the J79 engine.

Nose strakes near the tip of the nose were also found (even before the canard solution was reached) to improve high AoA performance but this came at the cost of buffeting at high AoAs, something that would have been unacceptable in air combat. The buffeting was cured on the suggestion of one of the IAI test pilots to add a wing leading edge saw-tooth which helped smooth the local airflow.

These modifications improved the Kfir's performance with the addition of wing area in the form of the canards that shifted the aircraft center of gravity forward, reduced the stability margin enough that the aircraft would be more responsive. The vortices that came off the canard smoothed the airflow over the delta wings which enhanced their lift and performance particularly at high angles of attack. The saw-tooth leading edges also slightly increased wing area and the vortices created by the saw tooth augmented the canard-produced vortices.

The combination of these modifications only added 187 lbs of weight to the new Kfir version designated C2. The side benefit of the structural strengthening of the fuselage for the canards (fuselage Section 10) is that that area was able to also accommodate an additional pair of weapons pylons under the intakes, giving the Kfir a total of five underfuselage pylon stations.

The Kfir C2 entered service with the IDF in 1977. The earlier Kfir C1s only got the nose strakes and a much reduced canard as the structural strengthening and modification to full C2 standards was deemed not worth the effort. Many of those earlier-variant Kfir C1s flew with US Navy and US Marine Corps adversary units in the 1980s as the F-21A Lion.

Source: International Air Power Review, Volume 15. AIRtime Publishing, 2005, "Warplane Classic: IAI Kfir- Israel's Lion Cub" by Shlomo Aloni, p137-139.

30 January 2010

The Most Ambitious UAV Ever: Quartz/AARS

One of the most ambitious if not the most expensive UAV design effort came in the 1980s as the Cold War was coming to its climax. Over $1 billion was spent on a black project called the AARS- Advanced Airborne Reconnaissance System or known by its code name, Quartz. The Quartz UAV was designed to be a very stealthy, long-endurance UAV that would penetrate Soviet air space in a time of war and identify what were called "strategic relocatable targets"- the rail- and road-mobile ICBMs of the Soviet's Strategic Rocket Forces. Quartz was sponsored by the US Air Force and the NRO, National Reconnaissance Office.

The requirement for a 24-hour endurance and low-observability tested the limits of aerospace technology of the day. In 1983 Lockheed and Boeing were selected to develop concepts for the Quartz program. Lockheed's initial design was a giant aircraft with a 267-foot wingspan propelled by two turboshaft engines driving massive 47-foot propellers. The engines were actually dual-cycle turboshaft/turbojet engines, with the engines operating as jets and the two-bladed props locked in horizontal for takeoff and landing. Once at cruise altitude, the engines shifted into turboshaft mode to drive the large props.

Little is known of Boeing's design for Quartz other than it may have been a flying wing design along the same lines as the Lockheed proposals. The need for low-observability and autonomous operation in denied airspace resulted in an expensive design that was compounded by the fact that only a few Quartz UAVs would be needed- the technology used was so sensitive that only the strategic imperative made it worth the risk of losing the aircraft in the event of malfunction or shootdown.

As the costs of the program soared, it became a victim of an inter-agency squabble between the CIA and the NRO who wanted Quartz and the USAF, who was losing interest due to the rising costs. In 1990 Lockheed and Boeing were directed to combine their efforts which resulted in a jet-powered flying wing not too dissimilar from the Northrop B-2 Spirit stealth bomber. As the costs still continued to climb, the USAF continued to back away from the program and even a redesign for a slightly smaller version failed to bring the USAF back aboard. Quartz was cancelled in 1992 when the NRO finally withdrew from the program as well.

In the 1990s, there were three "tiers" of UAV development based on operational capability. "Tier I" was for a low-altitude system that became the Gnat-750 UAV. "Tier II" was for a more capable medium altitude system based on the Tier I craft and that became the current Predator UAV family. The specification for "Tier III" would have been filled by the Quartz project, but with its cancellation, Tier III was split into two- Tier II+ was for the Quartz's performance without stealth and this became the RQ-4 Global Hawk UAV. Tier III- ("Tier III Minus") was stealthy but without the performance and payload of Tier II+. This design became the RQ-3 DarkStar. DarkStar, a joint effort between Boeing and Lockheed, had little in common with Quartz and itself would be canceled in 1999 in favor of further development of the Global Hawk.

However, it's believed that the current Lockheed/Boeing proposals for a next-generation bomber (the picture included in this blog post) are nearly identical save the cockpit to the resultant Quartz design.

Source: International Air Power Review, Volume 15. AIRtime Publishing, 2005, "Focus Aircraft: HALE/MALE Unmanned Air Vehicles Part 1: History of the Endurance UAV" by Bill Sweetman, p63-69.

29 January 2010

In 1967 Operation Combat Dragon commenced in Vietnam which would be the baptism of fire for the Cessna A-37 Dragonfly. An attack version of the T-37 trainer, the intent of the Dragonfly was to provide a low-cost yet capable close air support aircraft, a role that the faster jet fighter in the theater weren't exactly tailored to perform.

Conceived by Lt. Colonel Lou Weber, a veteran of the World War Two Flying Tigers, Operation Combat Dragon would introduce the Dragonfly into combat in a unique manner- whereas most combat aircraft had their weapons certification, weapons loading and maintenance procedures hammered out in operational testing in the United States before deploying to operational units, the Dragonfly would gain its combat certification by testing in actual combat.

Thirty pilots were selected for Operation Combat Dragon, all of whom had no more than 25 hours in the T-37. All came from all types of aircraft, from fighters to transports- Weber wanted to make sure that a pilot with any experience from any level could fly the A-37 in combat. Most deploying units to Vietnam had nine month training programs stateside before heading overseas- but with the A-37, the training was going to be done "on the job". Combat missions were to be flown in the III and IV Corps area of South Vietnam and forward air controllers favored the A-37- its slower speed allowed for pinpoint accuracy in delivering weapons on target.

The unit had the provisional designation 604th Air Commando Squadron and was based at Bien Hoa AB. In its first 3,000 sorties, not a single A-37 Dragonfly was lost in combat. Operation Combat Dragon ran from August 1967 to December 1967 and in that time frame, Lt. Col. Weber's strategy was soundly vindicated with 19,000 weapons drops and the combat experience led Cessna to develop an improved version, the A-37B. After nine months in combat, the unit had flown an astounding 10,000 sorties and reflected that it only took two men to maintain and turnaround the Dragonfly where as most jet fighters required 10 or more men per plane. On many missions a Dragonfly could be turned around for the next sortie in as little as 90 minutes. The unit would average twice the number of sorties as the more advanced and faster jets in Vietnam.

Source: Air & Space Smithsonian, January 2010. "Super Tweet- The A-37 Dragonfly carried 6,000 pounds of weapons. Bonus: They hit the target" by Stephen Joiner, p42-49.

28 January 2010

The Igloo White air-dropped acoustic sensors used in the Ho Chi Minh Trail during the Vietnam War to detect truck traffic weren't the last word in remote sensing technology for airborne interdiction. During Operation Iraqi Freedom, Steel Eagle was developed at the weapons research laboratories at Eglin AFB, Florida. Once a classified program, Steel Eagle came to light during the conflict as a possible asset in detecting and destroying mobile Scud missile launchers used by the Iraqis. Like Igloo White from the Vietnam War, Steel Eagle was a slim aircraft-dropped pod that contained acoustic and seismic sensors that activated once the pod was embedded in the ground near possible travel routes.

According to aviation author Steve Davies in his book on F-15E Strike Eagle units in combat (see source below), only about 35 of the Steel Eagle pods were made and were flight tested from an F-15E at the Nellis AFB ranges during OIF. The problem with the project is that there was no ballistics information on the pod provided for the weapons delivery system of the F-15E which made it difficult to accurately place. However, testing is said to have validated the basics of the system but no Steel Eagle pods were dropped during Operation Iraqi Freedom.

Technology that was validated in Steel Eagle is now part of the military's ARGUS project- Advanced Remote Ground Unattended System.

Source: F-15E Strike Eagle Units in Combat 1990-2005 (Osprey Combat Aircraft No. 59) by Steve Davies. Osprey Publishing, 2005, p86-87.

27 January 2010

Following the end of the First World War, Britain and France were determined to put the German aeronautical industry out of business for good with harsh terms being imposed by the Treaty of Versailles. One of the terms involved getting Germany's prized advanced Zeppelin fleet divided between Britain and France. The United States, having operated several LTA (lighter-than-air) patrol stations in France during the war where blimps were used to protect the Atlantic convoys, wasn't a party to the deal but rather than taking on Zeppelins (which the Germans ended up scuttling, infuriating the British and French), Navy personnel were sent throughout Europe to act as "observers" to the Armistice Commission that was essentially dissolving the German aviation industry. One of those Navy personnel, Commander Jerome Hunsaker, who after World War II would become chairman of NACA, NASA's predecessor, made several trips to Europe to study German Zeppelin technology between 1918 and 1920.

By 1919 Commander Hunsaker's influence on what he was learning in Europe convinced the then-Acting Secretary of the Navy, Franklin Delano Roosevelt, to approve preliminary construction of dirigibles to gain experience in LTA operations. The first designs were, like their British and German counterparts, designed for the use of hydrogen gas. But by the end of 1919 FDR on behalf of the Navy established the naval air station at Lakehurst, New Jersey by purchasing 1,700 acres from land that the Army thought was of little use.

During the testing of helium extraction, production and transport methods, the first helium gas arrived at Hampton Roads, Virginia, for testing in a Navy C-class blimp, the C-7. Ten C-class blimps were built in 1918 with production split between Goodyear and B.F. Goodrich and the control cars built by Curtiss Aircraft. It took several months to accumulate enough helium from Fort Worth and on 2 December 1921, the C-7 lifted off with 180,000 cubic feet of helium, making the world's first flight of a helium-filled airship. Fifteen sorties were made to determine the flight characteristics as well as handling methods for a helium-filled airship.

In 1921 the US Navy took the lead in aeronautical development by establishing the Bureau of Aeronautics (BuAer) with the airship-minded Captain William A. Moffett (later Rear Admiral) as its firs chief. One of Moffett's first acts as the head of BuAer was to rationalize airship development, placing Commander Hunsaker in charge. By the following year, the first American dirigible was ready for its first flight. The USS Shenandoah, designated ZR-1 and based on the LZ-49 Zeppelin design would be lifted by helium and the success of the Shenandoah led to the Navy pushing for control of the US helium supply as a strategic asset.

Early flight operations with the USS Shenandoah validated Hunsaker's belief that helium, something that was plentiful in the United States, would be a more suitable lifting gas as it was inert. Helium is often found in some natural gas deposits. Two of Hunsaker's assistants spent most of 1921 working with Linde Air Products Laboratory (then a division of Union Carbide) learning techniques and methods for the extraction, isolation and purification of helium. In 1925 the Bureau of Mines was assigned control of helium extraction and production, taking control of the only helium production plant in the United States at the time in Fort Worth, Texas. Funding would come from both the Army and the Navy defense budgets as helium was already considered a strategic asset.

25 January 2010

In the late 1960s the backbone of the Soviet Union's Strategic Rocket Forces (which in the USSR was an independent branch of the military) was the UR-100 ICBM designed by noted Russian rocket designer Vladimir Chelomei. The UR-100 had the NATO designation SS-11 and the code name "Sego" and was a two-stage, liquid propellant missile with a single warhead and was of relatively low accuracy but broadly comparable to the first generation of American Minuteman ICBMs. The Sego was an attempt to reach numerical parity with the United States with a missile that was relatively easy to produce and deploy, reaching IOC with the Strategic Rocket Forces in 1966 after three years of development and flight testing.

With the deployment of the American Minuteman III ICBM which now had three MIRV (multiple independently-targetable re-entry vehicle) warheads instead of a single warhead on the Minuteman I, the Soviets needed to match this technology and in the 1970s to the amazement of US intelligence analysts, deployed three ICBM types to replace the older SS-11 Sego.

The first to reach IOC in 1974 was an upgrade of the SS-11/UR-100 Sego- the UR-100U or SS-11 Mod 3 was based on the original SS-11 design but now had three warheads but the real centerpiece of the upgrade was a newly-hardened missile silo that could better withstand a US nuclear counterstrike.

Next to reach IOC in mid-1975 was the UR-100N which had the NATO designation SS-19 and the code name "Stilleto", which was also designed by Vladimir Chelomei to replace the UR-100/SS-11 Sego missile. The Stilleto was a two-stage liquid fueled missile with six MIRV warheads.

Right behind the Stilleto in reaching IOC with the Strategic Rocket Forces was the competing design to that missile, the UR-100MR which had the NATO designation SS-17 and the code name "Spanker". The Spanker was the first Russian ICBM to be designed with MIRV warheads, having four of them and in a first for the Russians, it used a cold-launch system where compressed gases were used to eject the missile out of the silo before engine ignition. The Spanker was designed by Vladimir Chelomei's rival, Mikhail Yangel .

But the real reason three ICBM systems were fielded by the Soviet Union was that there was disagreement over nuclear strategy. Yangel's SS-17 design would need new hardened silos but offered four warheads over the SS-11's single warhead, making it an effective counterforce to insure retaliation if the USSR were attacked by the United States. However, it was the most expensive of the systems. Chelomei originally offered the upgraded SS-11 Mod 3, which would have fit in existing silos but weren't as hardened as the SS-17 design's silos. Thus, this missile offered more warheads for less money, making it a threatening first strike weapon since it would have been vulnerable to a US counterstrike.

Soviet Premier Leonid Brezhnev called a meeting at his vacation home in Yalta to resolve the dispute with the president of the Russian Academy of Sciences, Mstislav Keldysh, appointed as head of the commission to resolve the dispute and set out a clear Soviet nuclear strategy. Halfway through the meetings Chelomei offered the SS-19 with its six warheads in competition to Yangel's four-warhead SS-17 design. Keldysh lamented in his memoirs that there was a rush to build missiles but there hadn't even been a decision on a strategic nuclear doctrine.

In the end, it was decided the best path forward was to accommodate everyone's interests and that is how in the 1970s the Soviet Union's Strategic Rocket Forces ended up fielding three new ICBM systems at tremendous cost, something that would further hasten the deterioration of the Soviet economy that led the the collapse of the USSR twenty years later.

Source: The Dead Hand: The Untold Story of the Cold War Arms Race and its Dangerous Legacy by David E. Hoffman. Doubleday Books, 2009, p18-19.

23 January 2010

Less than six months separated the first flight of the Boeing 377 Stratocruiser and the first flight of the Boeing B-47 Stratojet in December of 1947. While the Stratocruiser represented in many ways the ultimate development of the B-29 Superfortress, there was a design evolution that connects the B-29 and the B-47 as well.

The genesis of the B-47 came in the midst of the Second World War when the US Army Air Forces (the USAF wasn't an independent branch until 1947) looked to the future and knew that jets were the way to go and decided a jet-powered bomber based on their top of the line aircraft, the B-29 Superfortress was what was needed next. Boeing's design team began with what was essentially a jet-powered development of the B-29 but ran into difficulties meeting the range and performance levels that the USAF desired. When the war ended in August 1945, Boeing's chief aerodynamicist, George Schairer, was already in Germany with a USAAF technical team that was evaluating captured German aeronautical research.

At the Luftwaffe research center at Volkenrode, the technical team was reviewing wind-tunnel research into swept wings. In a dry well Schairer and the team found hastily-dumped papers that showed the performance leap possible by combining jet engines and swept wings.

Schairer wrote a seven page later to the engineering team at Boeing working on what would become the B-47 Stratojet. The design process at the time had a design that had fuselage mounted engines and a straight tapered wing and Schairer detailed in his letter what he had found at Volkenrode and his thoughts at how it might benefit the jet bomber design. As a result, the design was reworked to feature a 35-degress swept wing- at the time designated the Boeing Model 448, it was the first of two major technological breakthroughs in the design of the B-47. At this point the design still had its engines mounted in the fuselage and team found that the thin, swept wing could bend excessively in some flight regimes.

The second technological breakthrough was to relocate the jet engines in pods in the wings. The weight of the engines offset bending in the wings and resulted in a more aerodynamic fuselage. It would set the pattern for all large jet aircraft from then onward.

When the XB-47 made its first flight in December 1947, it was only 44 years to the day of the Wright Brothers' first flight at Kitty Hawk. But there was one other aircraft that beat the XB-47 into the air as the first with swept wings, and that was the XP-86 Sabre from North American Aviation (later redesignated F-86). North American also had representatives on the same technical team in Germany with George Schairer.

Source: 747: Creating the World's First Jumbo Jet and Other Adventures from a Life in Aviation by Joe Sutter with Jay Spenser. Smithsonian Books, 2006, p53-57.

21 January 2010

In electronic warfare, often the most effective countermeasure to the enemy's attempts at jamming and deception is a well-trained radio or radar operator. Throughout the 1950s as electronic warfare took on added importance during the Cold War, it was difficult at best to get training time on operational ECM systems. Most operational systems were strictly allocated to front-line units and often were scarce as new systems were constantly being developed and entered into service to meet new Soviet threats. As most operational systems were designed specifically to counter Soviet systems, those operational units couldn't be tested or trained since there were no Soviet examples available for training purposes- obviously!

Some units elected to train against US systems (often the service branches might train against each other), but an operational EW system had to be modified to work against US systems for the duration of the exercise and it was often said the surest way to make an electronic warfare system unserviceable was to take it out of the aircraft and put it back in again.

Peacetime exercises often were of limited value due to interservice rivalries. During one exercise in the 1950s in which SAC's B-47 Stratojets were to attempt to penetrate the US air defenses of New England (made up of Army missile units and USAF Air Defense Command interceptor aircraft), the Stratojet crews were instructed to "go easy" on the ADC fighters and "plaster" the Army missile units. The proper training of operators to deal with enemy electronic warfare and countermeasures requires that the students undergo a series of increasingly difficult scenarios rather than overwhelm them outright.

The US Navy was the first to recognize this need and in 1957 created a unit dedicated to creating a realistic ECM environment for training the fleet. Four Grumman TF-1 (redesignated C-1A after 1962) Traders that were usually used for carrier on-board delivery missions were modified into airborne jamming simulators. With a crew of five that included two pilots and three ECM operators, the TF-1s were crammed full of electronic warfare equipment as well as equipment for analyzing and grading the responses of the units being trained.

The weight of all the equipment was so great that the TF-1Q, as it was designated, was too heavy to operate safely from carriers and its range suffered as well. But this was of little issue to the Navy as the TF-1Qs were to be shore based and train fleet personnel in US waters. The first unit was VAW-35 based in NAS North Island in San Diego before the aircraft were split up with two TF-1Qs based at NAS Alameda with VAW-13 to work with the Pacific Fleet and two TF-1Qs were based at NAS Quonset Point, Rhode Island with VAW-33 to work with the Atlantic Fleet. In the years that followed, the TF-1Qs (redesignated EC-1A after 1962) were worked hard acting as enemy "Red" forces for carrier battle groups preparing to deploy overseas.

The value provided by a dedicated electronic aggressor force was such that the Navy in 1969 established the Fleet Electronic Warfare Support Group made up of the squadrons VAQ-34 "Flashbacks" and VAQ-33 "Firebirds" by which time the FEWSG operated a variety of aircraft as well as civilian contractor aircraft to provide the most realistic training environment for the Navy, a mission that continues to this day.

Source: The History of U.S. Electronic Warfare, Volume II- The Renaissance Years, 1946-1964 by Alfred Price. The Association of Old Crows/Port City Press, 1989, p203-205.

20 January 2010

During the late 1940s and early 1950s many aircraft manufacturers were conducting studies on the feasibility of converting existing piston-powered transports to turboprop power. The use of turboprops was seen as a low-risk advance that combined proven airframes with higher performance engines without sacrificing fuel economy, one of the weaknesses of jet engines of the day. With the Boeing C-97/KC-97 Stratofreighter in service with the USAF at the time, Boeing had pitched to the USAF several times a turboprop-powered Stratofreighter. All were under the same Model 367 number and at one point in 1953 Boeing went as far to built a partial mockup of the proposed Model 367-41.

The USAF, however, showed little interest in Boeing's proposals but in 1955, decided to investigate further the concept of a turboprop-powered C-97/KC-97 by commissioning Boeing to convert 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!

Both aircraft were flown in regular transport duties as well as trials work by the USAF until 1964, but by the time both aircraft had flown, Boeing and the USAF were shifting their efforts to developing the KC-135 Stratotanker and its even greater potential than the YC-97Js.

The first YC-97J, 52-2693, upon retirement in 1964 was used to provide parts and sections for the prototype Aero Spacelines B-377SG Super Guppy.

Source: International Air Power Review, Volume 20. AIRtime Publishing, 2006. "Warplane Classic: Boeing C/KC-97 Stratofreighter" by Bill Yenne, p128-129.

18 January 2010

In the 1950s the United States introduced three different systems to try and solve the problem of conducting electronic intelligence (ELINT) on targets deep in the Soviet Union which couldn't be picked up by the USAF and Navy ferret flights operating on the periphery. The first system was to mount ELINT antennas on giant weather balloons that would be launched in Western Europe and drift over the Soviet Union on prevailing winds before being recovered out in the North Pacific. Approximately 200 "Grand Union" balloons were built for the USAF and only about 20 were actually launched with little to no useful intelligence being recovered. The second system was to use ELINT antennas mounted on Lockheed U-2 spyplanes during overflights of the Soviet Union. Between 1956 and 1959, approximately 30 ELINT overflights were made, but only a handful of those missions were deep penetration missions.

The most productive of the systems and ironically the lowest risk due to its low manpower requirement as well as it could be located in the United States was introduced in 1958 as the PAMOR (Passive Moon Relay) system. Originating from experiments dating back to 1948's Project Diana which determined that communications signals could be bounced off the Moon to receivers beyond the horizon, PAMOR (sometimes referred to Moonbounce) was the natural extension. A CIA engineer, Jim Trexler, postulated that a sensitive receiver pointed at the Moon could pick up radar emissions from sites deep in the Soviet Union.

The first PAMOR dishes were built at the Naval Research Laboratory's Chesapeake Bay Annex on the bay's western shore as well as in California in Palo Alto. The definitive equipment was installed soon after in a valley near Sugar Grove, West Virginia (not far from the radio astronomy observatory at Green Bank). Using 150-foot dishes and sensitive listening and tracking equipment, the system readily produced results as the new early warning radar system code named "Tall King" was discovered. Designated P-14 by the Russians, the Tall King radar was a powerful system used for the detection and tracking at long ranges of airborne aircraft. Using known Moonrise and Moonset times, it was possible to draw a line on a map through the Soviet Union- somewhere along that line would be the transmitting radar. Over several weeks, it was possible to narrow down the precise location as this would be where the Moonrise/Moonset lines intersected.

In the latter half of the 1960s (starting in 1964 when it was first intercepted by a PAMOR dish), the system discovered a new high power advanced radar system that was found to be used by the Soviet ABM system to scan and track incoming ballistic missile warheads. Code named "Hen House" due to the configuration of the antenna, detailed analysis not only revealed the Hen House locations, but also radar characteristics such as frequency, power, dwell time, etc. From this analysis it was determined that the Hen House radar was very sophisticated as it could both track and scan and its dwell times were very short, which suggested a high level of computerization.

As the Soviets upgraded and fine-tuned the Hen House system for its ABM defenses, operators would practice and test the system by tracking the Moon, inadvertently making the job of the PAMOR teams much easier!

The discovery by the PAMOR program of the Hen House ABM system was significant as the characteristics of the system drove the design and planned employment of the US SLBM/ICBM nuclear deterrent. At its height in the late 1960s and early 1970s, the program never employed more than 100 personnel, making it one of the most successful ELINT efforts ever deployed.

Source: The History of U.S. Electronic Warfare, Volume II- The Renaissance Years, 1946-1964 by Alfred Price. The Association of Old Crows/Port City Press, 1989, p157-161.

17 January 2010

When the Saunders-Roe Princess flying boat made its maiden flight in August 1952, the engineers who designed it were well aware of the rise of the pure jet and had already been at work on a pure jet-powered successor to the Princess, the Saunders-Roe Duchess. With a cruising speed of 500mph and accommodating 74 passengers, the Duchess was to be powered by six De Havilland Ghost engines buried in the wing roots.

The Duchess would have had a wingspan of 124 feet and a gross takeoff weight of 130,000 pounds. The slight anhedral of the wings allowed for wingtip floats installed in a similar manner to the Martin P6M Seamaster. The 74 passengers were carried in forward and aft cabins with four-abreast seating and a cargo compartment in the center fuselage where the jet noise would have been the loudest in the cabin. Having the cargo compartment at the center of gravity also eased some design issues in the Duchess. The anticipated range of the Duchess would have been between 1,300 and 1,500 miles, modest when compared with what Boeing and Douglas were offering on their soon-to-arrive designs.

Unfortunately for Saunders-Roe, the impending arrival of the high-performance land-based jetliners from Boeing and Douglas would eclipse the Duchess with higher speeds and greater passenger and cargo capacity. Tasman Empire Airways had expressed significant interest in the Duchess, though, as a passenger jet seaplane would have been ideal on its routes amongst the smaller islands between Australia and New Zeland. However, interest from a single operator wasn't enough to bring the Duchess into production. It would not be until 1998 that a passenger-carrying jet seaplane would take to the air with the Beriev Be-200.
Source: An Illustrated History of Seaplanes and Flying Boats by Maurice Allward. Barnes and Noble Books, 1993, p129.

16 January 2010

The second pre-production Scottish Aviation Twin Pioneer, G-AOEO, first flew in August 1956 just in time to be showcased at the 1956 Farnborough Air Show- at the air show, Scottish Aviation presented the new aircraft design in Swissair colors. Between January and March 1957 the airline chartered G-AOEO to fly passengers into short runways high in the Alps. Two main services were trialled by Swissair- the first one was marketed as the "Swissair Pioneer Ski-Lift" and ran three times a week between Zurich-Kloten to ski resots at Davos and St. Moritz. On alternating days, G-AOEO operated the "Swissair Jura Airlift" which connected Zurich-Kloten to Geneva via La Chaux-de-Fonds high in the Jura Mountains. Both services were scheduled to connect to Swissair international arrivals and depatures at Zurich.

Although pleased with the STOL performance and the economics of the Twin Pioneer, no orders were forthcoming from Swissair though the airline did later purchase one for use in photographic survey flights.

G-AOEO crashed in December 1957 near Tripoli while on an African sales tour. All six aboard were killed, including the co-founder of Scottish Aviation. Metal fatigue was found to be the cause as the left hand wing was found almost a 1/2 mile from the main crash site. The crash weakened potential customer confidence in the Twin Pioneer which would affect its future sales prospects.

Source: British Airliner Prototypes Since 1945 by Stephen Skinner. Midland Publishing, 2008, p110-112.

14 January 2010

Early combat aircraft of the First World War were often fragile contraptions not ideally suited to the rigors of sustained aerial maneuvering. In Britain, Herbert Smith of the Sopwith Aviation Company designed a new biplane based on an earlier design, the Sigrist Bus (named for the manager of the Sopwith factory, Fred Sigrist), that never went into production. In most contemporary biplane designs, the two upper wings were joined by a central section. Support struts attached to the upper longerons of the fuselage to the ends of the central section and usually a second set of struts were attached to the inner part of the outer wings connected to an outer set of longerons on the fuselage.

In the new two-seat Sopwith design, there was no central section and the two upper wings were joined together. A W-shaped set of struts supported the upper wing of the biplane to the fuselage longerons and were considered "one and a half set of struts" instead of two sets of struts, which led to the new Sopwith's name, the 1 1/2 Strutter. The one and a half strut layout gave the upper wing tremendous rigidity like a railroad trestle.

But more remarkably in the Sopwith 1 1/2 Strutter, it introduced two features that are now commonplace on modern aircraft.

The first innovation was a variable-incidence horizontal stabilizer. The front spar of the tailplane was hinged on the rear fuselage and a worm gear actuated by a set of cables linked to a handwheel in the cockpit allowed the pilot to adjust the trim of the entire stabilizer. At a neutral setting, the tailplane was angled +2 degrees and the worm gear allowed the pilot to move the entire assembly more or less from that neutral setting depending upon the flying conditions.

The other innovation on the 1 1/2 Strutter were airbrakes on the trailing edge root of the lower wing. Pivoted at about quarter chord on each side, the airbrakes were operated by another handwheel in the cockpit that linked to a set of cables that raised the airbrakes up to 90 degrees upward and could be locked into position by the pilot. As the 1 1/2 Strutter had relatively clean lines for the day, it had a flat gliding angle and high landing speed (most aircraft of the day didn't have flaps) and the airbrakes were used to assist with the descent and landing.

Source: Aeroplane Monthly, December 2009. "Aeroplane Database: Sopwith 1 1/2 Strutter" by Philip Jarrett, p56-70.

12 January 2010

Warship in the Desert: The Muroc Maru

At the instruction of General Henry "Hap" Arnold, in 1933 Rogers Dry Lake in the Antelope Valley north of Los Angeles was chosen as a gunnery and bombing training range for the expanding US Army Air Forces. Set up six miles west of the town of Muroc by personnel from March Army Air Field in Riverside, a series of practice targets were set up throughout the dry lake bed site which included simulated structures, the outlines of naval ships for high level bombing practice, and even a track for a moving target. Retired elderly Keystone biplane bombers were set up as well on a simulated airfield. Two years after being established, a second site was set up on the dry lake bed just one mile north of the town of Muroc.

Initially needing only a caretaker group of 13 Army personnel, the Muroc bombing range operated as a branch of March Army Air Field and the size of visiting squadrons would result in groups of personnel of varying sizes temporarily taking up residence at Muroc. Not only bomber and attack squadrons passed through the range but fighter squadrons as well for ground strafing exercises. By the summer of 1941 the base had expanded considerably in anticipation of the coming war. By 1942 over 40,000 personnel were stationed at Muroc at any given time and this resulted in Muroc being established as an air base in its own right as Muroc AAF independent of March AAF.

One of the most unique targets at Muroc AAF was completed in March 1943 and was designated as "AAF Temporary Building (Target) T-799, a full-sized wooden mockup of a Japanese Atago-class heavy cruiser. It was made of wood and covered with chicken wire and tar paper. Over the tar paper it was covered with shredded chicken feathers to give the appearance of a solid warship. Constructed at the south end of Rogers Dry Lake, the target got the nickname "Muroc Maru" and cost the USAAF approximately $35,000, a hefty sum in those days for something to be used for target practice.

Sand berms were constructed around the Muroc Maru to simulate the bow wave and wake. Bomber crews practiced low-level skip bombing against the Muroc Maru. On particularly hot days, pilots reported that the mirage effect would give the appearance of the Muroc Maru sailing at sea. Due to the strong desert winds and temperature extremes, the chicken feather covering of the target wasn't as durable as the wood and chicken wire structure.

Flight testing of new aircraft began in 1942 at Muroc. Training activities ended at Muroc AAF in 1946 and with an independent US Air Force, it became Muroc AFB in 1948. The following year the base was renamed Edwards AFB.

As for the Muroc Maru, it was a declared a flight hazard and dismantled in 1950. Army engineers responsible for the dismantling weren't thrilled about the extent of unexploded ordinance in the structure of the target. Some of the sand berms remain at the site to this day as well as millions of nails and metal staples from the 1950 disassembly.

Source: X-Plane Crashes: Exploring Experimental Rocket Plane, and Spycraft Incidents, Accidents, and Crash Sites by Peter W. Merlin and Tony Moore. Specialty Press, 2008, p13-14.

11 January 2010

On his very first combat mission in 1915 flying a two-seat FBA flying boat to attack German gunboats, the young Alexander de Seversky would lose his right leg. After recuperation, he was assigned as the chief naval aircraft inspector for the Russian Imperial Navy's Petrograd district which gave him an appreciation for the design and production of aircraft. He worked closely with Dimitry Grigorivich on a series of flying boats that resulted in the M-9, the first Russian-designed naval aircraft to go into production during the First World War. Seversky encouraged Grigorivich to incorporate a machine gun mount as well as armor plating for the crew on the M-9.

Despite losing his flying status due to his injury, Seversky managed to perform an aerobatic display in the M-9 that enraged his superiors but won him the admiration of Czar Nicholas II, who ordered Seversky placed back on flying duty. Fitted with a wooden prosthesis and flying the plodding M-9 flying boat (it only had a maximum speed of 69 mph), he managed to score four kills against German aircraft. In 1917 he started flying a Nieuport 21 biplane and scored his fifth and sixth kills by single-handedly downing a German bomber and its fighter escort, bringing him to ace status.

In 1918 his status won him assignment to Washington D.C. as the Russian military attache with the embassy, but the Bolshevik Revolution that year resulted in him staying in the United States for good. He served as an assistant to Brigadier General Billy Mitchell in Mitchell's crusade to advance the cause for air power and Seversky would eventually establish his own aircraft manufacturing firm, Seversky Aviation, in Long Island, New York. In 1939 amidst a corporate reorganization Seversky was voted off the board by his own company which was renamed Republic Aviation. Another Russian emigre who worked for Seversky, Alexander Kartvelli, would take one of Seversky's designs, the P-35A fighter, and develop it further along a series of subsequent designs that culminated in the Republic P-47 Thunderbolt.

When he died in 1974, Seversky would hold 100 aviation-related patents and had received the Exceptional Service Medal for his advisory work for the U.S. Air Force in the 1960s.

Source: Aviation History, March 2010. "The Making of a War Hero" by James K. Libbey, p54-59.

10 January 2010

From the outset in the design of the Convair B-58 Hustler, the unique fuel/weapons pod carried underneath the sleek bomber was to be only one of a family of systems that were to be pod mounted as well- rather than have to develop different versions for different roles, different pods for different roles would be carried by "stock" B-58s. Some proposals were for air-launched ballistic missiles, others were for reconnaissance systems with cameras housed in the pod. There was even a proposal for a passenger-carrying pod. But many of these ideas never came to be.

But one system that did get flight tested was for an airborne side-looking radar that would allow a B-58 to get detailed radar imagery from stand-off distances. The first system to be built was the pod-mounted Hughes AN/APQ-69 radar system which first flew on a B-58 on 24 December 1959. The AN/APQ-69 was one of the largest airborne radar antennas ever flown with a 50-foot long antenna that took up all of a long square-section pod carried by the Hustler. Twenty-five test flights were made with the radar and it had a 10 foot resolution from 50 miles which was quite good for the technology of the day. However, the size and weight of the pod restricted the B-58 to subsonic flight and as the radar took up the entire pod, it couldn't be used to carry additional fuel as the fuel/weapons pods used by the SAC alert Hustlers. As such, the B-58 carrying the AN/APQ-69 was limited to only 3 hours' flying time, making it of limited usefulness. In addition, the bow wave from the blunt nosed pod hampered nose gear retraction and a 0.5G pushover after takeoff was necessary to "help" the nose gear retract.

A more advanced radar pod flew in 1961, this time it was a Goodyear AN/APS-73 radar- this time it was a SAR (synthetic aperture radar) which allowed for a smaller antenna but a more detailed radar picture and it was used in a pod that had the same cross-section as the MB-1 fuel/weapons pod already in use- this allowed the B-58 to use nearly all of its performance envelope and the pod could also carry a sizeable amount of fuel.

The AN/APS-73 was housed in a black fiberglass nose section of the pod with the aft 2/3 of the pod carrying fuel. There were two X-band rotating antennas in the pod nose that rotated on an axis that ran longitudinally the length of the pod. The radar range was about 80 miles and was flight tested under the code name Project Quick Check. While the system never went into production, it was used operationally on one flight during the Cuban Missile Crisis- a single B-58 flight carrying the AN/APS-73 was made to survey targets of interest on the island, making it the first and only flight of a B-58 Hustler into hostile airspace.

That particular aircraft, 55-0668, also was the same aircraft that flight tested the earlier Hughes radar pod. It survived the scrapping of the Hustler fleet in 1970 and is now on display at the Lone Star Flight Museum in Galveston, Texas.

Source: Convair B-58 Hustler: The World's First Supersonic Bomber by Jay Miller. Midland Publishing/Aerofax, 1997, p81-86.

07 January 2010

The first Air Force air-refueling tankers were KB-29 and KB-50s converted from bombers but by the 1950s the Boeing KC-97 became the standard air refueling tanker- this choice, however, was not without its difficulties particularly in refueling the B-47 Stratojet- the KC-97 wasn't able to reach the higher altitudes where the B-47 was most efficient and the B-47 had to descend to lower altitudes where its fuel burn was higher in order to link up with the KC-97. Furthermore, even with the KC-97's throttles "firewalled", the Stratojet had a tendency to stall during the link up and as a result, the refueling operation would have to carried out with the KC-97 in a shallow dive in order to gain speed above the stall speed of the Stratojet.

In 1953, the USAF trialled two B-47Bs outfitted with the British probe-and-drogue system developed by Flight Refueling, Ltd. One aircraft designated YB-47F and nicknamed "Pa" was fitted with nose mounted probe and the other aircraft, designated KB-47G and nicknamed "Ma", reeled out the hose-mounted drogue from its bomb bay. On 1 September 1953 the pair made the world's first all-jet air refueling.

Despite the higher speeds and ease of rendezvous, the fuel transfer rate with the system wasn't fast enough and in certain conditions was actually *less* than the burn rate of the six J47 engines of the receiver Stratojet. Only the flying boom used on the KC-97 was capable of the fuel transfer rates needed to give the Stratojets "legs" to reach distant targets. The interim solution was to fit the KB-50 and KC-97 tankers with auxillary jet engines to provide extra speed during refueling but the long term solution would arrive in the form of the Boeing KC-135 Stratotanker that had the speed and altitude performance to match SAC's bomber fleet.

Source: Boeing's B-47 Stratojet by Alwyn T. Lloyd. Speciality Press, 2005, p202.

06 January 2010

During the design of the first Lockheed U-2 spyplanes, designer Kelly Johnson held fast to his rule "one pound equals one foot of altitude" and if it wasn't completely necessary to the mission, it wasn't going on the aircraft. As a result, many of the navigational aids considered standard on most military aircraft were absent on the U-2. Central to the U-2's navigation equipment was the driftsight- a downward looking periscope that had two selectable magnifications. The circular driftsight dominated the center of the instrument panel on the U-2 until its replacement by GPS and glass displays in the 1990s. The driftsight give the pilot a 360-degree view underneath the aircraft and it was used for navigation in addition to sighting for the cameras.

If the ground wasn't visible due to overcast, dead reckoning was also used since the winds at the altitudes the U-2 operated were usually very light. The aircraft did have a radio compass, the AN/ARN-6, but on deep penetration flights of the Soviet Union, radio stations were far and few between.

A HF antenna system was planned for the U-2, allowing the pilot to tune into HF ground stations and determine his position by triangulation. Though tested successfully, the CIA realized that HF transmissions could betray the aircraft's position and the system, called System II, was dropped from the design.

The solution was to use the driftsight in combination with a specially-made sextant that was aligned with the driftsight's optical path. A mirror could be switched that diverted the view through the optical driftsight to the sextant unit that was mounted just ahead of the cockpit atop the nose. At the 50,000+ feet altitudes the U-2 operated, the sky was black as night even in midday and star fixes could be taken using the sextant coupled to the driftsight. Since the fully suited pilot wouldn't be able to compute the star fixes and positions during the mission, an essential crewmember to each U-2 mission was a flight-rated navigator who planned the star fixes and did all the calculations ahead of each mission. As the calculations were specific for a particular timeframe, it was essential that the U-2 takeoff within a prescribed window of time or the star fixes would have to be recalculated by the navigator.

Source: 50 Years of the U-2: The Complete Illustrated History of the "Dragon Lady" by Chris Pocock. Schiffer Publishing, 2005, p32.

05 January 2010

During the development of the hydrogen bomb there were concerns by the USAF that the delivery aircraft wouldn't be able to successfully exit the target area after dropping the weapon. As the development of the Atlas ICBM was still years away, Project Brass Ring was initiated in 1950 to create an unmanned version of the Boeing B-47 Stratojet to carry the H-bomb which would be designated MB-47 which in turn would be controlled by a manned Stratojet designated DB-47.

North American Aviation developed a sophisticated navigation and flight control system for the MB-47- but given the Air Force's requirements that the system be fully automatic, jam-resistant, and be accurate, it pushed the technology of the day and by 1952 it had to be cancelled due to cost overruns. The USAF then turned to Sperry Gyroscope to pick up where North American left off and it eventually cost a then-hefty sum of $2.3 million to complete. The MB-47 made its first flight on 7 May 1952 and by that summer both the MB-47 and the DB-47 controller had made several test flights with encouraging results. However, the cost of Project Brass Ring had nearly doubled from $4.9 million to just over $10 million.

By this point in the program SAC had determined that the Convair B-36 Peacemaker would be able to deliver the first production H-bombs if they were equipped with a parachute-retarding lay-down system. Furthermore, gaining permission from NATO members to forward deploy Stratojets in the UK, Spain, and French Morrocco made Project Brass Ring unnecessary and the program was terminated in April 1953.

Source: Boeing's B-47 Stratojet by Alwyn T. Lloyd. Speciality Press, 2005, p206-207

04 January 2010

It was in the late 1970s that analysts at Cessna realized that the vast majority of utility aircraft used in remote areas were either unsuitable for the role or were, in the case of the Douglas DC-3 and the De Havilland Beaver/Otter series, aging with no ideal replacement in the works. So on 20 November 1981 the Cessna Model 208 Caravan was launched, John Berwick, the chief engineer at Cessna's Pawnee Division in Wichita, Kansas, brought on board two men who were instrumental in design and development of the De Havilland Canada Beaver- the first individual was Russ Bannock, who first flew the Beaver on its maiden flight in August 1947 and later rose to De Havilland Canada's sales director after having demonstrated the Beaver worldwide.

The other addition was Dick Hiscocks who was the head aerodynamicist on the Beaver and later became De Havilland Canada's VP for engineering. Both Bannock and Hiscocks had recently retired from DHC and were brought in regularly to advise Cessna and review the program on a monthly basis. Two years after launch, the Caravan made its first flight on 9 December 1982.

At about the same time, Federal Express was looking at a small cargo aircraft as a feeder to replace trucks that were used to fly packages to/from small towns to larger feeder cities that transferred them to the larger jets in the cargo fleet. The founder and president, Fred Smith, initially wanted only twin-engined aircraft for the feeder role but was convinced by Cessna to a flying demonstration- Smith was sold and in 1985 ordered 30 Caravans featuring an underfuselage cargo pannier developed for Federal Express (but now offered to all Caravan customers). In their first six months of operation with the company, the Caravans had a 99 percent dispatch rate in over 2,000 hours flying time. FedEx also drove the development of a stretched Caravan, the Grand Caravan Model 208B which had four additional feet of fuselage for more cargo capacity. The first 208B went into service for the company in October 1986 and by 1996, the Caravan fleet had flown over 1 million hours for the company, by which point they had 300 Caravans in service. The 500th Caravan built would go to FedEx.

Source: The Legend of Cessna by Jeffrey L. Rodengen. Write Stuff Enterprises, 1998, p205-212.

03 January 2010

When the Tupolev Tu-16 Badger and Myasishchev M-4 Bison were revealed to the public at the 1954 May Day Parade in Moscow's Red Square, the United States realized that the Russians now had high-performance jet bombers capable of delivering atomic bombs to US cities. The USAF, via the Rome Air Development Center in New York, had the previous year started a program with General Electric on using jammers to modify the radar echoes of coastlines, rivers and cities to confuse the mapping radars used on strategic bombers. With the Badger and Bison unveiled in 1954, the work with GE took on added urgency.

In cooperation with the Strategic Air Command, GE engineers ran a test called the "Baltimore Project" to determine the nature of radar returns coming from a large city. A SAC Boeing B-29 with an APS-23 bombing/navigation radar was fitted with a selectable attenuator and the B-29 would overfly Baltimore, Maryland at different directions and with the attenuator set at different levels. This way they could filter out all but the strongest radar echoes. Combined with ground surveys of the areas of the city that were the most radar reflective, it was determined that oil storage tank farms were the most reflective followed by railroad yards and then factory complexes.

The engineers at GE then came up with what was called the Distributed Area Jammer (DAJ) which was a simple repeater that fit into a cylinder six inches across and 14 inches long. Twenty prototype DAJs were built which were installed on telephone poles and powered by the local power grid. They estimated that each DAJ unit would cost about a thousand dollars.

Tests using the prototype DAJs were conducted on Cape Cod, Massachusetts to see if they could use the jammers to alter the radar echoes of the coastline, which they found was easily accomplished by spacing the DAJs in a grid pattern a mile apart from the next DAJ. It was also found that clustering the DAJs close together produced a false radar echo that looked like a major city.

As preparations for production began with the intent of protecting a limited set of potential targets, Congress got wind of the DAJ project and each senator and representative demanded that their constituents be protected with a DAJ network. As a result, the cost spiraled upward as the USAF found that the number of DAJs needed just to protect the Eastern Seaboard alone made the cost unfeasible. As a result, the DAJ program was cancelled and it never went into production.

Source: The History of U.S. Electronic Warfare, Volume II- The Renaissance Years, 1946-1964 by Alfred Price. The Association of Old Crows/Port City Press, 1989, p131-133.

02 January 2010

Jet engine technology in the late 1940s was still immature enough that a jet-engined fighter often still lacked comparable range to a piston-engined fighter. As a result, both the USAF and US Navy saw the turboprop as the potential answer- the USAF hoped a turboprop fighter would offer a longer range and the US Navy was interested in the power of turboprop fighter to make takeoff from a carrier deck possible without a catapult. To evaluate the possibility, both branches agreed to fund an experimental turboprop fighter based on Republic's AP-46 design. The USAF would buy three and the US Navy would acquire a single example.

By 1951 the arrangement had changed to with only the USAF getting two AP-46 aircraft designated XF-84H. Although a development of the F-84F Thunderstreak, the XF-84H only had wing and canopy of the Thunderstreak with an all new fuselage and tail unit. A 5,580-horsepower Allison XT40 turboprop that drove via an 18-foot shaft a 12-foot three-bladed constant speed propeller. The Aeroproducts prop rotated at 3,000 rpm which meant that the blade tips traveled at Mach 1.18 and as such, created an immense amount of noise, leading to the XF-84H's name, the Thunderscreech. As the prop was constant speed, thrust was effected by adjusting the pitch of the prop.

With its first flight at Edwards AFB on 22 July 1954, it was immediately apparent the XF-84H had some serious flaws. Maximum deflection of the rudder was insufficient to counter the massive torque and p-factor of the supersonic prop. In addition, there were constant hydraulic problems, the elevator was limited in its pitch authority and the prop gearbox kept overheating.

But most famously, the XF-84H Thunderscreech was noisy. The supersonic prop blades were so loud that residents over 20 miles away from Edwards AFB filed noise complaints with the USAF! When the aircraft first taxied out under its own power and took off, the control tower crew often had to hide under their consoles shielding their ears. Any ground crew standing nearby often felt nausea and dizziness even with ear protection due to the Mach shockwaves from the prop blades.

As a result, Republic was banned from doing run ups on the flightline and it would have to be towed 7 miles away from the main ramp behind a ridge called "Rocket Hill" as it had rocket engine test stands in the area.

The second Thunderscreech arrived in May 1956 and was temporarily bailed to the US Navy in support of the VTOL tail sitting convoy fighter program as both the Lockheed XFV-1 and Convair XFY-1 used the same Allison XT40 turboprop engine. The last Thunderscreech flight was made on 9 October 1956 with cancellation following, much to the relief of the pilots, ground crew and most everyone at Edwards AFB!

Source: International Air Power Review, Volume 24 (Summer 2002). AIRtime Publishing, 2002. "Warplane Classic: Republic F-84, Thunderjet, Thundersteak, and Thunderflash" by David Willis, p124.