Monthly Archives: November 2018

Hughes (Kellett) XH-17 Heavy-Lift Helicopter

By William Pearce

On 31 January 1946, the Unites States Army Air Force issued a Request for Proposal involving the design of a heavy-lift helicopter capable of transporting a 10,000 lb (4,536 kg) external load. Additional specifications include the use of jet turbine propulsion and rotors equipped with tip jets. The Kellett Aircraft Corporation of Upper Derby, Pennsylvania was awarded a design contract on 2 May 1946, and the new helicopter was designated XR-17. If all went well with the XR-17’s design, a contract to build a test rig would be issued.

The massive Hughes XH-17 sits at rest before its first public flight on 23 October 1952. The notches in the rotor blade are where jets of pressurized air exit the rotor. (LIFE image via Google)

Kellett moved forward with the XR-17 design, which was centered around a pair of 4,000 lbf (17.79 kN) General Electric J35 (TG-180) engines driving a two-blade rotor. However, the engines were not mechanically attached to the rotors. Air was bled off from the compressor section of the modified engines and was ducted through the hollow rotors. The 400°F (204°C) air was exhausted from each rotor via four pressure-jets in the tip’s trailing edge. The jet of air emanating from the rotor tips caused the rotors to turn. This propulsion system was referred to as cold-cycle pressure-jet, because the air from the engine’s compressor section was much cooler than the air from the engine’s exhaust. To further augment power, General Electric GE33F pressure-jet burners sprayed and ignited fuel into the jet of air exiting the rotor. Kellett estimated that 1,000 hp (746 kW) was produced with the cold-cycle air jet alone, and 3,480 hp (2,595 kW) was produced with the tip burners in use.

By 27 August 1947, the XR-17 design had progressed well, and Kellett was awarded a contract to produce a test rig of the helicopter’s rotor system. Kellett went to work constructing the test rig and tried to save money wherever possible by using components of other aircraft. The company was having financial issues, and the XR-17 project had an uncertain future.

From left to right: Rea Hopper, Howard Hughes, Clyde Jones, Warren Reed, Colonel Carl Jackson, Gale Moore, Chalmer Bowen, and Marion Wallace. (LIFE image via Google)

In June 1948, the helicopter was redesignated XH-17. Through 1948, work continued on the XH-17 test rig, but the financial issues at Kellett only worsened. With the Air Force’s blessing, Hughes Aircraft purchased the XH-17 project and moved all materials and many Kellett personnel to Culver City, California. Work on the XH-17 resumed in March 1949 and progressed rapidly with full support from Hughes.

The Hughes XH-17 consisted of a cockpit from a Waco CG-15 glider attached to a custom-built tube steel frame. Its steerable front landing gear was made using the main wheels from a North American B-25 Mitchell, and its rear landing gear was made using the main wheels from a Douglas C-54 Skymaster. The XH-17’s fuel tank was originally a 636-gallon (2,408-L) extended-range bomb bay tank for a Boeing B-29 Superfortress. The helicopter’s 130 ft (39.62 m) two-blade main rotor turned at 88 rpm. Each blade was 12 in (.30 m) thick, 58 in (1.47 m) wide, and weighed 5,000 lb (2,268 kg). The large pressure-jet rotors had a very short fatigue life.

Rear view of the XH-17 illustrating the helicopter’s tube frame construction and relatively small tail rotor. (LIFE image via Google)

The XH-17 test rig was run for the first time around October 1949. Only bleed air was used to turn the rotors. After about three months of testing, the rotor burners were fired for the first time on 22 December 1949. This created a very a loud whop-whop-whop noise that coincided with the passing of each set of lit burners on the rotors’ tips. The noise was so loud that it could be heard eight miles (13 km) away, and the XH-17 caused numerous noise complaints to be filed against Hughes.

The XH-17’s wide stance was to facilitate positioning equipment under the helicopter. Note the large horn balance on the rotor’s leading edge. The stress and vibration of operating the 130 ft (39.62 m) rotor gave the blades a very short life. (LIFE image via Google)

Testing of the rig steadily progressed until June 1950, when a control link broke and caused the XH-17 test rig to rise about 10 feet (3 m) off the ground before it crashed back down. The rig was damaged, but the rotors and power system were unharmed. Rather than just rebuild the test rig, the decision had already been made to convert the rig into a flight-capable helicopter. Numerous systems were revised, and a tail rotor from a Sikorsky H-19 Chickasaw was added. The tail rotor was small compared to the rest of the XH-17. The rotor jets did not create a major torque reaction that needed to be counteracted like the main rotors of a conventional helicopter. The tail rotor was mainly for differential directional control. The wide-set and tall landing gear allowed loads to be driven under the helicopter and then attached for lifting.

The XH-17 was ready for flight in the summer of 1952. The complete helicopter was 53 ft 4 in (16.55 m) long and 30 ft 2 in (9.17 m) tall. The XH-17 had an estimated top speed of 90 mph (145 km/h) and a range of only 40 miles (64 km), due to the high fuel consumption of the rotor’s pressure-jet burner system. The helicopter had a normal weight of around 41,700 lb (18,915 kg) and a maximum weight with a 10,284 lb (4,665 kg) payload of 52,000 lb (23,587 kg).

The XH-17 was a rather awkward-looking machine, and it is easy to see why it was referred to as “Monster.” The glowing spots on the rotor blade’s tip are the pressure-jet burners. (LIFE image via Google)

During a test on 16 September 1952, the XH-17 made its first unofficial flight. Piloted by Gale Moore and Chalmer Bowen, the helicopter was accidently bounced off the ground during a hover test due to overly-sensitive controls. The controls were modified, and a much more controlled hover was established the following day. The XH-17 made its public debut on 23 October 1952 at Hughes Airport in Culver City. Two flights were made that day, and the XH-17 hovered, flew forward up to 45 mph (72 km/h), flew backward, and rotated 360 degrees. Moore and Bowen were again the pilots and were joined by Marion Wallace. They had nicknamed the XH-17 “Monster” on account of its odd appearance, but the helicopter was also known as the “Flying Crane.”

As the XH-17 program was progressing, the Air Force asked Hughes to design an improved and more powerful version in October 1951. The new helicopter was designated XH-28 and would use a cold-cycle rotor system with pressure-jet burners, similar to the arrangement on the XH-17 but with four blades. Power was provided by two Allison XT40-A-8 turboprop engines. Each 5,300 hp (3,952 kW) XT40 engine consisted of two T38 engines coupled to a common gear reduction. The engines in the XH-28 would drive a compressor unit to send air to the rotors. The XH-28 would weigh 52,000 lb (23,587 kg) empty and would be capable of lifting 50,000 lb (22,680 kg), for a total gross weight of 105,000 lb (47,627 kg). The Air Force awarded a design contract for the XH-28 to Hughes in January 1952.

The blades of the XH-17 operating at 88 rpm were easily distinguished, even when the helicopter was in flight. Note the glow of the tip burners and the size of the GE J35 engine. (LIFE image via Google)

A XH-28 mockup was constructed, and extensive testing was involved to create rotors with an extended fatigue life. Ultimately, rotors of a bonded titanium construction were chosen. Allison was hesitant to devote engineering resources to the engine design because the company was involved with so many other projects that it felt held more promise. In December 1952, the Air Force decided that its funds should be spent on jet fighters and bombers and that it would not support the XH-28 beyond 1953. The Air Force was willing to hand the project over to the Army, which was interested in the XH-28 as a way to transport tanks and other equipment. However, the Army soon decided that its funds would be better spent on smaller and less expensive helicopters and never took over the XH-28 project. On 17 August 1953, the Air Force cancelled the XH-17 and XH-28.

XH-17 flight testing progressed sporadically over three years. Later flights pushed the helicopter’s speed up to 70 mph (113 km/h) and altitude to 350 ft (107 m). The XH-17 made 33 flights for a total of 10 hours flying time. Flight tests were halted in December 1955 on account of the rotor blades reaching their fatigue life. On the XH-17’s last flight, the helicopter carried an 8,000 lb (3,629 kg) communication trailer, which pushed the XH-17’s gross weight to over 50,000 lb (22,680 kg) for the flight. At the time, the XH-17 was the world’s largest helicopter and could carry more than any other helicopter. Its 130 ft (39.62 m) rotor system is still the largest ever used. However, the XH-17’s noisy operation and short range limited its usefulness. The XH-17 and the XH-28 mockup and parts were eventually scrapped.

Full-scale mockup of the Hughes XH-28, which was planned as a larger, more capable heavy-lift helicopter than the XH-17. Vehicles could be driven onto the platform and secured, eliminating the need for the load to be suspended from the helicopter. (LIFE image via Google)

Sources:
– McDonnell Douglas Aircraft since 1920: Volume II by René J. Francillon (1990)
– Howard’s Whirlybirds by Donald J. Porter (2013)
– Howard Hughes: An Airman, His Aircraft, and His Great Flights by Thomas Wildenberg and R.E.G. Davies (2006)
– http://www.1000aircraftphotos.com/Contributions/VanTilborg/3138.htm

Studebaker’s XH-9350 and Their Involvement with Other Aircraft Engines

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By William Pearce

Before the United States entered World War II, the Army Air Corps conceptualized a large aircraft engine for which fuel efficiency was the paramount concern. It was believed that such an engine could power bombers from North America to attack targets in Europe, a tactic that would be needed if the United Kingdom were to fall. This engine project was known as MX-232, and Studebaker was tasked with its development. After years of testing and development, the MX-232 program produced the Studebaker XH-9350 engine design.

Although a complete XH-9350 engine was not built, Studebaker’s XH-9350 and Their Involvement with Other Aircraft Engines details the development of the MX-232 program and the XH-9350 design. In addition, the book covers Studebaker’s work with other aircraft engines: the power plant for the Waterman Arrowbile, their licensed production of the Wright R-1820 radial engine during World War II, and their licensed production of the General Electric J47 jet engine during the Korean War.

Contents:

Preface
1. Studebaker History
2. Waldo Waterman and the Arrowbile
3. Studebaker-Built Wright R-1820 Cyclone
4. XH-9350 in Context
5. XH-9350 in Development
6. XH-9350 in Perspective
7. Studebaker-Built GE J47 Turbojet
Conclusion
Appendix: MX-232 / XH-9350 Documents
Bibliography
Index

$19.99 USD
Softcover
8.5 in x 11 in
214 pages (222 total page count)
Over 185 images, drawings, and tables, and over 75,000 words
ISBN 978-0-9850353-1-0

Studebaker’s XH-9350 and Their Involvement with Other Aircraft Engines is available at Amazon.com. If you wish to purchase the book with a check, please contact us for arrangements.

Sample Pages:

Hitachi/Nakajima [Ha-51] 22-Cylinder Aircraft Engine

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By William Pearce

In December 1942, the Imperial Japanese Army (IJA) sought a new radial aircraft engine capable of more than 2,500 hp (1,864 kW). At the time, the most powerful Japanese production engines produced around 1,900 hp (1,417 kW). The new engine was given the IJA designation Ha-51 and was later assigned the joint Japanese Army and Navy designation [Ha-51]. However, the Imperial Japanese Navy did not show any interest in the engine.

The 22-cylinder Hitachi/Nakajima [Ha-51] engine had a general similarity to the Nakajima [Ha-45]. Note the cooling fan on the front of the engine and the dense nature of the cylinder positioning.

Some sources state that Nakajima was tasked to develop the new [Ha-51] engine, while other sources contend that Hitachi was in charge of the engine from the start. Both Nakajima and Hitachi had produced previous engines with the same bore and stroke as the [Ha-51]. However, the [Ha-51] shares some characteristics, such as fan-assisted air cooling, with other Nakajima engines. Regardless, development of the [Ha-51] was eventually centered at the Hitachi Aircraft Company (Hitachi Kikuki KK) plant in Tachikawa, near Tokyo, Japan. The Hitachi Aircraft Company was formed in 1939 when the Tokyo Gas & Electric Industry Company (Tokyo Gasu Denki Kogyo KK, or Gasuden for short) merged with the Hitachi Manufacturing Company.

The [Ha-51] was a 22-cylinder, two-row radial engine. Its configuration of 11-cylinders in each of two rows was only common with two other engines: the Mitsubishi A21 / Ha-50 and the Wright R-4090. Although the three engines were developed around the same time, it is not believed that any one influenced the others. Moving from nine cylinders in each row to 11 was a logical step for producing more power without increasing a radial engine’s length. The tradeoff was accepting the increased frontal area of the engine and additional strain on the crankpins.

The engine’s three-piece crankcase was made of steel and split vertically along the cylinder center line. The crankcase bolted together via internal fasteners located between the cylinder mounting pads. The cylinders consisted of an aluminum head screwed and shrunk onto a steel barrel. Each cylinder had one intake valve and one exhaust valve. The valves were inclined at a relatively narrow angle of around 62 degrees. The intake and exhaust ports for each cylinder faced the rear of the engine. The cylinders had a compression ratio of 6.8. The second row of cylinders was staggered behind the first row. Only a very narrow gap existed between the front cylinders to enable cooling air to the rear cylinders. Baffles were used to direct the flow of cooling air.

Drawing of the [Ha-51] with details of the cylinder intake and exhaust valves. The angle between the intake and exhaust valves was fairly narrow for a radial engine, a necessity to fit 11 cylinders around the engine while keeping its diameter as small as possible.

A single-stage, two-speed supercharger was mounted to the rear of the [Ha-51]. The supercharger’s impeller was 13 in (330 mm) in diameter and turned at 6.67 times crankshaft speed in low gear and 10.0 times crankshaft speed in high gear. Fuel was fed into the supercharger by a carburetor. At the front of the engine was a planetary gear reduction that used spur gears to turn the propeller at .42 times crankshaft speed. A cooling fan driven from the front of the gear reduction was intended to keep engine temperatures within limits once the [Ha-51] was installed in a close-fitting cowling.

The [Ha-51]’s fan-assisted cooling system was originally developed for the 1,900 hp (1,417 kW) Nakajima [Ha-45] Homare engine, which gives some credence to Nakajima being involved with the [Ha-51]. The [Ha-45] and the [Ha-51] also had the same bore and stroke. Nearly all Gasuden/Hitachi radial engines had a single row of nine-cylinders and produced no more than 500 hp (373 kW). Developing a two-row, 22-cylinder, 2,500 hp (1,864 kW) engine would be a significant jump for Hitachi, but much less so for Nakajima.

The [Ha-51] had a 5.12 in (130 mm) bore and a 5.91 in (150 mm) stroke. Its total displacement was 2,673 cu in (43.8 L). The engine had an initial rating of 2,450 hp (1,827 kW) at 3,000 rpm and 8.7 psi (.60 bar) of boost for takeoff, and 1,950 hp (1,454 kW) at 3,000 rpm with 7.7 psi (.53 bar) of boost at 26,247 ft (8,000 m). However, planned development would increase the [Ha-51]’s output up to 3,000 hp (2,237 kW). The engine was 49.4 in (1.26 m) in diameter, 78.7 in (2.00 m) long, and weighed 2,205 lb (1,000 kg).

Construction of the first [Ha-51] prototype was started in March 1944. Testing of the completed engine revealed high oil consumption and issues with bearing seizures between the crankpins and master rods. The gear reduction and cooling fan drive experienced failures, and difficulty with the supercharger led to broken impellers. Due to these issues, the engine was unable to pass a 100-hour endurance test. Three [Ha-51] engines and parts for a fourth had been built when the prototypes were damaged during a US bombing raid on the factory at Tachikawa in April 1945. Combined with the current state of the war, the setback caused by the air raid signaled the end of the [Ha-51] project. When US troops inspected the Tachikawa plant in late 1945, they found the three damaged and partially constructed [Ha-51] engines. One engine was mostly complete but lacked its supercharger section. Reportedly, this engine was reassembled by order of the US military, but no further information regarding its disposition has been found. All [Ha-51] engines were later scrapped, and no parts for them are known to exist.

Rear view of a [Ha-51] engine as found by US troops at Hitachi’s Tachikawa plant. The engine was fairly complete, with the exception of the supercharger and accessory section. This engine was reportedly reassembled at the request of the US military.

Sources:
– Japanese Aero-Engines 1910–1945 by Mike Goodwin and Peter Starkings (2017)
– “The Radial 22 Cylinder Engine “HA51” and Genealogic Survey of the Gas-Den Aero-Engine” by Takashi Suzuki, Kenichi Kaki, Toyohiro Takahashi, and Masayoshi Nakanishi Transactions of the Japan Society of Mechanical Engineers (Part C) Vol. 74, No. 746 (October 2008)
– “Hitachi Aircraft Company” The United States Strategic Bombing Survey, Corporation Report No. VII (February 1947)
– http://www.enginehistory.org/Piston/Japanese/japanese.shtml
– https://ja.wikipedia.org/wiki/ハ51_(エンジン)