Author Archives: William Pearce

Thomas X-8 engine

Thomas / Leyland X-8 Aircraft Engine

By William Pearce

John Godfrey Parry Thomas was a British engineer and was widely known as Parry Thomas. During World War I, Thomas was a member of the Munitions Invention Board and was brought on as the chief engineer at Leyland Motors in 1917 to help the firm develop an aircraft engine.

Allan Ferguson had been working at Leyland on the design of the aircraft engine. The engine Ferguson had designed was a 450 hp (336 kW), water-cooled W-18 with banks set at 40 degrees. Each bank consisted of two three-cylinder blocks, and there were plans to make a W-9 engine with just three banks of three cylinders. Long pushrods extended from camshafts in the crankcase between the cylinder banks to the top of the cylinders to actuate the overhead valves. Thomas felt that the W-18 engine would not be successful and proposed his own design, which won the approval of Leyland management.

Thomas X-8 engine

The Thomas (Leyland) X-8 engine was made from aluminum and had many interesting features. At the rear of the engine, the handle is attached to a dynamo for starting. Just above the dynamo is the crankshaft-driven water pump. The engine’s carburetors are mounted on either side of the water pump. Note the integral passageways leading from the carburetor to the cylinders. The oil sump tank is positioned in the lower engine Vee.

Assisted by Fred Sumner and Reid Railton, Thomas’ engine design was an X-8 with cylinder banks spaced at 90 degrees. Each cylinder bank consisted of two paired cylinders. The cylinder banks were cast integral with the aluminum crankcase, and nickel-chrome cylinder wet liners were heat-shrunk into the cylinder banks. An aluminum cylinder head was attached to each cylinder bank via eight bolts. A propeller gear reduction was incorporated into the engine. The gear reduction used bevel gears and reduced the propeller speed to .50 times crankshaft speed. The gear reduction kept the propeller position in line with the crankshaft.

A single overhead camshaft operated the two intake and two exhaust valves for each cylinder. The camshaft was driven via a vertical shaft at the rear of the engine. The valves were closed by leaf springs. Via adjustable screws, one end of a leaf spring was attached to an intake valve while the other end of the spring was attached to an exhaust valve. The springs were allowed to articulate at their mounting point so that as one valve was opened, additional tension was applied to the closed valve for an even tighter seal.

Two carburetors were positioned at the rear of the engine, with each carburetor providing the air/fuel mixture for one side of the engine. Each carburetor was mounted to an integral intake passageway in the crankcase, with four individual ducts branching off from the passageway. Each duct connected one cylinder to the intake passageway. Exhaust was expelled from the upper and lower engine Vees. Each cylinder had two spark plugs fired by either a magneto or battery ignition.

A water pump driven at the rear of the engine by the crankshaft circulated water through the engine at around 48 gpm (182 L). The coolant flowed into the cylinder banks and around the exhaust ports to keep the exhaust valves cool. A pipe system enabled water to flow through the hollow crankshaft at 10 gpm (36 L), cooling the three main bearings and two connecting rod bearings. The water also cooled the oil that flowed through the crankshaft and to the bearings. To further cool the oil, the water and oil flowed into the propeller gear reduction, where the oil passed along the finned outer side of the water-cooled propeller shaft.

Thomas leaf spring valves

While not of the X-8 engine, this drawing does depict the leaf spring valves, similar to the setup used in the X-8 engine. The leaf spring (5) held the valves (3 and 4) closed. Lobes (11) on the camshaft (12) acted on the rockers (9 and 10) to open the valves. The leaf spring mount (8) could move up and down to add tension on the closed valve for a tighter seal. (GB patent 216,607, granted 5 June 1924)

Attached to each of the crankshaft’s two crankpins was a master connecting rod, and three articulated rods were attached to each master rod. The crankshaft had both of its crankpins inline, which meant that the pistons for one cylinder bank would both be at top dead center at the same time. One source states that the crankpins were in the same phase, meaning the two cylinders of the same bank would be on the same stroke, essentially making the X-8 engine operate like two synchronized X-4 engines. This was reportedly done to prevent any rocking motion created by the front X-4 firing followed by a rear X-4-cylinder firing 90 degrees later. However, a different source says the cylinders were phased 360 degrees apart, which would make more sense. While the pistons of one cylinder bank were both at top dead center, one cylinder was starting the intake stroke while the other was starting the power stroke. The 360-degree phasing would create a rather smooth firing order, such as bank 1 front cylinder (1F), bank 2 rear cylinder (2R), 3F, 4R, 1R, 2F, 3R, and 4F. However, the engine’s true firing order is not known.

A dry-sump lubrication system was used. Oil from the engine was collected in a one gallon (4.5 L) tank mounted in the lower engine Vee. The oil was then returned to a main oil tank of approximately eight gallons (32 L) installed in the aircraft. For starting, the X-8 engine used an electric starter motor or a hand-cranked dynamo. The engine incorporated an interrupter gear for firing guns through the propeller arc.

The X-8 engine had a 6.0 in (152 mm) bore and a 4.5 in (114 mm) stroke. The engine displaced 1,018 cu in (16.7 L) and produced 300 hp (224 kW) at 2,500 rpm and 10,000 ft (3,048 m). Maximum engine speed was around 3,500 rpm. The X-8 engine weighed around 500 lb (227 kg). For the time, 500 lb (227 kg) was remarkably light for a 300 hp (224 kW) engine. The X-8 was noted as being very compact, but a list of engine dimensions has not been found.

Thomas X-8 drawing

Patent drawing of the X-8’s crankshaft with its inline crankpins. The water pump (4) housed the crankshaft-driven impeller (9). Water was pumped through an inlet (11), through a passageway (10), and into the pipe built-up in the hollow crankshaft. The water then flowed through the propeller shaft (36) to cool oil in an adjacent passageway (45).

The design of the Thomas X-8 was completed in December 1917 and submitted to the Air Ministry. Thomas initiated an extensive part-testing program that resulted in the creation of numerous test fixtures. In conjunction with the test-fixtures, A single-cylinder test engine was built and tested in 1918. The single-cylinder produced 37 hp (28 kW) at 2,500 rpm and 53 hp (40 kW) at 3,700 rpm. These outputs equated to 296 hp (221 kW) and 424 hp (316 kW) respectively for the complete eight-cylinder engine. However, the piston in the single-cylinder engine failed after five minutes of running between 3,500 and 3,700 rpm.

A complete X-8 engine was built and run for the first time in August 1918. Compression ratios of 5.8 and 6.3 were used on the single-cylinder engine, but the compression ratio of the complete engine has not been found. Reportedly, the engine was hastily assembled because government inspectors wanted the test two weeks earlier than planned. The X-8 engine’s lightly-built crankcase deformed and closed in the crankshaft bearing clearance, resulting in the engine seizing after a few hours of running.

With the end of World War I on 11 November 1918, further work on the Thomas X-8 engine was abandoned. A number of features from the aircraft engine were later used on the Leyland automotive straight-eight engine developed in 1920. Thomas went on to become a legend at the Brooklands Raceway, campaign one of the first aero-engined Land Speed Record (LSR) monster cars, and set a flying-mile (1.6 km) LSR of 170.624 mph (274.593 km/h) on 28 April 1926. Thomas tragically died in a crash attempting another LSR on 3 March 1927. His death marked the first time a driver was killed while in direct pursuit of a LSR.

Parry Thomas at Brooklands Getty

Thomas behind the wheel of his Leyland-Thomas racer at Brooklands on 4 October 1926. (Getty image)

Sources:
“AIR: Parry Thomas’s Aero-Engine” by William Boddy, Motor Sport (February 1995)
“The Life Story of Parry-Thomas” by Fred Sumner, Motor Sport (November 1941)
“Internal Combustion Engine,” US patent 1,346,280 by John Godfrey Parry Thomas (granted 13 July 1920)
Reid Railton: Man of Speed by Karl Ludvigsen (2018)
Parry Thomas by Hugh Tours (1959)

Hughes XF-11 no1 taxi

Hughes XF-11 Photo-Reconnaissance Aircraft

By William Pearce

In the early World War II years, the Hughes Aircraft Company (HAC) worked to design and build its D-2 aircraft intended for a variety of roles. However, the United States Army Air Force (AAF) was not truly interested in the twin-engine wooded aircraft. To cure design deficiencies and make the aircraft more appealing to the AAF, HAC proposed a redesign of the D-2, designated D-5.

Hughes XF-11 no1 front

The Hughes XF-11 was an impressive and powerful aircraft intended for the photo-reconnaissance role. The eight-blade, contra-rotating propellers were over 15 ft (4.6 m) in diameter. Note the deployed flaps between the tail booms. (UNLV Libraries image)

The initial D-5 design was an enlarged D-2 and employed Duramold construction using resin-impregnated layers of wood, molded to shape under pressure and heat. The proposed aircraft had a 92 ft (28.0 m) wingspan, was 58 ft (17.7 m) in length, and weighed 36,400 lb (16,511 kg). The D-5 was powered by Pratt & Whitney (P&W) R-2800 engines and had a forecasted top speed of 488 mph (785 km/h) at 30,000 ft (9,144 m) and 451 mph (726 km/h) at 36,000 ft (10,973 m). A 4,000 lb (1,814 kg) bomb load could be carried in an internal bay. The AAF was still not interested in the aircraft and felt that HAC did not have the capability to manufacture such an aircraft in large numbers.

In early August 1943, Col. Elliot Roosevelt, President Franklin Roosevelt’s son, was in the Los Angeles inquiring with various aircraft manufacturers to find a photo-reconnaissance aircraft. Col. Roosevelt, who had previously commanded a reconnaissance unit, was hosted by Hughes and taken on a personal tour of the D-2. At the time, the aircraft was undergoing modification to become the D-5 and was not available for flight, but Col. Roosevelt was sufficiently impressed.

Hughes XF-11 no1 taxi

Howard Hughes taxies the first XF-11 out for its first and last flight. The nose of the aircraft accommodated a variety of camera equipment. Note the cowl flaps and the large scoops under the engine nacelles. (UNLV Libraries image)

General Henry “Hap” Arnold of the AAF was put under pressure from the White House to order the D-5 reconnaissance aircraft into production. To ease the AAF’s concerns about the D-5’s Duramold construction, the design was changed to metal wings and tail booms and only the fuselage built from Durmold. Arnold made the decision to order the D-5 aircraft “much against [his] better judgment and the advice of [his] staff.” The AAF issued a letter of intent on 6 October 1943 for the purchase of 100 examples of the D-5 reconnaissance aircraft. An official contract for the aircraft, designated F-11, was issued on 5 May 1944. Two aircraft would serve as prototypes with the remaining 98 aircraft as production versions.

As contracted, the Hughes XF-11 prototypes were of an all-metal construction and powered by two P&W R-4360 engines. The aircraft had the same layout as the Lockheed P-38 Lightning but was much larger. The fuselage consisted of a streamlined nacelle mounted to the center of the wing. At the front of the fuselage were provisions for photographic equipment. The cockpit was positioned just before the wing’s leading edge, and the cockpit was covered by a large, fixed bubble canopy. The pressurized cockpit could maintain an altitude of 10,500 ft (3,200 m) up an aircraft altitude of 33,500 ft (10,211 m). Entry to the cockpit was via a hatch and extendable ladder just behind the nose wheel landing gear well. The pilot’s seat was offset slightly to the left. Behind and to the right of the pilot sat a second crew member, who would fulfill the role of a navigator/photographer. The second crew member could crawl past the pilot and into the aircraft’s nose to service the cameras while in flight. The nose landing gear retracted to the rear and was stowed under the cockpit.

Hughes XF-11 no1 first flight

One of the very few images of the first XF-11 in flight as it takes off from Hughes Airport in Culver City, California on 7 July 1946. Note the rural background that is now completely developed. (UNLV Libraries image)

The XF-11’s wings had a straight leading and trailing edges, with the leading edge swept back approximately 6 degrees and the trailing edge swept forward around 3.5 degrees. Mounted to each wing about a third of the distance from the fuselage to the wing tip was the engine. The engine nacelle was slung under the wing and extended back to the aircraft’s tail. A large flap was located on the wing’s trailing edge between the tail booms. Each wing had an addition flap that extended from outside of the tail boom to near the wing tip. Relatively small ailerons spanned the approximate 66 in (1.68 m) distance from the flap to the wing tip. The aircraft’s main source of roll control were spoilers positioned on the upper surface of the outer wing and in front of the flap. Each wing incorporated a hardpoint outside of the tail boom for a 700 gallon (2,650 L) drop tank, and 600 gallon (2,271 L) jettisonable tip tanks were proposed but not included on the prototype aircraft.

Each 3,000 hp (2,237 kW), 28-cylinder R-4360 engine was installed in the front of the wing and was housed in a streamlined cowling. Cowl flaps for engine cooling circled the sides and top of the cowling. Under the engine nacelle was a scoop that housed the oil cooler and provided air to the intercooler and the two General Electric BH-1 turbosuperchargers installed in each tail boom. Air that flowed through the oil cooler exited at the back of the scoop. Air that flowed through the intercooler was routed to an exit door on top of the engine nacelle, just above the wing’s leading edge. Exhaust from the superchargers was expelled from the sides of the engine nacelle, just under the wing. The turbosupercharger on the inner side of each tail boom could be shut down during cruise flight to take full advantage of the remaining turbosupercharger operating at its maximum performance. The main landing gear was positioned behind the engine and retracted to the rear into the tail boom. Attached to the end of each tail boom was a large, 11 ft 8 in (3.56 m) tall vertical stabilizer. Mounted in the 25 ft 8 in (7.82 m) space between the vertical stabilizers was the horizontal stabilizer. The left tail boom housed additional camera equipment behind the main landing gear well.

Hughes XF-11 no1 cockpit crash

The cockpit of the crashed XF-11 illustrates how lucky Hughes was to have survived. Hughes crawled out through the melted Plexiglas and was aided by residents who had witnessed the crash. Note the armored seat. The XF-11 had 350 lb (159 kg) of cockpit armor and self-sealing fuel tanks. (UNLV Libraries image)

The XF-11 had a wingspan of 101 ft 4 in (30.9 m), a length of 65 ft 5 in (19.9 m), and a height of 23 ft 3 (7.09 m). The aircraft had a top speed of 450 mph (725 km/h) at 33,000 ft (10,058 m) and 295 mph (475 km/h) at sea level. The XF-11 had a service ceiling of 42,000 ft (12,802 m), an initial climb rate of 2,025 fpm (10.3 m/s) and could climb to 33,000 ft (10,058 m) in 17.4 minutes. The aircraft had an empty weight of 39,278 lb (17,816 kg) and a maximum weight of 58,315 lb (26,451 kg). With its 2,105 gallon (7,968 L) internal fuel load, the XF-11 had a 5,000 mile (8,047 km) maximum range.

Delivery of the first XF-11 (44-70155) was originally scheduled for November 1944 with peak production of 10 aircraft per month being reached in March 1945—an ambitions timeline for any aircraft manufacturer. Delays were encountered almost immediately and gave credence to the AAF’s belief that HAC was not up to the task of designing and manufacturing aircraft for series production. By mid-1945, the XF-11 had still not flown, and the war was winding down. It was clear that the XF-11 would not be involved in World War II, and there was much doubt as to the usefulness of the aircraft post-war. As a result, the order for 98 production examples was cancelled on 26 May 1945, but the construction of the two prototypes was to proceed.

Hughes XF-11 no2 front

With the exception of its propellers, the second XF-11 was essentially the same as the first aircraft. The bulges on the nacelles under the wings were the exhaust outlets for the inner turbosuperchargers. (UNLV Libraries image)

The first XF-11 prototype was fitted with Hamilton-Standard Superhydromatic contra-rotating propellers. The front four-blade propeller was 15 ft 1 in (4.60 m) in diameter, and the rear four-blade propeller was 2 in (51 mm) longer at 15 ft and 3 in (4.65 m) in diameter. The impressive aircraft was finally finished by April 1946 and began taxi test. With Howard Hughes at the controls, an aborted high-speed taxi test on 15 April resulted in some minor damage and the need to rework some of the aircraft’s systems.

Once repaired, Hughes decided to make the XF-11’s first flight on 7 July 1946. The AAF had stipulated that the XF-11’s first flight should be no more that 45 minutes, the landing gear should not be retracted, the aircraft should stay near the airport and away from populated areas, communication should be established with the chase plane, and the flight should follow the plan discussed beforehand. While the flight was discussed with some, many involved with the aircraft were unaware of Hughes’ plans. Had his intentions been better known, someone may have reminded him about the propeller seal leak on the right engine. Hughes request 1,200 gallons (4,542 L) of fuel to be on board, which was twice as much as should be needed for the scheduled 45-minute flight. HAC’s Douglas A-20 Havoc would serve as a chase plane for the flight, but radio issues prevented communication between the two aircraft.

Hughes XF-11 no2 top

Top view of the second XF-11 illustrates the aircraft’s layout, which was similar to that of a Lockheed P-38. However, the XF-11 was a massive aircraft. Note that the rear of the fixed canopy has been removed. (UNLV Libraries image)

At around 5:20 PM, Hughes took the XF-11 off from Hughes Airport in Culver City, California on its maiden flight. Shortly after takeoff, Hughes retracted the gar, and the right main light remined illuminated, indicating a possible issue with the retraction. Hughes and the XF-11 flew out over the Pacific Ocean and turned back toward land. The landing gear was cycled several times during the flight in an attempt to resolve the perceived issue on account of the illuminated light.

After about an hour and 15 minutes, the oil supply in the right propeller was exhausted and the rear set of blades moved into a flat or reversed pitch. Had Hughes stuck to the 45-minute flight as the AAF ordered, the oil supply would not have been depleted. The reversed pitch propeller created a massive amount of drag on the right side of the aircraft. To the A-20 chase plane, it appeared that Hughes was maneuvering to land back at Culver City, some distance away. The chase plane broke formation to return to the airfield on its own. Had the two aircraft been in communication, the situation could have been discussed.

Hughes XF-11 no2 top rear

The trailing edge of the XF-11’s wing had a flap between the tail booms. Long flaps extended from the outer side of the tail booms almost to the wing tips. Note the relatively small ailerons at the wing tips. The wing spoilers are visible just in front of the outer flaps. (UNLV Libraries image)

Hughes, now alone, believed that the right main gear had deployed on its own and was causing the drag. Had Hughes left the gear down, he would have known the drag was a result of some other issue with the aircraft. Trying to keep the XF-11 straight resulted in the deployment of the left-wing spoilers, which further slowed the aircraft. Low, slow, and over a populated area, Hughes tried to make it to the open space of the Los Angles Country Club golf course in Beverly Hills. Landing short, the XF-11 crashed into four houses, broke apart, and caught fire. Hughes managed to pull himself from the wreckage, where he was helped further by neighborhood residents and arriving paramedics. Hughes suffers major injuries, including severe burns, at least 11 broken ribs, a punctured lung, and a displaced heart. Remarkably, he made a near-full recovery, but the incident started an addiction to codine, which would cause Hughes problems throughout the rest of his life.

Construction of the second XF-11 prototype (44-70156) continued after the accident. The second prototype used single rotation, four-blade propellers that were 14 ft 8 in (4.47 m) in diameter and made by Curtis Electric. Despite all of the new rules implemented because of his crash, Hughes was adamant that he pilot the first flight of the second XF-11 prototype. The AAF initially refused, but Hughes pressed the issue and made personal appeals to Lt.Gen. Ira Eaker and Gen. Carl Spaatz. Hughes also offered to put up a $5 million bond payable to the AAF if he crashed. With the posting of the bond, the AAF gave in. On 4 April 1947, Hughes flew the second XF-11 on its first flight, taking off from Hughes Airport. The flight was a personal victory for Hughes.

Hughes XF-11 no2 flight

The second XF-11 on an early test flight. The aircraft was later fitted with spinners. Note the turbosupercharger’s exhaust just under the wing and the oil cooler’s air exit at the end of the scoop. (UNLV Libraries image)

The second XF-11 was later delivered to the AAF at Wright Field, Ohio in November 1947. After further flight tests, the aircraft went to Eglin Air Force Base in Florida. The XF-11 was noted for having good flight characteristics, but in-flight access of the camera equipment was extremely difficult and some of the aircraft’s systems were unreliable. In 1948, the aircraft was redesignated XR-11 in accordance to the new Air Force designation system. The XF-11 was tested at Eglin from December 1947 through July 1949.

Other, existing aircraft, mainly Boeing RB-29s and RB-50s, were serving in the reconnaissance role intended for the XF-11. These aircraft proved much less expensive than the XF-11, making the impressive and powerful XF-11 irrelevant. While the XF-11 probably could have done the reconnaissance job better, money was tight in the post-war years and there were other, more-promising projects to fund. The XF-11 was transferred to Sheppard Air Force Base in Wichita Falls, Texas on 26 July 1949 and subsequently served as a ground training aid, never flying again. The aircraft was struck from the Air Force’s inventory in November 1949 and was eventually scrapped.

Hughes XF-11 no2 1948

The second XF-11 sometime in 1948 with the revised (red stripe) Air Force insignia. The aircraft has recently taken off and the very large nose gear doors are just closing. Note the underwing pylons. (UNLV Libraries image)

Sources:
World’s Fastest Four-Engined Piston-Powered Aircraft by Mike Machat (2011)
R-4360: Pratt & Whitney’s Major Miracle by Graham White (2006)
Howard Hughes: An Airman, His Aircraft, and His Great Flights by Thomas Wildenberg and R.E.G. Davies (2006)
McDonnell Douglas Aircraft since 1920: Volume II by René J. Francillon (1990)
“A Visionary Ahead of His Time: Howard Hughes and the U.S. Air Force—Part II” by Thomas Wildenberg, Air Power History (Spring 2008)
https://en.wikipedia.org/wiki/Hughes_XF-11

Mathis Vega 42 front

Mathis Vega 42-Cylinder Aircraft Engine

By William Pearce

Émile E. C. Mathis was a French automobile dealer who began manufacturing cars under his own name in 1910. Mathis was based in Strasbourg, which was part of Germany at the time. The Mathis automobile began to achieve success just before World War I. After the start of the war, Émile was conscripted into the German Army. Because of his knowledge of automobiles, the Germans sent Émile on a mission to Switzerland to purchase trucks and other supplies. Émile was given a substantial amount of money for the transaction, and he took the opportunity to desert the Germany Army and keep the funds. When Germany was defeated, Émile returned to his automobile company in Strasbourg, which was then in French territory near the German border, and resumed production.

Mathis Vega 42 front

The high-performance, 42-cylinder Mathis Vega aircraft engine. Note the camshaft-driven distributors attached to the front of each cylinder bank.

In 1937, the Mathis company began designing aircraft engines. A new company division, the Société Mathis Aviation (Mathis Aviation Company), was founded with offices in Paris and factories in Strasbourg and Gennevilliers. These were mostly the same facilities as the automobile business, with auto development out of Strasbourg and aircraft engine development centered in Gennevilliers, near Paris. Raymond Georges was the technical director in charge of the aircraft engines. The Mathis company started their involvement in aircraft engines with the rather ambitious Vega.

The Mathis Vega was a 42-cylinder inline radial aircraft engine. The liquid-cooled engine had seven cylinder banks, each with six cylinders. The cylinder banks had an integral cylinder head and were made from aluminum. Steel cylinder barrels were screwed into the cylinder bank. Each cylinder had one intake valve and one sodium-cooled exhaust valve. A single overhead camshaft actuated the valves for each cylinder bank. The camshafts were driven from the front of the engine. Camshaft-driven distributors mounted to the front of each cylinder bank fired the two spark plugs in each cylinder. The spark plugs were positioned on opposite sides of the cylinder. The two-piece crankcase was made from aluminum.

Mathis Vega 42 side

The Vega was a relatively compact engine. Note the exhaust port spacing on the cylinder banks. Presumably, different exhaust manifolds would be designed based on how the engine was installed in an aircraft.

At the front of the engine was a planetary gear reduction that turned the propeller shaft at .42 times crankshaft speed. At the rear of the engine was a single-speed and single-stage supercharger that turned at 5.53 times crankshaft speed. A single, two-barrel, downdraft carburetor fed fuel into the supercharger. Seven intake manifolds extended from the supercharger housing to feed the air/fuel mixture to the left side of each cylinder bank. Individual exhaust stacks were mounted to the right side of each cylinder bank. Attached to the back of the supercharger housing was a coolant water pump with seven outlets, one for each cylinder bank.

The Vega had a 4.92 in (125 mm) bore and a 4.53 in (115 mm) stroke. The 42-cylinder engine displaced 3,617 cu in (59.3 L) and had a compression ratio of 6.5. The Vega was 42.1 in (1.07 m) in diameter and 59.8 in (1.52 m) long. The first Vega was known as the 42A, and the engine was first run in 1938. The 42A produced 2,300 hp (1,715 kW) at 3,000 rpm and weighed 2,756 lb (1,250 kg). Reportedly, two examples were built as well as a full-scale model. It is not clear how much testing was undertaken, but some sources indicate the engine was flown 100 hours in a test bed during 1939. Unfortunately, details of the engine’s testing and the aircraft in which it was fitted have not been found.

An improved version, the 42B, was under development when the Germans invaded in May 1940. The Vega engine program was evacuated from Gennevilliers and hidden in the Pyrenees mountains in southern France for the duration of the war. Believing that the Germans would not have forgotten his desertion and miss-appropriation of funds during World War I, Émile fled to the United States in 1940. Émile offered the Vega engine to the US Military in October 1942, but no action was taken.

Mathis Vega 42 rear

Rear view of the Vega displays the intake manifolds, single carburetor, and the seven-outlet water pump. On paper, the Vega was a light and powerful engine, but no details have been found regarding its reliability.

After World War II, Émile returned to France, and work resumed on the Vega engine. The 42B was updated as the 42E (42E00). In all likelihood, the 42B and the 42E were the same engine; an example was exhibited in Paris, France in 1945. The Vega 42E produced 2,800 hp (2,088 kW) at 3,200 rpm with 8.5 psi (.59 bar) of boost for takeoff. The engine was rated for 2,300 hp (1,715 kW) at 3,000 rpm at 6,562 ft (2,000 m) and 1,700 hp (1,268 kW) at 2,500 rpm at 13,123 ft (4,000 m). The engine weighed 2,601 lb (1,180 kg).

The design of an enlarged Vega engine was initiated in 1942. Originally designated 42D, the larger engine was later renamed Vesta. The 42-cylinder Vesta was equipped with a two-speed supercharger that rotated 3.6 times crankshaft speed in low gear and 5.7 times crankshaft speed in high gear. The engine had a .44 gear reduction and utilized direct fuel injection. The Vesta had a 6.22 in (158 mm) bore, a 5.71 in (145 mm) stroke, and a displacement of 7,287 cu in (119.4 L). The engine had a takeoff rating of 5,000 hp (3,728 kW) at 2,800 rpm with 8.5 psi (.59 bar) of boost and a normal rating of over 4,000 hp (2,983 kW). The Vesta was 52.0 in (1.32 m) in diameter and weighed 4,519 lb (2,050 kg).

Like many other large engines built toward the end of World War II, the Vega failed to find an application, and the Vesta was never built. Mathis continued work on aircraft engines and produced a number of different air-cooled engines for general aviation. The design of these smaller engines was initiated during the war, and every attempt was made to maximize the number of interchangeable parts between the smaller engines. Some of the material for the smaller engines was liberated “scrap” provided by the Germans and intended for German projects. However, the general aviation engines were not made in great numbers, and production ceased in the early 1950s. No parts of the Vega engines are known to have survived.

Mathis Vega 42 R Georges

Raymond Georges overlooks the Vega engine mounted on a test stand in 1939. The pipes above the Vega are taking hot water from the engine.

Sources:
Les Moteurs a Pistons Aeronautiques Francais Tome 2 by Alfred Bodemer and Robert Laugier (1987)
Aircraft Engines of the World 1946 by Paul H. Wilkinson (1946)
L’aviation Francaise de Bombardement et de Renseignement (1918/1940) by Raymond Danel and Jean Cuny (1980)
“The Mathis 42E 00” Flight (6 September 1945)
https://sites.google.com/site/moteursmathis/
https://ww2aircraft.net/forum/threads/mathis-vega-42-cylinder-french-aero-engine.49170/

Hughes XH-17 hover front

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.

Hughes XH-17 side

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.

Hughes XH-17 group

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.

Hughes XH-17 rear

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.

Hughes XH-17 front


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).

Hughes XH-17 hover front

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.

Hughes XH-17 hover side

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.

Hughes XH-28 mockup

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

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: