Flader J55
Encyclopedia
The Flader J55, also known as the 124 within the company, was a small turbojet engine notable for its use of a supersonic
axial-flow compressor. Development started at Fredric Flader Inc. in 1947 and the first examples were delivered in 1949, but these delivered far lower power than predicted. Improved models followed in early 1952 that met the performance requirements, but demonstrated very poor reliability. When small engines from other companies became available, the J55 project was cancelled in 1952.
-like disks known as "stages", each of which compresses the incoming air in turn. As the air is compressed its volume decreases, so each stage has less diameter than the one before it.
In a normal turbojet, the compressors rotational speeds are limited so that the outer tips of the blades remain subsonic. If all of the stages are powered off of a common shaft, this means that the limiting rotational speed will be defined by the first stage, which is the largest. Stages further in will be operating with tip speeds that are much lower, which works against the general principle that faster rotational speeds are more efficient. Larger engines, like those on modern airliners, normally include two or three "spools", sections of the engine operating at different rotational speeds, allowing each section of the compressor to reach the highest RPM possible while remaining subsonic.
Additionally, in order for an aircraft to operate at supersonic airspeeds, aircraft normally use a series of ramps or cones to create shock wave
s that progressively slow the air to subsonic speeds before it reaches the compressor. These intakes create drag that must be overcome by the engines.
A compressor that works at supersonic speeds would thus have improved performance, at least in theory. This would allow it to operate at higher rotational speeds, as well as reducing or eliminating the need for the complex inlets. During the early days of engine development, supersonic aerodynamics were not well understood, and it was not clear whether such an engine would be more or less efficient than a conventional design.
In order to find out, between 1946 and 1948 engineers at the NACA Lewis Research Center
carried out an early research program on supersonic compressor stages. These demonstrated very encouraging results; not only did such a design work, but the compression ratio across a single stage was much higher than in a subsonic design, as much as two times. This would allow an engine with a given overall pressure ratio
to be built with fewer stages, making it smaller, lighter and less complex.
to develop the engine, but the Army cancelled the project shortly after. The company was saved by a US Navy contract for an 8 inches (203.2 mm) turbine for emergency power on small ships, but this contract was later won by Solar Turbines
and work at Flader ended.
In 1946 the Army started developing the requirements for a series of three unmanned aircraft, one of which was a high-speed radio controlled target drone, the XQ-2. Ryan Aeronautical won the contract with their Firebee
design, and on 7 February 1947 the Power Plant Laboratory at the Wright Air Development Center
issued a tender for a small engine to power the Ryan airframe. Flader's proposal, from 26 April 1947, proposed using a supersonic compressor in order to build a small engine suitable for the design. They predicted that the compressor would have a compression ratio about 2.75, roughly twice that of conventional designs. This was enough that only a single centrifugal-flow compressor
was needed to complete the compression cycle of the engine.
In spite of the risks involved, Flader's proposal won the tender and development started two months later.
on the blades. Additionally, after about 35 hours of running time the leading edges of the compressor blades were found to be curled over, apparently due to extremely high aerodynamic loads.
In mid-1949 Flader delivered two derated engines, XJ55-FF-1's, to the Air Force for testing. These delivered only 450 lbf (2,001.7 N) of thrust, far below what was needed to power the Firebee. However, Flader continued working on the design, and it had greatly improved by late 1951. In January 1952 they delivered one of these improved models and on 24 January it ran at 700 lbf (3,113.8 N), meeting the requirements. However, during a second test on 31 January the engine failed shortly after running for one minute at 700 lbf (3,113.8 N).
Although it appeared that the basic design was able to deliver its promised performance, at that point it was far from a complete design. Weight and fuel consumption were both above the design estimates, the various support systems like fuel and oil pumps were not self-contained, and it remained susceptible to compressor surging. Flader estimated that these problems would require another three years of development to fix.
and the Continental J69
, a licensed version of the French Turbomeca Marboré
. The Air Force decided to use the J69 in the Firebee, and cancelled development of the J55 shortly after.
Flader made several other one-off designs, but found no lasting work in the field and eventually sublet their plants to Eaton Manufacturing
in 1955. Eaton moved on, and Flader was wound down on 2 September 1957.
Normal operating speed was 28,600 rpm. Maximum thrust was 770 lbf (3,425.1 N), 700 for cruise. The engine was 15.75 inches (400.1 mm) in diameter, 79 inches long, and weighed only 300 lb (136.1 kg) dry.
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
axial-flow compressor. Development started at Fredric Flader Inc. in 1947 and the first examples were delivered in 1949, but these delivered far lower power than predicted. Improved models followed in early 1952 that met the performance requirements, but demonstrated very poor reliability. When small engines from other companies became available, the J55 project was cancelled in 1952.
Supersonic compressors
An axial compressor consists of a series of propellerPropeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
-like disks known as "stages", each of which compresses the incoming air in turn. As the air is compressed its volume decreases, so each stage has less diameter than the one before it.
In a normal turbojet, the compressors rotational speeds are limited so that the outer tips of the blades remain subsonic. If all of the stages are powered off of a common shaft, this means that the limiting rotational speed will be defined by the first stage, which is the largest. Stages further in will be operating with tip speeds that are much lower, which works against the general principle that faster rotational speeds are more efficient. Larger engines, like those on modern airliners, normally include two or three "spools", sections of the engine operating at different rotational speeds, allowing each section of the compressor to reach the highest RPM possible while remaining subsonic.
Additionally, in order for an aircraft to operate at supersonic airspeeds, aircraft normally use a series of ramps or cones to create shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
s that progressively slow the air to subsonic speeds before it reaches the compressor. These intakes create drag that must be overcome by the engines.
A compressor that works at supersonic speeds would thus have improved performance, at least in theory. This would allow it to operate at higher rotational speeds, as well as reducing or eliminating the need for the complex inlets. During the early days of engine development, supersonic aerodynamics were not well understood, and it was not clear whether such an engine would be more or less efficient than a conventional design.
In order to find out, between 1946 and 1948 engineers at the NACA Lewis Research Center
Glenn Research Center
NASA John H. Glenn Research Center at Lewis Field is a NASA center, located within the cities of Brook Park, Cleveland and Fairview Park, Ohio between Cleveland Hopkins International Airport and the Cleveland Metroparks's Rocky River Reservation, and has other subsidiary facilities in Ohio...
carried out an early research program on supersonic compressor stages. These demonstrated very encouraging results; not only did such a design work, but the compression ratio across a single stage was much higher than in a subsonic design, as much as two times. This would allow an engine with a given overall pressure ratio
Overall pressure ratio
In aeronautical engineering, the term overall pressure ratio is defined as the ratio of the stagnation pressure as measured at the front and rear of the compressor of a gas turbine engine...
to be built with fewer stages, making it smaller, lighter and less complex.
Flader proposal
Fredric Flader Inc. was formed in 1944 to develop small turbine engines, initially based on a contract with the US Army Air Force for a 5900 shp turboprop, the T33-FF-1. Flader opened a new plant in Tonawanda, New YorkTonawanda, New York
Tonawanda may refer to:*Glacial Lake Tonawanda*North Tonawanda, New York, a city in Niagara County, north across Tonawanda Creek from the City and Town*Tonawanda , New York, consisting of the Town of Tonawanda less the Village of Kenmore...
to develop the engine, but the Army cancelled the project shortly after. The company was saved by a US Navy contract for an 8 inches (203.2 mm) turbine for emergency power on small ships, but this contract was later won by Solar Turbines
Solar Turbines
Solar Turbines Incorporated, a wholly owned subsidiary of Caterpillar Inc., designs and manufactures industrial gas turbines for on- and off-shore electrical power generation, for marine propulsion and for producing, processing and transporting natural gas and oil. Solar Turbines is one of the...
and work at Flader ended.
In 1946 the Army started developing the requirements for a series of three unmanned aircraft, one of which was a high-speed radio controlled target drone, the XQ-2. Ryan Aeronautical won the contract with their Firebee
Ryan Firebee
The Ryan Firebee was a series of target drones or unmanned aerial vehicles developed by the Ryan Aeronautical Company beginning in 1951. It was one of the first jet-propelled drones, and one of the most widely-used target drones ever built....
design, and on 7 February 1947 the Power Plant Laboratory at the Wright Air Development Center
Wright-Patterson Air Force Base
Wright-Patterson Air Force Base is a United States Air Force base in Greene and Montgomery counties in the state of Ohio. It includes both Wright and Patterson Fields, which were originally Wilbur Wright Field and Fairfield Aviation General Supply Depot. Patterson Field is located approximately...
issued a tender for a small engine to power the Ryan airframe. Flader's proposal, from 26 April 1947, proposed using a supersonic compressor in order to build a small engine suitable for the design. They predicted that the compressor would have a compression ratio about 2.75, roughly twice that of conventional designs. This was enough that only a single centrifugal-flow compressor
Centrifugal compressor
Centrifugal compressors, sometimes termed radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.The idealized compressive dynamic turbo-machine achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller...
was needed to complete the compression cycle of the engine.
In spite of the risks involved, Flader's proposal won the tender and development started two months later.
Early testing
Flader worked in close concert with the engineers at Lewis. They sent an early version of the compressor to them for testing in June 1948, which demonstrated performance far below the predicted value. Worse, contrary to expectations, the performance decreased with increasing rotational speed, the opposite of what Lewis's earlier research had suggested, which was one of the biggest reasons for using the design. This was later attributed to a thick boundary layerBoundary layer
In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...
on the blades. Additionally, after about 35 hours of running time the leading edges of the compressor blades were found to be curled over, apparently due to extremely high aerodynamic loads.
In mid-1949 Flader delivered two derated engines, XJ55-FF-1's, to the Air Force for testing. These delivered only 450 lbf (2,001.7 N) of thrust, far below what was needed to power the Firebee. However, Flader continued working on the design, and it had greatly improved by late 1951. In January 1952 they delivered one of these improved models and on 24 January it ran at 700 lbf (3,113.8 N), meeting the requirements. However, during a second test on 31 January the engine failed shortly after running for one minute at 700 lbf (3,113.8 N).
Although it appeared that the basic design was able to deliver its promised performance, at that point it was far from a complete design. Weight and fuel consumption were both above the design estimates, the various support systems like fuel and oil pumps were not self-contained, and it remained susceptible to compressor surging. Flader estimated that these problems would require another three years of development to fix.
Cancellation
At that point, two new small engines with roughly the required power had come to market, the Fairchild J44Fairchild J44
|-See also:-References:* The History of North American Small Gas Turbine Aircraft Engines, William Fleming and Richard Leyes, AIAA, 1999-External links:*...
and the Continental J69
Teledyne CAE J69
|-See also:-External links:*...
, a licensed version of the French Turbomeca Marboré
Turbomeca Marboré
|-See also:-References:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:* *...
. The Air Force decided to use the J69 in the Firebee, and cancelled development of the J55 shortly after.
Flader made several other one-off designs, but found no lasting work in the field and eventually sublet their plants to Eaton Manufacturing
Eaton Corporation
Eaton Corporation is a global diversified power management company with 2010 sales of $13.7 billion. The company is a leading provider of electrical components and systems for power quality, distribution and control; hydraulics components, systems and services for industrial and mobile equipment;...
in 1955. Eaton moved on, and Flader was wound down on 2 September 1957.
Description
The J55 looked like a conventional axial-flow engine overall, but the equipment section was located in front of the engine in an oversized spinner area. Behind the spinner was the intake area and the supersonic compressor stage. Behind this was the single centrifugal stage, in a separate cylindrical section. This was followed by a canular combustion area and then a single turbine stage.Normal operating speed was 28,600 rpm. Maximum thrust was 770 lbf (3,425.1 N), 700 for cruise. The engine was 15.75 inches (400.1 mm) in diameter, 79 inches long, and weighed only 300 lb (136.1 kg) dry.