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Engine Test Facilities - Issue Four

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Introduction - Growth Of The NGTE

1.1 Introduction

The engine test facilities at the National Gas Turbine Establishment (N.G.T.E.) Pyestock were constructed to allow the testing of gas turbine and ramjet engines to be performed on the ground under controlled conditions simulating flight altitude and aircraft forward speed. The provision of the facilities provides an alternative way of proving partially developed engines without recourse to flight testing which is frequently limited in scope and exposes newly designed and most valuable equipment to a variety of risks.

The N.G.T.E. Engine Test Facilities comprise a complex plant installation requiring air process machinery, engine test chambers, data gathering systems and general services. All these aspects are described in this publication.

In order to meet the test requirements of large size engines considerable quantities of compressed air, cooling water and fuel have to be supplied. An extensive suction service to simulate altitude conditions is also needed. The plant providing these services is described in Sections 2 and 5.

The engine is tested in one of several test facilities which are described in Section 3. The selection of the facility will depend on many factors such as the type of test, engine size, operating parameters, etc. The information collected during the test is fed, via a complex data gathering system, either directly to the central computer which gives "on-line" analyses of engine performance or to secondary data processing and display systems for the presentation of transient information. The equipment providing these services is described in Section 4.

A high level of electrical power is consumed when running the test cells and testing is programmed with regard to the prevailing power supply position and tariff. Where necessary N.G.T.E. can generate a certain amount of its own electricity and details of this facility and of the electrical power distribution network are contained in Section 5.

A brief outline of the history of the N.G.T.E. and of the growth in the test facilities is given later in this Section. The comparison of N.G.T.E with other facilities in the Western World is also made to give an indication of the scope of testing available at N.G.T.E..

Of necessity the contents of this brochure are of a general nature, specific enquires and requests for further information should be addressed to The Director, Ministry Of Defense (Procurement Executive), National Gas Turbine Establishment, Pyestock, Farnborough, Hampshire. Enquires concerning component test facilities, aerodynamic and combustion rigs, material and oil laboratories, diesel test beds and noise pollution facilities all of which are available at N.G.T.E. should also be addressed to The Director, N.G.T.E.

1.2 The Growth Of The N.G.T.E.

The National Gas Turbine Establishment at Pyestock was formed in 1946 from the earlier wartime organisation Power Jets (Research And Development) Ltd. The first test facilities were provided to meet the needs of component testing and consisted of air compressing equipment and an associated test house. The early equipment known as the Old Site is now not used although the plant capacity is shown in Figure 1.1 up to 1952.

With the continued development of the gas turbine engine the need for more elaborate component test facilities was forseen and these were supplied by building the Plant House component test facilities. In parallel with this development the need for a full scale engine test facility which could simulate altitude and forward speed conditions was recognised and work began on the design of Cells 1 and 2. These cells were subsequently building and commissioned in 1952/4. Cells 1 provides a means of blowing supersonic air at an engine to simulate aircraft forward speed. This arrangement is known as free-jet testing and enables engine intake performance to be studied. In Cell 2 the test engine is connected directly to a chamber which is fed from the main compressed air supply in a radially inward direction so that thrust forces are balanced. This arrangement is known as component testing and is used for performance, engine integrity and combustion tests. Altitude simulation in both cells is achieved by the use of air driven ejector plant. The range of test conditions which can be attained is given in Figure 3.6 and the plant is described in more detail in Section 3. As aircraft size and performance increased, the need for facilities with corresponding greater range and flexibility arose, and so more sophisticated air processing equipment was needed to correctly simulate high and low temperature operating conditions. Cell 3 and the main Air House compressor/exhasuter plant were provided in 1955 to meet these needs. The air supply machinery is described in Section 2. The Cell 3 performance envelope for connected tests is given in Figure 3.13 and a more detailed description of the cell plant including the associated air heating and cold air processing plant appears in para. 3.3. to 3.7.

The arrival of supersonic air travel and the subsequent development of sophisticated air intake equipment brought the need for a test facility that could simulate supersonic airflows over a wide speed range to enable the interaction of intake and engines to be studied under rapidly changing conditions. Cell 4, a free-jet cell, was built and commissioned in 1966 to meet this requirement. The Cell 4 equipment includes a 25 square feet variable Mach number supersonic nozzle and a high speed pitching and yawing capability. Further details of the Cell 4 plant are given in Section 3 and the performance envelope is shown in Figure 3.36.

In parallel with the building of Cell 4, additional suction facilities were provided with the installation and commissioning of No. 9 exhauster plant described in para 2.3. This was followed in 1968 by the installtion of No. 10 exhuaster plant, described in para 2.4, which further extended the range of altitude conditions that can be simulated.

With the advent of large fan engines (Rolls-Royce RB211) for aircraft such as the Lockheed 'Tristar', the requirement arose for a facility capable of testing under altitude conditions very large diameter power plants of high thrust but low inlet and exhaust velocity. To meet this requirement Cell 3 West was designed and built, final commissioning taking place in 1969. In this cell air supplies for the engine are induced from atmosphere by suction applied at the engine exhaust end.

The atmospheric air is drawn through a large capacity inlet air cooler refrigerated by aqueous ammonia; the Cell 3 West plant is described in more detail in para. 3.8 and 3.9, and the performance envelope is given in Figure 3.24.

The expansion of the N.G.T.E. test facilities is illustrated in Figure 1.1 which shows the growth in the installed air pumping capacity over the years.

Fig. 1.1 Growth of N.G.T.E. Engine Testing Plant, 1944 - 81

1.3 N.G.T.E. compared with other facilities

The N.G.T.E. is one of the major altitude test facilities in the Western World. The air exhausting capacity available is an indication of an altitude test facility's limitations and as seen in Figure 1.1 the growth in engine thrust has been accompanied by a growth in air exhausting machinery at N.G.T.E.. Figure 1.2 shows the exhauster limit for N.G.T.E. in comparison with other test facilities. The range of facilities available at N.G.T.E. from the smaller ramjet facilities through the versatile Cell 3 connected facility, the Cell 4 free jet facility to the large fan engine facility make N.G.T.E. a unique test complex.

Fig. 1.2 A Summary Comparison of the altitude cell capabilty in UK, France, Germany and the USA.

1.4 Services available at N.G.T.E. for research and development work

The engine test facilities at N.G.T.E. are a scarce resource and are in constant use by commerical concerns and government departments of the United Kingdom and overseas customers. The uilk of the testing is confined to the research and development of gas turbine aero engines although a variety of other tests ranging from land based diesel engines to helicopter rotor and fuselage icing is undertaken in the five major altitude test facilities. The Establishment does not undertake production testing as this is nromally effected at sea level conditions at the engine manufacturer's own test site.

This publication deals with the plant and test system hardware available at the N.G.T.E. The detailed descriptions of the plant that appear in Sections 2 to 5 allow assessments to be made of the size and type of engine and tests that can be accommodated in each test cell. In the remainder of this section the wide range of support services available at N.G.T.E. required to test engines are briefly described. These range from the mechanical, aerodynamic and thermodynamic design of test installations, manufacture of ductwork and blowing nozzles, specification and provision of instrumentation and control services, to the tranfer of gathered data into meaningful engine performance measurements.

The staff at N.G.T.E. have the experience and expertise to define the engine test schedules, specify and write the computer software that will convert the raw data gathered during the engine test into engine thrust, specific fuel consumption and other measurements necessary to assess the engine performance. The staff participate in the research and development programmes and frequently contribute towards improvements in the customer's design.

The Establishment places importance on the need to provide accurate data for use in engine performance calculations. Comprehensive instrumentation and data gathering systems, together with on-line computation are available on all altitude test facilites. The accurate standards are maintained by the calibrations of pressure, temperature, thrust and flow measurement to be traced to the national standards at the National Physical Laboratory.

The design teams employed at N.G.T.E. undertake all work necessary to install the engine in the test facility. The customer's requirement is accessed and a feasibility study is undertaken to define which test cell(s) will be used and the customer is advised if the full requirements can be achieved. If necessary, the design team will specify and procure new plant facilities in order to achieve the test programme. The team will cover all aspects of the installations including the aerodynamic and thermodynamic effects, for example to ensure that upstream ducting and downstream exhaust diffusing systems are designed to produce neligible secondary effects on the engine test or to ensure the effects can be accounted for in the performance calculations.

When the detailed drawings of the installation hardware are complete the Establishment will undertake manufacture in the comprehensive workshop facilities that are available on the N.G.T.E. site (these facilities are not described in detail in this publication). Customers if they prefer can manufacture their own equipment from the drawings produced at the N.G.T.E.

The manufacturing facilities cover the normal machining processes of turning, milling, drilling, jig boring, etc. using conventional and numerically controlled machines. Ductwork of up to 5 feet diameter can be fabricated and machined. In addition, welding, sheet metal work and millwright services are available. To meet requirements outside the normal facilities or under workshop overload conditions a sub-contract organisation is available. Each test cell has a team of mechanical, electronic and electrical technicians available to install the equipment and engine into the test cell. These teams call on the expertise of engineers and scientists to ensure the engine is installed and furbished to a high standard. Inspection staff ensure that the work progresses to quality assurance standards normally expected within the aircraft industry.

These teams operate the facilities and test the engine to meet the customer's requirement. The customer's personnel participate in the test programme and work closely with the N.G.T.E. staff, especially during test periods when 'on-line' performacne data is used to assess and if neccessary modify test objectives to ensure effective and efficient use of the engine under test and the engine test facilities. Further information concerning the range of design manufacturing and testing services avaialble can be obtained by addressing enquires to The Director, N.G.T.E.

© Procurement Executive, Ministry Of Defence