The Importance of Spin Testing in Aerospace & Aviation

Spin testing grew out of the need for a means to establish the integrity of jet engine rotor disks when jet engines were first being developed towards the end of the Second World War. Barbour Stockwell was involved from almost the very beginning, providing the requisite high speed turbine spin test drives from the early 1950’s onward. 

An important application for these drives has been the performance of low cycle fatigue (LCF) tests on the engine rotor disks to demonstrate/establish the service life of these disks. Eventually, BSi’s capabilities grew into providing entire spin test facilities including the test chambers, controls, and all the requisite support equipment as well as the drives. While LCF testing of jet engine rotor disks remains an important application for these spin test facilities, these days the company’s equipment supports the aerospace industry in so many more ways:

  • Impellers and expanders. BSi equipment is in service worldwide performing overspeed tests on impellers and expanders employed in the environmental control systems of commercial and military aircraft. BSi also performs such tests at our own facility for a multitude of customers. 
  • Motors and generator rotors. It is not only turbomachinery rotors that must be subjected to rigorous testing to be deemed flightworthy. Aircraft electrical motor and generator rotors are also spin tested as part of quality assurance program to meet the high standards required to ensure aircraft safety. Such tests are performed on newly manufactured rotors and on rewound rotors before they are returned to service. BSi test rigs are employed to meet these requirements in North America, Europe and Asia. 

BSi’s Spin Testing Capabilities

BSi’s aerospace spin testing facilities rely on our Full Authority Spin Testing (F.A.S.T.) control system. As the most highly-developed spin testing control system, F.A.S.T. incorporates a TC-4 drive controller with optimal speed control and a fully customized computer system for data acquisition functions and equipment control. Our control system can continuously perform unmanned cyclic spin tests and monitor all crucial test parameters.

When the computer system detects a change or occurrence it will automatically notify our engineers. We can remotely access the system to continuously check the progress of tests and address issues that require test interruption. Various industries depend on our F.A.S.T system, including commercial aerospace and military and government aircraft.

Main Aerospace & Aviation Spin Testing Services

BSi’s testing facilities and rigs are ideal for aerospace and aviation applications, including jet engines, wound electrical rotors, and expanders and compressor impellers employed in environmental control systems. To meet the needs of these applications, we offer the following testing procedures:

 

Overspeed Testing 

This test is typically employed for quality assurance purposes. It subjects a rotor to speeds above what it would experience during normal operations. As the turbomachinery rotors are driven, the bore may yield as it passes its service speed. 

Overspeed testing is used to assure the quality of turbomachinery rotors and may or may not be employed on each and every production rotor. However, overspeed testing is often actually a part of the production process. For this so-called pre-spinning operation, semi-finished rotors are driven to speeds such that the rotor bore actually yields significantly. Disks treated in this manner provide greater stability during the finish machining operations and the residual compressive stresses have a beneficial effect on fatigue life. 

Generally, the test protocol demands the achievement of a specific level of growth rather than a target rpm, and the growth is substantial. Such growth of the bore demands careful tooling design to maintain concentricity of the rotor as the bore grows with increasing speed. BSi excels at designing such tooling and has an enviable track record in performing this disk pre-spinning. 

Overspeed tests are also performed on the Liquid Propulsion Rocket Engine Turbopump rotors. Since the required material strength for the application is frequently exhibited only at cryogenic temperatures, the spin tests are also conducted at cryogenic (80 Kelvin or -320°F) temperatures. BSi, in fact, supplied such a rig for performing such tests on NASA’s Space Shuttle Main Engine rotors. Since then, additional rigs have been supplied to a number of manufacturers of liquid propulsion rocket engines.  

 

Burst Testing

This test is performed to assure proper margin between burst and service speeds. It drives the rotor to a precise speed until it reaches the point of failure to record the margin. Jet engine manufacturers rely on burst testing to assess the quality of new materials and qualify new designs. It can also be part of a quality assurance process to test samples from production lots.

 

Low-Cycle Fatigue Testing

This testing assesses a rotor’s fatigue life by cycling the test rotor between low and high speeds several thousands of times. Elevated isothermal or gradient temperatures can also be employed. Low-cycle fatigue testing can test new materials and rotor designs and calibrate methods of analytical prediction. 

 

High-Cycle Fatigue Testing

In addition to LCF testing , there is a lot of interest nowadays in studying the behavior of the blades when subjected to excitation while rotating at service speeds. During this high cycle fatigue (HCF) testing, excitation is typically generated by impinging jets of air or oil on the blades, and the response is measured by employing a sophisticated Non-contacting Stress Measurement System (NSMS). Such testing requires very, very precise speed control.   

BSi has the ability to control speeds to +/- 1 rpm while rotating at tens of thousands of rpm. Since the bandwidth of a blade resonance can be exceedingly small, BSi’s ability to step up speed at less than 1 rpm per second is an important attribute. 

Spin Testing Rigs and Services From Barbour Stockwell

At BSi, we provide in-house testing services and rigs for the aerospace and aviation industry along with a range of other sectors. Our F.A.S.T control system allows for unmatched speed control and monitors critical parameters with remote access for real-time assessment. 

As an AS 9100D and ISO 9001:2015 certified facility, we can conduct testing in temperatures as low as cryogenic conditions and as high as 1100 °C with test rig speeds up to 250,000 RPM. For more information about how our testing services can benefit the aerospace and aviation industry, contact us or request a quote today.