Main Menu

See All Software See All Instruments See All Transducers See All Vibration Testing Equipment See All Electroacoustics See All Acoustic End-of-Line Test Systems See All Academy See All Resource Center See All Applications See All Industries See All Services See All Support See All Our Business See All Our History See All Global Presence

Main Menu

See All nCode - Durability and Fatigue Analysis See All ReliaSoft - Reliability Analysis and Management See All Test Data Management See All DAQ Software See All Drivers & API See All Utility See All Vibration Control See All High Precision and Calibration Systems See All DAQ Systems See All S&V Hand-held Devices See All Industrial Electronics See All Power Analyzer See All S&V Signal Conditioner See All Acoustic Transducers See All Current and Voltage Sensors See All Displacement Sensors See All Force sensors See All Load Cells See All Multi Component Sensors See All Pressure See All Strain Sensors See All Strain Gauges See All Temperature Sensors See All Tilt Sensors See All Torque Sensors See All Vibration See All Accessories for Vibration Testing Equipment See All Vibration Controllers See All Measurement Exciters See All Modal Exciters See All Power Amplifiers See All LDS Shaker Systems See All Test Solutions See All Actuators See All Combustion Engines See All Durability See All eDrive See All Production Testing Sensors See All Transmission & Gearboxes See All Turbo Charger See All Training Courses See All Acoustics See All Asset & Process Monitoring See All Custom Sensors See All Data Acquisition & Analysis See All Durability & Fatigue See All Electric Power Testing See All NVH See All Reliability See All Vibration See All Weighing See All Automotive & Ground Transportation See All Calibration See All Installation, Maintenance & Repair See All Support Brüel & Kjær See All Release Notes See All Compliance See All BKSV Worldwide Contacts

Main Menu

See All API See All Experimental Testing See All Piezoelectric Charge Accelerometers See All Piezoelectric CCLD (IEPE) accelerometers See All Electroacoustics See All Noise Source Identification See All Environmental Noise See All Sound Power and Sound Pressure See All Noise Certification See All Industrial Process Control See All Structural Health Monitoring See All Electrical Devices Testing See All Electrical Systems Testing See All Grid Testing See All High-Voltage Testing See All Vibration Testing with Electrodynamic Shakers See All Structural Dynamics See All Machine Analysis and Diagnostics See All Dynamic Weighing See All Vehicle Electrification See All Calibration Services for Transducers See All Calibration Services for Handheld Instruments See All Calibration Services for Instruments & DAQ See All On-Site Calibration See All Resources See All Software License Management

Putting The Surface Microphone Through Its Paces at Airbus

Based in Toulouse, France, Airbus is a global company with design and manufacturing facilities in France, Germany, the U.K. and Spain. The cooperation between the various entities that make up Airbus, goes back to the 1920s. Its first aircraft A300B, which was launched at the 1969 Paris air show, was the world’s first widebody twinjet. It could comfortably carry 226 passengers.

Thirty-odd years later, the A380 – the widest commercial airliner available today with seating for 525 passengers – will be entering into service. It is another testament to Airbus’ commitment to innovation and intelligent design. Therefore, Airbus came to Brüel & Kjær for the development of a transducer they could invariably use to measure sound pressure in limited spaces during flight-testing and where flush mounting of conventional microphone/preamplifier combinations would be impossible or cause undesired side effects.

After multiple prototypes, all of which were rigorously tested by Airbus, the Surface Microphone Type 4948 was born – a flat, small, robust, accurate and stable microphone designed especially for aerospace applications and usable up to 165 dB. Verification trials proved that the microphone could withstand all the requirements demanded of transducers mounted outside an aircraft during flight, including but not limited to de-icing detergent, turbulence, hailstorms, rain, high g levels, a temperature range from –50˚C to 100˚C, cruising altitudes of 30 000 feet, and mach 0.8.

True to their commitment, Airbus continues to utilise the surface microphone in their flight-testing programme – years after its development.

Flying the Design

Flight-testing takes place at Airbus’ Toulouse testing site. It is here the company’s various research and design labs submit prototypes to validate aircraft design and performance characteristics. The individual design teams decide the test criteria, including where to place test sensors. The test engineers at Toulouse then determine the test methods and parameters as well as the types of sensors to be used.

Surface microphones mounted on an Airbus wing for flight testing
Above and below: Surface microphones mounted on an Airbus wing for flight testing

To monitor thousands of design parameters Airbus has over 15 000 transducers of different types: acoustic, vibration etc. Their acoustic transducers are used for various applications, including interior noise and exterior noise. For the approximately 200 surface microphones on hand, their robustness, dynamic range and mounting flexibility make them especially suited for acoustic fatigue analysis.

Acoustic fatigue analysis investigates a component’s material properties for weaknesses under acoustic stress. Results help designers choose suitable materials and help determine the lifecycle of individual components to ensure aircraft safety. There is always one model per aircraft family at the Toulouse site to perform regular acoustic fatigue tests.

Test Setup

To test for acoustic fatigue, surface microphones are mounted on the surface of the structure, including locations that were previously considered impossible due to shape, accessibility or safety issues. Even fuel tanks and other sensitive component surfaces can be measured without endangering personnel or risking the loss of the component, as microphone mounting requires no drilling. For curved surfaces like a leading edge, engineers insert the microphone into a customised ‘glove’ that conforms to the curved shape, and then mount the ‘glove’ using an industrial adhesive. With the A380 model, at least 60 surface microphones are mounted on its exterior during acoustic fatigue tests. The ultra-flat design of the microphone and aerodynamic mounting minimises the influence on airflow and thus the measurement.

Cables are held in place with metallic tape and connected to a data recorder or other data acquisition device

Cables are held in place with metallic tape and connected to a data recorder or other data acquisition device, The plane is then flown, at times to its maximum altitude (40 000 ft.) where air temperatures can be down to –55˚C. During a flight, noise level measurements are taken based on the sound pressure on the structure’s surface. When relevant, reference measurements are also taken in the interior for comparison. Data is either recorded for later examination or processed in real-time using telemetry. The typical noise frequency is around 6 kHz.

If measurements are required within the aircraft, for example, within the cockpit, test configurations can easily be altered in-flight and new measurements made without landing, thus saving time – for some tests, up to several weeks’ work. A team outside of the test lab handles the actual data analysis, investigating, for the most part, peaks in the measurement.

Accuracy and Quality

To ensure the accuracy of measurements, all surface microphones are calibrated for sensitivity and frequency response in the lab prior to mounting, and then checked with a pistonphone once mounted. After flight-testing, the microphones are returned to the lab for an additional calibration check. This routine provides the test engineers with a verification of the measurements’ accuracy and minimises the cost of errors due to faulty or inaccurate measurements.
From the start, Airbus’ decisions in design, testing and sound and vibration solutions are always taken in consideration of customer satisfaction, as well as market and company expectations.