Aviation

In aviation, inertial reference systems are used for navigation. They determine the position, speed and flying attitude of an aircraft in relation to the Earth. Such systems are equipped with inertial measurement units (IMUs), which as part of an attitude heading reference system (AHRS) are used to determine changes in the roll, pitch and yaw angles. However, these systems can operate with the required precision only if the bias stability of the integrated gyroscopes is better than 5 °/h.

The gyroscopes ASC 281 (uniaxial) and ASC 283 (triaxial) are ideally suited for use in these IMUs, since they feature bias stability of <0.1 °/h.

We make aviation safer with inertial sensors that provide testing and measuring engineers with precise data. Sensors for these applications must not only withstand high temperatures and pressures – they should also be lightweight.

The compact design of the ASC IMU 7 has especially proven itself here. Aircraft manufacturers position IMUs during flight tests at different locations within the cabin to locally measure the inertial variables with a defined temporal resolution.

The ASC IMU 7 with its modular concept is ideal for these measurements, since it allows engineers to create a custom configuration for your requirement. For acceleration measurements you can choose between Low Noise (LN) and Medium Frequency (MF) versions with a measuring range from ±2 g to ±50 g and an angular rate range from ±75 °/s to ±900 °/s.

Aircraft and their components, such as wings, are always subject to vibrations during flight. Self-induced vibrations in aircraft within defined limits are not deemed critical. In the worst case, depending on parameters such as construction and flying speed, normal modes can overlap and resonate, causing aeroelastic fluttering of the aircraft components. Under some circumstances this can even result in component failure. To determine the behavior of components under real and especially under harsh conditions, flutter tests are conducted to measure the stability under load of single aircraft components.

For example, the ASC 5521MF triaxial sensor features a wide frequency response range from 0 Hz to 7 kHz and excellent shock resistance up to 6,000 g. For hard-to-access installation positions, on the other hand, the ASC 4111LN, ASC 4211LN and ASC 4221MF are ideal due to their compact and lightweight design (less than 3 grams).

Vibrations within the structure of a helicopter are unavoidable. If normal modes overlap and resonate in the worst case, this can result in total loss of the helicopter within a very short time. During take-off and landing, contact with the ground is crucial. Either the vibrations are limited or components of the helicopter are deformed by impacts. This results in minimal structural changes that cause imbalances in the overall system.

Such vibrations can be prevented or at least reduced by means of design rules. However, ground resonance can never be fully precluded. That is why extensive tests of the entire frequency response range are carried out during the helicopter’s development phase.

Ideal sensors for this application are the triaxial capacitive accelerometers ASC 5421MF, which are designed for the medium frequency range starting at 0 Hz as well as the triaxial piezoelectric accelerometers of type ASC P203, which are optimally suited for vibration analysis up to 9 kHz.

Aircraft and their components are subjected to extreme conditions during flight, take-off and landing. Fatigue, overload or material defects cause changes in structural rigidity. This is monitored by regular modal and structural analyses of aircraft and their components. These analyses require lightweight, high-frequency accelerometers that minimize the mass load of the test structures as much as possible.

The triaxial IEPE accelerometer ASC P203 is used for modal tests, since it weighs only 6 grams (titanium housing) or 7.3 grams (aluminum housing) and is designed for shock resistance up to 5,000 g. Both the triaxial IEPE accelerometer ASC P203 and the uniaxial versions ASC P101 and ASC P401 providing a very high dynamic range of up to 15 kHz (±1 dB) and are available with measuring ranges from ±50 g to ±2,000 g.