The aerospace industry has some of the most difficult operating conditions imaginable. Sensors of all kinds used in this industry must stand up to the environment and be able to perform under harsh conditions, fit in extremely tight spaces, and have electronics that can compensate for variable conditions in order to provide precise, repeatable results.

In particular, flight instruments measuring fluid flow in aircraft fuel and hydraulic systems are required to operate over extreme temperature ranges, while enduring heavy vibration and shock, and withstand electromagnetic interference and voltage transients. And, as aerospace test environments become more severe (higher temperature, greater vibration) and test application requirements for measurement devices grow more stringent (smaller, lighter, more stable, higher accuracy), obtaining meaningful data can be challenging.

Typical Flow Applications

From monitoring the fuel consumption of rotary and fixed wing aircraft, missiles and drones, to evaluating the performance of hydraulic fluid and lubricants, aerospace applications place high demands on flow sensing technology. Accurate and dependable flow meters are required for numerous fluid measurements on board aircraft and in component test stands, such as:

Fuel Management: Aerospace companies rely on flow transducers to provide accurate, instantaneous fuel flow rate and total fuel consumption data. Paired with cockpit displays, flow meters must offer easy installation and high reliability. Fuel Ballast: As fuel is consumed, there is a ballast issue that can be resolved by fuel manipulation. This is often accomplished by pumping the fuel to different tanks, which requires measurement of the fuel transferred to balance the aircraft.

Hydraulic System Verification: Measuring hydraulic fluid leakage or displacement during a flight test requires a flow meter that is highly repeatable, capable of differential flow, and extremely compact and rugged. Instrumentation suppliers are called upon to answer the size, safety and durability requirements of flight test engineers in a wide range of hydraulic system applications.

Product R&D: By pairing a flow meter with a flow computer or smart transmitter, aerospace equipment manufacturers can perform precise metering of fuel flow in engine test cells, fuel and hydraulic fluid flow in component test stands, and hydraulic fluid flow in hydraulic mules.

Qualification and Acceptance Testing: During the development process for new flight-qualified components or systems, turbine meters can be used to validate compliance with performance requirements over a wide range of operating conditions. In the process of acceptance testing, the excellent accuracy achieved by turbine meters prevents manufacturers from narrowing the window of acceptance due to the uncertainty of the flow measurement. For example, a ±100 pound per hour (PPH) flow requirement can be narrowed to ±90 PPH by a flow measurement with ±10 PPH uncertainty, thereby increasing the risk that a good part will be rejected.

Performance Evaluation: Unmanned aerial vehicles (UAVs), drones and missiles are frequently called upon to stay in flight for extended periods of time, or even loiter over an area. Aerospace designers developing these and other advanced platforms seek instantaneous fuel flow rate data that can be used as feedback to control engine performance.

Maintenance, Repair, and Overhaul (MRO): When flow specifications are involved, turbine meters offer a precise tool to verify that fuel and hydraulic components meet the original manufacturer’s specifications following maintenance, repair, or overhaul. As with qualification test procedure (QTP) and acceptance test procedure (ATP), the accuracy of these meters reduces the chance that a conforming component will fall out of the acceptance window.

Why Turbine Meters?

Figure 1. The turbine flow meter is a popular measurement device among aerospace engineers.
One of the preferred types of flow meters among aerospace engineers is the turbine meter (Figure1). It is widely used for obtaining precise flow measurements in clean, known liquids with relatively low viscosity. Available in compact, lightweight packages with rugged materials of construction, turbine meters are used to measure diverse fluids ranging from aircraft fuel to hydraulic fluid, lubricant, cryogenic fluid and coolant. They also offer a versatile metering solution that can be designed and manufactured based on custom specifications for packaging, end-fittings, mounting, electronics, etc.

Turbine flow meters employ a proven measurement technology, which is digital in nature and provides exceptionally reliable outputs. The meter functions by sensing the linear velocity of the fluid passing through the known cross sectional area of its housing to determine the volumetric flow rate. The fluid, as it passes through the meter, imparts an angular velocity to the rotor, which is proportional to the linear velocity of the flowing fluid. Since the linear velocity of the flowing fluid through a given area is directly proportional to the volumetric flow rate, it follows that the speed of rotation of the rotor is directly proportional to the volumetric rate.

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