Modern aircraft sensors play a critical role in the flight economy and safety of the aircraft, its passengers and the cargo it carries. There are several types of sensors used in modern aircraft. Temperature Sensors – As the name suggests, these are sensors used to measure the temperature of various engine components within the aircraft. Temperature sensors are usually used to record Cylinder Head Temperature (CHT), Exhaust Gas Temperature (EGT), Engine Oil Temperature (EOT), Fuel Temperature (FT), Hydraulic Fluid Temperature (HFT) etc. These sensors usually work on the Resistance Temperature Detector (RTD) principle which essentially means that change in resistance (ohms) in a metal amalgam is directly proportional to temperature changes applied to it. So when an electrical current is passes through it, the change in resistance is calibrated and displayed as temperature of that particular component at the point where the sensor is placed. Liquid Level Sensors – A liquid level sensor is generally mounted in thermowells and directly installed into reservoirs, tanks, sumps and gearboxes in the aircraft. These sensors are generally available as single point or multiple point interface elements or liquid levels and connected to onboard display units in the cockpit. Flow Sensors – As the name suggests, a flow sensor is used to monitor the flow rate or any liquid be it aviation fuel or oil. The flow sensor is mounted within a thermowell and it might also contain an electronics unit that connects to a Slimline Pressure Gauge. The flow sensor is usually directly installed into pipe that carries the liquid for which the flow rate is being measured. Pressure Sensors – A pressure sensor is used to measure pressure that is above or below a pre-set figure at the sensing location. The pressure sensor is directly installed into ducts, pipes, tanks, sumps, reservoirs or gearboxes in the aircraft. It can be specified to indicate either absolute or differential pressure. Proximity Sensors – Proximity sensors are usually used to confirm the status of something that opens or closes e.g. doors, landing gear door, cargo bay door and so forth. It is also used to confirm if the landing gear is extended or retracted. RPM Sensor – The aircraft spark plugs are powered by a mini power generator in the form of a Bendix Magneto generator. The Bendix Magneto is essentially a small generator with a transformer, breaker switch and a distributor to guide the high voltage to the spark plugs. It is important that this magnet rotate within the prescribed range and to confirm this, you need the Aircraft Flight Instruments which is a small cylindrical device that plugs into the magneto and provides a feedback to the RMP display unit in the cockpit. Together, all these sensors provide critical information to the pilots and the pilots can either concentrate on flying when every reading is in the green or, take corrective action as required if one or more sensor provides abnormal feedback. The sensors therefore, have a direct bearing on the safety of the aircraft.
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As of today aviation fuel costs are down but that in itself is no reason to fly Rich of Peak (RoP) unless you really need to. Flying Lean of Peak (LoP) not only saves money on your fuel bill, it also keeps your engine cleaner which means you would be saving on maintenance costs as well. But to know whether or not you are saving anything, you need modern sensors connected to modern digital gauges installed in your cockpit. These modern digital gauges should include a Exhaust Gas Temperature (EGT) gauge, a Cylinder Head Temperature (CHT) gauge and a highly accurate Fuel flow indicator like the digital fuel flow indicator manufactured by JP Instruments. When you run the aircraft engine using the RoP technique, there is an excess of fuel in the cylinder. While this may help keep the engines cooler, the exhaust ends up contaminating the oil and creating a hell of an overall mess including quicker carbonisation. There simply is no reason to be running the aircraft in the RoP technique. Also, cylinder pressure is much higher (between 80 to 100 psi) in RoP than in LoP. Let us understand how you save money with LoP. When you operate the cylinder in LoP, it results in a longer, gentler, slower push on the piston because the peak cylinder pressure develops later from piston top dead centre than if the cylinder were to be operating in RoP. This means the Aircraft Flight Instruments pressure only develops when the piston has travelled further along its downward stroke. So instead of a hammer blow (as in the case of RoP), there is now a gentle push because the piston inside the cylinder has already travelled far into the downward stroke of the cycle. Higher cylinder pressure equates to higher CHT's. So in reality, operating RoP will result in higher internal cylinder pressures which in turn results in higher CHTs. whereas operating LoP at exactly the same Horse Power as the cylinder operating RoP will result in roughly 35°F lower CHT's. So your aircraft engine can actually run LoP at a lower CHT while producing the same horse power i.e. better speed, lesser fuel flow (as confirmed by the digital Aircraft Gauge), lower Cylinder Head Temperatures – isn't that what every pilot wants? Besides, when the aircraft engine is running in LoP, all fuel in the cylinder is used so there is nothing to blow back and contaminate the oil. Lower CHT and cylinder pressure also means lesser carbon deposits settling on the internal engine components as well so you save on the maintenance bill too. A common misconception amongst most pilots is that you only operate LoP at low power settings. In reality, you can operate at up to 75% power without using a lot more fuel and this will be proved by your digital fuel flow indicator. |
AuthorJ.P.Instruments was founded in 1986 in Huntington Beach, California, USA. Its founder, Joseph Polizzotto, is now the current CEO. Archives
May 2019
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