Chapter 15-Transition to Jet Powered Airplanes |
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Table of Contents General Jet Engine Basics Operating the Jet Engine Jet Engine Ignition Continuous Ignition Fuel Heaters Setting Power Thrust to Thrust Lever Relationship Variation of Thrust with RPM Slow Acceleration of the Jet Engine Jet Engine Efficiency Absence of Propeller Effect Absence of Propeller Slipstream Absence of Propeller Drag Speed Margins Recovery from Overspeed Conditions Mach Buffet Boundaries Low Speed Flight Stalls Drag Devices Thrust Reversers Pilot Sensations in Jet Flying Jet Airplane Takeoff and Climb V-Speeds Pre-Takeoff Procedures Takeoff Roll Rotation and Lift-Off Initial Climb Jet Airplane Approach and Landing Landing Requirements Landing Speeds Significant Differences The Stabilized Approach Approach Speed Glidepath Control The Flare Touchdown and Rollout |
OPERATING THE JET ENGINEIn a jet engine, thrust is determined by the amount of fuel injected into the combustion chamber. The power controls on most turbojet and turbofan powered airplanes consist of just one thrust lever for each engine, because most engine control functions are automatic. The thrust lever is linked to a fuel control and/or electronic engine computer that meters fuel flow based upon r.p.m., internal temperatures, ambient conditions, and other factors. [Figure 15-3] Figure 15-3. Jet engine power controls. In a jet engine, each major rotating section usually has a separate gauge devoted to monitoring its speed of rotation. Depending on the make and model, a jet engine may have an N1 gauge that monitors the low pressure compressor section and/or fan speed in turbofan engines. The gas generator section may be monitored by an N2 gauge, while triple spool engines may have an N3 gauge as well. Each engine section rotates at many thousands of r.p.m. Their gauges therefore are calibrated in percent of r.p.m. rather than actual r.p.m., for ease of display and interpretation. [Figure 15-4] Figure 15-4. Jet engine r.p.m. gauges. The temperature of turbine gases must be closely monitored by the pilot. As in any gas turbine engine, exceeding temperature limits, even for a very few seconds, may result in serious heat damage to turbine blades and other components. Depending on the make and model, gas temperatures can be measured at a number of different locations within the engine. The associated engine gauges therefore have different names according to their location. For instance: ò Exhaust Gas Temperature (EGT)ùthe temperature of the exhaust gases as they enter the tail pipe, after passing through the turbine. ò Turbine Inlet Temperature (TIT)ùthe temperature of the gases from the combustion section of the engine as they enter the first stage of the turbine. TIT is the highest temperature inside a gas turbine engine and is one of the limiting factors of the amount of power the engine can produce. TIT, however, is difficult to measure. EGT therefore, which relates to TIT, is normally the parameter measured. ò Interstage Turbine Temperature (ITT)ùthe temperature of the gases between the high pressure and low pressure turbine wheels. ò Turbine Outlet Temperature (TOT)ùlike EGT, turbine outlet temperature is taken aft of the turbine wheel(s). |
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