457
References
hovering flight. This means that the through-flow velocity of the rotor is the induced
velocity. First, calculate the theoretically required induced power. Then, determine
the shaft power, assuming that the rotor efficiency is 0.70. This rotor efficiency is
very disadvantageous compared to that of a propeller, where it may be around 0.90,
as rotor through-flow with a helicopter in hovering flight is very inhomogeneous.
Due to ground proximity the required induced power is somewhat lower (the flow
partially thrusts on the ground). On the other hand there is a downward drag on the
fuselage due to rotor through-flow. Both effects approximately counterbalance each
other.
12.7.7 Ramjet
For supersonic flight at very high Mach numbers, e.g. flight Mach number around
5, engines that can be switched from turbojet configuration to ramjet configuration have been studied for some time. With these, the gas turbine is switched off at
a sufficiently high Mach number. Aerodynamically compressed air runs from the
inlet through a combustion chamber to the nozzle. Calculate the overall efficiency
at flight Mach number 5 and nozzle inlet temperature 1675 K. Assume that the efficiency of the aerodynamic compression is 0.90 (losses due to shockwaves during
supersonic flight) and take 0.97 nozzle efficiency. Conclude that the overall efficiency is quite high.
References
1. Ballal DR, Zelina J (2004) Progress in aeroengine technology (1939–2003). J Aircr 41:43–50
2. Crichton D, Xu L, Hall CA (2007) Preliminary fan design for a silent aircraft. J Turbomach
127:184–191
3. Cumpsty NA (2010) Preparing for the future: reducing gas turbine environmental impact—
IGTI scholar lecture. J Turbomach 132:041017, 1–17
4. Mattingly JD, Heiser WH, Pratt DJ (2002) Aircraft engine design. AIAA education series,
ISBN 1-56347-583-3
5. The Jet Engine. (1986) Rolls-Royce, ISBN 0-902121-04-9
6. The Jet Engine. (2005) Rolls-Royce, ISBN 0-902121-2-35
References
hovering flight. This means that the through-flow velocity of the rotor is the induced
velocity. First, calculate the theoretically required induced power. Then, determine
the shaft power, assuming that the rotor efficiency is 0.70. This rotor efficiency is
very disadvantageous compared to that of a propeller, where it may be around 0.90,
as rotor through-flow with a helicopter in hovering flight is very inhomogeneous.
Due to ground proximity the required induced power is somewhat lower (the flow
partially thrusts on the ground). On the other hand there is a downward drag on the
fuselage due to rotor through-flow. Both effects approximately counterbalance each
other.
12.7.7 Ramjet
For supersonic flight at very high Mach numbers, e.g. flight Mach number around
5, engines that can be switched from turbojet configuration to ramjet configuration have been studied for some time. With these, the gas turbine is switched off at
a sufficiently high Mach number. Aerodynamically compressed air runs from the
inlet through a combustion chamber to the nozzle. Calculate the overall efficiency
at flight Mach number 5 and nozzle inlet temperature 1675 K. Assume that the efficiency of the aerodynamic compression is 0.90 (losses due to shockwaves during
supersonic flight) and take 0.97 nozzle efficiency. Conclude that the overall efficiency is quite high.
References
1. Ballal DR, Zelina J (2004) Progress in aeroengine technology (1939–2003). J Aircr 41:43–50
2. Crichton D, Xu L, Hall CA (2007) Preliminary fan design for a silent aircraft. J Turbomach
127:184–191
3. Cumpsty NA (2010) Preparing for the future: reducing gas turbine environmental impact—
IGTI scholar lecture. J Turbomach 132:041017, 1–17
4. Mattingly JD, Heiser WH, Pratt DJ (2002) Aircraft engine design. AIAA education series,
ISBN 1-56347-583-3
5. The Jet Engine. (1986) Rolls-Royce, ISBN 0-902121-04-9
6. The Jet Engine. (2005) Rolls-Royce, ISBN 0-902121-2-35