Thus civil turbofans today have a low exhaust speed ( low " specific thrust " & mdash; net thrust divided by airflow ) to keep jet noise to a minimum and to improve fuel efficiency.
32.
However, a high specific thrust turbofan will, by definition, have a higher nozzle pressure ratio, resulting in a higher afterburning net thrust and, therefore, a lower afterburning specific fuel consumption ( SFC ).
33.
The lower the specific thrust of a turbofan, the lower the mean jet outlet velocity, which in turn translates into a high thrust lapse rate ( i . e . decreasing thrust with increasing flight speed ).
34.
Therefore, a future SST might well benefit from a variable cycle engine, where the specific thrust ( and therefore jet velocity and noise ) is low at take-off, but is forced high during supersonic cruise.
35.
If the aircraft burns a large percentage of its fuel with the afterburner alight, it pays to select an engine cycle with a high specific thrust ( i . e . high fan pressure ratio / low bypass ratio ).
36.
However, the ideal Combat VCE would have the high reheat thrust / good reheat SFC associated with a high specific thrust engine, but would have the low SFC of a low specific thrust engine in dry power and throttled back.
37.
However, the ideal Combat VCE would have the high reheat thrust / good reheat SFC associated with a high specific thrust engine, but would have the low SFC of a low specific thrust engine in dry power and throttled back.
38.
Curve fitting the data resulted in the specific thrust of 20? �N / W, resulting in the apparent photon momentum multiplication factor of 2, 990?50 and the true OC mirror reflectance used in this demonstration of 0.99967?.00002.
39.
A very low specific thrust ( i . e . very high bypass ratio ) turbofan is proposed for the aircraft . Engine handling and low jet noise are facilitated by the use of a variable area final nozzle, to rematch the fan.
40.
Improved materials, and the introduction of twin compressors such as in the thermodynamic efficiency of engines, but they also led to a poor propulsive efficiency, as pure turbojets have a high specific thrust / high velocity exhaust better suited to supersonic flight.
