AIRCRAFT INVESTIGATION
performance calculations for the Pratt & Whitney JT4A-3 aircraft engine
Pratt & Whitney JT4A-3 turbojet engine of 70.31 [KN] (15806 [lbf]) thrust
introduction : 1958 country : USA importance : ***
applications : Douglas DC-8-21
max. rating (take-off) : 70.31 [KN] (15806 [lbf], 7170 [kgf])
weight engine(s) dry : 2100.0 [kg] = 33.48 [N/kg]
General information :
Civilian version of the military J75 engine
by-pass ratio : 0.00 : 1
overall pressure ratio (OPR) : 12.5 : 1
rpm LP : 6720 [rpm]
rpm HP : 8975 [rpm]
axial flow engine
no water injection
LP compressor stages : 8 [ ]
HP compressor stages : 7 [ ]
HP turbine stages : 1 [ ]
LP turbine stages : 2 [ ]
stages : 8 + 7 + 1 + 2
fan diameter : 109.0 [cm] engine diameter : 0.0 [cm]
air mass flow : 116 [kg/s]
design hours : 1114 [hr] time between overhaul : 557 [hr]
estimated specific fuel consumption (cruise power) :78.0 [kg/KNh]
An ejector was fitted on the DC-8's equipped with JT3C, JT4A or RR Conway engines.
The device developed by Douglas to suppress the sound and reverse the thrust of the DC-8. The corrugated exhaust nozzle is combined with a cylinder which extends beyond the nozzle during take-off. This "ejector" is claimed to reduce the sound level by 3-4 decibels and increase the thrust sufficient to offset the loss caused by the nozzle. The indentation near the forward lip of the ejector is one of the two doors which close to form a thrust brake (thrust reverser). Noise level with the ejector ring and nozzle combined is said to be reduced by 9-12 decibels.
Normally extended for T/O and landing, it is retracted in flight after T/O because it is no longer needed and creates drag at higher speeds, and then it is extended during the descent/approach phase. It is operated hydraulically to extend and retract, and can be extended by an air bottle in the event of a hydraulic failure.
Literature :
Pratt & Whitney J75 - Wikipedia
DISCLAIMER Above calculations are based on published data, they must be
regarded as indication not as facts.
Calculated performance and weight may not correspond with actual weights
and performances and are assumptions for which no responsibility can be taken.
Calculations are as accurate as possible, they can be fine-tuned when more data
is available, you are welcome to give suggestions and additional information
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(c) B van der Zalm 27 June 2022 contact : info.aircraftinvestigation@gmail.com python 3.7.4