$7\mathrm{.}21$: A three$-$spool pusher$-$type propfan, or unducted fan engine $($UDF$)$ is fitted to an aircraft flying at a speed of $200$ m$/$s and altitude of $6$ km $($Ta$=249\mathrm{.}2$ K and Pa$=47\mathrm{.}182$ kPa$)($Fig$.7\mathrm{.}27).$ The engine is composed of three spools: intermediate$-$pressure spool composed of an intermediate$-$pressure compressor driven by an intermediate$-$pressure turbine, a high$-$pressure compressor driven by a high$-$pressure turbine, and the unducted fan $($resembling a low$-$pressure compressor$)$ driven by a low$-$pressure turbine. The maximum temperature is $1400$ K$,$ and fuel having a heating value of $40,000$ kJ$/$kg is used. It has the following particulars:

$1.$ The bypass ratio

$2.$ The ratio between thrust force generated by unducted fan and nozzle

$3.$ The total equivalent horsepower

$4.$ The propulsive efficiency Fig. $7\mathrm{.}34$b Control volume for hovering helicopter