Effective Date: 15 June 98
Both fan and core nozzle exit plane minimum flow areas will be measured by engine manufacture on each instrumented engine and supplied to airframe manufacture. The measured areas are used in calculation of nozzle airflow.
The measurement of core nozzle exit plane is relatively straightforward since there are no physical obstructions at the measuring station. Six diameters will be measured approximately 30 degrees apart. The average diameter will be used to calculate the area as shown below.
Area = AE = %\ (D)2/4 ( -l)
D = (%Dn)/n
The calculation of the fan nozzle exit plane area is complicated by the presence of the pylon splitter at the measuring station.
Referring to Figure -l, the fan nozzle area consists of an annular area less the pylon splitter area.
The average fan radial segment is,
RF = (%#RFn)/n ( -2)
where n = 11 (every 30 Deg except O Deg)
COS % = OF/RC ( -3)
OD = OF + FD = OF + EA ( -4)
Combining Equations ( -3) and ( -4),
OD = RC COS % + EA ( -5)
RO = RF + RC ( -6)
From the right triangle AOD,
(R0)2 = (OD)2 + (AC/2)2 ( -7)
Substituting Equation ( -5) into ( -7),
(R0)2 = (RC COS % + EA)2 + (AC/2)2 ( -8)
EF = AC/2 ( -9)
0 = SIN-l EF/RC = SIN-l AC/2RC ( -lO)
Substituting Equation ( -6) into ( -8),
(RF)2 + (RC)2 + 2(RF)(RC) - (RC COS % + EA)2 - (AC/2)2 =0 ( -ll)
Substituting Equation ( -lO) into ( -ll),
(RF)2 + (RC)2 + 2(RF)(RC) - [RC COS (SIN-l (AC/2RC)+ EA]2 - (AC/2)2 = 0 ( -12)
In equation (-12), RF, AC, and EA are measured quantities. The one unknown is RC.
To calculate the area of the pylon splitter (Ap),
EH = %RC ( -13)
The core circumference (CE) is,
CE = 2 EH + CEM = 2%RC + CEM ( -14)
where CEM is measured.
As shown in Figure l, the pylon area is,
AP = ACGE + A3 - A4 - Al - A2 ( -15)
Areas Al and A2 are measured on the engine using a template, and a planimeter to calculate the area.
Using the standard equations for the area of a segment of a sector:
A3 = (R0)2 (2c%#- SIN 2%,%) ( -16)
A4 = (RC)2 (2% - SIN 2%) ( -17)
From Figure -l,
ACGE = (AC) (EA + CG) 1/2 ( -18)
Each of the terms of the right hand side are measured quantities. The angles c%-and % are,
<%# = SIN-l AC/2RO ( -19)
% = SIN-l AC/2RC ( -20)
Substituting Equations ( -16), ( -17), and ( -18) into Equation ( -15), the pylon area becomes
AP = (AC) (EA + CG)% + (R0)2 (2%=% - SIN2c%- ) - (RC)2 (2 % - SIN 2 0) - Al - A2 ( -21)
In the above equation,
AC, EA, CG, Al, A2 Measured quantities
%# && Equations ( -19) ( - 20)
RC Equation ( -12)
RO Equation ( -6)
Finally, the fan nozzle exit plane area is
AB = -%#(R02 - RC2) - AP
where AP is from Equation ( -21), RO from ( -6) and RC from ( -12).