Apparatus for determining the gross thrust of a jet engine

Claim 2

Apparatus for use in a jet type engine having a diffuser, a tailpipe, and a nozzle, for determining the total pressure at the entrance to the nozzle, comprising: first pressure responsive means for detecting the total pressure PT5 in the diffuser and providing a first signal representative of said total pressure, second pressure responsive means for detecting the static pressure PSN at the nozzle entrance and providing a second signal representative of said static pressure, third pressure responsive means positioned between the upstream side of the diffuser and the nozzle entrance and upstream of said second pressure responsive means, for detecting the static pressure PS6 and providing a third signal representative of said static pressure, and computer means for combining said first, second and third signals to determine iteratively the nozzle total pressure PTN according to the relationship PTN Eta (PTN, PT5, PS6, PSN, C1, C2, gamma , K1) where C1 is a dimensionless constant related to tailpipe geometry C2 is a dimensionless constant related to the fluid flow characteristics in the tailpipe, gamma is the means ratio of tailpipe gas specific heats, and K1 is a dimensionless constant used to obtain a prediction of the flameholder region total pressure, and to provide a fourth signal representing said nozzle total pressure PTN.

Claim 3

Apparatus for use in a jet type engine having a diffuser, a tailpipe, and a nozzle, for determining the total pressure at the entrance to the nozzle, comprising: first pressure responsive means for detecting the total pressure PT5 in the diffuser and providing a first signal representative of said total pressure, second pressure responsive means for detecting the static pressure PSN at the nozzle entrance and providing a second signal representative of said static pressure, third pressure responsive means positioned between the upstream side of the diffuser and the nozzle entrance and upstream of said second pressure responsive means, for detecting the static pressure PS6 and providing a third signal representative of said static pressure, and computer means for combining said first, second and third signals to determine iteratively the nozzle total pressure PTN according to the relationship PTN eta (PTN, PT5, PS6, PSN, C1, C2, gamma , K1) where C1 is a dimensionless constant related to tailpipe geometry C2 is a dimensionless constant related to the fluid flow characteristics in the tailpipe, gamma is the means ratio of tailpipe gas specific heats, and K1 is a dimensionless constant used to obtain a prediction of the flameholder region total pressure, and to provide a fourth signal representing said nozzle total pressure PTN.

Claim 4

Apparatus for use in a jet type engine having a diffuser, a tailpipe, and a nozzle, for determining the total pressure at the entrance to the nozzle, comprising: first pressure responsive means for detecting the total pressure PT5 in the diffuser and providing a first signal representative of said total pressure, second pressure responsive means for detecting the static pressure PSN at the nozzle entrance and providing a second signal representative of said static pressure, third pressure responsive means positioned between the upstream side of the diffuser and the nozzle entrance and upstream of said second pressure responsive means, for detecting the static pressure PS6 and providing a third signal representative of said static pressure, and computer means for combining said first, second and third signals to determine iteratively the nozzle total pressure PTN according to the relationship PTN eta (PTN, PT5, PS6, PSN, C1, C2, gamma , K1) where C1 is a dimensionless constant related to tailpipe geometry C2 is a dimensionless constant related to the fluid flow characteristics in the tailpipe, gamma is the means ratio of tailpipe gas specific heats, and K1 is a dimensionless constant used to obtain a prediction of the flameholder region total pressure, and to provide a fourth signal representing said nozzle total pressure PTN.

Claim 5

Apparatus as defined in claim 1 and further including apparatus for utilizing said fourth signal for determining the gross thrust of said engine and providing an output signal representing said gross thrust comprising: means receiving said fourth signal representing the total pressure at the nozzle entrance PTN and a fifth signal representing ambient static pressure Pso and providing an output signal representing nozzle pressure ratio Alpha e PTN/Pso, a first and a second decision circuit means, a first and a second logic means, said first decision circuit means being responsive to a signal indicating the nozzle is convergent-divergent to select said first logic means and responsive to a signal indicating the nozzle is convergent only to select said second decision circuit means, said second decision circuit means being responsive to said signal representing Alpha e being less than ( gamma +1/2) / 1, where gamma is the exhaust gas ratio of specific heats, to select said first logic means and responsive to said signal Alpha e being equal or greater than ( gamma +1/2) / 1 to select said second logic means, said first logic means providing, when selected, an output representing gross thrust FG in accordance with the relationship FG AN.Pso.f1 (PTN, PSN) .fc (PTN/Pso) where AN is the area of the nozzle entrance, fc (PTN/Pso) is a function of the nozzle pressure ratio for complete expansion, said second logic means providing, when selected, an output signal representing gross thrust FG in accordance with the relationship FG AN.Pso.f1 (PTN, PSN) .fI (PTN/Pso) where fI (PTN/Pso) is a function of the nozzle pressure ratio for incomplete expansion.