An evaluation of nozzle pressure ratio as a means of determining in-flight gross thrust of the Ball-Bartoe Jetwing with the Pratt & Whitney JT15D-1 turbofan engine installed

The ability to measure or estimate accurately a turbine engine's in-flight thrust is a necessity if accurate measurements of aircraft drag and performance are to be established. Some method must be applied that uses measurable engine parameters and flight conditions to determine the engine thrust in flight. . This investigation considers the use of nozzle pressure ratio as a means of determining the in-flight gross thrust of the Ball-Bartoe Jetwing.

A brief survey is made of four methods used by other investigators to predict in-flight thrust. The fundamental equations are developed for the use of nozzle pressure ratio as a reference for determining the in-flight gross thrust of a turbojet engine. The calibration procedure to develop the basic reference curves for in-flight gross thrust determination is discussed with the results for the Ball-Bartoe Jetwing presented. The effects of the augmentor winglet of the Jetwing on in-flight gross thrust are considered with a method proposed to determine the maximum augmentation. The in-flight gross thrust predicted by fan duct pressure ratio, the turbine exhaust pressure ratio, and the engine fan speed are compared for representative in-flight data. The Pratt & Whitney method of using fan speed as the primary reference for in-flight thrust was employed as the standard to compare the thrust predictions from the fan duct and turbine exhaust pressure ratios.

The maximum thrust augmentation obtained from the winglet augmentor was found to be 3.5 percent or less. The use of the pressure ratio of either the fan duct or the turbine exhaust for referencing in-flight gross thrust for the Ball-Bartoe Jetwing was found to show significant differences between static and in-flight data, and is considered unusable in this application.