Masters Theses

Date of Award

5-2003

Degree Type

Thesis

Degree Name

Master of Science

Major

Aviation Systems

Major Professor

Robert B. Richards

Committee Members

Ralph Kimberlin, Frank Collins

Abstract

Flight test demonstrating safe separation of stores from aircraft has gained greater importance since World War II. With the expansion of aircraft flight envelopes, the impact of the aircraft flow field on store separation has also expanded. At best the store fell away from the aircraft; at worst it could tumble or hit the aircraft causing significant structural damage. Early safe separation flight test programs took a simple approach, starting slow and in straight and level flight and then in small increments, building up to supersonic straight path dives. Unfortunately, this approach required a great deal of stores as well as numerous flights. As the cost of operating test aircraft and weapons has increased, this approach has become increasingly expensive.

Wind tunnels have been used with great success since the dawn of aviation as a tool to engineer new concepts in aerodynamics. Once only the domain for flow visualization of airfoils, they have matured into a system that can test high angles of attack at full scale to small scale hypersonic flow. From this growth has emerged the capability to model the flow field around an aircraft and predict the separation characteristics of weapons from the aircraft. By using the wind tunnel to find the worst-case separation characteristics, flight test engineers could reduce the build up necessary and the number of flights required. This was seemingly the answer to the need of program managers as the way to reduce risk and cost.

This thesis examined the results of two modern safe separation programs, the Mk-82 Joint Direct Attack Munition (JDAM) and the GBU-24B/B Low Level Laser Guided Bomb, for the technical and cost impact of the wind tunnel. This examination has shown that the realities of flight test and the limitations of wind tunnel predictions have combined to reduce the wind tunnel effectiveness in providing a cost savings to safe separation programs. For the JDAM, the wind tunnel was able to significantly reduce the number of flights required to demonstrate safe separation, but weapon umbilical failures required more flights to be added back into the program. The GBU-24B/B on the U.S. Navy’s new Super Hornet aircraft is in jeopardy of failing to meet fleet operational requirements as a result of waiting for wind tunnel data. In contrast, the GBU-24B/B program conducted on the older Hornet was completed without the wind tunnel in significantly less time and cost.

Program managers and engineers must weigh the benefits of having wind tunnel data with the risks that come with the wind tunnel. In some cases, the wind tunnel may come at a higher a price and require more time than a conventional flight test program without wind tunnel predictions.

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