USAF Aircraft Research Articles

Aircraft Crash Rates and Cumulative Hours: USAF Data for 25 Airframes, 1950-2006

Long-term trends in aircraft crash rates are of interest to researchers in aerospace medicine, the acquisition community, the aircraft industry, and the flying public. Data were obtained from the USAF Safety Center database for all major accidents (Class A Mishaps) and for annual flight hours for fiscal years 1950 through 2006. Regression analysis was accomplished on the logarithmic transformation of the cumulative flight hours and cumulative crash rate for each aircraft. The relationship between crash rate, y, and flying hours, t, is approximately linear on logarithmic coordinates, so it can be expressed as a power relation, y = bt(m), where the exponent, m, reflects the slope. The model fit was significant for all 15 USAF fighter, attack, and training aircraft studied (r2 = 0.78-0.99) with all aircraft showing a negative exponent ranging from -0.25 to -0.75. This power function with a negative exponent model also fit four of five bomber aircraft and four of five transport aircraft studied. The Predator unmanned aircraft also fit this model with a slope of -0.37. This study exposes a strong inverse relationship between cumulative flight hours and crash rate for most USAF aircraft, indicating a high degree of organizational improvement. Learning was not confined only to aircrew, as evidenced by similar improvements in unmanned aircraft. The data do not support an increasing risk of crashes as aircraft age. Further research should be conducted on different flying organizations to further define the characteristics of organizational learning in aviation.

Managing change through roadmapping

Presently the USAF is operating with 90 different Model Design Series (MDS) aircraft. The 90 MDS aircraft make up a total of 5778 airframes, each with a different number of Line Replaceable Units (LRUs) which make up the avionics systems. Some of the MDSs have as few as 53 avionics LRUs while others as many as 495. The total dollar value of the USAF aircraft avionics LRUs is approximately $42.4B and $30.68B in spares. Depot repairable cost to maintain these components each year is approximately $1.2B. Each MDS is assigned specific missions and the avionics systems are developed to support those missions. Due to the evolution of mission types and user needs, change is constant for the avionics manager.

53659 USAF research and development programs for aging aircraft

For the pasf thirty-five years the United States Air Force has used the USAF Aircraft Structural Integrity Program (ASIP) to maintain safe and economical operation of aging aircraft. This program has been supported over the years by Air Force laboratory programs in the areas of fracture mechanics, corrosion prevention, flight loads, nondestructive evaluation, human factors, and maintenance and repair. These efforts provided the Air Force with the technology required to support the operational aircraft maintenance programs based on damage tolerance. The Federal Aviation Authority in the United States has also focused much of their attention on aging aircraft issues in the commercial fleet of aircraft. There are close parallels between the military and commercial approaches for damage tolerance derived inspection programs. There has also been a mutual need to develop the capability to estimate the time of onset of widespread fatigue damage that could degrade the damage tolerance capability of aircraft. It is the purpose of this paper to discuss the USAF research and development programs in aging aircraft and to identify the technology areas where the USAF and the FAA are cooperating to find solutions to current problems.

USAF single event sonic boom prediction model: PCBOOM

The United States Air Force is required to analyze the environmental impact from sonic booms produced by supersonic maneuvering aircraft. To meet this need, a single event prediction model PCBOOM3 has been developed. This model uses full ray tracing propagation theory and includes the effects of aircraft maneuvers, non-standard atmospheric profiles, and winds. Calculations include focused superbooms when they occur. Input parameters are flexible to allow general supersonic maneuvers. The program accepts user-defined F functions, and has F functions built in for current USAF aircraft. The model predicts the location and waveforms of sonic booms on the ground. Predicted sonic boom footprints are in the form of contours (psf, CSEL, etc.) and isopemps, or as tabular values at specific points. Signature output is provided in either graphical or tabular format for arbitrary points within the footprint. This program will enhance the ability to predict sonic booms for operational planning or for incident investigation. It will also be used as a research tool to investigate sonic boom generation and propagation. [Work supported by USAF AL/OEBN.]

Design features which influence flow separations on aircraft

SummaryFeatures of aircraft which influence flow separations, and hence the onset of buffeting, should be always of interest to an aerodynamicist. The present compilation of such features is based on notes made during a visit to the USAF Aircraft Museum in Dayton, Ohio. Although two low-speed aircraft with high aspect ratio wings are considered, the emphasis is primarily on transonic and supersonic military aircraft, with wings of lower aspect ratio.Some recommendations are made to stimulate research into improved methods to control flow separation, particularly for future transonic and supersonic aircraft.

Auditory signals in military aircraft: ergonomics principles versus practice

The complete ensembles of auditory signals in selected USAF aircraft (the F-4D, F-15, two models of the F-16, the C-5, and the C-141) are described and evaluated. Human factors research related to the design of speech and non-speech auditory signals is reviewed. Major findings are: that auditory signals are not well standardised among the aircraft, even between those with similar combat roles; that a relatively large number of non-speech auditory signals are used, which may make it difficult for the aircrew to recall the meanings of all the signals; that some non-speech signals are sufficiently similar that they may be confused, particularly in high workload and stressful conditions; and that the criticality of the warnings is not reliably indicated by any characteristic of the signals. Four problem areas requiring further research are discussed: reduction of signal loudness, enhancement of the distinctiveness and masking resistance of non-speech signals, effects of concurrent warning signals on aircrew performance, and additional uses of auditory information.

USAF Toxicology Research on Petroleum and Shale-Derived Aviation Gas Turbine Fuels

As one of the nation’s largest users of aircraft turbine fuels, the USAF has interest in assuring the safe use of these hydrocarbons by its military and civilian workers. This concern stimulated research to define potential adverse health effects and develop criteria for safe exposure limits for military aviation fuels. The first inhalation exposure to JP-4, the primary fuel used in USAF aircraft, was conducted in 1973. Since this initial subchronic study, the USAF has conducted numerous subchronic and one-year oncogenic inhalation studies to establish health criteria for aviation fuels. This paper summarizes the status of studies to define the toxicity of petroleum and shale-derived aircraft turbine engine fuels and discusses the preliminary findings of toxic nephropathy and primary renal tumors observed in male Fischer 344 rats.

Physical, Chemical, and Crystallographic Characterization of Anodic Coatings on High Strength Aluminum Base Alloys

Durability of adhesive bonded joints in moisture and salt spray environments is essential to USAF aircraft. Structural bonding technology for aerospace applications has depended for many years on the preparation of aluminum surfaces by a sulfuric acid/sodium dichromate (FPL etch) treatment. Recently, specific thin film anodizing techniques, phosphoric acid, and chromic acid anodizing have been developed which not only provide good initial bond strengths but vastly improved environmental durability. These thin anodic films are in contrast to the commonly used thick anodic films such as the sulfuric acid or "hard" sulfuric acid anodic films which are highly corrosion resistant in themselves, but which do not provide good initial bond strengths, particularly in low temperature peel.The objective of this study was to determine the characteristics of anodic films on aluminum alloys that make them corrosion resistant. The chemical composition, physical morphology and structure, and mechanical properties of the thin oxide films were to be defined and correlated with the environmental stability of these surfaces in humidity and salt spray. It is anticipated that anodic film characteristics and corrosion resistance will vary with the anodizing processing conditions.

Application of fracture mechanics to aircraft structural safety

Design requirements have been developed to insure structural safety for current and future USAF aircraft. New structure is assumed to be flawed. Materials, stress levels and structural arrangements are chosen so as to prevent damage from growing to catastrophic size prior to detection. Safety from damage induced through service usage is insured by providing inspection capability and by meeting specific residual strength and safe crack growth requirements. Compliance with these requirements implies the capability to predict growth rates under complex loadings and to calculate the fracture strength of structures fabricated of relatively tough materials which may exhibit large amounts of crack tip plasticity prior to failure. This paper will review significant factors leading to the development of damage tolerance criteria and illustrate the role of fracture mechanics in the analysis and testing aspects necessary to satisfy these requirements.

Aircraft Water Vapor Measurements Utilizing an Aluminum Oxide Hygrometer

A hygrometer for water vapor measurements from an aircraft has been developed. An aluminum oxide hygrometer mounted in an aircraft Rosemount air temperature scoop was flown on NASA and USAF aircraft. Water vapor measurements were conducted up to 40,000 feet with penetration into the stratosphere. Good agreement was obtained with simultaneously flown remote sounders of water vapor. During transcontinental flights the hygrometer demonstrated adequate response to measure the natural variability of water vapor near the tropopause. Rapid response was demonstrated in pursuit of the jet wake of an F-104 at 35,000 feet.

Non‐Technical Factors in Supervisors' Ratings of Job Performance

SummarySupervisory ratings were analyzed to determine whether supervisors could rate aircraft mechanics on several dimensions of on‐the‐job proficiency, or whether their ratings contained nothing more than global general impressions. Three samples of USAF aircraft mechanics were administered a test of technical competence, while supervisory and co‐worker ratings were obtained on them. The rating instruments contained a large number of detailed items, plus one over‐all item. Special effort was directed at items which reflected motivational areas, or those “non‐technical” variables which appear to modify job performance so that technical skill does not perfectly predict actual performance.Several clusters of rating dimensions were obtained from both the supervisory and co‐worker rating instruments. These dimensions tended to correlate differentially with measures most likely to reflect technical skill, so that the ratings of technical skill correlated highest with them, while the other dimensions had negligible correlations with test and experience. Rater agreement was at the level usually found for rating instruments, although evidence showed supervisors were better raters than co‐workers.Using a criterion of grouped co‐worker over‐all ratings, it was found that the supervisory rating dimensions were a useful addition to the test of technical competence in predicting over‐all proficiency. This was interpreted as evidence of the existence of non‐technical variables in the supervisory ratings, since technical competence was covered in the test.