Hornet Aircraft Research Articles

Fatigue crack growth lessons from thirty-five years of the Royal Australian Air Force F/A-18 A/B Hornet Aircraft Structural Integrity Program

As the Royal Australian Air Force (RAAF) retires its fleet of F/A-18 A and B model Hornets, it is opportune to reflect upon some of the in-service fatigue crack growth lessons accrued from 35 years of the aircrafts Aircraft Structural Integrity Program (ASIP). In this paper, the authors have selected a small number of the key lessons and observations arising from real-world fatigue problems in the RAAF Hornet fleet that have contributed to advances in the state of the art of fatigue crack growth measurement and prediction. The importance of the lead crack concept, quantitative fractography, fatigue testing, nucleating discontinuities, the physically short crack regime, as well as individual aircraft tracking are given prominence. It is hoped that this review of the metal fatigue challenges for a highly stressed lightweight structure that have driven research into fatigue crack growth will be valuable to those aspiring to make impactful contributions to the field and the sustainment of aircraft fleets worldwide.

On the dominant noise components of tactical aircraft: Laboratory to full scale

This paper investigates the dominant noise components of a full-scale high performance tactical aircraft. The present study uses acoustic measurements of the exhaust jet from a single General Electric F414-400 turbofan engine installed in a Boeing F/A-18E Super Hornet aircraft operating from flight idle to maximum afterburner. The full-scale measurements are to the ANSI S12.75–2012 standard employing about 200 microphones. By comparing measured noise spectra with those from hot supersonic jets observed in the laboratory, the dominant noise components specific to the F/A-18E aircraft at different operating power levels are identified. At intermediate power, it is found that the dominant noise components of an F/A-18E aircraft are essentially the same as those of high temperature supersonic laboratory jets. However, at military and afterburner powers, there are new dominant noise components. Their characteristics are then documented and analyzed. This is followed by an investigation of their origin and noise generation mechanisms.

Outcomes from the fatigue testing of seventeen centre fuselage structures

This paper summarises some of the significant outcomes of a fatigue test program for ex-service aircraft structure. Seventeen F/A-18 Hornet aircraft aluminium alloy 7050-T7451 centre fuselages (referred to as centre barrels (CBs)) were tested, torn down and inspected in this program. Significant results of the test program included the demonstration of the repeatability of service fatigue cracking locations, the collection of data to characterise the types of defects that typically nucleate fatigue cracks in aircraft components and a more accurate assessment of the safe operating life of this structure. The results of the program also enhanced the existing understanding of fatigue cracking in aluminium alloy 7050-T7451. Furthermore, the improved understanding of the fatigue cracking that occurred in service F/A-18 CBs and the damage tolerance of this structure allowed increased aircraft availability and reduced maintenance costs in the Royal Australian Air Force (RAAF) F/A-18 fleet.

Pelanggaran Kedaulatan Indonesia oleh Pesawat F-18 Hornet Milik Amerika Serikat (Ditinjau Dari Konvensi Chicago Tahun 1944 Dan Konvensi Hukum Laut Tahun 1982)

The sovereignty is the highest attribute of a state that shoul be respected by another states. In any situation it must not be violated by others but the result of this research shows that F-18 Hornet air craft is state air craft has done a sovereignty collision over Indonesian air space with fly without permission of Indonesian government and made some manuver in civil flight line that endangered the safety of navigation of civil air craft aviation. This reserch also shows that the military strenght of USA is bigger than Indonesian’s, influence the sovereignty colission over Indonesian air space, made by F-18 Hornet. Therefore in the international relationship between states, then diplomatic settlement is the best way to choose. Beside that, it is important to determine the limit between air space and outer space, then coul be knew how far the souvereingty of a state over air space.

Fatigue cracking from a corrosion pit in an aircraft bulkhead

For aircraft, the repair and management of corrosion can be a major through life cost driver as well as an availability degrader. A common form of corrosion in aircraft structural alloys is pitting corrosion. This paper describes fatigue cracking in a laboratory environment that had initiated from a significant corrosion pit in a locally shot-peened aluminium alloy 7050-T7451 bulkhead of an F/A-18 Hornet aircraft. Extensive study of this material under Hornet type loading has shown that if the initial equivalent pre-crack size is determined, then the fatigue crack growth follows the lead crack form, as was the case for this corrosion-pit initiated crack in the absence of retardation affects. This is a valuable observation which should allow the growth of cracks from corrosion pits to be determined through fatigue crack modelling without the need to account for the potential of corrosion-assisted fatigue effects, which are postulated here to be insignificant for combat-type aircraft. The main outcome of the investigation was that whilst the physical size of the corrosion pit was large (442μm deep) its effect as a fatigue crack initiator i.e. its effective pre-crack size (EPS), was significantly smaller (i.e. approximately 10μm deep).

Real Time Pulsed Eddy Current Detection of Cracks in F/A-18 Inner Wing Spar Using Discriminant Separation of Modified Principal Components Analysis Scores

The aluminum inner wing spars of F/A-18 Hornet aircraft may undergo stress corrosion cracking along the spar between the fasteners that secure carbon-fiber/epoxy composite skin to the wing. Inspection of the spar through the wing skin is required to avoid wing disassembly. The thickness of the skin varies between 9 and 21 mm (0.36-0.83 in) and fasteners may be either titanium or ferrous. Pulsed eddy currents (PECs), generated by a probe centered over the fastener, demonstrate the capability of detecting simulated cracks within spars with the wing skin present. Comparison of signals from separate pick-up coils, mounted to either side of the excitation coil, is used to detect differences in induced eddy current fields, which arise in the presence of cracks. To overcome variability in PEC signal response due to variation in: 1) skin thickness; 2) fastener material and size; and 3) centering over fasteners, a large calibration data set is acquired. Multidimensional scores from a modified principal components analysis (PCA) of the data are reduced to 1-D using a discriminant analysis method. Under inspection conditions, calibration PCA scores combined with discriminant analysis permit rapid real time go/no-go PEC detection of cracks in F/A-18 inner wing spar.

Pulsed eddy current detection of cracks in F/A-18 inner wing spar without wing skin removal using Modified Principal Component Analysis

Stress corrosion cracks may develop between fasteners in the aluminum inner wing spars of F/A-18 Hornet aircraft. These fasteners secure carbon-fibre/epoxy composite wing skin, of nominal 13mm thickness, to the spar. Inspection of the spar through the wing skin is required in order to avoid wing disassembly. Pulsed eddy currents, generated by a probe design that utilizes the ferrous fastener as a flux conduit, are demonstrated as having the capability of detecting simulated cracks within the spar with the wing skin present. Differentially connected pickup coils are used to sense differences in response due to asymmetries in induced eddy current fields arising in the presence of cracks. To overcome variability in PEC signal response due to variability in magnetic coupling to the fastener, a large measurement set was analyzed using Modified Principal Component Analysis (PCA). The modified PCA minimizes residual sum of squares to extract eigenfunction scores, which are used to detect the presence of cracks ending on one side of the fastener hole. The ability of the method to sense simulated cracks independent of confounding measurement parameters was demonstrated.

The Development of Neutron Radiography and Tomography on a SLOWPOKE-2 Reactor

Abstract Development of neutron radiography at the Royal Military College of Canada (RMC) started by trying to interest the Royal Canadian Air Force (RCAF) in this new non-destructive testing (NDT) technique. A Californium-252 based device was ordered and then installed at RMC for development of applicable techniques for aircraft by the first author. A second and transportable device was then designed, modified and used in trials at RCAF Bases and other locations for one year. This activity was the only foreign loan of the U.S. Californium Loan Program. Around this time, SLOWPOKE-2 reactors were being installed at four Canadian universities, while a new science and engineering building was being built at RMC. A reactor pool was incorporated and efforts to procure a reactor succeeded a decade later with a SLOWPOKE-2 reactor being installed at RMC. The only modification by the vendor for RMC was a thermal column replacing an irradiation site inside the reactor container for a later installation of a neutron beam tube (NBT). Development of a working NBT took several years, starting with the second author. A demonstration of the actual worth of neutron radiography took place with a CF-18 Hornet aircraft being neutron and X-radiographed at McClellan Air Force Base, Sacramento, CA. This inspection was followed by one of the rudders that had indications of water ingress being radiographed successfully at RMC just after the NBT became functional. The next step was to develop a neutron radioscopy system (NRS), initially employing film and then digital imaging, and is in use today for all flight control surfaces (FCS). With the third author, a technique capable of removing water from affected FCS was developed at RMC. Heating equipment and a vacuum system were utilized to carefully remove the water. This technique was proven using a sequence of near real time neutron images obtained during the drying process. The results of the drying process were correlated with a relative humidity gauge and an NDT technique that could be performed at Canadian Forces (CF) Bases was developed. In order to determine the structural integrity of the component having undergone this water removal, further research was required into the effect of water inside composite honeycomb structures. This need has led to the present development of neutron tomography on the reactor at RMC, which is capable of determining the exact location of water ingress inside composite components. This technique has been successfully applied to coupons as well as to complete rudders.

Susceptibility of F/A-18 Flight Controllers to the Falling-Leaf Mode: Linear Analysis

The F/A-18 Hornet aircraft with the original flight control law exhibited a nonlinear out-of-control phenomenon known as the falling-leaf mode. This unstable mode was suppressed by modifying the control law. This paper employs the falling-leaf phenomenon as an example to investigate the applicability of linear analysis tools for detecting inherently nonlinear phenomenon. A high-fidelity nonlinear model of the F/A-18 is developed for controller analysis using F/A-18 High-Alpha Research Vehicle aerodynamic data in the open literature. A variety of linear analysis methods are used to investigate the robustness properties of the original (baseline) and the revised F/A-18 flight control law at different trim points. Classical analyses, e.g., gain and phase margins, do not indicate a significant improvement in robustness properties of the revised control law over the baseline design. However, advanced robustness analyses, e.g., μ analysis, indicate that the revised control law is better able to handle the cross-coupling and variations in the dynamics than the baseline design.

Susceptibility of F/A-18 Flight Controllers to the Falling-Leaf Mode: Nonlinear Analysis

The F/A-18 Hornet aircraft with the original flight control law exhibited a nonlinear out-of-control phenomenon known as the falling-leaf mode. This unstable mode was suppressed by modifying the control law. This paper employs the falling-leaf phenomenon as an example to investigate the applicability of linear analysis tools for detecting inherently nonlinear phenomenon. A high-fidelity nonlinear model of the F/A-18 is developed for controller analysis using F/A-18 High-Alpha Research Vehicle aerodynamic data in the open literature. A variety of linear analysis methods are used to investigate the robustness properties of the original (baseline) and the revised F/A-18 flight control law at different trim points. Classical analyses, e.g., gain and phase margins, do not indicate a significant improvement in robustness properties of the revised control law over the baseline design. However, advanced robustness analyses, e.g., μ analysis, indicate that the revised control law is better able to handle the cross-coupling and variations in the dynamics than the baseline design.

Comparison of neutron radiography with other non-destructive techniques for the inspection of CF188 flight control surfaces

Neutron radiography, utilizing either film or a CCD camera, has been previously used to identify water ingress within the composite layers and the aluminum honeycomb core of flight control surfaces on the CF188 Hornet aircraft . Through transmission ultrasonics, X-radiography and infrared imaging have also been utilized to identify the presence of water in these components. At present, infrared imaging of the flight control surfaces is routinely carried out as a field-level inspection, but a quantitative validation of the results had not previously been conducted. Although infrared imaging is a simple, nonintrusive and inexpensive method of inspection, neutron radiography is recognized as the most accurate method for indicating and quantifying the presence of water in the flight control surfaces. A quantitative comparison was recently carried out using CF188 rudders to validate the results of various nondestructive techniques relative to neutron radiography.

Nonlinear Model Development from Flight-Test Data for F/A-18E Super Hornet

Applied procedures for nonlinear aerodynamic model development and extraction from flight data for the F/A-18E Super Hornet aircraft are addressed. Parameter identification maneuver design, flight-test support technique, and aerodynamic model development are included. All-axis 3-2-1-1 maneuvers were designed to best excite the longitudinal and lateral-directional system natural frequencies of interest. The work was in support of leading edge flap degraded modes studies for the F/A-18E aircraft investigated by the Naval Air Systems Command. In this flight-test program, the effect of off-schedule, differentially frozen, leading-edge flaps was examined with the aircraft in power-approach configuration. A variety of processes was employed to develop fully nonlinear longitudinal and lateral-directional aerodynamic incremental model corrections. This effort included total aerodynamic coefficient reconstruction from flight-test data and equation error analysis for model structure development/estimation

Development of neutron radioscopy for the inspection of CF188 flight control surfaces

Neutron radioscopy, using a cooled charged coupled device (CCD) camera and a neutron-sensitive scintillation screen, was developed at the SLOWPOKE-2 Facility at the Royal Military College (RMC) to detect water ingress into the composite layers and the aluminium honeycomb core in flight control surfaces on the CF188 Hornet aircraft. The response of the CCD camera system was tested at different neutron fluxes utilising the SLOWPOKE-2 at RMC and the Breazeale Nuclear Reactor at Pennsylvania State University.

Quantitative Filter Debris Analysis (QFDA) as a means of monitoring wear in oil-lubricated systems

In this study, the trace analytical technique of instrumental neutron activation analysis (INAA), using the SLOWPOKE-2 Facility at RMC, was used to develop an application termed Quantitative Filter Debris Analysis (QFDA). The preliminary step, which consisted of the quantitative analysis of filter debris samples from CH-124 Sea King helicopter main gear boxes (MGB) for 19 elements associated with engine wear, confirmed that distinct ranges of normal and abnormal wear rates exist in the CH-124 MGB and, more importantly, validated the INAA procedures. The second step, which consisted of the analysis of both oil and filter debris samples from the CF-188 Hornet aircraft engine by the INAA technique and an Atomic Emission (AE) method, confirmed that little useful wear information can be found in the oil of a finely-filtered engine system and demonstrated the potential of QFDA as a means of monitoring wear by analyzing the oil filter debris. What appears to be normal wear rate ranges were identified for the CF-188 Hornet aircraft engine. The potential of monitoring the wear health of oil-lubricated systems using QFDA was confirmed by this investigation.

Multi-echelon repair level analysis MERLA : Simon L. Devries and Scott A. Wicker. Proc. a. Reliab. Maintainab. Symp., 126 (1986)

Stress corrosion cracks may develop between fasteners in the aluminum inner wing spars of F/A-18 Hornet aircraft. These fasteners secure carbon-fibre/epoxy composite wing skin, of nominal 13 mm thickness, to the spar. Inspection of the spar through the wing skin is required in order to avoid wing disassembly. Pulsed eddy currents, generated by a probe design that utilizes the ferrous fastener as a flux conduit, are demonstrated as having the capability of detecting simulated cracks within the spar with the wing skin present. Differentially connected pickup coils are used to sense differences in response due to asymmetries in induced eddy current fields arising in the presence of cracks. To overcome variability in PEC signal response due to variability in magnetic coupling to the fastener, a large measurement set was analyzed using Modified Principal Component Analysis (PCA). The modified PCA minimizes residual sum of squares to extract eigenfunction scores, which are used to detect the presence of cracks ending on one side of the fastener hole. The ability of the method to sense simulated cracks independent of confounding measurement parameters was demonstrated.

Time variable failure rate prediction: Alan C. Durr. 1981 Proceedings Annual Reliability and Maintainability Symposium, Philadelphia, Pennsylvania, p. 122 (27–29 January 1981)

Stress corrosion cracks may develop between fasteners in the aluminum inner wing spars of F/A-18 Hornet aircraft. These fasteners secure carbon-fibre/epoxy composite wing skin, of nominal 13 mm thickness, to the spar. Inspection of the spar through the wing skin is required in order to avoid wing disassembly. Pulsed eddy currents, generated by a probe design that utilizes the ferrous fastener as a flux conduit, are demonstrated as having the capability of detecting simulated cracks within the spar with the wing skin present. Differentially connected pickup coils are used to sense differences in response due to asymmetries in induced eddy current fields arising in the presence of cracks. To overcome variability in PEC signal response due to variability in magnetic coupling to the fastener, a large measurement set was analyzed using Modified Principal Component Analysis (PCA). The modified PCA minimizes residual sum of squares to extract eigenfunction scores, which are used to detect the presence of cracks ending on one side of the fastener hole. The ability of the method to sense simulated cracks independent of confounding measurement parameters was demonstrated.

Redux Bonding of Aircraft Structures

That synthetic glues for wood were used extensively for making Mosquito and Hornet aircraft during the 1939-45 War, and are now used for making Vampires in many European countries, is well known to aeronautical engineers, but not so well known is the fact that, since 1944, synthetic glues for metals have been used in the production of many hundreds of military and civil aircraft. A glue for metals, which gives joints stronger than can be obtained by riveting and which is also resistant to the severe conditions to which aircraft are exposed in service, offers the possibilities of savings in structure weight and of aerodynamically cleaner wing and fuselage surfaces. Such a glue may also be expected to be of value in the manufacture of pressurised fuselages, because it will avoid the large number of small leaks occurring at the rivet heads and may also help to solve the difficult problem of making integral fuel tanks in aircraft wings.