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Technical Paper

Wiring Assessment of Aging Commuter Class Aircraft

The reliability and maintenance of electrical wiring and electrical components in aging aircraft have become areas of concern for the aviation industry. Numerous investigations have been conducted on the aging aspects of wiring and systems of large transport and military airplanes, with funding primarily from the FAA (Federal Aviation Administration), Air Force, and NASA. However, because of the large number of smaller general aviation aircraft in service, a need for examining the condition of wiring, electrical components and maintenance procedures for smaller aircraft exists. The Aging Aircraft Research Laboratory at the National Institute for Aviation Research (NIAR), Wichita State University, has conducted a comprehensive teardown evaluation of three high time commuter class airplanes. This teardown included assessment of aircraft wiring, electrical systems and circuit breakers through general and intrusive visual inspections and laboratory tests.
Technical Paper

Wind Tunnel and Flight Development of Spoilers for General Aviation Aircraft

Wind tunnel tests have been carried out to develop a spoiler lateral control system for use with the GA(W)-1 airfoil with a 30% Fowler flap. Tests show that unfavorable aerodynamic interactions can occur between spoiler and flap for large flap deflections. Providing venting of lower surface air through the spoiler opening substantially improves performance. Results of tests with a number of spoiler and cavity shapes are presented and discussed. Applications of two-dimensional wind tunnel results to the design of satisfactory manual lateral control systems are discussed.
Journal Article

The Fatigue Behavior of Fastener Joints

The fatigue behavior of Hilok fastener joints under constant amplitude loading has been investigated experimentally. The effects of load transfer in an unbalanced joint configuration was characterized in terms of a stress severity factor relative to the open-hole configuration. The experimental data indicates that the clamp-up forces dominate the performance of fastener joints with the open-hole fatigue life being the lower bound at the stress levels investigated. The failure modes were observed to transition from a net-section type failure across the minimum section to a fretting induced failure at some distance from the hole. The experimental data has been used to develop stress severity factors to be used as a measure of the fatigue quality of the fastener joints.
Technical Paper

The Application of Neural Networks for Spin Avoidance and Recovery

This paper presents a method by which artificial neural networks can be trained and used to identify a possible spin entry, differentiate between an incipient spin and a stabilized spin, and predict required recovery controls. These were then implemented into a simulation and tested using data from actual flight tests conducted by NASA Langley Research Center, to verify that artificial neural networks can successfully be used for this application. The spin avoidance and recovery system functioned properly. In addition, a weighting system was developed to predict possible spin characteristics of aircraft, depending on the relative magnitude of the three principal moments of inertia.
Technical Paper

Tail Icing Effects on the Aerodynamic Performance of a Business Jet Aircraft

Experimental studies were conducted to investigate the effect of tailplane icing on the aerodynamic characteristics of 15%-scale business jet aircraft. The simulated ice shapes selected for the experimental investigation included 9-min and 22.5-min smooth and rough LEWICE ice shapes and spoiler ice shapes. The height of the spoilers was sized to match the horns of the LEWICE shapes on the suction side of the horizontal tail. Tests were also conducted to investigate aerodynamic performance degradation due to ice roughness which was simulated with sandpaper. Six component force and moment measurements, elevator hinge moments, surface pressures, and boundary layer velocity profiles were obtained for a range of test conditions. Test conditions included AOA sweeps for Reynolds number in the range of 0.7 based on tail mean aerodynamic chord and elevator deflections in the range of -15 to +15 degrees.
Technical Paper

Summary of the Effect of Multiple Site Damage on the Linkup Strength of 2024-T3 Aluminum Panels

An aging aircraft accumulates fatigue cracks commonly referred to as multiple site damage (MSD). A simplified engineering fracture mechanics model, generally referred to as the linkup model (or plastic zone touch model), has been used with some success to describe the MSD fracture phenomenon in 2024-T3 aluminum panels. A disadvantage of the linkup model is that it gives excessively inaccurate results for some configurations. A modified linkup model has been developed through empirical analysis of test data taken from unstiffened panels with MSD cracks at open holes. The modified linkup model was then validated with test data from stiffened panels including single-bay panels with the lead crack centered between stiffeners and two-bay panels with the lead crack centered beneath a severed stiffener. Further validation of the modified linkup model was done with test data from panels with bolted lap joints. Test results were obtained from 112 different panels.
Technical Paper

Studies of Light-Twin Wing-Body Interference

The results of an analytical study of aerodynamic interference effects for a light twin aircraft are presented. The data presented concentrates on the influence of a wing on a body (the fuselage). Wind tunnel comparisons of three fillets are included, with corresponding computational analysis. Results indicate that potential flow analysis is useful to guide the design of intersection fairings, but experimental tuning is still required. While the study specifically addresses a light twin aircraft, the methods are applicable to a wide variety of aircraft.
Technical Paper

Studies of Hingeline Gap, Trailing Edge Treatment, Lower Surface Deflector on Spoiler Characteristics and Flow

Wind tunnel test have been conducted to determine effects of certain design variables on spoiler performance and spoiler flow field characteristics. Measurements include forces, oil flow surveys on a vertical splitter plate, and wake velocity and turbulence measurements using a dual split-film anemometer system. Results include the effects of spoiler design variables, such as: hingeline gap, lower surface venting and deflector, spoiler trailing edge notching and spoiler porosity. Hingeline gap, porosity, lower surface venting and lower surface deflector can be designed to reduce control dead-band tendency. Wake turbulence studies show that certain modifications can be utilized to diminish peak frequencies in the wake.
Technical Paper

Studies of Flow Separation and Stalling on One- and Two-Element Airfoils at Low Speeds

Research has been conducted on the nature of airfoil behavior at pre- and post-separated angles of attack. Detailed wind tunnel studies have been made of boundary layer and wake fields for the GA(W)-1 airfoil, and the airfoil with a 0.3 chord Fowler flap. Experimental data are compared with theoretical predictions from a multi-element viscous flow computer program. Theoretical predictions are reasonably accurate for unseparated flows, but have serious errors when separation is present. Some recent techniques for modeling post-separated flow behavior are discussed in light of the present experiments.
Technical Paper

Strength of Stiffened Panels with Multiple Site Damage

Multiple site damage (MSD) on aging aircraft accumulates from fatigue loading over a period of time. For ductile materials such as 2024-T3 aluminum, MSD may lower the strength below that which is predicted by conventional fracture mechanics. An analytical model referred to as the linkup (or plastic zone touch) model has previously been used to describe this phenomenon. However, the linkup model has been shown to produce inaccurate results for many configurations. This paper describes several modifications of the linkup model developed from empirical analyses. These modified linkup models have been shown to produce accurate results over a wide range of configurations for both unstiffened and stiffened flat 2024-T3 panels with MSD at open holes. These modified models are easy to use and give quick and accurate results over a large range of parameters.
Technical Paper

Spy Blimps Revisited: A Performance Comparison between Two Competing Approaches

While operational airships globally number in the low dozens, interest in buoyant or semi-buoyant platforms continues to arouse imaginations of commercial and military planners and developers alike. The airship-as-advertisement business model is the only model that has proven sustainable on any scale since the crash of the initially successful LZ-128 Hindenburg effectively ended regular passenger and cargo transport by airship, and the 1962 termination of the US Naval airship program terminated regular large-scale surveillance from airships. Efforts in the US and Japan during the 2000's to have a self-sustaining sight-seeing business model using the modern semi-rigid Zeppelin NT both failed. In theory, the buoyant nature of airships provides compelling endurance and cost-per-ton-mile capability which fills a niche arguably not currently occupied by other modes of transportation.
Technical Paper

Results of Analytical Modeling of 3-D Machining Processes with Flat Faced Tools

A generalized upper bound model for calculating the chip flow angle in oblique cutting using flat faced tools with single cutting edge and multiple or curved cutting edges has been developed. The chip flow angle and chip velocity are obtained by minimizing the cutting power with respect to both these variables. The chip flow angles predicted by this model show good agreement with experimental values of chip flow angles for various tool geometries and cutting conditions. The model has the potential to be extended to the more complex machining processes such as drilling and milling.
Technical Paper

Response of an Advanced Flight Control System to Microburst Encounters

An envelope protection scheme is proposed for responding to a microburst. This approach is based on limiting the allowable maximum inertial deceleration of the aircraft when flying at low airspeeds. This technique is shown in simulations to be very effective at preventing stall and resulting in minimal loss of altitude. It is speculated that the same scheme can also protect an aircraft in the event of other forms of windshear encounters, such as making a sudden turn to downwind.
Technical Paper

Residual Strength of an Aluminum Panel with a Centric Hole and One Cracked Ligament

The residual strength of an aluminum panel with a centric hole and one cracked ligament was investigated experimentally. Each of the 7075-T6 aluminum panels which were tested included a cracked ligament of varying length on one side of the centric hole and an uncracked ligament on the other side of the hole. The failure of such a panel subjected to uniform tensile loading normally occurs according to the lower of two modes: brittle fracture or a net section type of yielding. On the other hand, the question of whether one or both ligaments fail is not easily answered. Results show that one or two ligament failure depends upon test conditions such as crack length and loading method. For short crack lengths, the uncracked ligament will fail almost simultaneously with the failure of the cracked ligament.
Technical Paper

Refill Friction Stir Spot Joining Rivet Replacement Technology

The Refill Friction Spot Joining (RFSJ) is an emerging solid-state spot welding technology that thermo-mechanically creates a molecular-level bond between the work-pieces. RFSJ does not consume any filler or foreign materials so that no additional weight is introduced to the assembly. As the solid-to-liquid phase transition is not involved in RFSJ in general, there is no lack of fusion or material deterioration caused by liquefaction and solidification. Unlike the conventional friction stir spot welding, RFSJ produces a spot joint with a perfectly flush surface finish without a key or exit hole. Currently, the aerospace industry employs solid rivets for fastening the primary structures as they meet the baseline requirements and have well-established standards and specifications.
Technical Paper

ProRAPP: A Computer Program for Propeller/Rotor Noise Prediction

The current emphasis on environment protection by reducing noise pollution has led to stricter noise standards for general aviation aircraft. As a result, there is a growing demand for a computational tool to predict the noise during the design process. A computer program, called ProRAPP, has been developed for the prediction of noise generated by propeller/rotor blades. The acoustic pressure is calculated using a form of Ffowcs Williams-Hawkings equation which is suitable for numerical implementation. For noise predictions, the observer can either move with the propeller/rotor hub or it can be fixed to the ground. Experimental data from both wind tunnel and flight tests are used to validate the numerical results.
Technical Paper

Preliminary Design Considerations for Zero Greenhouse Gas Emission Airplanes

Global warming concerns are stimulating accelerated research and development of alternative fuels and propulsion systems for automobiles. The potential application of these emerging technologies to airplanes is reviewed. Preliminary designs of zero greenhouse gas emission airplanes using hydrogen fuel and either internal combustion or fuel cell-electric motor propulsion are presented for a wide body jet transport, medium jet transport, business jet, and single engine propeller airplane. The hydrogen fueled internal combustion engine airplanes offer the easiest path to zero emissions, but the greater efficiency of the fuel cell airplanes allows designs requiring substantially less fuel. The single engine propeller airplane is the easiest to modify for hydrogen fuel, because of the relatively high mass and volume of the engine being replaced. Technology improvements needed to make zero emission airplanes viable are suggested.
Technical Paper

Prediction of Variation in Dimensional Tolerance Due to Sheet Metal Hydroforming using Finite Element Analysis

This study presents the prediction of the dimensional variation of holes due to sheet metal bending using the hydroforming technique. Sheet metal with pre-drilled holes was evaluated for a bending operation using a hydroforming technique. Sheet metal with a variety of thicknesses, bending radii, and bending angles was evaluated. Variation in the dimensional tolerance due to the bending was attained using the minimum radial separation method. A dataset of dimensional variation in the holes was developed and used for development of the artificial neural network, which was able to predict the dimensional variation of the hole if an unknown pattern of inputs was provided.
Technical Paper

Performance Evaluation of Computational HIC Component Tester for Aerospace Application

The necessity of avoiding the destructive and non-repeatable FSST (Full Scale Sled Test) makes it desirable to devise a cheaper and more repeatable method which can supplant this test procedure. This need developed the HCTD (HIC Component Testing Device) which is capable of providing conservative HIC results with higher repeatability. The computational model of the HCTD is validated against one of the tests conducted at CAMI with polyethylene foam. This validated model is used to conduct a series of tests with input parameters similar to the sled test to develop the correlation between the sled test and HCTD. This study hence concludes that a validated computational model of HCTD can be successfully utilized to address the HIC compliance issues for a foam padded surface.
Technical Paper

Parametric Investigation of Ice Shedding from a Business Jet Aircraft

Ice particles shed from aircraft surfaces are a safety concern because they can damage aft-mounted engines and other aircraft components. Ice shedding is a random and complex phenomenon. The randomness of the ice fragment geometry, size, orientation and shed location in addition to potential particle breakup during flight poses considerable simulation challenges. Current ice shedding analysis tools have limited capabilities due to the lack of experimental aerodynamic coefficients for the forces and moments acting on the ice fragment. A methodology for simulating the shedding of large ice particles from aircraft surfaces was developed at Wichita State University. This methodology combines experimental aerodynamic characteristics of ice fragments, computational fluid dynamics, trajectory analysis and the Monte Carlo method to provide probability maps of shed particle footprints at desired locations.