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Journal Article

Small Airplane Considerations for the Guidelines for Development of Civil Aircraft and Systems

On September 30, 2011, certification authorities released Advisory Circular 20-174[1], Development of Civil Aircraft and Systems, which recognizes the Society of Automotive Engineers (SAE) Aerospace Recommended Practice (ARP) 4754A and the European equivalent ED-79A [2], in order to address “the concern of possible development errors due to the ever increasing complexity of modern aircraft and systems.” ARP4754A/ED-79A describes a process of development assurance which helps reduce the risk of design errors in the development of aircraft systems. This process is necessary for complex systems not easily comprehended by deterministic analyses or tests. This ARP was developed “in the context of Title 14 of the Code of Federal Regulations (14 CFR) part 25,” a category which includes complex systems such as full fly-by-wire flight controls. However, this paper shows that such systems are the exception to most, recent civil airplane designs.
Journal Article

Development and Test of Safe, High Power Lithium Ion Main Batteries for General Aviation Aircraft

Advanced chemistry batteries may help reduce weight and increase aircraft performance. Lithium Ion chemistries' high energy density enables 40% weight savings over existing baseline, Lead Acid and Nickel-Cadmium (Ni-Cd) batteries. Baseline requirements for Lithium Ion batteries were developed by studying Cessna's aircraft product line. Nanoscale phosphate-based Lithium Ion cathodes improve safety through inert failure modes, while delivering higher power over conventional oxide-based Lithium Ion and baseline chemistries. Cells and batteries were tested under selected load, environmental, and temperature conditions using procedures adapted from RTCA DO-293 and DO-160. On-board aircraft testing verified performance compatibility. Safety tests verified inert failure mode and flight environment compatibility. Test results showed nanoscale phosphate Lithium Ion batteries are promising as a safe, high power Lithium Ion main battery in general aviation aircraft.
Technical Paper

The Effect of Forming Pressure on Springback in 2XXX Aluminum Alloys

In the aircraft industry, hydroforming is widely used to form parts using aluminum alloys in tempered condition T-XXXX. Success of this process depends on accurate springback prediction. The magnitude of springback and its variation is high in aluminum alloys in tempered condition T-XXXX. Process and material variability causes variation in springback. Wide range of pressures and press types in hydroforming process attribute to process variability. Forming pressures can be varied to control springback. This study looks at the effect of forming pressure on springback in hydroforming of aluminum alloy 2024-T3 and 2524-T3 in two most popular industrial hydropresses. The study forms the basis for developing a new model for springback prediction in the future.
Technical Paper

Climb Performance Analysis Using a GPS Reference Method

Certification of climb performance has traditionally been accomplished using reciprocal heading climbs. This was done to eliminate wind gradient effects. However, the FAA allows climb certification to be done on a single heading when inertial methods are used. A method was developed utilizing a DGPS system that allows an engineer to apply the inertial corrections to a single climb without the need of INS equipment. This method has been validated on several aircraft by comparing conventional reciprocal heading climb results to results obtained using the GPS method on the same climbs. The GPS climb method presented here can potentially reduce the number of climbs required for development and certification as well as provide more consistent data.
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

Simulation of Aircraft Landing Gear Dynamics Using CATIA, CATDADS, DADS and NASTRAN at Cessna Aircraft

This paper discusses how CATIA solid models of a landing gear system, combined with a NASTRAN flexible model of the aircraft are simulated using CATDADS and DADS to predict the dynamic response, loads, and general design factors for the aircraft and associated landing gears. Several landing gear design factors are predicted and quantified using DADS and CATDADS to solve the 3D nonlinear equations of motion. Position, velocity, acceleration, and gear loads are analytically determined and used to compare to physical tests. Aircraft loads due to symmetric landing and taxi conditions as well as asymmetric landing conditions are analytically determined using a full flexible aircraft model coupled with the landing gears.
Technical Paper

Continued Electromagnetic Protection of Aircraft and Systems

Aircraft electromagnetic protection has always been focused on the design, test and analysis required for certifying aircraft. That focus is now expanding to include the continued airworthiness of electromagnetic protection over the entire life of the aircraft. A better understanding of the scope and magnitude of maintaining assurance is needed for continued electromagnetic protection and safety over the lifetime of the aircraft. Wire bundle shielding of aircraft wiring harnesses, electrical bonding, and grounding are all used to provide electromagnetic protection in general aviation aircraft. The effectiveness of these protection methods is assumed to be maintained using periodic detailed visual inspections and DC bond checks after any replacements or repairs. This assumption appears valid because of the low number of catastrophic occurrences involving lightning strikes.