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Small remotely piloted aircraft (10-25 kg) powered by internal combustion engines typically operate on motor gasoline, which has an anti-knock index (AKI) of >80. To comply with the single-battlefield-fuel initiative in DoD Directive 4140.25, interest has been increasing in converting the 1-10 kW power plants in the aforementioned size class to run on lower AKI fuels such as diesel and JP-8, which have AKIs of ~20. It has been speculated that the higher losses (short-circuiting, incomplete combustion, heat transfer) that cause these engines to have lower efficiencies than their conventional-scale counterparts may also relax the fuel-AKI requirements of the engines. To investigate that idea, the fuel-AKI requirement of a 3W-55i engine was mapped and compared to that of the engine on the manufacturer-recommended 98 octane number (ON) fuel.

The rapid expansion of the market for remotely piloted aircraft (RPA) includes a particular interest in 10-25 kg vehicles for monitoring, surveillance, and reconnaissance. Power-plant options for these aircraft are often 10-100 cm3 internal combustion engines. Both power and fuel conversion efficiency decrease with increasing rapidity in the aforementioned size range. Fuel conversion efficiency decreases from ∼30% for conventional-scale engines (>100 cm3 displacement) to <5% for micro glow-fuel engines (<10 cm3 displacement), while brake mean effective pressure decreases from >10 bar (>100 cm3) to <4 bar (<10 cm3). Based on research documented in the literature, the losses responsible for the increase in the rate of decreasing performance cannot be clearly defined. Energy balances consisting of five pathways were experimentally determined on two engines that are representative of Group-2 RPA propulsion systems and compared to those in the literature for larger and smaller engines.

Current efforts to extend controlled flight into the post-stall regime will bring about major changes in aircraft dynamic capability. These changes will have far-reaching implications in terms of the specification, design, evaluation, and operational use of future fighter aircraft. Significant research continues to be accomplished in developing the technologies required to design and build supermaneuverable fighters. This paper discusses some of the background to current agility research and addresses the research which must be accomplished in order for the Air Force to specify requirements for and evaluate these aircraft.

One important issue in uncertainty analysis is to find an effective way for propagating uncertainty through engineering systems which have significant random variation parameters in space or time. In this paper, the polynomial chaos expansion (PCE) was selected since this approach can reduce the computational effort in large-scale engineering design applications. An implementation of PCE, which includes different probability distributions, is the focus of this paper. Two existing techniques, a generalized PCE algorithm and transformation methods, are investigated and verified for their accuracy and efficiency for non-normal random variable cases. A nonlinear structural model of an uninhabitated joined-wing aircraft and a three pin-connected rod structure are used for demonstrating the method.

The work concerns the selection of measurement parameters for selected non-destructive testing methods of Mi helicopter rotor blades after repair. Considered repair cases involve metal cracks in the sandwich skin and repair damage of honeycomb structure (puncture, dent). In the event of a crack, repair is performed by applying a composite-metal repair package. In case of damage of the core, its broken piece is replaced by a new one and then applied the same metal-composite package as in the case of crack repair. The present work focuses on detecting disbond between skin and core below repair patch and cracks under the repair package. Detecting cracks and assessing their length is important because the repair technology provides the repair package without removing of cracked part of skin. Authors have used laser shearography and C-scan methods for MIA and ET.

Polish Armed Forces are currently operating hundred helicopters belonging to Mi family. Metal fuselage is usually resistant to the battle and the human factor. Unfortunately, metal rotor blades of Mi helicopters are sensitive to operating conditions. Single blade is made from monolithic aluminum spar and mutually separated trailing sections, which are bonded to the spar. The sections are constructed of metal sandwich panels. During aggressive military operating conditions blades sections are often damaged by debonding from the spar, fatigue cracks of section skin, dents and perforations as well as erosion. The manufacturer assumed that structurally damaged sections should be exchanged. Provided repair technologies are applied only to cosmetic damages. Unfortunately, there is a limit to number repairs which prevents replacement of two neighboring sections due to the high temperature of curing cycle during the section replacement.

Numerical simulations indicate that blast loading on aircraft structural joints can impart loading rates in excess of 10 Mlb/sec (ten million pounds per second, Reference 1). Experimental evidence, on the other hand, suggests that mechanical joint failure loads are highly loading rate dependent; for example, the failure load for a dynamically loaded tension joint can double from its static value. This paper discusses the progress and to-date findings of research on the assessment of strength failure of aircraft structural joints subjected to loading rates expected from an internal explosive detonation, and several associated experimental procedures to generate such dynamic loading. This work is conducted at MDC and at the University of Dayton Research Institute (UDRI) in support of the FAA Aircraft Hardening Program.

In this work we present our recent effort in developing a novel heat exchanger based on endothermic chemical reaction (HEX reactor). The proposed HEX reactor is designed to provide additional heat sink capability for aircraft thermal management systems. Ammonium carbamate (AC) which has a decomposition enthalpy of 1.8 MJ/kg is suspended in propylene glycol and used as the heat exchanger working fluid. The decomposition temperature of AC is pressure dependent (60°C at 1 atmosphere; lower temperatures at lower pressures) and as the heat load on the HEX increases and the glycol temperature reaches AC decomposition temperature, AC decomposes and isothermally absorbs energy from the glycol. The reaction, and therefore the heat transfer rate, is controlled by regulating the pressure within the reactor side of the heat exchanger. The experiment is designed to demonstrate continuous replenishment of AC.

Aircraft engine power is degraded with increasing altitude according to the resultant reduction in air pressure, temperature, and density. One way to mitigate this problem is through turbo-normalization of the air being supplied to the engine. Supercharger and turbocharger components suffer from a well-recognized loss in efficiency as they are scaled down in order to match the reduced mass flow demands of small-scale Internal Combustion Engines. This is due in large part to problems related to machining tolerance limitations, such as the increase in relative operating clearances, and increased blade thickness relative to the flow area. As Internal Combustion Engines decrease in size, they also suffer from efficiency losses owing primarily to thermal loss. This amplifies the importance of maximizing the efficiency of all sub-systems in order to minimize specific fuel consumption and enhance overall aircraft performance.

The engines used to power small unmanned aerial systems are often modified commercial products designed for use by hobbyists on small model aircraft at low altitude. For military applications, it is desirable to fly at high altitudes. Maintaining power from the engine at the reduced ambient air pressures associated with high altitudes requires some method of increasing air delivery to the intake manifold. Conventional turbochargers and superchargers are typically very inefficient for the low mass flows associated with small engines. Due to its unique characteristics, a pressure wave supercharger (PWS) can avoid many scaling-related losses. This project designed a small-scale PWS for turbo-normalization of a Brison 95 cc two-stroke engine for a small unmanned aerial vehicle. A larger PWS called the Comprex®, designed by Brown Boveri Company, was simulated using a quasi-one-dimensional Computational Fluid Dynamics (CFD) code developed at the NASA Glenn Research Center.

The purpose of this study is to set up a laboratory test apparatus to analyze aircraft flight control EMAS' electrical and thermal energy flow under transient and dynamic flight profiles. A hydraulic load frame was used to exert load to the EMA. The actuator was placed within an environmental chamber which simulates ambient temperature as function of altitude. The simulated movement or stroke was carried out by the EMA. The under test EMA's dynamic load, stroke, and ambient temperature were synchronized through a real time Labview DAQ system. Motor drive voltage, current, regenerative current, and motor drive and motor winding temperature were recorded for energy analysis. The EMA under test was subjected to both transient and holding load laid out in a test matrix.

Many of the engines used in Remotely Piloted Aircraft (RPA), come directly from the remote-control (R/C) aircraft market, which turn a propeller but are not necessarily built for the greatest efficiency or reduced fuel consumption. The DoD “single fuel concept” is pushing these platforms to be able to operate with JP-8 using an Otto Cycle engine. Additionally, with increased environmental concern with fossil fuels, possible future DoD requirements could require the use of bio-derived liquid fuels. The research presented in this paper takes steps to satisfying both the efficiency and single fuel requirements. The Fuji BF-34EI engine was successfully shown to operate effectively with JP-8, Diesel, Algae-based Diesel and Camelina based Hydroprocessed Renewable Jet fuel. When generally compared over the entire engine operating map, between AVGAS and JP-8, the latter is shown to present a 10-20% lower brake specific fuel consumption (BSFC).

One of the main challenges in the power systems of future aircraft is the capability to support pulsed power loads. The high rise and fall times of these loads along with their high power and negative impedance effects will have an undesirable impact on the stability and dc bus voltage quality of the power system. For this reason, studying ways to mitigate these adverse effects are needed for the possible adoption of these type of loads. One of the technologies which can provide benefits to the stability and bus power quality is Energy Storage (ES). This ES is designed with the capability to supply high power at a fast rate. In this paper, the management of the ES to mitigate the effects of pulsed power loads in an aircraft power system is presented. First, the detailed nonlinear model of the power network with pulsed power loads is derived. Due to the large size of this model, a model order reduction is performed using a balanced truncation and a second order approximation.