Browse Topic: Gliders
Very strong role models who have a marked enthusiasm for their subject are needed at every point along an employee's education and work career. THERE HAS PROBABLY NEVER BEEN SUCH A DEMAND for professionally qualified engineers, and yet both the number and diversity of people entering the profession continue to decline. Worldwide, there are very many and diverse initiatives to improve the situation-some generally encouraging interest in the profession, and others targeting specific audiences. There have been some local successes, but the overall picture remains discouraging. For a long time, there has been a growing awareness of a diminishing of interest in the engineering profession on the part of potential students. The principal hypothesis is that the image of the profession is poor, requiring hard work to qualify but delivering only a modest reward. Other hypotheses include a lack of flair in the management of young engineers that limits their experience rather than creating a vision.
When comparing the potential of advanced versus conventional powertrains, a traditional approach is to hold glider design constant and simulate “comparable performance” to a conventional vehicle (CV). However, manufacturers have developed hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV), and all-electric vehicle (EV) powertrains in gliders designed to synergistically enhance fuel saving benefits of such powertrains by further reducing road load and engine output power (or continuous power for the EV) where no conventional powertrain option is provided. In the U.S. marketplace, there are now several examples of both hybrid and plug-in hybrid electric vehicles using gliders common to top selling CVs and a few using low load gliders to further reduce fuel consumption. We use fuel consumption estimates from FuelEconomy.gov for a number of plausible CV versus HEV, PHEV, and EV comparisons to estimate the potential additional annual fuel savings and greenhouse gas (GHG) emission benefits, using Argonne National Laboratory's GREET model, obtainable when consumers make the behavioral choice to purchase various electrified powertrains in low road load gliders. When electric generation comes from natural gas, PHEVs and EVs in low load gliders can provide about the same GHG benefits as low load HEVs, with less gasoline use. If renewables are used in conjunction with natural gas, the GHG benefits increase. In comparison to HEVs in standard gliders, there will be even greater benefits.
Equipment made with lightweight materials can improve fuel consumption and increase available payload capacity. There are a variety of design techniques to achieve lightweight vehicles. One option that has been widely used is materials selection and the choice of less dense materials such as aluminum, magnesium alloys, or composites. There are several drawbacks to these material options including reduced material strength, ductility, and stiffness as well as higher cost. Another option involves using ferrous materials under innovative processing conditions. When both the weight and cost per unit of strength are considered, ductile iron, also known as nodular iron, is a very attractive material to consider. While denser than aluminum, ductile iron's higher strength can result in weight reduction by allowing thinner section size.
Gliders can climb to substantial altitudes without employing any on-board energy resources but using proper piloting skills to utilize rising air currents called thermals. Recent experiments on small Unmanned Aerial Vehicles (UAVs) indicate a significant potential to increase both the flight velocity and the range of gliders by means of such maneuvers. In these experiments the velocity to approach a thermal has been recognized as a critical performance factor, and is chosen as the controlled variable. Accurate longitudinal controllers are required to track the optimal flight trajectories generated using path planning algorithms. These controllers are challenged by the presence of uncertain and time-varying aircraft dynamics, gust disturbances, and control actuator limitations. With a broader objective of utilizing thermals to optimize the flight performance of autonomous UAVs, we focus on handling elevator constraints imposed on an uncertain aircraft model whose parameters are estimated online. We implement an adaptive control design with two different add-on schemes to address both the actuator magnitude and rate constraints. The first approach is based on an anti-windup compensator, whereas the second one uses the reference governor. The two constrained control methodologies are compared through simulation results.
Biomorphic gliders are small robotic microflyers proposed for use in scientific exploration of planetary atmospheres and terrains that capture some key features of insect and bird flight. Biomorphic gliders as biomorphic flight systems are a subset of biomorphic explorers. The multidisciplinary system concept of "Biomorphic Explorers" represents small, dedicated, low-cost explorers that possess some of the key features of biological systems, not easily captured by conventional robotic systems. Such features particularly include versatile mobility, adaptive controls, bioinspired sensor mechanisms, biomorphic sensor fusion, biomorphic communications, biomorphic cooperative behavior, distributed operations, and biomorphic energy generation/conversion. Significant scientific and technological payoff at a low cost is realizable by using the potential offered by a large number of such cooperatively operating biomorphic explorer units in concert with the traditional exploration platforms such as the lander/rover, orbiter, etc., for example.
Since the advent of the helicopter toward the end of World War II, there has been a marked increase of interest in the uses of rotary-wing aircraft in technical as well as in non-technical circles. A promising future for the helicopter was predicted in both military and commercial services. Although its predecessor, the autogiro, receded into oblivion, apparently because of its inability to hover, many new combinations of hovering rotary-wing machines have been since proposed and tried. It seems that the search for an "ideal" aerial vehicle was only intensified by the birth of the helicopter. Among the new machines with indisputable advantages, and promising future, are the gyrodyne, the convertoplane, and a number of other "all-purpose" and "special-purpose" machines. To their list must be added rotary-wing gliders, which were also conceived and successfully developed within the recent past. Although the rotor operation in rotary-wing gliders is essentially identical to that of an autogiro, the advantages of this type of craft did not become apparent until it was designed specifically as a glider and judged on its own functional merits. The first outstanding feature of the rotary-wing glider is its unusually low-empty weight. The average empty weight of fixed-wing gliders is 50-60 per cent of the gross weight, while rotary-wing machines readily achieve a much lower figure of 20-30 per cent. As a good approximation, it may be conservatively stated that a rotary-wing glider will lift twice the payload of its fixed-wing counterpart, based on the same gross weight. By the same rule, it lifts three times the payload of a helicopter of equal gross weight. Reasons for this will become apparent in the subsequent discussion.
BY working from notebook memoranda, personal correspondence files, old photographs, and the original laboratory instruments, the author has been able to gather together the story of how the Wright brothers, starting in 1899 with an idea for controlling the flight of a glider, were able, by 1903, to develop a machine that was capable of powered flight. The author describes this airplane and its engine as well as the 1904-1905 and 1908 ones. The latter was the first airplane to pass U. S. Army acceptance tests.
FROM Karavodine's inefficient tube in 1908 through American developments after the recovery of German V-1 bombs, Mr. Edelman sketches the history of pulsating jet engines. Work in the United States has centered on instrumentation, tube geometry, fuel injectors, air inlet valves, fuel properties, and performance estimation. Realized performance is still low in comparison with predictions of best possible performance; but the author suggests use of the pulsating jet for helicopters having jets at the blade tips, for gliders, for starting turbines of aircraft gas turbine powerplants, and for auxiliary power with conventional aircraft.
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