Browse Topic: Weather and climate
The biography of Henrich Focke is well known and documented. During a small period from October 1954 to February 1956 he held lectures at the Technical University of Stuttgart during the winter semester. In the summer period he returned to Brazil for continuation of his contract work on the "Convertiplane" (a quad-tiltrotor aircraft) and the "Bei-jaflor" (a small single rotor helicopter). The topic of Focke's lecture in the winter semester 1954-55 was "Design of Fixed-Wing Aircraft", but the lecture manuscript of it is unavailable. In the following period 1955-56 Focke lectured about "Helicopter Design" and the manuscript was recently found in the central archive of DLR. It covers 123 pages of text with sketches and graphs and provides deep insights into the helicopter design philosophy of Henrich Focke.
Civil and military rotorcraft operators desire enhanced capabilities from their vehicles in terms of mission efficiency, effectiveness, productivity, and availability. A critical element of this challenge is associated with providing cold weather availability. Currently, cold weather operations are enabled by regulatory actions leading to Limited Approvals, Qualifications, Clearances, and Restrictions. Cold weather certification (clearance of a new aircraft) and continuing airworthiness (maintaining effectiveness of fielded aircraft) are data driven processes. This work provides guidance on an Icing Encounters Survey (IES) based data gathering method supporting continuing airworthiness organizations in improving fleet safety and capabilities during cold weather operations.
Heavy wind and high sea states pose challenges to operating unmanned rotorcraft on-board a naval ship, in particular the recovery phase. A novel autonomous landing strategy for unmanned rotorcraft is proposed and investigated. The new landing strategy makes use of a prediction of the future deck motion based on a sensor on the ship deck. The study is based on a nonlinear simulation environment which includes the dynamics of a 100 kg unmanned helicopter and the dynamics of an ocean-going patrol vessel of the Royal Netherlands Navy. The performance of the autonomous landing strategy is evaluated for a wide variety of environmental conditions (sea state) and operational conditions (ship speed and heading). The results clearly indicate that the environmental conditions have a strong influence on the landing performance in terms of touchdown velocity and landing accuracy. Furthermore, the autonomous landing strategy is effective in reducing the mean and peak value of the touchdown velocity compared to a standard automatic landing strategy. A reduction of as much as 60% in landing impact is observed for the worst case environmental and operational condition considered. The results confirm and underline the potential of the novel landing strategy.
ABSTRACT This study examines the performance of a quadcopter in edgewise flight conditions with flow simulated using the commercial Navier-Stokes solver, AcuSolve, with a Detached Eddy Simulation (DES) model. The rotating volume around each rotor interfaces with the remainder of the computational domain using a sliding mesh. Simulations were conducted for an AeroQuad Cyclone quadcopter at 10 m/s forward speed, 5 deg nose-down pitch attitude, operating in both cross and plus configurations. From the results it was observed that in the cross configuration, the aft (South) rotors showed a 19% reduction in lift (relative to an isolated rotor at the same forward speed, pitch attitude and RPM), with an associated 3% reduction in torque. The loss in lift was primarily at the front of the aft rotors due to the downwash induced by the forward rotors, therefore reducing the aft rotor nose-up pitching moments by 54% (relative to operation in isolation). In the plus configuration, sections of the East and West rotors close to the aircraft center-body operate in upwash induced by the North rotor, increasing the lift generated by 5.5% and 7.6% respectively, relative to operation in isolation. The South rotor sees both upwash (and increased lift) along the advancing and retreating edges induced by the East and West rotors, as well as downwash at the front (and reduced lift) induced by the North rotor, but no significant overall changes in thrust or torque.
Corrosion occurs in diverse environments mainly on metallic parts. Helicopters are made of a huge percentage of metallic parts and need to have several maintenance steps to guarantee its functioning and its durability. The military helicopters are flying in different kinds of environment, which cover large spectrum of severity of the atmospheric corrosion [1]. In maritime conditions, the most influencing factor is the Time of Wetness, which is a direct result Relative Humidity and Salt loading. The main material used for aircraft and that is suffering from corrosion is aluminium. There are plenty of data to follow the corrosion as a function of the environmental conditions, mainly on the sensitivity with sodium chloride, Relative Humidity, film thickness, etc... [2][3]. The maintenance efficiency on helicopters is dependent on the environmental severity. The U.S. armed forces estimate $10.2 billion in corrosion costs for their aviation and missile fleets during 2016 [4] [5] [6]. The aim of the present analysis consists of defining the Condition Based Maintenance related to corrosion risk to better apply a maintenance program when it is really needed.
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This SAE Recommended Practice defines a procedure for determining the adhesion strength characteristics of heat-cured metal bonding adhesives subjected to induction heating.
This SAE Recommended Practice applies to the abrasion resistance testing of decorative tapes, graphics, and pin striping. It may also have relevance to certain vehicle labels and plastic wood grain film. The resistance to abrasive damage is judged qualitatively by its effect on the legibility, pattern, and color of the graphic marking. This recommended practice is intended as a guide toward standard practice but may be subject to frequent change to keep pace with experience and technical advances. This should be kept in mind when considering the use of this recommended practice.
This recommended practice defines a procedure for the construction and testing of a 180 deg peel specimen for the purpose of determining the bondability of glass to elastomeric material in automotive modular glass. This test method suggests that elastomeric material of less than 172 mpa modulus be used as the encapsulating material. The present practice of encapsulating automotive glass is described as molded-in-place elastomeric material onto the outer edge of the glass using thermoplastic or thermosetting material that quickly sets in the mold. The glass is removed from the mold with the cured elastomeric material bonded to the perimeter of the glass. This encapsulated glass module can now be bonded with a sealant adhesive into the body opening of a vehicle.
eVTOL aircraft operating within the air transportation system will undoubtably be exposed to inclement and adverse weather conditions, which may well include operation in icing conditions, whether planned or encountered inadvertently. Design compromises necessary to provide VTOL operations may make continued operation in an icing environment particularly challenging, especially for eVTOL aircraft having only limited excess power for operation of anti-icing or deicing equipment. This paper describes a research program to assess the impact of accreted icing on the performance of eVTOL aircraft, as part of a program for implementation of an Icing Detection Filter that leverages detailed knowledge of that performance impact on the distributed electrical propulsion and lift systems on the vehicle. Modeling approaches for prediction of icing accretion and the associated performance losses, particularly as they can be measured through monitoring of the onboard electrical power system, are described.
Helicopters are routinely used to transport crew to and from maritime wind farms. Inclement weather situations and demanding tasks put a high workload on pilots during these missions. This paper describes two test campaigns assessing the utility of a low cost Head-mounted display (HMD) to reduce workload for commercial maritime operations. This system was implemented within the Air Vehicle Simulator (AVES) at the German Aerospace Center (DLR). Three tasks were flown with experienced offshore pilots, performed in a realistic scenario. Independent subjective assessments of both workload and situational awareness were obtained. Results from the studies show that the overall workload for all missions decreased when using the HMD. Opinions regarding overall benefit and advantages of the system were found to vary between pilots and missions.
Attempting to pick through bad weather - becoming disoriented in diminished visibility or striking a wire or obstacle at low altitude - remains one of the major causes of fatal helicopter accidents. It is more common than engine failure, more common than mechanical failures, and more common than systems failures. While some feel the answer involves more tools to enable low-flying helicopters to avoid terrain and obstacles, a better solution is to keep helicopters safely away from terrain and obstacles using instrument flight rules (IFR) when weather conditions demand. For single engine helicopters, which form the largest population of helicopters, this means finding cost effective ways to provide them with safe and practical IFR capability. IFR capability is commonplace in airplanes, even among entry-level and training aircraft. An IFR rating is typically the first rating sought after an airplane pilot receives their license. For helicopters, there is currently not a parallel culture of shifting to the safety of IFR operations when weather demands. The reasons are complex, but a significant factor affecting this culture today is that the entryl evel IFR rotorcraft is generally a twin-turbine-engine helicopter. By the time a helicopter pilot gets to this level of machine, he or she is typically well versed in the "alternate" methods of weather avoidance. Unfortunately, even IFR rated helicopter pilots tend to default to a practice of attempting to fly below the weather using visual flight rules (VFR). Increasing the availability of IFR-capable helicopters by restoring practical, low-cost IFR solutions to single engine rotorcraft is the first step in a process intended to change the rotorcraft safety culture. This paper describes a 5-year effort by associations, industry, and regulators to remove the obstacles to certifying low-cost IFR helicopters. By mid-year 2019, two single-engine helicopters were certified for IFR operations, ending an absence of more than 20 years from the marketplace, but these were newly-manufactured aircraft. The remaining challenge is to apply what has been done in order to allow cost-effective retrofits of IFR capability to the existing fleet of VFR helicopters. The hope is that, with the trail now blazed, others will follow, and we will see even more single-engine rotorcraft with IFR capability and fewer weather-related accidents.
In the winter months of January-March 2019, two Bell 525 test aircraft completed cold weather testing at Yellowknife Canada, some 1900 nm from Bell’s Flight Research Center in Arlington, TX. Testing was aimed at demonstrating aircraft stability, performance, and flight characteristics at extreme temperatures as required by CFR Part 29. Since regulations only permit limited temperature extrapolation, the cold temperature tests must include the limit of forward speed in a dive (VNE), and assessments of performance, controllability, autorotation, and static stability. This paper describes some of the unique environmental conditions and factors that any rotorcraft development program could experience in cold weather testing. The paper also gives a technical description of the required testing, where arctic conditions reached as low as -40° F or C (the temperature scales are the same at this temperature). Testing exposed the aircraft to overnight cold-soaks that brought fluids, seals, windshields, electronics, and elastomeric bearings to their low temperature specification, all at the same time. For the 525, test results demonstrated that the aircraft was ready for start-up and operation in extreme cold. The criteria necessary for meeting certification requirements in cold weather were also demonstrated in the series of tests and showed that the rotor was free from any adverse effects due to aerodynamic compressibility, had low vibration, acceptable loads and was free from any instability, even at speeds greater than VNE.
As imbedded as it is in technology, the history of flight is also chock full of people stories. The history of the helicopter, one of the most versatile flying machines ever designed, abounds in such stories. This text looks at the development of Intercity Airlines Company's SG Mark VI by a unique team based for a time in Montreal, Quebec. Bernard W. Sznycer and Selma G. Gottlieb conceived one of the most advanced and innovative helicopter of its day. Designed to minimize vibrations and facilitate production, the SG Mark VI first flew in July 1947. Canada's Department of Transport awarded a Certificate of Airworthiness to a second prototype, in April 1951. The SG Mark VI was the first helicopter designed within the British Commonwealth of Nations to be so honored. Sadly, by then, American helicopters all but dominated the civilian and military markets. The SG Mark VI was abandoned during the winter of 1953-54 and both Sznycer and Gottlieb returned to the United States.
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