Turbine-powered Aircraft Research Articles

Benefits of Parallel Hybrid Electric Propulsion for Transport Aircraft

As battery and electric machine technologies improve, the electrification of aircraft propulsion systems may have the potential to reduce the energy consumption and emissions of transport aircraft. Incorporating electrical components adds a dimension to the propulsion system design space and introduces new tradeoffs between weight and efficiency. In this article, we apply numerical optimization to the conceptual design of regional transport category airplanes to quantify the energy efficiency benefits of parallel hybrid electric propulsion, identify the mechanisms of the benefits, and characterize the scaling effects of design parameters such as range and electrical technology parameters such as battery specific energy. The results show that the state-of-the-art technology may provide energy savings up to 1%–8% over conventional turboprop engines, while projected improvements in electric technology may allow greater savings of up to 14%, albeit at a reduced range relative to conventional gas turbine-powered aircraft. By supplementing the gas turbine engine with electrical power in high-thrust conditions, the overall efficiency of the propulsion system can be improved throughout the mission. Improvements in battery specific energy and power electronics specific power are identified as enablers for efficient hybrid electric aircraft propulsion.

Superhydrophobic heat exchangers delay frost formation and reduce defrost energy input of aircraft environmental control systems

Commercial aircraft operate over a wide range of atmospheric conditions, with temperatures exceeding 40 °C during takeoff and dropping below -50 °C at cruising altitudes near 10 km. An aircraft environmental control system (ECS) works to keep the crew and passengers comfortable by supplying them with conditioned air. The refrigeration unit of these aircraft, known as the air cycle machine (ACM), sees extreme conditions, ranging from engine bleed air exceeding 100 °C at the ACM compressor inlet to subzero temperatures at the ACM turbine outlet. These conditions can cause the ACM's condenser to frost, reducing the efficiency of the ECS. Engine bleed air can be used to defrost the condenser at the price of further reducing efficiency and cabin comfort. A larger condenser can alleviate frosting but will increase the cost and weight of the aircraft. An alternative is to apply a superhydrophobic coating to the condenser to provide increased resistance to frost growth with a minimal impact on nominal heat exchanger efficiency. In this work, we modified the surface wettability of an aluminum heat exchanger and tested it in a wind tunnel under a wide range of hot-side temperatures to study both frosting and defrosting performance. The superhydrophobic heat exchanger showed considerable improvement in system efficiency, sometimes completely eliminating frost growth and lowering the cycle normalized defrost time by up to 50%. A superhydrophobic coating on the ACM condenser of a turbine-powered aircraft has the potential to increase overall efficiency of the ECS and improve the energy efficiency of aircraft.

Improving safety in organ recovery transportation: Report from the ASTS/UNOS/AST/AOPO transportation safety summit.

Despite the passage of a decade since the tragic loss of an organ recovery team from the University of Michigan, there are currently no national standards governing air and ground transportation of organ recovery personnel. Consequently, the American Society of Transplant Surgeons, the Association of Organ Procurement Organizations, and the United Network for Organ Sharing jointly convened a transportation summit to review and update recommendations for national transportation standards. Expanded air transport quality assurance protocols, including a requirement for two engine turbine-powered aircraft piloted by two qualified pilots certified through onsite inspections was recommended. Ground transportation providers must ensure adequate safety restraints are available, ambulance avoided if possible, and the use of lights and sirens minimized. Finally, adequate insurance coverage for all team members, including trainees should be provided and should not rely on carrier liability insurance policies. The summit participants have committed the support of their organizations to promote and enact these regulations nationally.

Accident-precipitating factors for crashes in turbine-powered general aviation aircraft

General aviation (14CFR Part 91) accounts for 83% of civil aviation fatalities. While much research has focused on accident causes/pilot demographics in this aviation sector, studies to identify factors leading up to the crash (accident-precipitating factors) are few. Such information could inform on pre-emptive remedial action. With this in mind and considering the paucity of research on turbine-powered aircraft accidents the study objectives were to identify accident-precipitating factors and determine if the accident rate has changed over time for such aircraft operating under 14CFR Part 91.The NTSB Access database was queried for accidents in airplanes (<12,501lb) powered by 1–2 turbine engines and occurring between 1989 and 2013. We developed and utilized an accident-precipitating factor taxonomy. Statistical analyses employed logistic regression, contingency tables and a generalized linear model with Poisson distribution.The “Checklist/Flight Manual Not Followed” was the most frequent accident-precipitating factor category and carried an excess risk (OR 2.34) for an accident with a fatal and/or serious occupant injury. This elevated risk reflected an over-representation of accidents with fatal and/or serious injury outcomes (p<0.001) in the “non-adherence to V Speeds” sub-category. For accidents grouped in the “Inadequate Pre-Flight Planning/Inspection/Procedure” the “inadequate weather planning” sub-category accounted (p=0.036) for the elevated risk (OR 2.22) of an accident involving fatal and/or serious injuries. The “Violation FARs/AIM Deviation” category was also associated with a greater risk for fatal and/or serious injury (OR 2.59) with “Descent below the MDA/failure to execute the missed approach” representing the largest sub-category. Accidents in multi-engine aircraft are more frequent than their single engine counterparts and the decline (50%) in the turbine aircraft accident rate over the study period was likely due, in part, to a 6-fold increased representation of single engine airplanes.In conclusion, our study is the first to identify novel precursive factors for accidents involving turbine aircraft operating under 14CFR Part 91. This research highlights areas that should receive further emphasis in training/recurrency in a pre-emptive attempt to nullify candidate accident-precipitating factor(s).

Reducing Pesticide Drift by Considering Propeller Rotation Effects From Aerial Application Near Buffer Zones

&lt;p&gt;Off-target drift of chemical from agricultural spraying can damage sensitive crops, destroy beneficial insects, and intrude on human and domestic animal habitats, threatening environmental quality. Reduction of drift from aerial application can be facilitated at the edge of a field by offsetting spray ½ or 1 boom width from the field edge or by switching off one boom. For single boom application (and especially when spraying in a cross wind), there is some question whether off-target drift of sprayed crop protection agent is influenced by which boom is spraying and if direction of propeller rotation has any effect. An experiment was conducted to determine the effect of propeller wash rotation on aerial spray drift from turbine-powered aircraft. Spray samplers were placed at three sample lines to collect drift fallout and air-entrained particles 104, 134, 195, and 317 meters downwind, perpendicular to the flight path. An aqueous mixture of malathion was applied from the aircraft through fifty hollow cone nozzles. Five total replications were conducted over two days. Each replication had four treatment combinations of actively spraying boom and airplane direction. Results showed that neither active boom nor boom location (upwind or downwind) was statistically significant for either sampling method at the 0.05 level. Blocking the study to account for weather differences increased statistical precision. Thus when analysis was limited to the second day of testing, propeller wash direction was significant at the 0.10 level for the fallout sheets (P = 0.0773), and at the 0.05 level for high volume (Hi-Vol) air samplers (P = 0.0200). Higher concentrations occurred when propeller wash spiraled downwind. Based on results of this study, recommendations for pilots spraying with a single boom near a boundary is to spray so that propeller wash rotation occurs upwind.&lt;/p&gt;

Tradeoffs in Jet Inlet Design: A Historical Perspective

The design of the inlet(s) is one of the most demanding tasks of the development process of any gas turbine-powered aircraft. This is mainly due to the multi-objective and multidisciplinary nature of the exercise. The solution is generally a compromise between a number of conflicting goals and these conflicts are the subject of the present paper. We look into how these design tradeoffs have been reflected in the actual inlet designs over the years and how the emphasis has shifted from one driver to another. We also review some of the relevant developments of the jet age in aerodynamics and design and manufacturing technology and we examine how they have influenced and informed inlet design decisions

Thermal Barrier Coatings

If you've flown in a turbine-powered aircraft recently, you almost certainly flew in a plane that used thermal barrier coatings (TBCs) in the engines. What's more, if the plane you rode in used current generation turbine engines, the TBCs were included as a part of the initial engine design. This represents a significant change from relatively recent thinking, when TBCs were considered a "Band-Aid" solution to thermal management problems in turbines. The vast change in attitude is the result of one overriding factor: TBCs work.

Suction Fuel Systems for Turbine Powered Aircraft

Suction Fuel Systems for Turbine Powered Aircraft

Analytical method for designing turbine nozzle partitions

other conditions for providing a system circuit flow and keeping hot spots from occurring, it is anticipated that the hydraulic system would probably use a series of bleeds. That is, high-pressure fluid is diverted to the low-pressure side to produce system circulation. Usually -J to gpm flows are sufficient to accomplish the desired system temperature stabilizations. These system bleeds are now being used in certain present subsonic turbine-powered aircraft. Although some present high-temperature systems are using the MLO-8200 series of fluids, it is felt that these disiloxane based fluids have lower lubricity values than the petroleum based fluids. More than 4000 hr of operation have been conducted in laboratory tests with the MLO-7277 fluid in the 550°F range. Of this time, more than 250 hr were conducted on one test pump. The fluid used for this high-speed transport will be required to have thermal stability, inasmuch as there may be as many as four thermal cycles, or four Mach 3 flights/ 24-hr period. Care must be given to eliminate both air and water from the system to provide the correct system response and eliminate any possibilit}^ of spongy system operation.

Effects of Jet Fuel Spillage and Blast on Pavements

The author discusses challenges posed by jet fuel spillage and heat and blast on airport pavements as turbine-powered aircraft increasingly operate from civil airports.

International Civil Aviation Organization

The eleventh session of the International Civil Aviation Organization (ICAO) Assembly met in Montreal from May 20 to June 2, 1958. Represented at the meeting were 52 contracting states; two non-contracting states (the Soviet Union and Yugoslavia) sent observers, as did the UN, the International Labor Organization, and the International Air Transport Association. After statements by various delegations, the President of the ICAO Council reviewed the activities of the organization since the last Assembly meeting in 1956. He stated that the intervening period had been one of great activity in ICAO centering around preparations in all fields for the advent of turbine-powered aircraft. A specially created Jet Operations Requirements Panel had studied the requirements of the new long-range jet aircraft, and a Special Implementation Panel had been created by the Council. A preliminary study of the economic implications of long-range aircraft had been prepared by the Air Transport Committee and was being submitted to the Council. He stressed that while special attention was being given to the coming operations of jet aircraft, this emphasis should not cause the organization to disregard the continuous growth of aviation during 1956 and 1957. The technical assistance activity of ICAO had continued, during the period under review, to give important support to implementation through the assignment of experts and technicians and the training of students in countries where there were technical assistance missions, as also by granting fellowships and scholarships for study abroad.

Reply to Discussions of the Wright Brothers Lecture

A NUMBER OF THE POINTS raised in the discussion are concerned with the inherent restrictions on the operation of turbine-powered aircraft. As Mr. Kelly comments, if for any reason it becomes necessary to depart from the flight plan, there is, by comparison with piston-engined aeroplanes, much reduced flexibility of choice of operating speed and altitude. Mr. Hazen points out that some alleviation of this handicap is possible on a multiengined aeroplane by shutting down engines and, that with a coupled installation, this can be done without stopping propellers; so the need for an apology to the passengers would not arise. For an aeroplane with eight engines, for each engine shut down the best altitude falls by about 4,000 ft. at the expense of about 25 m.p.h. in cruising speed and an increase of about 4 per cent of fuel consumed. In any case, reserves must be carried to provide for the possibility of inadvertent engine failure. Whereas at first sight the procedure of selecting the best combination may appear to place an added burden on the flight crew, if ambient conditions are known, there is no ambiguity as to the right course of action. The argument Mr. Kelly used in his comparison of the net performance of aeroplanes powered with piston, turboprop, and turbojet engines is appropriate and can be extended to the case of greater ranges. I t emphasises the danger of too general a conclusion and the increasing need for tailoring an aeroplane for specific routes. For example, if intermediate stops are compulsory for refuelling, then, in addition to the effect on block speed, time is lost on the ground and the cruising speed at altitude is a quite unreliable measure for journey time. Also, the daily and seasonal variation of wind speeds, known to increase in velocity with altitude, may in some cases disproportionately penalise turbine aircraft with fuel reserves. The less flexible aeroplane suffers by its reduced ability to overcome adverse atmospheric conditions. In making a case for the use of turboprops for shortrange medium-altitude operation, Mr. Fink calls for a low-compression engine. I t appears likely that, in selecting the best engine characteristics, the value of the compression ratio should bear some direct relationship