Short Takeoff Vertical Landing Research Articles

Fire hazard identification on the flight deck of a short-take-off/vertical-landing type aircraft carrier: fire scenarios selection

ABSTRACT The flight deck of aircraft carriers in operation is exposed to fire risks which must be mitigated by fire safety measures such as firefighting and suppression systems. To develop advanced fire safety measures, the quantitative risk assessment and management is essential, where fire hazards must be identified in a probabilistic manner considering operational conditions (e.g. sortie generation rates) and site-specific ocean environmental conditions (e.g. humidity, wave and wind profiles). In this paper, a set of realistic fire scenarios on the flight deck of a hypothetical short take-off/vertical landing (STOVL) type aircraft carrier are selected, which shall be used for the quantitative fire risk assessment and management. Potential fire hazards are formulated as a function of random parameters associated with operational and ocean environmental conditions, and probabilistic sampling technique is used to select hundred fire scenarios. Fire exceedance diagrams are established in association with fire-impacted (leak) area through the selected fire scenarios.

Thermomechanical behaviour of airfield concrete pads supporting joint strike fighter F-35B

The Lockheed Martin F-35B Lightning II is the Short Take-Off/Vertical Landing (STOVL) aircraft variant of the joint strike fighter. The new dual-cycle propulsion system, which permits the STOVL operations, exposes the airfield pavements to extremely critical thermal conditions (temperatures exceeding 930°C and heating rate of about 85°C s−1). This study permitted to analyse the thermomechanical behaviour of an ordinary concrete pad during the F-35B aircraft vertical landing. The numerical analysis provided a detailed picture of the pavement stress state generated by the jet gases, opening the scenario to different planning solutions. The results highlighted how the damage, in the form of thermomechanical spalling, occurred in the top 2–5 mm of the pavement surface. One of the possible design solutions for high-performance vertical landing pads, supporting the F-35B aircraft, could be a two-layered pavement characterised by a thin (2.5 cm) fibre-reinforced Very High-Strength Concrete overlay.

Analysis of Heat Effects on Marine Corps AM2 Mat Mechanical Properties

Navy AM2 mats are used as portable aircraft landing platforms for the Short Take-off/Vertical Landing (STOVL) aircraft operations. This investigation presents the study performed to determine whether the surface discoloration is a precursor to degradation in the mechanical property of the AM2 mat material. The red discoloration on the mat surfaces had a clear correlation with the decrease in yield strength, ultimate strength, and hardness properties.

An unsteady, moving mesh CFD simulation for Harrier hot-gas ingestion control analysis

Hot gas ingestion (HGI) can be a problematic feature of short take-off vertical landing (STOVL) aircraft during the descent phase of landing, or while on the ground. The hot exhaust gases from the downwards pointing nozzles can be re-ingested into the engine intakes, causing power degradation or reduced engine surge margin. The flow-fields that characterise this phenomenon are complex, with supersonic impinging jets and cross-flows creating large ground vortices and fountain up-wash flows.A flow solver has been developed to include a suitable linear mesh deformation technique for the descending aircraft configuration. The code has been applied to predict the occurrence of HGI, by simulating experimental results from a 1/15th scale model of a descending Harrier. This has enabled an understanding of the aerodynamic mechanisms that govern HGI, in terms of the near-field and far-field effects and their impact on the magnitude of temperatures at the engine intake.This paper presents three sets of CFD results. First a validation exercise shows predicted results from the twin-jet with intake in crossflow test-case. This is an unsteady Reynolds averaged Navier Stokes (URANS) solution for a static geometry (there is no moving mesh). This allows comparison with experiment. Secondly, a full descent phase URANS Spalart-Allmaras (SA) turbulence model calculation is done on an 8·5m cell mesh for half the flow domain of the Harrier model and test-rig without dams/strakes. This shows how the HGI flow mechanisms affect the engine intake temperature profiles, for the case where there are no flow control methods on the underside of the aircraft. Thirdly, the full descent phase URANS SA turbulence model calculation is done on a 22·4m cell mesh for the full flow domain of the Harrier model and test-rig, with the dam/strake geometry included in the structured mesh region.

Control Optimization of the Transient Performance of the Selective Bleed Variable Cycle Engine During Mode Transition

The transient performance of the selective bleed variable cycle engine (VCE) has been optimized during the transition from subsonic to supersonic mode. The selective bleed VCE concept has been developed with a short take-off vertical landing (STOVL) aircraft in mind and the engine is characterized by its twin mode VCE feature. The transition optimization is constrained by the requirement of maintaining thrust and compressor surge margins. The engine variable geometry component schedules and the fuel flow are used as optimization variables. A differential algebraic formulation of an inter-component volume model is used to model the transient behavior of the engine. Sequential quadratic programming (SQP) is applied to the nonlinear transient engine model directly, in order to solve the multivariable control problem. It is predicted that the mode switch can be carried out safely without violating the constraints and that the time required is limited by the actuator time of the hydraulic system.

Design of a wide envelope controller for a STOVL gas turbine engine

ABSTRACT This paper describes a novel approach to the design of a control system for a short take-off, vertical landing (STOVL) aircraft gas turbine engine. A multi-level multiobjective genetic algorithm (MOGA) is employed to design controllers at both individual operating points, using system linearisations and small signal response characteristics, and over the full-flight envelope, using a nonlinear model and large signalresponses. The proposed approach should allow the selection of smoother controller parameters over the flight envelope and ensure that more consistent control demands are made at off-design operating points.

Calculations of hot gas ingestion for a STOVL aircraft model

Hot gas ingestion problems for STOVL (Short Take-Off, Vertical Landing) aircraft are typically approached with empirical methods and experience. In this study, the hot gas environment around a STOVL aircraft was modeled as multiple jets in crossflow with inlet suction. The flow field was calculated with a Navier-Stokes, Reynolds-averaged, turbulent, 3D CFD code using a multigrid technique. A simple model of a STOVL aircraft with four choked jets at 1000 K was studied at various heights, headwind speeds, and thrust splay angles in a modest parametric study. Scientific visualization of the computed flow field shows a pair of vortices in front of the inlet. This and other qualitative aspects of the flow field agree well with experimental data.

A Large Hemi-anechoic Enclosure for Community-Compatible Aeroacoustic Testing of Aircraft Propulsion Systems

A large hemi-anechoic (absorptive walls and acoustically hard floor) noise control enclosure has been erected around a complex of test stands at the NASA Lewis Research Center in Cleveland, Ohio. This new state-of-the-art Aeroacoustic Propulsion Laboratory (APL) provides an all-weather, semisecure test environment while limiting noise to acceptable levels in surrounding residential neighborhoods. The 39.6 m (130 ft) diameter geodesic dome structure houses the new Nozzle Aeroacoustic Test Rig (NATR), an ejector-powered M = 0.3 free jet facility for acoustic testing of supersonic aircraft exhaust nozzles and turbomachinery. A multi-axis, force-measuring Powered Lift Facility (PLF) stand for testing of Short Takeoff Vertical Landing (STOVL) vehicles is also located within the dome. The design of the Aeroacoustic Propulsion Laboratory efficiently accomodates the research functions of two separate test rigs, one of which (NATR) requires a specialized environment for taking acoustic measurements. Absorptive fiberglass wedge treatment on the interior surface of the dome provides a hemi-anechoic interior environment for obtaining the accurate acoustic measurements required to meet research program goals. The APL is the first known geodesic dome structure to incorporate transmission-loss properties as well as interior absorption into a free-standing, community-compatible, hemi-anechoic test facility.

Pegasus‐Powered Harriers Join the Italian Navy

PEGASUS‐powered Harrier aircraft are set for an active first year of service with the Italian Navy, introducing this new Harrier customer to the operational benefits of fixed‐wing STOVL (short take‐off, vertical landing) air power.

Integrated Propulsion System Requirements for Control of STOVL Aircraft

This paper describes an evaluation of propulsion system requirements and capability for a Short Take-Off/Vertical Landing (STOVL) aircraft employing modulation of the propulsive lift distribution for pitch and roll control in hover. The effects of propulsive lift nozzle configuration and propulsion system dynamic response were evaluated using a combined system simulation consisting of a six degree of freedom aircraft model, engine model, and integrated flight/propulsion control. The response and stability of propulsive lift control are compared with control by reaction jets supplied by engine bleed. Aircraft performance is demonstrated in simulated STOVL maneuvers using a dynamic pilot model. The conclusion of this study is that propulsive lift control of aircraft pitch and roll is feasible and can provide as much as a 10 percent increase in engine lift rating over systems that employ reaction control alone. The dynamic response of practical propulsive lift configurations, however, is less than that of reaction control configurations, which must be offset through integration of the propulsion system and its control.

Three-dimensional turbulent flow code calculations of hot gas ingestion

The development of short takeoff, vertical landing (STOVL) aircraft has historically been an experiencebased endeavor. In this study, a three-dimensional turbulent flow computational fluid dynamics (CFD) code was used to calculate the hot gas environment around a STOVL aircraft operating in ground proximity. Preliminary calculations are reported herein for a typical STOVL aircraft configuration to identify key features of the flowfield and to demonstrate the capability of a current three-dimensional CFD code to calculate the temperature of the gases ingested at the engine inlet for typical flow and geometric conditions.

STOVL engine/airframe integration

A capable, supersonic, Short Takeoff, Vertical Landing (STOVL) tactical combat fighter aircraft must have a highly integrated engine and airframe. Vertical landing and short takeoff with powered lift require dividing engine flow between front and rear nozzles for resultant vertical thrust through the aircraft center of gravity. Several effects of exhaust jets can influence cycle selection and system configuration. These considerations affect engine location, special exhaust nozzle systems, cycle bypass ratio, aircraft supersonic drag, engine fuel consumption, and dry-engine thrust. In jet-borne flight, the aircraft pitch, roll, yaw, and altitude control are provided by modulation of front and rear exhaust thrust and compressor bleed. Satisfying these demands is challenging, but good solutions are being found in ongoing design studies initiated September 1986 by NASA and the Department of Defense. Even though a bypass ratio of about 1.0 may be needed for hover thrust balance, emerging engine technologies allow fan pressure ratios of 4 to 5. Resulting high pressures in front ducts and nozzles minimize frontal area, provide high specific thrust, and reduce fuel consumption for high combat thrust levels. New materials and structural concepts reduce the weight of aircraft, engines, and vectoring STOVL nozzles. Digital electronic controls enable the necessary integration of propulsion flight controls.

Trends in Military Aircraft Propulsion

The major factors determining the choice of engine cycle for a combat aircraft are the requirements of the design mission and those of aircraft speed and agility. The requirement for jet-borne flight in short take-off vertical landing (STOVL) aircraft imposes further demands on cycle and configuration. The changing nature of combat aircraft requirements is the reason for changes in engine design. Specific thrust is shown to be the major parameter defining engine suitability for a particular role. An examination of mixed turbofan characteristics shows that specific thrust is also the key to understanding the relationships between engine characteristics. The future development of combat engines is discussed, in particular the implications of stoichiometric limits on cycle temperatures and the benefits of variable cycle engines are examined. Recent work on advanced STOVL (ASTOVL) aircraft is reviewed and aircraft/engine concepts designed to meet the requirements of the role are assessed. Experience shows that the technology for these advanced engines must be fully demonstrated before production to minimize the risks and costs of the development programme.