Browse Topic: Cowlings
Helicopter tail shake constitutes a significant limitation to both passenger comfort and aircraft stability. Under powered descent conditions, elevated Angle of Attack (AoA) cause flow separation around the rotor hub and engine cowling, leading to the development of an unsteady wake dominated by large-scale turbulent structures. To support the helicopter tail shake phenomenon investigation, a dedicated Particle Image Velocimetry (PIV) experimental setup was designed in this work, together with four aerodynamic devices aimed at mitigating tail shake. These components were then tested through a wind tunnel campaign with the PIV setup. The proposed aerodynamic components were conceived to either deflect the hub wake away from the tail empennages or to decrease the Turbulent Kinetic Energy (TKE) within the wake. To achieve these objectives, a dorsal fin, a horse-collar, and two spoiler configurations inspired by automotive applications were designed and experimentally evaluated. The devices were tested both as standalone solutions and in combined arrangements on a scaled helicopter wind tunnel model featuring a rotating hub and blade shanks. The vertical velocity component, was used as an indicator of wake deflection, and the Turbulent Kinetic Energy was used as an indicator of wake turbulence. The Horse Collar and the Large Spoiler showed a reduction in both indicators suggesting possible tail shake mitigating capabilities, and additional improvements were achieved when the two devices were deployed in combination.
The bird strike performance of the flight critical components of a rotorcraft is to be proved. The study investigates the bird strike performance of the cowling structure through experiments and simulations by considering a Building Block Approach. Based on this approach, bird impact tests on a rigid plate and composite panels are performed to validate Smoothed Particle Hydrodynamics method (SPH) bird model and composite material model in LS-DYNA. The composite material properties are obtained from the coupon level test results. After the composite material model is calibrated and validated, the bird strike performance of the cowling structure at critical locations is assessed. A good correlation between the experimental and numerical results was obtained at coupon, sub-component and component levels. The developed composite material modeling technique and validated bird models may be used in showing bird resistances of other airframe components of similar structure of the rotorcraft.
The multi-role utility helicopter T625 GÖKBEY is designed by Turkish Aerospace and it is equipped with a pair of two-spool CTS800-4AT turboshaft engine developed by Light Helicopter Turbine Engine Company (LHTEC). Components of the cowlings, intakes and exhausts were designed with supplementing CFD analyses and performance of various alternatives were evaluated. Final designs were achieved based on the helicopter performance and engine limits. In order to verify the estimated engine installed performance in design phase, performance of the instrumented engine with its integrated equipment on the platform is examined using flight test data. This paper focuses on the CFD simulations based performance predictions of the air induction system, exhaust system, and IPS blower exhaust. A comprehensive study is assessed to create more realistic models by using flight test data.
The Electroimpact Automatic Fan Cowl Riveter exhibits new and unique design features and automated process capabilities that address and overcome three primary technical challenges. The first challenge is satisfying the customer-driven requirement to access the entire fastening area of the fan cowl doors. This necessitates a unique machine design which is capable of fitting ‘inside’ a fan cowl door radius. The second challenge is determining drill geometry and drill process parameters which can produce consistent and high-quality countersunk holes in varying mixed-metal stack-up combinations consisting of aluminum, titanium, and stainless steel. The third challenge is providing the capability of fully automatic wet installation of hollow-ended titanium rivets. This requires an IML-side countersinking operation, depositing sealant throughout the OML and IML countersinks and the hole, automatically feeding and inserting a rivet which is only 5mm long and 6mm in head diameter and flaring the rivet tail to a ‘sub-flush’ condition.
The H160-B is the latest helicopter design from AIRBUS HELICOPTERS with the extensive use of sandwich technology in the airframe. A sandwich with face sheets from CFRP and honeycomb cores is a robust outer skin of a helicopter. Furthermore it shows a very good tolerance to impact damages and a very good reparability. At Airbus Helicopters great experience is available which is required to understand and to control all manufacturing parameters, that are driving the quality of such parts. Powerful inspection technologies are in place to maintain the high level of manufacturing quality. In this paper an overview of the parts on this Helicopter made with sandwich technology will be given. These are cowlings and structural parts as well as principal structural elements (PSE) on main load paths. The respective certification requirements and related means of compliance demonstrations will be explained in detail. Special attention is paid to the applied methods for the damage tolerance demonstration of sandwich. The design and strength analysis was done with a combination of FEM analysis and analytical method, using basic allowable derived and validated by tests.
In the modern automobile scenario in developing countries, customers are getting more meticulous and market more competitive. Now even the budget vehicle customer expects desirable vehicle performance in specific use cases of the vehicle that were previously not focused by designers. Hence, the focus on perceived quality challenges automobile engineers to go the extra mile when it comes to the cost-effective design of parts that are tangible to the customer. A vehicle's cowl cover is one such exterior component. The primary functions of this part are to provide air intake opening for the HVAC system and cover the components like wiper motor. The aesthetic function is to cover the gaps between windshield, hood, and fender as seamlessly as possible. A specific role of cowl cover, which calls for a designer's attention, is its load-bearing capability. This component has to be stiff enough to bear external loads like snow accumulation or application of hand on the part by customer or service personnel. Simultaneously, it plays a significant role in absorbing the energy of a pedestrian's head impact during a crash. This engenders a need to optimize the cowl cover design for energy absorption in one direction and deformation resistance in another direction. This paper explains the methodology in which a cowl cover can be designed to cater to the need for directional load bearing without adversely affecting the pedestrian impact performance of the part. With the help of FEA, cost-effective design approaches for improving the stiffness of cowl cover assembly are studied, and their effect on pedestrian energy absorption is checked. Finally, the study identifies and discusses the concepts which have favorable stiffness with a limited impact on pedestrian energy absorption.
A large amount of heat generated in the engineering compartment in a hovering helicopter may lead to premature degradation of inner skin of its engine cowling and cause serious failure on the engine cowling. This study proposes a solution of improving heat resistance of the helicopter engine cowlings by replacing the currently used intumescent coating with a ceramic coating material, Cerakote C-7700Q. Oven and flame tests were designed and conducted to evaluate the heat resistance of Cerakote C-7700Q. The test results show that the currently used painting scheme of the engine cowlings failed the 220°C oven test while after replacing the epoxy seal coat with the Cerakote, the new painting system passed the 220°C test in regards to painting bubbling. Based on that, a new painting scheme with C-7700Q implemented was recommended. It is suggested that the most time- and cost-effective solution to improve thermal performance of the helicopter engine cowlings is to repaint the current engine cowlings with the proposed new three coating system of Cerakote, surface protection HS7072-622, and intumescent paint as a fireproof lacquer. This study also explains why serious appearance defects occurred in the inner skin of the engine cowling when the aircraft is hovering. The present work can be converted to a design project for senior mechanical engineering students to develop their design and teamwork skills and enhance their capacity for solving real-world engineering problems.
Within the framework of NACOR project in CleanSky 2 AIRFRAME ITD, ONERA and DLR performed parallel investigations dealing with the RACER high-speed demonstrator, and especially with its tail parts, each partner respectively focusing on vertical fins (ONERA) and horizontal stabilizer (DLR). During this design phase, most of the CFD simulations were steady-state and neglected the effect of the rotor (or rotor-head) and of the propellers. It however turned out that the rotor-head had a significant effect on the vertical fins and that it was essential to take into account its rotation in time-accurate simulations: the wake from the rotor-head, the upper deck and the engine cowlings indeed strongly impacts the left vertical fin because of the clockwise rotation of the rotor-head. It induces strong oscillations on the tail unit loads, and the mean tail unit lateral thrust is also significantly increased. Moreover the main conclusions of this 'aerodynamic interactions' investigation are almost identical, no matter what the computed configuration: rotating rotor-head, rotating rotor-head with actuator-disk, rotating full-rotor or rotating full-rotor with propellers effect.
The effective cooling of a two wheeler scooter engine depends on the efficient performance of the cooling fans. In scooters, centrifugal fan with axial air inflow and radial outflow with either backward curved or forward curved blades are used. The air flow enters the unit axially and then spreads out turning to 90 degrees into radially outward direction before meeting the engine. The work aims at the study of performance characteristics of the forward and backward curved fans when put in to engine cowling and to compare the power consumed and flow delivered by the fans. The objective is to compare and reduce the power consumed by the cooling fans and to increase the air flow velocity across the engine surfaces. A Conjugate Heat Transfer analysis has been done to study the effect of forward and backward cooling fans on flow delivered, power consumed and engine surface temperature. RANS K-Epsilon two equation turbulence model was used to solve the 3-D numerical model. Moving Reference Frame (MRF) model was used to simulate the rotary motion of the fan. The engine cowling geometry was modified to avoid recirculation near the fan region and to have flow expansion near the engine head and block. An experimental validation of the fan with the modified cowling profile is done for flow rate, power consumed, temperatures across the fin surfaces. The power consumption was reduced by 31.27% (80 Watts @ 8000 RPM) by the optimized fan for the same operating point. A complete numerical methodology has been developed for the selection of fan for effective engine cooling.
To improve the performance and durability of two-stroke engines, temperature of the liner/block is an important parameter, which needs to be optimized. In this paper, an attempt is made to measure and investigate the maximum liner temperature of a forced-air-cooled two-stroke engine. The vehicle was tested on both chassis dynamometer and test track to identify the maximum liner temperature during operating conditions. Thermocouple locations were selected at or near the hot spots (TDC & Exhaust port) in the cylinder block. The chassis dynamometer test revealed that the maximum liner temperatures for the test vehicle were near the exhaust port reference position (34 mm from the top face of cylinder block) and TDC reference position (8 mm from the top face of cylinder block near the exhaust port). The Computational Fluid Dynamics (CFD) simulation was used to study the flow pattern around the block and the results revealed that design modifications can be done on the base cowl to improve and optimize the cylinder block liner temperature. Hence, the base cowl was experimentally modified using prototype cowls and was tested on chassis dynamometer to verify the temperature reduction. The target of reducing the maximum liner temperature for the test engine below the critical value (240°C) was achieved using the finalized experimental prototype cowl. Confirmation trials on the test track for the finalized prototype cowl demonstrated that there was a temperature reduction of 9% at exhaust reference position and 5% at TDC reference position.
In-flight icing occurs when supercooled water droplets suspended in the atmosphere impinge on cold aircraft surfaces. Thin layers of accreted ice significantly increase aerodynamic drag while thick layers of ice severely alter the aerodynamics of control surfaces and lift. Chunks of ice can break away from the airframe and cowlings and be ingested into engines causing considerable damage. Developing durable surfaces that prevent the nucleation of supercooled water or reduce ice adhesion to a point where airstream shear forces can remove it would allow the design of a more robust, energy efficient deicing/anti-icing system for aircraft and other applications. In this work, a simulations based framework is developed to predict anti-icing performance of various nanocomposite coatings under the in-flight environment. The intrinsic multiscale feature of our model allows a rational design of durable anti-icing coatings targeting different (macroscale) structures in an aircraft body through tailoring (nano to microscale) material chemistry and surface morphology. This work is an integral part of the Aerospace Simulations and Optimization Platform (AESOP) currently being developed for aerospace materials design.
The main objective of this work is to investigate, by means of numerical simulations, the performance of the engine nacelle ventilation cooling system of a helicopter under hover and forward flight conditions, and to propose a simplified method of evaluating the performance based on rotor downwash flow by taking the synthetical effect of engine nacelle, exhaust ejector and external flow of a helicopter into account. For the engine nacelle of a helicopter, an integrated model of the nacelle and exhaust ejector was set up including the domain of external flow. The unstructured grid and finite volume method were applied for domains and control equations discreteness, and the standard k-ε model was applied for solving turbulent control equations. Using the business CFD software, the flow field and the temperature field in the nacelle were calculated for single inlet scheme and double inlets scheme, total up to 9 schemes. The performance of the exhaust ejector was computed. And the influence on the ventilation cooling performance of the nacelle was analyzed for different inlet number, inlet size and inlet position. The comparisons were completed between flight trials and numerical simulation results, and they show good agreement. The results show that the method can predict the performance of the ventilation cooling system of the nacelle. Moreover, the study indicates that, for the same inlet scheme, the temperature of the nacelle in forward flight is lower than that under hovering condition, but the pumping coefficient of the exhaust ejector in forward flight is higher. The inlet position should avoid being located on the underside of the cowl. It is also indicated that the simulation results can be regarded as a reference for the design and optimization of the system.
This paper talks about using an approach to simulate snow mass falling from roof of cab on the cowl tray of a commercial truck and predicting the durability life of the cowl tray based on this loading. It has always been a challenge for analysts to model the behavior of snow/slurry in dynamic simulations especially where the area of concern is structure and not the fluid. The conventional approach followed in most industries would be either to model snow as soft rubber or to divert from the conventional Lagrangian algorithm for mesh movement towards Eulerian method (or ALE algorithm). Although modeling snow as soft rubber captures the basic physics of the problem, it is not able to correctly simulate the fluid structure interaction behavior and the pressure wave movement inside the snow/slurry when it comes in contact with the structure. This is a big shortcoming as the reverberating motion of pressure wave inside the fluids causes cyclic loading of the structure which raises durability issues in the structure. On the other hand, Eulerian or Arbitrary Lagrangian-Eulerian-algorithm is computationally expensive and more fluid oriented than structure oriented. The method presented in this paper talks about a unique approach where snow has been modeled using null elements with equation of state defined. The simulation captures the physics of the problem to a good level of detail and is a good approach for simulating fluid-structure interaction behavior where the primary area of concern is the structure.
Progressive demand being placed on more efficient and quite engines require engine subsystem to be optimized without compromising their performance. Cooling system is one of the important engine sub system to be optimized to achieve better performance with reduced noise levels and with minimum power consumption. In the present paper an effort is made to optimize a fan-driven air-cooling system for a small 4-stroke scooter engine. Complete three-dimensional analysis has been done with commercially available computational fluid dynamics (CFD) codes. Analytical results are validated with the experimental results. A good correlation has been observed between analytical and experimental results. The work is done in two phases. In the first phase, complete flow and heat transfer analysis of the present system has been done. Flow analysis revealed flow blockage, significance of leakage through various parts of the cowling, and separation of the flow inside the vane passages of the fan. In the second phase, the system is modified to minimize the leakages and streamlining the flow inside the cowling. Vane layout of the fan is changed to decrease the fan power consumption and fan loses. Improvement in the efficiency of the cooling system without compromising on engine performance has been achieved. Quantitatively, a decrease of 43% fan power consumption and 3 dB of the noise level have been achieved.
The penetration of rainwater through the heating ventilation and air conditioning system, HVAC, of a vehicle directly affects the provision of thermal comfort within the vehicle passenger compartment. The first element of a typical HVAC system, namely the cowl box is considered. The purpose of the airway from the cowl grille openings to the air filter, immediately before the blower, is to ensure proper water separation from the incoming air stream before entry onto the air filter and onwards into the rest of the HVAC system. This is achieved by ensuring standing water within the cowl is quickly drained and that water rain droplets or water flows from the windshield and body are separated from the air stream, hence minimising the effect on the total system volumetric flow rate. An experimental study is conducted to examine the effect of plane baffles on the airflow filed within a rectangular duct. A set of plane baffle plates is placed within the cowl duct. Flow visualisation methods are used to acquire the airflow properties within the rectangular duct. The experimental observations and measurements are compared to results of numerical simulation employing the finite-volume method and assuming a fully developed flow. Good agreement is found between measured and computed velocity profiles.
The company finalizes development of the Sovereign and prepares it for FAA certification, which is expected late this year. Engineers at Cessna Aircraft Co. recently conducted the first engine run for the Sovereign. The aircraft's power plant is one of the few remaining systems being tested prior to first flight, which is scheduled for early spring. FAA certification is expected to be awarded in late 2003, with customer deliveries beginning in early 2004. The Sovereign will be powered by two Pratt & Whitney PW306C engines, each with a takeoff thrust of 5686 lb flat-rated to ISA +15°C, enabling a cruising speed of up to 444 kts. Controlled by dual Full Authority Digital Electronic Control (FADEC) systems and using a single-pivot thrust reverser design, the engine has 3000 h HIS and 6000 h TBO maintenance intervals. The company has finalized the design of the aircraft's engine nacelle assembly, which consists of the engine cowling, inlet assembly, throttle quadrant, and thrust reverser. The engines were certified in May 2001 and were installed on the prototype airframe in November.
This Aerospace Recommended Practice (ARP) outlines the basic general design considerations for aircraft towbars.
Items per page:
50
1 – 50 of 83