Aircraft Design最新文献

The flow over multi-element airfoils with flat-plate lift-enhancing tabs was numerically investigated. Tabs ranging in height from 0.25 to 1.25% of the reference airfoil chord were studied near the trailing edge of the main element. The two-dimensional numerical simulation employed an incompressible Navier–Stokes solver using a structured, embedded grid topology. The effects of various tabs were studied at a constant Reynolds number on a two-element airfoil with a slotted flap. Both computed and measured results indicated that a tab in the main-element cove improved the maximum lift and lift-to-drag ratio relative to the baseline airfoil without a tab. Computed streamlines revealed that the additional turning caused by the tab may reduce the amount of separated flow on the flap. A three-element airfoil was also studied over a range of Reynolds numbers, with computed results shown to be in good agreement with experimental data.

The results of five graduate classroom design teams are reviewed in order to assess the feasibility of carriercapable tactical waverider-configured aircraft designed for cruise Mach numbers in the range 3≤M_∞≤5. The efforts of the design teams suggests that such aircraft are probably feasible for combat radii of $\text{580}\text{nm}\text{<R<1500}\text{nm}$. Low-speed research to support the development of such aircraft indicates that within the subsonic flight regime, waverider planforms may be statically unstable, vortex lift may be less strong for waverider configurations than for similar simple delta wing planforms and lift, drag and pitching moment data appear to be well behaved within a large (−20°≤α≤20° data shown herein) angle-of-attack range.

Adverse flow environments pose challenging design constraints in aircraft engine components and component interactions. Some examples of such flow environments are: steep pressure gradients, random and periodic unsteadiness, shock wave interactions and 3-D boundary layer separation. These adverse flow environments and interactions promote the growth of various kinds of instability waves inherent in gas turbine engines, e.g., vorticity wave, entropy wave and acoustic or pressure wave instabilities. A series of smart subsonic and supersonic flow controllers are presented with applications to the design of aircraft gas turbine engine components. They are on-demand vortex generators capable of injecting co- and counter-rotating streamwise vortices in subsonic, transonic and supersonic flow. The strength and location of the vortex is a control variable and must be optimized via a closed-loop control algorithm. The subsonic smart VG assumes a ramp-type geometry (similar to Wheeler vortex generators) and the smart supersonic VG is a tailored cavity with a movable flap concealing the cavity. The movable flap is actuated inward to expose the cavity to transonic or supersonic flow. The depth of the cavity is controlled via a closed-loop feedback control system which ties the strength of the vortex to the “desired” performance as measured by one or more sensors. Candidate cost functions are proposed in the optimization routine for each component in a gas turbine engine.

A two-dimensional numerical investigation was performed to determine the effect of a Gurney flap on a NACA 4412 airfoil. A Gurney flap is a flat plate on the order of 1–3% of the airfoil chord in length, oriented perpendicular to the chord line and located on the airfoil windward side at the trailing edge. The flowfield around the airfoil was numerically predicted using INS2D, an incompressible Navier–Stokes solver, and the one-equation turbulence model of Baldwin and Barth. Gurney flap sizes of 0.5%, 1.0%, 1.25%, 1.5%, 2.0%, and 3.0% of the airfoil chord were studied. Computational results were compared with available experimental results. The numerical solutions show that some Gurney flaps increase the airfoil lift coefficient with only a slight increase in drag coefficient. Use of a 1.5% chord length Gurney flap increases the airfoil lift coefficient by ΔC_l≈0.3 and decreases the angle of attack required to obtain a given lift coefficient by Δα_L=0>−3°. The numerical solutions show the details of the flow structure at the trailing edge and provide a possible explanation for the increased aerodynamic performance.

It is stated in most flight dynamics texts that the phugoid approximations provide poor estimates while the short period approximations are accurate. The survey in this paper reveals that there are at least five approximations to the phugoid. The extent of departure of each of these from the exact value is determined for a fairly extensive database representing various aircraft in different flight conditions. It is found that most of them are inadequate in predicting the phugoid characteristics accurately. Nonetheless, two approximations to the phugoid frequency that seem to have remained unnoticed are seen to be exemplary. On the other hand, no worthy approximation exists for the phugoid damping. With this background, a fresh approximation for the phugoid mode is put forth herein. It is derived by equating the coefficients of the product of the short period equation (which has been shown to be very accurate) and the phugoid equation (as yet unknown) to the coefficients of the fourth-order characteristic polynomial. The new approximation is shown to be accurate.

The United States Navy needed a replacement for aging T-39 Naval Flight Officer (NFO) training aircraft. NFOs perform radar and navigation functions on Navy aircraft. It was decided that conversion of FAA certified business aircraft would be the most economical approach. They also upgraded the ground-based training systems. The Cessna Aircraft Company won the competition, proposing the Citation Model 550 which had to be heavily modified to meet the rigorous training requirements, including high G air intercept maneuvers and high-speed low-level flight. Wing, tail, tailcone, and windshield beef-up and higher thrust engines resulted in a new FAA certification and a new model number assigned to the aircraft as well as the Military T-47A designation. The interior of the aircraft was changed to accommodate an instructor, two students in the cabin and one in the copilot position. The copilot instrument panel was dominated by the radar display similar to Navy attack aircraft and the airplane was flown single pilot. Cessna, on its own initiative, performed a full-scale fatigue life test and gathered field service data to prove the design was satisfactory. The Navy declared the T-47A training system was the most successful during the T-47A tenure.

The aim of this paper is to introduce a risk analysis procedure to be applied when a completely new project is to be started. The object of the analysis is a new aircraft project carried out in the Aerospace Department of the Polytechnic of Turin. This project is quite unusual not because of the involved technology but for the very big dimensions (take-off weight=1350 t). This procedure can indicate the industrial risk level whether the project will be developed further.

Current Air Force, Navy, and Marine Corps fighter/attack aviation aircraft are 1970s-vintage designs which will reach the ends of their service lives in the early part of the next century. While the Air Force is developing the highly-advanced F-22, it cannot be used to replace all current assets, especially F-16’s, simply due to cost. A “low-end” complementary design is required, much as the F-16 was the “low” of a “high-low mix” with F-15’s. The Navy’s F-18 E/F will have improved characteristics compared to earlier versions, but it does not fully utilize newer technologies and specifically will not have the attainable levels of stealth and range-payload performance, nor will it offer next-generation STOVL capability for the Marines. RAND’s Project Air Force conducted research into the tradeoffs in requirements specification for a next-generation attack fighter during the period from 1993 to 1995. As a part of that, this author developed and analyzed a representative notional design concept for a Next-Generation Attack Fighter (NGAF), then conducting trade studies of range, performance, payload, and technologies, followed by study of alternative approaches to attaining tri-service capability.

This paper presents a flexible and relatively fast analytical method to carry out the off-design analysis of a powerplant installation for a supersonic transport aircraft (bypass engines). The procedure does not impose any constraints on the operating points of the turbines (like, for instance, requiring them to remain choked), except those corresponding to actual physical limitations, such as bounds on the compressor exit temperature and the turbine entry temperature. The result of the procedure is a single, closed-form expression that yields an off-design operating point of the engine at a given Mach number, altitude and low-pressure turbine pressure ratio.