Blown Flap Research Articles

Reduction of noise generated by flow of fluid over plate

This letter describes a method of reducing the noise generated by a fluid stream flowing subsonically over a plate and also presents some substantiating test data. This concept may prove useful for reducing the noise of STOL aircraft employing the externally blown flap or the augmenter wing, which configurations are now under exploratory development.

Reduction of Noise Generated by Flow of Fluid over Plate

This paper describes a method of reducing the noise generated by a fluid stream flowing subsonically over the edge of a plate and also presents some substantiating test data. This concept may prove useful for reducing the noise of STOL aircraft employing the externally blown flap or the augmenter wing, which configurations are now under exploratory development.

Fundamentals Regarding Reduction of Noise Arising from Jet Interaction with Deployed Lift-Augmenting Flaps

Proposed lift-augmented STOL aircraft are expected to require noise reductions on the order of 20 dB to meet community noise goals, according to a number of recent model studies. A predominant source of noise associated with the concepts and configurations currently under consideration is the interaction of the exhaust stream with deployed flaps. This flow-surface interaction produces both large-scale aerodynamic force fluctuations, which radiate like point dipoles at low frequencies, and smaller-scale surface pressure fluctuations, which radiate only from the leading and trailing edges of these surfaces. The fundamentals of the relevant noise-producing processes are reviewed and basic noise reduction concepts developed using parametric source models. Experimentally observed noise reductions on a 1/15 scale externally blown flap (EBF) system are presented for two of the noise reduction concepts—modification of the acoustic transduction process using variable impedance surfaces, and modification of the incident flow field through introduction of high porosity mesh grids upstream of the flaps.

Mean Flow and Pressure in a Straight Suction Duct with Deflected Inflow

SummaryThe momentum analysis of the mean flow of an incompressible fluid in a straight suction duct with porous walls dealt with in a previous paper is extended to account for deflection of the inflow towards a direction parallel with the axis of the duct. Ducts with a continuous distribution of porosity and ducts with a relatively small number of rather large ports are considered and the results are applicable to regions where the velocity and pressure can be assumed to be distributed uniformly across planes normal to the mean flow inside them. Some measurements made with a one-quarter full-size scale model of the straight and more or less regularly obstructed suction duct used in the boundary layer control system of a high-lift research aircraft show that at least part of the theory permits a reasonable prediction of pressures.

Basic investigation on an unswept rectangular wing with an externally blown flap

As far as we know, all work on externally blown flaps has been aimed at providing a basis for studies of the flight performance and handling qualities in respect of certain aircraft projects, one of which is the Dornier STOL transport aircraft. Theoretical work so far has only been possible in as much as the jet flap theory was extended to include any possible momentum distribution and finite jet thickness at the flap trailing edge. We know virtually nothing about the phenomenon of the jet flow spreading between the engine nozzle and the flap trailing edge. This question was studied on a simple wind tunnel model of an externally blown flap.

Externally blown flaps, aerodynamic feasibility study of a STOL‐transporter

TYPICAL STOL CHARACTERISTICS can be achieved for medium and heavy jet transport aircraft by means of externally blown flaps. As part of a project study conducted by Dornier AG., concerning a 40t STOL transport aircraft, the aerodynamic and flight mechanical feasibility is demonstrated. The basic data was supplied by wind tunnel tests with the model of a transport aircraft. With a view to V/STOL capability, the engine jet deflection was optimised by means of a novel slot flap design on a simple rectangular wing.

Circulation‐controlled Rotor Aircraft

THE successful development of the gas turbine powerplant made available large quantities of compressed air to the aircraft designer, who realised that the aerodynamics of the aircraft could be significantly modified by its use. This is currently used in naval aircraft where blown flaps have reduced the take‐off and landing speeds. Experimental aircraft have flown with higher lift coefficients on the wings than has been realised using blown flaps. One such aircraft is the B.A.C.‐Hunting 126 jet flap aircraft which uses an internal form of the jet flap. An alternative form of the jet flap has been suggested in America in which the efflux from jet engines mounted in pods below the wing is deflected on to the lower surface of conventional trailing edge flaps which deflect the gas flow and so form an external jet flap.

Blown Flaps for Stol Operation

There has been some speculation anions STOL aircraft designers (hat a net increase in lift might be realized from a combination of blown flap and slip‐stream deflexion. A recent wind tunnel investigation confirms the speculation for large flap deflexions. At small flap deflexions, however, the lift gained by the combination is less than the sum of the separate contributions. The effect at medium flap deflexion is dependent on the strength of the slipstream. These results should be applicable to most configurations with a blown plain flap in the slipstream behind the propellers.

Month in the Patent Office

In a boundary layer control system for applying different degrees of suction to openings 11, 12, 13, 14 at different spanwise locations along a wing, the respective suction openings are connected by pipes 61, 62, 63, 64 to the first four stages of an air compressor 27 through annular compartments 47, 48, 49, 50 of increasing diameter. The compartments are formed with inlet guide vanes 35, 39, 41, 32, together with supporting struts 43, 44, 45, 46. As shown the compressor 27 is coupled to a turbine 29 driven by the exhaust gases from a main engine 72, the inlet pipe 76 having a control valve 78 connected to a lever 79 operating a mechanism for controlling a variable‐area jet nozzle 79a, so that the area of the nozzle opening is automatically reduced when the exhaust is bled off to the turbine 29. If the number of suction openings is greater than the number of compressor stages, more than one opening may be connected to some of the stage inlets, throttling devices being fitted in some of the connexions if required.