Search results

The purpose of this paper is to analyze experimentally subsonic wake of a supercritical airfoil undergoing a pitch–hold–return motion. The focus of the investigation has been narrowed to concentrate on the steadiness of the flow field in the wake of the airfoil and the role of reduced frequency, amplitude and the hold phase duration.

All experiments were conducted in a low sub-sonic closed-circuit wind tunnel, at a Reynolds number of approximately 600,000. The model was a supercritical airfoil having 10% thickness and wall-to-wall in ground test facilities. To calculate the velocity distribution in the wake of the airfoil, total and static pressures were recorded at a distance of one chord far from the trailing edge, using pressure devices. The reduced frequency was set at 0.012, 0.03 and the motion pivot was selected at c/4.

Analysis of the steadiness of the wake flow field ascertains that an increase in reduced frequency leads to further flow time lag in the hold phase whereas decreases the time that the wake remains steady after the start of the return portion. Also, the roles of amplitude and stall condition are examined.

Examination of a pitch–hold–return motion is substantial in assessment of aerodynamics of maneuvers with a rapid increase in angle of attack. Moreover, study of aerodynamic behavior of downstream flow field and its steadiness in the wake of the airfoil is vital in drag reduction and control of flapping wings, dynamic stability and control of aircrafts.

In the present study, to discuss the steadiness of the flow field behind the airfoil some statistical methods and concept of histogram using an automatic algorithm were used and a specific criterion to characterize the steadiness of flow field was achieved.

The general reasons for considering a fresh approach to the calculation of air‐worthiness design tail loads and associated torques due to elevator‐induced pitching manoeuvres are discussed. Then follows a description of the manoeuvre itself, elevator actions to be assumed, and the proposed method of calculating the various response quantities. The analytical treatment of Czaykowski given to the unchecked manoeuvre is extended to cover the checked case in Appendix I, Part III and a comparison is made of the two types of manoeuvre. The application of the work to auto‐pilot feed‐back failure causing hunting of the elevator control is also dealt with. The effect of aircraft size, weight, e.g. position, forward speed and altitude on the various response quantities are discussed, with particular emphasis on the importance of the manoeuvre margin. To avoid possible confusion of terms the two types of elevator‐induced manoeuvre mentioned above and discussed in this paper are defined as follows:

IN a recent address Mr. S. J. Noel‐Brown, a work study consultant who is frequently called in by local authorities, said that 209 such bodies, out of a total of 1,800, had shown a lively interest in the subject. Of these many used outside consultants or had joined in group schemes. Some authorities, however, were still living in the quill pen era, scarcely having heard of typewriters. They were struggling along with laborious, out‐of‐date equipment.

IN this issue there is a Letter to the Editor (page 42). Its author is D. A. Barron, Chief Work Study Engineer of Marconi's Wireless Telegraph Co. Ltd., at Basildon. The letter is important from two aspects. Firstly, because it enables the writer of this column to clear up any misconceptions lingering in people's minds regarding references to Charles Bedaux in past editorials appearing in this journal.

This paper aims to propose a dedicated measurement methodology able to simultaneously determine the stability derivative C_mα̇ and the pitch damping coefficient sum C_mq + C_mα̇ in a wind tunnel using a single and almost non-intrusive metrological setup called MiRo.

To assess the MiRo method’s reliability, repeatability and accuracy, the measurements obtained with this technique are compared to other sources like aerodynamic balance measurements, alternative wind tunnel measurements, Ludwieg tube measurements, free-flight measurements and computational fluid dynamics (CFD) simulations. Two different numerical approaches are compared and used to validate the MiRo method. The first numerical method forces the projectile to describe a pure oscillation motion with small amplitude along the pitch axis during a rectilinear flight, whereas the second numerical approach couples the one degrees of freedom simulation motion equations with CFD methods.

MiRo, a novel and almost non-intrusive technique for dynamic wind tunnel measurements, has been validated by comparison with five other experimental and numerical methodologies. Despite two completely different approaches, both numerical methods give almost identical results and show that the holding system has nearly no impact on the dynamic aerodynamic coefficients. Therefore, it could be assessed that the attitude of MiRo model in the wind tunnel is very close to the free-flight one.

The MiRo method allows studying the attitude of a projectile in a wind tunnel with the least possible impact on the flow around a model.

Knight's Industrial Law Reports goes into a new style and format as Managerial Law This issue of KILR is restyled Managerial Law and it now appears on a continuous updating basis rather than as a monthly routine affair.

THE Rotol airscrew is the modern development of the Gloster‐Hele‐Shaw Beecham unit originally designed by Dr. Hele‐Shaw, developed by the Gloster Aircraft Company, and test flown in various aeroplanes some years ago. It is interesting to recall that this early British airscrew anticipated the present demand for constant‐speed control. The first models, which were arranged either for hydraulic or electric operation, had welded hollow steel or forged aluminium alloy blades; the current types, the constant speed and fully feathering hydraulic models, may be fitted with wooden blades. Unfortunately there are restrictions upon the publication of a description of the feathering airscrew, owing to a number of novel features in connexion with its design and construction, but it has been fully flight‐tested and will soon be on the Open List. However, the following description of the hydraulically operated constant‐speed model covers the latest details available for publication.

THE purpose of this paper is to give some account of the work on spinning and the progress which has been made since S. B. Gates and L. W. Bryant presented their paper to the Society, which was published in more comprehensive form by the Aeronautical Research Committee as R. & M. 1001.

After briefly outlining the main features of the variable‐pitch propeller, this paper proceeds to describe the development of the piston‐engined hydraulically operated propeller as a brake, both in the air and on the ground. Examples are given of the magnitude of the braking effort of a propeller when windmilling under controlled conditions and when in reverse pitch under power. The advent of the gas turbine, originally intended as a means of jet propulsion, opened up a new field of application for the variable‐pitch propeller and this application with its attendant problems and their solution is discussed. Three types of gas‐turbine power plant, together with the appropriate propeller arrangements are reviewed. These arc: (I) the direct‐connected turbine; (2) the compound‐compressor turbine; and (3) the free‐propeller turbine.

This article deals with some of the stability, control and handling problems that have arisen as a result of drastic changes in aircraft configuration coupled with the advent of supersonic flight at high altitude. The article will be published in two parts. The present part contains a brief introduction to the subject of aircraft stability and control in addition to a description of the longitudinal characteristics of supersonic aircraft. The second part will be published in our next issue, and will deal with the lateral characteristics of supersonic aircraft. Some of the problems encountered in the design of the flying control system for this type of aircraft and an indication of the methods and techniques used for solving the various stability problems are also presented in the second part.