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James W. Telford

Abstract

Many directly measured aircraft performance details related to the unstable behavior of the Desert Research Institute's (DRI) research aircraft after ice accumulation, which led directly to its crash were recorded on its final flight. The data system, with the fully gimballed inertial platform, remained fully operational during the flight, including the final spiraling dive, with negative (upside down) accelerators. The observations show a reduced lift effect involving transition to what seems to be partial stall on the inboard wing. This effect induced, at onset, a reduction of the lift coefficient at a higher angle of attack and at a greater airspeed than was consistent with flight measurements before and after. When normal conditions were temporarily reestablished, lift returned. This anomalous behavior appears to have produced an equivalent to control reversal in pitch, in which forward pressure on the control column could have induced increased lift and a nose up response. This seems to have led to an extreme nose up climb, followed by stall and a deep negative angle of incidence spiral dive, from which recovery could not be effected. The evolution of such instability does not appear to be widely understood and seems to be an apt topic for further investigation. The possibility of its occurrence seems to be a point requiring a cautionary note.

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James W. Telford

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James W. Telford

Abstract

The theory of isolated turbulent plumes given earlier is used to study a field of plumes. Each plume is immersed in the turbulent downdraft which comprises the return flow. The field of flow is specified by three parameters: the heat flux into the atmosphere at the surface, the depth of the convecting layer, and the intensity of turbulence at the surface (where turbulence is steadily generated by the wind) and where a plume element which leaves the surface returns there in a downdraft after a period of the order of 103 sec. The change in air properties during this period is of the essence of the problem. Since the process is driven by the changing density resulting from heating, the equations describing the field must be time-dependent in this essential respect. Wind is neglected, and the horizontal pressure gradient assumed to he the same at all heights.

The derived plume properties-size, temperature excess, upward velocity and turbulent intensity-are in agreement with observation. The formulation predicts a maximum possible depth for convection in the form of a field of plumes, depending on the magnitude of the heat flux and surface turbulence. As a result, it is suggested that the theory of a field of plumes could lead to a prediction of the onset of a different form of convection, such as on a larger scale, resulting from instabilities in the convecting layer as a whole.

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James W. Telford

Abstract

Several atmospheric phenomena have been studied in the past in which buoyant fluid convects upward as a compact “blob” of cloudy or smoky air. In such volumes there is a strong updraft in the middle of the blob, and slower rising, or descending air around the outside. Such blobs of cooler diluted air are an important candidate dynamical entity for diluting cumulus and stratus clouds with dry air entrained from above; they have been identified in observations of marine stratus clouds.

In the past they have been studied in water tank experiments but no adequate theoretical description has been available. This paper presents a theoretical analysis that will allow formulation of the dynamical equations so they can be developed for use in nonself-similar conditions. The rising vortex, in the theoretical model for the self-similar buoyant blob, spreads at the same angle as observed in previous studies with water tank experiments.

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James W. Telford

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James W. Telford

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James W. Telford

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James W. Telford

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James W. Telford

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