The Recovery of an Aeroplane from a High Speed Dive: A Critical Manoeuvre Examined by a Step by Step Method and by Approximations

Abstract

Detailed step by step calculations have been made of the recovery with fixed elevator from a high speed dive for three different aircraft; for these calculations measured wind tunnel data were used. The aircraft differed markedly in the behaviour of their restoring margin Km=− (∂Cm/∂CL)M. The calculations demonstrated in all cases an initial, rapidly damped, short period oscillatory phase, a nearly constant value of ρV2 throughout the recovery, and subsequent to the initial oscillatory phase Cm was small. These results enable three different approximate methods for calculating the recovery after the initial oscillatory phase to be developed. The first is applicable where only a rough estimate of the recovery characteristics is required and the value of Km is about 0·3 or greater; it is very simple and quick to apply. The second is only a little more complicated and is found to give reliable results where Km is of the order of 0·1 or greater. The third method is the most complicated of the three but is still fairly simple and quick and it can be expected to give reliable results in all cases except where Km is appreciably negative for a considerable portion of the recovery. In the latter case, however, the aircraft is liable to be unstable and detailed step by step calculations or simulator studies are essential for an accurate assessment of the recovery. The main features of the initial oscillatory phase are satisfactorily predicted by Gates' manoeuvrability theory if the restoring margin Km is adequately positive (that is, greater than about 0·005) and if this factor docs not vary rapidly with Mach number at that stage. No detailed investigation has been made for aircraft diving at supersonic speeds; however, it seems likely that the general results of this investigation will still apply in such cases.

Citation

Young, A.D. and Neumark, S. (1958), "The Recovery of an Aeroplane from a High Speed Dive: A Critical Manoeuvre Examined by a Step by Step Method and by Approximations", Aircraft Engineering and Aerospace Technology, Vol. 30 No. 11, pp. 332-341. https://doi.org/10.1108/eb033037