A method for determining the water stability of a seaplane in take-off and landing

Abstract

A direct method of determining the water stability in take-off and landing of full-scale seaplanes is described. The customary method of measuring full-scale stability is by steady runs over a range of speed and attitudes. This is tedious ; it does not give the true take-off stability and does not give the landing stability. The steady-run stability is assumed to correspond very closely to the take-off stability but was originally used to obtain fun-scale conditions comparable with model scale. This report gives a method of analysis of take-off records of attitude against speed, and results Obtained by this method are compared with the steady-run results. Results on the Scion fitted with a ½ scale Sunderland hull and Saro with a 1/2.75 scale Shetland hull are used to establish the method, but it has also been checked against the available date on the full-scale Seal and Sunderland I. The take-off stability limits show remarkable agreement with the corresponding steady run limits (to within ½ dec) of the Scion and Saro. Evidence on the Seal and Sunderland is insufficient for a definite conclusion in these cases, but there is no disagreement between the results obtained. The method is accurate and quick to use, but takes no account of of the amplitude of porpoising so that a few steady runs would still be necessary to establish this where required. By use of this method the investigation of the stability characteristics of a seaplane under different conditions of weight, c.g. and flap angle can proceed quickly on the evidence of about eight take-off records at each condition, these records covering the full attitude range. The method may also be applied to find landing stability from landing records.