From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison of Pegasus and Kestrel engine performance focusing on valve timing and port contours.
Identifier | ExFiles\Box 134\2\ scan0037 | |
Date | 30th May 1935 | |
-2- off with 8" of boost. This latter figure is very disturbing and indicates that if we are to run our engine at much higher speeds a big improvement in the orifice coefficient of our valving will be essential. Some of the differences between the two heads which may account for the difference in performance are as follows:- (a) Timing. Pegasus IO. 10°E.{Mr Elliott - Chief Engineer} EO. 66°E.{Mr Elliott - Chief Engineer} IC. 52°L. EC. 35°L. Kestrel IO. 20°E.{Mr Elliott - Chief Engineer} EO. 70°E.{Mr Elliott - Chief Engineer} IC. 50°L. EC. 5°L. The Kestrel timing is that used on the single cylinder test and the main difference between the two timings is the long duration of opening of the exhaust valve. The Aero Universal Unit will be of great use in investigating the effect of valve timing on m.e.p., although unfortunately it does not follow that the best timing on a single cylinder is the best for a main engine, particularly with inline cylinders. (b) Port Contours. The improvement in breathing capacity of the Ramp over the Standard Kestrel head was obtained merely by improved port shape as the valve sizes were the same. If this gain of 17% could be obtained at the first attempt to improve the porting it is only reasonable to assume that there is more to come, particularly in view of the Pegasus figures. We have already designed an alternative inlet and exhaust port for the Kestrel Ramp Head which is to be fitted to the Aero Universal Unit, and have in mind several other port contours which we wish to have flow tested, in the form of wooden models. An examination of a Pegasus cylinder head port, which incidentally is machined all over, will reveal an absence of any sharp edges where the valve seat inserts terminate as the inserts finish flush with the port face. Contd: | ||