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).
Options for increasing engine capacity and performance at altitude.
| Identifier | ExFiles\Box 179b\2\ img121 | |
| Date | 15th November 1932 | |
| To R.{Sir Henry Royce} From Hs.{Lord Ernest Hives - Chair} c. to Bg. Wor.{Arthur Wormald - General Works Manager} c. to RS.{Sir Henry Royce's Secretary} Lr.{Mr Ellor} c. to RP. Lp.{Mr Lappin} c. to E.{Mr Elliott - Chief Engineer} Hs.{Lord Ernest Hives - Chair}S/WJ.15.11.32. LARGER CAPACITY ENGINES. /for We have shewn on the appended print the estimated performance at altitude to be expected by increasing the engine capacity. The power curves are based on the same M.E.P. for the same piston speed as given by the standard Kestrel engine fitted with Gos.1 Blower, it being assumed that an increase in engine capacity the blower would be proportionately increased. Nearly 20% increase in capacity would be obtained with a bore of 5.3 and stroke of 5.85 which preserves the same stroke/bore ratio as the standard Kestrel. The weight we should estimate to be about 1170 lbs. For the same piston speed the normal R.P.M. would be 2350 which is equivalent to 2500 R.P.M. on the Kestrel. The estimated altitude power curve is shewn as (1). We see no reason for limiting the piston speed to this value and Curve (2) shews the result of running at 2500 R.P.M. normal - the same as the higher rated Kestrel. This would give an approx. rating of 720 HP. at 11,000 ft., providing we were not limited by detonation. Actually we should expect to be better off due to running at the higher piston speed than the standard Kestrel and provided the blower was equally as satisfactory in this respect as Gos.1. Increasing the bore to 5.5 and stroke to 6" (giving approx. the same stroke/bore ratio) we think would be too large and if this were limited to the same normal piston speed as the higher rated Kestrel would only give the same performance as the previous case. The longer stroke appears to afford little advantage if limited to the same piston speed. By increasing the speed up to 2500 R.P.M. we get the top curve giving a rating of 795 HP. at 11,000 ft. We consider however an engine of this size to be too large for the purpose we are considering. We must naturally expect to have our engine capacities somewhat smaller and working at higher speeds and M.E.P. than the air cooled engines in order to get down to the same weight. When considering the weight of our engine we should take into consideration the weight of the combined radiator, water piping, etc. which comprises the cooling system. It would appear that 20% increase in capacity is a reasonable amount to bring us into line with some of the other water cooled engines and enable our performance to be in advance of the larger air cooled engines. | ||