LSR Horsepower

Sir,

I would query the suggestion in your fascinating interview with Capt. Eyston that “Thunderbolt” might have gone better if Merlin-powered.

The R engine, of which it had a pair, was, of course, the racing unit developed from the Buzzard, to power the Schneider Trophy seaplanes. The Merlin, a significantly smaller engine, appeared later and was very much a production engine for general service, rather than a racing special. In 1937 Capt. Eyston would probably have found it very difficult to acquire a Merlin, since these were badly needed for Hurricanes: but in any case, power figures given in L. J. Setright’s estimable book, “The Power To Fly”, suggest that he would have been much better off with the R.

The Key figures are:

R:

1931 speed record, methanol mixture : 2,530 b.h.p. 1931 bench test : 2,783 b.h.p.

Merlin 2

1937, 87 octane : 1,030 b.h.p.

1937, sprint version, methanol : 2,160 b.h.p.

Merlin RM 17 (most powerful Service unit) :

1944, 100/150 fuel, 15-minute rating : 2,640 b.h.P.

As you will see, the Merlin in production form never did catch up with the R, which is scarcely surprising when one remembers that the former had only 27 litres to the latter’s 36.7. In addition, the R in its highest-rated forms needed around 60 per cent methanol, and had a quite staggering thirst for castor oil. However, if brute force was needed, the R was the answer—unless, of course, one could find a Sabre and really do the thing properly!

London, W 11 Sandy Skinner

[I think what Capt. Eyston probably meant was that if he had been able to go for the LSR again in “Thunderbolt” after the war, as Cobb did with the Railton Special, a couple of Merlins might have given him the record at 400 m.p.h. to Cobb’s 394.2 m.p.h. Cyril Posthumus, in the best book yet about the LSR, gives the output of the Rolls-Royce R-type engine used by Eyston as 2,350 b.h.p., so if the Merlin RM17 had an extra 290 h.P., a couple would clearly have made a big difference, especially as it was a more compact, probably lighter engine. Even taking Mr. Skinner’s figures there would be an additional 220 b.h.p. to play with. An interesting speculation is what would have happened had Eyston or Cobb installed a couple. of Napier Sabre’s, this H-24-cylinder 36.7 litre engine developing 5,500 b.h.p. at 4,200 r.p.m. in racing form and 3,750 b.h.p. in service rating (vide Setright) for a bulk little greater than that of the Merlin—ED.]