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jjuutinen · Joined: 13 Jul 2003 Posts: 180

Anyone in possession of this book: could you check out if the book mentions a Napier Sabre test run at 3750 hp? I remember readiung this book years ago in a library mentioning such a test, but the book is no longer available at that library.

gwhite · Joined: 13 Jul 2003 Posts: 58

You may want to contact the Napier Power Heritage. The new book by Alan Vessey quotes the highest rating for a production Sabre as 3,050hp for a VIIA. However this is the power rating for its type test. Undoubtedly, far higher power was extracted during testing; this was typical for any manufacturer so 3750 is not out of the realm of possibility.

jjuutinen · Joined: 13 Jul 2003 Posts: 180

Graham, I think I once contacted them and the info I received was very vague at best. By the way, a late 1940s Jane´s AWA gives 3055 hp as Sabre VII´s combat (5 min) rating.

sithomas · Joined: 01 Jan 2019 Posts: 28

Direct from the book:
"It was eventually succeeded by the Napier Sabre, whose design by F.B. Halford began in the mid-1930s with a planned power output of 2,000 hp (1,492 kW). Eventually this 24-cylinder (it had four banks of six cylinders arranged as two flat, horizontally opposed twelves, one above the other, with the two crankshafts geared together) developed 3,750 hp (2,797 kW) for a non-stop 175 hours This was undoubtedly due to the combination of sleeve valves and liquid cooling. though this combination almost guaranteed a fire in the air intake when trying to start with the Coffman cartridge starter on a frosty morning The Sabre could run at speeds up to 4,500 rpm and give 5,500 hp (4,100 kW) at a boost pressure of 45 lb/sq in (316 kg/sq. cm) from the two-stage supercharger. With a power-to weigh; ratio of 0.68 lb/hp, this 22.4-liter (1, 570-cu in) engine of 5 in (127 mm) bore and 4.75 in (120 mm) stroke was one of the peaks of aircraft engine design."

Notes:
The capacity quote is incorrect. The author appears to have inadvertently transposed L with cubic inches. Should be 2,240 cu. in / 36.7 L.

The 3,750 hp for 175 hours was mentioned in a Historic Engine Facebook thread by a friend of a Napier employee. In that post he mentions it was in response to an Air Ministry quip about the Sabre not being reliable, and the Air Ministry told them to stop the test after it had been running 175 hours.

The claim of 5,500 hp / 4,500 rpm / 45 psi from the two stage supercharger is likely not all concurrent, if even any of them are correct.