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I understand that the reason Roy Fedden persisted with sleeve valves was that he couldn't find a way to make a two-row radial with four valves. I can't remember the source for this, but I would note that all the poppet-valve two-row radials had only two valves.
For Bristol the only real alternative is the Wright R-2600. It fits both dimension and weight wise. It also fits time wise. The R-2800 is too late.
The question becomes can Bristol actually build it and which version. British casting wasn't up to US standards in the early 30s which is why they went to forged cylinder heads and US companies stayed with castings for a number of years more.
this is the first i have seen this set up. what were the virtues of the sleeve valve? seems like a very cumbersome system of heavy parts that had to overcome a lot of friction.
The nice thing about the R-2600 is that it was a developed design - R-2600 powered Boeing 314 Clipper's were flying around the globe, entering regular service in January 1939
From Wikipedia:
The first 314, Honolulu Clipper, entered regular service on the San Francisco-Hong Kong route in January 1939. A one-way trip on this route took over six days to complete. Commercial passenger service lasted less than three years, ending when the United States entered World War II in December 1941.
At the outbreak of the war in the Pacific, the Pacific Clipper was en route to New Zealand. Rather than risk flying back to Honolulu and being shot down by Japanese fighters, it was decided to fly west to New York. Starting on December 8, 1941 at Auckland, New Zealand, the Pacific Clipper covered over 31,500 miles (50,694 km) via such exotic locales as Surabaya, Karachi, Bahrain, Khartoum and Leopoldville. The Pacific Clipper landed at Pan American's LaGuardia Field seaplane base at 7:12 on the morning of January 6, 1942.
The sleeve valve was promoted by Harry Ricardo in the 1920s as a solution to detonation problems with spark ignition engines running the poor fuels of the time.
It eliminated one point of the pre-ignition - the hot exhaust valve - and allowed higher compression than poppet valve engines.
The three major aero engine builders in the UK had some involvement with sleeve valves. Bristol, of course, had a range of sleeve valve engines - the Perseus, Taurus, Hercules and Centaurus. Napier had the Sabre.
Rolls-Royce's experience started with them assisting Ricardo in converting a Kestrel to a sleeve-valve Diesel (Diesel was another are being pushed as they don't have the issue of pre-ignition) known as RR/D. This was later converted to a spark ignition petrol engine (the RR/P) by Rolls-Royce. In the mid 1930s the Exe was designed and one built for testing. The program was cancelled in 1941. In 1943/44 Rolls-Royce designed the Eagle 22 (similar to the Sabre but bigger and heavier) and the Pennine (larger version of Exe).
What curtailed the uptake of sleeve valves was the invention of the internally sodium cooled exhaust valve and the development of higher octane, more detonation resistant, fuels with Tetra-Ethyl Lead (TEL).
What about an up-sized, liquid-cooled version of the Dagger?
ie H-24, ~2,200-2,250 cid (Griffon and Sabre ~2,240cid).
In fact, it could be the Sabre, except with poppet valves instead of sleeve valves.
Or perhaps Napiers would opt for a Merlin sized engine using the layout of the Lion.
How would it compare to the Mercury, the diameter is only half-an inch more?
A R-2800 powered Hawker Typhoon (in lieu of the Napier Sabre) might be interesting.
14 cylinders compared to 9. Fewer valves more spark plugs for maintenance.
Mercury was around 200lbs lighter.