Questions part 3: Another variety pack. (1 Viewer)

[Engineman]

I do not have any numbers and I may very well be mistaken.
The Sleeve valve vs Poppet valve arguments can be very partisan and without real numbers to back them up. Then we wind up with theory.
It may be true (quite likely?) that the oil to cylinder interface is 'transparent' to heat transfer.
What is not so transparent is the sleeve moving up and down about 2 1/2 inches at 1/2 rpm. For most of the length of sleeve this doesn't really matter. It does matter ( I think?) up in the head area and in the area where the ports are.
What is the heat transfer across the 'gaps' which are moving? What is filling these 'gaps'? Oil or oil/air mix or ??? Granted a 2 1/2in movement means that the sleeve is spending a lot of time in the middle of that movement but that is at/near the hottest part. What is the heat transfer in the top 1 1/4 in of the horizontal fins around the head? What is the heat transfer in the area of the cylinder where the 5 ports are?
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I have read a number of articles that exhibit at least some bias (or perhaps I am revealing my own).

https://www.newcomen.com/wp-content/uploads/2019/11/The-Piston-Engine-Revolution-Chapter-6-Hassell.pdf

Page 11 (?) talks about the US having to use two valve heads instead of 4 valve heads on two row radials. Trouble with this is that the US very rarely used more than 2 valves in any radial engine. US was moving to the sodium filled exhaust valve in the larger engines by 1930. By 1940 they were using them in 200-300hp radials built by Continental, Jacobs and Lycoming let alone P&W and Wright's bigger engines. It was basic design practice in the US for cylinders of certain size/power regardless of number of cylinders or rows. By 1930 P&W and Wright were moving to totally enclosed valve trains which Bristol never did on their poppet valve engines. I will note that totally enclosed valve train does not mean either pressure lubricated or even supplied by engine oil. That took a while longer. The Sleeve valve certainly solved the Bristol radial valve lubrication by grease gun problem, but that problem didn't exist for many other engine makers.

Both sides are guilty of mixing time lines. And both sides rarely mention the difference (and problems) that better fuel made.
Financial considerations are rarely mentioned like the amount of money invested in tooling in both camps (Sleeve valve and poppet) and other financial considerations like tariffs for the British and indeed the British commonwealth after WW II and for part of the 1950s.
The post war Sleeve engines (Bristol) were great engines if you don't count cost. Maybe they were great even if you do count cost but getting costs are hard. Both for initial purchase and maintenance/overhaul. This is complicated by the US engines dominating the market and having easier access to spare parts and repair facilities around the world so again, direct comparisons are hard.

Bristol obviously did a great job in mastering their aircooled sleeve valve radials and I feel the long cruising power TBO of late engines was a strongpoint. The full development did come at great cost, but it was achieved and the Bristol technology also saved the Napier Sabre from oblivion.
You can see some of the features in that good cutaway engine. If you look at the junkhead, you can see that the thickness of metal is carried up to the upper fins to transfer heat from both the cylinderhead face and from the hot sleeve which moves up into the junkhead. The junkhead is also heavily finned on its inside faces. A point to note, is that the exhaust port is very short, and this must greatly reduce the heat transfer compared to a conventional twin overhead poppet exhaust valve configuration. However, effective cooling by air is very demanding in these complex engines, whereas liquid cooling can offer high cooling rates and control in even the most awkward places inside an engine and this helped with engines like the Merlin (27L) and the Sabre (37L) while the aircooled Centaurus required a considerable 54L.

Eng

 

[Bretoal2]

We had some discussion on heat flow across the sleeve in page 3&4 of this thread a few years ago: Advantages of sleeve valves for H-24 engines? (which you might remember, as you were a prolific poster in that thread)

Yes, specially post 56.
Ricardo's opinion is, of course, invaluable!
One might assume his views were based on his laboratory engines, which lacked the displacement and power of the large engines developed by Bristol. However, Fedden's testimony corroborates this, confirming that in his own large engines he, too, observed the "transparency" noted by Ricardo .