The only other well developed sleeve-valve engine was the Dagger VIII. It was an air-cooled H24-cylinder design with a displacement of 1037 in3 - very significantly smaller than the Merlin & V-1710 - with a CR of 7.5 and max boost of +5 lbs on 87 grade fuel.
An example would be if we compare the Merlin 25 to the Sabre. Both engines were liquid-cooled with 1-stage/2-speed superchargers. The Merlin 25 had a CR of 6 and a maximum boost using 130 grade of +18 lbs/66.5"Hg. The Sabre had a CR of 7. This means the best we should expect in terms of boost from the Sabre, everything else being equal, would be:
6 x 66.5 / 7 = 57"Hg or +13.3 lbs when using 130 grade fuel
What was the highest realistic boost used by the Sabre in service - when using 130 grade fuel? IIRC the boosts were:
Sabre IIB_____2400 BHP at 3700 rpm at +11 lbs (1944)
Sabre VA_____2600 BHP at 3850 rpm at +15 lbs (1946)
2. Is the supercharger more or less efficient (in terms of heat added to the charge)? As far as I know the Merlin 25 supercharger was considered more efficient than the Sabre supercharger. Greater heat rise due to the supercharger would result in a lower altitude rating and/or a lower boost rating and/or lower BHP.
The Griffon engines in my lists are the 65 and 85, both well developed and using the 'Hookerized' supercharger and inter-/after-cooler. As far as I know none of the Sabre series used an inter-/after-cooler. Yet the Sabre still had the advantage in output. If the Sabre had a supercharger and inter-/after-cooler similar to the Griffons we can assume significantly improved performance from the Sabre.
There are no (I think) reasonably developed sleeve-valve liquid-cooled engines in the 1650-1710 in3 range. This makes (I think) any direct comparison to the Merlin or V-1710 impractical.
I recall one of the claims made for the superiority of the sleeve valve was that the engine could run higher compression ratio for the same boost, or higher boost for the same compression ratio.
I really don't care what you do. I made a statement, and provided my source. As I said, it is worth reading the whole book to get the big picture. Taking a snippet as a means to understand a general pattern will not work.What are the examples?
Or do you expect me to buy a book to read two pages?
I just paraphrased from the book. It was written by an ex-Napier employee who as I understand is/was the president of the Napier Power Heritage Trust.Is there proof? Or just suspicion?
It didn't get a fair trial in 2023. Anyone who says the sleeve it too complicated has not spent the time to understand it.You don't think sleeve valve engines had a fair trial in WW2?
What would have been a fair trial?
A minor point, but the P & W R-2180 was half of an R-4360, Wright made the R-3350.An awful lot depends on when. The R-2600 is a bit of puzzle in itself. There are three totally different engines that share the same bore and stroke. The 3rd engine (the BB) started production in the middle of 1943 and is the 1900hp for take-off version but that doesn't line up with the Military power even at low level. This engine was only used by the Navy with few, if any, commercial sales after the war. Wright may (guessing) have seen the hand writing on the wall and concentrated on the R-3350 and the R-1820 and not tried to split their effort 3 ways. They had enough problems with R-3350 in 1944/45 anyway.
So this makes it rather difficult to compare to the Hercules engine/s.
Engine..........................take-off...................................Military high gear..............................Max continuous high gear
Hercules XVIII.............1725hp/2900rpm.............1600hp/2900rpm/15,500ft.................1300hp/2400rpm/ 9,500ft
Most any Hercules after the 100 really blows the R-2600 into the weeds, but the R-2600 was pretty much frozen in time from the Spring of 1943 onwards.
Now if you want to go backwards a 1940 R-2600 with 1600hp (the A ) for take-off edges out the 1940 Hercules III
They built about 1900 R-2600 A's in 1940.
P & W tried to build a post war R-2180 14 cylinder engine of 1800hp take-off (wet) and lost their shirt. (1/2 an R-3360) Only one company (SAAB) bought any.
There is a lot of the Hercules saga that is not easy to find.
One book goes through the cylinder head something like this.
Development stage, single piece sand casting, got to 540 sq.in cooling area.
First production engine, die cast single piece, 581 sq in cooling area.
early war time (MKs not given) two piece with die cast bottom shrunk into the flange, 728 sq in.
later heads with better casting got 777 sq in with increase fin pitch. decrease in CHT of 15 degrees C and cut 3 oz of the weight.
A number of experimental heads followed with a machined copper based head being the head used after the war. It was at least the 3rd head incorporating copper for better heat transfer.
The A5B was already being used in the DB7A & B and the Vengeance, so possibly the AM wanted to keep using the same engine.The R-2600-A5B was a 1939-40 engine but that is probably what the US was willing to export at the time.
The R-2600-BA engine was the 1941 version (443 built in 1941) and this was the 1700hp take-off power version. Used a steel crankcase instead of the Aluminum of the A series engines.
Might very well have used more fuel than the A.
But the BA could run 100rpm faster and had about 3000ft more altitude at max cruise.
BTW the R-2600 A5B was supposed to be rated on 90-91 octane fuel, the R-2600 A5A was supposed to run on 100 octane (US 100 octane)
Hercules XI was supposed to run on 100 octane (British)?
I am all for comparing engines, as long as the comparison is fair.
The British ordered the A5B engines, they got A5B engines, that may be all they could get. They got the results they got.
However that doesn't mean that the test shows the results of a best practice poppet valve engine vs a best practice sleeve valve engine.
Things changed by the year if not sometimes a bit quicker.
Was there any technical reason for sleeves being actuated in the way they were? Could they have travelled straight up and down the bore?Here is a graph of boost (Y axis in PSI-Gauge), vs date (x-axis).
See if people can work out which one is the Merlin and which one is the Sabre (the Centaurus is nearly identical to the Sabre trendline)
(You can if you wish disregard the final data point as its for a sprint run so is an unfair item, the point before it is the Merlin-100 type test value)
The Merlin was a pretty run of the mill layout and the short stroke high speed design of the Sabre is certainly more forward thinking, but
the sleeve didn't do much for it.
These days normally aspirated poppet valves will be able to achieve well above 100% volumetric efficiency, so the cylinder filling argument just evaporates really.
In my view a poppet valve Sabre would have been very good indeed, although it weighs about 700lbs more than a Merlin...
View attachment 730411
First B-25 flew with a R-2600-9 engine in Aug 1940. Granted military prototypes (or next thing to it) don't have to use engines with type certification (civil).The A5B was already being used in the DB7A & B and the Vengeance, so possibly the AM wanted to keep using the same engine.
The BA is obviously a better engine, however the US was still not allowing military engines to be sent to the UK.
The civil GR-2600-B5 was also a 1700 hp TO engine, but it only received its type certificate on Jan 9, 1941. It would take a while for the design information to be sent to Short, and then the installation designed and the engines installed. The first Stirling to be fitted with the A5B (N3657) was allocated to 19MU on Feb 2, 1941.
Lumsden says the Hercules XI could run on either and gives power for both fuels. Of course in mid to late 1941 I tend to doubt that 87 octane would have been used in actual operations out of England.The C-W engine summary states the A5A uses 90 octane. The Hercules manual and Stirling manual I have are late war revisions, and nominate 100 octane. I don't know if the Hercules XI was earlier set up for a lower octane.
two reasons against it.Was there any technical reason for sleeves being actuated in the way they were? Could they have travelled straight up and down the bore?
The sleeve isnt running at 1300F, (704 C) - gas temperature is not metal temperature. If it was, the oil film would carbonise almost instantly.re Heat conduction of sleeves
(2) That a moving sleeve, provided that only a thin oil film was maintained, appeared to be almost transparent to heat.
"The High-Speed Internal-Combustion Engine", Ricardo, Fourth Edition, 1954 Reprint, p349. [Ricardo made significant changes between editions.]
Fedden's paper "The Development of the Mono-Sleeve Valve for Aero Engines" Feb, 1939 stated in response to a question:
"I must again emphasize Mr. Ricardo's remarks about the transparency of the sleeve and the rubbing motion of the oil film, which is the real crux of that problem."
I had to do a heat transfer calculation on a 1/2" pipe at 1300°F, and was surprised to see that the temperature difference across the carbon steel pipe was 0.84 K. I changed the conduction coefficient to that of KE965 and the thickness to 1/8" and ran calcs from 2500°F to 500°F. I found that the temperature difference across the sleeve varied from 8 K at 2500°F to 0.5 K at 500°F. For me there seems no reason to doubt Ricardo's claim, with the same caveat - the oil film must be maintained.
ne fuel, the R-2600 A5A was supposed to run on 100 octane (US 100 octane)
Hercules XI was supposed to run on 100 octane (British)?
Close but no cigar:two reasons against it.
Greater chance of scoring the walls. It something gets in between the sleeve and the jacket or between the sleeve and the piston the is a better chance of it working it's way back out rather than plowing a groove.
You may need a longer sleeve (?)
View attachment 730427
Both Bristol and Napier used the 5 port design and with a reciprocating sleeve you may need a 6th port to get the air flow you want.
Not sure what this does to either sleeve strength or to cooling. the back and forth action may get the sleeves to go over more cool areas?