Advantages of sleeve valves for H-24 engines? (1 Viewer)

[hobbes154]

Second possibly stupid question for the day: was there any particular advantage of sleeve valves for the H-24 engine layout, or 24 cylinder engines in general?

I know with 2-row radials it was harder (not impossible) to make 4 poppet valves per cylinder work, compared with single row radials or V-12s.

Is there any similar logic for why Napier and RR went for sleeve valves on the Sabre and Eagle (also the X-24 Exe and Pennine) despite not being 'all in' on sleeve valves for everything like Bristol was? Alternatively it could just be a coincidence of two technologies coming into vogue at the same time, but it's interesting that RR kept playing with it late war when the Bristol radials and Sabre had been so troublesome and RR had done so well with poppet valves.

Possibly relevant:

• In older H-24s the Napier Dagger had 2 poppet valves per cylinder and the Fairey Monarch 3. The X-24 Vulture had 4.
• The Wiki Sabre page says: "The layout of the H-block, with its inherent balance and the Sabre's relatively short stroke, allowed it to run at a higher rate of rotation, to deliver more power from a smaller displacement, provided that good volumetric efficiency could be maintained (with better breathing), which sleeve valves could do.[6]" Which I understand as saying sleeve valves help you turn high revs which is often (not always) the goal with 24 cylinder layouts?

 

[WARSPITER]

Biggest advantage I know of was that the Napier H24 had a Typhoon wrapped around it.

 

[ThomasP]

The practical advantage of the sleeve valve vs poppet valve might be demonstrated by the relative BHP vs displacement. The list below shows the ratings at the end of the war (or just post-war) for the major Allied larger engines.

_____________________________________super___________valve______BHP
_______________in3______Type________ charger__________type_______dry
Merlin_________1650_____V12_____2-stage/2-speed_____poppet_____2030
V-1710________1710_____V12_____2-stage/2-speed_____poppet_____1800
Griffon________ 2240_____V12_____2-stage/2-speed_____poppet_____2200
Griffon________ 2240_____V12_____2-stage/3-speed_____poppet_____2400
Sabre_________2240_____H24_____1-stage/2-speed_____sleeve_____ 2600
Hercules______ 2360_____R14_____1-stage/2-speed_____sleeve_____ 1800
R-2600_______ 2600_____R14_____1-stage/2-speed_____poppet_____1750
R-2800_______ 2800_____R18_____2-stage/2-speed_____poppet_____2300
Eagle 22______ 2817_____H24_____2-stage/2-speed_____sleeve_____ 3200
Centaurus_____3272_____R18_____1-stage/2-speed_____sleeve______2500
R-3350_______ 3350_____R18_____ turbo-supercharged_ poppet_____2200 (2500 for A-bomb missions?)
R-4360_______ 4360_____R28_____ turbo-supercharged_ poppet_____3250

Take note of the BHP per displacement of the H24 engines (in particular) vs the equivalent size poppet valve engines. While this list does not give anywhere near all the various pluses and minuses, I think it indicates a very good reason why Napier and Rolls Royce pursued the sleeve valve in their liquid-cooled engines.

 

[WARSPITER]

Pictures I have seen of the H24 also seem to show a fairly compact engine - probably due to the lack of heads.

 

[Tony Kambic]

Pictures I have seen of the H24 also seem to show a fairly compact engine - probably due to the lack of heads.

There is a scientific paper comparing sleeve versus poppet valves on the Aircraft Engine Historic Society Website. I am a member and read the document probably 10 years ago. I cannot locate it right now and I don't believe I can share it here anyways.

 

[Simon Thomas]

The sleeve allows a better BMEP and BSFC than the 2 or 4 poppet valve head. (Ignoring Turbo Compounding) The downside is a heavier engine for the same capacity. The cost issue is always brought up. The cost to develop the sleeve valve was 2 million pounds. This is spread over around 80,000 sleeve valves engines. Spreading the development cost over the engines results in around 25 pounds per engine. I understand that the Perseus was around 2500 pounds, so the % increase for the cost of development is not much.

It is important to look at the timing to gain an understanding of how the Sleeve valve became an orphan.

From 1932 (Perseus type rated) to 1938 (Centaurus type rated) the sleeve valved engines looked to give no improvement over similar sized poppet valves. This is exacerbated by the Wrights and Pratt & Whitney using 100 octane fuel, and most of the British engines staying with 87 Octane fuel to ensure continued operation throughout the Commonwealth with little or no 100 octane in many places.

Only in late 1938 Bristol developed how to mass produce the sleeves.

1939-1941 was just pandemonium for all the engine manufacturers trying to open shadow factories, increase production, uprate existing engines and develop new engines.
In the same period the jet engine is being developed, which took time away from the best and brightest engineers, experimental shops and test facilities.

All the time RR was playing politics and some in the Air Ministry were dancing to their tune, which resulted in unfair decisions against Napier and Bristol. The RR Eagle development was aided greatly after the Air Ministry removed an engine and all documentation from Napiers and sent it to RR. The Centaurus was also held back by the AM, and also part of the reason for the Centaurus numbers being so low during the war was they were built in an underground factory, which took time to make and staff. The staff were not exactly excited about working underground.

In late 1942 the Air Ministry forced Bristol to provide Napier the manufacturing technology to make sleeves with the appropriate tolerances.

By 1943 the jet engine was looking like the future, so there was no point anyone else spending millions and tying up resources, who were already stretched far too thin, to develop a sleeve valve engine.

 

[tomo pauk]

All the time RR was playing politics and some in the Air Ministry were dancing to their tune, which resulted in unfair decisions against Napier and Bristol. The RR Eagle development was aided greatly after the Air Ministry removed an engine and all documentation from Napiers and sent it to RR.

Care to post some sources (bar what Setright says)?

The Centaurus was also held back by the AM,

Sources?

The staff were not exactly excited about working underground.

Staff's job was not to be excited.

 

[Simon Thomas]

"Fedden" Bill Gunston
"By Precision into Power" Vessey
Productivity and morale do have some connection.

 

[tomo pauk]

"Fedden" Bill Gunston
"By Precision into Power" Vessey

Not in the mood to do wild goose chasing.

Productivity and morale do have some connection.

Country is in a major war, the biggest thus far. Being in an underground facility doing engineering job beats the heck out from being in infantry or serving as a sailor in North Atlantic, for any given level of snowflakeness.

 

[hobbes154]

Thanks for the comments, I'm aware there are a lot of pros and cons to sleeve vs poppet valves generally, but what I was trying to get at is whether there was any particular advantage of the combination of H-24 (or X-24) and the sleeve valve that wasn't true for say a V12?

Take note of the BHP per displacement of the H24 engines (in particular) vs the equivalent size poppet valve engines.

There are no poppet valve H24s in that list. I assume most of the advantage over an equivalent displacement V12 or R14/18 is just in having smaller cylinders that can be run at higher rpm [edit: compare the Sabre and Hercules, or the Eagle and Centaurus, all sleeve valve], and any extra advantage to the sleeve valve per se is paid for with higher weight as Simon Thomas said. (Also I think late war R-2600s were making 1900hp?)

By 1943 the jet engine was looking like the future, so there was no point anyone else spending millions and tying up resources, who were already stretched far too thin, to develop a sleeve valve engine.

RR kept going with the Eagle and Pennine into 1945 and maybe later for the Eagle?

 

[Shortround6]

Problems at Bristol include (but not limited to) Firing Roy Fedden by the Bristol board of directors in Feb 1942 (they gave him 6 months notice but cut his authority in the mean time).
Now when you fire your chief engineer in the middle of the war and the guy who has been responsible for sleeve valve progress for over a decade things are not going to go smoothly.

A lot of sleeve valve partisan's tend to overstate things.

The "head" of the sleeve valve engine was not quite as compact or simple as it is often claimed. Yes the bolt heads/plugs the seal the top of cylinder bore are not complicated on the Sabre (ask Bristol about how many different designs they went through on the Hercules) but the intake, exhaust ports and cooling passages and the space for the sleeves to extend upwards during the cycle killed a lot of the theoretical advantage.
The sleeve valve interfered with cooling compared to the poppet valve. Yes the Poppet had isolated hot spots. The Sleeve valve had wider areas of heat problems.
The sleeve valves were always operating behind the poppet valves in regards to boost pressures.
Please note that the air cooled radials needed deeper heads than the Sabre to fit in the needed cooling fin area.

Also note that not all poppet valve engines were the same. You had the Merlin flat cylinder head/combustion chamber, the Allison 45 degree or close to it cylinder head, you had the American radials with hemi heads and near 90 degree valve angles and so on.

And it is not just the size and shape of the valves and sleeve ports but the size and shape of the manifolds and passages and ports in the cylinders.

 

[Simon Thomas]

The Eagle started as a design project towards the end of 1942. (TP - Flight April 24th, 1947, p625, paragraph 3, third line) They kept going until 1949, but only made 15 of them.

Getting back to the original question, the bore is controlled by the cooling, flame speed, swirl, octane, boost and rpm. Having to increase power when the bore limit is reached requires more cylinders. Six in a row is about as far as was successful, so the H-24 was needed to get beyond the Griffon powers. Air cooled and liquid cooled had differing cooling constraints, with the liquid cooled heads having more BMEP capacity.

These threads talk more to the issue, you will have to hunt around a bit to find the exact discussions.

In retrospect, were the BMW radial engine developments a mistake?

So the RLM(?) decreed in the early-mid 30'ies that BMW should drop work on liquid cooled aero engines and instead focus on radials. In a way a sensible decision from the perspective of not putting all the eggs in one basked, considering Daimler and Junkers were already focused on inlines. But...

ww2aircraft.net

Jumo 213 vs. Napier Sabre

Being the peak engine developments of their specific countries which one was more modern, had more potential, was more efficient, more powerful, overall better?

ww2aircraft.net

 

[Simon Thomas]

Not in the mood to do wild goose chasing.

Vessey, p143. First paragraph, second line.

 

[hobbes154]

These threads talk more to the issue, you will have to hunt around a bit to find the exact discussions.

In retrospect, were the BMW radial engine developments a mistake?

So the RLM(?) decreed in the early-mid 30'ies that BMW should drop work on liquid cooled aero engines and instead focus on radials. In a way a sensible decision from the perspective of not putting all the eggs in one basked, considering Daimler and Junkers were already focused on inlines. But...

ww2aircraft.net

Jumo 213 vs. Napier Sabre

Being the peak engine developments of their specific countries which one was more modern, had more potential, was more efficient, more powerful, overall better?

ww2aircraft.net

Interesting discussions, I had already read the first, but it only touches on sleeve valves in passing?

Most people in the second (aside from yourself!) seem to be against sleeve valves full stop, at least with higher octane fuels and boost pressures.

So perhaps we can say sleeve valves and 24-cylinder engines were both logical responses to the problem of how to get maximum power out of 87 octane fuel and the resulting limited boost? Which fits with Napier going for sleeve valves in the Sabre after using poppet valves in the Dagger. But I still don't understand what RR were thinking with the Eagle and Pennine years later.

Would it be particularly hard to build an H24 with 4 poppet valves/cylinder?

 

[WARSPITER]

Would it be particularly hard to build an H24 with 4 poppet valves/cylinder?

I wouldn't expect so as it's really two flat 12 cylinder arrangements and flat (horizontally opposed) designs
ran valves.

 

[z42]

I think it's more about who the designers were, and in what timeframe the engine was designed, than anything particularly unique about a H24 or X24 layout vs a "boring" V12.

Ricardo was an early and very influential proponent.

 

[Shortround6]

But I still don't understand what RR were thinking with the Eagle and Pennine years later.

It might have been a case of seeing if they had missed something, crossing their "T"s and dotting their "i"s so to speak.

Would it be particularly hard to build an H24 with 4 poppet valves/cylinder?

Probably not. The H-24 with poppet valves, even if not 4 valves per cylinder had considerable interest if not sales.
It offered (but sometimes failed to deliver) easy development.
Take a V-12, flatten it out make an opposed 12 then either stack on top of or side by side to make a 24 cylinder engine.
Lycoming built an H-2470 and it flew in the Vultee XP-54 but used two valves per cylinder.
RR drew up an H-24 using four Merlin cylinder blocks but it didn't go any further (?).
Hispano-Suiza built a few H-24s using 12Y cylinder blocks before the war for a planned transatlantic flying boat and tried to revive it after the war with 12Z cylinder blocks but found no takers.
Arsenal of France tried to do the same with Jumo 213 cylinder blocks after WW II since they had inherited Jumo 213 production tooling as a satellite factory for the Jumo from the war.
Also no takers.
I may have left out a few(?)

Since in a conventional V-12 the valve gear is pretty much in the head except for the cam drive there is not real complication to go from 2 valves to 4 valves.
Radials used cam rings in the crankcase and drove the valves with pushrods so trying to add extra cam rings or a slew of pushrods was a lot more difficult.
Bristol had an extra complication because Fedden was using 4 valve heads instead of two valve heads like just about every other radial engine maker.

 

[ThomasP]

re weight differences of H24 vs V12 and R-xx

_____________________________________super___________valve______BHP_____weight
_______________in3______Type________ charger__________type_______dry_______lbs
Merlin 130_____1650_____V12_____2-stage/2-speed_____poppet_____2030_____1730
V-1710-145____1710_____V12_____2-stage/2-speed_____poppet_____1800_____1725 (weight includes Auxiliary Stage SC)
Griffon 65_____ 2240_____V12_____2-stage/2-speed_____poppet_____2200_____2075
Griffon 85_____ 2240_____V12_____2-stage/3-speed_____poppet_____2400_____2165
Sabre VA______2240_____H24_____1-stage/2-speed_____sleeve_____ 2600_____2360
Hercules 100__ 2360_____R14_____1-stage/2-speed_____sleeve_____ 1800_____1920
R-2600_______ 2600_____R14_____1-stage/2-speed_____poppet_____1750_____2045
R-2800_______ 2800_____R18_____2-stage/2-speed_____poppet_____2300_____2340
Eagle 22______ 2817_____H24_____2-stage/2-speed_____sleeve_____ 3200_____3900
Centaurus_____3272_____R18_____1-stage/2-speed_____sleeve______2500_____2725
R-3350_______ 3350_____R18_____ turbo-supercharged_ poppet_____2200_____2670
R-4360_______ 4360_____R28_____ turbo-supercharged_ poppet_____3250_____3540

NOTE The weights above are 'dry' (ie no fluids) and may or may not be 'bare' (ie no accessories). In all cases the weight is not the installation weight (ie they do not include the oil and coolant radiators, plumbing, etc, and in the case of the radials do not include turbos and inter-cooler/after-coolers if present).


re R-2600 at 1800-1900 BHP for TO

I only used BHP at altitude for the list above. Also, I only used ratings for 100/130 grade. If we use TO BHP then the numbers will go up for most of the engines.

Also, as far as I know the R-2600 with 1800-1900 BHP for TO was not a production engine?

All of the engines were production engines except for the Eagle 22, but it is the only H24 with sleeve valves in development at the end of the war comparable in size/output to the larger radial engines. It had passed its type tests at the ratings above in mid-1945 (I think).

 

[tomo pauk]

Vessey, p143. First paragraph, second line.

Thanks, I'll look it up.

 

[tomo pauk]

Also, as far as I know the R-2600 with 1800-1900 BHP for TO was not a production engine?

It was, the -20 was used on the later TBMs and SB2Cs.