"No sleeve-valve engines" scenarios

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wuzak said:
Production of the sleeves and bores for reliable operation and not excessive oil usage a good enough reason? That problem plagued Bristol for years and had defeated Napiers before Bristol was ordered to help.
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No, because that reason was sufficiently overcome, with Centaurus serving postwar, including combat ops in Korea and Malaya. It's Tomo's thread, let's ask him to defend it with a reasonable premise and foundation that the rest of us can build upon.

With no sleeve valve distractions in the 1930s onwards, perhaps there's an opportunity for other outliers to step forward in British aeronautical engine designs. Such as diesel, with Napier's Culverin leading the charge? Or Frank Whittle gets the nod earlier?
 
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I have no wish to defend the initial premise, and the premise is not about why sleeve-valve engines are not continued with. Premise is that sleeve-valve engines are not made by anyone due to insurmountable technical problems, full stop.
My intention is that we have a meaningful conversation about alternatives that might come out from, predominately, Bristol and Napier, as well about the repercussions on the aircraft that might be powered by those engines, anywhere between late 1930s and post-war. Plus, how much the UK/Allied war effort might benefit here.
So please feel free to suggest the alternatives to Perseus, Taurus, Hercules, Centaurus, Sabre, and a host of sleeve-valve engines that were produced in token numbers (Exe, Aquila, Eagle 4-6, etc.) and give pros and cons to what other people might suggest.
 

It may not be that they don't work. It is that their reason for being (list of advantages over the poppet valve) was getting shorter all the time until it just about vanished.
In the 1920s there was quite a list of advantages of the sleeve valve over the poppet valve, some quite real, some rather theoretical. The list may be over 20 items and has been gone over before. Some of them were freedom from broken valve springs, This one may never have disappeared but was substantially reduced in the late 20s/early 30s with better metallurgy for the valve springs. Another was the elimination of hot spots that lead to pre-ignition and allowed higher compression to be used for given grade of gasoline. Largely solved by the adoption of the sodium cooled valve in the 20s. Bristol used to proclaim the simplicity of the Sleeve Valve by comparing the number of parts in Mercury cylinder and valve train to the number of parts in a Perseus cylinder and sleeve valve. Made an impressive photograph, but the Bristol 4 valve cylinder was the most complicated air cooled radial cylinder on the planet. They also left out all the parts inside the crankcase that actuated the pushrods (not that many parts) and actuated the sleeve valves (a lot more and perhaps harder to make/fit?). One "advantage" was real knee slapper (funny). The Sleeve Valve engine was "cleaner" and less likely to leak oil on the airplane. SInce Bristol had 5-7 grease fittings on each cylinder (I forget) this was true, and most of the valve train was flapping about in the breeze but only if you are comparing Bristol engines. Most everybody else in the early 30s was incloseing the valve gear and working on lubricating it with the engine oil, no fitting a grease gun to 45 or more grease fittings every dozen or so hours of flight.

AS above, in the 1910s, 20s and 30s the poppet valve was far from perfected but getting better all the time, something the Sleeve valve community failed to recognize. I would note that sleeve valve use in heavy duty engines was not the best predictor of performance (in durability terms) in light weight/high performance engines.



Problem is nobody in the late 30s knew you could even make 150PN fuel. In fact they didn't even know you could make 100/130 fuel. They knew you could make 100PN fuel (100 octane) and they knew that certain blends performed even better when running rich but they didn't know by how much. You cannot plane an engine program around fuel you hope might be available 3-5 years in the future.
 

The Exe, Aquila and such just free up R&D. Even the Aquila, even if it powered several planes was only about 5 engines, (same engine went in several planes?) so they made no difference to production.
The Perseus is pretty much interchangeable with the Mercury.
The Taurus is a "never should have been" regardless of valve type. A 14 cylinder engine of 1550 cu in is too much effort for too little result. One of it's main attractions/advantages was never used in a production aircraft.

Small frontal area/low drag doesn't matter when the planes you stick it on are flying parachutes.

The only engine that really matters in WW II is the Hercules, the Centaurus came too late to really influence things. Perhaps the poppet valve alternative could have showed up sooner?
If it did then the need for the Sabre really goes away.
The Sabre was planned as a next generation engine, a whole generation of aircraft was planned around it but as the program crashed and burned all of these other aircraft found other powerplants or were simply canceled leaving the Hawker fighters as the only real production aircraft (more than 20 or so) and since the Typhoon didn't work as intended it is hard to say wither all the the work was really worth it. Were 3300 Typhoons really worth 4800 Spitfires (or pick another number that reflects the difference in weight/cost)
 
As mentioned earlier, production aircraft engines using sleeve valves were unique to Bristol until Napier built the Sabre: no one else traveled that path as far as did Bristol. Other companies, e.g., Continental in the US set foot on that path, but didn't follow (Continental may have had the Depression didn't intervene).

Sleeve valve do have some theoretical advantages, including fewer "hot spots" and better volumetric efficiency (see, for example, http://www.enginehistory.org/members/articles/Sleeve.pdf and https://www.enginehistory.org/Piston/Before1925/Argyll/pioneer_sleeve_valve_(1).shtml), but most manufacturers found the added complexity (look at the mechanism to drive the sleeves in a Centaurus), increased oil consumption, and manufacturing difficulties serious enough to preclude the sleeve valves' benefits. Engine designers do this all the time: packaging (this is why V-6s are so popular; they fit better in most modern cars than do L-6s), manufacturing (this is the only reason for 90 degree V-6 engines; they can use much of the same tooling as for V-8s), marketing (wouldn't you rather have a V-8?), etc.

Had Bristol put half the engineering effort into developing their poppet valve engines as they did in their sleeve valve engines, they'd have poppet valve equivalents to the Hercules and Centaurus, and Napier would still try to produce a poppet valve H-24.
 

The problems were overcome, as we know now, but that was far from certain in the mid 1930s when these decisions would have been made.
 
Alternative engine by Napier?
- H-24 layout, say 37-38L, 3200 rpm? (expensive, perhaps the best potential for power)
- H-16, 40L, 2800 rpm? ( not so risky, not too expensive, good power)
- W-18 'broad arrow', 40L, 3000 rpm? (biggest risk?)
- a big V12, 40+-L, 2500+- rpm? (least risky, cheapest, also least power)
 
The Merlin XII, in 1940, was producing about 4.2 hp/in^2. A poppet valve Sabre (let's call it the Claymore) should manage about 2000 hp in its first version.
 
Another effect of having a reasonably powerful radial in series productin by second half of 1930s might be that Spitfire has the 1st call on 'better' Merlins. Like the Mk.X before 1940, and Mk.XX in time for BoB.

swampyankee said:
The Merlin XII, in 1940, was producing about 4.2 hp/in^2. A poppet valve Sabre (let's call it the Claymore) should manage about 2000 hp in its first version.
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It probably could, I was trying to be a bit conservative in my estimates.
 


They all have advantages and disadvantages.
A common way to design engines was to figure out how much power you could get out of a certain size cylinder (using a certain type of fuel) and then design an engine with the right number of cylinders to get the desired power.
Easy in theory and a lot of engines started that way. Problems came up when crankpins and bearings wouldn't stand up to the amount of power that was asked of them. RR Vulture classic example. Another problem was torsional vibration. The bane of many 16 cylinder engines (and a few straight eights)

One reason the Napier Lion had a good reputation. short stiff crankshaft and crankcase with only 4 throws. They traded frontal area for weight and stiffness. Extending the engine into an 18 cylinder brings the longer, whippier crankshaft and a longer heavier crankcase.

An H-16 is going to be short, but light? but with the largest frontal area per unit of power.
 
Successful aircraft W-18s were built by, among others, Isotta Fraschini; the demise of this configuration almost seems more due to fashion than to any intrinsic flaws.

Liquid-cooled engines could get about 4.25 hp per square inch of piston area in 1940. About 6.25 inches seems to be the largest bore anybody used in a production aircraft engine; assuming this power density could be maintained, this would be about 130 hp/cyl. Of course, this increased with time: one production variant of the Merlin produced 2,060 hp, or about 170 hp/cyl (7.5 hp/in^2) Extrapolating this to 6.25 in bore would give about 230 hp/cyl. The R-2800 produced about 4.25 hp/in^2 early in the war; its most powerful version was about 6 hp/in^2
 
A poppet valve engine of the same bore and stroke as the Sabre would have pretty much the same outside dimensions.

The sleeves, however, took up some space. I haven't been able to find the dimensions of the sleeve for the Sabre, but did find that the sleeves for the Hercules had a 0.139in wall thickness.

That means that the poppet engine could have a bore of 5.278in (134.06mm) for a total capacity of 2,494in^3 vs 2238in^3 for the Sabre.

Or, the overall length could be shortened by 1.5 inches or more, by reducing the bore spacing.

Also, the sleeve in it reciprocating cycle protrudes into the crankcase. Could the width of the engine be reduced by reducing the rod length?
 
swampyankee said:
Successful aircraft W-18s were built by, among others, Isotta Fraschini; the demise of this configuration almost seems more due to fashion than to any intrinsic flaws.
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Success at one level of stress/performance does not guarantee success at a higher level of stress/performance. A W-18 combines two (or more?) problems. The long crankshaft of the V-12 (6 throws) and the higher loading of the rod bearings by having more than two cylinders act on them. Getting an good firing order is also a bit of problem. The V-12 has two cylinders firing every 720 degrees of crankshaft rotation and with a 60 degree angle between banks you can get a 300 degree-420 degree separation between firing impulses. The W-18 gets into some weird timing trying to fit 3 firing impulses into 720 degrees of rotation especially with some of the angles involved.

See : Isotta Fraschini W-18 Aircraft and Marine Engines
for some interesting information. Other companies used different cylinder bank angles.


Liquid-cooled engines could get about 4.25 hp per square inch of piston area in 1940.
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While power per sq in of piston area is interesting I am not sure it is all that useful comparing engines or predicting performance. I am willing to convinced otherwise but consider
engine A with power of 3.72hp per sq in and engine B with a power of 4.28 hp per sq in. what could we do to get engine A up to the power level of engine B????
how about add 1in to the stroke?
Engine A is a Bristol Mercury, Engine B is a Pegasus, please note the effect of having 7.5ins of fuel. air mixture acting on each sq in of piston area even if the average pressure was low.

It may be useful in comparing engines of similar size and/or stroke but it does have some limits.
 

I think you'll find that every cylinder fires within 720° crank angle in a 4 stroke (every 360° in a 2 stroke).

A 60° V-12 with a 120° crank throw angle has 60° between firing impulses, the theoretical ideal.

The same is the case for 120° and 180° V-12s.

For a W-18, even firing intervals would have to be 720/18 = 40°. I am not sure how that would be achieved.
 


Increase RPM.

Articulated connecting rods have their own problems, even in V-12s, as if the geometry isn't right, the two banks can end up with noticeably different strokes.

HP/in^2 scales better with engine size than HP/in^3.
 

One bank straight up (call this 0 degrees), one at 40 degrees, and one at 320 degrees. It would also work if the banks are at 0/80/280 degrees (which is more a "T") or 0/120/240 (although that's a Y). Since W-18 engines were, and are, currently produced, albeit now longer for aircraft; see W18, and Isotta Fraschini W-18 Aircraft and Marine Engines, I would argue that problem's been solved. As for loading per crankpin? Radials will have 5, 7, 9, or (very rarely) 11 cylinders on each crank throw. I don't think 3 or 4 would be insuperable.
 
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