"No sleeve-valve engines" scenarios

[Shortround6]

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.

Excuse me, I did not word my sentence clearly. I was referring the the firing impulses on each crank pin/connecting rod bearing. The whole engine may have a cylinder firing every 60 degrees of crankshaft rotation but the 60 degree angle V-12 has the cylinders on each crank pin firing at the 300 degree-420 degree spacing. If you have 180 degree V-12 (flat engine but not a boxer) you get the pair of cylinders firing at an even 360 degrees. I believe the 120 degree bank angle gets you a 240-480 firing interval?

Edit, I had a brain fart. the 180 degree V-12 will have the the cylinders firing at 180-540 degrees, one piston is at TDC while the other is a BDC. End edit

The Issota Fraschini engines did use the 40 degree spacing between banks. Now plot the the crank rotation for one set of cylinders with the top dead center (theoretical firing point) using one crankpin and see what kind of spacing you can get.

 

[Shortround6]

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.

The problem is not necessary solved for all applications. It was solved for the applications the Isotta engines were used for.
Solving the crankshaft rotation problems for a 1900-2300rpm engine is not the same as solving them for a 3000rpm engine. Whole new world of vibration problems.

Comparing radial engines to inlines is also a bit problematic. Radials use very short and beefy crankshafts with large journals. They are not subject to the torsianl vibariton poblems of V-12 s or W 18s., They do have problems of their own, front row of cylinders is trying to go in one direction while th rear row goes in another direction.
Yes you can build a W -18 with a stiff enough crankshaft and crankcase to take the loads, the problem comes in with what does it weigh?
This was the big bugaboo with V-16s which often were actually two V-8s coupled in the middle with the drive shaft (and cam drives) coming out of the middle of the engine. this extra long arrangement actually being lighter than a true V-16 engine with all the drives/accessories on one end.

 

[swampyankee]

Given the limits in 1940, a 2000 hp V-12 may not be practical; 16 or more cylinders would likely be needed. Napier liked H engines; they would probably pick that configuration.

That rarity, a liquid-cooled radial may also be an option.

Overall, I think that eschewing sleeve valves would have a trivial effect on Britain's war effort: poppet-valve equivalents of the Sabre, Hercules, and Centaurus could be produced without any more effort than that which went into the sleeve-valve engines actually produced. Yes, sleeve valves had some advantages, but they were not so much better than poppet valves that the RAF would have to limp along with engines that were little more than flying boat anchors. Every other nation -- and even the UK, itself -- managed to produce high-output engines with poppet valves. One need only look at every single major engine manufacturer except Bristol and Napier. I think one can argue that sleeve valves were a detour in engine technology.

 

[Shortround6]

The limit may be fuel related. The Merlin in the Speed Spitfire had made over 1800hp(?) and run at 1600hp for 10 hours. Granted this was not on gasoline but the basic structure and supercharger technology to get the required amount of air through the engine existed.

Another question is at what altitude do you rate the engine. A table in "Aircraft Engines" by A. W. Judge (1940) shows a Merlin II rated at 990hp at 12,250ft at 2600rpm (manifold pressure not given) but having a potential ground power of approximately 1500hp. Which turns out to be not that far off the mark. (1440hp at 5,000ft at 3000rpm/16lbs boost for Merlin III in a sea Hurricane),

Designers were a lot more obsessed with hp per sq/ft of frontal area at the time which influenced cylinder arrangements.

 

[swampyankee]

Designers were a lot more obsessed with hp per sq/ft of frontal area at the time which influenced cylinder arrangements.

"Obsessed" is probably the correct word. To a very great extent, piston-engined, propeller driven aircraft are too slow for frontal area, per se, to be terribly important. What is very important is to avoid separation, both externally and within the cooling system (if nose shape was that important, the P-39 would have been a stellar performer instead of a mediocre one). Cooling system design got better in the 1930s -- the exposed cylinders and Lamblin radiators of the 1920s had largely vanished by 1940. Heck, even the flying airbrake that was the Swordfish had a NACA cowling to improve cooling performance and reduce drag!

Of course, cooling system design is hard. Nobody had a perfect lock on it, although North American, with the Mustang, probably came closest. I don't know who did the best design for radial engine cooling (please don't say Focke Wolf; there's a reason nobody else needed a fan, and it wasn't because FW was better than anybody else)

 

[tomo pauk]

Of course, cooling system design is hard. Nobody had a perfect lock on it, although North American, with the Mustang, probably came closest. I don't know who did the best design for radial engine cooling (please don't say Focke Wolf; there's a reason nobody else needed a fan, and it wasn't because FW was better than anybody else)

Let's recall that cooling system of the P-51 series changed from P-51 to A-36 & P-51A, then again it was changed when going to the Merlin, and then again when going to the 'lightweight Mustangs' - 4 versions of cooling system in 4 years.

When introduced (timing is perhaps the most important thing in a shooting war), the BMW 801 installation was probably the best in the world, but it was not ideal, or best possible. Yes, fan allowed for tighter cowling (drag -), but also consumed up to 50 HP at altitude, and up to 60 (70?) HP down low. The oil system was well protected, but at a cost of around 150 lbs worth or steel armor. Ram air intakes were very streamlined, but were also messing up the ram effect and with it robbed some of altitude performance; there was also no possibility to install air filters. If external air itakes were installed (an easy thing) for the better altitude power, the air filters were a possibility, but they were draggy and thus the aircraft were slower down low. Probably the best thing were the individual exhausts - a well-designed and executed exhausts were adding perhaps 12% to the propulsive power at ~20000 ft, while a badly-executed exhausts (talk P-36, MC.200, Ki-27, earlier Ki-43s and Zeros) will perhaps add just a few %.
The BMW 801 was of a small diameter for the power it produced.

 

[wuzak]

Comparing radial engines to inlines is also a bit problematic. Radials use very short and beefy crankshafts with large journals. They are not subject to the torsianl vibariton poblems of V-12 s or W 18s., They do have problems of their own, front row of cylinders is trying to go in one direction while th rear row goes in another direction.

Which is why radials, particularly the larger radials, tend to have dynamic dampers set into the counterweights on the cranks, whereas V-12s tended have a TV damper at one end of the crank, or not at all.

Its why Pratt & Whitney spent thousands of hours getting on top of torsional vibrations, and Rolls-Royce didn't. The Merlin didn't even have a TV damper, just using torsionally flexible shafts to drive the prop and the supercharger. With a little bit of clutch slip on 2 speed units.

 

[jetcal1]

I am not sure the Hercules had any more problems than many other engines in it's first few years. Open to correction.
However the problems really started when they tried to mass produce it (and/or the Taurus/Perseus) as they couldn't keep the sleeves round and some were crapping out after 20 hours?
The hand built prototypes and low production Perseus engines didn't show the problem.
Oil consumption went up and plugs fouled. On occasion the sleeve jammed and the sleeve drive mechanism broke.
A major crisis in the making.

My bad the problems were actually a touch more mundane and related to reduction gear failures during testing and the failure of the MK VI to make rated HP for the Beaufighter.

 

[jetcal1]

Why are the Fairey Prince or Monarch engines being overlooked here?

 

[wuzak]

Why are the Fairey Prince or Monarch engines being overlooked here?

Because they weren't very good.

 

[Shortround6]

Why are the Fairey Prince or Monarch engines being overlooked here?

They had some, shall we say, interesting features. Some may have been good, some not so good.
In the opinion of some of people in charge at the time the not so good outweighed the good.

Fairey also didn't have an engine factory. They had a small experimental shop. they may have actually built only a 1/2 dozen or so engines in the 1920s/30s.

 

[jetcal1]

Because they weren't very good.[/QUO TE]

Having read the reports (Ain't the internet great!), One could draw the conclusion that by mid-1941 there was a four year old engine that had seen limited development that was running quite reliably at a lower HP on 87 octane fuel.

Considering this engine had no ministry support or funding, you have to wonder if it could have been developed into something beyond "they weren't very good" in the context of this thread.

 

[jetcal1]

They had some, shall we say, interesting features. Some may have been good, some not so good.
In the opinion of some of people in charge at the time the not so good outweighed the good.

Fairey also didn't have an engine factory. They had a small experimental shop. they may have actually built only a 1/2 dozen or so engines in the 1920s/30s.

Partially agree after reading the reports. Please see reply to Wuzak.

 

[swampyankee]

Because they weren't very good.

A category into which I would put the Armstrong "dog" engines.

 

[Shortround6]

Please note the rather convoluted path of the intakes with part of the path actually part of the crankcase? Also note the 4 exhausts for bank of 6 cylinders.
This thing had a crap load of breathing problems.
Then you have the issue of of weight or perhaps the lack of weight.
You have essentially two 1558 cu in engines that weigh under 1100lbs apiece side by side. This seems a little light for a high output engine turning 3000rpm.

 

[swampyankee]

There were a lot of British high-powered engines much closer to service than the Fairey Prince or Monarch and the Armstrong "dog" series. One example would be the RR Vulture.

 

[jetcal1]

Because they weren't very good.

The report from

There were a lot of British high-powered engines much closer to service than the Fairey Prince or Monarch and the Armstrong "dog" series. One example would be the RR Vulture.

Which had far more developmental resources and money thrown at than the Fairey engines...................

 

[jetcal1]

Please note the rather convoluted path of the intakes with part of the path actually part of the crankcase? Also note the 4 exhausts for bank of 6 cylinders.
This thing had a crap load of breathing problems.
Then you have the issue of of weight or perhaps the lack of weight.
You have essentially two 1558 cu in engines that weigh under 1100lbs apiece side by side. This seems a little light for a high output engine turning 3000rpm.

If the sleeve valves failed, would this engine have done better if it had the same resources thrown at it as the Vulture?

 

[fastmongrel]

According to the Rolls Royce Heritage Trust the Vulture had been fixed or rather a prototype engine with a modified bottom end had been built and run succesfully in a test cell. Unfortunately by this time the Air Ministry, the RAF and the aircraft manufacturers had understandably had enough of the Vulture and all its problems. Interesting to think if the sleeve valve Sabre had been a total failure (rather than a problem child that needed a proper manufacturer to sort out its troubles) RR might have been forced to get the Vulture working as an urgent matter.

Strangely enough the Vulture seemed to work just fine in the Hawker Tornado perhaps a bomber slogging along caused problems that were less likely to occurr in a high reving fighter

 

[wuzak]

If the sleeve valves failed, would this engine have done better if it had the same resources thrown at it as the Vulture?

Had Rolls-Royce developed the engine it would have, no doubt, been far more useful.

Had Fairey been given the money to develop the engine then I doubt it, since they had little engine experience, no production experience and not enough engineers.