2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Tommy Cookers.

From the 3rd page of your first link (Napier Deltic):

The exhaust opens 34.5 degrees before the inlet (or transfer).
The exhaust closes 5.5 degrees before the inlet (or transfer).


From the 4rth page of your first link (Napier Deltic):

This means that one piston in each cylinder must lead the other by 20 degrees.
. . .
The ideal exhaust port lead for this type of engine is that which allows the combustion pressure to fall below the scavenge pressure at the point of inlet port opening. The inlet port is closed after the exhaust port, and thus the blower supercharges each cylinder after the exhaust port has closed. During the period that both ports are open, the air flow from the blower scavenges the cylinder of all exhaust gases and assists in cooling the cylinder walls and piston crowns.




From http://www.pattakon.com/pattakonPatAT.htm :







The above PatATi model / RC engine (ring-less piston, bore less than, say, 1 inch) comprises only three moving parts, as the simplest 2-strokes: a piston, a connecting rod and a crankshaft.

No matter how simple it is, it offers as asymmetric intake as the best “reed valve 2-strokes” (which cannot run at really high revs) and as the best “rotary valve 2-strokes”.

It also offers as asymmetric transfer as the Opposed Piston Junkers and Achates Power 2-stroke engines. If desired, the transfer can close after the exhaust (as happens in the famous Napier Deltic).


It is funny: the Napier Deltic:



a monster engine, one of the most advanced / complicated / expensive reciprocating piston engines ever, had to compromise with the wrong port timing (20 degrees phase difference between each pair of crankshafts), while the above tiny and simple single-cylinder PatATi model engine can achieve the desirable / ideal asymmetry in the intake and in the transfer processes.


I hope it is now obvious that with the PatATi architecture, the most important processes in the 2-stroke engines are substantially changed / affected / improved, while the number of moving parts remains the minimum: a piston, a connecting rod and a crankshaft.

Thanks
Manolis Pattakos

[J.A.W.]

Indeed Manolis, the Deltic rotated one of its crankshafts opposite the other two to get that timing.

Here is a curious variation on the opposed theme 2T mill, with a radial 120` triple design firing 3 pistons from 1 chamber.
( Scroll down the article for diagram/drawings/photos/patents)

https://oldmachinepress.com/2014/02/24/ ... l-engines/

[manolis]

Hello J.A.W.

For some reason your posts are published with one or two days delay.


You write:
“. . . repeating the claim of lower S-V oil consumption”

The specific lube consumption of the Sleeve valve airplane engines was about half than that of the poppet valve airplane engines of that era.

But we talk for extreme specific lube consumptions: about 5gr/kWh for the sleeves (0.008lb/HP/Hour), and 9gr/kWh (0.0015lb/HP/Hour) for the poppet valve engines.

Supposing a specific fuel consumption of 250gr/kWh (32% BTE), the oil-fuel ratio is 1:50 in the sleeve valve aero engines and 1:28 in the poppet valve aero engines.

Such a specific lube consumption fits with 2-stoke engines (the modern giant 2-stroke marine engines run on specific lube consumption of 0.7gr/kWh, i.e. seven times lower than in the old sleeve valve 4-stroke aero engines.

In order sleeve valves to be used in a modern car / motorcycle engine, it is required a control mechanism to keep the oil from escaping to the exhaust and from getting into the combustion chamber degrading the combustion and increasing the emissions (MIT, http://www.pattakon.com/tempman/Lubrica ... Diesel.pdf )



You also write:
“. . . the Deltic rotated one of its crankshafts opposite the other two to get that timing.”

The reverse rotation of the one crankshaft is not a problem (except during assembly).

In the following Napier Deltic animation (from Wikipedia):



the lower crankshaft (it controls only exhaust ports) receives about two times the power received by the top left crankshaft (which controls only transfer / inlet ports).



In the Michel three-crank opposed-piston engine:



an interesting thing is the way the three crankshafts are synchronized:

“All three crankshafts rotated in the same direction. There was an additional, projecting crank at the end of each crankshaft. Attached to this crank was a triangular casting that connected the crankshafts together at the rear of the engine. This triangular member drove the generator and the water, oil, and Bosch fuel injection pumps. The fuel injection pump was positioned in the upper V of the engine.”

Thanks
Manolis Pattakos

[Tommy Cookers]

another treatment of the radial's rods and crankshaft ......
http://oldmachinepress.com/2014/01/12/n ... al-engine/

and the traditional 'slipper type rod' way of getting equal motion from all pistons (GM-Electromotive 16-184 X-16 2 stroke poppet valve Navy diesel)
https://oldmachinepress.files.wordpress ... ection.jpg

there's the (4 stroke) 42 cyl Zvezda M503/56 cyl M520 (5300 hp/engine), descendants of the Yakovlev M501 favoured by USSR over the Junkers 224
apparently in production today, presumably a master rod type

and (it is said), after WW2 it was determined that .....
the sleeve valve Hercules cost 2x the Merlin's cost (to do the same job) and the Sabre cost was 4x the Merlin's
the numerous sleeves and their numerous drives being very expensive to make
and the sleeve impedes piston cooling
NACA showed that detonation was driven by piston crown temperature not poppet valve temperature (sodium-cooled presumably)

btw the Deltic was in (Japanese Navy) service at 3700 hp/engine and a version at 4100 hp was under test at Napier

[J.A.W.]

T-C, regarding "cost", development/construction costs of the sleeve valve mills may well have been higher than
for the old-school R-R V12, but the Hercules TBO & cost of running & overhaul was likely lower.

Its important to include economies of scale, too, since only ~5,000 Sabres were built altogether, & almost all of
them went into useful airframes, unlike the Merlin, which was churned out in the multiple tens of thousands,
yet went into many many airframes of dubious value, especially from mid-war, when they'd have been better used in
a properly designed tank, rather than obsolescent P-40s/Hurricanes/Halifaxes/Spitfire V's or scattered over Germany in
their thousands, in really costly attacks, sometimes at the rate of hundreds per night.

If more Sabres had been available a 'Super Mosquito' or Hawker equivalent utilizing twin Sabres could've made
two trips to Berlin per night at a 400mph cruise, & at much less cost - both in numbers & losses , of aircrew & aircraft.

By 1944, really only the Mustang & Mosquito were making best use of the Merlin, but the Sabre powered Tempest
stopped more of the pulse-jet Nazi V1 cruise-missiles from splattering down on London, by dint of it prodigious power,
power - that the Merlin could not match.

[wuzak]

Manolis, thanks for the interesting mechanical analysis..

R-R never got far with their single crankshaft X-configuration engines & eventually did a 'Chinese copy' of Napier's Sabre..
( see 1st post of current page of "Feliks..." thread for a Sabre H-24 graphic) R-R's Sabre copy failed due to harmonics issues..

Unlike the Sabre, the R-R H-24 fired 2 cylinders simultaneously, & coupled the crankshafts through a simple spur gear..

Don't know that the Eagle 22 failed due to harmonics, or that it was outdated before it went to production by gas turbines.

Remember that the Sabre had 7-8 years of development before it was truly reliable. The Eagle had barely 3 when it was axed.

[wuzak]

my source (the Graham White book) now seems misleading re Exe and Pennine big end design
the Exe was a split b.e. (like the Vulture), the Pennine wasn't
and apologies, yes of course, they were 4 strokes, but air-cooled, so the bore centres would be larger and so ease the b.e. design

fwiw I now think the Vulture piston motion had 3 geometries, eg for commonality of link rods and compression height ?
(I have scanned the diagram from the GW book but attempts to send it to you in a PM don't seem to work)
but surely a geometry common to all the link rod piston motions is in principle possible ?

another source says the only remaining Vulture problem was b.e. bolt failures
and that RR wanted it cancelled as they were busy and preferred their later PV24 design (presumably another liquid-cooled X-24)
in stating that the Vulture had Merlin-size bore centres maybe GW is being informed by recollections of the PV24 design
an X-24 basically as 2 short-stroke Merlins that could have been looking at 4000 - 4500 hp

The Pennine had a split big end for its master rod, as not doing so would require a built-up crank. Which is clearly not the case.

For comparison, Pratt & Whitney's R-2800 had a built up crankshaft and single piece master rods. The R-4360, which used basically the same cylinder geometry, had a one-piece crankshaft and split bearing master rod.

I've never heard of the PV24.

The Vulture had a few issues left to solve, but they would require more resources than Rolls-Royce had to give at a key point in the war.

The bore spacing of the Vulture, Merlin and some other RR engines:
Vulture – 6.1in
Kestrel/Peregrine – 5.625in
Merlin – 6.075in
Griffon – 6.9in

The main outstanding issue was the big end of the master rod. The way that the original was designed left not very much room for the bolts, and Rolls-Royce could not pre-tension them as they would in their other engines.

It was considered that the engine could be designed to do away with the master and slave rod arrangement, to be replaced by two fork and blade rods side by side. It would mean that two banks would be offset relative to the others.

Another change that would have been made is to replace the reduction gear (4 spur type gears) with an epicyclic gear reducer, saving as much as 200lbs (90kg) of weight.

The Vulture is known to have tested at over 2,500hp before its cancellation, so around 1940/41.

Only one Pennine was built, it being discontinued in favour of gas turbines. The prototype was rated at 2,800hp. Its nominal bore and stroke dimensions were 5.4" x 5.0" - same bore as a Merlin but with a short stroke.

FWIW, the Rolls-Royce R was developed from the Buzzard for the 1929 Schneider Trophy. It continued with the fork and blade rods of the Buzzard, but at more than twice the power - 2,300hp.

For the 1931 race the R was reworked for more power, but reliability suffered - the rods were failing. Rolls-Royce's solution to this was to do away with the fork and blade rods and substitute a master and slave rod system.

[wuzak]

The Sabre was intended to be capable of running as a 2T, but even running 1/2 time as a 4T, the best available prop's of the day - were at their limits coping with its power outputs.

I find that very hard to believe.

The Sabre program may have started as a 2 stroke Diesel before evolving into the 4 stroke spark ignition engine that it became. Not quite the same thing.

The inspiration for the Sabre's development is Ricardo's work with 2 stroke sleeve valve engines. Both Rolls-Royce and Napier embarked on 2 stroke Diesel projects based on Ricardo's work, Rolls-Royce's evolving to become the Crecy. It is likely that is where the Sabre began.

[J.A.W.]

The Sabre was intended to be capable of running as a 2T, but even running 1/2 time as a 4T, the best available prop's of the day - were at their limits coping with its power outputs.

I find that very hard to believe.

Really? Here's F/O Ron Dennis - quoted at the wwiiaircraftperformance site:

"All our machines were fitted with Rotol airscrews when the maximum rpm were increased to 3,850 from 3,700,
& the boost to +13lbs from +11, as the de Havilland airscrew could not absorb the power, & more than once
shed a blade with somewhat detrimental effects..."

I recall reading that S. Camm, Hawker's chief designer virtually accused R-R of sabotaging his progress via
non-availability of Rotol prop's suitable for the Sabre, as payback for his rejection of R-R engines..

One of the major faults of the R-R Eagle II, ( Sabre copy), & that AFAIR - was deemed due to a harmonics issue - was the
failure of the the shaft that drove both magnetos, this was somewhat problematic..

It certainly seems odd that if the Vulture was almost 'cured', that work on the Eagle II was even considered worthwhile,
except perhaps as another attempt to stymie a competitor..

[wuzak]

I wasn't talking about the prop issue.

In any case, Rotol was joint venture between Rolls-Royce and Bristol to build propellers for their engines. It is, therefore, not surprising that they were reluctant to interrupt production to suit the low volume product of a competitor.

Also curious since de Havilland were building Hamilton Standard props under licence, and I'm sure something that suited an R-2800 or R-3350 should have done well for the Sabre.

The Vulture wasn't "almost cured" as such - there still needed significant design and prototype work to be done.

Why the Vulture wasn't redone in later years is anybody's guess. Perhaps Rolls-Royce were on the sleeve-valve fad, since they also built the Pennine.

The Pennine showed what could be done. At 2,750ci it was slightly smaller than the R-2800 in capacity, but the prototype was rated at 2,800hp @ 3,500rpm and +12psi boost, somewhat less boost than the R-2800 needed to match that power number.

Considering that a Merlin could produce 2000hp WEP in 1944, a Vulture with a short stroke and the same piston speed should have been capable of around 4,000hp.

I also wonder why they didn't make the Eagle 22 as a liquid cooled variant of the Pennine. It would have been more compact and far lighter.

The Vulture with its OHCs had a smaller frontal area than the Sabre.

In fact, a proposal for a twinned Merlin 61, with basically two complete Merlins side by side including supercharger and accessories, would have been lighter than the Eagle and more powerful to boot.

[wuzak]

One of the major faults of the R-R Eagle II, ( Sabre copy), & that AFAIR - was deemed due to a harmonics issue - was the failure of the the shaft that drove both magnetos, this was somewhat problematic..

I think the fact that the magnetos were driven by the one shaft was as much the problem as anything.

[Tommy Cookers]

the old machinery press article says the Pennine had (unsplit) master rods and a crankshaft assembled around the rods
(as the drawing that manolis posted on the previous page)

regarding the supposed propellor issue, the Sabre's friends seem to have been demanding a luxury that had been denied to others ....

prop pitch can easily be increased to the super-optimal, to absorb greater power but with reduced efficiency and disproportionate adverse torque in roll
this causing important control difficulties at low airspeed
established fighters suffered this as, with development for war-winning, power was increased without any possible increase in prop diameter
newer types, eg Typhoon, Thunderbolt, Corsair apparently enjoyed a designed-in margin (a relatively larger swept area) intended to avoid this problem

[wuzak]

the old machinery press article says the Pennine had (unsplit) master rods and a crankshaft assembled around the rods
(as the drawing that manolis posted on the previous page)

Re-reading that article and looking closely at the cutaway it does seem that the crank was built up.

It, thus, appears that I was wrong.

[J.A.W.]

It, thus, appears that I was wrong.

Good call, & so with the Eagle II magneto drive failures..

The R-R Vulture X-24 engine as fitted to the Tornado, due to its greater depth, required mounting ahead of the mainspar..
This compares to the more compact Sabre fitment in the Typhoon sister aircraft - rearward & above, so it meant that
the already completed Tornado production facilities & components built by Avro - had to be scrapped, when the Vulture was..

It was mooted to fit the big Bristol Centaurus radial to the Tornado, but apart from prototypes, nothing came of them,
perhaps due to the Centaurus then not actually then being in production, as such..

It must also be remembered that the Sabre engine allowed for a higher thrust line, & larger diameter prop's - than the
radials which would fit in equivalent airframes, with the Typhoon swinging a broad chord blade 14 ft unit, of 3, then 4 blades.

Edit: corrected noted R-R engine name.

[wuzak]

The Vulture's dimensions were (from RRHT):

Length overall - 87.625in.
Width overall - 35.8in.
Height overall - 42.175in.
Weight - 2450lb

The Sabre's dimensions were (VA, from Wiki):
Length overall - 82.25in.
Width overall - 40in.
Height overall - 46in.
Weight - 2360lb

The Vulture was 5in longer, but it certainly wasn't "greater in depth".

I believe the earlier Sabres weren't as tall as the VA. But still taller than the Vulture.