Advantages of sleeve valves for H-24 engines?

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Simon Thomas said:
From "Short Stirling, The First of the RAF Heavy Bombers" written by Pino Lombardi 2015. Page 181 Paragraph 1. Trials were made with both the Hercules II and the Wright Cyclone (actually the GR-2600-A5B). The findings were the sleeve valve had the following advantages over the poppet valve.
(2) Performance
(3) Fuel Consumption
(4) Noise

This comparison is obviously the same aeroplane with the only change being the engines, which provides the only like-for-like real world comparison I have found.

I showed a comparison of the performance curves and bsfc in this thread:

Short Stirling Engines - Hercules XI & Wright GR2600A5B

Does anyone have a copy of the performance curve for the Wright GR2600A5B fitted to the Short Stirling? I am hoping to compare the performance curves of that and the Hercules XI. In the book "Short Stirling, The First of the RAF Heavy Bombers", Pino Lombardi writes However, Hercules engine...
ww2aircraft.net ww2aircraft.net
Click to expand...

I am confused.
In the first line you write "Hercules II" and the thread is about the Hercules XI engine. Typo? and I am one of the Forum typo champions;)

However this does not really help the discussion as the Hercules II was 1938 engine and the Hercules XI was a 1941 engine. (at least in Lumsden)
The problem comes in with GR-2600-A5B being a 1939-40 engine, Why the British ordered those engines I have no idea. Perhaps it was all they could get. But they were not the latest practice of the Wright company in 1941(443 BA models built)-42 (over 6000 built).
The BA's were the 1700hp version.
Power chart here (TBF installation)

This much closer to the Hercules XI power level. According to Lumsden the Hercules XI was set up to run on 100 octane fuel. I have no idea of what the GR-2600-A5B was running on the British test. They made GR-2600-As until just about the end of 1944 but most ran on 100 octane. It didn't change the take-off power but it may have changed the throttle openings at different RPMs/altitudes.

I can appreciate trying to compare different engines in the same airframe and sometimes (a lot of times) there isn't a lot of selection. But if we are trying to compare the engines at a certain point in time we need to try to use the best/most recent practice of both companies.
 
Simon Thomas said:
From "Short Stirling, The First of the RAF Heavy Bombers" written by Pino Lombardi 2015. Page 181 Paragraph 1. Trials were made with both the Hercules II and the Wright Cyclone (actually the GR-2600-A5B). The findings were the sleeve valve had the following advantages over the poppet valve.
(2) Performance
(3) Fuel Consumption
(4) Noise

This comparison is obviously the same aeroplane with the only change being the engines, which provides the only like-for-like real world comparison I have found.

I showed a comparison of the performance curves and bsfc in this thread:

Short Stirling Engines - Hercules XI & Wright GR2600A5B

Does anyone have a copy of the performance curve for the Wright GR2600A5B fitted to the Short Stirling? I am hoping to compare the performance curves of that and the Hercules XI. In the book "Short Stirling, The First of the RAF Heavy Bombers", Pino Lombardi writes However, Hercules engine...
ww2aircraft.net ww2aircraft.net
Click to expand...
JAW: "There still were (& are) a number of those advantages - which are inherent mechanical attributes - remaining relevant, as it happens."

The point I understood being made by J.A.W. was that there were advantages relevant to today, not if just about the best sleeve valve ever made was fractionally
better than a very run of the mill 2-valve per head poppet engine.

I would say that this sort of study is more or less a nonsense in as far as using it to compare sleeves vs non sleeves, as they are completely different engines, all you`re doing is comparing the engines not the method of their valve operation. It would be impossible to normalise the other factors to isolate what effect the sleeves were having. Its also
a terrible comparison anyway for reasons mentioned. You might as well test a Kestrel against an R-2800 and say "look see, air cooled is better"

There is no global law today against using sleeves for any production vehicle you wish, yet nobody bothers.

The reasons for adopting it, relevant once about a century ago, simply dont exist now.

Lets address these three points:

1) Performance, it obviously does not have the best performance as in wartime it was never boosted above +11lbs with any sucess (+17lbs came after the war ended), meanwhile
the best poppets were running +25lbs and the Merlin 100 type tested during the war and passed at +30lbs. No amout of arguing about a bit of swirl here or tumble there is going to
get you ahread when you cant even run at half the boost of your competitors. The Sabre did reasonably
well as it ran fast, a good design idea which was due to the short stroke and nothing what-so-ever to do with
sleeves (which have appaulingly high friction and inertia - Napier admitted that also the oil consumption
was horrific and they never got it even near a poppet valve for that figure either).

(Sabre VII oil consumption was about 50% higher than a BMW-801 and about 25% higher than a Merlin)

2) Fuel consumption, nope, the best consumption was shown by direct injected poppet valve engines, which
were getting towards 190g/Hp/Hr

Bog standard DB 601 = 213 grams/hp/hr
Sabre VII = 248 grams/hp/hr (at maximum weak cruise, its a lot worse for other conditions)
Merlin-66 = 225 grams/hp/hr (maximum cruise)



3) Noise - The only wartime report I`ve EVER read which mentions noise being a problem were when the
2-stroke was being considered for the Spitfire. The noise was considered likely to be so deafening as to
be able to actually incapacitate the pilot.
 
Last edited:
Snowygrouch said:
It says 140 PN fuel and no water.

There was all sorts of messing about with fuels and you`ll even find 160 grade mentioned in some papers, we can only
surmise it was about a half way house between 130 and 150 grade.
Click to expand...

What power does +30psi give the Merlin?

~2,200hp?
 
2340hp
@ +30lbs boost,
3000rpm - date 28th Oct 1944
Bhp/Litre = 87 (this is higher than any type tested Sabre power rating)

Now if you want a LOT of power, you`d get that spinning faster, but you cant due to the long stroke (Sabre has 121mm instead of 152mm of the Merlin). Which is why you
suddenly see what might have been with a poppet valve sabre with its tiny stroke, you could have had a wartime "sabre" which
ran 500 hours and went to +30lbs boost at 4000rpm. That would have been a party trick worth having.
 
For those of us who have forgotten
Sabre...................5 in/127mm bore............................4.75/121mm stroke............................3046fpm piston speed at 3850rpm
Merlin.................5.4in/137mm " "...............................6.0/ 152mm " " ..................................3000fpm piston speed at 3000rpm
Griffon................6.0in/152mm " "...............................6.6/ 168mm " " ..................................3025fpm piston speed at 2750rpm
 
Bretoal2 said:
A QUESTION...

We have seen in this forum, about a year ago (more or less...) , a very unusual graph comparing the main great engines of WWII. It integrated, as I remember, power, RPM and BMEP.

The Sabre was credited by 3.900 hp and the drawing showed that this was obviously "out or range".

I'm unable to find back this drawing. Any idea ? Thanks !
Click to expand...
This one?
PXL_20230627_024142451.jpg

It's from 'Power to Fly' by Setright.
 
Shortround6 said:
I am confused.
In the first line you write "Hercules II" and the thread is about the Hercules XI engine. Typo? and I am one of the Forum typo champions;)
Click to expand...
I was quoting verbatim from the book. When I looked at the history cards of the three Stirlings that were running the Cyclone, almost all the adjacent serial numbers were constructed with Hercules XI engines. I figured that would be the XI would be the most appropriate comparison.

Shortround6 said:
However this does not really help the discussion as the Hercules II was 1938 engine and the Hercules XI was a 1941 engine. (at least in Lumsden)
The problem comes in with GR-2600-A5B being a 1939-40 engine, Why the British ordered those engines I have no idea. Perhaps it was all they could get. But they were not the latest practice of the Wright company in 1941(443 BA models built)-42 (over 6000 built).
The BA's were the 1700hp version.
Power chart here (TBF installation)

This much closer to the Hercules XI power level. According to Lumsden the Hercules XI was set up to run on 100 octane fuel. I have no idea of what the GR-2600-A5B was running on the British test. They made GR-2600-As until just about the end of 1944 but most ran on 100 octane. It didn't change the take-off power but it may have changed the throttle openings at different RPMs/altitudes.

I can appreciate trying to compare different engines in the same airframe and sometimes (a lot of times) there isn't a lot of selection. But if we are trying to compare the engines at a certain point in time we need to try to use the best/most recent practice of both companies.
Click to expand...
I have to assume that the Brits bought the best engine they could lay their hands on when they were building the Stirling. Hopefully someone has the date, but I understand that the US could not sell military engines to the UK until after the US gave approval. Hence the civil GR-2600-A5B was bought, not the military R-2600-21 or whatever.

Feel free to propose any more appropriate comparisons. Was there ever an airframe with both the Sabre and Griffin?
 
Simon Thomas said:
I have to assume that the Brits bought the best engine they could lay their hands on when they were building the Stirling. Hopefully someone has the date, but I understand that the US could not sell military engines to the UK until after the US gave approval. Hence the civil GR-2600-A5B was bought, not the military R-2600-21 or whatever.
Click to expand...
Maybe they wanted to standardize engines?
The GR-2800-A5B was used in most of the A-20s, it was used in the early Martin Baltimore's ( the first 3-4 marks).
In 1940 and early 1941 I am not sure what was going on as far as releasing certain model engines for overseas sale. By late 1941 things were very different and the while the Dutch didn't their B-25s in time they had been ordered with the 1700hp engines.

All I know is that the GR-2600-A5B was not the latest and greatest R-2600 at the time the Hercules XI showed up. In fact the 5th production R-2600A was delivered in March 1938.
Wright was working on the R-2600-B in Nov 1938, test ran the first one June 1940 and delivered the 5th production engine June 1941 if that helps any.
The later R-2600-BB engines (1900hp) kept the bore and stroke, much like some of the later Hercules only kept a few parts.
 
Snowygrouch said:
I would say that this sort of study is more or less a nonsense in as far as using it to compare sleeves vs non sleeves, as they are completely different engines, all you`re doing is comparing the engines not the method of their valve operation. It would be impossible to normalise the other factors to isolate what effect the sleeves were having. Its also
a terrible comparison anyway for reasons mentioned. You might as well test a Kestrel against an R-2800 and say "look see, air cooled is better"
Click to expand...
They were the closest I could find with adequate data to make a comparison. To just compare valve mechanisms, I suggest "The High-Speed Internal Combustion Engine" by Ricardo. [for the avoidance of doubt - this is a joke]
Snowygrouch said:
There is no global law today against using sleeves for any production vehicle you wish, yet nobody bothers.

The reasons for adopting it, relevant once about a century ago, simply dont exist now.
Click to expand...
There is at least one who does. They used to make sleeve valve RC plane motors until a few years ago, but dropped them in favour of drone motors. They are rather small, but they are current production sleeve valve engines. RCV Engines | DF140LC 4 Stroke Cylinder Engine The sleeves only rotate, so they are different to the common elliptical path sleeves.

Snowygrouch said:
1) Performance, it obviously does not have the best performance as in wartime it was never boosted above +11lbs with any sucess (+17lbs came after the war ended), meanwhile
the best poppets were running +25lbs and the Merlin 100 type tested during the war and passed at +30lbs. No amout of arguing about a bit of swirl here or tumble there is going to
get you ahread when you cant even run at half the boost of your competitors. The Sabre did reasonably
well as it ran fast, a good design idea which was due to the short stroke and nothing what-so-ever to do with
sleeves (which have appaulingly high friction and inertia - Napier admitted that also the oil consumption
was horrific and they never got it even near a poppet valve for that figure either).

(Sabre VII oil consumption was about 50% higher than a BMW-801 and about 25% higher than a Merlin)

2) Fuel consumption, nope, the best consumption was shown by direct injected poppet valve engines, which
were getting towards 190g/Hp/Hr

Bog standard DB 601 = 213 grams/hp/hr
Sabre VII = 248 grams/hp/hr (at maximum weak cruise, its a lot worse for other conditions)
Merlin-66 = 225 grams/hp/hr (maximum cruise)


3) Noise - The only wartime report I`ve EVER read which mentions noise being a problem were when the
2-stroke was being considered for the Spitfire. The noise was considered likely to be so deafening as to
be able to actually incapacitate the pilot.
Click to expand...
1) The Sabre and the Merlin are even further apart than the R-2600 and the Hercules.
Have you got data on sleeve friction? One mention I found was from the Mono-Sleeve Valve paper by Fedden. In the discussion it says:
I can say quite truthfully that there is no measurable difference in mechanical efficiency between the Perseus and Mercury engines. Up to any speed that we have been able to motor these engines it has been found that the poppet valve and sleeve valve are comparable.​
Papers on car engines from the 20's give actual numbers, but not sure how applicable they would be to aero engines.

2) Aircraft Engines of the World (not sure which edition, must be post war) states the following for cruising.
Sabre IIA - 210 g/hp/hr
Sabre VA - 225 g/hp/hr
Sabre VII - 230 g/hp/hr

3) So noise may be one characteristic in which the sleeve valve is superior to the poppet valve. 🎧
 
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