British poppet valve radials

[Admiral Beez]

How did British poppet valve or traditional (non-sleeve) valve radial aero engines compare to those of other nations?
These would include the widely-used Bristol Pegasus and Mercury plus smaller runs and concept engines like the Alvis Pelides, the in-line radial Armstrong Siddeley Deerhound and the smaller Pobjoy Niagara. Was there any hope for British non-sleeve radial engines?

 

[Shortround6]

Short answer...

Nope.

longer answer.
Fedden was too caught up in the sleeve valve development and the poppet valve Bristol engines stagnated for too long. The Mercury was actually a pretty good engine but it was too small and the Pegasus was pretty much a Mercury (same bore) with a really long stroke, which limited rpm and the small bore (and pretty much same valves) as the Mercury tended to limit power. In comparison Wright was doing major changes to the Cyclone ever couple of years if not sooner. usually with massive increases in cylinder finning for better cooling.

The Alvis Pelides was doomed due to it's parent, the Gnome-Rhone engines. With no center bearing on the two row crankshaft it could withstand neither high rpm or high boost. Please note this engine was the same bore/stroke/ displacement as the Bristol Hercules. Yes the sleeve valve helped but the center bearing and better crankshaft allowed it to run a lot faster.

The Pobjoy Niagara was a cute engine but come on. It was a 2,835 cc 7 cylinder engine. It may have been smooth running or had some other attribute/s but it was an expensive way to get the kind of power other people were getting from 4 or 5 cylinder engines.

 

[Admiral Beez]

The inline Deerhound looks more like a liquid cooled motor. Those rear pots must get warm.

 

[wuzak]

Armstrong-Siddeley originally wanted the Deerhound to be liquid cooled, but the Air Ministry wanted a competitor for Bristol in the high power air-cooled engine market.

The Deerhound I was cooled front to rear, but the Deerhound II and III had reverse cooling - the air entered at the back and was pushed forward.

With careful baffle design the cooling should have been no more of a problem than for the R-4360.

 

[Shortround6]

Many pictures of air cooled engines do not show the sheet metal baffles.

For a good article on the Deerhound see;
Armstrong Siddeley 'Dog' Aircraft Engines

 

[Deleted member 68059]

Fedden was too caught up in the sleeve valve development and the poppet valve Bristol engines stagnated for too long.

Thats true enough, but might be worth (for context) remembering that Feddens early engines WERE poppet valves, and the reason they stagnated was that he switched in his thinking to Sleeve. So there was never any serious intention to do any development of the existing poppet valve engines at Bristol after that point.

So politically there was no hope for British radial poppet valve engines after he made that choice, but from a techical standpoint going back to when he WAS developing them, there was a great deal to be said for them. Who else was making air cooled radials with 4-valve heads at the time ? Or running direct fuel injection tests? (modified Pegasus, "Draco")

The Pegasus went on to break the world high altidude flight record many times in the 30`s, and was an prolifically produced and extremely sucessful engine. If it had been updated (if Fedden hadnt switched to sleeves), and in twin-row configuration, I see little to separate it in potential from any American radial, and in fact the 4-valve head layout gives it a breating and hence power advantage (providing the rest of it were done to a good standard, of course).

32,000 were made, and it set three world high altitude flight records in 1932, 1936 and 1937. It was also the first engine over Mount Everest, and in 1938 set the world's long-distance record.

In terms of weight/performance I see little to separate it from the Wright Cyclone or P&W single row radials of the same era (the P&W are less powerful but smaller & lighter,
the Wrights about equivalent)

I`m not defending Fedden, I think he was very wrong to leave the poppet for the sleeve, mind you even Sir Harry Ricardo thought the sleeve was great, for a while, so you cant call Fedden stupid relative to possibly the most brilliant engine scientist Britain ever produced.

The altitude records were not on a standard engine, it had a second supercharger fitted, however that goes for anything that does 50,000ft and so
I think that deserves better than a "Nope"

 

[cherry blossom]

There is an interesting article "Comparison of Sleeve and Poppet-Valve Aircraft Piston Engines" by Robert J. Raymond at https://pdfs.semanticscholar.org/a085/821e7a5073685530cf2b7060294dbdd42175.pdf

ps. Sorry! I had just been reading the article but on reflection it isn't relevant to the question.

 

[MiTasol]

Other British poppet valve engines were successful as well. The Bristol Jupiter was built under licence in several countries and the AS Cheetah was a solid reliable engine so Nope is definitely an overstatement.
Even more pertinent is that the Kestrel, Merlin and Griffon are all poppet valve engines and I doubt anyone would fit them in the Nope category.

 

[Shortround6]

Sorry guys, I stand by the"nope" as the original question was.

How did British poppet valve or traditional (non-sleeve) valve radial aero engines compare to those of other nations?

Now perhaps I did infer a point in time of the late 30s or later from the "(non-Sleeve)" part of the statement

and

Was there any hope for British non-sleeve radial engines?

Pretty much eliminates Kestrel, Merlin and Griffon engines from the discussion as they are not radials.

The Jupiter was great engine of the 1920s (and definitely pre sleeve valve) and was built under licence in 17-18 countries and maybe more.
However it used 146 X 190mm cylinders (or imperial equivalent) and as such was the direct ancestor of the Bristol Pegasus.

Bristol (meaning Fedden) started work on the Mercury in 1925 to replace the Jupiter and the short stroke Mercury allowed for higher RPM and smaller diameter. In 1927 they went back to the original stroke for the start of the Pegasus.

The Alvis engines were based off of Gnome Rhone engines which in turn were based of the Jupiter engine (they all used 146mm bore cylinders) which is one reason the ALvis engines went nowhere. There were others including perhaps politics.

The Mercury was a very fine engine for a 1520 cu in/ 24.9 liter engine but that size was just too small for the commercial aircraft market of the late 30s and the military market of the late 30s and WW II. Many Mercury's were built and used but most planes powered by them were quickly moved to less than 1st line combat roles. Now the same could be said for the P & W R-1535 14 cylinder two row radial as it was quickly supplanted by the R-1830 (30 liters) and P & W refused to do any more development work on it. P & W also pretty much stopped developing the R-1690 Hornet (27.7 liters) in the late 30s because it was too small and also competed with their own R-1830. Don't forget that P & W started work on the R-2800 (45.9 liters) in 1936/37.
Wright was not only doing major work on the R-1820 (29.8 liters)( a number of generations of the engine that had little or no parts interchangeability from generation to generation) they were also working on the R-2600 (42.6 liters) and R-3350 (54.9 liters) (which had to almost start over again in the early 40s)

A 14 cylinder Mercury would have been 38.7 liter engine.

Perhaps Snowgrouch can answer this question much better than I can but it seems to me (and I could well be wrong) that the Bristol 4 valve cylinder head was a bit less than ideal.
Yes it had 4 valves, yes it had a pent roof (or at least sort of ) combustion chamber but the actual valve and port layout was bit odd. Instead of both inlet valves being on one side or slope of the pentroof and the exhaust valves on the other side or slope the Bristol engines put one intake valve and one exhaust valve in each side or each slope. I don't know if this hurts the gas flow or has no effect?
In any case as mentioned elsewhere the big American radials used Hemi heads or darn close to it with big valves, large angles and large ports leading to and from the valves.

In fact even some American trainer engines used some pretty good head design for the times.

The 4 valve heads on the Bristol engines may have interfered with getting enough cooling fins in the head area?

The Deerhound may have worked, it might not have, I have no idea but it was 1-2 years away from production. The Deerhound I was 37 liters the Deerhound II was 42 liters and the Deerhound III was even bigger. Which basically means it was still in early development.

By the mid to late 30s the British poppet valve engine was in sorry shape development wise, however well the individual engine designs served in the first few years of the war. The potential was too little and promised to be too late had anyone wanted to shift back from sleeve valve engines.

 

[Simon Thomas]

From "Fedden - the life of Sir Roy Fedden" Bill Gunston:

In 1934 LOT (Polish Airlines) ordered two of the brand-new DC-2Bs to be powered by engines made at Bristol, the choice being the Pegasus VI medium-supercharged variant running on 87-octane fuel and driving Hamilton controllable-pitch metal propellers. The engines for the first Douglas were delivered to Santa Monica on 30th March 1935, and flight testing began on 3rd July. The results were outstanding.
...
Compared with the regular Cyclone-powered DC-2, the Polish transport cruised 3 mph faster at 180 mph and burned only 28.8 gal/hr of fuel instead of 31.7.

I would guess this would be about the last time a Bristol poppet valve engine was superior to a similar sized Wright or P&W.

 

[Admiral Beez]

The Pobjoy Niagara was a cute engine but come on. It was a 2,835 cc 7 cylinder engine.

I know, but I stIll admire its compact proportions. Here's a pic I took today at the British Science Museum. I'd bet if this engine was made today it would find buyers in the light aircraft market.

 

[Admiral Beez]

I know looks count for little, but the A/S Tiger looks better than the Bristol Jupiter. Just look at those shiny push rod tubes on the photo I took today at the Science Museum (the backlighting is terrible for photos there). They remind me of the tubes on my 1969 Triumph Tiger motorcycle. Yes, I'm a sucker for lost causes.

 

[special ed]

Home builders might like it for a "sorta WW1" project. When I was in Civil Air Patrol Cadets in the mid fifties, I would hang around the airport and check the red painted trash barrels at the hangars. One day a barrel appeared to have been emptied but I looked in anyway. At the bottom was a very small 5 cyl radial which just fit the diameter. As I was in khaki uniform and the barrel and engine was extremely greasy, no action was taken. Besides, my mother would not have allowed it, although my dad would but he would have been overridden on my possession.

 

[Shortround6]

Nice Pictures.

The American small radial market, like the Pobjoy was fading fast in the very late 30s.
There were some European small radials including a 40hp cylinder one around 1930.

But most of the aircraft owners in the 1920s-30s-40s were a pretty practical bunch of people and the Flat-4 and Flat-6 engines came to dominate the market and even pushed out the inline 4 and 6 cylinder engines. Using 5 cylinders when 4 would do or using 7 cylinders when 6 would do was not going to last very long.

The Popjoy used small cylinders running fast to get power and required a reduction gear for the propeller.
They may have been smooth and nice to fly behind but the cost to overhaul them would have been higher than the larger, slower turning radials and the flat fours offered lees vibration than the inline 4 cylinder engines.

A lot of the engines in the 1920s and 30s were going through major changes ever few years. A/S was building these in the 1920s

Note the much cruder cooling fins compared to the Tiger engine of the 1930s.
Also note that the 1920s Bristol Jupiter not only had the crude finning of it's time but used a different cylinder head from the later Mercury and Pegasus engines. The Jupiter used parallel valves and not the inclined valves of the later engines for an easy identification feature.

What people choose to fly behind for nostalgia maybe a lot different than what they would choose to fly behind in a "working" aircraft like an air taxi or doing flight instruction and racking up hundreds of hours a year.

 

[Admiral Beez]

Here's the tag from the earlier A/S Jaguar. I'd not heard of Green or Heron. I wonder had Heron stayed if A/S would have made a better Tiger and follow ons to better compete with Bristol.

 

[MiTasol]

Here's the tag from the earlier A/S Jaguar. I'd not heard of Green and Heron. I wonder had they'd both stayed if A/S would have made a better Tiger and follow ons to better compete with Bristol.

View attachment 663460

I like the way the label is multicultural and using HP as the standard for power and Kg for the standard for weight.

 

[Shortround6]

S. D. Heron also had one or more patents concerning the sodium cooled exhaust valve.

 

[Admiral Beez]

S. D. Heron also had one or more patents concerning the sodium cooled exhaust valve.

Is this the guy who made the Heron head?

Heron cylinder head - Wikipedia

en.wikipedia.org