Rolls royce Pennine dimensions

Nick Sumner

Live! From the Belly of the Beast!
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31 May 2006
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Does anyone have any dimensions for the RR Pennine engine, ie Length X Breadth X Height? I have the cylinder dimensions.

I contacted the Rolls-Royce Heritage Trust and received a reply from Mr Ian Craighead whom I have to thank for furnishing me with the following information.

"The Pennine had a capacity of 45.73 litres (2791 cu. ins.). The overall length (over propeller shaft and starter) was 106 ins. Its height was 37.50 ins and width 39 ins. The engine dry weight was 2850 lbs. It developed 2740 bhp at 3500 rpm at sea-level maximum take-off conditions and up to 2800 bhp under combat settings. It differed from the Exe by having an epicyclic reduction gear which meant that the propeller shaft was in line with the crankshaft. It never progressed beyond the initial development phase as the advent of the jet engine eclipsed its potential."
More information from Mr. Craighead;

"+12psi boost at Max take-off and combat settings. Yes, it was a single stage, two speed supercharger."
Some of the late piston engine projects are quite facinating. And some were grevious wastes of a countries resources in war time. Rolls development of the Eagle II when Napier had the Sabre* in production was something that the UK really couldn't afford. One almost universal constant for all of the allied engine projects in this class is they seem almost universally to be sleeve valved engines. Was the Pinnine also a sleeve valve engine. Personally from the stand point of the sleeve valves advantages over the poppet valve in terms of specific consumption vs the greater cost of the sleeve valve in manufacturing cost and manhours for fighter aircraft the the sleeve valves advantages IMO don't make all that much sense. You have to put this in terms of just what was the average life of an engine under combat conditions vs what its TBO actually was. Of all the late piston engines under development and testing in the mid 40s the I really would of liked to hear run at least once was Roll's Crecy. And from what I have heard once is all you be able to take.

*Actually Pratt & Whitney had their H24 X-1800 and H-3130running on test before Napier had the Sabre up and running. But they abbandoned them in favor of the 28 cylinder R-4360 with the Air Corps and Hap Arnold's consent.

PS What was the Pinnine bore and stroke?
The Pennine was a sleeve valve engine. 5.4 inch bore, 5 inch stroke.
Er... was there a pun intended on "pennine dimensions" or am I a little twisted?
The Pennine was a direct evolution of the Exe engine which was designed for the Fairey Barracuda. Unlike the Exe it used an epicyclic reduction gear which meant that the propeller shaft was in line with the crankshaft. I've not heard of it being earmarked for civil use, the Exe was intended for naval use from the outset.

I'm not sure what you mean Stargazer? The Pennines are a range of hills in England.
Nick Sumner said:
I'm not sure what you mean Stargazer? The Pennines are a range of hills in England.

Oh blast. Just realized that the English for "pénien" is NOT "penine" but "penile"!!!

I have a note from 'The magic of a name: the Rolls-Royce story, the first 40 years' by Peter Pugh suggesting that the Pennine and a paper engine called the Snowdon were being put forward as civilian engines as insurance against gas turbine failure. The images I have seen online of the Pennine inside a cowling do remind me of the Merlin 620 power unit for the DC-4M.
Not a great view of the RR Pennine in the middle unfortunately, but it gives an idea of the size when compared with the Vulture alongside. The one in the background is a notional vertical 24H with Merlin Cylinders.

Pic from RRHT Derby


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Here is the photo I think he was talking about.


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Have to say that cowling looks rather crude for a flight
rated unit, for test bed use perhaps?

...suggesting that the Pennine and a paper engine called the Snowdon were being put forward as civilian engines as insurance against gas turbine failure.

In 'Rolls Royce aero Engines' page 94, Gunston states;

"Around 1942 the design was completed of the Pennine. one of the best aero engines ever made, but during
the war it never attracted any support.
At last RR managed to get one on test in 1945, hoping it would find a
market in post-war civil aviation, but by this time everyone was captivated
by the gas turbine...
...the only planned application was the Miles X airliner. Miles never had political we got the Brabazon instead."

Regarding the Snowdon, from the same source;

"It would have had 32 Pennine cylinders arranged in the form of front
and rear X-16 engines sharing a common crankcase.
All the 5,000-odd horsepower came out through a pinion
amidships, driving shafts along each side, each one driving a
reduction gear to one half of the giant contra-rotating propeller."

And lastly, because we haven't had one yet, here's a picture of
th Rolls Royce Pennine engine, same source as above.



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I think RR should have killed the vulture and go with the Exe with 15lbs boost.With a weight saving.
I scanned some of my pics of Pennine/ exe a year or two back:
The Exe and Pennine are described as "pressure air cooled" - but in the images I have seen, only the Pennine has a fan. Was the idea simply to use ram air from the prop slipstream? And did they also expect any entrainment effect from the exhausts?
A A Rubbra wrote about Exe in RRHT Historical Series No 16 .. I've scanned in the pages...


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Thanks! Prop used as cooling fan, then. You could almost call an old Porsche 911 "pressure air cooled", then, since I suspect that it would not run very well without the big fan.

The Exe/Pennine and Crecy constitute two unique diversions in reciprocating aircraft engines.
The penultimate paragraph in Rubbra's piece says it all, I think. Reading that with the two pictures from Old Machine Press's article referred to by Johnbr above makes it clear.. I've put the pics below:


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Must be the only instance where a prototype engine worked so well that it was used in the company bus.
The intriguing thing is that the sleeve valves worked very well... during the thirties Bristol were having great problems:
first with getting the relative hardnesses of each surface of the sleeve valve system to be correct and then getting this scaled up to production quantities... the first took at least three years and the second 5.. basically all of the thirties wiped out in problem solving.
Rolls subcontracted the conversion of a supercharged Kestrel to diesel sleeve-valve in the 1927-30 period. Ricardo did the work and two test bed engines were built. The bore was reduced by 0.25 inches to 4.75 (19.2 litre vs 21.25) to accommodate the sleeve and they were driven by a spur gear train on the outside of the cylinder block. The first engine gave an output of 350 hp and was over twice the weight of a Kestrel... at 2128 vs 950 lb... not surprising for a technology demonstrator. The second engine was modified to run on petrol and delivered 680 hp @3,000 rpm.
It has been asserted that the resulting experience fed into the Napier Sabre project.No doubt A J Rowledge would have fed the knowledge into the Exe design.
Having acquired a copy of RRHT's HS21 Crecy book I find there is more information on the Kestrel.
The diesel engine, known as RR/D, was disappointing as not only was power lower than expected but the white metal big end bearings failed, cracks appeared in forked con-rods and crankcase walls and pistons failed! Derated to 250 hp it was sold to Wakefield Castrol for use by E T Eyston in the car 'Spirit of the Wind-; known as 'Flying Spray' for the diesel record attemt it achieved 159 mph at Bonneville in 1936- a world record that stood until 1953.
There is also a cutaway in the book ... see below
I have just scanned in my pic of the 2nd Kestrel engine ...see below:


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Remember what the engineers at Derby, Lovesey and Hooker in particular, said about power generation. It is not the cubic capacity of an engine that determines the power output but the amount of fuel-air mixture that can be swallowed by that engine. That is why the Merlin developed such an increase in power over the world war 2, not an increase in capacity but an increase in supercharging. The fuel octane increase helped also in allowing detonation to be kept at bay at higher compression ratios... so could Snowdon do it? the way I thought it was a 100 litre engine that would deliver 5,000 hp; with 4,000hp coming from the 61 litre version?
tartle said:
by the way I thought it was a 100 litre engine that would deliver 5,000 hp; with 4,000hp coming from the 61 litre version?

Let's have a chat about this. I have never been clear on the 61L, 75L and 100L engines. I have seen them called the Exe 61, Exe 75, and Exe 100. I have seen both the 61L and 100L called Snowden. Some sources give no mention of the 61L, while others give no mention of the 100L, and most give no mention of the 75L. It seems like the 61L achieved some "off-paper" development, but the 100L did not. I have seen numbers for the 61L from 3000-5000 hp and 4,000-5,000 hp for the 100L, but no numbers for the 75L.

It makes sense that the 61L would produce 4,000 hp (or maybe even 3,500) and the 100L 5,000 hp (or maybe more). In comparison...

Exe - 4.225 x 4.0 x 24 = 1,346 cu in (22.1 L) 1,200 hp (54.3 hp/L)
Pennine - 5.4 x 5.08 x 24 = 2,792 cu in (45.8 L) 2,750 hp (60.0 hp/L)
61L - 5.4 x 5.08 x 32 = 3,723 cu in (61.0 L) 3,000 hp (49.2 hp/L) seems low, 3,500 hp (57.4 hp/L) seems reasonable and 4,000 hp (65.6 hp/L) seems a little high
75L - 6.4 x 6 x 24 = 4,632 cu in (75.9 L) ? hp
100L - 6.4 x 6 x 32 = 6,176 cu in (101.2 L) 4,000 hp (39.5 hp/L) seems low and 5,000 hp (49.4 hp/L) seems reasonable

In looking at the numbers, it seems the 61L was a 32-cylinder Pennine (admitted oversimplification). The fact that they share the same bore and stroke (and probably cylinders, pistons, rods, sleeves, etc.) gives some credence to there being some development of the 61L engine. The 75L on the other hand, was an enlarged Pennine, and the 100L was a 32-cylinder 75L (oversimplification again). Could it be that the 61L was to be a 3,500 hp engine, the 75L 4,500 hp engine and the 100L 5,500 hp engine?

Which is the Snowden? Would the 61L be the Snowden because some work might have occurred? Would the 75L or 100L be the Snowden because they were a different bore/stroke than the Pennine and Exe? Or would Snowden be the name of the next "X" engine regardless of what size it was?

Ah, the madness of it all. Anyway, I changed the 61L "Snowden" output to 4,000 hp, even though I think 3,500 might be a more realistic number. 5,000 hp was certainly too high.

Thank you,
I have avoided the issue of naming up to now.. will have to delve deeper. It may be that the Pennine name was used to cover a family of related (or scaled) projects which were renamed as they got more serious.
Taking into account some of the target outputs that have been suggested for the Exe and Pennine gives the following, though they seem rather too convenient to be true:

Exe (22.1L) 1,500hp gives 67.87hp/L
Pennine (45.8L) 3,000hp gives 65.5hp/L
61L at 65.6hp/L gives 4,000hp
75L at 65.6hp/L gives 4,920hp (damn near 5,000hp)
100L at 65.6hp/L gives 6,560hp (damn near 6,500hp)


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