Inverted V engine vs. V engine

Tante Ju said:

Short lifespan was not uncommon for piston engine in 1944! By then, power was very great - so was strain. 40 hours - similiar for Soviet VK 107, or German DB 605D. Or consider Jumo 004B.

May not as disadvantage as seems. Consider combat sortie - 1 hour. This means plane will fly 30-40 combat sortie before engine needs replace.. but will plane be not even hit once this time? Or shot down? For wartime, it is ok. For peace - not OK.

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For war time it is only OK (as in barely acceptable) if you are desperate and flying short missions. Mustangs and P-38s flew 6-8 hour Missions. Engine swaps every 5-6 Missions?
Even Griffon Spitfires with 90 gal drop tanks could stay up for 2-3 hours depending on speed. 15-20 sorties?

The British didn't NEED Griffon Spitfires to defend England. Production of a MK XVIE with a high altitude rated engine Might have covered any real shortfall of Griffon engined models.
Or used Tempests, or used lend lease American planes.
Point is the British didn't have to use short lived engines at that point in the war to achieve any military objective.

Tante Ju said:

Short lifespan was not uncommon for piston engine in 1944! By then, power was very great - so was strain. 40 hours - similiar for Soviet VK 107, or German DB 605D. Or consider Jumo 004B.

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I would hardly call the power output of the Griffon straining the engine.

Do you have any specifics of why the Griffon needed to be changed after 40 hours?

The griffon was eventually put in the shackleton maritime recon plane with 4 engines. If it was intrinsically unreliable it would never have been selected.
40 hrs from a four engined plane means an engine change every 10 hrs average.

The Shackleton had the worst conditions for engine life, stooging around for 24 hours but needing to keep revs up to generate enough electrical power for the search systems, tea and dinner so it is rather good to find that the most interesting thing about the Griffon 58 is that it gave 2540bhp for take-off and had something like a 1250 to 1300 hour "life" with a half-life cylinder block and piston change. (official figures).

The 'mass' production facilities were set up for Merlin production and so the changeover would have meant severe delays in supply to all the aircraft programmes reliant on Merlins. Griffons were to be made at Crewe which was a step up from 'craft' production at Derby. As was usual the initial production of Griffons was at Derby so the aircraft procurement was around how Derby saw the build up of production rate. Ford supplied single stage Merlin engines for bombers etc. This was the reason Griffon Spits were not more plentiful.. this and the fear of what would happen if orders were switched but then Derby hit problems.

Tartle said:

The Shackleton had the worst conditions for engine life, stooging around for 24 hours but needing to keep revs up to generate enough electrical power for the search systems, tea and dinner so it is rather good to find that the most interesting thing about the Griffon 58 is that it gave 2540bhp for take-off and had something like a 1250 to 1300 hour "life" with a half-life cylinder block and piston change. (official figures).

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How is constant running at moderate power is "worst condition"? Worst condition is something like used in a fighter - quick change in throttle, power up, power down. Not good for engine, big thermal, mechanical stress.. Best condition is on a bomber. Low power employed typical, and at constant. There is also more space for powerplant, oil, cooler etc.

"Front line MR.1 aircraft were delivered to Coastal Command in April 1951 with their operational debut during the Suez Crisis.

All marks suffered from using the Griffon engines — thirsty for fuel and oil, noisy and temperamental with high-maintenance needs. In 1961, MR.2's engines needed top overhauls every 400 hours and went through a spate of ejecting spark plugs from their cylinder heads. It was not unusual to see an engine changed every day in a unit of six aircraft. They were constantly on the cusp of being replaced, but the potentially beneficial Napier Nomad re-engine did not happen."

Avro Shackleton - Wikipedia, the free encyclopedia

Note this is 16 years after World War II... I would expect Griffon improve in time, and have better TBO than fighter like Spitfire in 1945 (40 h). Still, it was troublesome. If 1200 h was "official" figure, 1/3 was realistic.

The numbers I quoted are for the actual achieved overhaul hours on the Griffon. I note Wikipedia does not reference the 400 hrs statement.... doesn't mean it isn't true for a phase of life development....but no context.
When the Shackletons got on station they then stooged around at low speed and low altitude for the next day and night. The ideal for doing this would have been to put all props into coarse pitch, wind up the boost a bit, and effectively stooge around in overdrive with your foot down a little. That would have minimised pumping losses, and kept the engine loaded with some torque such that it did not run fast and light. However as I referred to coffee, meals, avionics, etc. These factors dictated that the engines be run at sufficient speed to generate electrical power. The engines therefore had to run at higher rpm, but lower boost: bad for engine life, and bad for fuel burn. Worst of all, you needed sparking plugs which were hard as hell at 2540bhp---2750rpm, well over 20lb boost and water/methanol on top of 100 Octane---yet soft as grease at stooge.
These comments came from the man in charge of engineering these beasts. Note that Smiths Industries developed very special hard-soft spark plugs for the Griffon, using Iridium electrodes... as I said "A very challenging duty cycle".
As to the Nomad ... it was several development challenges combined into a single package. The Napier Sabre was an engine of very little life and using that technology was a challenge, especially given the duty cycle in Shackleton; the axial technology was a challenge and the manufacturing techniques unusual; combining it was therefore a fascinating challenge beyond what Napier could hope to achieve, given their state of the art at the time... Simplicity was not on the list of desirable features. At least the Griffon was for a high-performance engine relatively simple. Give me the real figure of 1200 hrs overhaul any day.
P.S my experience of the Gazelle makes me believe the Nomad would not have made it!

Tante Ju said:

How is constant running at moderate power is "worst condition"? Worst condition is something like used in a fighter - quick change in throttle, power up, power down. Not good for engine, big thermal, mechanical stress.. Best condition is on a bomber. Low power employed typical, and at constant. There is also more space for powerplant, oil, cooler etc.

"Front line MR.1 aircraft were delivered to Coastal Command in April 1951 with their operational debut during the Suez Crisis.

All marks suffered from using the Griffon engines — thirsty for fuel and oil, noisy and temperamental with high-maintenance needs. In 1961, MR.2's engines needed top overhauls every 400 hours and went through a spate of ejecting spark plugs from their cylinder heads. It was not unusual to see an engine changed every day in a unit of six aircraft. They were constantly on the cusp of being replaced, but the potentially beneficial Napier Nomad re-engine did not happen."

Avro Shackleton - Wikipedia, the free encyclopedia

Note this is 16 years after World War II... I would expect Griffon improve in time, and have better TBO than fighter like Spitfire in 1945 (40 h). Still, it was troublesome. If 1200 h was "official" figure, 1/3 was realistic.

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I don't think bombers would be nearly as easy on engines as you think. Taking off and getting to altitude took a high throttle setting for a long period of time. Then assembling the formations would require alot of throttle adjustments, then maintaining formation for many hours required constant throttle jockying. Not big throttle changes, just constant changes, all the way to the target and back. The early part of the mission, full bomb load and full gas load, would require high power settings for hours, just to maintain height.

double post

After 16 years of service and an untold number of spark plug changes (100s?) I don't see ejecting spark plugs as unusual. The metal fatigue on the aluminum threads by the torquing of the steel spark plug.

Considering that the Griffons in the Shackletons used up to 25lb of boost for take-off, WEP settings by anybodies standard, routinely may have something to do with it.

I would certainly like to see the conditions that Spitfire engines were only lasting 40 hours, Some Napair Sabres had a pretty short life also after moving to front line airstrips after the Normandy Invasion. They needed the quick fitting of air-filters to get engine life back up to acceptable figures.

I might understand Griffon engined Spitfires flying from such forward airstrips having a short engine life.

Shortround6 said:

Considering that the Griffons in the Shackletons used up to 25lb of boost for take-off, WEP settings by anybodies standard, routinely may have something to do with it.

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No doubt, but the Merlins were using 25lb boost as well and I can't recall them ejecting plugs. Of course the Merlins were not old well used engines either like the Griffons in the Shack.

I don't think the Merlins were using 25lbs of boost for takeoff.

Granted the Shackletons only used this power setting once for every 10-14 hour flight but many fighters could go a number of flights without using the 25lb settings and in peace time may have been prohibited from using that setting except in extra special circumstances.

When they talk about ejected spark plugs, I don't think they mean the threaded metal base and all. Sometimes the ceramic center fails and shoots out, not a uncommon occurance in high output auto engines under race conditions.

Returning to the topic of the original thread:
Thread reply #79... the top right data points are interesting... the RM17SM version of the Merlin is shown on three data points. the 30psi boost point at 2200 bhp is an engine going through a 150 hout type test... so is a service rating; the two data points above that point are for short periods... sprint results we might ssay that indicate future possibilities. The Rolls-Royce approach of focussing on improvements and making step changes when necessary, and after they had demonstrated them on a test rig is a good way of deploying limited resources. Mercedes did not seem to have such a clear strategy, or backing from ministries/militaries, and so resources in contrast to Rolls-Royce seem to be spread thinly across more options hence Jerry Wells uncovering a large set of models/prototypes of DB6xx engines. IBM did a lot of studies of engineering companies and projects (in the 1980s) and showed that an individual with three projects was the most productive .... one project means hanging around for other 'stuff'; two better as one can fill in the gaps by switching; three is even better at smoothing 'gaps'; four to six means that you spend more time remembering where you got to and going to meet or find so effectiveness drops. Even if the layouts of \/ and /\ are a matter of choice with, maybe a small swing in favour of less degree of difficulty with \/, then technology choices can play a big role in the outcome.. as Jerry pointed out in the thread replies #97 98 I posted earlier... Junkers choice of bearing lubrication was better then Mercedes... this means more time to tackle performance improvement rather than development issues. The net result is the divergence of Merlin and DB performance improvement curves in #79.

That may be nice speculation, but there are million more possible reasons for the spread. For the BMW801 there were many incremental performance increases realized through small to medium modifications between 1942 and 1945. But mostly due to the fact that there was such a high demand that noone dared interrupting production, they were not put into any production models until it was way too late. I could imagine the same could be true for the DB601/605-series.

There was no lack of demand for the Merlin either. Devons book 'Planning in Practice' really makes the point at how hard it was, in fact, to plan production of engines and marks of engines which really drove aircraft schedules.
The point I made before about three levels of flexibilty that enabled Rolls-Royce to bring in incremental change quite easily to Derby production; reasonably easily at Crewe, but only occasionally at Ford, Trafford Park and RR Glasgow. I think this setup of flexible-skilled to inflexible-'automated' allowed continuous improvement of the Merlin.
But what was the setup in Germany? I really don't know, but it would be interesting to know. Does anyone have the information to help us draw some informed speculations on the matter?

Jerry Wells posted this on the Engine History discussion board early this year...I have copied it here as I believe it is the best summary of the DB situation (Note I say the DB situation as it is becoming clear that the design solutions for the /\ configuration determined the degree of difficulty of development of the particular engine. The \/ configuration may have been marginally less challenging- but this is debatable- but the design solutions made the Merlin a bit of a challenge (ramp head, carburettor float flow chamber controls).
So it is as well to remember Kranzberg's first law:
'Technology is neither good or bad nor is it neutral.'
The technology and detail choices can make a \/ or /\ less or more useful in practice....
There is some documentary evidence in existence which confirms that the reason for the differential compression ratios in the DB 600 series inverted V-12 engines was due to oil control problems.
Jerry Wells writes:

"It needs to be remembered that the development of the German inverted V-12 motors took place very quickly. The specifications for high-powered aero-engines were determined by a "think-tank" which was assembled in Berlin at the behest of the RVM in 1928. It was at this point that the requirement for the engines to be of the inverted kind was laid down.

German aero-engine manufacturers had almost no experience of inverted engines, particularly V-type ones.

The development of the Bf 109 illustrates the tight time-line that occurred re the German V-12 engines, eg the 1935 Bf 109V1 had a Kestrel engine installed, the 109V2 had a JUMO 210. The first DB600 engine in a Bf 109 didn't happen until 1937!!

The oil control problem would not have manifested itself for some time due to the rush to get the DB engines into production. Probably, the earlier 601 engines would have got low-compression pistons fitted into the left-hand banks after one or two overhauls.

The literature pertaining to the earlier engines would have been written and published long before the oil control problem was recognized hence no mention of different CR's in the manuals etc.

The interesting indirect evidence for the CR difference comes from a study of the Junkers 211. It was a similar engine so why did it not suffer from the same problem?? Answer - the lubrication system used was very different to that in the DB. End-feed type instead of convential gallery design. End-feed gives much better control over oil flows through the crankshaft and big-end bearings.

The off-set supercharger had nothing to do with this."

Well said Jerry!

But it makes you wonder what they thought when the German delegation saw Rolls-Royce's inverted engine mockup in 1933!

'The romance of engines' By Takashi Suzuki, Chapter 37 and 38 discusses the technology of the DB600 series especially the bearings and Takashi Suzuki advances some well thought out possibilities for the changes of technology in the bearings that may also have been informed by feedback from in-service operation of the engine. Page 368 has a useful diagram. Google have useful chunks of the book to whet our appetite!

Marcel, In looking through FLIGHT(British Archives) I have found quotes from the Arsenal firm that they were getting more power out of THEIR JUMO 213 than RR Griffon engine.The post was dated soon after WW2.