"WORN OUT ENGINES"

[FLYBOYJ]

Hoping to get some input from some of our resident engine experts (ShortRound6, GregP, Tomo, MiTasol, Bill M and Calum, to name a few, I know there's more). I've seen many publications (and some posts on here usually referencing another source) making references to "worn out engines," or "tired engines." I've even seen this in "Bloody Shambles." In my years in aviation I've identified a "worn out engine" as one that is not meeting manufacture's performance specifications, being operated beyond overhaul limits, having accessories (Magnetos, carburetors, generators, FIUs) operating beyond overhaul limits or having items like motor mounts, engine control cables or control cable rod end bushings worn. I even think we might throw oil leakage in there in many cases. IMO I think this term has been thrown around in many cases without merit or substance, and it seems that over the years it was taken at face value. I think in some cases even pilots may have abused this term.

As many of you know, engines can be overhauled and brought back to original performance specifications. I've seen many general aviation engines (which are a lot less robust than engines from WW2) with thousands of hours on the core overhauled to the point where little difference will be noticed when compared with a new engine.

When I see this term in a post or a publication with no specifics I take it with a grain salt unless specifics are given. What's your take on this? Do you think this term is over-used without merit?

 

[MiTasol]

Worn out engines can have run as little as 10% of their programmed overhaul life for a number of reasons.

The Merlins in the RAAF were often totally stuffed at that stage of life in some areas as they ingested coronus (coral dust) during ground operations including take off and coronus is effectively a very fine grinding compound when inside an engine so the whole inside of the induction system and cylinders were damaged.

In the induction system there was erosion, especially at all bends where the outside of the bends were rapidly sandblasted from polished smooth to very rough. In the supercharger the impeller and vanes are ground away destroying the efficiency and again in the rest of the system right through to the cylinders the polished insides of the system are abraded causing turbulence which results in reduced airflow.

Once inside the cylinders the dust grinds away the cylinder sidewalls and piston rings reducing compression and when the piston moved down the rings crape some of the coronus into the crankcase and oil system which results in all the clearances in the oil system opening up and some finer passages being clogged.

The Allisons in the P-39/40 were far less affected as they are downdraft engines taking air into the aircraft significantly higher off the ground and in the case of the P-40 the intake was immediately behind the prop where the propwash is still clean. NAA did the same on the Mustang but Supermarine never learned.

All these reductions in internal airflow and compression rapidly result in a significant reduction of power and therefore the engine is below its minimum output and "worn out"

Running past the recommended overhaul period does not automatically mean an engine is worn out. I remember one well known P-40 owner in the 1970's had well over 2,000 hours on his engine and it easily made full power because he was religious about his engine maintenance and did oil changes far more often than the TO required. He also serviced changed or overhauled all his critical parts like filters, mags, (coolant, oil and fuel) pumps, radiators and oil coolers at or before the recommended overhaul periods because there is no functional test to determine if they are operating correctly and can be expected to continue so. Overhauling coolers, especially oil coolers, ensures that accumulated crud in the system does not reduce the coolers efficiency. Clogged and contaminated oil coolers have killed many engines and that clogging can be in both the air and fluid side of the cooler.

There are many other things that can wear out an engine. Running overheated or over boosted are obvious. One idiot I knew killed his 0-470s in under 300 hours (cracked cylinders and cracked crank cases) until I went on a flight with him. At the end of the runway prior to releasing the brakes he wound the mixture back until he got peak EGT because that meant peak power. I slammed the mixture full rich, chopped power and ordered him back to the hangar where I told him to go study his engine basics - the engine uses fuel for cooling at all high power settings.

Many a light aircraft owner has come to grief, and often died, through failing to carry out required maintenance on both Bendix and Slick mags and these components usually have an overhaul life far lower than the engine the are keeping running. The it flew in so it will fly out attitude is the utmost stupidity yet many believe it.

 

[EwenS]

...........but Supermarine never learned.

I give you the Supermarine Seafire FR.47 (introduced during the production run)












And the Supermarine Spiteful / Seafang (introduced during development)

Vickers Supermarine Spiteful

The final development of the Spitfire

www.baesystems.com

Supermarine Seafang Naval Fighter Prototype Aircraft

Page details technical specifications, development, and operational history of the Supermarine Seafang Naval Fighter Prototype Aircraft including pictures.

www.militaryfactory.com

Then it was onto jets.

 

[tomo pauk]

The Allisons in the P-39/40 were far less affected as they are downdraft engines taking air into the aircraft significantly higher off the ground and in the case of the P-40 the intake was immediately behind the prop where the propwash is still clean. NAA did the same on the Mustang but Supermarine never learned.

Had nothing to do with Supermarine or with NAA. Engines, or their carbs, dictated the intake placement.
NAA went with underside intake for P-51B/C/D/F/G/K/H because carb was updraft.

 

[tomo pauk]

As many of you know, engines can be overhauled and brought back to original performance specifications. I've seen many general aviation engines (which are a lot less robust than engines from WW2) with thousands of hours on the core overhauled to the point where little difference will be noticed when compared with a new engine.

(not that I'm a real expert, more likely just an individual that is a bit more informed than the average Joe)

It depended a lot on the purpose of the engine (is it for fighters, bombers, transports, trainers) - the more instances of engine running at aggresive setting, the less hours was it able to run between the overhauls. Eg. the V-1710 was making 362 'flying hours' until overhaul on average in 1st quarter of 1945, vs. R-1820 on a B-17 doing 591 'flying hour' - all for aircraft on the CONUS (source Vee's for victory, pg. 332).

 

[Tony Kambic]

I was told this is from an PW1830 at about 400 hours. Ate the valve.

 

[FLYBOYJ]

Worn out engines can have run as little as 10% of their programmed overhaul life for a number of reasons.

The Merlins in the RAAF were often totally stuffed at that stage of life in some areas as they ingested coronus (coral dust) during ground operations including take off and coronus is effectively a very fine grinding compound when inside an engine so the whole inside of the induction system and cylinders were damaged.

Great point - I could see how a freshly overhauled engine can be exposed to this over the course of a few days and begin o run like crap.

In the induction system there was erosion, especially at all bends where the outside of the bends were rapidly sandblasted from polished smooth to very rough. In the supercharger the impeller and vanes are ground away destroying the efficiency and again in the rest of the system right through to the cylinders the polished insides of the system are abraded causing turbulence which results in reduced airflow.

Once inside the cylinders the dust grinds away the cylinder sidewalls and piston rings reducing compression and when the piston moved down the rings crape some of the coronus into the crankcase and oil system which results in all the clearances in the oil system opening up and some finer passages being clogged.

Again, a victim of environment even though the engine many have low time on it

The Allisons in the P-39/40 were far less affected as they are downdraft engines taking air into the aircraft significantly higher off the ground and in the case of the P-40 the intake was immediately behind the prop where the propwash is still clean. NAA did the same on the Mustang but Supermarine never learned.

All these reductions in internal airflow and compression rapidly result in a significant reduction of power and therefore the engine is below its minimum output and "worn out"

Again, great points that I think was ignored during wartime correspondence and by post war authors

Running past the recommended overhaul period does not automatically mean an engine is worn out. I remember one well known P-40 owner in the 1970's had well over 2,000 hours on his engine and it easily made full power because he was religious about his engine maintenance and did oil changes far more often than the TO required. He also serviced changed or overhauled all his critical parts like filters, mags, (coolant, oil and fuel) pumps, radiators and oil coolers at or before the recommended overhaul periods because there is no functional test to determine if they are operating correctly and can be expected to continue so. Overhauling coolers, especially oil coolers, ensures that accumulated crud in the system does not reduce the coolers efficiency. Clogged and contaminated oil coolers have killed many engines and that clogging can be in both the air and fluid side of the cooler.

I was flying an old C150, ran the engine to 3000 hours. On a flight I had the engine partially fail, I was able to return to my home airport to find one jug had the rings coming apart, the other jug had valves in pieces. Pre-emptive maintenance always helps!

There are many other things that can wear out an engine. Running overheated or over boosted are obvious. One idiot I knew killed his 0-470s in under 300 hours (cracked cylinders and cracked crank cases) until I went on a flight with him. At the end of the runway prior to releasing the brakes he wound the mixture back until he got peak EGT because that meant peak power. I slammed the mixture full rich, chopped power and ordered him back to the hangar where I told him to go study his engine basics - the engine uses fuel for cooling at all high power settings.

Many a light aircraft owner has come to grief, and often died, through failing to carry out required maintenance on both Bendix and Slick mags and these components usually have an overhaul life far lower than the engine the are keeping running. The it flew in so it will fly out attitude is the utmost stupidity yet many believe it.

I've run into this as well especially on Bendix mags.

 

[FLYBOYJ]

(not that I'm a real expert, more likely just an individual that is a bit more informed than the average Joe)

I think way more than the average Joe!

It depended a lot on the purpose of the engine (is it for fighters, bombers, transports, trainers) - the more instances of engine running at aggresive setting, the less hours was it able to run between the overhauls. Eg. the V-1710 was making 362 'flying hours' until overhaul on average in 1st quarter of 1945, vs. R-1820 on a B-17 doing 591 'flying hour' - all for aircraft on the CONUS (source Vee's for victory, pg. 332).

Good points as well - again, ignored or not mentioned by many authors!

 

[FLYBOYJ]

I was told this is from an PW1830 at about 400 hours. Ate the valve.

Was this from a crash site?

 

[pbehn]

Further to Timos point about use. If you frequently go to the limits of what is allowed with over boosting like war emergency power for 15 minutes, the engine may still run, but does it run as well as it did a month ago. In a fighter say in the BoB the engines were used to climb as fast as possible then fight, what effect has frequent high positive and negative G and sometimes no G at all on the engine and its oil? I suspect the wear was much more than just normal max continuous. The Motorcycle I raced was a modified road bike, it was worn out doing the mileage that was normally required to run in a new one on the road, not just the engine, but the steering head races, swing arm bushes and break disc, tired was a good word to describe it. These engines were run for hours on proving tests, did they produce the same power at the end as at the beginning, I wonder?

 

[Tony Kambic]

Was this from a crash site?

It was not. I am not sure if the aircraft ( 4 engine ) was in flight or taxing but they sensed a problem with this engine.

 

[MiTasol]

I give you the Supermarine Seafire FR.47 (introduced during the production run)












And the Supermarine Spiteful / Seafang (introduced during development)

Vickers Supermarine Spiteful

The final development of the Spitfire

www.baesystems.com

Supermarine Seafang Naval Fighter Prototype Aircraft

Page details technical specifications, development, and operational history of the Supermarine Seafang Naval Fighter Prototype Aircraft including pictures.

www.militaryfactory.com

Then it was onto jets.

I stand corrected but do note that the FR 47 was very very late in the types development. Was it post war on Germany?
If so my comment could accurately read but Supermarine never learned until the European war was almost over because the Spiteful was a 1945 aircraft

 

[gumbyk]

Running past the recommended overhaul period does not automatically mean an engine is worn out.

I had a client (a flight training organisation)who ran their C-172 engines to 4000 hours on an approved extension. To get this, they had an engine that went to over 4,500 hours as an exhibit. everything was still within service tolerances. on the other side of the equation, I've seen engines that are well worn with less than 1,000 hours on them. It's not only the number of hours, but how regularly the aircraft fly, the length of each flight, and how stressed the engine is, as well as build quality at overhaul (balancing conrods, clearances, etc). The engines noted above were IO-360 engines which are designed for around 200 hp, but were only making 160hp - so 75% at full throttle.

The other thing is that a 'worn out' engine may still run perfectly well. Our Tiger had only about 600 hours on it, and ran really sweetly. We had an incident with it that required a tear-down on the engine, and discovered that it was well-worn.

However, I've also seen instances where particular pilots have refused to fly a certain machine because they believed that the engine was worn out, while others were happy to fly it, it ran smoothly, and made rated power, so there is certainly an amount of subjectivity involved.

 

[MiTasol]

Had nothing to do with Supermarine or with NAA. Engines, or their carbs, dictated the intake placement.
NAA went with underside intake for P-51B/C/D/F/G/K/H because carb was updraft.

Yes but the NAA intake is immediately behind the prop instead of as close to the carb as possible.
This means the air is taken in front of all the dust stirred up by the prop air flow and as high above ground as possible instead of in the middle of all the dust thrown up and as low to the ground as possible. The Supermarine location maximizes dust collection while the NAA location minimizes it.

 

[tomo pauk]

Yes but the NAA intake is immediately behind the prop instead of as close to the carb as possible.
This means the air is taken in front of all the dust stirred up by the prop air flow and as high above ground as possible instead of in the middle of all the dust thrown up and as low to the ground as possible. The Supermarine location maximizes dust collection while the NAA location minimizes it.

Okay, roger that. Truth to be told, the low-set intake (or two of them) was a feature of Merlin-powered aircraft like the Battle, the Merlin-powered multi-engined A/C and Hurricane.
Supermarine eventually learned it.

 

[MiTasol]

The other thing is that a 'worn out' engine may still run perfectly well. Our Tiger had only about 600 hours on it, and ran really sweetly. We had an incident with it that required a tear-down on the engine, and discovered that it was well-worn.

I am a strong believer in spectrographic oil analysis on certain engines - especially ones that have had low utilization or been in storage like that Gypsy may have been. A certain T-28 I was partially involved with had an engine that had not run for years and I strongly recommended oil analysis to the owner and several hours of ground running before flight even though cylinder removals and internal visuals suggested the engine was okay. The engine failed after a few flights and the aircraft ended on its belly costing far more than a couple of samples would have.

Another factor is the honesty of the previous operator of an engine. I know some private pilots fly five and log one on there aircraft and at one stage I fitted a very low hour engine to an aircraft and it ran like a bag of shit. A quick check showed that the crankshaft was bent so we investigated the history and found the aircraft the logbook showed it came from went in vertically doing a low level loop a week before the date the engine was removed and sold by the insurer.

 

[gumbyk]

I am a strong believer in spectrographic oil analysis. A certain T-28 I was partially involved with had an engine that had not run for years and I strongly recommended oil analysis to the owner and several hours of ground running before flight even though cylinder removals and internal visuals suggested the engine was okay. The engine failed aft er a few flights and the aircraft ended on its belly costing far more than a couple of samples would have.

In the right situation, Oil analysis is good. However, no piston engine manufacturer provides limits that I know of. Lycoming couldn't even tell me where metal might have been coming from when I gave them unusual results. You need to know what to expect. A freshly overhauled engine will have huge amounts of metal in the oil as everything beds in. For monitoring, I found things like acidity, and silicon levels gave a better indication of how the engine was being operated.

 

[nuuumannn]

I remember one well known P-40 owner in the 1970's had well over 2,000 hours on his engine and it easily made full power because he was religious about his engine maintenance and did oil changes far more often than the TO required.

The differences between GA and airline maintenance demonstrated here... With airlines this would be construed as unnecessary and would ultimately cost the operator, therefore maintenance is strictly in accordance with the Maintenance Manual. Nothing is done as a pre-emptive measure unless it is in accordance with some bit of official paperwork somewhere, regardless of how time or effort saving it might be. If the airline or manufacturer get something wrong, it's on them! Although engineering can make recommendations to manufacturers and operators for changes to the MMs.

(not that I'm a real expert, more likely just an individual that is a bit more informed than the average Joe)

You know much more than most of us about this stuff, Tomo, and frequently demonstrate it, too.

Supermarine eventually learned it.

Yup, they put a big filter in the intake. A PR.XI versus a Mk.I.

Spitfire static-7

RAFM 114

 

[EwenS]

I stand corrected but do note that the FR 47 was very very late in the types development. Was it post war on Germany?
If so my comment could accurately read but Supermarine never learned until the European war was almost over because the Spiteful was a 1945 aircraft

Yes the FR.47 was the very final version of the Spitfire, being in simple terms the final fully navalised version of the Spitfire F.21/22/24 / Seafire 45/46/47 series which had finally begun to enter service after a prolonged development in early 1945. The FR.47 itself came off the production line between April 1946 and Jan 1949 for a total of 87, some of which saw service in the early months of the Korean War.

Delving back into "Spitfire the history" reveals that comparative tests between aircraft with the two intake types revealed that the earlier intake "was superior in all performance respects". It was thought that one reason related to the width of the blade roots of the contraprops fitted as standard interfering with the airflow to the intake.

The first production Spiteful was came out of the factory in March 1945 with only 19 built through to early 1947. Seafangs were even rarer. Both types were only used for test purposes.

By the time these aircraft appeared the day of the piston engined fighter was over and jets were already in service.

 

[MiTasol]

The differences between GA and airline maintenance demonstrated here... With airlines this would be construed as unnecessary and would ultimately cost the operator, therefore maintenance is strictly in accordance with the Maintenance Manual. Nothing is done as a pre-emptive measure unless it is in accordance with some bit of official paperwork somewhere, regardless of how time or effort saving it might be. If the airline or manufacturer get something wrong, it's on them! Although engineering can make recommendations to manufacturers and operators for changes to the MMs.

Than some airlines would be more accurate but this is getting much rarer. In modern airlines this tends to be limited to doing ETOPS maintenance on aircraft that only do non ETOPS flights.

Way back I worked for a Canadian company called Gateway Aviation HQd in Edmonton who were allowed to operate all their Pratt 985 and 1340 engines at 1200hr TBOs when everyone else did 800hrs. They also got more life on the 1830s and Continentals. The owner was an accountant who religiously obeyed his Chief Engineer on maintenance so all engines were oil changed twice as often as Pratt called for and were oil diluted before every oil change. On oil change all oil coolers were drained and all oil tanks were part filled with fuel and then drained after a half hour. The shit this removed from the coolers and tanks had to be seen to be believed. Over the life of the engines the extra labour and consumables was more than repaid in long reliable life and low overhaul costs.

Now too many accountants with no engineering input make all the decisions and demand life extensions wherever possible

One airline that claims it has never had an accident (its had plenty) has had one accident and multiple incidents because they do not even do risk analysis on things like refusing to let pilots use thrust reverse. That put a 747 in the grass a long way past the runway and cost more to repair than replace and they call it an incident.