The Secret Horsepower Race by Calum Douglas (and piston engine discussion)

[TomcatViP]

Regarding the discussion on bolts and torques for the Merlin engine, Packard replaced the chaos of English Imperial bolts made of various standards and quality with the American one, a much more rational choice. Hence, all the tightening torques had to be calculated again (different thread, different diameter, dissimilar materials...).

Also, @Calum, I would not recommend you give advice for bolts installation based on what seems to be your F1 racing experience. Bolts have to be used with much more relaxed constraints in the normal usage (for example, a 50% load margin is a reasonable and efficient one in most case).
Some bolt manufacturers have published very well done and comprehensive bolts datasheet that summarize most user case with practical indications.
In most cases, readers will face a problem around a design built according to a norm. Datasheet like this are then the perfect and safe source to search for such information.
Calcuting specific bolts tightening pattern is the work of an Engineer.

 

[Scott Kenny]

[...]

What surprises me is that since 1937/38, AMX had been going all in on diesel engine development. So either there is a misunderstanding in the letters and AMX just wants to study the fuel injection system in general for application to their diesel developments, or they recently started work on another line of engines, this time using gasoline/petrol.

At the same time, the ARL design bureau was cooperating with the Edgar Brandt Establishment to develop a petrol tank engine with "direct fuel injection"*. A postwar account on clandestine work during the occupation said this engine used the Fabian injection process, but I have been unable to find what that meant. I am also not sure if they really mean direct fuel injection as in german aircraft engines, or if it just the way the French talked about another form of injection.

*The ARL noted that fuel injection for tank engines could decrease specific fuel consumption by as much as 15-20% while increasing power density by 20% on a weight basis.

Simple mechanical direct injection works the same way in gas and diesel engines.

You have a high-pressure fuel pump that has to exceed the pressure in the cylinder to push fuel past a check valve. Said fuel pump usually has a variable displacement chamber per cylinder, and at the right time in the compression stroke the fuel pump quickly slams the appropriate load of fuel into the line to the injector, through the check valve.

I mean, the inside of a naturally aspirated diesel engine has ~20bar just from the compression ratio, not counting the effects of the heat due to compression. IIRC the big R3350 gas engines used a 3500psi injector pump, and the (really crappy) GM 350 Diesel used a similar setup.

You can make a fancier direct injection system that uses a constant volume fuel pump and has the injector triggered by a camshaft similar to the one used to open a poppet valve in the cylinder. That's the method that the old Detroit Diesels used (-53, -71, and -92 series engines). Works well, needs a special dial indicator base to perfectly time. I'm not sure how exactly they controlled how much fuel went in unless the whole fuel cam moved.

 

[Calum Douglas]

Regarding the discussion on bolts and torques for the Merlin engine, Packard replaced the chaos of English Imperial bolts made of various standards and quality with the American one, a much more rational choice. Hence, all the tightening torques had to be calculated again (different thread, different diameter, dissimilar materials...).

Also, @Calum, I would not recommend you give advice for bolts installation based on what seems to be your F1 racing experience. Bolts have to be used with much more relaxed constraints in the normal usage (for example, a 50% load margin is a reasonable and efficient one in most case).
Some bolt manufacturers have published very well done and comprehensive bolts datasheet that summarize most user case with practical indications.
In most cases, readers will face a problem around a design built according to a norm. Datasheet like this are then the perfect and safe source to search for such information.
Calcuting specific bolts tightening pattern is the work of an Engineer.

Pretension to at least 75% yield is a perfectly normal target in any sensible design which has nothing to do with racing. Oh and I`ll say whatever I like thank you very much.

There is no scenario in which torque to 50% is quote "efficient". Provide sources and data for this >


HJ

 

[TomcatViP]

Baah

 

[F119Doctor]

Pretension to at least 75% yield is a perfectly normal target in any sensible design which has nothing to do with racing. Oh and I`ll say whatever I like thank you very much.

There is no scenario in which torque to 50% is quote "efficient". Provide sources and data for this >

View attachment 754063
HJ

I’ve never gotten into the design weeds of any specific bolted joint, but engineering school it was noted that a properly designed joint should always have the threaded fasteners clamping load higher than the operating loads. Of this is the case, the fastener would never see any alternating loads and thus would never fatigue. In addition, I know that several auto manufacturers torque their piston rod big ends to the yield point, which would be approximately 100% of preload capability while negating preload variability due torque measurement and friction variations.

 

[Pasoleati]

There is one puzzling question: Why didn't Wright go totally to direct injection with the R-3350 post-war as at least some strictly post-war models (according to Jane's CA models; BA and BD models had direct injection) had single-point injection to the impeller? It is very annoying that there is no thorough book on the R-3350.

 

[Nicknick]

I’ve never gotten into the design weeds of any specific bolted joint, but engineering school it was noted that a properly designed joint should always have the threaded fasteners clamping load higher than the operating loads. Of this is the case, the fastener would never see any alternating loads and thus would never fatigue. In addition, I know that several auto manufacturers torque their piston rod big ends to the yield point, which would be approximately 100% of preload capability while negating preload variability due torque measurement and friction variations.

Tightening the bolts over the yield point is done to minimize tolerances in the bolt forces. Under max. operational load, the bolts will stretch even a little further, but than the stretching will come to an end. The fasteners still don't fatique because the load variation is small enough.

Keep in mind, that most of the tightening moment is used to overcome friction and not to produce the desired axial force. Friction is allways hard to predict, so tightening bolts by a given moment will cause significant variations in bolt forces. If roundness matters (cylinder and conrod big ends), overstretching the bolts is the common method. Of course, there are alternative solutions (like measuring the stretching of a conrod bold with a micometer) but those need much more effort.

 

[Nicknick]

@Scott Kenny : Diesel injection pumps usually have a constant pumping cylinder volume and a variable opening timing. The Injection ends, when the pressure inside the pumping cylinder is relieved. This method enables a constant injection begin with a variable ending, which was good enough in the old days.

In modern Common rail pumps, it is slightly different, the plunger moves upwards and the built up of pressure starts when the intake valve is beeing closed. This method allows the use of an electromagnetic valve with very little valve actuating forces, since it it pressed in the seat by the chamber pressure.

I think, the Detroit Diesels had a system with pressure increase by an differential piston and were fed with low pressure oil.

 

[F119Doctor]

Tightening the bolts over the yield point is done to minimize tolerances in the bolt forces. Under max. operational load, the bolts will stretch even a little further, but than the stretching will come to an end. The fasteners still don't fatique because the load variation is small enough.

Keep in mind, that most of the tightening moment is used to overcome friction and not to produce the desired axial force. Friction is allways hard to predict, so tightening bolts by a given moment will cause significant variations in bolt forces. If roundness matters (cylinder and conrod big ends), overstretching the bolts is the common method. Of course, there are alternative solutions (like measuring the stretching of a conrod bold with a micometer) but those need much more effort.

In modern P&W turbine engines, the most critical threaded fastener joints have the nut torqued to a lower pre-torque level, followed by an angle of turn. This is usually followed by loosening the fastener, then reapplying the pre-torque and verifying it returns the the previous position. If it does, then the final angle of turn is applied.

If you have access to both ends of a bolt, physically measuring stretch is the most accurate method for determining the preload applied.

 

[Pasoleati]

One question: Why didn't DB adopt Junkers-style end oil-feed crankshaft lubrication system? Rolls-Royce did change to that system in the Merlin 100-series, so perhaps it just demonstrates how incompetent DB was.

 

[Calum Douglas]

One question: Why didn't DB adopt Junkers-style end oil-feed crankshaft lubrication system? Rolls-Royce did change to that system in the Merlin 100-series, so perhaps it just demonstrates how incompetent DB was.

There is no evidence to show why not, I would suspect that DB were just totally overwhelmed by just tackling the basic problems which came out of the metals shortages and were left with insufficient development capacity to make major improvements.

You can see that from how long it took the DB 605 "D" model to come out, it took them over 2 years to get it into production.

Definetly Jumo had the best engine design office in Europe for liquid cooled engines, in terms of the core engine, but then they had quite a weak knowledge of supercharging compared to both DB and RR. The early 211 superchargers were awful. I think DB had a better supercharger design office than Jumo, at least until about 1944., after that DB had their best compressor people on Turbojets.

I am about 90% certain that the crank nose oil feed on the Merlin 100 was copied from Jumo, so its highly probably even they didn't come up with it on their own. They would have seen it on the Jumo 211`s captured from the Lammermuir Hills He111, from which the engines were taken and sent to RR very early, in October 1939.

 

[Pasoleati]

There is no evidence to show why not, I would suspect that DB were just totally overwhelmed by just tackling the basic problems which came out of the metals shortages and were left with insufficient development capacity to make major improvements.

You can see that from how long it took the DB 605 "D" model to come out, it took them over 2 years to get it into production.

Definetly Jumo had the best engine design office in Europe for liquid cooled engines, in terms of the core engine, but then they had quite a weak knowledge of supercharging compared to both DB and RR. The early 211 superchargers were awful. I think DB had a better supercharger design office than Jumo, at least until about 1944., after that DB had their best compressor people on Turbojets.

I am about 90% certain that the crank nose oil feed on the Merlin 100 was copied from Jumo, so its highly probably even they didn't come up with it on their own. They would have seen it on the Jumo 211`s captured from the Lammermuir Hills He111, from which the engines were taken and sent to RR very early, in October 1939.

Indeed. Surely DB people must have known the Junkers-system before RR people.

One question: Is there any data of the TBO effects of operating the DB 605AM with MW 50 at 1,7 ata vs. standard 1,42 ata + no MW 50? In Finnish service the 605A with 1,42 ata disabled the official TBO was 100 hours (never achieved) whereas the Bristol Pegasus TBO was 400 hours (not always achieved)...

 

[Calum Douglas]

Indeed. Surely DB people must have known the Junkers-system before RR people.

One question: Is there any data of the TBO effects of operating the DB 605AM with MW 50 at 1,7 ata vs. standard 1,42 ata + no MW 50? In Finnish service the 605A with 1,42 ata disabled the official TBO was 100 hours (never achieved) whereas the Bristol Pegasus TBO was 400 hours (not always achieved)...

Possibly, I am not going to conduct a big research effort to determine this as I am too busy, however, the important point here is that the use of "internal coolants" like MW50 is that you can get a major raise in engine power WITHOUT the normally matching raise in cylinder temperature.

Therefore, any reliability issues related to temperature will likely be unchanged (or nearly so). These would be valves, and pistons, spark plugs are a bit more difficult as they are impacted by boost pressure not just temperature.

However, if you put the power up, the forces need to come out somewhere, so the obvious weakpoint is the bearings, so if you have weak bearings and/or bad oiling, you will suffer considerable early damage by use of MW50. I would think that any use of MW50 on a DB600 series would result in early overhaul necessity due to bearing wear.

 

[Pasoleati]

Possibly, I am not going to conduct a big research effort to determine this as I am too busy, however, the important point here is that the use of "internal coolants" like MW50 is that you can get a major raise in engine power WITHOUT the normally matching raise in cylinder temperature.

Therefore, any reliability issues related to temperature will likely be unchanged (or nearly so). These would be valves, and pistons, spark plugs are a bit more difficult as they are impacted by boost pressure not just temperature.

However, if you put the power up, the forces need to come out somewhere, so the obvious weakpoint is the bearings, so if you have weak bearings and/or bad oiling, you will suffer considerable early damage by use of MW50. I would think that any use of MW50 on a DB600 series would result in early overhaul necessity due to bearing wear.

Thank you for proving my point as I have elsewhere stressed that power increases through ADI cause much less temperature rise than through raising the PN of the fuel itself.

According to an investigation report on a Finnish DB 605A that failed at roughly 35 hours, the cause was the failure of the main bearings at the front end of the engine. The commentary added in the report by a unit commander states that the DB is unsuitable for training as "harsh dive recoveries stress the engine construction more than combat service" suggesting that the crankcase lacked adequate rigidity. It seems that the Jumo 211 did not suffer from this as obviously in the Ju 87 it was constantly subject to high g dive recoveries.

 

[HoHun]

Hi Pasoleati,

The commentary added in the report by a unit commander states that the DB is unsuitable for training as "harsh dive recoveries stress the engine construction more than combat service" suggesting that the crankcase lacked adequate rigidity.

What kind of data did he base his comments on? In the absence of digital engine controls and any other devices with the capability of logging engine data, I don't see how he'd be able to determine the cause for certain, especially considering that he had only a very small sample size to work with.

I haven't come across any concerns regarding dive recovery stress from Luftwaffe sources, and they obviously operated a lot more DB 605 engines than the Finnish Air Force and would have had a much better statistical basis for drawing conclusions from their maintenance records.

Was the commander in question in command of a training unit or a combat unit?

Regards,

Henning (HoHun)

 

[HoHun]

Hi Calum,

Therefore, any reliability issues related to temperature will likely be unchanged (or nearly so). These would be valves, and pistons, spark plugs are a bit more difficult as they are impacted by boost pressure not just temperature.

However, if you put the power up, the forces need to come out somewhere, so the obvious weakpoint is the bearings, so if you have weak bearings and/or bad oiling, you will suffer considerable early damage by use of MW50. I would think that any use of MW50 on a DB600 series would result in early overhaul necessity due to bearing wear.

"Flugmotoren und Strahltriebwerke" by von Gersdorff et al. confirms that spark plug life was reduced by MW50 use:

"The application of this power increase [by MW50 injection] was permissible for up to 10 minutes without any negative effects. Merely the spark plug life was limited to 15 to 30 hours."

No mention of bearing wear, though. The Me 109 also carried 70 L of MW50, which at a consumption rate of 180 L/h was good for a bit more over 20 minutes of MW50 operation, which I'd take as an indication that it was in fact meant for routine use.

Regards,

Henning (HoHun)

 

[Pasoleati]

Hi Pasoleati,



What kind of data did he base his comments on? In the absence of digital engine controls and any other devices with the capability of logging engine data, I don't see how he'd be able to determine the cause for certain, especially considering that he had only a very small sample size to work with.

I haven't come across any concerns regarding dive recovery stress from Luftwaffe sources, and they obviously operated a lot more DB 605 engines than the Finnish Air Force and would have had a much better statistical basis for drawing conclusions from their maintenance records.

Was the commander in question in command of a training unit or a combat unit?

Regards,

Henning (HoHun)

It was based on his experience as a fighter squadron commander. He specifically wrote in a different report regarding experience gained on the 109 that the use of the Bf 109 for combat training should be minimized because the engine cannot handle "high stress pullouts and rough throttle handling of trainee pilots". It is quite evident in his commentary that such failures had been isolated incidents.

As for that not being mentioned in German sources, the thing is that DB sent, I recall, two technical experts here. Their regular response (they were very skilled, nevertheless) to even most minor engine problems was "take it out, put new one in". Finnish mechanics had to tell them that no way, that's not going to work here as there are simply no new engines to put in. Faults had to be found and corrected in situ. In other words, Germans could apparently afford engine changes after a few tens of hours.

 

[Pasoleati]

I will translate the commentary ASAP and post it here.

 

[HoHun]

Hi Pasoleati,

It was based on his experience as a fighter squadron commander. He specifically wrote in a different report regarding experience gained on the 109 that the use of the Bf 109 for combat training should be minimized because the engine cannot handle "high stress pullouts and rough throttle handling of trainee pilots". It is quite evident in his commentary that such failures had been isolated incidents.

You can't really base a meaningful conclusion on isolated incidents, and in conjunction with the remark on rough (throttle) handling by trainee pilots, I think it's clear that this wasn't meant as a technical analysis. There are more ways to mishandle an engine, like not operating it at the proper temperatures, and I'd guess this was more likely to happen in training squadrons. Additionally, with him being a combat squadron commander and the engines being a scarce resource in the Finnish Air Force, it made good sense for him to provide reasons the engines should be used for combat rather than for training.

Finnish mechanics had to tell them that no way, that's not going to work here as there are simply no new engines to put in. Faults had to be found and corrected in situ. In other words, Germans could apparently afford engine changes after a few tens of hours.

Good point, the Finns didn't have the maintenance and industry infrastructure to operate in the same manner as the Germans. I'm not quite sure if that can be considered an aspect of logistics, but it's clear that the Finns were operating in a context of technological austerity.

My impression is that the Germans decided very early on that they wanted to have very rapid engine changes, probably to facilitate repairs on an engine without having to ground the aircraft it belonged to. This does in fact require a large enough pool of ready spares, though - and here the Germans according to Eisenlohr weren't necessarily doing so well, as they ordered a large number of aircraft with what he considered a much too small reserve in spare engines. Not sure what they meant for German repair logistics in WW2, though.

Regards,

Henning (HoHun)

 

[Pasoleati]

Translation:"Attachment 1 Commanding Officer's statement:" I state that the reason for the engine failure is that the training program for the pilots flying the MT in the Flying Squadron 30 is too stressing for the airplanes. To complete the training program, every pilot has to fly 4-5 hours of combat training aerobatics, which, as usual, stresses the airplanes and especially their engines more than normal squadron operations. I think that the MT (meaning 109) is not suitable for type training and that such training be kept to a minimum to spare the airplanes. The original 5-hour training is adequate and I suggest that the additional 5-hour combat training be left out, as such training with frequent high-power pullout causes overheating and lubrication problems, especially with bearings on the front end of the engine. I also refer to my earlier requests to shorten the assigned training program. Signed Captain K. Lahtela.""

 

[F119Doctor]

In one of Graham White’s books, he noted that one P&W radial suffered bearing failures during engine overspeed in high speed dives. The solution was the silver lead plain shell bearing with an indium flash. When German engineers examined captured P&W engines, they thought the indium was a contaminant, instead of an important part of the design. This suggests two possible issues with the Bf109:

1. The propeller constant speed blade angle ran out of travel during high speed dives, resulting in engine overspeed that was beyond the capability of the bearings

2. The bearings were just not capable of handling the large gyroscopic propeller loads encountered during high speed pullout.

I know that many of the German engines used ball and roller bearings instead of plain shell bearings, unknown whether this had anything to do with the life shortfall reported by Norway.

 

[Scott Kenny]

In one of Graham White’s books, he noted that one P&W radial suffered bearing failures during engine overspeed in high speed dives. The solution was the silver lead plain shell bearing with an indium flash. When German engineers examined captured P&W engines, they thought the indium was a contaminant, instead of an important part of the design. This suggests two possible issues with the Bf109:

1. The propeller constant speed blade angle ran out of travel during high speed dives, resulting in engine overspeed that was beyond the capability of the bearings

2. The bearings were just not capable of handling the large gyroscopic propeller loads encountered during high speed pullout.

I know that many of the German engines used ball and roller bearings instead of plain shell bearings, unknown whether this had anything to do with the life shortfall reported by Norway.

I would lean more towards option 1, but option 2 is definitely possible.

Without a prop hub capable of going to (nearly) full feather, running out of blade angle in a dive is VERY likely.

And nobody puts full feathering props on single-engined aircraft.

 

[aim9xray]

And nobody puts full feathering props on single-engined aircraft.

 

[Scott Kenny]

View attachment 757905

Fine.

Nobody put full-feathering props on a single-engined aircraft at the time, or really until the PT6 was available. And then it was cheaper to take a complete engine+prop from a PT6-powered twin engined plane and install that into the nose of a single.

 

[HoHun]

Hi Scott,

Nobody put full-feathering props on a single-engined aircraft at the time, or really until the PT6 was available. And then it was cheaper to take a complete engine+prop from a PT6-powered twin engined plane and install that into the nose of a single.

I believe the vast majority of German propeller hubs, being electrically actuated, could go to fully feathered even on single-engine aircraft.

Specifically, here's a quote from the Me 109 manual "Bf 109 G-2 mit Motor DB 605 - Bedienungsvorschrift-Fl - Bedienung und Wartung des Flugzeuges - Juni 1942" mentions on p. 20 under "Emergency Procedures" (my translation):

- "Airscrew to feathered position - Switch off automatic system and hold thumb switch down until feathered position is reached".

P. 17 mentions diving:

- "The automatic system is to be switched on before the dive, if previously the aircraft was flown on manual control".

P. 13 notes that one would normally fly with the automatic system on, unless one was flying for range or for duration, in which case the manual control allowed operation with exact rpm/boost figures according to the aircraft's range table.

There's also another note regarding diving on that page:

- "Caution: On initiating a full-power dive by 'pushing over' and when rashly applying power, impermissible overspeeding of the engine is to be expected."

Conceivably, smooth power application upon entering the dive is something the Finnish trainees might only have learned during their course, which would lend credibility to the observation that training was harder on engines than operation. Still, it would be more of a guess than of an engineering analysis.

Regards,

Henning (HoHun)

 

[tomo pauk]

In one of Graham White’s books, he noted that one P&W radial suffered bearing failures during engine overspeed in high speed dives. The solution was the silver lead plain shell bearing with an indium flash. When German engineers examined captured P&W engines, they thought the indium was a contaminant, instead of an important part of the design.

Would you be so kind to check out whether the last sentence is supported by a footnote pointing out to a source? In your spare time, of course.

 

[Calum Douglas]

In many cases the worst load case is something unexpected, in the case of a propeller housing for example, the max stress may well be at very low speeds where max rate of airframe change in degrees per second can take place, caused of course by the enormous gyroscopic loads generated by the spinning propeller itself being made to change direction.

I am sceptical that DB had issues with insufficient crankcase mechanical properties, they put quite a bit of effort into testing the cases to failure (they would literally insert a huge steel bar into the prop housing and break the crankcase casting front end totally off in a stress rig.

It is of course possible that they did have problems in the very early days pre-war, perhaps someone had some hours in something with a DB600 inside, and those issues stayed with him. All very early versions of aero engines were scrapheaps biding their time, anyone who had flown something with a Merlin Mk II for example would probably have developed a very cautious throttle-hand for the rest of their lives.

 

[F119Doctor]

In one of Graham White’s books, he noted that one P&W radial suffered bearing failures during engine overspeed in high speed dives. The solution was the silver lead plain shell bearing with an indium flash. When German engineers examined captured P&W engines, they thought the indium was a contaminant, instead of an important part of the design.

Would you be so kind to check out whether the last sentence is supported by a footnote pointing out to a source? In your spare time, of course.

The book is R-2800 Pratt & Whitney's Dependable Masterpiece, by Graham White. The info is from Chapter 3, page 65. The bearing in question was the master rod big end bearing, with a steel shell with a thick layer of fatigue resistant silver and a 0.001 thick inner layer of lead alloyed with 4% indium.

The references provided in the book for this section are:
3.4 Overhaul Manual, Double Wasp A and B Series Single Stage Engines, Third Edition, Pratt & Whitney Aircraft, July 1943
2.1 The Pratt & Whitney Aircraft Story, Pratt & Whitney Div., United Aircraft Corp., East Hartford, Conn., 15 May 1952
3.67 Analysis and Lubrication of Bearings, Milton C. Shaw and Fred E. Macks, McGraw-Hill Book Company Inc. , New York, 1949

From the book:
"This technology, developed in 1937, and known in the industry as the "Hobbs" bearing, was a key contributor to the success of US aircraft engines in WW II. Pratt & Whitney shared the fruits of their efforts with its competitors. As in interesting aside, when German engineers investigated and studied aircraft shot down during WW II they were impressed by the quality of American bearings - particularly plain bearings. But, they could not understand why the silver bearings were "contaminated" with lead/indium"

I don't know if the German engineer story is taken from either of the provided references, or if this was something that Graham White obtained from other sources.

 

[F119Doctor]

The Silver Lead/Indium bearing development story from The Pratt & Whitney Aircraft Story, Pratt & Whitney Div., United Aircraft Corp., East Hartford, Conn., 15 May 1952. It does not include the German analysis story. Sorry about each of 4 pages being separate files, that was the only way I could access them online.

 

[tomo pauk]

I don't know if the German engineer story is taken from either of the provided references, or if this was something that Graham White obtained from other sources.

Thank you for the feedback.
It is very unfortunate that the 'contamination' by indium story is not backed up by an exact and known source in the book.

 

[Pasoleati]

Hohun, did you even try to pay attention? The attachment I translated was preceded by a very detailed damage assessment. Forward end bearing failure led to conrod failure causing the engine to seize. The point is that comparable failures did not occur in any other FAF aircraft of the same period used the exactly similar way. They did not occur in Fokker D.21 (Mercury) and D.X (Pegasus) despite both lacking constant-speed props and being flown substantially more per airframe and the D.X being used for harsh dive-bombing training and combat. Neither did the H-S suffer that in the M. S. 406. So if a certain mode of failure occurs only in one engine make & model among many, logic dictates that the one having those failures has something wrong. And that is not "lack of smooth throttle opening". A war engine must be capable of war handling.

 

[HoHun]

Hi Pasoleati,

Hohun, did you even try to pay attention? The attachment I translated was preceded by a very detailed damage assessment.

So where did you post that very detailed damage assessment?

Regards,

Henning (HoHun)

 

[F119Doctor]

Thank you for the feedback.
It is very unfortunate that the 'contamination' by indium story is not backed up by an exact and known source in the book.

I did review the other reference provided, and did not find any citation of the "contamination" story in that book.
3.67 Analysis and Lubrication of Bearings, Milton C. Shaw and Fred E. Macks, McGraw-Hill Book Company Inc. , New York, 1949

 

[Pasoleati]

The failure occurrent 15.5.1944 with a total of 29:30 hours on the engine. The investigation board report lists serial number, local weather etc. down to the amount of oil remaining in the tank. The engine had been checked before the 15.5. on 13.5.

The report sheet lists various parts from prop to lubrication system and engine attachments. Following are direct translations:
"Mechanic's statement: The engine ran faultlessly on 15.5.44 when I tested it."
"Pilot statement:"Engine running completely normal before the failure. After a climbing roll a sudden strong vibration set in. I reduced power but the vibration remained as strong. The oil pressure dropped immediately below the limit, I landed right away at the base and stopped the engine. "

Tech. section:

"Lubrication system: failed."
"Other observations: Crankcase cover and the crankcase itself ruptured at the 1st and 7th cylinders. Conrods in cylinders 1 and 7 broken."

"Do all parts appear properly lubricated no, big-end bearings of conrods 1 and 7 seized."

The report concludes "The board concur with the statement of the unit commander regarding the use of the MT for training."

In other words, the investigation board agreed that the engine was not suitable for training due to being weak.

 

[Calum Douglas]

The failure occurrent 15.5.1944 with a total of 29:30 hours on the engine. The investigation board report lists serial number, local weather etc. down to the amount of oil remaining in the tank. The engine had been checked before the 15.5. on 13.5.

The report sheet lists various parts from prop to lubrication system and engine attachments. Following are direct translations:
"Mechanic's statement: The engine ran faultlessly on 15.5.44 when I tested it."
"Pilot statement:"Engine running completely normal before the failure. After a climbing roll a sudden strong vibration set in. I reduced power but the vibration remained as strong. The oil pressure dropped immediately below the limit, I landed right away at the base and stopped the engine. "

Tech. section:

"Lubrication system: failed."
"Other observations: Crankcase cover and the crankcase itself ruptured at the 1st and 7th cylinders. Conrods in cylinders 1 and 7 broken."

"Do all parts appear properly lubricated no, big-end bearings of conrods 1 and 7 seized."

The report concludes "The board concur with the statement of the unit commander regarding the use of the MT for training."

In other words, the investigation board agreed that the engine was not suitable for training due to being weak.

Sounds like bearing failure to me, the bearings will take a few seconds to seize, but a crankcase crack will be a very sudden catastrophic event (in other worse the bearings went first). Given the calamity of German aero engine bearings in WW2, this is in my view, probably just an indication of the typical issues being experienced by all DB605 series engines in service at that time everywhere. "weak" here (until a complete translated manuscript is provided) appears to mean the general overall state of the engine reliability as a whole is insufficient, which is exactly how the engine would have been described for combat use as well at that time.

 

[HoHun]

Hi Calum,

"weak" here (until a complete translated manuscript is provided)

"Weak" is Pasoleati's word, not actually from the report.

What's your take on judging an engine on the basis of a single investigated case?

Regards,

Henning (HoHun)

 

[Calum Douglas]

Hi Calum,



"Weak" is Pasoleati's word, not actually from the report.

What's your take on judging an engine on the basis of a single investigated case?

Regards,

Henning (HoHun)

All aero engines had individual cases of severe failures at very low hours. It is only possible to make judgements by use of results "fleet wide", in other words of cases which resulted in alterations to the service interval (or impromptu enforced replacement of a component) in official documents. It is possible to imply almost anything with the use of specific cases. However, to be frank, I am not even sure of what the specific point is that is being argued over here. Is it that "training" is worse than combat for engines, or that DB engines were less reliable than their immediate German contemporaries, or that crankcases in DB engine fail a "lot" in flight ?

 

[HoHun]

Hi Calum,

However, to be frank, I am not even sure of what the specific point is that is being argued over here.

As far as I can tell, Pasoleati thinks that the Finnish proved beyond doubt that the DB 605 was a bad design. I my opinion, they neither attempted that, nor did they coincedentally succeed in it.

Regards,

Henning (HoHun)

 

[Pasoleati]

Hi Calum,



"Weak" is Pasoleati's word, not actually from the report.

What's your take on judging an engine on the basis of a single investigated case?

Regards,

Henning (HoHun)

You don't get it. These incidents occurred more than once, but since I don't have any realistic access to the pertinent archive (these are not digitized and I don't drive 500 km to and fro to simply please you), I can use only what I get from others. This document was just the one available to me.

Do you honestly believe that a training unit commander would ask for reduction in training hours based on a single incident? Especially considering the fact he clearly stated that he has requested that before.

The fact is that during the war, not a single Finnish DB 605 achieved the lousy 100 h TBO!

 

[HoHun]

Hi Pasoleati,

These incidents occurred more than once, but since I don't have any realistic access to the pertinent archive (these are not digitized and I don't drive 500 km to and fro to simply please you), I can use only what I get from others.

So you have evidence of one incident and agree that it would be ridiculous to draw any conclusion from single incidents.

As stuff you claim something about usually turn out not to support what you say as soon as I can see it for myself, I'll just wait until there's more I can see for myself.

Regards,

Henning (HoHun)