Engine failure due to main bearings failure? - ED Forums
 


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Old 11-30-2019, 01:17 PM   #1
Hiromachi
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Default Engine failure due to main bearings failure?

Yesterday, during evening flying session two instances of engine failure occured to me. Previously I had no issues with FW-190 engine operation and last failure happened over a year ago, so I was pretty stunned.
So what have happened is that during the dive I felt as if I hit a wake turbulance or something of this nature, with aircraft shaking pretty violently. Immediately after this my RPM went to 0 and MP gauge shown fluctuating needle, jumping from 1.1 to 1.4 Ata. But engine clearly produced no power and attempts to restart it failed. Fortunately I was able to glide myself back home.

Second time I experienced similar behavior as well during the dive, when I tried to follow the target below. Same story, weird engine behavior and then complete loss of power. Second time in less than 2 hours and I knew this wasnt accident or random situation, but something else.
And then I was reminded of this:
Quote:
Originally Posted by Yo-Yo View Post
Supercharger is adjusted for TO (or wet WEP if available) MP at SL at full throttle at low speed. Ram pressure, though, can be a problem, but the speed builds up not too fast to make MP adjusting unavailable.
At climb at higher altitudes the MP can be higher than at the SL.

The new kind of failures we will introduce is a main bearings failure due to LOW MP... in less than a minute the bearings will be dead. Thus, it will cure the bad habit to retard throttle at high speed.
https://forums.eagle.ru/showpost.php...postcount=1900

Yes, in both instances I was descending at high speeds (600+ km/h) with throttle partially closed (1.4 - 1.5 Ata or more). Thus, the brief explenation above fits the factual situation and results. Yet I dont recall this mechanic being explained in depth in any changelog, so I would like to ask Yoyo if he could provide more extensive description.
Most importantly:
- why it happens ? I thought that main bearing failure is caused by lugging the engine, thus it shouldn't happen when you retard the throttle because there is very low load. Or I could see damage to bearings when moving throttle suddenly and in a wide range (i.e. slamming forward or something);
- what is the safe limit of engine operation vs speed ? I mean, throttle is the main mean to control acceleration in descend. One doesnt want to overspeed and exit dive with no wings, so running with full throttle might not be the good idea at all times in dive.
- how can it be observed prior to happening ? I cant recall seeing any feedback prior to it happening.

Thank you for the answer in advance. I'd really like to learn more about to avoid such situations in the future.
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Old 11-30-2019, 05:43 PM   #2
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I’ve had some lurch in the p51 lately in high speed dives, guess this explains it pretty cool it’s in already.

My observations in p51 was a sudden yaw movement due to engine not providing any torq, like you at first I thought it was wake turbulence but when the engine and MP dropped out was like oh boy what’s this...
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Old 11-30-2019, 05:58 PM   #3
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I'm not a mechanical expert and would like to understand by which causality chain low manifold pressure will cause main bearing failure. I would expect such a failure when there is lack of lubrication but fail to see how low MP would disrupt lubrication. Can somebody explain?
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Old 12-01-2019, 11:53 PM   #4
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Quote:
Originally Posted by Hiromachi View Post
Yesterday, during evening flying session two instances of engine failure occured to me. Previously I had no issues with FW-190 engine operation and last failure happened over a year ago, so I was pretty stunned.
So what have happened is that during the dive I felt as if I hit a wake turbulance or something of this nature, with aircraft shaking pretty violently. Immediately after this my RPM went to 0 and MP gauge shown fluctuating needle, jumping from 1.1 to 1.4 Ata. But engine clearly produced no power and attempts to restart it failed. Fortunately I was able to glide myself back home.

Second time I experienced similar behavior as well during the dive, when I tried to follow the target below. Same story, weird engine behavior and then complete loss of power. Second time in less than 2 hours and I knew this wasnt accident or random situation, but something else.
And then I was reminded of this:

https://forums.eagle.ru/showpost.php...postcount=1900

Yes, in both instances I was descending at high speeds (600+ km/h) with throttle partially closed (1.4 - 1.5 Ata or more). Thus, the brief explenation above fits the factual situation and results. Yet I dont recall this mechanic being explained in depth in any changelog, so I would like to ask Yoyo if he could provide more extensive description.
Most importantly:
- why it happens ? I thought that main bearing failure is caused by lugging the engine, thus it shouldn't happen when you retard the throttle because there is very low load. Or I could see damage to bearings when moving throttle suddenly and in a wide range (i.e. slamming forward or something);
- what is the safe limit of engine operation vs speed ? I mean, throttle is the main mean to control acceleration in descend. One doesnt want to overspeed and exit dive with no wings, so running with full throttle might not be the good idea at all times in dive.
- how can it be observed prior to happening ? I cant recall seeing any feedback prior to it happening.

Thank you for the answer in advance. I'd really like to learn more about to avoid such situations in the future.
I have no idea about the failure. Main bearings failure is only on its way to the project. The track could help.
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
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Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 12-01-2019, 11:57 PM   #5
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Quote:
Originally Posted by LeCuvier View Post
I'm not a mechanical expert and would like to understand by which causality chain low manifold pressure will cause main bearing failure. I would expect such a failure when there is lack of lubrication but fail to see how low MP would disrupt lubrication. Can somebody explain?
The mechanics of the piston rod and crankshaft is balanced with regards of inertia forces and gas pressure forces. At low MP lack of gas pressure forces causes more disbalance and higher bearing loading.
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 12-02-2019, 07:23 AM   #6
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At low MP prop starts shifting from pulling to braking the plane so the forces are shifted, But as i think about it V 12 are less prone to this typ of damage because number of main bearing per cylinder is much greater then in radial engine.
It simply looks like this you want to keep some tension on internal parts of the engine and you don't want to be cranking loose at high rpm, Same with rollers bearing if it is not loaded properly rollers can stop rolling and it will kill bearing quick.
I don't remember exactly in which NK-8 or D-30 engines designers reduced rollers numbers(half) in one of the shaft bearings because of low bearing load, later 2 il 62s crashed during catastrophic engine fail it came out that bearing was loaded too much.
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Old 12-03-2019, 12:37 AM   #7
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Hi all,
yes this is true. Mass, Inertia, and Centrifugal Force are balanced in the engine/propeller assembly, when cruising, however the propeller is constantly trying to move forward faster than the aircraft is. in other words the propeller is constantly trying to rip itself from the engine, due to the forward thrust of the propeller. The engine is built to withstand this forward motion, through thrust bearings, and the thrust in the gear train is actually designed too pull rearwards on the prop and crankshaft to help compensate.(this is important). so we wing over in a dive. the problems occur when the propeller starts to drive the engine, instead of the engine driving the propeller. in example, diving at less than full pitch on the prop or suddenly pulling back on the power in a dive... the prop just wants to separate from the engine,((reduction gear)) plus the gear train is loaded in the opposite direction, because the prop is driving the engine, instead of the engine driving the prop , as designed. the Anton had similar issues with breaking the supercharger impeller shaft, but it was a gear train backlash issue at low (under 1000) RPM, due to the rough running of the radial engine causing chatter in the gear train, and the impeller shaft was the weak link in the chain.
Yo-Yo is right when he said there may be some hurt feelings when the P-47 drops, just in engine management wise, as the 2800 goes, (and all radials)... if it had a weak link, the main bearings were it. man I want my Jug.
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Old 12-03-2019, 12:57 AM   #8
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Thanks for the explanation Andy! Makes sense in my brain.
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Old 12-03-2019, 01:30 AM   #9
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thank you I am glad it helped. it is really due to working the powertrain in the opposite direction of witch it is designed., and as the Jumo goes, If I remember correct, it had roller bearings on the crank and rods, so bearing thrust was even more critical
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Old 12-03-2019, 08:06 AM   #10
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If engine is equipped with prop reduction gear box i think reversed thrust will not affect engine crank shaft it self but only the gear box. I think main bearings fail is due to what Yo-Yo said.
Yo-Yo will we get fatal gearbox case fail in extreme dives so we can loose prop some day ? Last i checked i climbed to 40k ft and dived straight down nothing happened
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