Engine failure due to main bearings failure? - Page 2 - ED Forums
 


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Old 12-03-2019, 12:31 PM   #11
Yo-Yo
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Originally Posted by grafspee View Post
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
No, the main damage is exactly for the cranck shaft bearings for the reason that the plain bearings are very sensitive to the local pressure. And, by the way, for some radial engines the power-on pressure was very close to the maximal for the allowed for bearings alloy. So, any, power-off disbalance leads to overstressing.
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Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 12-03-2019, 12:38 PM   #12
grafspee
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Originally Posted by Yo-Yo View Post
No, the main damage is exactly for the cranck shaft bearings for the reason that the plain bearings are very sensitive to the local pressure. And, by the way, for some radial engines the power-on pressure was very close to the maximal for the allowed for bearings alloy. So, any, power-off disbalance leads to overstressing.
I was talking about forces on shaft created by prop drag, when gear box is present and prop no longer pulling or pushing crank shaft in engine case, so how this can affect crank shaft in any way.(forces parallel to crank shaft axis)
I though that main crank shaft is mounted on the rolling bearings in radial engines not plain bearings, probably im wrong about it.
German planes are the best if you cut throttle Control unit will reduce rpm problem solved
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Old 12-11-2019, 06:33 AM   #13
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Originally Posted by Andy1966 View Post
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.
The P47D 30 has dive breaks so it's not a huge issue. The P51D on the other hand falls apart around 490 to 505mph.So not being able to idle in a dive will make the P51D so much more painfull to dive in.
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Old 12-11-2019, 08:09 AM   #14
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The P47D 30 has dive breaks so it's not a huge issue. The P51D on the other hand falls apart around 490 to 505mph.So not being able to idle in a dive will make the P51D so much more painfull to dive in.
P-51 dont have radial engine so wont be affected you just need to follow manual so minimum MP is something like 25"
Btw you can cut throttle but you will have to drop rpm before
-30 had automatic prop pitch so it will lower rpm at lower MP
im kind afraid of modeling this by by ed i already can see jammed engines because you cut throttle at landing approach.
Same with 67" in p-51 once you use it for more then 3 min engine will blow on you even after you land it and turn it of it will bang you in the face "BANG"
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