View Full Version : Engine Bearings.

13th Jun 2002, 16:04
I understand how for example an oil pressure bearing works on the turbo on my car, or how the shell bearings work on the crank; but both of these have no real thrust transmitted onto the bearings laterally…i.e. in my car engine or turbo, the shaft isn’t being ‘pulled.’ On both piston and turbine aircraft engines, how is the thrust produced by the prop or fans transmitted to the rest of the engine? I assume you effectively have to have 2 bearing surfaces…1 retaining the circumference of the shaft, and a second stopping the shaft moving by being effectively ‘pulled’ by the produced thrust. Sorry if this doesn’t make too much sense….

13th Jun 2002, 16:19
There are one or more 'thrust bearings' which can be ball/roller type or plain ('oil') bearings. They might be separate bearings or one bearing may have both functions. Many automotive engines have a thrust face on one of the crank bearings since there is some thrust load due to clutch actuation forces (if a manual transmission). Obviously the loads are much higher on an aircraft engine, however.

Do an internet search on 'thrust bearing' and you'll probably find a lot of info :cool:

13th Jun 2002, 19:53
Yes...and one operator tried to use the OLD design bearings in RB.211's, never mind RR advice (what do they know??!)...which led to...bankruptcy.

14th Jun 2002, 00:58
Not sure where you are coming from here. As an ex-engineer with a major airline I believe that RR engines are the best one can purchase for any a/c. Apologies for being a tad light, but their bird ingestion testing is the best for example. OK there may have been pylon issues wrt 767's but who else throws frozen chickens into engines as part of their testing ?

Just my two-pennyth worth

14th Jun 2002, 01:11
You miss my point Lost_luggage34, it was the AIRLINE that did not take RR advise, and it cost them dearly.

14th Jun 2002, 13:24
Surely, using the incorrect/superceeded/non approved bearings in an engine would mean that the engine no longer conformed to the manufacturers specs which would mean that the only way it could be legally flown would be with an NTO (no technical objection) from the manufacturer. Without this the said engine would be illegal, the certifying engineer shouldn't sign for it and even if he did, as it did not meet specs without authority, its' C of A would be invalid.

I have a feeling this is another aviation myth.

:D :D

14th Jun 2002, 16:21
Unfortunately mono, not a myth, and a LOT of guys are out of work as a result.
When these RB.211 machines arrived on the property, I asked the DirMaintenance if he was going to send guys to RR for training. His only reply was..."we have no problem with DC-8s, why should we send guys to Derby?"
Big mistake, IMHO.

15th Jun 2002, 05:50
411A, yeah, good plan - it's just a machine, they must all be the same .... :):)
When will they learn?

Willit Run
15th Jun 2002, 16:31
As I was part of that little bearing debacle, I am, with alot of other folks, kinda pissed about losing our jobs because of this cheap judgement.
We had a good thing going, and life on the ole tristar was rather good!!!
Oh well! life goes on, Time to get over it

15th Jun 2002, 18:02
> I assume you effectively have to have 2 bearing surfaces…

Not always. You can make a bearing handle axial or radial loads, or a combination of both. I'm sure you can find drawings if you
do a web search.

15th Jun 2002, 19:57
Ball Brarings take both Axial and Radial loads, thats why all Thrustbearings are Balls.

15th Jun 2002, 20:24
Taper Roller bearings can take axial as well as radial loads, they have the bearing surfaces at approximately 45 degrees to each other with rollers in between.

Ball or plain bearings can also be designed to work in the axial plane. Instead of the two bearing surfaces being inside one another like two sections of tube, they oppose one another like a record player turntable (or bicycle wheel) bearing.

If you can't remember record players (Gosh, I'm so old) try imagining two CDs placed on on top of another. The type of bearing to allow them to rotate against each other would be the same type as that required in an engine as a thrust bearing.

Over the years they have all been tried!