Thanks for your reply.

What happens if oil doesn't get changed regularly or is unfiltered?

Okay.  Can you describe the harm that your engine may incurr if the oil ran through the engine for 50 hours without being filtered or changed?  Will it pretty much just "die" upon that activity? 

Are there drastic differences in the engine oil/ oil filter systems/ functions of plane engines as opposed to car engines?

Thanks again.

Thanks, again, for taking the time to respond to my questions.  The questions are not asked in relation to any plane specifically.  Just trying to learn a little more about the subject matter, so feel free to elaborate if you'd like.

I think the "life" of ones oil and ones filter would depend on the condition of, how and how often the plane is flown.  Many variables
come into play.  The recommend oil/filter change should, pretty much, asure that the oil/filter's life hasn't been expended.
At the price of these engines and their maintainance, I don't know of anyone who would want to find out how long the "life" is.

I knew an auto mechanic that had a shop that contracted with Budget RentA Car.  He told me that Budget's policy was to take the cars out of service for oil changes.  They felt that the down time for the maintainance would be less if they just ran the engines untill the croaked.  He further advised the average life for those engines were about 57,000 miles.  Then replace the trashed engine.  I did get to see the inside of one of those motors....pretty ugly!

I think it depends on your engine.  Consult the engine manual for recommended times.  We change our oil every 50 hours and the filter every 100 hours.  Have we gone 70 hours between oil changes?  Sure we have.  But that is when we are flying a lot and simply don't have time to change the oil.  Put in a quick drain and then change the oil yourself.  Get a certified mechanic to change the filter for you.  They will properly safety wire it and then cut it open to check for metal.

Just remember, fuel and oil are about the cheapest things you put into an aircraft.

Here's the link to the site that Jack mentioned...pretty interesting.
<http://www.generalaviationnews.com/editorial/articledetail.lasso?-token.key=10409&-token.src=column&-nothing>

Follow your service manual is all I have to say.  The 50 hour oil change/ 100hr. oil & filter change has worked for us.  We have a small charter company and I am 1000 hours into my third set of engines.  All have made it to TBO and then some.  Our cylinders are making it to TBO now that we have switched to TCM steel cylinders.  We use Aero Shell straight weight oil i.e. 100W, 80W, and 65W.  This has worked for us for years now, but again, follow your service manual.  We do.