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Keeping a plane in the air for 2 months

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1390558.  Tue Sep 21, 2021 4:33 pm Reply with quote

What I wonder about is, would the engine parts not require the odd drop of oil or other lubrication if they have to keep working for 2 months nonstop?

Anybody knowledgeable (or anyone with some healthy imagination) - please advise.



1390562.  Tue Sep 21, 2021 5:21 pm Reply with quote

These days aero engines circulate and re-use oil (like cars) and while they will always lose a little through combustion and leakage it's a very small amount. So in principle two months running just needs a larger oil tank to allow for the losses. Even in older times when engines consumed larger amounts of oil* there was provision to over-fill oil tanks for "ferry" flights. This is even true of jets - the RAF Harrier GR3s that went to joint the task force in the Falklands War carrier 60% more oil than normal through the simple expedient of brim-filling the oil tank.

So it's possible to simply carry more for long flights, but that's not the whole story. In internal combustion engines (and to a lesser extent jets & turboprops) the oil also washes the engine's internals, carrying away combustion products some of which are acidic. Over time the oil's detergent gets "full" of sooty deposit and also gets progressively more acidic, which if left to go too far starts corrosion inside the engine (a bad thing). That's the main reason why you have to change the oil in your car's engine every year (or more frequently for high-mileage use).

The problem is more severe in aeroengines because they run for longer periods and at higher average power settings that car engines, so a typical light aeroplane gets its oil/filters/plugs service every 100-150 running hours to avoid expensive damage. Now a 2 month flight obviously involves more than 150 hours of constant running, so they will have to address this issue in one or both of two ways:

1. Use special additives which can delay the onset of dangerous acidity and mitigate the poorer lubrication properties as the oil gets loaded with soot

2. Install an oil scrubber unit in the return line to the oil tank

Both of these approaches work, but they are only partially effective and the oil scrubber is a heavy device which has a finite supply of reagents. But I think it's a fair guess that these chaps have done their sums and have this all worked out.

There are other issues - two flying months (call it 1500 flying hours) is actually close to the overhaul life of a typical light aero engine, and in that time it would normally have had several minor servicing actions with changes of spark plugs, greasing of magnetos and linkages, changes of accessory drive belts, seals and especially the carbon vanes in the vacuum pumps. I doubt they would be intended to do engine servicing while in flight(!) so they must have a strategy to mitigate this. The same applies to all sorts of things like flight instruments, brakes, control surface cables & hinges etc etc.

There's also the minor issue of food, water, washing and human waste from the crew - but again, they must have solutions for these or they wouldn't attempt the flight.


* back in the early 80s when I was still flying actively I was part of a group who wanted to buy one of the Ex-RAF Chipmunks when they sold off the fleet, because they were wonderful flying machines (real "pilot's aeroplanes") and I had over 70 hours on them. They were powered by a DH Gypsy Major Mk10 engine - the final development of a pre-war design which wasn't noted for its fuel economy, but the killer was its appetite for oil. Even when new they drank about 2 pints of oil per hour, and once they got to a later stage of maturity they could drink 2-3 gallons per flight. Aero engine oil isn't cheap, and it made the oil costs almost as much as the fuel costs. So we sadly concluded couldn't afford to run one.

1390564.  Tue Sep 21, 2021 5:57 pm Reply with quote

Ta, PDR.

Would all these ways to counter lubrication problems have been similar to those when that 1950 flight took place or would that have been more primitive?


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