Thursday, March 17, 2011

Thirty Minutes of Oil

Oil: I'm supposed to put Exxon 2380 oil in this airplane and it goes all around and makes things slippery, cooled, cleaned and sealed. Done. Yeah, right.

C'mon, Aviatrix, it's not that bad. Half an hour on the oil system and then you can go play with your toy flight simulator. Minimum oil temperature for start is -40. You don't need units there, the Fahrenheit and Celsius scales cross at -40. I'd be cross, too. In addition to the standard four functions of oil referenced above, oil pressure on this airplane takes part in propeller operations, specifically normal blade adjustment, negative torque sensing, and the unfeathering pump. It's used in three parts of the anti-icing system, and it has gauges and annunciator lights associated with it.

Oil lubricates the reduction gear, so that the propeller rpm can be 2000 instead of the 42,000-odd rpm of the main engine, and oil pressure in the propeller hub drives the propeller towards fine, against the pressure of the feathering spring, using the usual system of flyweights governing a pilot valve to keep the propeller on speed. Feathering dumps the oil from the hub, allowing the feathering spring to drive the blades all the way to 89%, while negative torque adjusts the blade angle to windmill in the 18-28% range, waiting for the pilot to either feather or attempt a restart. It's a kind of half-hearted autofeather.

Anti-icing has already been described, oil circulates in the oil cooler inlet lip, and then if its temperature is still above 55 degrees it goes to the oil cooler, else it goes through the filter and back to work. Fifty-five is the oil's lucky number because that's also the pressure differential across the oil filter that will cause it to bypass the filter. Oil heat also anti-ices the lower part of the engine air inlet, provides the heat for the fuel anti-icing heat exchanger, and makes the airplane nice and warm if you put your hands against the nacelle after shutdown.

Would you believe that that took me thirty minutes? It did include going off to get another book to look at a diagram of the propeller system. I need to know more than this, but I need a break.


nec Timide said...

Spoiler alert!

I was watching Mayday the other day (you have blogged about it in the acient past). The new season has the investigation into the double engine failure of the 777 landing at Heathrow. The cause is realated to the fuel anti-icing head exchanger design on that airplane. It was all the more interesting for having read your description of the system before watching the show. Thanks for that!

Unknown said...

In a previous post you mentioned useless data cluttering your brain. According to my useless brain data centre the 42,000 odd RPM mentioned is actually 41,730. That number has been stuck in my head for 28 years now. Please send help.

Vince said...

IIRC in a recently-released NTSB report the pilots of the Cougar helicopter that went down in the ocean offshore of Newfoundland in March of 2009 may have thought they had 30 minutes of oil in their transmission, so when I saw the title of your post I was thinking this was what you were blogging about. Instead I learned that the engine turns *a lot* faster than I thought it does... cool stuff as always!

Lord Hutton said...

I went flying today. I didn't have to check the oil!

Cedarglen said...

Sure! I can believe the 30 minutes. Why? Because you NEED to know this stuff and for two reasons. First, if you are going to drive this airplane, you DO need to know damn near everything about how it works. The PAX behind your valult and all of the crew sort of depend upon your knowing this stuff and using it when critical decisions have to me made. (In your Norther flying envirnment, enexpected stuff happens. Pilots who are prepared deliver their loads and fly again. Need I say more? Second, it is obvously material that you NEED to know for your exams and that pending test or check ride. If you want the job, you present with known material. As noted, the compwtiton is tough and there are a lot of pilots who would like to have the 'slot' that you are competeting for. WHile I think that the line is pr probably asking as bit too much of prospective pilots - as described by you - Iguess they also have that right. They can affor d to be picky - today. In a few more years, perhaps not so. If you can live with this job's details for a few years, you will be a better pilot and you will probably book a lot of cycles and hours. Is it a career, or just a caree move? Only YOU can know that. Obviously, a lot depends upon your chrono-age and your logbook hours if/when you sign on. I hope that you get an offer.
*Added*: I like your learning methods, very similar to mine. Annoying to some, but explaining the details to a novice is a GREAT way to double-check your own understanding; said novice will have questions and had better be able to answer them!! It is an excellent method - for some. Yes, it worked well for me. I hope that you get the offer and yes, I would ride on your your airplane. -C.