Up here in the midwest, it looks like spring may be here.
With the return of warm weather, many pilots will be thinking of getting their airplanes out of the hangar and going for a $100 hamburger or to their first fly-in of the season. This brings up the question: What should a pilot do before flying an aircraft that has been sitting for a while?
Looking at it from a fuels and lubricants angle, the most important item is the crankcase oil. Crankcase oil should be changed before you put the plane away for the winter.
And while crankcase oil does not wear out, it becomes contaminated with very small particles of dirt and metal, as well as with unburned fuel and the acid that can form while the plane is sitting.
Whenever an engine is started, raw fuel is pumped into the inlet of the engine in order to have a rich enough mixture to start. Some of this raw fuel gets into the cylinders and, on start up, is not completely burned. This is usually on the cylinder walls and it subsequently ends up in the crankcase, where the sulphur in the fuel combines with the moisture from condensate to form acid.
Over time, this acid will attack the cam and lifters and other wear surfaces to form rust. This rust on startup will act as a rubbing compound to start wear on critical surfaces.
That’s why changing the oil before winter storage is critical. Coating all of the engine parts with fresh clean oil is the most important maintenance item before you put your plane away for the winter.
So if you changed the oil before putting your plane in storage, it should be good to go — maybe.
During those months in storage, your engine draws in warm moist air. Then at night, it will cool down and moisture will drop out. This means there will be moisture in the oil when you start it in the spring.
When you start flying your aircraft again in the spring, your engine oil temperature needs to be in the 180°F range to ensure that you boil off the water in the oil during flight. As oil passes through an engine, it will normally pick up 50°F at the warmest spots. You need to take steps to ensure your oil temperaturs hits the 180° mark during cruise conditions.
An exception to these suggestions is if you filled your crankcase with a preservative oil before storage for the winter. Preservative oil is based on straight mineral oil, so I would recommend changing to an ashless dispersant or AD oil for your more active flying periods.
What about the fuel system?
There is not too much that needs to be done to the fuel system prior to the start of your spring flying.
If your aircraft was stored in a hangar, there may be a small amount of condensate in the tanks. If your aircraft was tied down out in the elements, there is a greater chance of water in the fuel tanks.
If you sump your tanks a few times and rock the plane in between, you should get most of the water out.
An exception here is if you have a bladder tank in which the bottom has rippled. Then you may need to take some extra measures to ensure that all of the water is removed.
In some tests conducted years ago, they found more than a quart of water could be trapped in those ripples that would not drain out with normal sumping.
The 100LL in your tank should still be good and on spec after the winter. It will usually store for over a year without forming gum. If you are using mogas, it should be good for at least six months. But if you have fuel containing ethanol in your plane, you are on your own.
Grease is the word
The other thing to check is grease.
Everything should be fine here, especially if your aircraft was stored inside.
If your aircraft is tied down out in the elements, you need to carefully check all control surfaces and their movement points. Rain and snow can get into them and freeze. This could cause binding or improper drag, so check and lubricate as necessary.
If your plane is in the elements, water also can enter the wheel bearings and lead to problems. Carefully inspect and re-pack the wheel bearings if needed.
There are a lot of other things on the airframe that need to be checked, like baffles and seals. So, take your time and do a complete inspection before heading out.