The landing gear on our planes is really taken for granted — even though it’s often the only thing between you, your airplane, and the ground. Many planes have tubular or spring steel landing gear, but others have pressurized struts, and those struts can really cause you problems if you don’t maintain them within the required pressure ranges as called out by the manufacturer.
As an example, one of my friends helped his mechanic with his annual inspection. After checking the fluid level in his struts, he used a strut pump (a small pump that generates the high pressures needed to properly balance the strut) to pump up his strut. The manual for the airplane called for approximately 2 inches of extension on the strut, which my friend was able to reach quickly. Extension is defined as the amount of shiny chrome barrel left exposed.
… BUT HE DIDN’T STOP THERE. My friend was wondering what his plane would look like if he pumped the struts up even more, SO HE DID! Instead of stopping at 2 inches, he took the struts up another 4 inches, for a total of 6 inches of extension with the plane on the gear. The plane looked like a stork of sorts — it was sitting WAY HIGH in the air.
To my friend, THE PLANE LOOKED REALLY NEAT. For some reason, after the annual was finished, the mechanic didn’t question the strut extension, and my friend went for a ride. The first thing he noticed was that it was hard to get into the plane. The step was now four inches higher than it was, and he had a heck of a time getting into the plane. Still, he managed to figure out a way to climb in, and started up the engine.
Taxiing was easier, since he could see more from his new, higher perch. My friend taxied out to the active runway and took off, made a circuit, and then landed. On landing, the gear proved to be a bit balky — the gear legs, under higher pressure, accepted the plane’s landing with a jolt, instead of the gentle settling that had usually been the case in the past. After his little jaunt, the mechanic noticed what was going on, and insisted the struts be properly set.
WHAT WAS WRONG?
While nothing bad happened at the time, over charging a strut can cause problems. First off, a strut gets part of its structural strength from BOTH PIECES of the landing gear — both the chrome piston that extends, and the steel barrel that it slides within. These pieces work as a team to share the load. With the strut fully extended, the load is concentrated in a single, small spot. This can lead to stress fatigue and even failure if side loads are encountered that exceed the strength of the materials!
WORSE YET, without the cushion provided by the strut gas / oil balance, the landing gear attach points are more likely to be damaged on a hard landing. This damage can usually be seen in the bolts or even the fixtures that the landing gear are bolted into, which can only be described as prohibitively expensive to repair.
BOTTOM LINE: You need your gas charged struts to make a safe landing every time, so don’t mess with them. Follow the manufacturer’s instructions on how to charge them. Keep them clean and properly serviced. Finally, DON’T overcharge them … unless you want an opportunity for your mechanic to have to charge YOU to repair them!