Ownership: Show a little strut love

The air/oil struts used on many GA airplanes use a combination of oil—typically hydraulic fluid—and a gas—usually nitrogen—to absorb the forces of takeoff and landing and to ease ground handling. The small amount of fluid is kept under pressure by the gas, all of which is trapped in the strut cylinder. An O-ring keeps the air and oil in while allowing the strut to slide up and down on the gear leg at a controlled rate. Lose the air or oil, and the strut collapses. You can bet it will happen at the most inconvenient time—on a weekend at a remote airport.

Proper maintenance is the key to reducing ramp surprises.

Struts are required to be inspected during the annual inspection, but many mechanics don’t do much more than that. You can help during each preflight by wiping the shiny gear leg with a cloth dampened with hydraulic fluid. Doing so will allow you to notice any dirt that might indicate an O-ring has dried out, an early warning of a future fluid leak.

The pilot’s operating handbook will usually indicate the amount of gear leg that should be showing. In my Beechcraft Bonanza A36, for example, it’s about three inches for the main gear and about four to five inches on the nose gear. Or, as the Bonanza experts like to say, three to four fingers on the mains and five on the nose. You can test the effectiveness of your nose strut by pulling down on the propeller hub. If you even come close to completely collapsing the strut, it’s in need of service.

Woodie Diamond, secretary of the Northeast Bonanza Group, noticed mine were a little soft at a recent fly-in. He encouraged me to contact Howard Aircraft at nearby Eastern West Virginia/Shepherd Field Airport in Martinsburg, West Virginia. There, Howard Aircraft owner Andre Frye uses an innovative system from Bogart Aviation to quickly and easily replenish struts.

A few days later I was in Martinsburg with Diamond and Frye crawling around under the Bonanza. They quickly hooked up a hose from the Bogart system to the nose gear and used the nitrogen in the strut and the weight of the airplane to force the old fluid out. The more typical strut maintenance process requires the airplane to be put on jacks and the gear to be partially retracted. From that position, the mechanic must then manually exercise the strut to force out the fluid—a time-consuming and difficult process. The Bogart system allows the servicing to occur on the ramp and without jacks. Frye estimates the Bogart system cuts the labor time in half.

With the strut cleared, Diamond pumped a couple of ounces of new fluid back into the strut and cleared it again, a means of purging the innards. He then pumped in a few more ounces of new fluid that also contained an O-ring preservative. The preservative, which costs an extra $5 per strut, keeps the O-rings healthy and flexible. Next, nitrogen is pumped in to inflate the strut to the proper height. The nose gear took maybe 15 minutes to complete. Then it was off to do the mains, each of which took another 15 minutes or so.

In just over an hour from start to finish, the logbook entry was done and I tested the nose strut by putting my foot on the nose tire and pulling down on the propeller hub. The nose bobbed down a little but stopped with a couple of inches of strut still showing.

Diamond says properly serviced struts allow the airplane to lift off and touch down with more “authority.” Although it’s hard to describe, he’s right. Even taxiing out at Martinsburg, I noticed the airplane felt more solid and less springy. On takeoff, the transition from runway to flight felt more precise. On landing, the gear seemed to grab the runway and allow the airplane to settle with less weaving and bobbing than before.

Frye charges $125 for the service, plus the premium for the preservative, if desired. As a longtime owner, I learned a lot that morning and now have more respect for the struts, still hard at work 45 years after the airplane left the factory.

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