Still, there's tremendous variety in the kind of underpinnings in the trainer fleet. Most low-wing airplanes have the main gear mounted to the wings themselves, an arrangement that often permits wider-stance gear; this can help make the airplane more stable during touchdown in crosswinds. Some low-wing airplanes, such as the Beech Skipper, Piper Tomahawk, and Grumman singles, have the main gear attached to the fuselage proper. This setup means that the wing-attachment structure can be simpler, with the gear loads going right into the fuselage with less of a bending action than is present with wing-mounted gear. High-wing Cessnas have the gear attached to the fuselage.
Cessna for many years used spring-steel, leaf-type main gear-essentially a solid metal leg attached to the airplane at one end and to the wheel at the other end. Durable and relatively inexpensive to produce, this gear was used on Cessna singles until the mid-1970s and is still used on utility models such as the 206.
Cessna eventually traded leaf springs for tubular main gear on most of its singles. The company said that the main advantage was that tubular gear rides better on choppy pavement and has less tendency to spring back, providing a bit of forgiveness for sloppy landing technique. Also, the tubular gear is somewhat gentler on tires: Leaf springs bow inward toward the airplane's centerline during flight, so the first point of contact on touchdown is on the outside edge of the tire. As the weight of the airplane transfers to the gear, the tires scrub sideways in response to the spreading of the gear. Tubular gear does this too, but to a lesser extent.
From the cockpit, you'll notice the tubular gear to be more forgiving of imprecise touchdowns and less likely to bounce you back into the sky. Also, the lower stance of the newer airplanes makes them slightly less sensitive to the effects of wind on the ground, but you should still know which way to position the ailerons and elevator for windy conditions.
Under the nose, Cessnas use what's known as an air/oil strut (often referred to as an oleo, which is just another name for oil). Imagine a tube within a tube. The larger, outer member is attached to the airplane and the smaller, inner member to the nosewheel. Inside the smaller diameter tube are air and oil-the spring and damping mediums respectively. (The air compresses under landing loads; the oil is displaced.) Most fixed-gear Pipers use the air/oil strut on all three wheels, as do the non-retractable Socatas.
Advantages of air/oil struts include a smooth ride and positive damping during touchdown. On the other hand, this type of strut is prone to seal failure, which allows the air to escape and the strut to go "flat." Never fly an airplane with a flat strut because there will be metal-to-metal contact during taxi and touchdown, which can lead to landing-gear and airframe damage. A flat strut means reduced propeller clearance, too.
Still another fixed-gear type uses rubber biscuits for a shock medium. Some Beech singles, Ercoupes, and the rare Mooney Master are among the airplanes that use individual rubber doughnuts to provide a cushion in the gear system. It's a simple and durable setup, but it can give a bouncy ride during taxi and prove challenging under some takeoff and landing conditions. Go out and watch a Mooney do its crow-hop just before the pilot rotates, and you'll get the idea.
While all of the systems have their differences, there are a few general guidelines to follow during preflight inspection to make sure everything is as it should be:
- Check for leaks. Look for red brake fluid along the belly and along the leg. Look for seeping strut fluid on the nosewheels and main gear of airplanes with air/oil struts. If there's a greasy mess all over the wheel or strut, it's likely a seal is going (or has already departed) and should be fixed immediately.
- Make sure the strut has the proper extension. This is but one way to tell if there's enough air in the strut. The pilot's operating handbook has the information.
- Make certain that the exposed shaft on the air/oil strut is clean. Conscientious owners wipe down these chromed struts with an oil-wetted rag after a flight to keep corrosion at bay and to keep debris from chewing up the seals.
- Inspect attachment points, looking for loose or missing rivets and hardware as well as wrinkles in the skin near the gear-attachment points. Ripples in the airplane's hide indicate a hard landing in the past and possible structural damage.
- Check the tires. Look for nicks, cuts, abrasions, and proper inflation. Also make sure any fairings or wheelpants are securely fastened.
While the gear systems might be quite different in configuration, they all must do the same thing-keep the airplane controllable during takeoff and landing and make it possible to get to and from your tiedown spot without attracting a crowd.
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