A groundloop occurs, when, for various reasons, the
front end of your aircraft decides to switch places with the
back end. We won't go into just why that happens here, you can
discuss that around the campfire. But, once the plane reaches
that point of no return there's no stopping it, you're basically
going along for the ride. If the landing gear attach bolt fails the damage that occurs is very predictable and consistent. Depending on runway conditions and aircraft speed, a typical groundloop at 40 mph on a gravel / dirt runway takes less than 10 seconds and may go something like this: When the pilot loses directional
control the aircraft turns sideways. At that point the forces
acting on the landing gear attach bolt change from a shear load,
to a tension load. The gear box was not designed for this type
of loading thus the main landing gear attach bolt fails. At this
point the gear leg is no longer attached to the aircraft. Not
a good situation! As the wheel end of the gear leg folds under the fuselage, the inboard end of the gear leg tears up through the floorboard and continues out through the side of the fuselage. This severely alters the forward door post as it happens. Serious personal injury can result here because the gear leg comes up through the floor right where people in the front seats could have their feet resting. The bottom and side of the fuselage wrinkle as the fuselage tries to embed the wheel and gear leg to the ground. The lower cowl is crumpled as the prop blades chew their way down the runway. Each blade strike takes out a shovel sized divot until the engine comes to an abrupt stop. This has been known to cause very undesireable and expensive internal stess on the engine, let alone your brain. When the wingtip hits the ground, the wing bends up just outboard of the strut attach point. The horizontal stabilizer and elevator hit the ground and are bent up. With enough momentum the entire fuselage can buckle and twist. It's over now and if you're fortunate enough to have had the gear leg miss your feet, you may be able to climb out under your own power and begin assessing the $25,000 to $30,000 in damage that just occurred to your once perfect Skywagon (1998 prices). Figuring 10 seconds, that works out to about $3,000.00 per second which is undoubtly some of the most expensive flying you'll ever do. Note: The bolts shown in the above illustration were removed (they actually removed themselves) from two separate aircraft involved in groundloops. One was completely sheared in half, the other bent as the nut was stripped off under the tension load. |
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