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Old July 22nd 03, 02:16 PM
journeyman
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On Mon, 21 Jul 2003 23:19:57 -0400, Mike wrote:
I've read the term ground loop in a lot of articles and accident reports but
what exactly is a ground loop?


As others have pointed out, it's when a plane on the ground
uncontrollably does a 180. It usually starts with a swerve, typically
due to a gust of wind.

In a taildragger, picture your favorite shopping cart pushed backward,
the center of gravity is behind the main wheels. If you draw a
diagram of the forces, you'll see that the momentum vector will tend
to cause the tail to tend to continue swinging out after a swerve.
After a certain point, the CG will be outside the wheel and there's
nothing you can do to stop it from continuing to swing around. This
tends to be hard on the landing gear and wingtips. You want to keep
the momentum vector between the wheels if you want to stay in control.

There's an old-timer/instructor at The Place I Used To Rent From (whom
I never had the chance to fly with, unfortunately) who intentionally
groundloops the tailwheel on a grass runway (easier on the landing gear)
and at slow speeds (less likely to tip over). Good training exercise
if you're with someone who knows what he's doing (Rev definitely knows
what he's doing).

In the Olden Days, when aircraft didn't have brakes and you just landed
in any convenient field, groundlooping was how they stopped. In an
emergency, it may be a better choice than hitting something hard and/or
expensive.

Ground maneuvering in a tricycle-gear airplane is more stable The
mains are behind the CG and inertia will tend to straighten it out.
As mentioned, it is still possible to ground loop a nosedragger. One
of the easiest ways is to touch down nosewheel first on landing.


Morris