On Sun, 17 Apr 2011 11:26:44 -0700, Matt Herron Jr. wrote:

I recently used SeeG to find out what would happen to my CG if I took
off with the tail dolly still attached, and I thought I would share my
results.

I fly a Ventus C, and I wanted to know if I would still be within normal
operating limits and would have enough elevator authority to keep from
ballooning/stalling on take-off (or possibly on release from tow). The
tail dolly weighs about 9.5 lbs according to the bathroom scale, and my
tape measure showed the moment arm from the leading edge to the
estimated center of mass of the installed dolly to be about 145 inches.

SeeG ( http://www.glideplan.com/ ) shows my normal, dry center of
gravity to be 57% aft. I duplicated my glider in the program, then
added a moment arm called Tail Dolly. I input 9.5 lbs for the mass and
145 inches for the arm and found that my CG shifted aft to 88% of
limits. This is a little over 30% change in CG position. OK in my
case, but it might be alarming for those that fly with the CG a little
farther aft. I ran the numbers with the airplane full of water and it
went from 58% aft to 81% aft, a little less of an impact as one might
expect from the overall increase in mass.

I would be curious to hear if others have done this and what the numbers
came out to.

Matt Jr.

Many years ago, my father was instructing at a beginners course for about
7 folks, running a midweek operation with the 'minimally' experienced
crew, a professional winch driver at the other end of the field and a
mornings worth of training for the course members on running a launch
point. Some way into the week, just after lunch, my dad was sat in the
back of a K7 with a student up front, the ground crew did the usual and a
launch was initiated, my dad felt something was wrong immediately, but
not wanting to worry the student just decided to fly this circuit
himself, he says the glider felt very 'light', and there was a trembling
that felt like mild turbulence coming through the elevator, he decided to
fly a very gently circuit and landed without issue...

Getting out of the glider he discovered a large tyre still sitting on the
horizontal stabiliser... he describes it as a truck tyre. ... nobody
dared to think about calculating where the C of G might have been., also
the circuit flys over the center of a busy local village, if the tyre had
'departed' there, things might have been bad on the ground.

Suffice to say the course got a very detailed run down of proper tie down
and launching procedures for the rest of the afternoon, and my dad got a
lesson in expecting the unexpected of the inexperienced.

Luck, and the forgiving nature of the venerable K-7 probably allows my
dad to tell a decent tale in the clubhouse in the evenings, it could have
been different.