On Apr 18, 10:34*am, Andy wrote:
On Apr 17, 11:26*am, "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.

Since my fully ballasted CG is at the aft limit of the envelope I know
for sure that the addition of the tail dolly will put it well aft of
the aft limit. *However the ASW-28 aft limit is variable with flight
mass, probably to protect from the tail tank failing to dump, *so that
says nothing about whether it would be controllable.

So the next theoretical question would be - if you know you were daft
enough to takeoff with the tail dolly on, does dumping ballast make it
worse or better? Does your CG move forward or aft if you dump ballast?
Should you dump just long enough to clear the tail tank but not the
wing tanks?

Easier to take it off before flying, and that's one thing anyone
hooking up a glider should check for.

Andy

My CG doesn't move more than 1-3% with water because I have a tail
tank. But the increased mass of the glider when wet means that the
dolly will have less of an effect on the CG. When wet, the dolly
moves the CG back to 81%. When dry, the CG moves back to 88%.

Matt