LS-4a

noel.wade wrote:
I flew years with 3 pounds of lead shot secured in a bag at the top of
the vertical fin above the battery cover (removed the black foam to
make more space). My local authority was ok with that and I never had
a problem, but also never ground looped.

Ramy

The bottom line is that cantilevering that kind of weight on the top
of the tail is just not something that the aircraft designers and
engineers anticipated. The structure wasn't designed for it - so just
because it has worked doesn't mean that it won't fail in the future,
or that it works on all gliders.

Disregarding structure, there are performance reasons to keep the mass
concentrated down in the fuselage. The closer to the center of
rotation that you place some mass, the less force it takes to put that
mass into motion.

Here's a thought-experiment: Imagine rolling the aircraft. Imagine
looking at the airplane from behind as it executes a perfect aileron
roll. If you put the weight down low in the tail-boom, the rest of
the tail rotates *around* that mass and it doesn't have to travel very
far or move very fast. If it was way out at the tip of the tail, it
would move through a much bigger circle over the same time period.
That means it travels farther and has to move faster. It takes energy
to start and stop the movement of that mass.

In short: Handling is going to be less crisp and it will be harder to
make subtle attitude corrections with a bunch of mass out at the tip
of the tail (or the tip of a wing, or any extreme end of the glider).

Take care,

--Noel


But glider designers DO put the substantial mass of a battery at the tip
of the tail.

On May 6, 3:27 pm, Greg Arnold wrote:

But glider designers DO put the substantial mass of a battery at the tip
of the tail.

Only on a couple of glider models, and you should always check to
ensure that it was part of the original design.

It is likely that specific battery sizes and weights were assumed.
Simply adding lead or other weight (beyond the battery) is NOT what
the glider-designers had in mind!

The bottom line is that adding weight at the top of the vertical fin
has no "up-side" versus installing the weight at the aft end of the
tail-boom near the tailwheel/skid. But it has a LOT of potential down-
sides, when its stuck way up on the top of the fin!

So why? Just because its convenient? The time it takes to get the
rudder off of most gliders (to install the weight properly) is
negligible.

--Noel

On May 6, 7:54*pm, "noel.wade" wrote:
On May 6, 3:27 pm, Greg Arnold wrote:



But glider designers DO put the substantial mass of a battery at the tip
of the tail.

Only on a couple of glider models, and you should always check to
ensure that it was part of the original design.

It is likely that specific battery sizes and weights were assumed.
Simply adding lead or other weight (beyond the battery) is NOT what
the glider-designers had in mind!

The bottom line is that adding weight at the top of the vertical fin
has no "up-side" versus installing the weight at the aft end of the
tail-boom near the tailwheel/skid. *But it has a LOT of potential down-
sides, when its stuck way up on the top of the fin!

So why? *Just because its convenient? *The time it takes to get the
rudder off of most gliders (to install the weight properly) is
negligible.

--Noel

Check the flight manual for your particular glider.
My ASW 24 is designed to accept up to 13.24 pounds of ballast in the
battery / trim box at the top of the fin.

OK, story time...........shortly after I gently touched down on the
edge of a barley field, I watched a Discus land a bit deeper in the
barley. He caught a wing tip and spun around 90 degrees. The left wing
was down but the fin and stab laid over (right) a good 30 degrees.
Then it just sat there and shook for several seconds. I believe he
came within a nats-hair of breaking the boom. Now lets add several
pounds of lead to the top of the fin and repeat this little
experiment.......................
JJ

wrote:
On May 6, 7:54�pm, "noel.wade" wrote:
On May 6, 3:27 pm, Greg Arnold wrote:



But glider designers DO put the substantial mass of a battery at the tip
of the tail.

Only on a couple of glider models, and you should always check to
ensure that it was part of the original design.

It is likely that specific battery sizes and weights were assumed.
Simply adding lead or other weight (beyond the battery) is NOT what
the glider-designers had in mind!

The bottom line is that adding weight at the top of the vertical fin
has no "up-side" versus installing the weight at the aft end of the
tail-boom near the tailwheel/skid. �But it has a LOT of potential down-
sides, when its stuck way up on the top of the fin!

So why? �Just because its convenient? �The time it takes to get the
rudder off of most gliders (to install the weight properly) is
negligible.

--Noel

Check the flight manual for your particular glider.
My ASW 24 is designed to accept up to 13.24 pounds of ballast in the
battery / trim box at the top of the fin.

On May 7, 6:36*am, JJ Sinclair wrote:
Then it just sat there and shook for several seconds. I believe he
came within a nats-hair of breaking the boom. Now lets add several
pounds of lead to the top of the fin and repeat this little
experiment.......................
JJ


I know of a Std Jantar that was found to have a floppy empenage
(reduced torsional stiffness in the boom just forward of the fin).
Turned out there was internal damage at the base of the fin even
though there was no external skin cracking. The glider had been
involved in a ground loop but had flown many hours afterwards with no
suspicion that it was unsafe.

So if you ground loop, with or without fin ballast, don't assume
nothing was damaged just because the tail didn't separate.

Andy