Wing Ballast Distribution

Also helps stabilize the glider in a spin.

Could you explain this statement for us newbies... this is opposite of
what I would have expected so I would like to understand why it is so.

Thanks!
-tom

tstock wrote:
Also helps stabilize the glider in a spin.

Could you explain this statement for us newbies...

Just don't worry. All moderately current regulations ask that a glider
is recoverable from a fully developed spin with any possible ballast
distribution.

On Dec 10, 4:37*pm, tstock wrote:
Also helps stabilize the glider in a spin.

Could you explain this statement for us newbies... this is opposite of
what I would have expected so I would like to understand why it is so.

Thanks!
-tom

Dave's right, but I think he was just poking fun. The higher
rotational inertia tends to flatten the spin and make it harder to
recover from. Most of the long wing ships aren't certified for
spinning even without ballast.

Craig

Craig wrote:
On Dec 10, 4:37 pm, tstock wrote:
Also helps stabilize the glider in a spin.
Could you explain this statement for us newbies... this is opposite of
what I would have expected so I would like to understand why it is so.

Thanks!
-tom

Dave's right, but I think he was just poking fun. The higher
rotational inertia tends to flatten the spin and make it harder to
recover from. Most of the long wing ships aren't certified for
spinning even without ballast.

Craig


Presumably, the higher rotational inertia also makes it harder to get
into a spin.

jcarlyle wrote:

Why would aircraft designers want to keep weight towards the wing
tips? Does it have something to do with going from a 15m to an 18m
span? Wouldn’t the increased moment of inertia and wing spar bending
negatively affect performance?

-John

Loading the wings mitigates wing bending. Wings want to fold up from
fuselage loads, so spreading a wing loading can reduce stress at the
wing/fuselage junction.

Brian W

Andy wrote:

Ballast towards the wings tips increases the g-limit at any given
weight versus ballast towards the wing root. It may or may not affect
the flutter limits - but my initial hypothesis would be that it
reduces the natural frequency of the wing in bending which would
probably help on flutter. /snip/
9B

For the usual wing that has some sweep back, wing bending provides
reduced AofA which is favorable: swept forward wings do the opposite,
unless they are very stiff. Lateral weight distribution plays into this
effect too.

Brian W

Dave Nadler wrote:
On Dec 10, 1:02 pm, SoaringXCellence wrote:
The weight toward the tips provides an interial resistance to roll.
That means the ride is a little smoother as the wing has greater
resistance to differential vertical gusting across the wingspan. It
is the same principle that tightrope walkers use by carrying a long
heavy pole.

Also helps stabilize the glider in a spin.

Hmmm... I don't think so. Twin jets are noted for more severe spin
characteristics.

Brian W

Spin loading and sharp edge gust loading are different wing cases.

Brian W

JJ Sinclair wrote:
I believe it was the Constellation that was bpopping rivets in
turbulence, the fix was 300# of lead in each wing tip.
JJ

Dave Nadler wrote:
On Dec 10, 1:02 pm, SoaringXCellence wrote:
The weight toward the tips provides an interial resistance to roll.
That means the ride is a little smoother as the wing has greater
resistance to differential vertical gusting across the wingspan. It
is the same principle that tightrope walkers use by carrying a long
heavy pole.
Also helps stabilize the glider in a spin.

Frank Whiteley wrote:
On Dec 10, 3:25 pm, JJ Sinclair wrote:
I believe it was the Constellation that was bpopping rivets in
turbulence, the fix was 300# of lead in each wing tip.
JJ

LAK-12 has 20lbs in the leading edge of each tip.

Frank Whiteley

Front loading of aeroelastic surfaces has a comparable effect to forward
(dynamic) balancing of control surfaces like flaps, elevator, ailerons:

It pushes away the flutter envelope.

Brian W

On Thu, 10 Dec 2009 10:02:55 -0800 (PST), SoaringXCellence
wrote:


The weight toward the tips provides an interial resistance to roll.
That means the ride is a little smoother as the wing has greater
resistance to differential vertical gusting across the wingspan. It
is the same principle that tightrope walkers use by carrying a long
heavy pole.

I beg to differ - at least for certain gliders it's vice-versa.

In the AS 22-2 (the mother of all ASH-25s) it is strictly required to
fill the outer wing tanks first (and empty them last) - the limiting
factor is the bending momentum of the wing of course.

The interesting part:
Even with completely filled outer wing bags (about 120 lbs per wing)
the roll rate doesn't suffer at all.
But filling the inner wing tanks (about 100 lbs per wing) instead of
having a co-pilot on board reduces the roll rate significantly.

Don't ask me why.