Aerodynamics of carrying water

Y'all,
Been many years on rec.aviation.student but even more years since
gliding. Unable to explain the 'why' of water ballast to increase
performance in gliders to argumentative airplane student.

I need a simple explanation in 25 words or less.

Gene Whitt

Gene Whitt wrote:
Y'all,
Been many years on rec.aviation.student but even more years since
gliding. Unable to explain the 'why' of water ballast to increase
performance in gliders to argumentative airplane student.

I need a simple explanation in 25 words or less.

Gene Whitt

For the long answer, see
http://home.comcast.net/%7Everhulst/...t/ballast.html

The real short answer is - see the polar at the end of the above
article. One curve is with ballast, the other without.

The slightly longer answer is that a glider's best glide, for instance,
occurs at one speed. Increase the weight and that same best glide (more
or less) now occurs at a higher speed. You can go faster and maintain a
better L/D than you would without ballast.

Tony V.

Gene:

1: A glider's best glide ratio is unaffected by its weight.
2: However, a heavier glider flies and sinks faster at
the same glide angle than a lighter one.
3: When lift conditions are strong, the pilot accepts the
higher sink rates to achieve higher speeds over the ground.



Pete

Gene Whitt wrote:
Y'all,
Been many years on rec.aviation.student but even more years since
gliding. Unable to explain the 'why' of water ballast to increase
performance in gliders to argumentative airplane student.

I need a simple explanation in 25 words or less.

Gene Whitt



--

Peter D. Brown
http://home.gci.net/~pdb/
http://groups.yahoo.com/group/akmtnsoaring/

The best illustration used to be: Remember when you
rode your coaster wagon downhill alone and also with
a buddy in it? It always went faster with two people.

Who knows anything about coaster wagons anymore?

At 03:30 11 October 2005, Pete Brown wrote:
Gene:

1: A glider's best glide ratio is unaffected by its
weight.
2: However, a heavier glider flies and sinks faster
at
the same glide angle than a lighter one.
3: When lift conditions are strong, the pilot accepts
the
higher sink rates to achieve higher speeds over the
ground.



Pete

Gene Whitt wrote:
Y'all,
Been many years on rec.aviation.student but even more
years since
gliding. Unable to explain the 'why' of water ballast
to increase
performance in gliders to argumentative airplane student.

I need a simple explanation in 25 words or less.

Gene Whitt



--

Peter D. Brown
http://home.gci.net/~pdb/
http://groups.yahoo.com/group/akmtnsoaring/

On 11 Oct 2005 06:01:11 GMT, Nyal Williams
wrote:

The best illustration used to be: Remember when you
rode your coaster wagon downhill alone and also with
a buddy in it? It always went faster with two people.

Who knows anything about coaster wagons anymore?

Think of a 400-pound skier.

rj

Nyal Williams wrote:

The best illustration used to be: Remember when you
rode your coaster wagon downhill alone and also with
a buddy in it? It always went faster with two people.

And I suppose it would go faster uphill, with two people pulling it
back: not a very good analogy, I think, since the heavy glider will
climb more slowly. "Going faster" isn't the issue, but instead, why
heavy is better than light. After all, both the heavy and the light
glider can fly the same speeds right up to Vne. It's because the heavy
glider can cruise faster for any given L/D, and (in strong conditions)
loses relatively little in the climb.

The aerodynamic reason it can cruise faster at any given L/D is that the
angle of attack determines the L/D, and the heavy glider needs extra
airspeed to generate the extra lift for that weight.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

The beauty of the soapbox derby example--like Nigel's--is that it points out
that the glide slope is the same. With the added weight you have the same
glide slope but a higher speed.
The other way to make the soapbox derby car go faster was to reduce drag....
"Eric Greenwell" wrote in message
...
Nyal Williams wrote:

The best illustration used to be: Remember when you
rode your coaster wagon downhill alone and also with
a buddy in it? It always went faster with two people.

And I suppose it would go faster uphill, with two people pulling it back:
not a very good analogy, I think, since the heavy glider will climb more
slowly. "Going faster" isn't the issue, but instead, why heavy is better
than light. After all, both the heavy and the light glider can fly the
same speeds right up to Vne. It's because the heavy glider can cruise
faster for any given L/D, and (in strong conditions) loses relatively
little in the climb.

The aerodynamic reason it can cruise faster at any given L/D is that the
angle of attack determines the L/D, and the heavy glider needs extra
airspeed to generate the extra lift for that weight.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Gene Whitt wrote:
Y'all,
Been many years on rec.aviation.student but even more years since
gliding. Unable to explain the 'why' of water ballast to increase
performance in gliders to argumentative airplane student.

I need a simple explanation in 25 words or less.

Gene Whitt

A ballasted sailplane has more energy at a given altitude and airspeed
than an unballasted sailplane. (potential + kinetic). At cruise
speeds the energy is dissipated predominantly to overcome parasite drag
which is independent of weight. Start with more energy, expend the
same to overcome drag, so give up less altitude. Edit to 25 words.

Andy

On 11 Oct 2005 03:52:06 -0700, "Andy" wrote:


Edit to 25 words.

"A glider is a gravity-powered machine. The heavier it is, the more
power it has."

16 words, beat that!

-Pat

But I need the same amount of power to go the same speed don't I? Why
does more power reduce my sink rate?

I think you'll need more than 16 words.


Andy