How much water for a 1000K attempt?

Andy Blackburn wrote:
At 18:48 02 August 2005, Eric Greenwell wrote:

Tactically, one should take off with full ballast early
enough to have a
chance of completing the flight, and drop whatever
it takes to stay up.


That's one approach - but keep in mind that the difference
in climb rate between full and empty (in a 45-degree
bank) is less than 50 fpm.

The _sink rate_ in calm air might differ only that much, but I've seen
much bigger differences in climb rate in contests, due to the width of
the thermal and the ability to maneuver. In addition, the glider with
the lighter wing loading can often continue up another 400-500' in good
lift, while the heavier can't. And this is with climb rates in the 2-4
knot range, not just really weak conditions.

I've experienced these differences in gliders only 1 pound/sq ft apart
in wing loading. It's not necessary to be empty to have a worthwhile
climb advantage in modest conditions.


Furthermore, the McCready-derived XC speed differential
for full versus empty water is 6-9 knots. The actual
difference with streeting, etc. may be greater. That
amounts to about an hour less time on course with water
versus without. To break even without ballast

I wasn't suggesting Tim fly without ballast, only that a partial load
might be a better choice if he could start 30-60 minutes earlier.

you'd
have to make about 80 miles before you could get started
on course with ballast.

If you flew 6 hours in good conditions, you'd have an extra 36-54 miles
over the empty glider. If it got started an hour earlier in the
conditions we often have, it could make that 50 miles pretty easily by
starting downwind.

I'm thinking this would only be true if the day developed
with either very weak (0.5-1.5 knots climb, dry) or
very narrow thermals for a very long time (1-2 hours).
Under those conditions I don't think you're making
80 miles even if you have Helium in your wings.

I'd recommend taking tows until you can stay up with
full water.

I think it depends very much on your weather and your glider. I'm sure
that's good advice for Tonopah and other strong areas, but I don't think
it will work here in the Pacific NW. Tim will need to experiment some,
and, I hope, report back to us in a year.

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

Eric Greenwell
Washington State
USA

As I read this, I think about how that one hour of
less
flying means different things. Less exhaustion, for
one.

The most impressive thing to me about the 1-26 diamond
guys isn't the flight itself, but the amount of time
spent doing it. The super-long wave flights (Kestrel?)
were similarly impressive just from the endurance perspective
alone.

I personally have seen forecast conditions and experienced
times when a 300km flight looked possible, but the
gliders I had available had low enough performance
that I personally didn't have the recent experience
with endurance flights to make the 300km with what
I considered an adequate margin of safety.
For me, the difference between a 3 hour and a 6 hour
flight is
still quite significant. A flight of over 10 hours
(which one might need for a 1000km) looks quite daunting
to me. IIRC some of the Kestrel wave flights exceeded
this.

For the guys who are recommending max wing loading,
how much of this is because you want to make the flight
as
short as possible for endurance reasons?

In a similar vein, a 500km downwind seems a lot different

(in endurance terms) than a triangle or O&R.

At 02:36 03 August 2005, Andy Blackburn wrote:
At 18:48 02 August 2005, Eric Greenwell wrote:
Tactically, one should take off with full ballast early
enough to have a
chance of completing the flight, and drop whatever
it takes to stay up.

That's one approach - but keep in mind that the difference
in climb rate between full and empty (in a 45-degree
bank) is less than 50 fpm.

Furthermore, the McCready-derived XC speed differential
for full versus empty water is 6-9 knots. The actual
difference with streeting, etc. may be greater. That
amounts to about an hour less time on course with water
versus without. To break even without ballast you'd
have to make about 80 miles before you could get started
on course with ballast.

I'm thinking this would only be true if the day developed
with either very weak (0.5-1.5 knots climb, dry) or
very narrow thermals for a very long time (1-2 hours).
Under those conditions I don't think you're making
80 miles even if you have Helium in your wings.

I'd recommend taking tows until you can stay up with
full water.

9B




Mark J. Boyd

In a comfortable glider (both physically and mentally comfortable),
there really isn't much difference between 3 and 6 hours. In fact,
after an undercalled task, landing after only 3 hours sometimes seems
like a relight! Compared to long flights in power planes (boooring,
unless at 500 ft and 500 knots, or 100 ft and 100 knots), it always
amazes me how fast 6 hours can go by on a really fun (fast, high, low
stress) soaring flight.

On the other hand, anything over an hour in an uncomfortable
(physically) glider is torture. I really enjoy flying 1-26s, but
almost all the ones I've flown have been rentals and none have fit very
well - so there was never any problem in deciding to land after an hour
or two.

Water? Because it feels so goood! Like a big heavy Cadillac, cruising
along nice and fast...and faster means you can cover more ground and
see more scenery before you land, not to land earlier.

Finally, a 500 k downwind is a lot more of an endurance test than a 500
k O&R - that 500 k drive back is really tiring!

Kirk

On Sun, 31 Jul 2005 21:31:36 -0700, ttaylor at cc.usu.edu wrote:

I am working on the planning for a 1000K attempt. One question I have
is how much water should I launch with in my Ventus B? I can carry up
to 40 gallons (150 liters), but for a 1000K flight I will need to launch
in early weak conditions, followed by strong conditions latter in the
day.

Plan your flight in advance. Start with the number of flying hours
available in the day, select your take off and landing times, average
speed on each leg and ETA for each turn point. Then based on the required
average speeds, you can estimate what thermal strengths you will need and
the optimal wing loading. Obviously you have to carry the water ballast
from launch.

The details will depend on your location, aircraft, personal skills etc.
Certainly they will look different in Norway to South Africa. For a 1000km
task in a 15m glider, you will need to plan for strong lift, or a long
day, or both. You will probably need to fly close to max AUW.

Write down the flight plan and carry it in the cockpit so you have a
target to measure your progress against during the flight. You will
discover that you have very little margin for loosing time. Most important
is a cut off time for your last turnpoint. If you fall behind schedule and
can't make the turnpoint by that time, then turn short, go home and try
again the next day. If you push on and land out, you will probably not get
home in time to attempt another big flight the following day.

(Motor glider pilots have an advantage, they can push on to the point
where they have just enough daylight to motor home before sunset.)

One tricky decision that you are almost certainly going to face, is what
to do if you have taken a launch with a heavy water load, and you find you
can't stay up. Do you dump some water, stay airborne and jeopardise the
rest of your task or risk a landing with full ballast in the hope of
getting airborne again while there are still enough hours in the day to
complete the task. If you dump all the water and land, by the time you
have filled it again you will have lost too much time.

Motor gliders have another tactical advantage over pure sailplanes in this
aspect, they can launch early and use their motors until conditions are
good enough to stay up, then start their task.

One last comment, if the day is good for 750km but not 1000km, you will
probably achieve a better distance if you declare and plan for 750 than if
you go for the 1000. But on the other hand if you don't go for the big
one, you will never get it!

Have fun!

Ian

At 04:24 03 August 2005, Eric Greenwell wrote:
I'm sure
that's good advice for Tonopah and other strong areas,
but I don't think
it will work here in the Pacific NW. Tim will need
to experiment some,
and, I hope, report back to us in a year.

Always good to know how conditions develop at your
intended site. There are 'speed sites' where the length
of the day is the limiting factor rather than the strength
of the day. At these sites loading up will help you
get home before sunset.

Apparently there are sites in the northern latitudes
where the conditions develop slowly (e.g. narrow, 1-2
knot thermals for several hours before noon), then
get strong later. In these cases it may be optimal
to go with little or no ballast. I've never seen a
day like this, but maybe that's because I fly further
south where the days 'pop' to a significant portion
of full strength when you reach trigger temperature.
Also, in places like the Great Basin, you'll often
find the high ground working (full strength) an hour
or more before the valleys get cooking, so a well-placed
tow release can help a lot.

9B

Try taking off with full water and dumping early only if absolutely
necessary to sustain.

Dino



taylor at cc.usu.edu" wrote in message
oups.com...
I am working on the planning for a 1000K attempt. One question I have
is how much water should I launch with in my Ventus B? I can carry up
to 40 gallons (150 liters), but for a 1000K flight I will need to
launch in early weak conditions, followed by strong conditions latter
in the day.

Options would be to launch with 20 to 40 gallons. Twenty to thirty
would probably give a good balance for early climb and later running.

Any suggestions for an optimum balance?

Thanks,

Tim