Ballast dump time Discus

Ballast dump times are usually nothing but a reasonable guess so I
decided to measure them. Put a Discus CS wing on the standards
(horizontal) and filled her up. Times are for one wing thus double the
volume for real life and with vent holes as in flight.

20L: 73 seconds
40L: 105 seconds
60L: 150 seconds

That'll be 4.4, 8.8 and 13.2 gallons

Measuring the tail tank showed a strange result; dumping 2L took about
80/90 seconds but dumping 4L took over 10 minutes with only
significant dumping when the scotch from the "4L" and "3L" marks were
removed. With the scotch on the vent holes there was barely any
dumping though the upper two vent holes were definitely open. A club
member suggested that the water was polluted a bit and that using
fresh drinking water should solve this. I decided however that I won't
use tail ballast. But then that's easy to say if you're only 60 kg's I
guess ;-)

Hope this'll be usefull for some people.

J. Nieuwenhuize.

"J. Nieuwenhuize" wrote in message
oups.com...
Ballast dump times are usually nothing but a reasonable guess so I
decided to measure them. Put a Discus CS wing on the standards
(horizontal) and filled her up. Times are for one wing thus double the
volume for real life and with vent holes as in flight.

20L: 73 seconds
40L: 105 seconds
60L: 150 seconds

That'll be 4.4, 8.8 and 13.2 gallons

Measuring the tail tank showed a strange result; dumping 2L took about
80/90 seconds but dumping 4L took over 10 minutes with only
significant dumping when the scotch from the "4L" and "3L" marks were
removed. With the scotch on the vent holes there was barely any
dumping though the upper two vent holes were definitely open. A club
member suggested that the water was polluted a bit and that using
fresh drinking water should solve this. I decided however that I won't
use tail ballast. But then that's easy to say if you're only 60 kg's I
guess ;-)

Hope this'll be usefull for some people.

J. Nieuwenhuize.


I gather you dumped the water on the ground during this test.

The pressure on the dump valves in flight varies with speed of the glider.

View this video the water from the high pressure of the under wing works
back up into the low pressure
http://video.google.com/videoplay?do...22228558&hl=en

At high speed we have started dumping at 50 km out and still had water
coming out after landing.

www.mals.net

On Apr 16, 8:20 pm, "Mal" wrote:
I gather you dumped the water on the ground during this test.

The pressure on the dump valves in flight varies with speed of the glider.

I agree with Mal. On ground dump times may be interesting but they may
not be representative of in flight dump times. The only way to know
dump time at thermalling speed, as for a low save, is to measure it in
that condition. Similarly the only way to know dump time on a fast
final glide is to measure it in that condition.

I created a dump time graph for my 19b and taped it in the cockpit. I
ran a stop watch during a dump and could adjust the glide computer to
the new weight for a partial dump. I even considered building a
simple counter triggered by microswitches on the dump valves. Of
course I thought that function should be built into the glide
computer.

As I got older I found other things to worry about.

Andy

"Mal" wrote in message
...

"J. Nieuwenhuize" wrote in message
oups.com...
Ballast dump times are usually nothing but a reasonable guess so I
decided to measure them. Put a Discus CS wing on the standards
(horizontal) and filled her up. Times are for one wing thus double the
volume for real life and with vent holes as in flight.

20L: 73 seconds
40L: 105 seconds
60L: 150 seconds

That'll be 4.4, 8.8 and 13.2 gallons

Measuring the tail tank showed a strange result; dumping 2L took about
80/90 seconds but dumping 4L took over 10 minutes with only
significant dumping when the scotch from the "4L" and "3L" marks were
removed. With the scotch on the vent holes there was barely any
dumping though the upper two vent holes were definitely open. A club
member suggested that the water was polluted a bit and that using
fresh drinking water should solve this. I decided however that I won't
use tail ballast. But then that's easy to say if you're only 60 kg's I
guess ;-)

Hope this'll be usefull for some people.

J. Nieuwenhuize.


I gather you dumped the water on the ground during this test.

The pressure on the dump valves in flight varies with speed of the glider.

View this video the water from the high pressure of the under wing works
back up into the low pressure
http://video.google.com/videoplay?do...22228558&hl=en

At high speed we have started dumping at 50 km out and still had water
coming out after landing.

www.mals.net


Maybe someday I'll solve the mystery of how 2 liters of water gets into the
nose of my Nimbus 2C when dumping ballast. All possible tubes are plugged
and the under seat area and around the wheel box is always dry. The only
wet area is the foot wells.

Bill Daniels

Maybe someday I'll solve the mystery of how 2 liters of water gets into the
nose of my Nimbus 2C when dumping ballast. All possible tubes are plugged
and the under seat area and around the wheel box is always dry. The only
wet area is the foot wells.

Bill Daniels-


Bill-

Sounds like a pee tube problem. Try "Depends."

Mark

wrote in message
oups.com...
Maybe someday I'll solve the mystery of how 2 liters of water gets into
the
nose of my Nimbus 2C when dumping ballast. All possible tubes are
plugged
and the under seat area and around the wheel box is always dry. The only
wet area is the foot wells.

Bill Daniels-


Bill-

Sounds like a pee tube problem. Try "Depends."

Mark


A quite predictable response, Mark. My 'capacity' is quite a bit less than
2 liters.

No, it's really ballast water and despite 3 years of searching, I can't find
any route for it to get there. For a while I thought it might somehow be
sucked forward inside the rudder cable guide tubes but they were dry each
time I checked.. There are several unused static ports but the associated
tubes are plugged with golf tees. All other tubes go to instruments. The
only clue is that dumping at high airspeed makes the problem worse.

Bill Daniels

Hi Bill,
try a lipstick camera in the footwell.
It may take a few flights, progressively moving the camera "upstream" when the flow source is found.

Bagger

With the Jantar Std 3 that I used to fly, which had water dumps under the
wing, when dumping at high speed I used to get water trickling forward past
my elbows and find a small pool of water under the rudder pedals after the
flight. I never really managed to work out how it got into the fuselage
either.

"Bill Daniels" bildan@comcast-dot-net wrote in message
. ..


Maybe someday I'll solve the mystery of how 2 liters of water gets into
the nose of my Nimbus 2C when dumping ballast. All possible tubes are
plugged and the under seat area and around the wheel box is always dry.
The only wet area is the foot wells.

Bill Daniels