Water explanation, please.....

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mac
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Postby mac » Fri Jul 14, 2006 11:09 am

I have no direct experience in RL, but wouldn't be enough to put a safety valve along the hose?
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Freebird
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Postby Freebird » Mon Jul 24, 2006 9:37 pm

I worked for a while as a glider repairer & filling with a hosepipe has a risk of doing some serious structural damage which may not be visable externally, get enough pressure & you will unzip your wings :)

As far as C of G goes I'm not sure how it works with Condor but in real life you are looking to get the C of G somewhere near the aft limit which is dependant on cockpit load (pilot weight) & the amount of water in the wing tanks. I supose Condor should really only allow you to load the tank within the C of G limits although this doesn't appear to be the case. The fin tank is dumped along with the wing tanks & I remember Andy Davis coming to me for a split pin after his brand new Discus (the original Discus) became rather pitch sensitive during the approach. He found he had still water in the fin tank as the factory had omitted the pin & the dump valve became disconnected. I remember wondering at the time if a world class pilot found it a handfull what would have happened if it had been a 100hr pilot.

As for dumping in Condor on final glide theres no reason to get rid of it until you have crossed the line, you could even land with it although its easy just to pull the plug as you pull up. In RL its normal to start dumping a km or so away from the line as its not recomended to land with full tanks. Unless things have changed since I have been away from gliding.

JBL
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Postby JBL » Thu Oct 12, 2006 4:19 pm

How long does it take to empty ballats in condor on the nimbus 4?

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Fransois
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Postby Fransois » Thu Oct 12, 2006 4:45 pm

JBL wrote:How long does it take to empty ballats in condor on the nimbus 4?


I tried to count it the last flight i made and I have been counting 300 seconds.
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master
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Postby master » Sat Oct 14, 2006 10:46 am

1 liter per sec, i think in all planes
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Postby JJJ » Sat Oct 14, 2006 2:40 pm

asw22 is 2l/sec
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Freebird
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Postby Freebird » Tue May 08, 2007 12:45 pm

Open class dumps through 4 valves (certainly the ASW22 does & I think the Nimbus) & the rest have only 2 so it works out at about 1L per second with everything except open class where 2L per second drains.

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Postby Voets O » Fri Aug 31, 2007 11:25 am

simpel

Dani
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Postby Dani » Fri Feb 29, 2008 10:09 pm

I'm relativly new to Condor and gliding, but isn't water a problem in the tanks when you go above 4000, 5000 or even 10 000m high? Doesn't this water freeze, leading to structural damage? As you well know, water will extend by 1/10 of its volume when freezing.

As an airline pilot I know that temps are really low up there, around -25 at 5000 and -50°C at 10 000m.

How do you plan your high altitude trip?

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Postby sliderG102 » Sat Mar 01, 2008 1:32 am

when i just want to fly high altitude i dont take any water with me^^
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nimbusgb
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Postby nimbusgb » Mon Mar 03, 2008 10:05 am

Dani wrote:I'm relativly new to Condor and gliding, but isn't water a problem in the tanks when you go above 4000, 5000 or even 10 000m high? Doesn't this water freeze, leading to structural damage? As you well know, water will extend by 1/10 of its volume when freezing.

As an airline pilot I know that temps are really low up there, around -25 at 5000 and -50°C at 10 000m.

How do you plan your high altitude trip?

Thanks
Dani


Yes it is a problem. However high altitude flying and water carrying for cross country speed generally are different 'missions' so generally water wouldn't be carried when wave flying ( and most flight manuals will specifically prohibit it ). Some guys who are pushing the envelope a bit will fly using antifreeze and an OAT sensor ( Not sure of the effect of ethelyne glycol on composite tanks/wing structure ) . At 30k plus you run into the IAS/TAS problem so going faster is not an option because you get into Va and Vne trouble.

The IAS/TAS groundspeed advantage at altitude makes up for the lack of carrying water, so high speed and high altitude tasks are still possible!

At 30k plus and minus 20 degrees C In jeans and T shirt I can attest to the fact that is seriously cold up there. Video camera shut down at 25k. Orange juice froze etc :)
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agreschk
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Postby agreschk » Thu Jun 12, 2008 5:16 pm

Usually i fill up the tanks when going cross country. But i never been very fast.

Lately i tried only half full tanks in Ventus on a free flight server. I was surprised by the very good handling and performance of the glider. While others had problems in thermals i could easily gain altitude and my ground speed was almost as fast as with full tanks.

I think im gonna try it in a competition and see if its better.

Wiley
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Postby Wiley » Tue Nov 11, 2008 6:04 pm

Some things I have learned.

In addition to taking on balast I have set the CG to the tail. For full balast I set the CG all the way to the tail. If I only take on half balast I set the CG not quite to the tail.

What this does it allow me to set the trim to neutral in normal flight which helps reduce drag. Also I realized that with the CG set to the tail I don't have to pull the stick back as far when circling nor do I run out of stick when trying to tighten my circles. Again reducing drag.

Even with no balast I think some tail CG bias is helpfull.

The speed and responsiveness of the planes have increased markedly.
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Fiddeflygare
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Postby Fiddeflygare » Wed Nov 12, 2008 1:20 pm

Wiley wrote:Some things I have learned.

In addition to taking on balast I have set the CG to the tail. For full balast I set the CG all the way to the tail. If I only take on half balast I set the CG not quite to the tail.

What this does it allow me to set the trim to neutral in normal flight which helps reduce drag. Also I realized that with the CG set to the tail I don't have to pull the stick back as far when circling nor do I run out of stick when trying to tighten my circles. Again reducing drag.

Even with no balast I think some tail CG bias is helpfull.

The speed and responsiveness of the planes have increased markedly.


I will not comment the part about you getting better handling with the C/G to the tail but i dont see how you would get less drag with the trim in neutral position? On a real life high performance glider and even most older gliders of glass/carbonfiber construction the trim only affects the stick as for example in my clubs LS8. This means that you would get the same drag having trimmed the aircraft to the speed you want as if you have the trim in neutral and push the stick forward in order to maintain your desired speed. Since you don´t have a trim rudder on the elevators.

Regarding Water ballast dumping during real cross country soaring it normally depends on how you will land when you should dump the ballast. I have been tougt to start dumping between 4-5km:s out from the finish line if its over an airfield. if you have lots of altitude when crossing finish line you don´t have to dump before. If you are gonna land straight in (passing finish line rolling on the ground) you can dump the ballast a little earlier. The general idea is that you should not have any ballast left when touching down on the field even though most gliders is landable with ballast left. The problem is that the wing tanks might empty themselves unevenly. This makes it more possible that you will have a ground loop when landing with risks of damaging the glider. This easily occurs if you are turning in one direction for a longer period of time during the dump.
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Postby OXO » Wed Nov 12, 2008 1:49 pm

Fiddeflygare wrote:I will not comment the part about you getting better handling with the C/G to the tail but i dont see how you would get less drag with the trim in neutral position? On a real life high performance glider and even most older gliders of glass/carbonfiber construction the trim only affects the stick as for example in my clubs LS8. This means that you would get the same drag having trimmed the aircraft to the speed you want as if you have the trim in neutral and push the stick forward in order to maintain your desired speed. Since you don´t have a trim rudder on the elevators.



All conventional aircraft with main plane and tailplane have the tailplane generate "negative lift", i.e. a force in the downwards direction. This is because the main wing aerofoil is not stable in the longitudinal direction (fore-aft).

If you run the c.g at the aft limit by putting more ballast in the tail, it is possible to reduce the lift generated by the tail, and therefore reduce it's drag.

BUT - this is a very very small difference and not really significant.
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