Water explanation, please.....

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mojo
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Water explanation, please.....

Postby mojo » Mon May 02, 2005 1:16 pm

Hi all

I think I've finally got to grip with most of the concepts on offer in Condor, but would appreciate a bit of advice on the pros and cons of taking on water (ballast). I appreciate that increased speeds would be a factor, as would increased sink-rates, but I could do with some info on the effects of water placement. Why tail-heavy, or nose-heavy etc.

Also, what conditions would prompt you to consider ballast.

In anticipation, thanks!!!

Mojo :?:

astir
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Postby astir » Mon May 02, 2005 1:34 pm

Well, Im not a pro in this but...

Water is always good if you just get up at the beginning of race (before race actually) because then you have more kinetic energy and you go further than without it.

And it also chance glide ratios so that you will lost less altitude with higher speeds.

And what comes to tail ballast, I think its only a way to make plane more stabile and nicer to different weight pilots. So if you are heavy you might would take tail ballast so you can trim it easier :) to go slower in turns.

With lighter pilots you take cognizance that centre of gravity wont go too back, because then plane is really dangerous. Could go to flat spin and so on.

Something like that :shock: Somebody can clarify my assumptions.


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AIRMAN
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Postby AIRMAN » Mon May 02, 2005 3:26 pm

Actually, more load results in higher speeds, but also bigger sink rate (see the polar diagram in condor). Main thing is that the glide ratio stays the same. So if you take two gliders, one with and one without water ballast and 'throw' them from one altitude, they will fly at the same glide ratio and land on the same spot. But the glider with water will travel this distance faster at the same loss of height. That is very important in cross country flying where you must get from one to another lift source as fast as possible. At the end of flying day you drop the ballast and because of lower sink rate your glider is more effective in weaker thermals.
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Postby Lecso » Mon May 02, 2005 4:25 pm

The ballast take out the optimal speed (speed of best glide ratio) to the higher speeds... so your glider will give you the best gliding ratio at higher speed.
Its the most important...
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Uros
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Postby Uros » Mon May 02, 2005 5:33 pm

Hi,

the C/G position affects the handling of the glider quite significantly. With front C/G the glider will be less responsive around lateral axis (pitch), but easyer to fly. In most occasions you can pull the stick all the way back without fear that the glider will be stalled. For beginners this is the prefered setting, but for more experienced, the glider is simply too lazy in some occasions. They should position the C/G more to the tail. But with the C/G to far back, even the most experienced pilots will have difficulties when circling in narrow and/or turbulent thermals.

As for water load. The main reason for loading water is that the average cross country speed (according to MC theory) increases with water load, assuming that the average climb rate stays the same. But here is the problem - you can't expect that you will climb the same with water. When thermals are strong and wide, the climb rate decrease will be relatively small. But if the thermals are weak and/or narrow, the relative decrease in climb rate can be quite significant. There is no exact rule of how much water to take (except in idealized conditions), so your choice should be based on experience.

As a rule of thumb - in medium to strong conditions full water is the way to go. If the thermals are then difficult to center or too narrow, then the water can be dumped (dump rate is cca 1 l/sec). In weak conditions I'd prefer half water and then see how it goes.

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Uros Bergant,
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mojo
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Postby mojo » Mon May 02, 2005 5:33 pm

Cheers folks

So, basically, it's best to take plenty of water on board, especially where speed is a factor ie competions. You can always ditch it in a crisis, right?

I think I understand now, guys.

Thanks for your time.

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Postby Tomcat84 » Mon May 02, 2005 7:38 pm

mojo wrote:Cheers folks

So, basically, it's best to take plenty of water on board, especially where speed is a factor ie competions. You can always ditch it in a crisis, right?

I think I understand now, guys.

Thanks for your time.


only if the thermals are good enough. If the thermals are weak then you will lose too much climb performance and take ages to get back to altitude between your transits.
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Rolo(ACS)
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waterrrrr

Postby Rolo(ACS) » Wed May 04, 2005 4:42 pm

in theory you do best if you always fill up with water, even with marginal weather.

You can use the extra wing load for the initial glide after race start and dump before you get to your first thermal.

Very marginal way of getting ahead but hey, all bits help.

Since you dont actually have to sweat loading the water in the sim its an option. In real life it involves dragging around with watercans ;)

hm what am i talking about, my plane only holds 60 L hehe

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nimbusgb
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Re: waterrrrr

Postby nimbusgb » Fri May 13, 2005 2:23 pm

Rolo(ACS) wrote:Since you dont actually have to sweat loading the water in the sim its an option. In real life it involves dragging around with watercans ;)

hm what am i talking about, my plane only holds 60 L hehe


There's 300 litres in the wings of my Nimbus 3. My solution - buy a long hosepipe! I don't understand this obsession with 20 litre containers!

:roll:
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MY
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Postby MY » Tue Jun 14, 2005 3:41 pm

Regarding CG.

Eventhough Condor doesn't simulate it, it also have an effect on the performance of the glider. The further back the CG is (staying within the CG envelope of course) the better the glider will.. uhm, well..glide :) .

Why?
On all conventional gliders the C of G is forward of the centre of lift. One force pointing down(cg) and one pointing up(centre of lift).
Think of these two forces as strings. Now if you pull these two strings, the nose of the glider will pitch down. What then keeps the nose up? The horizontal stabilizer. The horizontal stab. needs to provide negative lift to keep the nose up. Lift creates drag (induced drag). More lift, more drag.
In addition, the wing needs to produce lift equal to the weight of the glider PLUS the negative lift produced by the horiz.stab.

Now if we move the cg back, the arm between cg and centre of lift lessens, reducing the lift requriement of the horiz. stab.
This gives less lift requrement from the wing, and as a function of that, less drag.

A great performance gain on a glider? Probably not, but very noticable on larger aircraft. Typically 10 kts on a Saab 340...

Now if only someone would host a multiplayer game, I would not have written this. So blame yourselves! :D

Edit: I noticed it is infact simulated after reading the manual :oops:
but with a very small performance gain.

BR

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Postby Sebb » Tue Jun 14, 2005 6:16 pm

In reality the CG is a lot noticable on a glider. Our technologic master of the club put only 1kg ballast into the tail fin of the ASW19 owned by our club, and everybody who flew it said it is better then anytime before!

CG is needed if you take water ballast but you haven't got a water tank in the tail fin. So you need the ballast in the fin, otherwise your glider would for example climb miserable!

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Postby TimKuijpers » Tue Jun 14, 2005 7:25 pm

banditman wrote:Regarding CG.

Eventhough Condor doesn't simulate it, it also have an effect on the performance of the glider. The further back the CG is (staying within the CG envelope of course) the better the glider will.. uhm, well..glide :) .

Why?
On all conventional gliders the C of G is forward of the centre of lift. One force pointing down(cg) and one pointing up(centre of lift).
Think of these two forces as strings. Now if you pull these two strings, the nose of the glider will pitch down. What then keeps the nose up? The horizontal stabilizer. The horizontal stab. needs to provide negative lift to keep the nose up. Lift creates drag (induced drag). More lift, more drag.
In addition, the wing needs to produce lift equal to the weight of the glider PLUS the negative lift produced by the horiz.stab.

Now if we move the cg back, the arm between cg and centre of lift lessens, reducing the lift requriement of the horiz. stab.
This gives less lift requrement from the wing, and as a function of that, less drag.

A great performance gain on a glider? Probably not, but very noticable on larger aircraft. Typically 10 kts on a Saab 340...

Now if only someone would host a multiplayer game, I would not have written this. So blame yourselves! :D

Edit: I noticed it is infact simulated after reading the manual :oops:
but with a very small performance gain.

BR

Well, I could remember a flight...
Where I was flying with BB (karlkoch or Björn Blom) the same plane (ls8) and same ballast (full).
The only difference was that I had the C/G fully to the tail..
But, when flying into a thermal I was very happy! 2.5 meters!
But after a few seconds BB joined the thermal and he was laughing because he had 3.5!
I tought it could be because I was at the top of the thermal or something like that.
I desided to go on to another thermal...
Aprox 60k later, we ended up quite low and BB found a small thermal...
I was 1k ahead but turned to him...
first i was about 30m higher then him in the thermal but he slowly came along side.
Then I desided to fly exactly the same path as he did, but he still kept on gaining on me!

So, the stories you guys are telling, don't correspond with my condor experience...
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Re: waterrrrr

Postby triffid » Sun Jul 10, 2005 3:52 am

nimbusgb wrote:
Rolo(ACS) wrote:Since you dont actually have to sweat loading the water in the sim its an option. In real life it involves dragging around with watercans ;)

hm what am i talking about, my plane only holds 60 L hehe


There's 300 litres in the wings of my Nimbus 3. My solution - buy a long hosepipe! I don't understand this obsession with 20 litre containers!

:roll:

Plus I have up to 13 lts in my tail, thought at my weight I normally fly with 200 in wings 8 in tail around 800 all up.
Took of twice with every thing full... TOOOOO scary good of tow in a straight line .. but after 10km on tow and only 400ft above terain !!!! :shock: :shock: :shock: :shock: :shock:
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Postby Lowmick » Sun Jul 10, 2005 1:46 pm

When is best time to release ballast? On final glide or after it before landing?
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Postby desktopsimmer » Sun Jul 10, 2005 2:11 pm

Don't know if this is the best practice, but I dump water if I need to climb at bit more than planned, but I generally leave the most I can for final glides and do a victory dump after crossing the line! PS I've only won a few races, practice make perfect :)
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