Water explanation, please.....

Discussion related to the Condor...

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markjt
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Postby markjt » Sun Jul 10, 2005 2:47 pm

Lowmick wrote:When is best time to release ballast? On final glide or after it before landing?

The basic rule is: Keep as much water as you can for as long as you can.
If you have any water, and you reach final glide height, then you must keep all the water you have: Heavier = faster.

Always start with full water unless it is obvious from the weather settings etc. that the lift is weak. Even if you start with full water, fly 10km to the 1st thermal and then dump it all, you will have reached that thermal faster than without water, and at the same height (all other things being equal).

The really crucial and difficult decision is when to dump water if the lift is weak-moderate and/or hard to centre. In RL some gliders are a real handfull with full water and just don't climb well. Remember that with water you will normally have to fly faster in thermals than without. This makes your turn radius larger, and the effective thermal strength will usually be less.

It is all a compromise between amximum climb rate and maximum speed between thermals.

Mark
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baktair
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Postby baktair » Tue Nov 15, 2005 1:11 am

Look into the future!!!!

If you dump your ballast too early, becouse of weak thermals, you may drop more than a hundred km. It heppaned in real, when trying to beat the 500km. Took off at 11 LCT, thermals were weaker than they looked. Ballast dumped, but soon after, found 2.5 , 3 meters. A great loss of avarage speed.
So when you hold some water onboard, you must be sure about the weather!!!
HA-4417

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Padding
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Postby Padding » Tue Jan 03, 2006 5:58 am

MY 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


Seems to me that you want to have the c/g tuned right against the lift at (aprox 1/3 from the wingnose). And not all to the back because then you would have to generate a constant positive lift with the stabilazor and thus generate extra drag.


... wrote: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...


my theory explains this, you expirieced extra drag because of the constant positive lift generated by your stabilazor.

Padding
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Postby Padding » Tue Jan 03, 2006 6:00 am

MY 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


Seems to me that you want to have the c/g tuned right against the lift at (aprox 1/3 from the wingnose). And not all to the back because then you would have to generate a constant positive lift with the stabilazor and thus generate extra drag.


... wrote: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...


my theory explains this, you expirieced extra drag because of the constant positive lift generated by your stabilazor.

Padding
Posts: 12
Joined: Sat Dec 17, 2005 2:08 am

Postby Padding » Tue Jan 03, 2006 6:01 am

MY 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


Seems to me that you want to have the c/g tuned right against the lift at (aprox 1/3 from the wingnose). And not all to the back because then you would have to generate a constant positive lift with the stabilazor and thus generate extra drag.


... wrote: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...


this is explainable with my theory....guess i'm right?

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kloudy
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Postby kloudy » Tue Jan 03, 2006 10:37 am

you're repeating yourself, mate.

The fact is when a wing is generating lift, it wants to rotate forward, i.e. pitch down. This is a natural tendency for a lifting surface.
Please don't ask me to explain why in this forum as it is all in the texts and on the web.
And I'm lazy.

Just look for pitch stabiltiy and pitching moment.
Therefore, the following is simplified and somewaht sketchy but conveys the general idea.

The foreward pitching of the wing is affected by the attached stabilzer (hence it's name) by creating a downward moment at the end of the tailboom keeping the leading edge up..
These forces are always in opposition to one another.

If, somehow, one could reduce the degree of force needed at the stab', then less energy would be lost thru drag (opposing forces of thrust and lift).

If the cg is closer to the center of pressure (cp), then less downward force is required at the aft moment. Less downward force (negative force of lift) creates less resultant drag (induced) and overall efficiency increases.

In aerodynamics there is never a "free lunch". The result is a decrease in positive pitch stability which has its own bugaboos such as neutral pitch stabiltiy and actually negative stabiltiy which can result in unrecoverable stall of the wing on the craft.
There are almost infinite relationships and trades to be made in configurations. Sometimes another fella is just "the besst at finesse" in controlling his ship most efficiently. CG is just one of the thousands of fluid dynamic trades to be made in any flight moment.

try not to get bogged down in one aspect of the scheme and fly your wing often and smooooth.

just my 0.0168091 Euros.
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JJJ
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Postby JJJ » Tue Jan 03, 2006 1:11 pm

some water explane from me:)


In Start
before start i take evrytime full ballast if it is weak full ballast
if thermal is somthin like 0.5/1m/s i dump 20sec/50sec if thermal is 1/1.5m/s i dump 15sec if thermals are above 1.5m/s i dump 10sec if termal are more if 2m/s i dont dump


Finishif its a race finish i dump ballast after he said ....Completed task... whit a rolling finish (straight-in) i dump FULL ballast if the speed is under the 180km/u whit 3/4ballast after 160km/u 2/4 Ballast 140km/u 1/4 ballast after 140km/u
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TimKuijpers
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Postby TimKuijpers » Tue Jan 03, 2006 1:16 pm

kslappy101 wrote:If the cg is closer to the center of pressure (cp), then less downward force is required at the aft moment. Less downward force (negative force of lift) creates less resultant drag (induced) and overall efficiency increases.

This encounts the lift of the wings also...
When the C/G is further to the back, the lift-vector will get in front of the C/G.
This means the created lift will provide a pitch up moment.
This means the elevator doesn't need to create that much drag anymore..

At least a negative C/G means prettier flying, so that what counts for me.. :)
Think positive, flaps negative.

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TheSoarer151
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Postby TheSoarer151 » Sun May 21, 2006 4:37 am

Withtoo much tail ballast, one must watch out for the fact the plane sometimes wants to spin. Also if you are doing a speed ridge course, unless the ridge is weak and u need to thermal to get over the gaps, you want to have forward ballast or more nose ballast because it makes the flight a lot smoother.

tatali0n
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Postby tatali0n » Wed May 31, 2006 2:03 pm

Question:

To dump the ballast in Condor, do you have to hold the W key down until the tanks are empty, or just press it once to open the valves and dump the water?

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OXO
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Postby OXO » Wed May 31, 2006 2:06 pm

One press opens the tap. a second press closes it again.

You can check this by using F2, and you will see the water coming out.
OXO,
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TimKuijpers
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Postby TimKuijpers » Wed May 31, 2006 4:36 pm

Or just look at the pictures at the water-valve-handle
Think positive, flaps negative.

ronald
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Postby ronald » Wed May 31, 2006 4:52 pm

i moostly let them open till i landed

Sticky Digit
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Postby Sticky Digit » Thu Jul 13, 2006 9:41 pm

Hi all,
I have been reading the content on Waterballast. Can I suggest that Nimbusgb should read his flight manual more carefully:- The reason we all use 20 litre barrels is because if you continue to fill with a hosepipe you will come to grief in a major way.
If you place a hose in the fill/vent of your Glider, then whatever the water pressure per square inch is coming out of your tap will be multiplied by the area of your wing bags/tank the instant you are full. I have watched as this happened with an ASW22. The wing skin ahead of the main spar on the underside of the wing just blew out and dropped the full wing bag on the ground. :( Please don't get caught out like this. I don't know about the Nimbus case but most manufacturers state that your water resevoir must be a maximum of 1 mtr above the level of the inlet on the Glider when filling.
Best wishes Sticky Digit. :D

TimKuijpers
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Postby TimKuijpers » Fri Jul 14, 2006 10:45 am

I fill it with a hose, but only when there is an opportunitie for the air/water to come out at the other side. (ASW20 will spit it out like a dolphin)
Else I will put the hose in a funnel that way the worst scenario is a wet trousers.
Think positive, flaps negative.


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