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Old Nov 09, 2011, 12:21 PM
yyz
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Cross-country/GPS triangle sailplane design using XFLR5

If you were following the "XFLR5 Wing Design Help Needed" thread a while back (http://www.rcgroups.com/forums/showthread.php?t=1356201), the hijinks have resumed -- with some interesting results -- here:

http://www.rcaerotowing.com/forum/sh...?120-Eta-Biter

This plane is being designed with flat-out straight-line performance as its primary design goal.

Mike
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Old Nov 09, 2011, 06:18 PM
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What are you allowed to have for a max gross weight in scaled contests ?

That's a big factor in the design of AMA or FAI XC ships.

Mike
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Old Nov 09, 2011, 07:02 PM
yyz
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Originally Posted by ThermalSeeker View Post
What are you allowed to have for a max gross weight in scaled contests ?

That's a big factor in the design of AMA or FAI XC ships.

Mike
Mike,

The regulations for the planes are spelled-out in Section 2 of this document:

http://www.eurocup.gps-triangle.net/...V3.41%20EN.pdf

These ships are aero-towed or self-launched (electric motor) so you don't have the winch launching, weight limiting issues that the FAI/F3H ships are constrained by.

Mike
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Old Nov 10, 2011, 09:38 PM
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....The regulations for the planes are spelled-out in Section 2 of this document:

http://www.eurocup.gps-triangle.net/...V3.41%20EN.pdf .....
Ok I understand a little now. First is the max wingloading of 115g/dm2 . That works out to about 37 oz/sqft. That makes sense and is understandable, however it then goes on to say that wingloading applies only to gliders that are scaled to 1/3 scale. All others will have a correction factor applied...then doesn't say what the correction factor is.

Lastly it states that under no circumstances will the weight of the glider exceed the number that is derived from a rather strange formula. There's no units in the formula so I assume the units for wing area are dm2 and the end result will be in kg. I don't know the numbers for your ship but it would be handy for you to know your max weight allowed so you can design in the strength that you want and know that you won't have your dream ship disqualified due to weight.

Mike
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Old Nov 12, 2011, 07:17 PM
yyz
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Originally Posted by ThermalSeeker View Post
Ok I understand a little now. First is the max wingloading of 115g/dm2 . That works out to about 37 oz/sqft. That makes sense and is understandable, however it then goes on to say that wingloading applies only to gliders that are scaled to 1/3 scale. All others will have a correction factor applied...then doesn't say what the correction factor is.

Lastly it states that under no circumstances will the weight of the glider exceed the number that is derived from a rather strange formula. There's no units in the formula so I assume the units for wing area are dm2 and the end result will be in kg. I don't know the numbers for your ship but it would be handy for you to know your max weight allowed so you can design in the strength that you want and know that you won't have your dream ship disqualified due to weight.

Mike
It will likely end up too light if anything. I've already designed in provisions for ballast to bring the wing loading up to maximum.
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Old Nov 15, 2011, 06:05 PM
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Mike weight limit is 11# is'nt it?
Greg's plane is already the ultimate for straight line speed in XC
Now for Triangle racing it's different - so which one is it?
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Old Nov 15, 2011, 09:22 PM
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I took a shot at the gross weight of your glider at 1/3.5 scale.

Per the rules cited above

Gross weight =
11.5*Original Wing Area/((((Square Value of scale factor/9)-1)/1.2)+1)/9

Assuming the wing area is supposed to be in Meters squared and an asw-22 BL at 26.5 meter span having 16.3 meters squared wing area

Assuming the scale factor of 3.5
Assuming the finish weight is in kg

I get 16kg or 35 lbs for a max weight.
At 14.28 ft sguared that's a 39oz/ft sq wing loading at max weight.

If my assumptions above are right, that ship ought to scream when fully ballasted up, if you can climb.

Mike
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Old Nov 15, 2011, 11:18 PM
yyz
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Mike weight limit is 11# is'nt it?
Greg's plane is already the ultimate for straight line speed in XC
Now for Triangle racing it's different - so which one is it?
For F3H (FAI cross-country) the max is 11 lbs. not so for GPS Triangle racing.
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Old Nov 15, 2011, 11:27 PM
yyz
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Originally Posted by ThermalSeeker View Post
I took a shot at the gross weight of your glider at 1/3.5 scale.

Per the rules cited above

Gross weight =
11.5*Original Wing Area/((((Square Value of scale factor/9)-1)/1.2)+1)/9

Assuming the wing area is supposed to be in Meters squared and an asw-22 BL at 26.5 meter span having 16.3 meters squared wing area

Assuming the scale factor of 3.5
Assuming the finish weight is in kg

I get 16kg or 35 lbs for a max weight.
At 14.28 ft sguared that's a 39oz/ft sq wing loading at max weight.

If my assumptions above are right, that ship ought to scream when fully ballasted up, if you can climb.

Mike
Mike,

I'm building the stretched ASW22 DB (28 meter) version so I get a bit more area. All of the XFLR polars are calculated at 10 and 15 kg AUW.

Mike
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Old Nov 16, 2011, 06:26 AM
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Mike,

I'm building the stretched ASW22 DB (28 meter) version so I get a bit more area.......

Mike

I saw that but one quick attempt using Ms Google to find the wing area didn't reveal what the area might be for the stretched version. Given your 25 foot span and 30+ oz wingloading I can imagine the excitement a ship like yours would be. I wanted to see a ball park for how much weight that you have to work with. My guess is that given the spars and nose weight that you're going to need for this size of a ship that you are likely going to be in the 25 to 30 pound empty weight to begin with even before ballast. Hopefully Santa has plenty of carbon fiber headed your way this year.

Mike
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