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nickc(at)mtaonline.net
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 Posted: Mon Nov 09, 2009 11:05 pm Post subject: "Starved horse" or "Solid"...... |
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Hello Kolbsters,
I am not an engineer of any type, but it is hard for me to believe that if the numbers were run that the solid wing would not out lift the starved horse wing. It is my understanding that the thickness of the wing is one of the factors that affect how much a wing can lift. That said, the different may not be that great.
Clear skies,
Nick Cassara
Proto-type Kolbra Under reconstruction
Palmer, Alaska
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Fri Nov 13, 2009 4:44 am Post subject: "Starved horse" or "Solid"...... |
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Nick, Yes, the starving horse look does have some effect, but is relatively minor. Check out "Theory of Wing Sections" by Abbot and VonDoenhoff from your local library and look at the graphs in the back for any of the old timey airfoils, the 2400, 4400, even the 23000 series. NACA tested them at thicknesses of 2 to 3 percent of chord intervals so a 2415 is 3 percent thicker than a 2412 and so on. On a Mk III wing the chord is 60" +/- so 3 percent is 1.8" The ribs are only about 1/2" taller than the troughs on my Mk III, so lets call it 1 percent. Take a look at the lift coefficient curve for the 2410 and compare it to the 2412 (for the trivia buffs, this is the airfoil section used on the beloved C172, among others).
The difference is very small for any of the curves, but let's use the one for a Reynolds number of 3 million. Let's look at the lift coefficient for an angle of attack of 4 degrees.
For the 2410 it's about .62, for the 2412 it's about .65 So let's interpolate and just for grins assume there's a 2411 some where and at 4 degrees AOA it's .635 .015 ain't a big number but let's see what it means in actual by golly pounds of lift.
When you do the dynamic pressure X lift coeffiecient X wing area (call it 150 sq ft) for 60 mph we get 811 lb. for our 2411, and 830 lb. for the 2412 and a difference of 19 lb. of lift. Of course this doesn't count anything Mr Bernoulli might add back by sucking the cloth upward and back towards the idealized shape of the 2412.
If you run the numbers for a good climb at 50 mph and an AOA of 8 degrees Cl is 1.06 for the 2410 and 1.1 for the 2412. Split the difference again and we get 1.08 for the 2411.
The 2411 produces 958 lb. and the 2412, 976 lb. for 18 lb. of lift difference.
Note: for anyone backtracking the numbers I used .0022 for rho, not .00237 because, while I fly at 59 degrees F getting down to sea level means I have to fly 1270 feet underground and it's too dark to see well down there.
Rick Girard
On Tue, Nov 10, 2009 at 12:34 AM, Nick Cassara <nickc(at)mtaonline.net (nickc(at)mtaonline.net)> wrote:
[quote]
Hello Kolbsters,
I am not an engineer of any type, but it is hard for me to believe that if the numbers were run that the solid wing would not out lift the starved horse wing. It is my understanding that the thickness of the wing is one of the factors that affect how much a wing can lift. That said, the different may not be that great.
Clear skies,
Nick Cassara
Proto-type Kolbra Under reconstruction
Palmer, Alaska
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