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Old May 21, 2005, 08:26 PM
Will work for foam
wingnutt's Avatar
United States, WI, Muskego
Joined Apr 2005
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wing design question - blended airfoils

I'm designing a new wing and am shooting for low drag (who isnt) as it will be a thermal ship. For now the plan is to use a high lift root airfoil (S5020), blended to a low lift, symetrical tip airfoil (S8020). While running numbers through the Panknin spreadsheet i found that using the MH-45 at the tip instead of the S8020 i will need less washout - which should be less drag.

My question is this, am i really loosing drag, or am I just trading it to the inherent drag of the Cm & Ao of the MH-45? In fewer words, would there be less drag with the S8020 with more washout, or the MH-45 with less washout at the same Cl?

Thank you,
wingnutt
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Old May 22, 2005, 12:35 AM
Холодная война все еще здесь.
RCWorks's Avatar
Joined Aug 2003
1,628 Posts
Quote:
Originally Posted by wingnutt
I'm designing a new wing and am shooting for low drag (who isnt) as it will be a thermal ship. For now the plan is to use a high lift root airfoil (S5020), blended to a low lift, symetrical tip airfoil (S8020). While running numbers through the Panknin spreadsheet i found that using the MH-45 at the tip instead of the S8020 i will need less washout - which should be less drag.

My question is this, am i really loosing drag, or am I just trading it to the inherent drag of the Cm & Ao of the MH-45? In fewer words, would there be less drag with the S8020 with more washout, or the MH-45 with less washout at the same Cl?

Thank you,
wingnutt
The MH-45 is going to do you better.
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Old May 22, 2005, 01:56 AM
Striving to Rip the Bring
raptor22's Avatar
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I don't think you should even use the MH series of airfoils,b ut go with sonething liftier.

You definetely DONT want to go symmetrical at the tip. YOu will have a ship that has very poor spiral stability at high speeds because the typical wing "death spiral" will become much worse.

Importantly, what is your consturction technique? the MH series of airfoils are pretty much all hypercritical, so you would be best with molded stuff or at least a bagged wing. This means oyur performance will suffer with a straight foam wing.

the drela AG series of foils are all great thermallers and relatively forgiving if you can reinforce the foam properly (really thin). They are not designed for wings, but their low camber design yields a very low Cm.

--Alex
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Old May 22, 2005, 10:53 AM
Will work for foam
wingnutt's Avatar
United States, WI, Muskego
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Thanks Skunkworksrc, i was leaning that way.

Alex,
You always have great responses and i apreciate your input. i have looked at both the MH and the Drela foils and even the SD7037 with its derivatives, but all of them require a crazy amount of washout (-7 to -11 deg). with the S5020 or even a S5010 thinned to 8% im only looking at -3.3 deg washout. plus, the ship will be pretty light (3.5 to 4.5 oz/sqft) so penetration is more of a factor than a high Cl foil. True that with flaps on a MH, Drela or SD foil plane you can dial in negative camber for penetration to overcome any drag caused by the emmense washout, simplicity is another factor on this design (2 channels). the test bird will have a 48" wingspan and if all goes well a 60" or 2M version will be built.

Here are the design parameters so far:
Wingspan: 48"
Root chord: 7.75"
Tip chord: 5"
Root airfoil: S5020 or S5010-8%
Tip airfoil: MH-45
Sweep at 1/4 chord: 20 deg
Washout: -3.3 deg
CG: 6" from LE
Stability Factor: 7%
All up flying weight: 6 to 8 oz

If anything looks terribly out of whack, please let me know.
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Old May 22, 2005, 11:08 AM
Striving to Rip the Bring
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oh, i was expecting a little more sweep. I guess its good you are cutting down ont he sweep, though, since sweep really cuts your performance.

You may also like to look at the mg06 for really low drag. it's relatively low cl, but shoudl take reflex nicely and is very low drag. Also symmetrical.

--Alex
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Old May 22, 2005, 12:32 PM
Will work for foam
wingnutt's Avatar
United States, WI, Muskego
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Alex,

SWEET!! i will definately give it a look-see.

Thanks again,
Steve
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Old May 22, 2005, 09:00 PM
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Sanford, FL
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Quote:
Originally Posted by wingnutt
Stability Factor: 7%

How do you calculate this ?


Thanks,
Digsy
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Old May 27, 2005, 05:12 AM
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Rennes, FRANCE
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25 - XCG (unit : % of MAC)
also called static margin (3-10% usually on FW)

manu.
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Old May 27, 2005, 11:07 PM
dougmontgomery's Avatar
Glendale,Az.
Joined Oct 2004
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Wingnutt, I have been experimenting with my hot wire on various airfoils. I am currently pleased with the effects of a full symetrical at the root and flat at the tip so the tip is less apt to stall. I would like to make some 23012 series where the center of lift will not rotate the wing nose down at higher speeds. Doug
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Old May 28, 2005, 07:23 PM
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Sanford, FL
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Quote:
Originally Posted by Manu DM
25 - XCG (unit : % of MAC)
also called static margin (3-10% usually on FW)

manu.

Thanks

Sorry how do I calculate the XCG ? (I'm a noob...)
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Old May 28, 2005, 07:35 PM
Striving to Rip the Bring
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Quote:
Originally Posted by digsy
Thanks

Sorry how do I calculate the XCG ? (I'm a noob...)
It's where yopu chose to place your cg at %MAC. MAC is mean aerodynamic chord. normally, you would start at aroung 18-20%. Do a search for MAC if you ahve no idea how to find it.

Basically, its the chord-line that produces equal area on either side of it.

--Alex
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Old May 28, 2005, 07:37 PM
Striving to Rip the Bring
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Quote:
Originally Posted by dougmontgomery
Wingnutt, I have been experimenting with my hot wire on various airfoils. I am currently pleased with the effects of a full symetrical at the root and flat at the tip so the tip is less apt to stall. I would like to make some 23012 series where the center of lift will not rotate the wing nose down at higher speeds. Doug
That's good, but adds a nose-down pitching moment. To avoid it, just decrease the sweep.
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