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Old Mar 10, 2007, 09:40 PM
Experimental pilot
Grandview Missouri
Joined Jul 2006
188 Posts
Help!
Maximum lift.

I would like to know what the best airfoil shape is for MAXIMUM lift. A shape that will lift when looked at funny. If anyone could post a diagram of said airfoil, I would greatly appreciate it!

I am unfamiliar with the #'s of airfoil shapes though, so please be gentle.

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Old Mar 11, 2007, 01:22 AM
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Punta Gorda, FL
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Your question is simple but there is no simple answer. Lift is a force that depends on wing shape (span, thickness and chord), angle of attack, airspeed and size.

The airfoil shape depends on coefficient of lift. Please don't use "lift" for "coefficient of lift." See:
http://en.wikipedia.org/wiki/Coefficient_of_lift

Change your question. Tell us your purpose so that we can help you understand answers.
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Old Mar 11, 2007, 07:22 AM
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There is more.

The "best" airfoil shape depends on several factors incuding maximum lift coefficient. The "best" airfoil shape depends on your application. Please, be specific for your use.
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Old Mar 11, 2007, 07:22 AM
no prop = no turbulence!
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Why do you think there are so many airfoil shapes? It's because there are lots of different conditions to fly in and lots of SIZES of wings. You can't use the same airfoil for B747 and a small HLG. The 747 also needs much lift, but in different SPEED, it's much bigger and also has huge wing LOADING. How big is what you plan? How fast does it have to be? How will it fly? Look at S3021 and AG16. Both of them offer high performance but in much different speeds. Or look at Jedelsky wing. Would you use this airfoil for a giant or full scale?
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Old Mar 11, 2007, 08:46 AM
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What reynolds number are you working at?????
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Old Mar 11, 2007, 09:51 AM
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The "best" airfoil with maximum lift coefficient might not be practical. The "best" airfoil has several ideals to pick from. Their ideals are convlicting!! So must find the meld of several non-ideals.

From Don Sackhouse:
"The Four Blind Men and the Elephant (an old Hindu parable)

One day four blind men encountered an elephant for the first time. They approached it cautiously, but with great curiosity. The first one grabbed hold of the trunk and declared "Aha! An elephant is just like a snake!" The second found an ear and replied "No, an elephant is exactly like a tent." The third bumped into a leg and decided the elephant was just like a tree, and the fourth caught the tail and maintained that the elephant was just like a rope. They all went home arguing, each steadfastly insisting that he was right and the other three were wrong."
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Old Mar 11, 2007, 11:56 AM
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Quote:
Originally Posted by woro
Why do you think there are so many airfoil shapes? It's because there are lots of different conditions to fly in and lots of SIZES of wings. You can't use the same airfoil for B747 and a small HLG. The 747 also needs much lift, but in different SPEED, it's much bigger and also has huge wing LOADING. How big is what you plan? How fast does it have to be? How will it fly? Look at S3021 and AG16. Both of them offer high performance but in much different speeds. Or look at Jedelsky wing. Would you use this airfoil for a giant or full scale?
The question is simple and should have a simple answer.
This is a modelers forum, so velocity for operation is less then 10mtr/sec.

Just open a profile catalog and seek the one with the higest CL.
Check out S1210 that has a smidgeon better performance then the S1223 - a husky load lifter that requires a good amout of power, ballast, and/or massivity.
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Old Mar 11, 2007, 12:46 PM
Experimental pilot
Grandview Missouri
Joined Jul 2006
188 Posts
WOW! Um, well I am looking at a stable airframe (sort of a glider style) applying video, I would like two airfoils front and back, a slow-ish flier. Maybe 10-15 lbs. I want to use it for mainly video, and I would like to utilize thermals in saving power useage. Oh, and DC flight, maybe DC turbine?

Thank-you VERY much for your input, I apologize for not clarifying, it was kinda late here. Hm, I have changed my location twice, it says I am still in Florida, I am in MO. now. You all are very kind to respond! I like the shape of the S1210 12%, very shexy!
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Old Mar 11, 2007, 01:45 PM
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Fun flight

Quote:
Originally Posted by SST32
WOW! Um, well I am looking at a stable airframe (sort of a glider style) applying video, I would like two airfoils front and back, a slow-ish flier. Maybe 10-15 lbs. I want to use it for mainly video, and I would like to utilize thermals in saving power useage. Oh, and DC flight, maybe DC turbine?

Thank-you VERY much for your input, I apologize for not clarifying, it was kinda late here. Hm, I have changed my location twice, it says I am still in Florida, I am in MO. now. You all are very kind to respond! I like the shape of the S1210 12%, very shexy!
If I was younger, I would like to use the S1210 on a park flyer! A 'park flyer' that would haul me up to start flight at the current winch altitudes, and carry me for a similar duration as the modern toy sailplane...for similar duration, because of similar airspeeds and sink levels.

I am talking about a 600 lb 'park flyer' RTF (with me aboard) here. Object is for duration close to the airport, like the weekend warior flights with 121's at the Dallas Glider club. Even though performance would be inferior to the 121, the low air speed would make working thermal lift a lot easier.

If they keep increasing winch power, this thought may be positive for a future avocation. LOL
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Old Mar 11, 2007, 02:28 PM
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S1210 and S1223 airfoils are not practical, with thin trailing edge, in my opinion. Try building them.
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Old Mar 11, 2007, 03:10 PM
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Quote:
Originally Posted by Ollie
S1210 and S1223 airfoils are not practical, with thin trailing edge, in my opinion. Try building them.
Low AR (at about 6 feet chord for the park flyer) the molded TE can be quite feasable. For the modeler however, one must improvise a bit, and probably do a bit of distortions to accomplish goals; that would still be effective at the low airspeed envolved.
There is a difference in 'just working', and perfection. I am in it for fun. Blanchard profiles are much easier to work with, but not a maxim for CL. From further discriptions, I think they would be the better bet for the application/project.
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Old Mar 11, 2007, 03:16 PM
greg
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somerset, nj
Joined Feb 2005
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but doesn't sst32's goal really sound like duration, and doesn't that mean best lift to drag?

and when minimizing drag, aren't you really interested in selecting the airfoil that has minimum drag at an acceptable airspeed determined by the weight and planform?

and when does the the maximum lift coefficient come into play? i can understand while thermalling, because you want to minimize airspeed, but is another case when taking off?
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Old Mar 11, 2007, 04:40 PM
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Practical pig design

Quote:
Originally Posted by ciurpita
but doesn't sst32's goal really sound like duration, and doesn't that mean best lift to drag?

and when minimizing drag, aren't you really interested in selecting the airfoil that has minimum drag at an acceptable airspeed determined by the weight and planform?

and when does the the maximum lift coefficient come into play? i can understand while thermalling, because you want to minimize airspeed, but is another case when taking off?
Take a GL and toss a pound of ballast into it. Lift to drag has noticeably mproved, however scratching to stay up @ less than 300 feet AGL is rather difficult, and success demonstrates pilot skill! At 1000 feet AGL, fly a full size 121 against a Marske Monark (man on man), and you will discover what a 28 mph thermal airspeed will accomplish against the 121's 45 mph. Less bank angle definitely equals faster climbs!

My math shows that having the correct airspeed for the conditions is far more important then having the best potential lift to drag ratio when attempting to realistcally squeeze out duration within a task window. Open ended and extremely light (i.e. no task window limitation) a machine can stay up for hours - no telling where it will end up?

Cargo version of Payload FF used the high lift profiles for takeoff and duration flights of about 30 seconds.

Thornberg played with a 22 ounce GL (with finger hole), and was unbelievable with it at the club's NM funfly HL meets; however, my 30 ounce GL would frequently get on top of him in short launch action because my programmed 6 mtr/sec; which is the airspeed that worked for all my machines in winds less than 13 mph. [Please note that I am nowhere near Thorny's, nor the top flyers in the club's skill level]
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Old Mar 11, 2007, 05:18 PM
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There is between L/D (range) and L^2/D^3 (duration or power factor). The drag is most important because of induced drag Cdi= Cl^2/ pi x Aspect Ratio. With duration the design is very, very important with high aspect ratio and limited Cl^2.

Using wing low aspect ratio or either of two airfoils, S1210 and S1223, means the aircraft has a very, very slow and not very fast air speed. The aircraft is like a parachute or paraglider more than sailplane. The aircraft is very slow to climb or climb with lots and lots of power (climb on the prop rather than wing). I think the model aircraft design is very bad from my point of view.
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Old Mar 11, 2007, 06:11 PM
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Punta Gorda, FL
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SST32,

Keep your project design simple. Use a S3021 airfoil with tip to tip flaps. Use an wing with an aspect ratio of 12 to 15. Use with negative 2 degree flaps for wind penetration. Use zero degrees flaps for climb. Use the positive 3 to 4 degree flaps for thermal soaring. Use a wing with enough area to keep the wing loading about 8 to 16 ounces per square foot.
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