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General Forums => Aircraft and Vehicles => Topic started by: Ex-jazz on July 02, 2009, 11:49:56 PM

Title: AERODYNAMICS: Airfoil Cl,Cm & Cd diagrams with -90/+90 AOA scale?
Post by: Ex-jazz on July 02, 2009, 11:49:56 PM

Hi

I try understand, how the airfoil/wing is working in extreme AOA conditions.

I can find a lot of  Cl,Cm & Cd diagrams, which are from -5 to +15 degrees AOA. See link
http://marlongofast.tripod.com/zipped_aeronotes/clarky.htm


Is there available a Cl,Cm & Cd  diagrams with -90/+90 AOA scale?
Even a the principle level diagram would be enough to get the general idea.

Nice link: How to read polar diagrams
http://www.mh-aerotools.de/airfoils/hdipolar.htm

Thanks

Title: Re: AERODYNAMICS: Airfoil Cl,Cm & Cd diagrams with -90/+90 AOA scale?
Post by: Stoney on July 03, 2009, 04:47:54 AM

XFOIL may be capable of -90/+90 sweeps, but only if the lift/drag values stay in the "normal" range at those extreme variations in AoA.  It doesn't like large sweeps like that anyway and sometimes will create errors by skipping some of the single angles of attack.  Also, on laminar flow airfoils, it can get fairly unpredictable past the stall AoA.  I've never tried to compute anything more than a -5 AoA on the other side of the spectrum.

I'm curious as to why you need such a large spectrum of AoA?  20 degress of AoA would be considered "extreme" by most aero types.

Title: Re: AERODYNAMICS: Airfoil Cl,Cm & Cd diagrams with -90/+90 AOA scale?
Post by: hitech on July 03, 2009, 07:29:51 AM

Ex-jazz, good luck on finding some, I have only ever found 1 that went the full range. If you happen to find many I would love see them.

HiTech

Title: Re: AERODYNAMICS: Airfoil Cl,Cm & Cd diagrams with -90/+90 AOA scale?
Post by: Ex-jazz on July 03, 2009, 09:22:52 AM

@ Stoney
Thank for the XFOIL hint
I'm coding with python a flight dynamics model for the blender game engine. It's my hobby project :)

@ Hitech
I just googled with 'cl-vs-alpha' and this popup:
http://www.aerospaceweb.org/question/airfoils/q0150b.shtml

Title: Re: AERODYNAMICS: Airfoil Cl,Cm & Cd diagrams with -90/+90 AOA scale?
Post by: Mace2004 on July 03, 2009, 10:21:19 PM

Just curious but why do you ask?  The wing has ceased to function as an airfoil well before reaching 90deg AOA.

Title: Re: AERODYNAMICS: Airfoil Cl,Cm & Cd diagrams with -90/+90 AOA scale?
Post by: Ex-jazz on July 03, 2009, 11:43:03 PM

Quote from: Mace2004 on July 03, 2009, 10:21:19 PM

Just curious but why do you ask?  The wing has ceased to function as an airfoil well before reaching 90deg AOA.

I try to simulate the acting lift-, drag- & moment-forces of the wing over wide range AOA's. For this I need a Cl, Cd & Cm look-up tables, which are covering the 180deg AOA.

BTW I assume the Cm has similar curve than CL, just invert.

Title: Re: AERODYNAMICS: Airfoil Cl,Cm & Cd diagrams with -90/+90 AOA scale?
Post by: Stoney on July 04, 2009, 12:16:45 AM

Quote from: Ex-jazz on July 03, 2009, 11:43:03 PM

BTW I assume the Cm has similar curve than CL, just invert.

I've never really studied Cm past the normal AoA's but it isn't similar to the Cl curves.  Cm is affected most by camber.  Symetrical airfoils possess almost no pitching moment, while highly cambered airfoils, especially those with design lift coefficients in the .4 or higher range have pretty high Cm--especially those with further aft centers of pressure, like the NACA 6-series, for example.  I may be telling you something you already know if I didn't understand your statement above correctly.

Title: Re: AERODYNAMICS: Airfoil Cl,Cm & Cd diagrams with -90/+90 AOA scale?
Post by: bozon on July 04, 2009, 01:06:42 PM

Quote from: Ex-jazz on July 03, 2009, 09:22:52 AM

I'm coding with python a flight dynamics model for the blender game engine. It's my hobby project :)

Flight dynamics model with python?! I hope it is really simple and requires no loops...

Regarding the +-90 deg, are you looking to model a plane falling belly forward out of the sky?

Title: Re: AERODYNAMICS: Airfoil Cl,Cm & Cd diagrams with -90/+90 AOA scale?
Post by: Ex-jazz on July 04, 2009, 03:17:04 PM

@Stoney
You are right. The symmetrical airfoil Cm is next to none, compared to the cambered airfoil .

I purchased the Profile 2, which use the XFOIL for the calculations :)

(http://fdm4bge.1g.fi/Files/10001/apics/Profili2_4polais.png)

@Bozon
My target is to made a light but plausible / believable sub-sonic single engine contra prop driven traditional designed airplane FDM, based to the aerodynamic very basics. I try to keep it as simple as possible.

I think it's good to know, how the Cl, Cm & Cd are acting in general example for the stall model coding.

 :)