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Old Sep 26, 2012, 12:11 AM
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Spitfire Airfoil question

Hi, I would like some opinions on using the original NACA 2213 and 2209 in a 1/6th scale MK XIV including the washout +2 (root), -0.5 deg (tip). (wingspan 1,87 m, root chord 42 cm, and about 6,5 kg). I have seen one or two commercial models using these airfoils or similar in 1/4 scale, but Im not sure what is used in 1/6 scale versions.

Any advice/experience on this is welcome!
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Old Sep 26, 2012, 04:00 AM
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Those foils are semi symmetrical, nothing fancy that I can see.
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Old Sep 26, 2012, 08:44 AM
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Use it - It is a workable configuration.
In that size tho -the weight of the finished model is of far more importance than minute washout .
building an exact replica of that shape in wood is a labor of love
I once figured out how to do it as a foam core -also a lot of work setting up the twist and bow in the foam block.
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Old Sep 26, 2012, 10:03 AM
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I'm too lazy to do 'scale', but I do love my Spit -

Spitfire 5 (5 min 11 sec)
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Old Sep 26, 2012, 10:09 AM
agnotology
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The old NACA 4 series airfoils are based on the Clark Y/Goe 398 thickness form, which works pretty well at model scales in most of the NACA variations. The 2213 and 2209 should be good at the size you are contemplating.

Those pointy tips on the Spit mean the Re is very low out there, particularly at model sizes. That was a problem with the real thing at high altitude, hence the later versions "clipped" the low Reynolds Number tips for better performance, and fewer tip stall problems. The clipped wing versions would be a bit better at model sizes too.

Kevin
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Old Sep 26, 2012, 11:02 AM
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Quote:
Originally Posted by eflightray View Post
I'm too lazy to do 'scale', but I do love my Spit -

http://www.youtube.com/watch?v=qS5wJ0Wa_w4
That is a great model- I have a small one I am setting up
at 6 ft it is obviously a good size for fun flying performance
My scale Dalotel /Bucker are also larger models (80" spans) - makes flying more fun
I am using 10 cell Hacker setups -with 20x14 " props
What power setup did you select?
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Old Sep 26, 2012, 01:17 PM
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I think I "gotcha" on this one Kevin. The clipped wing Spits were done for added roll rate and a little more speed at low altitudes. They later came up with extended tips for the photo recon Spits that were flown at high altitudes to add a little wing area. The books on the Spitfire history are pretty consistent on the reasons for those mods.

But that aside with our models and the low Reynolds numbers at the tips an extra degree of washout would not be a bad idea at all. And as a free flighter I'm also in agreement with the "Light is Right, and Lighter is Righter" school of thought as well.
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Old Sep 26, 2012, 01:45 PM
An itch?. Scratch build.
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South Wales U.K.
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[QUOTE=richard hanson;22839206]That is a great model- I have a small one I am setting up
at 6 ft it is obviously a good size for fun flying performance
My scale Dalotel /Bucker are also larger models (80" spans) - makes flying more fun
I am using 10 cell Hacker setups -with 20x14 " props
What power setup did you select?[/QUOTE]

Motor - BL4030 385kv
Prop - APCe 16" x 10"
Lipo - 6s 4400mAh

But then the flying weight is 7Lb - 2oz, (3.23Kg).

My build thread - http://www.rcgroups.com/forums/showthread.php?t=1592598
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Old Sep 26, 2012, 01:52 PM
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[QUOTE=eflightray;22840612]
Quote:
Originally Posted by richard hanson View Post
That is a great model- I have a small one I am setting up
at 6 ft it is obviously a good size for fun flying performance
My scale Dalotel /Bucker are also larger models (80" spans) - makes flying more fun
I am using 10 cell Hacker setups -with 20x14 " props
What power setup did you select?[/QUOTE]

Motor - BL4030 385kv
Prop - APCe 16" x 10"
Lipo - 6s 4400mAh

But then the flying weight is 7Lb - 2oz, (3.23Kg).

My build thread - http://www.rcgroups.com/forums/showthread.php?t=1592598
Looks like a good combo-plenty of punch off the line - The response of a well setup electric really beats th e IC setups with the small screaming propellers
My Dalotel literally explodes into the air. Prior power was with a ST2300 on tuned exhaust and 18x8 props- this is far better .
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Old Sep 26, 2012, 02:00 PM
agnotology
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Quote:
Originally Posted by BMatthews View Post
I think I "gotcha" on this one Kevin. The clipped wing Spits were done for added roll rate and a little more speed at low altitudes. They later came up with extended tips for the photo recon Spits that were flown at high altitudes to add a little wing area. The books on the Spitfire history are pretty consistent on the reasons for those mods.

But that aside with our models and the low Reynolds numbers at the tips an extra degree of washout would not be a bad idea at all. And as a free flighter I'm also in agreement with the "Light is Right, and Lighter is Righter" school of thought as well.
You're right Bruce. They were clipped just for roll rate to keep up with the 109. The high altitude ones had even pointier tips, but more wing area. The low-altitude version doesn't seem to always have clipped wings:

http://spitfiresite.com/2010/04/conc...g-types.html/2

Only the British would build an elliptical wing in war time, when it was an elliptical span loading you want not an elliptical planform. And it turns out elliptical is not the best span loading shape for minimum induced drag either, if you don't assume a planar wake like they did back in the '30s to keep the math doable.

Kevin
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Old Sep 26, 2012, 02:52 PM
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IIRC the "clipped and cropped" Spits were done following evaluation of MkV's vs Fw190's, which were found to be both faster and superior in roll rate. The clipping was a sort of "stop gap" to try to narrow the margin until the MkIV was introduced. Roll rate was much improved apparently, but thats about all.

The "modification" for low altitude was really down to the smaller but higher boost supercharger fitted which was aimed at increased performance at low level and initial climb rate.

Just for what its worth, the "high altitude" MkVII had some rather horrible looking extended wingtips;

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Old Sep 26, 2012, 03:20 PM
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I believe that the additional roll rate was meant to exceed rather than just match that of the BF109 and FW190. The Merlin engined Spitfires were limited to positive G loads, and it was relatively common for a German fighter being chased in a turn to just pitch the nose down (outside the turn) and hit the rudder inside the turn to go in a fast vertical dive. The Spitfire could not chase in this maneuver, the float carburetors would run dry, so the pilot had to roll inverted and pull towards the diving fighter, losing distance and aim in the process.
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