# Outerra forum

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### AuthorTopic: gathering & working airfoil data..  (Read 24952 times)

#### bomber

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##### Re: gathering & working airfoil data..
« Reply #15 on: March 29, 2015, 03:36:33 pm »

Oh more investigation has reveal this....

to generate a lift of 2300lb at 57mph (49.5kn)... the Cl needed is greater than any Cl prediction (in a reasonable reynolds number) by either javafoil or xfoil....and to top it all we know we have a twist in the wing of 1.5 deg at the root to -1.5 at the tip which make it even worse.

So is someone telling porkies here ?
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

#### bomber

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##### Re: gathering & working airfoil data..
« Reply #16 on: March 29, 2015, 06:27:16 pm »

So all I did was adjust the lift modifier to get the correct lift force at the correct speed, and the correct lift to drag of 7.5

So anyone got an idea where all this extra lift that the cesna has over the ask-13 is coming from ?
Could it be fairy dust ?

Simon
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

#### bomber

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##### Re: gathering & working airfoil data..
« Reply #17 on: March 30, 2015, 08:53:56 am »

ok adjusted the drag modifier to give a drag 0.0319 at zero lift...

POH says L/D is 9:1.... we get 8.28 at 10mph wind so I'm happy here

and we have a lift of 1.61 generating the required lbs force at the correct speed..

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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

#### bomber

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##### Re: gathering & working airfoil data..
« Reply #18 on: March 30, 2015, 11:18:40 am »

This is the equivalent whole plane lift n drag for the Ask-13...

Anyone spot the huge elephant in this room ?

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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

#### PytonPago

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• It´s way too complex, dont let me try to explain !
##### Re: gathering & working airfoil data..
« Reply #19 on: March 30, 2015, 12:52:57 pm »

Its just a tiny fox-hole on the hillside ... a proper trench position actually ... someone has a fine soldier on the loose.
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We are still undeveloped as long as we don´t realize, that all our science is still descriptive, and than beyond that description lies a whole new world we just haven´t even started to fully understand.

#### Uriah

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• We do these things not because they are easy. -JFK
##### Re: gathering & working airfoil data..
« Reply #20 on: March 31, 2015, 05:53:29 am »
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#### bomber

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##### Re: gathering & working airfoil data..
« Reply #21 on: March 31, 2015, 08:49:39 am »

Nice article Uriah and validates the use of force normals, thank you very much.

However it doesn't tell the whole story with regards the 2 systems...

I've experimented with both, a year on one, a year on the other and then backwards and forth... and then it dawned on me...
When looking closely at the forces created by the airfoils, force normal system with it's reference to the airframe works best.
When looking closely at the drags, induced, skin and form then the lift/drag system with it reference to the wind frame works best.

However they're mutualy exclusive, you either use one of the other.... not both... even JSBsim manual says so...

And that's why I spent a few years going back and forth..... untill deciding to ignore it and use BOTH systems... because we have a computer not a piece of paper and slide rule.

Simon

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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

#### bomber

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##### Re: gathering & working airfoil data..
« Reply #22 on: March 31, 2015, 04:00:33 pm »

Levi, I don't want to mess with the official 172, so can you knock up an otx, adding these files as per the ask_13...
don't forget to rename the Flight Damage Model file to the name of the plane...

Which reminds me, Devs can we please not have to do that...

For those that fly it whilst I'm down the pub tonight... it's a glide model to demonstrate the aerodynamics... the engine comes when we're happy with this...

Oh and I've not tested it, I like to live dangerously

http://target4today.com/_posted_files_/Cesna_172/Cesna_172.zip
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

#### Levi

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• Posts: 585
##### Re: gathering & working airfoil data..
« Reply #23 on: April 01, 2015, 01:33:36 pm »

Levi, I don't want to mess with the official 172, so can you knock up an otx, adding these files as per the ask_13...
don't forget to rename the Flight Damage Model file to the name of the plane...
The plane is standalone, and installs under my username.
FDM files are located within main package, as I usually do.

Oh and I've not tested it, I like to live dangerously
It works. Though, the steering on ground (when using rudder pedals) is inverted.
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#### Levi

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##### Re: gathering & working airfoil data..
« Reply #24 on: April 01, 2015, 02:14:39 pm »

don't forget to rename the Flight Damage Model file to the name of the plane...

Which reminds me, Devs can we please not have to do that...
Oh, you can actually have any name for your FDM. You'll just have to write that name within the .objdef files, like this:
Code: [Select]
`"physics" : "jsbsim/Flight-Damage-Model", `
And the folder (c172) located in c172/FDM/aircraft, must have the same name as your FDM .xml file.

Code: [Select]
`c172/FDM/aircraft/Flight-Damage-Model/Flight-Damage-Model.xml`
But I still prefer having the FDM named the same as the aircraft...
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#### bomber

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##### Re: gathering & working airfoil data..
« Reply #25 on: April 01, 2015, 02:50:22 pm »

Thanks Levi,

http://target4today.com/_posted_files_/Cesna_172/c172.xml

updated the fdm for the steering, for those interested the nose wheel had a -2 for steering and that's for tail draggers..
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

#### Levi

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• Posts: 585
##### Re: gathering & working airfoil data..
« Reply #26 on: April 02, 2015, 12:37:03 pm »

Here's the updated .OTX (link remains the same): c172(New_FDM).Levi.otx
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