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Old Nov 29, 2014, 12:37 AM
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CG app prophecy

There will come a day when someone will hack a CG app that will spit out the CG of your plane from a top view of the plane, in any scale and in any popular image format.
The app will even adjust the result for biplanes.
True or false?
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Old Nov 29, 2014, 01:58 AM
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Why bother with image formats? Just use the smartphone camera to take a picture of the plans top view or the plane itself.
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Old Nov 29, 2014, 03:33 AM
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jkettu, that's what I mean by image formats, like jpg, bmp, tif, etc. Most photos are jpg and some are bmp.
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Old Nov 29, 2014, 06:22 AM
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The airfoils/profiles of the wing and stabilizers [fore and/or aft] as well as the vertical spacing, plus wing-twist/washout or washin for fwd-sweep!, and which is above/below the other as well as fore/aft spacing between the surfaces .... not to mention biplanes! .... are essential to getting an accurate CG prediction

L
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Old Nov 29, 2014, 08:17 AM
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Take the top view - convert it to a piece of paper - cutout outline of model
fold it into thirds
the fold line at first third is CG
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Old Nov 29, 2014, 08:55 AM
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For a first cut .... that will definitely work


[but likely some others here will get snippy about it]
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Old Nov 29, 2014, 08:59 AM
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In fact what you need is to determine the Neutral point of your aircraft. Than you can decide where to put the CoG in relation with the performances/stability you desire.

Such program/software do exist but you need to have a good 3D model of your aircraft in the right format (for the program/software you use).

Such program/software do not come cheap and, as for everything involving virtual aerodynamic, you need some experience to be able to interpret the results and use the software properly.
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Old Nov 29, 2014, 09:13 AM
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I studied ornithology and origami and saw the obvious relationship, which lead to a deep understanding of the laws concerning flights of fancy---
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Old Nov 29, 2014, 09:48 AM
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yeh, very fancy


Charlie Parker Septet 1946 ~ Ornithology (Take 3) [ AKA Bird Lore ] (3 min 19 sec)
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Old Nov 29, 2014, 09:53 AM
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It's a play on words: Parker somehow wound up with the nickname "Bird" short for "Yardbird", used to play at Birdland*, named after him!. There even used to be signs in NYC saying "Bird Lives!"



* http://en.wikipedia.org/wiki/Birdlan...k_jazz_club%29
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Old Nov 29, 2014, 10:03 AM
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Yeh - I also played alto - gave up the scene before it got me
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Old Nov 29, 2014, 10:17 AM
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One hurdle to overcome is the fact that pictures are distorted by perspective, so you would need to know the camera lens data to compensate for the fisheye effect. The other issue is that the program would need to figure out if a plane is a biplane or if there's other hidden geometry.
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Old Nov 29, 2014, 10:57 AM
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Well, there's software that can read and translate hand writing that's used by the post office. So I suppose just about anything is possible. But as mentioned the picture would need to be taken from directly above the model or plans. Also with plans I don't see how it'll differentiate between the outer line and the structural lines. So it would be a problem and a half to just manage that. A more or less clean 3 view would not be bad though. But a picture of just the plane would be tough. It would likely need some operator input to base the outlining off colours that would be ignored or selected to determine outlines.

And it would not be able to adjust for perspective. So any camera tilt or issues of positioning that distorts the areas and distances would certainly cause an issue. And THAT is something you couldn't work out from one picture. But if you could take a number of pictures of an actual plane and if the software contained some serious photo interpretive software it could "build" a 3D rendering. But it would have to know the actual true focal length of the lens and the image sensor size to do this. Again I suspect that the higher price security and intelligence agencies would have this capability. It's an extension of the old manual method after all. And there is likely versions for us regular folks. But I imagine that such stuff doesn't come cheap.

So will it all come together? Possibly and with care by the person taking the picture. A scan of a plan would be a better option. No risk of camera distortion that way.

Will it happen? I doubt it. It's simply a LOT easier to do some measuring and input the numbers like we have now. Adding on the stuff needed to do this from a photo or scan of a plan would involve some serious software.
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Old Nov 29, 2014, 12:07 PM
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One method I will ALWAYS use on not-too-large totally original designs is to securely tether the plane [loop string securely around fuselage and use tape to hold line on wingtip or wherever to try various "exit points"], then sling plane in a circle around me. Once rough CG is determined, THEN try tethered "on its own" with power to check thrustline and control authority.

All of this is an iterative, sometimes lengthy process, but safer and actually less time-consuming then rebuilding or repairing crash damage.
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Old Nov 29, 2014, 12:07 PM
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What, the actual CG? As opposed to the neutral point?

Wouldn't the app need to know if, say, the back end of the plane was made of lead and the front end of the plane was made of balsa?

Quote:
Originally Posted by djacob7 View Post
There will come a day when someone will hack a CG app that will spit out the CG of your plane from a top view of the plane, in any scale and in any popular image format.
The app will even adjust the result for biplanes.
True or false?
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