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Wing Inertia - what is it?

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Old 12-30-2018, 06:05 PM
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tailskid
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Default Wing Inertia - what is it?

Model Aviation's latest issue on page 40 and following was an article that used the term "wing Inertia" as the opposite force from lift. I have never heard that term before, so can anyone help me understand that concept?
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Old 12-30-2018, 08:20 PM
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Inertia is not a force.
There are only forces that are related to the natural inertia of a solid body or fluid.

Copied from
https://en.wikipedia.org/wiki/Inertia

"In common usage, the term "inertia" may refer to an object's "amount of resistance to change in velocity" (which is quantified by its mass), or sometimes to its momentum, depending on the context. The term "inertia" is more properly understood as shorthand for "the principle of inertia" as described by Newton in his First Law of Motion: an object not subject to any net external force moves at a constant velocity. Thus, an object will continue moving at its current velocity until some force causes its speed or direction to change."
"​​​​​​​Another form of inertia is rotational inertia (→ moment of inertia), the property that a rotating rigid body maintains its state of uniform rotational motion. Its angular momentum is unchanged, unless an external torque is applied; this is also called conservation of angular momentum."

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Old 12-31-2018, 11:40 AM
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.....an article that used the term "wing Inertia" as the opposite force from lift.
I haven't read that article but the way you wrote your part of the post in quotes doesn't make sense. The inertia of the wing is not directly related to the lift of the wing. And it's not accurate to say that inertia is the opposite of lift.

Both light and heavy wings will make the same lift if of the same size and same angle of attack. But the heavy wing has more "inertia" that resists changes in rolling. So it takes more control input to force a heavy wing into a given roll rate or to stop the rolling compared to a light wing. And a heavy wing will tend to not be as affected by turbulence than a lighter wing. By the same token though when a heavy wing IS disturbed it will require more rolling force to correct the disturbance.
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Old 12-31-2018, 03:11 PM
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I will try to post a pic
Attached Thumbnails Click image for larger version

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Old 01-01-2019, 09:40 AM
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Originally Posted by tailskid View Post
I will try to post a pic
The small fonts are non-legible.
Could you add some context?
Why several schematics showing different force distributions?
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Old 01-01-2019, 01:09 PM
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Originally Posted by tailskid View Post
Model Aviation's latest issue on page 40 and following was an article that used the term "wing Inertia" as the opposite force from lift. I have never heard that term before, so can anyone help me understand that concept?
I would check the author of said article and avoid any of his advice.
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Old 01-02-2019, 09:28 AM
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The author appears to know his subject. The problem is that he has attempted to condense a number of college level aero engineering courses into a short magazine article. I fear the only people who will follow what he's saying are engineers who have already taken all the courses themselves.
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Old 01-02-2019, 12:54 PM
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I don't get that magazine so have not read the article. But the diagrams showing the wing's lift acting against the wing's inertia is rather odd. For static conditions everyone else labels those arrows as either "aircraft weight" or "aircraft mass" with the idea that gravity works on the mass to produce what we call "weight". So unless the article is talking about the effects of control inputs and how the wing's inertia due to its mass affects the rolling inputs I sort of wonder about the use of that term in what seems to be the context of the diagrams given the static case picture at the top of the stack. Perhaps if we could read the small print, which is totally unreadable in the picture, the use of the term in this situation might make sense.
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Old 01-17-2019, 08:35 PM
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I read that article also - had to reread it 2-3 times to figure out why he used the word Inertia. I believe he was incorrect. I believe he was talking about the weight of the wing, which makes more sense to me. Inertia is not measured in units of force, so it cannot act against Lift.

So reread the article, and just insert wing weight in place of wing inertia. I agree with OTRCMAN's conclusion, about the author having to condense many details into a simplified explanation. Using the term inertia confused things.

Added: I also presume this to be wing weight and not aircraft weight. Why? Because if one uses his diagram and want to use those numbers to calculate wing bending loads at the wing/fuselage intersection, wing weight would be opposing lift. I would typically leave that entire term (wing weight) out. It's probably a magnitude (or more) less than the lift, and will provide you a more conservative answer.

Last edited by Ron S; 01-17-2019 at 08:40 PM. Reason: another detail added
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Old 01-17-2019, 09:57 PM
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Thank you! I will re-read it and see if I can comprehend it now.
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Old 01-18-2019, 02:46 PM
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If I may butt in and confuse things ...

I believe the author is referring to the inertia that develops during vertical acceleration. It is additive to weight (when pushing upward and visa-versa). That is inertia and impacts the design as the author states.

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Old Yesterday, 08:43 AM
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Typical cring-worthy MA News article by amateur "engineer". I wish this publication would vet these authors better.
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