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I have an airfoil connected to two supporting uprights, and each upright has a load cell to the front and to the back, between the bottom of the uprights and a test mount surface. From this system I would like to attain a decent approximation of the down force of the system subject to an air current.

The thing puzzling me is that I figure it might(?) be possible for the drag forces to impact the readings of the load cell (due, perhaps, to some resulting torque); if there's any merit to that concern, I'm curious how the physics works out such that I could have a reasonably accurate reading of the down force, unperturbed by any lateral/angular forces involved. If not, an explanation as to why that's so would be greatly appreciated.

As an aside, I've only recently made my way through set theory, calculus and linear algebra over the last year, but I haven't had any time to bone up on physics just yet (that's coming up soon!), so it's possible my question is pretty elementary. My apologies if that's so. Also, I suspect there's more physics involved than engineering, which is why I went with the physics exchange - I hope that was reasonable.

At any rate, some pointers would be greatly appreciated, as well as any references to the literature that would apply to this problem.

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  • $\begingroup$ What kind of load cells are they? Will they allow you to measure horizontal (drag) force? $\endgroup$ – Tom B. Mar 24 '18 at 3:09
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Drag will indeed show up as equal and opposite vertical forces (torque) at the front and back load cells at the base of the uprights (and as a horizontal force if you can measure that) The pitching moment of the airfoil itself will also show up as a difference in vertical components from front to back. Fortunately for you, since you are only concerned about total downforce, the drag will cancel out in the vertical direction, so adding the downforces will give you what you want.

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