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AoA sensor tab

Here is an Angle of Attack (AoA) sensor I took from here. If you are interested to know the AoA detail, just click the link. You may see what is inside it. But not sure what airplane's AoA sensor it was, he didn't mentioned it, but he said from Soviets' airplane. And my question is, why is the trailing edge is not smooth and gradually reduce the tip, not just like wings trailing edge? I mean, in the trailing edge there will be curl or eddy's current. Why didn't it make symmetrical between the leading edge and its trailing edge so it will smoothly release the air?

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  • $\begingroup$ It's probably more accurate that way, and the drag penalty is trivial. But as to why it is more accurate that way-- ?? $\endgroup$ Mar 3 at 18:13

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From a couple of patents it seems it's a preferred shapeexample:

enter image description here

In cross-section, the vane 4 preferably has a wedge shape as shown in FIG. 3 with a narrow or knife-like leading edge.

But why is it preferred?

A 1971 paper on AOA sensor design references a 1967 paper that compared various shapes, which says the single wedge shape is inferior but remains popular due to "vague intuitive reasoning," citing a 1935 work that I'm yet to find. Also a streamlined shape would have bad characteristics because a streamlined shape "is meant to diminish aerodynamic action" at low angles of attack.

So, a streamlined shape is not good, a flat plate is better, and the wedge shape is popular but not for any particularly good reason, and supposedly works well enough.

Also from the 1971 paper, the drag force is negligible and "does not appear in the equation of vane response."

Much google-fu later, another research undertaken by NASA (1976) tested various flat plates of various aspect ratios (among other shapes), with no mention of the cross section. Oscillation damping according to that report is a function of arm length, and is independent of airspeed.


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    $\begingroup$ +1 A flat plate is easily bent. The triangular profile is stiffer and is in equilibrium with two balanced non-zero aerodynamic forces. $\endgroup$
    – Jim
    Mar 4 at 12:33
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    $\begingroup$ I can't prove it but I think the wedge is less susceptible to oscillations. An airfoil would oscillate around the equilibrium position much more than a wedge does. $\endgroup$ Mar 4 at 20:19
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    $\begingroup$ @PeterKämpf: I found a NASA paper – that wasn't easy; the basic keywords of this topic bring everything up but AOA vanes(!) – which you may be able to glean something from; see post update. $\endgroup$
    – user14897
    Mar 6 at 11:58
  • $\begingroup$ @ymb1, thank you for your explanation even still no firm answer, but at least I now understand about it. $\endgroup$ Mar 16 at 1:45
  • $\begingroup$ @PeterKämpf thank you for your info. It is also make sense. $\endgroup$ Mar 16 at 1:46
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The shape seems to be a combination of a wedge and a parachute, which would adjust rapidly to a change in airflow and have structural strength.

A cone has 10 times more drag than an airfoil, and, importantly, a sharp leading edge that will respond instantly to a change in airflow.

The wedge/drag combination minimizes reading lag from inertial acceleration, allowing for heavier and stronger construction. It looks like a meat cleaver, and will likely last as long too. This would be an important consideration flying through frozen precipitation, such as hail.

A slight "boat tailing" or rounding of the trailing edge, along with the mass of the vane, would render reading fluctuations from trailing edge turbulence much less than the "steering" effect of drag and the leading edge "wedge". In short, the design is rugged and reliably works.

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  • $\begingroup$ Notice where the "pivot point" is compared with the US Patent 5,438,865 $\endgroup$ Mar 4 at 17:16

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