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I have read several topics on the manner with two completely different answers, and just want to make sure I get it right.

When slipping to the right in a C172 (right aileron, left rudder), the static port, located on the left of the fuselage, is slightly blocked from the wind, reducing the pressure in the diaphragm, making the airspeed to OVER-read, correct?

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    $\begingroup$ Suggestion: test it and find out and report back. Stabilize in constant pitch attitude, and report on effects of right versus left rudder inputs, using ailerons as needed to keep wings level. $\endgroup$
    – quiet flyer
    Sep 5 at 20:36

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In a slip, the pitot tube will not be directed into the relative wind, and so the pitot pressure will be lower. This will tend to cause the airspeed to read slower than your actual airspeed.

A decrease in static pressure will cause the airspeed read higher than your actual airspeed. Which of these effects will dominate is not something that can be reliably determined from first principles.

The only thing you can really trust in a slip is not to trust your airspeed indicator!

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  • $\begingroup$ You did not address the OP's specific question. MIght there not be a case where the direction of sideslip causes to airspeed indiicator to over-read? Due perhaps to impingement of the airflow upon the static port? $\endgroup$
    – quiet flyer
    Sep 5 at 20:28
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    $\begingroup$ @quietflyer A reduction of the static pressure would cause the airspeed indicator to over-read, as I say in the first sentence of my second paragraph. However, it is accompanied by the tendency to under-read caused by the reduction of pitot pressure. Since these two effects compete with one another it's not clear which wins without actually testing it in a plane (or a wind tunnel/simulation, I suppose). $\endgroup$
    – Chris
    Sep 5 at 21:13

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