What are the effects on airspeed measurements, if the pitot tubes were installed right on the engine covers of an aircraft instead of being on the nose. Would the reading be false? If so, would the reading be underestimated or overestimated and why?
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asked Dec 17, 2017 at 9:53
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$\begingroup$ Related, maybe duplicate: Which air stream pressure / speed is measured by the pitot? $\endgroup$– minsCommented Dec 17, 2017 at 18:57
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There is a very good reason to install pitot tubes in a place with relatively constant environmental circumstances: calibration.
When installed at around the nose of the aircraft, the pitot always have a good view of the airflow, at all angles of attack and of sideslip. These parameters do distort the pressure reading, that is why during aircraft development the prototype tows a flying pitot tube and compares measurements. These measurement sets are used for calibration.
If it was installed on the engine covers, not only the aircraft state but also the engine state would have influence on the reading. A nightmare to calibrate, and prone to unforeseen errors for instance if a fan blade breaks off and the wobbling fan causes an airstream situation that was not accounted for.
Best to use the prime location: the nose.
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1$\begingroup$ On a related note, all of the GA aircraft that I am familiar with have the pitot tube located about the midpoint of the wing. If you look at the calibration tables you can see they provide an accurate reading in normal flight, but give a a misleading reading when flaps and slower speeds (resulting in higher angles of attack) upset the airflow. $\endgroup$– JScarryCommented Dec 17, 2017 at 18:05
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$\begingroup$ @JScarry Are the readings too low, or one way or the other? $\endgroup$– user7241Commented Dec 17, 2017 at 19:09
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$\begingroup$ There was a picture that showed pressure differences along the length of an aircraft posted somewhere on this site, which showed there is a couple of good locations for the sensors where the differences are small and one is a bit behind the nose. I have unfortunately forgotten suitable search terms that would find it. $\endgroup$ Commented Dec 17, 2017 at 19:09
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$\begingroup$ @JanHudec Do you mean static or total pressure? $\endgroup$– user7241Commented Dec 17, 2017 at 19:13
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$\begingroup$ @jjack, I think it was static. Total remains the same, doesn't it? $\endgroup$ Commented Dec 17, 2017 at 19:30