13
$\begingroup$

This question applies to aircraft being tested, presumably within a certification program.

I've seen what looks like either a ball or "shuttlecock" at the end of a tether attached to the top/rear extremity of an aircraft's vertical fin. An example can be seen toward the end of this video.

What is its purpose? Is is part of or does it contain any instrumentation, or is it there to provide direct visual indication of something - such as trailing airflow patterns?

$\endgroup$
11
$\begingroup$

That is a static pressure line. The "shuttlecock" device on the end pulls the line out behind the aircraft, where it can get a more accurate pressure reading, away from the air flowing around the aircraft that affects the regular pitot-static system. It will also be more accurate during flight conditions that normal aircraft rarely experience, but need to be accurately analyzed during testing.

Static pressure thingy
Cropped from this image

Static pressure has an effect on the performance of the aircraft, so during testing that is one value they want to measure accurately during flights. Once testing is complete there is no longer a need for that information, and the regular pitot-static system takes the measurements needed.

The line can be seen in this photo, and in this video, you can see the reel inside the rear of the aircraft that is used to pull in the line when it is not in use.

$\endgroup$
  • 1
    $\begingroup$ I've seen high-performance aircraft (e.g. jet fighters) fitted with long forward-pointing spikes during testing. I presume they are for the same purpose? If so, what would call for a spike vs a trailing line? $\endgroup$ – Anthony X Apr 19 '15 at 21:56
  • 3
    $\begingroup$ @AnthonyX Yeah, similar purpose, but not identical. The spike is for measuring pitot or impact pressure; the shuttlecock is for static. $\endgroup$ – egid Apr 19 '15 at 22:32
  • $\begingroup$ Oh OK I thought a spike would have had both pitot and static ports. $\endgroup$ – Anthony X Apr 21 '15 at 2:10
  • 1
    $\begingroup$ @AnthonyX The pitot boom or YAPS boom (the spike) does have both pitot and static ports. As seen here: aerosonic.com/products/flight-test-equipment $\endgroup$ – Mark Jones Jr. Jan 13 '18 at 13:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.