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What is the purpose of the four square block checkerboard painted on the aft fuselage of Boeing's flight test aircraft? It is either break in markings for fire rescue or some sort of optical measurement for speed, distance associated with flight testing, I believe.

enter image description here

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    $\begingroup$ A picture would help here, would you mind adding one? $\endgroup$ – Ron Beyer Oct 20 '18 at 0:23
  • $\begingroup$ I am looking for a picture, but haven't found one yet. $\endgroup$ – Kim Oct 20 '18 at 16:07
  • $\begingroup$ I found a picture of the LH 737 prototype with this painted on the fuselage. <facebook.com/…> $\endgroup$ – Kim Oct 20 '18 at 16:14
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the checkerboard mark allows accurate indication of the position of the plane using cameras as the plane flies by. by tracking the movement of the checkerboards between frames of a series of camera shots, the plane's speed, roll rate, acceleration, etc. can be measured.

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  • $\begingroup$ A little hairsplitting if you will, but I‘d say these parameters can be calculated rather than measured... great answer though! $\endgroup$ – Cpt Reynolds Oct 20 '18 at 8:28
  • $\begingroup$ indeed, but photogrammetry is a good failsafe in case your telemetry links fail. $\endgroup$ – niels nielsen Oct 20 '18 at 13:02
  • $\begingroup$ Yes, of course! What I mean is that with photogrammetry, you calculate the rates and accelerations rather than measuring them (you measure pixel displacement and then derive test aircraft flight mechanics parameters) $\endgroup$ – Cpt Reynolds Oct 20 '18 at 16:13
  • $\begingroup$ I have added a link to a picture (see above) that shows what I am asking about. I appreciate your answers. Is this still used today, or has it been replaced with telemetry? $\endgroup$ – Kim Oct 20 '18 at 16:19
  • $\begingroup$ @Kim It's not telemetry per se but accelerometers (AHRS) became much smaller, cheaper, and accurate, and GPS became available. Though some test flights still require chase planes, in general its cheaper, easier, and safer to rely on on-board instrumentation. Also in the old days, you'd do photogrammetry by manually measuring the image. Now we have computers that can in real-time correlate natural features on the plane, exactly the same principles as AR apps on your smartphone. $\endgroup$ – user71659 Dec 14 '18 at 3:41

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