3
$\begingroup$

Some of the last words from the doomed Challenger crew were "reading 486," which the Boston Globe describes as a routine air speed callout.

Would this be vehicle speed relative to the air, or would it be the speed of the air itself? What units would the speed be in?

http://archive.boston.com/news/nation/articles/1986/07/29/transcript_from_the_challenger_tape/

$\endgroup$
4
  • $\begingroup$ Thanks @RussellBorogove! Good to know! Metric airspeed would be my first guess if I'd done the metric conversion. Would love to know if it was something else though. $\endgroup$
    – user36480
    Jan 25 '21 at 8:40
  • 1
    $\begingroup$ Indicated air speed in knots is a good candidate as well. Mach 1.5 at 35kft should read about 485kts. $\endgroup$
    – asdfex
    Jan 25 '21 at 10:25
  • 1
    $\begingroup$ Actually, it's EAS, equivalent airspeed taking compressibility of air into account. Don't have a source for this... Link: aerospaceweb.org/design/scripts/atmosphere $\endgroup$
    – asdfex
    Jan 25 '21 at 13:16
  • $\begingroup$ Y'all should write these up as answers... $\endgroup$ Jan 25 '21 at 13:36
6
$\begingroup$
  • The units are knots, the parameter is Equivalent Airspeed (EAS). Equivalent Airspeed is the speed you'd have to be flying at sea level standard conditions to give your current dynamic pressure.
  • Back in the steam gauge era of the shuttle cockpit, the crew had a tapemeter showing them EAS (red arrow, ignore green box from previous answer)

enter image description here

Thanks to user asdfex who in a comment linked to a cool web calculator for these parameters. I put Mach 1.5 and 35000 ft into that, and got this pretty-close result. The dynamic pressure's a bit high but they were calling values out in round numbers and time marches on since they made the call.

enter image description here

Sources:

$\endgroup$

Your Answer

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