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So let’s say there’s two aircraft, which are the same, and both are cruising at 28,000FT, the only difference is one plane is doing 260 knots and the other is doing 280 knots. If they both pitched down reaching a vertical speed of -15,000FT/Min at the same exact time, would the aircraft going 280 knots still hit the ground first despite sharing a vertical speed the entire time??

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  • $\begingroup$ The question is too vague. As asked, it seems like a straightforward physics problem, and a trivial one at that (since you've declared that the vertical movement is identical for both aircraft), nothing really to do with aviation. On the other hand you haven't defined "ground". If the "ground" is actually a mountain some distance ahead, the horizontal speed will matter more than vertical, because that defines how soon the aircraft will reach that ground. $\endgroup$ – Peter Duniho Jan 22 at 20:01
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No, both would reach the ground at the same time, although the one with the higher airspeed would go farther before hitting the ground, assuming atmospheric conditions are invariant.

On the other hand, if both aircraft have the same flight path angle, the one with the higher airspeed would have a higher sink rate.

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  • $\begingroup$ Didn't do the math, but 15,000 feet/min is nearly a vertical descent. $\endgroup$ – Ron Beyer Jan 22 at 18:26
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    $\begingroup$ @Ron Beyer Do the math. $a^2 + b^2 = c^2$. Descent angle is closer to 45 degrees. $\endgroup$ – Robert DiGiovanni Jan 22 at 18:59
  • $\begingroup$ @RobertDiGiovanni I'm not sure how you can apply that formula, it's descent rate, not distance. From 28,000 feet at 15,000 feet/min it takes 2 minutes. The descent angle is actually 88 degrees. $\endgroup$ – Ron Beyer Jan 22 at 19:46
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    $\begingroup$ @RonByer The steepest would be near SL with 260KCAS=440ft/s. 15000fpm = 250ft/s. So that gives a descent angle of -30deg. At 28000ft, it's more like -25deg. Still extremely steep indeed. $\endgroup$ – JZYL Jan 22 at 19:55
  • $\begingroup$ @Ron Bayer covert the airspeed to miles per minute (4.5 ish) and the descent rate is around 3 miles per minute. The airspeed is the hypotenuse. Also there is feet per knot conversion. And yes, TAS! Thanks JZYL! $\endgroup$ – Robert DiGiovanni Jan 22 at 23:55

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