Is an aircraft technically flying Mach 1 with a strong tailwind?

[z.khalid]

Probably a silly question.
Say an aircraft is doing Mach .85
LSS is 661 knots in MSL.
This decreases with increasing altitude.

Technically pilots are flying (with strong winds) more than the speed of sound?

Please excuse my ignorance if I'm missing something here.
Thanks!

[appfo09]

Good Question !

You can give us some clues. I have an answer in mind but it might sound wrong or stupid so first I would like to here some opinions !

[Lord Spandex Masher]

Define local speed of sound and you have your answer.

[Private_flyer]

You have a groundspeed greater than that of the speed of sound, correct.

However, you are not supersonic.

For speed of sound and figuring out if you are supersonic or if the airflow over any part of the aircraft is supersonic the only thing that matters is the relative speed of the aircraft/part of the aircraft and the air. The ground has nothing to do with it all. So while your GS is great than LSS it has no significant impact on the operation.

[Dairyground]

Agreed, locally the aircraft is subsonic. However, air at lower levels will probably be moving at much les than the M0.15 in which our hypothetical aircraft is travelling.

So if the disturbance caused by the aircraft reaches the ground it will be propagated at a speed greater than the local speed of sound. So a shockwave should form somewhere between the aircraft and the ground. I suspect that at the distance where this is likely to happen the disturbance will be so attenuated that the phenomenon is not easily observable.

But can it occur and has it been observed?

[Higher for hire]

Dairyground,

I dare to disagree.

So if the disturbance caused by the aircraft reaches the ground it will be propagated at a speed greater than the local speed of sound. So a shockwave should form somewhere between the aircraft and the ground.It seems to me like you are mixing two completely different things up here. Let me try to get this straight although it's a bit difficult to explain without a picture. A shockwave or "disturbance" effectively is nothing else than a soundwave and can never travel faster than the local speed of sound because the speed at which such a wave is traveling itself defines the speed of sound. If an aeroplane flies with Mach 0,85 there is no sonic boom whatsoever, neither at altitude nor on the ground regardless of how high the groundspeed may be.

As it concerns supersonic aircraft there is a common misconception regarding the traveling speed of the wavefront along the ground. If a fighter aircraft flies with lets say Mach 3.0 then it produces a shockwave in the shape of the "Mach cone". This shockwave travels vertically from the aircraft to the ground at sonic speed (because it actually is a soundwave, see above). The intersection of the Mach cone with the ground of course is moving horizontally with the ground speed of the aircraft, in this case around Mach 3.0 - that's why an observer on the ground can get the impression that there is a blastwave moving along the earth's surface at supersonic speed. In fact the shockwave is hitting the observer from above not head on like a bomb blast for instance.

Hope this makes it a bit clearer.

[sevenstrokeroll]

you are technically exceeding MACH ONE when your airspeed indicator/machmeter is exceeding mach one.

you are going fast, congratulations...but the air around the plane )or speed probes( is not supersonic. you are reading .85 mach...you aren't making a sonic boom


if you are civilian. there are few ways to exceed mach one. concord, concordski, DC8 on one flight over edwards, and a few lucky ride alongs in military planes are it.