LH463
Topic Author
Posts: 68
Joined: Sun Apr 02, 2006 6:51 am

### Mach Kias?

Hey Guys,
I was just wondering if an airplane had to break the sound barrier by passing it on it's KIAS. I know the actuall speed depends on many factors such as temperature, air density etc., but is there any way the sound barrier could be broken by an aircraft (normally incapable) with a tail wind? (Assuming it can withstand the forces)

Thank's,
LH463
Turning final...

pilotpip
Posts: 2830
Joined: Fri Sep 19, 2003 3:26 pm

### RE: Mach Kias?

Winds only affect your groundspeed. Airspeed is only relative to the speed of the relative wind around the aircraft. If the aircraft is in level flight at say, mach .99 and there is a tail wind, it is at mach .99. It will not break the speed of sound because it is traveling at an airspeed that is below the speed of sound.
DMI

viv
Posts: 2953
Joined: Tue May 31, 2005 5:17 pm

### RE: Mach Kias?

 Quoting LH463 (Thread starter):there any way the sound barrier could be broken by an aircraft (normally incapable) with a tail wind

No, because airspeed does not increase in a tailwind (or decrease in a headwind).
Nikon D700, Nikkor 80-400, Fuji X Pro 1, Fujinon 35 f/1.4, Fujinon 18 f/2

bri2k1
Posts: 952
Joined: Sun Dec 19, 2004 4:13 am

### RE: Mach Kias?

 Quoting Viv (Reply 2):No, because airspeed does not increase in a tailwind (or decrease in a headwind).

That's right, and actually, the opposite happens. God forbid I bring out the conveyor belt loonies again, but I hope we can agree on this. If, at some place on the surface of the Earth, the wind blew as fast as the speed of sound in those particular conditions, an observer standing there would experience winds at the speed of sound (not a good idea).

Extending the concept a little, if an airplane was crusing in still air at, say, mach .75, or 75% of the speed of sound in those conditions, and a sudden current of wind came by, aimed directly at the nose of the plane, aligned with the fuselage, at least as fast as 25% of the speed of sound, it would suddenly be flying through the air faster than the speed of sound. Not being designed for it, and not having the power to sustain flight at those speeds, it would experience a violent deceleration. Most planes would probaly sustain significant structural damage. Fortunately, even in turbulent air, it's highly unlikely that winds on Earth will ever change quickly enough in a short enough time to make this happen.
Position and hold

113312
Posts: 647
Joined: Sat Apr 16, 2005 9:09 am

### RE: Mach Kias?

Speed of sound varies with temperature only.

Gsoshutout55
Posts: 118
Joined: Fri Feb 24, 2006 12:13 pm

### RE: Mach Kias?

 Quoting 113312 (Reply 4):Speed of sound varies with temperature only.

god, i hope your kidding. And you claim to be an airline pilot?

XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

### RE: Mach Kias?

]

 Quoting GSOShutout55 (Reply 5):Quoting 113312 (Reply 4): Speed of sound varies with temperature only. god, i hope your kidding. And you claim to be an airline pilot?

Sorry bud, my man is correct. It's a function of temperature only.
Chicks dig winglets.

seanp11
Posts: 281
Joined: Tue Jan 10, 2006 6:16 am

### RE: Mach Kias?

 Quoting XFSUgimpLB41X (Reply 6):Quoting GSOShutout55 (Reply 5): Quoting 113312 (Reply 4): Speed of sound varies with temperature only. god, i hope your kidding. And you claim to be an airline pilot? Sorry bud, my man is correct. It's a function of temperature only.

Perhaps GSO was confused by how m.80 can be around 280 kias at altitude, and is closer to 400 kias closer to the ground.

Woodreau
Posts: 1442
Joined: Mon Sep 24, 2001 6:44 am

### RE: Mach Kias?

 Quoting 113312 (Reply 4):Speed of sound varies with temperature only.

Pressure and salinity too ... oops wrong medium. I see y'all are talking about air not seawater.

But average speed of sound about ~3000kts in seawater - more useless trivia for you guys.
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