What altitude does mach# become meaningless?
#1
Gets Weekends Off
Thread Starter
Joined APC: Sep 2017
Posts: 617
What altitude does mach# become meaningless?
Just watched the launch of SpaceX and it got me wondering? What altitude does one have to reach in order for mach # to become meaningless? Is it a sudden thing, or gradual?
#2
Gets Weekends Off
Joined APC: Jul 2015
Position: MD-88 FO
Posts: 1,558
I’d say once you leave the atmosphere completely. Sound doesn’t travel in the vacuum of space so there would be no Mach number.
#3
Meaningless in what respect? In terms of using external control surfaces? More a function of air density than actual Mach number. The higher you go the more irrelevant Mach is.
The NF-104 had rocket thrusters because it went high enough the rudder and ailerons ceased to work.
https://youtu.be/TwpJ7fIDmCI
It was used when you went over 75,000 feet IIRC. Without them it was kind of like running out of speed in a rolling uphill scissors only more so. You could move the controls but the aircraft was basically in ballistic flight because the density of the air flowing over the control surfaces was inadequate to provide any meaningful control.
The RCS starts about 45 seconds in to the video.
The NF-104 had rocket thrusters because it went high enough the rudder and ailerons ceased to work.
https://youtu.be/TwpJ7fIDmCI
It was used when you went over 75,000 feet IIRC. Without them it was kind of like running out of speed in a rolling uphill scissors only more so. You could move the controls but the aircraft was basically in ballistic flight because the density of the air flowing over the control surfaces was inadequate to provide any meaningful control.
The RCS starts about 45 seconds in to the video.
#4
On re-entry, the shuttle started measuring mach at M 25. Nope, didn't forget the decimal.
#5
Gets Weekends Off
Thread Starter
Joined APC: Sep 2017
Posts: 617
I'd love to know what IAS M25 is during reentry!
#6
#8
#9
Line Holder
Joined APC: Aug 2008
Position: MD-11 CA
Posts: 65
The max q condition is the point when an aerospace vehicle's atmospheric flight reaches maximum dynamic pressure. This is a significant factor in the design of such vehicles because the aerodynamic structural load on them is proportional to dynamic pressure. This may impose limits on the vehicle's flight envelope.
Thread
Thread Starter
Forum
Replies
Last Post