# Tag Info

Accepted

### The SR-71 flew at 2193 mph. Mathematically, how can this be Mach 3.3?

The SR-71 was only capable of Mach 3.3 flight at altitude. You can see the limitations in the pilot's operating handbook(POH) for the aircraft: At higher altitudes the relative speed of sound is ...
• 101k
Accepted

### What is the reason for changing the speed reference (IAS or Mach number) with altitude?

Aircraft are limited by both air speed (VMO, affects loads on the structures) and Mach (MMO, formation of shock waves resulting in buffet). At low altitudes, the speed of sound is high so an aircraft ...
• 73.4k

### What prevents a Machmeter from being the standard airspeed indicator?

Machmeter-based tachometer would not indicate something between IAS and CAS, it would indicate TAS but for the same¹ instrument and position errors the normal airspeed indicator has. However, ...
• 56.3k

### What prevents a Machmeter from being the standard airspeed indicator?

...Machmeter scale both in knots and Mach numbers The simple answer is that unlike say (MPH vs KTS) the equivalents change with altitude so one scale would have to move. For example at sea level Mach ...
• 101k

• 61.8k

### What's the relationship between mach number and drag force on an airplane?

The plot you show is typical for airplanes which are not designed for supersonic flight. Yes, there is a maximum in the drag coefficient around or slightly above Mach 1, but in a properly designed ...
• 234k
Accepted

### Why do I keep getting different results to an aircraft's turn radius when I plug variables into different calculators and solve on my own?

Units are the root of all evil in most of these situations. The original equation has a constant of 11.26. This would correspond to a Velocity expressed in some particular unit (knots, mph, km/h, m/s, ...
• 51.8k
1 vote

### How do swept back wings delay shock wave

If you are unsure why air will accelerate when flowing over a wing, read this answer first. Now keep in mind that local curvature will determine the amount of acceleration. In a straight wing that ...
• 234k
1 vote

### How do swept back wings delay shock wave

It increases the effective chord, the effective chord line being parallel to the longitudinal axis, whereas the true chord is perpendicular to the spar axis. It sort of tricks the air into thinking a ...
• 132k
1 vote

### What's the relationship between mach number and drag force on an airplane?

The plot you show is actually typical for rockets or missiles. Here's the CD0 for AIM-9 at sea level: As for F-16 and Mirage-2000, you'll find a pretty flat curve above M1.0 as the Cx0 and CD0 (...
• 355

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