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39 votes
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 ...
Dave's user avatar
  • 101k
23 votes
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 ...
fooot's user avatar
  • 73.4k
16 votes

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, ...
Jan Hudec's user avatar
  • 56.3k
6 votes

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 ...
Dave's user avatar
  • 101k
5 votes

Cruise Mach Number less or more than Critical Mach Number

The critical Mach number $M_{crit}$ is defined as the lowest Mach number at which the airflow over some point over the airfoil reaches supersonic speed, that is, Mach 1. Usually, flying greater than $...
Darjan's user avatar
  • 1,157
4 votes

Would air having an infinite speed of sound be ideal?

I think there's some misconception, and I hope you correct me if I'm wrong, the title is "infinite Mach", but you're saying you want to raise speed of sound to infinity, this means mach no. ...
أحمد صلاح's user avatar
3 votes
Accepted

How can TAS be calculated from indicated temperature and Mach number?

TAS is Mach number ($M_a$) multiplied by the speed of sound ($a$). $$\textrm{TAS}=M_a\cdot a$$ The speed of sound depends on the temperature of the (static) air $T_s$. $$ a = \sqrt{\gamma RT_s}$$ The ...
DeltaLima's user avatar
  • 83.5k
3 votes

Does Indicated Stall speed increase with altitude (Coffin Corner)?

I think part of your confusion comes from mis-interpretation of the amber bands on the PFD. The picture you show looks like it is from a Boeing 777, which has the red barber pole and the amber band ...
Bianfable's user avatar
  • 56.5k
3 votes

How do swept back wings delay shock wave

The key is to minimize how fast the air is going over the wing. Aerodynamics for Naval Aviators has information on this subject in and around page 226. Aerodynamics for Naval Aviators. The ANA will ...
EquipmentOperator's user avatar
3 votes

Would air having an infinite speed of sound be ideal?

Hypothetically, if aerodynamicists had the opportunity to somehow raise the speed of sound in air to an infinite level so that air was no longer compressed, how would this affect aircraft related ...
sophit's user avatar
  • 13.5k
3 votes

Is the Mach number shown by an Air Data Computer considered a "true" Mach number?

Indicated Mach is what your Mach indicator reads during flight. True Mach is basically indicated Mach that has been corrected for pitot-static system position error and instrument error. (Same as the ...
Matt's user avatar
  • 31
2 votes

What prevents a Machmeter from being the standard airspeed indicator?

The needle would move very little at lower airspeeds and would be subject to non-linearity. Velocity follows directly from $p_{total} - p_{static} $, while Mach number is a fraction. From Wikipedia: $...
Koyovis's user avatar
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2 votes

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 ...
Peter Kämpf's user avatar
2 votes
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, ...
Ralph J's user avatar
  • 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 ...
Peter Kämpf's user avatar
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 ...
John K's user avatar
  • 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 (...
LJQCN101's user avatar
  • 355

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