# Tag Info

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### Is it dangerous for a supersonic aircraft to fly at exactly Mach 1?

Make sure to read this answer to understand what is special about Mach 1. Pilots regularly report that, approaching Mach 1, the airplane is shaken by oscillating shocks (they don't use that term, ...
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### Could an airliner exceed Mach 1 in a zero-G power dive and safely recover?

There is actually some data (albeit limited) on this scenario: On August 21st 1961 this test was performed in a DC-8. When this test was performed they were supersonic for about 16 seconds which took ...
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### Why are the grid fins on Starship pointy and sharp?

Such design, with hyperbolic leading edges, has been invented by MBDA (Airbus branch for missile systems) represented by BAE Systems (defense contractor), and is described in the European patent 3 599 ...
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### Could an airliner exceed Mach 1 in a zero-G power dive and safely recover?

The TWA Flight 841 accident in 1979 involving a Boeing 727 comes pretty close to your conditions. Not a zero-G dive but an unintended spiral dive starting at 39,000 feet, reaching mach 0.96 at 31,800 ...
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### Why does directional stability decrease at supersonic speeds?

It is a combination of several effects: Aeroelasticity: With the higher forces at high speed, the structure deforms such that the effective flow angle at the tail surface is reduced. The supersonic ...
• 225k
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### Does the sound barrier apply to a silent aircraft?

The sound barrier has nothing to do with the noise the aircraft makes. It has to do with the fact that if it is going fast enough the air can't get out of the way. This creates a shock wave where the ...
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### Does the sound barrier apply to a silent aircraft?

I'll try to keep this really simple, as OP's question leads me to believe they are not familiar with the physics involved. As indicated by others here, the sound barrier is not directly related to ...
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### Why do shockwaves progressively move aft as speed increses?

The answer is deeply rooted in the theory of compressible fluid dynamics, so for a fully satisfactory take on the matter you might want to refer to a textbook on that topic (such as Thompson or ...
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### Why does air density drop when speed nears the Mach 1?

We start with the Laplace equation for the speed of sound: $$a = \sqrt{\frac{\gamma \cdot p}{\rho}}$$ and differentiate and square it: $$a^2 = \frac{\delta p}{\delta\rho}$$ Now we can write: \delta ...
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### Is it dangerous for a supersonic aircraft to fly at exactly Mach 1?

Drag forces grow quickly as you approach the speed of sound, and then fall off somewhat after you are above the speed of sound. This means flying near the speed of sound puts you in a high-drag regime,...
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### Could an airliner exceed Mach 1 in a zero-G power dive and safely recover?

After you break the sound barrier, a shock wave will be generated in front of your main wings and tail wings. Though the design of wings on modern planes may hold that situation and can still generate ...
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### Why do 20-series Learjets have such an extreme susceptibility to mach tuck?

The early series 20 Lears have always had boundary layer separation issues, so much so that any time the wings are removed and reinstalled the aircraft must be test flown. Mach tuck is an issue with ...
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### How to reduce the noise of the supersonic passage(bang)?

Most supersonic aircraft have points where the cross-section suddenly changes, such as the fuselage nose, the wing root leading edge or the wing trailing edge. The points of sudden change produce ...
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### What would the density profile of this shock wave look like, roughly?

The shock observed is effectively the same as the one over a wing. Compression waves are normally considered of infinitesimally small thickness, although due to the non-continuous nature of gases made ...
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### Can a transonic airfoil have two shock waves?

Very Interesting results. I must say I have never before seen such a peculiar case. Yes, theoretically it seems possible to have this situation, but it's difficult to say if this is possible in ...
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### What does account for a high coffin corner of a plane?

The best you can do is to make the wing loading low. Wing aspect ratio helps, too, and if you look at existing designs, it will be similar to that of gliders and certainly higher than that of ...
• 225k

### Is it possible to hear a sonic boom when the aircraft is exactly at Mach one?

No, if standard atmospheric conditions apply. Since speed of sound is proportional to temperature and temperature normally decreases with altitude, the speed of the aircraft at Mach 1 is subsonic in ...
• 225k

### What is the ideal volume distribution for minimization of transonic drag?

Since Drag is proportional to S'', the key is to derive a shape that has a minimum S''. The result is the Sears-Haack body. The Sears–Haack body is the shape with the lowest theoretical wave drag ...
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### Is the highly optimized high subsonic cruise airfoil less safe for higher AOA flight?

The short answer, whales aside, is yes. Such wings, called "supercritical" because the critical Mach# is elevated, tend to suffer from leading edge stall that makes the aircraft's natural stall ...
• 118k

### Why do some Mach trimmers move the elevator?

I think it's because the 9 uses free floating elevators with servo tabs to move them. The columns just move the servo tabs which means the actual input forces are really low and there is feel spring ...
• 118k

### Could an airliner exceed Mach 1 in a zero-G power dive and safely recover?

Could an airliner exceed Mach 1 in a zero-G power dive and safely recover? There is only one answer here and that is NO, especially for the A320 in your example (there are other airliners better ...
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### Is it dangerous for a supersonic aircraft to fly at exactly Mach 1?

Mach buffet precedes mach, and begins in the transonic range. The transonic range does not begin or end at 1.0 M1. It begins typically around .85 and may continue to 1.2 to 1.5. Buffeting may occur ...
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### Why does directional stability decrease at supersonic speeds?

Because: Here you see a fuselage viewed from above. The horizontal line at the right end of the ellipse is the tailfin. On top is a subsonic plane, and at the bottom is a supersonic one. The thin ...
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### Why does the condensation cone disappears when the airplane starts flying supersonic

Condensation occurs when the air accelerates, which is accompanied by drop in pressure and temperature that can push it below the dew point if humidity is high. As explained in What is compressibility ...
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### What are the difficulties in building transonic airliners?

That is because as you approach the transonic regime, the drag on the airframe begins to rise and can reach up to ten times the subsonic drag. after you go supersonic, the drag falls down again- and ...
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### Are there any airliner crashes that can be definitively attributed to Mach tuck?

I've never heard of one, but note that the pitch down effect of Mach tuck starts below Mcrit, and below Mmo for that matter, and airliner trim systems have a "Mach Trim" function to drive the stab to ...
• 118k
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### Why does transonic drag happen?

Airflow around aircraft and especially over wing is not uniform. The lowest transsonic speed is when the airflow at some point of aircraft (usually over wing) goes supersonic. Depending on aircraft, ...
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