# Tag Info

66

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, though, they speak of buffeting) and once the Mach meter needle crosses the 1, the airplane becomes calm and flight smooth again. Since the flow speed around the ...

44

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 a lot of planning to pull off. You first need to climb higher than the plane typically does to have enough altitude to pull this off, then make sure you ...

22

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 3 599 442 A1 filed on July 2018: The curve helps reducing drag, especially at supersonic velocities, an important factor for missiles and rockets, for which fuel is ...

16

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 feet, becoming a 90 degree nose-down dive at 29,000 feet with total loss of control authority. With speed brakes ineffective, the pilot extended the landing ...

15

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 lift curve slope of the tail surface decreases with Mach while that of the fuselage stays roughly constant, so with higher Mach the tail contribution to ...

10

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 aircraft is pushing the air aside. A shock wave is where the speed of the air transitions from faster than sound to slower than sound and involves the release ...

7

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 noise, but rather to the nature of sound itself: Sound is just a pressure wave moving through the air. In turn, the speed of sound is the speed at which a ...

7

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 Shapiro). I will try to give a qualitative explanation. For our discussion here, let's consider a shockwave as the way to abruptly slow down a supersonic flow and ...

6

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, where you are putting work into the flow as shock waves are trying to establish themselves at various points on the airframe. Unless your airframe is ...

6

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 some lift (which is impossible for traditional wings, leading to a fatal stall), the control surfaces on your main wings and tail wings will nearly lose their ...

5

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 all aircraft capable of trans-sonic flight, but on the early Lears this is apparently exacerbated by the susceptibility to boundary layer separation from the ...

5

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 sharp changes in air pressure, i.e. loud sonic booms. Concorde was one example. By designing the plane's cross-section to vary smoothly from end to end, the ...

5

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 of particles, this normally makes the shock on the same order of magnitude as the mean free path of a gas molecule (See here for the values at different ...

5

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 reality or not. I found another similar behavior mentioned here: One of the three aerofoils has dual shock. It's difficult to say whether it's a physically correct ...

5

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 airliners or GA airplanes. This answer covers the characteristics which make a high altitude possible and, besides wing loading, mentions the factor $\text{Mach}^2 \... 4 No, if standard atmospheric conditions apply. Since speed of sound is proportional to temperature and temperature normally decreases with altitude, the speed of the aircraft at Mach 1 is subsonic in warmer, lower air. This means also that the Mach shock will diffuse and be audible on the ground either as a protracted rumble or not at all, depending on the ... 4 Since Drag is proportional to S'', the key is to derive a shape that has a minimum S''. The result is the Sears-Haack body. The Sears–Haack body is the shape with the lowest theoretical wave drag in supersonic flow, for a given body length and given volume. The area is given by:$\$ S(x) = \frac {16V}{3L\pi}[4x(1-x)]^{3/2} = \pi R_\text{max}^2[4x(1-x)]^{...

4

That's because Bernoulli's principle breaks down at and above supersonic velocities. In the subsonic realm, when an atom is sped up, it doesn't have much time to spend pushing around a fixed place (it passes by that place quickly). In doing so, the static pressure drops as the speed increases. And in doing so, the neighboring atoms, who are also not doing ...

4

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 behaviour dangerous. These airplanes typically require stick pushers (as @Peter Kampf mentions in this answer, the 737, even the later ones that got redesigned ...

4

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 unit in the system. For mach trim they just have a servo motor that applies a little pull to the column via the feel spring unit, and the rod extends to tell ...

4

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 suited to tolerate higher transonic speeds). Yes, it's possible to recover from such a condition, but nothing about it would be safe. Recovering from this ...

4

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 at any point within that range. Mach is not a point that is reached uniformly by the entire aircraft. This is to say, mach airflow will be reached at some ...

4

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 lines are pressure, the thick ones are forces, and the arrows show flow direction and magnitude. As you can see, at subsonic speeds suction is more dominant, ...

4

The rearward shifting center of pressure in the transonic regime is the culprit, which messes with the balance, though there seems to be workarounds: [...] the rearward shift in center of pressure at transonic speeds has made the problem of achieving balanced hinge moments throughout the speed range difficult. Such was the case for the horn-balanced, flap-...

3

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 this makes the transonic regime the worst place to operate a plane from a fuel burn standpoint. So you either stay subsonic, operating below the drag rise point, ...

3

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 counteract it. Fortunately, in the speed range of a commercial airliner, the amount of tuck is modest and it's not really a controlability issue, just an ...

3

They are unrelated definitions. Mmo is set by the designer with input from actual flight testing, Mmo is a maximum safe speed and is only concerned with practical operation and structural integrity. Mach divergence is a physics phenomena. Mmo can be much lower or higher than the Mach divergence from one aircraft to the next. Mmo has a similar purpose to Vne ...

3

The displacement effect causes the flow around a thick body to speed up more than around an equivalent but thinner body. The thicker body pushes the air aside and around itself more, causing the flow to accelerate relative to the vehicle and to become supersonic at a lower flight Mach number. Wing sweep has a similar effect, as only the orthogonal speed ...

3

Concorde afterburners were reducing overall fuel consumption. To understand why there is a special drag penalty around Mach 1, please read this answer. Now to your graphs in the question body. The first one with the steep drag peak at Mach 1 is for a straight wing which never was designed to fly trans- or supersonically. You do get such results, but only if ...

2

Not only does it produce a sonic boom at Mach 1, it will be the loudest boom that that particular aircraft can produce. Image source In the picture, 4 is the shok wave. The one at M1 is vertical, and has all the concentrated pressure differential in it. An aircraft flying at supersonic speeds forms two shock cones, one at the nose and one at the tail, with ...

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