# Tag Info

19

Definition of terms: A shock wave by itself is not a "sonic boom". A sonic boom is an event, produced by the shock(s) passing over something - an observer, a building, the ground. The "boom" is characterized by a rising/falling/rising pressure disturbance called an "N-wave" because the disturbance has the shape of an N when plotted. A model in a supersonic ...

15

Uwe's comment on the question is spot on. The characteristics of the flow through the nozzle depend critically on the pressure ratio - the two pressures being the pressure at the entrance to and exit from the nozzle. Above the critical pressure ratio flow through the nozzle is subsonic and it is not choked at the throat. Below the critical pressure ratio, ...

13

The grid fins are a critical control surface to the returning Falcon 9 first stage, but are only useful during certain parts of the flight after the second-stage has separated. The grid fins provide virtually none of the control authority to the descending stage in the final seconds of the landing process, once the "landing burn" has started. With the ...

13

Yes, it produces a sonic boom. But the shockwave travels in the same direction as the rocket (i.e. up) and doesn't reach the ground.

10

You don't need a "bell-shaped" nozzle for a rocket -- a simple cone (often with an included angle of 30 degrees, it seems) is sufficient. Cones are easier to design (they only have one design parameter, which isn't even that sensitive) and easier to construct (they can be made with the simplest machining methods). For this reason, many early rockets used ...

9

Think about what a sonic boom is. It's the shock wave caused by 'bunching up' of the compression waves of the body, moving through the air. To see this, consider: For a stationary body emitting pressure waves, at any one point in time you only hear the sound emitted at another (slightly older) point in time. However if the body is moving faster than the ...

9

I don't think it's that bad a question that it deserves all the criticism it's gotten. Basic idea, fly really high and as fast as possible, then point towards the Earth and use Earth's gravity to go even faster and escape the Earth. Problem #1. Flying really high doesn't look like your diagram. The highest aircraft, if the Earth is the size of a beach-...

7

The scale model of a vehicle with a SIAD for use, for example, in a ballistic range is made out of steel. This is ok, because the SIAD will not significantly change shape in flight. The shape of a parachute on the other hand changes a great deal in flight, so a rigid model will not represent the behavior even close to correct. Any attempt to make a small ...

6

Skylon's design is, in fact, for a hypersonic SSTO that is partially air-breathing, much as you describe. It has some important differences, though. The first of these is that it does not use a dive to speed up. userLTK's answer explains why using gravity acceleration to get fast enough to get to orbit won't work; briefly, orbit is when you already are ...

3

The answer is much simply presented in the book by John D Anderson - Modern Compressible Flow with historical perspectives. Refer Chapter 5. $$\rho = \mbox{density}$$ a = speed of sound, Ma = Mach number, u = speed of fluid, A = area Area velocity relationship can be deduced from the continuity relationship - \...

3

Excellent question, which took me a moment to figure out. But I'll walk you through the end results. The equation of mass conservation can be written as $$(1)\;\;\; \rho v A=const. ,$$ with the gas mass density $\rho$, the gas velocity $v$ and the cross-sectional area $A$. For our purposes we can recast this into (2)\;\;\;\nabla \ln \rho + \nabla \ln v + \...

2

At the risk of repeating an existing answer or two... You can't take advantage of the gravity of the body you want to escape as a means to make that escape. Earth's gravity gives every object within its reach some amount of potential energy due to that object's mass and distance. The further an object, the greater its potential energy. We are all familiar ...

2

No, to hear a sonic boom, the object must not only be traveling faster than the speed of sound, but also it must be traveling towards you. If an object is moving towards you at less than the speed of sound, then the Doppler effect will cause you to perceive any sound it’s making as being a higher frequency. If it’s moving towards you faster than the speed ...

1

The only answer I can find is a NASA Facts sheet about sonic booms for aircraft "The width of the boom "carpet" beneath the aircraft is about one mile for each 1000 feet of altitude. An aircraft, for example, flying supersonic at 50,000 feet can produce a sonic boom cone about 50 miles wide" Source: https://www.nasa.gov/centers/dryden/pdf/120274main_FS-016-...

1

Signals (like pressure change) can propagate upstream in subsonic flow so the flow ahead of the throat will sense the throat ahead. That is my best explanation. From an equation standpoint I remember from engineering thermodynamics class (I looked the details up): dA/A = -(1-M^2) dV/V where A is crosssectional area, M is Mach number and V is velocity. So ...

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