56 votes

How is it possible for supersonic aircraft to push air out of the way?

The idea that force can only be transferred/propagated at the speed of sound is a simplification. It's a very reasonable simplification, which works in a very wide array of cases, but it's a ...
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33 votes

How is it possible for supersonic aircraft to push air out of the way?

It is only the pressure wave that can propagate at the speed of sound. This means that a molecule of "air" that is ahead of a subsonic aircraft can get pushed out of the way without hitting that ...
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  • 16.6k
30 votes
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Why does this shockwave not touch the body that creates it?

After passing through the shock wave, the air still has to evade the body. If the shock-wave touched the body, the air would have to escape through infinitely thin space at infinitely high pressure ...
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  • 54.1k
10 votes

Why does this shockwave not touch the body that creates it?

In case of an infinestimally thin body in supersonic flow, the disturbances created propogate as Mach waves. However, as the the thickness of the body increases, the flow has to physically turn away ...
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  • 98.6k
9 votes
Accepted

Can a supersonic plane use a subsonic wing if the nosecone shock produces subsonic airflow around the wing?

Normally, the flow speed at the wing is about the same as the speed ahead of the bow shock. Only if the fuselage is still conical and expanding at the wing station would the local flow speed be ...
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8 votes

How is it possible for supersonic aircraft to push air out of the way?

Supersonic aircraft do not push the air out of the way in front of the aircraft. They only push it sideways out of the way after the aircraft has passed the air (for the air beside the aircraft), or ...
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  • 4,353
8 votes
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How is the camera positioned for these plane-to-plane Schlieren images of shock waves?

Where is the camera relative to these target aircraft, and what's behind them? Straight from NASA themselves: NASA flew a B-200, outfitted with an updated imaging system, at around 30,000 feet ...
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  • 31.5k
8 votes
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How high could modern transonic commercial transport designers reasonably push L/D ratios?

First of all, I am sceptical regarding your graph. The Fokker F-28 or the Short 360 are way too good while the Boeing 767 looks poorer than what other sources claim. Size alone helps already by making ...
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7 votes

Why does this shockwave not touch the body that creates it?

Perhaps, at the root of your question, there is a misunderstanding of the nature of a shock wave. A shock wave is a surface, an ensemble of points, where the properties of the gas change ...
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7 votes
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How does the X-59 achieve low-noise supersonic flight?

As of the date of this answer, the X-59 has not yet flown, but according to the designers... The ground noise is expected to be around 60 dB(A), about 1/1000 as loud as current supersonic aircraft. ...
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  • 11.2k
7 votes
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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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6 votes

How does the V22 Osprey manage such high rotor speeds without shock waves?

The Osprey's engines drive the rotors at 412 RPM in heli mode or 333 RPM in forward-flight mode, according to this article. With a rotor radius of 5.8m, that puts the tip velocity at 250m/s, or about ...
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  • 855
5 votes
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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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  • 888
5 votes
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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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  • 197
5 votes
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Can a flow which is initially supersonic, become subsonic without a shock wave?

Yes, it is possible . The shockless transition from supersonic to subsonic. It has been tested both experimentally and numerical solution. Read this AIAA Paper. But in your case I would suggest you ...
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5 votes
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Since shock waves have non-negligible viscosity, why do the normal shock relations ignore friction/viscosity?

Neglecting friction does indeed lead to inaccuracies. Those, however, are small for weak shocks, so using the equations for inviscid shocks gives a good approximation. Especially in the times before ...
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4 votes
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How does a wing mounted jet engine on a supersonic airplane prevent the interference in the flow due to Shock?

Flow conditions are not so different, only the reaction of the flow to an obstacle is. By shaping the intake appropriately, supersonic flow is handled easily, and shocks will be helpful in ...
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4 votes
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What is the difference between a shock wave and an expansion wave?

An adiabatic expansion lowers temperature, an adiabatic compression raises temperature, analogous to the way a refrigerator and an air conditioner work. Or a bicycle pump, it gets quite hot while you'...
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  • 57.8k
4 votes

How is the camera positioned for these plane-to-plane Schlieren images of shock waves?

Supplementary answer: As the question mentions this NASA page shows a diagram of traditional Schlieren photography and it's the idea I had in my head. I assumed you'd need a carefully prepared light ...
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  • 4,556
4 votes
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Could ramjets be implemented on sub/super-sonic aircraft wings due to the shockwaves generated by them?

Regardless of the shape of the wing, ramjets only outperform turbojets at supersonic airspeed. Ramjets work because the speed of the incoming airflow is such that there is no rotating compressor/...
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  • 57.8k
3 votes
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"Fundamental of Aerodynamics" 5th editon, example about oblique shock. Is the author's solution wrong?

Continue reading, I have found the answer. Look at problem 9.3, page 663: And here is the author's solution:
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  • 930
3 votes
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Is high speed buffet possible at supersonic speed?

All pilots who transited into supersonic speed on older designs which were not perfected for transsonic flight reported that suddenly all that shaking and vibrating stopped and flight became smooth ...
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3 votes
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Why does strong shock wave-boundary-layer interaction produce a bubble reattachment?

After the rear shock leg, the subsonic flow inside the boundary layer decelerates further, which causes an expansion of the streamtubes and therefore reattachment. Note that with the presence of the ...
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  • 823
3 votes
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What is primary cause of shock induced separation (shock stall)?

The simplest answer is that a shock wave for a boundary layer means a sharp adverse pressure gradient. You probably know already that adverse pressure gradient will thicken a boundary layer and thick ...
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  • 604
3 votes

Could ramjets be implemented on sub/super-sonic aircraft wings due to the shockwaves generated by them?

Looking at the Wikipedia article on ramjets, we have: Although ramjets have been run as slow as 45 metres per second (160 km/h), below about Mach 0.5 (170 m/s; 610 km/h) they give little thrust and ...
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  • 2,839
2 votes

Why is the flow ahead of a shock wave chaotic?

The wind tunnel design is not providing clean smooth airflow. Turbulence at supersonic speed does not travel upstream so the turbulence must be created by the wind tunnel design.
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  • 1,904
2 votes

How do a narrow airframe and canards keep supersonic shock waves from coalescing?

After a lot of digging around, I found this. ...the main noise-reduction technique is to redesign the aircraft to reshape the acoustic signature. A sonic boom consists of a double bang on the ...
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  • 11.2k
2 votes
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How does a weak shock-wave boundary-layer interaction create wave drag (other than through direct shock losses)?

As you know, wall shear stress $\tau_w$ (and thus friction drag) can be described as: $$ \tau_w = \mu \frac{\partial u}{\partial y} \vert_{y=0} $$ where $\mu$ is the dynamic viscosity of the fluid and ...
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  • 354
2 votes

Do ramjets use variable geometry supersonic inlets?

Why is that the ramjets do not require [variable geometry] to maximize pressure recovery? Turbofans, in aircraft that have variable geometry intakes, such as in an F-111 or F15, operate from ...
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  • 4,353
2 votes

Shock wave on airfoil

With a higher flight velocity (still subsonic), the supersonic pocket on the upper side of the wing starts earlier and takes longer until it collapses into the shock. That is quite normal, as the ...
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