Well, the vapour cone appears when the forming shockwave causes the conditions right behind it to go below the dew point, which causes water vapour to condense into cloud droplets.
Basically, the air pressure in the shock front is quite high, and immediately behind it it gets lower - because it's a shockwave, it doesn't only have a high-pressure zone, but also a low-pressure zone behind it). When the partial pressure of water vapour remains constant but total pressure drops, that means the relative humidity increases - and if it goes over 100% there is a chance of condensation occurring, if suitable nucleation points are available.
It is essentially same phenomenon as wing tip vortices - or, for that matter, vapour clouds appearing on top of aircraft's wings when pulling high g's. It is dependant on the relative humidity of the air, and the degree of pressure reduction by the passing object. The higher the pressure differential, the more likely it is to bring humidity to over 100% and cause condensation.
But it is very much affected by atmospheric conditions. For example flying in very dry air - such as over a desert - would be unlikely cause any visible condensation, while if you're flying in humid air such as over ocean or maybe right below low-hanging clouds, just flying through the air may trigger wingtip vortices and pulling some angle of attack will likely cause clouds to form over your wings as you pass through the humid air. Likewise, approaching speed of sound in these conditions can lead to very stable vapour cloud forming even as you approach the trans-sonic flight regime where shockwave starts to form, and as long as the conditions are right, the water keeps condensing and then vapourizing as air passes your aircraft.
Actually it would probably be very simple to make this effect dependant on map parametres.
The way I would do it is by making a simple equation approximating whether the conditions for vapour cloud are right. It would need to have a table of relative humidity values for maps, or it could use a "default" value if no value for that particular map is supplied.
Weather could affect humidity - for example, rain or thunderstorm would cause relative humidity to shoot close to 100% while clear weather over desert would probably have humidity closer to zero.
After that it would be fairly simple to make an approximation for calculating the speed at which a vapour cloud can exist at a particular map and weather.
In fact, same calculations could be applied to the angle of attack at which wing tip vortices appear. It would be very, very awesome to adjust that effect so that even flying straight and level could cause those vortices to happen if weather conditions are right. Additionally, planes that use the "over-wing-cloud" effect (like that new VTOL Yak) would also benefit from this...
It's unfortunate that I don't have time or skills to make it myself, but if anyone is interested in trying to implement this, I would be more than happy to offer consultation on how the thermodynamics of phase transitions work in these kinds of situations. While this might seem like total over-simulation, I find small things like this incredibly beneficial for immersion.
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Topic: Sonic Boom Vapor Effect? (Read 5047 times)
