Tommy Cookers wrote: ↑
Mon Sep 24, 2018 6:55 pm
the usually seen aircraft con-trails are exhaust condensate not vortical condensate ...
and usually flying is for efficiency operating at a low lift coefficient so giving only weak vortices
btw whoever compiled the F1 rules & stats 1950-59 has slipped up
having shown as 1952-3 F1 rules the F2 rules to which the 1952 & 1953 WDC GPs complied
though iirc those had a 500cc limit for supercharged engines not 750cc as shown
Aircraft Contrails actually have 2-3 definitons, or rather, there are 2-3 different types; one of which is exhaust emissions. These are formed by the water vapour in the exhaust gasses condensing due to the low ambient temperature at altitude and the impurities in the exhaust emissions, such as sulfur compounds, serve as a surface where droplets can then form and then freeze - which produces the contrail.
However, the second type are formed due to decreases in pressure. As a wing generates lift, it causes a vortex to form at the wingtip. The reduction in pressure and temperature across each vortex can cause water to condense and make the cores of the wingtip vortices visible; that is, to form a pressure drop contrail.
One thing you are correct in implying is that pressure-contrails do not happen typically at altitude - which is implied by the line "Aircraft contrails are a familiar sight to anyone who has so much as glanced at the sky" because they are typically seen at lower altitudes where the humidity is much higher - e.g. take off and landing. But it doesn't sound as poetic to say "look at a plane taking off"...
As for the "efficiency" of lift generation vs. the strength of the vortex, at low CLs, your induced drag is lower than at high CLs... So when you are travelling at the necessary speed for level flight (i.e. Lift = Weight), then at a low CL, you are travelling faster and so your velocity curl rate is pushed over a longer axial distance which reduces the strength of the vortex. However, these types are typically visible at low speeds and form due to humidity so depending on weather, you may still see a "strong" core. On some aircraft though, there is a pressure based contrail which forms off the nacelle and is used to keep the flow attached around the pylon for the engines though and that can be seen quite well under, once again, specific atmospheric conditions.
As for the rules and stats, I'll get someone to check that and make a change if required - thanks mate.
I just found an awesome image of contrails and had to share it