Hm, looking at the video a bit more carefully , maybe you are on to something... Would make a lot more sense then dumping fuel

Sort of in agreement. The two "clouds" come from exactly where the exhausts are. A fuel dump would be elsewhere. Between the engines, for example.

Fuel is precious on a fighter. You just do not dump it, simple as that. Drop tanks are a different story, they might need to be released in some cases.

However, that is not a contrail. Contrails do not spin (To my knowledge) and it was too low for a contrail (The MQ-9 wasn't contrailing).

I don't think so. Looking at the video, the vapour trail is narrower than the engine outlet. It looks like a narrow stream of liquid until it's disturbed by the engine wake.

Russian pilots were spooked by suddenly meeting a drone mid-flight (it might as well be stationary compared to their own speed), pulled up hard to avoid a crash, causing the drone to wobble and crash, and in the end nobody is to blame?

@JustACoder contrails definitely spin on multi engine acft, make a question of it here on ASE, and the answers will show that :) Contrailing is related to the relative humidity of exhaust and surrounding air, and it is not unheard of to use techniques/chemicals to prevent the formation of contrails. They are not exactly beneficial to drone opertations...

@Coomie looking at the video on a larger screen, I have to admit I'm glad I left the one percent chance for the fuel. It does seem the starting point of the vapor trail is very narrow... If I get strong enough evidence it actually was fuel, I'll have to admit I was wrong and delete this aswer.

I think you could also safely add to your answer that on jetfighters fuel is dumped from one single outlet and the relevant trail would be a single one.

@Coomie the stream being narrow does not rule out the contrail theory at all! I think this is just the transition from a laminar exit flow of the exhaust gases to becoming turbulent in the wake, hence the sudden broadening of the contrail.

I have never see a contrail starting so narrow and so close to an engine. But then again, my contrail experience is limited to mostly civil aircraft. I have seen fuel gushing out of wing tip tank vents during zero-gravity flights, and the cloud effect is similar to what can be seen in the video.

@U_flow Where would a laminar flow get there? At these scales?

@VladimirFГероямслава yes that is true. Perhaps another type of transition then? I am no expert in these kind of aerodynamics. What do you think?

@U_flow I think it is turbulent everywhere,but there can be a transition to an area with more intensive turbulence and with vortexes of larger dimensions. I do not know about contrail/fuel because I do not know enough about jet engines and do not know whether it is, for example, possible to get the fuel from the afterburner fuel nozzles without igniting it.

Note that there are no contrails visible from the wingtips, etc.

@MikeB but I believe that is normal. The contrail originates from the engines, because moisture is condensing on the particles of the engine exhaust

I meant to say vortices. Not 100% related, but also pre-empting anyone suggesting that. Note the way that the effect switches on instantly, rather than gradually appearing - that is not 'natural' - there was clearly a transition of some sort that started it.

Hard to say, I go back and forth. According to the media, the US-Military claims that it was a fuel dump. However it does not look like a fuel dump.

@U_flow I think it indeed fuel coming from the afterburner, as I have guessed, but did not know for sure. See, eg.g., metabunk.org/threads/…