Ninthace here are some answers that might fit:
1. Firstly, this is not really an airship as you would normally think of. The Thermo-Skyship (or Thermoplan) that the Russians built uses bleed air, heated to up to 1200 deg C, to supplement normal ballonettes full of helium to create a significant amount of buoyancy. Just like the Hybrid Air Vehicle Airlander, they create more lift in forward flight by the shape of the hull as a lifting body (plenty of examples of that). Vertical flight is augmented by vectored thrust by rotating the jet turbines, and as the Thermo-Skyship weighs nearly at ‘lighter than air’ then less thrust is needed for vertical lift. Once lifted it transitions to horizontal flight by a fixed engine at the rear (with thrust vectoring nozzles) and rotating the lift jets to the horizontal giving it at 150kts-200kts forward speed (or maybe more depending on the design). To generate that near to negative bouyancy in flight then the engines at close to idle may produce enough heat to keep the hot air flowing into the lifting body shape making appear to hover (as per the YouTube video above).
2. As stated, they were experimenting with rigid structures by using light-gauge alloy plating instead of normal airship farbric/rubber skins. Research it, rigid airship structures are a thing and oddly enough Thermo-Skyship and Thermoplan used such. Also, look at the shape in the 1990 photo - it is seriously faceted - the same techniques to make it low observable to radar as used on the earlier stealth aircraft of the time.
3. Look at the weather in the photo. It looks like a fairly low cloud base. So it was either flying low level beneath it - which would make it suddenly appear to an observer on the ground - or it it was flying above the cloud and had a malfunction that saw it drop, very slowly due to its partial negative bouyancy through the cloud into view. Now, the approach speed of a Hunter is around 130-135 kts, so flying around slow speed would be possible (obviously a Harrier could go slower, but if it is a Harrier it is more likely a GR3 given the timeline).
4. Where did it go after the picture? Maybe back to VMC on top? Maybe to West Freugh, maybe to BAe Warton or the Wren Skyship company had set up on Jurby on the Isle of Man from 1982 (they even built a big airship sized hangar there). At the time of the photo Jurby Army Trg Camp was still MOD and the TA used its domestic accommodation from time to time. It’s fairly quiet at Jurby on the north of the Isle of Man, so that is possible.
I agree, this could be a “Surgeon’s Photo” equivalent of Nessie, but from what I understand many poured over it for years. To me it seems more plausible that someone spotted a compartmented research aircraft on camera on that day in 1990. There are many things that still have “kept their lid on” from the Cold War (or the end of it) and the technology is certainly feasible, if only to compare it to the Russian (that started as Soviet) Thermoplan in the other video. The observer sees this object, the shock of seeing something so unusual that means their brain fills in the gaps of ‘what they want to see’, then you get a story about some UFO type thing. Brains are good at giving things to believe on recollection!
