That's something that we have overlooked in my opinion. I have some new results I'd like to share. Here is my line of reasoning.
1) The movement of Gimbal, relative to the background (clouds), that we see, is mostly
due to Gimbal motion. Parallax is secondary here because the fighter is behind Gimbal, and Gimbal goes away from the fighter. This is a very different situation than GoFast, for which the parallax effect is very important as GoFast is on the side, coming towards the fighter.
2) Because the motion we see is primarily from Gimbal, we can, very roughly, but meaningfully I think, estimate its speed from the time it takes to cross the field of view (FOV). We know it's 0.7 deg. Looking at the cloud features, a rough estimate is that it takes 2 seconds for a cloud "peak" to cross the FOV. Therefore, let's say Gimbal crosses the FOV in 2 seconds. It's not crossing it perpendicularly, but sideway, because it's seen from the back/right. From previous reconstructions, geometrical and also from flight simulations, that angle is at minimum 45deg. Even if it's less, this is only a factor 1.7 (sqrt 2) in the following calculations.
3) In GeoGebra, it's easy to create a cone with a radius that corresponds to the FOV, in function of the distance. For a given distance, the diameter of the cone, divided by the time Gimbal takes to cross it (~2sec), multipled by sqrt(2) (to account for the angle of crossing) gives us a rough speed estimate.
I've made the model here : https://www.geogebra.org/3d/xkxcpncc
The position of Gimbal can be moved, the corresponding distance to the fighter is indicated in Nautical Miles (NM).
The corresponding minimum speed (i.e. perpendicular trajectory) for Gimbal is given.
You'll see that at greater distances, the speed quickly become unrealistic for a plane. At 90 NM (~100 miles), the "distant plane" would have to go at ~5000 km/h.
"Sane" speeds (500-1000 km/h) are only found between 5 and 15Nm, which is consistent with previous estimates for the distance. A larger FOV makes for even greater speeds. I think the angle of crossing of 45deg is an underestimation, is is probably larger than that (see for example the DCS simulation of MclachlanM
in the previous page). So if something the speed is likely underestimated.
Those are rough estimates, but even considering uncertainties along the way, the number I get at large distances are way beyond what is possible for a plane. I see people discussing a rocket in the other thread, would that be a plausible candidate? What is the speed of a rocket ?
Again, if it's a plane, how come its features cannot be seen for such a relatively close distance from the fighter ?
I'll be happy to correct some mistakes I may have made, I'm simply trying to fuel the discussion in a new direction and see if we can learn from it.