GoFast : is the background moving relatively to the movement of the jet ? Or the camera only ?

jarlrmai

Senior Member

MclachlanM

Active Member
Did the calculations for 30seconds in and got 423 knots ocean speed
This doesn't seem that far off the near 400knots the plane is doing and could easily be explained by wind?

Edit: well the speed of ocean and jet don't need to match of course, that's only if the object is directly in the middle.

Minus the speed of the object X 2 if it is in the middle.

I don't think the full diagonal is passing through the camera

Try this in your blender simulation, change the ocean texture to a checkerboard pattern with a known size of squares.

This is my fault sorry,

It turns out it really matters that the two videos are aligned at the right time and my Blender recreation was a bit rough and ready, the wind speed I got from the start of the video does seem to make up for the apparent ground speed, it's probably better if someone who knows how to use blender/unity can double check this.

Wind speed of 150 knots, 170 degrees (checkers are 20m), I think this is very close:


 
This is my fault sorry,

It turns out it really matters that the two videos are aligned at the right time and my Blender recreation was a bit rough and ready, the wind speed I got from the start of the video does seem to make up for the apparent ground speed, it's probably better if someone who knows how to use blender/unity can double check this.

Wind speed of 150 knots, 170 degrees (checkers are 20m), I think this is very close:


Hi! Very good job. Have you tried to recalculate the ground track of the jet with a crosswind of 120 knots?
 

MclachlanM

Active Member
Hi! Very good job. Have you tried to recalculate the ground track of the jet with a crosswind of 120 knots?
Crosswind has an unintuitive effect, the F18 is travelling in the direction of the upper right corner in the video, so sidewinds pull the apparent velocity of the ground to the top and bottom of the video.




If the pilots report later that the wind is travelling 120 knots to the west then it makes sense for the plane to be flying with the wind in GOFAST (the object would also be travelling with the wind and a bit slower as it is at 13,000 feet).

For the purposes of things in air this speed doesn't matter but when looking down, the surface will appear to travel at this speed, working out the speed of the ground at a point where the camera isn't slewing gives us a speed of 150 knots which seems about right and modelling this is consistent with the video so I am happy that the wind is correct here:
Wind speed of 150 knots, 170 degrees (checkers are 20m), I think this is very close:

Your browser is not able to display this video.
Your browser is not able to display this video.
 
Crosswind has an unintuitive effect, the F18 is travelling in the direction of the upper right corner in the video, so sidewinds pull the apparent velocity of the ground to the top and bottom of the video.




If the pilots report later that the wind is travelling 120 knots to the west then it makes sense for the plane to be flying with the wind in GOFAST (the object would also be travelling with the wind and a bit slower as it is at 13,000 feet).

For the purposes of things in air this speed doesn't matter but when looking down, the surface will appear to travel at this speed, working out the speed of the ground at a point where the camera isn't slewing gives us a speed of 150 knots which seems about right and modelling this is consistent with the video so I am happy that the wind is correct here:
Thank You very much.
I was asking you to consider a crosswind situation compared to fighter because this completely changes the parameters to get the video.
gofast_graphic.png
In green the ground track with zero wind, a situation physically not possible.
In red, however, the situation with a crosswind of 120 knots. This is likely very similar to the track recorded on the USS Roosevelt Radar.
The trajectories and viewing angle change completely.
The crosswind situation is the most compatible with the closure rate data acquired by ATFLIR.
By changing the intensity of the wind we will always have different results. The goal is to reach an absolute background speed of no more than 30 knots, i.e. the maximum wind detected by the NOAA surface analysis between 20 and 31 January 2015.
Unless what we see is not the sea but a cloud layer, just like the one visible on GIMBAL and which was constantly present off the coast of Virginia at that time.
 

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