You need a "<" block for the speed. In the left side of that, you put the "(velocity Surface)length", in the right side you put the speed. Then, that whole thing (the filled < block) is put into the "and" block (which side doesn't matter here). And in the other side, you put the "not(misc Grounded)".

3 mistakes:
1. Where you entered "Fuel Tank", you need the id of that fuel tank. Click on the fuel tank in the designer and open its properties. In "Additional Settings", you can find its id.
2. "Activated" just activates it. Click on "Activated" and choose "Explode" instead.
3. The blue part in the "Wait until..." block is a bit wrong. Make sure it looks exactly like the one in the picture I sent you before.

Pictures

Where to find the part id?

How the blue part should look

I can't see the picture (I assume there is one...). Can you send me the link?
Edit: Can see it now

@TheVizzyLucky you mean this?