Where can I find an explanation of the various details on vehicle HUDs?

Solution 1:

Here are is an explanation of the Jet and Copter HUDs (via Reddit and Reddit)

F/A 18 Super Hornet: See above full sized.

Mil MI-28 Havoc: See above full sized.

As an additional note, aligning the I-beam with the vertical bit of the crosshair ensures that your rockets will fly to their target. This also works by aligning the 'O' in between the two | | in the Sideslip Indicator (see image above).

Solution 2:

There is really nothing too useful there to be honest. The only extra hud feature I find useful is in the jets the cross-hair circle makes it easy to lead enemy jets with the guns. The HUD is mostly supplemented for realism, but I guess the altitude could be handy...I just use my better judgement while flying.