I am interested in developing a realistic cockpit HUD; the kind you find on fighter aircraft. Sadly, I’ve no real life experience with one, and photo’s aren’t really helping me understand the projection involved. I’ve played Apollo 11 VR experience and in the docking section of that there’s a HUD which looks like its located at a fixed position in cockpit space, but it is only visible through the HUD glass. Is this the way a real HUD appears, and if so, how would I do that in UE? I want to be able to look at the same point from a different angle, not through the HUD glass and not have the graphic floating in space. Hope you know what I mean…
This might be the sort of thing you are talking about?
Perhaps if you can link a video of what you mean we may be able to help more 
It was actually difficult to find a video which really captures it.
First, try the beginning of that one… note the parallax involved. The green display (which is what I want to recreate) appears to hang in the air several feet outside the cockpit, towards the nose. But it is only visible through the glass part of the display system, if you move your head to the side, you can see around the glass and that there is nothing out in space on front of you. But when you return your head to the central position you can again see the info appears to be shown on a flat, fixed plane out in front, but only visible through the combiner glass
Also this following video at about 50secs in, once again, the green text and markers appear to be hanging stationary out on front of the cockpit (over his sofa) but when you move sideways you can see around the hud and there is nothing there in reality.
And if it helps, exactly what I do NOT want to have:
In this video you can see they have faked the hud by actually having it out on front (on the main display). This is unrealistic. To look around the projection glass and not have the green stuff magically out in space is very important to me.
In a typical game I would do that the same way, as collimator sight. Get your HUD rendered to texture, and use it in HUD material. Offset the coordinates to achieve close to infinite parallax. I’m not sure about caveeats in VR, but should be pretty much same, provided that parallax offset is the same for both eyes. What gozu linked pretty much covers it.
I am unable to get bump offset to do this. The image trivially looks like it’s displayed through the object, but when you move around it doesn’t quite work, for instance, if you move closer or further away, the image gets compressed on the horizontal (circles become () shaped). There is also some weird parallax when moving side to side.
This may be due to me not calculating coordinates correctly, but if so, I need an example where the HUD texture is just very plainly stationary in space, with the material acting as a gateway or portal through which you can see the HUD, from all angles and distances. The provided example using bump offset contains many issues with the perspective, and I havent even started in VR yet 