Being able to visualize doesn't mean being able to visualize everything you've ever seen perfectly. I have friends who work on helicopters (technical work behind the scenes, engineering stuffs), some who could draw a detailed helicopter (happen to be excellent at technical drawing) and some who couldn't (like me, lousy artists). And if you're not familiar with the object, it will be even harder to draw it accurately (even if you are a good artist).

No, my drawing would be quite awful either way. With a picture for reference, it might be more "accurate" in the sense of discrete details, like say it has two blades while my imagined one had four, but I wouldn't be any better at drawing the relative dimensions or shape.

In this scenario, I happened to visualize (rather accurately, after checking) an AH-64. Not some abstract helicopter concept.

I'm someone who can copy a picture or scene in front of me to near photo-realism level of detail, but usually makes cartoon-like pictures without a reference. I can visualize 3-D Tetris blocks in my head and rotate them at will, and read off information (like, if letters were assigned to the faces of the blocks, I could spin the whole chunk around and read off according to instructions). I think the main difference here is due to two factors: 1. Time investment, and behind that, 2. Contextual demands. With a reference, one may feel more _expected_ to produce a high-fidelity drawing, and take the appropriate time. But if someone simply asks, "Draw a horse", I would usually try to make a basic outline, and not worry too much about the details. The difference between a photo-realistic drawing, and one that is like a child's, is tens of hours of focused work, because reality is very easy to picture for many people, but reproducing that level of detail requires a lot of pencil-strokes.