It depends on what you are trying to do.
Usually sheet-metal specular surfaces benefit from large light sources or reflectors with smaller light sources added to emphasize specific areas. A large softbox might work well for you with several images taken and blended. Light from overhead usually looks a bit more natural unless you are going after that spotlight from the tower at night kind of look.
I once shot a polished metal plane using a large white van as a reflector to bounce light on the metalwork.
Essentially you might consider the soft light as fill and the hard light for local emphasis.
When you say that softboxes tend to grey-down the paint, do you mean that large reflections on the paint are an issue?
I would treat this as essentially four subjects.
the prop, the engine inside the cowling, the red paint, and the rest of the sheet-metal.
Each wants a bit different lighting.
-bob
Thanks, Bob. Your suggestions give me a few things to try.
Re the angle, this is a large tail dragger so the upward tilt is natural perspective and some bottom lighting helps accentuate it. What I am trying to do is to float the paint and the engine in low key monochrome metal.
Yes, when I use reflectors to light the metal, they tend to locate into areas as light gray blocks because they are small relative to the subject. However, the hangar ceiling (30' up) is white, and long exposures on LF film can use that to light aluminum fairly well. Sadly, I find it is too dim with digital and my relatively small lights. I'll rent some bigger lights and try the ceiling.
I was being lazy by lighting too much at once. I will try to just reflect for the metal, then use the polarized directs for the paint, engine and prop. Isolate and then combine.