Sometimes they are painted in alternating bands of red and white, so that from above, when the blades are rotating, they give the illusion of a bullseye pattern. Other times I have seen helicopter blades that look as if one blade were painted a different color than the others (often white, while the others are dark. This looks really odd to me in flight, as one blade is very visible… makes it look as if the other blades were missing!).
Is there a reason for this, or is the blade color left to the whim of the guy with the paint brush?
I have a 1’ prop on a model airboat that’s black with white tips, so it doesn’t become invisible and end up with someone trying to insert fingers through it. I’d imagine the heli rotors are that colour for a similar reason.
Is there no way the rotor blades could be painted so that they look relatively innocent while stationary but once spinning reveal a “hidden” image? For example, a pair of boobies, or a similarly creative logo.
I’m guessing that if it could be done it would’ve been done already. Okay then, you know those clocks where you twang a plastic arm back and forth and the LEDs light up in the exact sequence necessary to spell out the time, which seems to float uncannily before you? Couldn’t they do that? With LEDs on chopper rotor blades? To produce the station logo on a news chopper, say?
It’d look great in an advert. Everybody’d be like “whoah”.
There are a few technical reasons why they don’t, but no reason why they couldn’t. First, you would have to transmit power from the fixed fram to the rotating frame. This is not so easy. Remember, if you have wire going into the blades when the rotor rotates the wire will wrap around the shaft (the pendulum you describe oscillates instead of rotating). This can be overcome with a slipring though. Second, you would have to build the lights into the stucture and replacements would be extraordinarily difficult. Much of the strength of a blade comes from its skin (in torsion) so putting holes in it, while it does happen on occasion, is avoided.
So, it is an expensive and tricky prospect that hasn’t been seen to be worth the cost. Ironically, my research requires doing everything I just described to make the helicopter less noticeable (noisy) rather than more noticeable.
Oh, and as for the first part and “revealing hidden images” you could accomplish it two ways. 1) you could use the same kind of LED technology we just talked about or 2) you would have to have strobe lights illuminating the blades timed just right to reveal the image.
flight mentions some of the technical difficulties of applying this idea to helicopter blades, but apart from that, yes it can be done - there are a number of such devices already in production - one in fact that provides a large disc-shaped full-colour VDU by means of rows of bright LEDs on rotary arms. There is a web page with some video footage somewhere on this, but I can’t find it.
A few years ago, someone came up with a scheme to display a text image (sponsor name, of course) on the rotating wheels of racecars in the Champ car series. Same basic concept. I think they used LEDs.
