Active Noise Reduction Whisper Mode on Apache AH-64 and newer Stealth Choppers!

originally posted by: playswithmachines
Yes i'm well aware of the state of electronics in '82, and would think that the silent mode was mostly shaped blades, rear pitch etc, but then the electronics we see & what the military have, are worlds apart. The early processors were developed for guiding early ICBM's and it's amazing what you can do with just 256Kb of code.

I recently got me some mil-spec SMD chips, which can be used in space, one day soon i hope to get round to testing them in that environment

The cockpit door on the Cocorde was bulletproof, they were obviously thinking ahead....

THAT is an interesting fact about the Concorde.
I did NOT know about it having bulletproof cockpit doors!

a reply to: StargateSG7

CEDAR

originally posted by: aholic
a reply to: StargateSG7

CEDAR

are you talking about this:

www.cedar-audio.com...

The only thing I can say is that as you have
correctly pointed out previously is the SIZE
and response time of any transducer(s) required
to counteract noise levels from choppers
such as the AH-64 during flight if using
phase-shifting.

MY GUESS is that a hemispherical transducer
MIGHT be able to be mounted on the forward
camera pod on the AH-64 Longbow OR it might
be able to be on a vision/radar pod located
ABOVE the blades.

a reply to: StargateSG7

The things is, attacking the noise they way you're stating, by removing the pressure gradient in the air, (ala bose) you'd effectively be removing the lift from the helicopter. By canceling out even 30 to 90 degrees of the compression wave you'd reduce the efficiency of the blades by roughly the same amount. To completely remove the sound, well, the helo would go nowhere.

In other words, think of two blades, counter rotating, creating equal exacting opposite pressure against each other precisely simultaneously. That's what you'd need to silence the rarefaction effect. But then of course your helicopter wouldn't move.

We depend on the downward force of the air to lift the bird up. Cancellation of those waves would severely mess with that.

So what do we do? We angle the noise away from our target. Basically upwards or to the side and upwards. Look carefully at the tail of the Comanche. Blade spacing is also crucial. If you're an audio engineer you'll understand harmonics and even the slight difference in the spread of the rotors results in a different "timbre" of copter. White and broadband noise blends easily into the atmosphere very well, so preventing these obvious harmonics has been a project of ours as of late. Hope that helps you out.