"Four times as quiet as a normal 'copter" - what marketing nonsense! This is like a politician saying he is four times less dishonest than another one.

Paris - because she is four times as unintelligent as the normal female celeb.

Sounds good for the urban jungle, especially in black but it's still not a flying car and that's what I want.

Mine's the penguine that got hit by the silent rotor

Ok, I'll take it as a quarter, but which quarter?

The decibel a logarithmic unit, so if I have four times quieter than 8db is it actually 6db or 2db in this context?

White paint is the lightest.

The white colour is just the perfect camouflage for a black chopper. Skynet have detected(calculated) that we are afraid, with reason, of black choppers and have cleverly started to disguise it's newest black choppers (search and destroy hover crafts) with an innocent white.

I recommend terpentine guns to reveal any chopper's true colour.

Sorry you can't have two of them, I'll get my coat.

Well it's dB, but point taken. It can get more complicated when you take into account frequency weighting, where we meatbags hear very high/low frequencies as "quiet" regardless of the dB level.

I would imagine they're not measuring "quietness" in dB - they're probably looking at energy lost due to sound in watts.

Mine's the one with "pedant" on the back

The typical 'throbbing' noise of helicopters is caused by the conflicting airflows from the main and tail rotors. Replace the tail rotor by venting the engine exhaust through directional nozzles instead. No more interference, so all you can hear is a large fan and internal combustion engine (that never shifts gears). Above 300 feet, that's pretty darn hard to hear from the ground.

"disguise it's newest black choppers (search and destroy hover crafts) with an innocent white."

Yes, white's good and everything, but cute pink camouflage choppers might work too, to match this:

http://blog.riflegear.com/archive/2007/12/26/hello-kitty-ar-15---evil-black-rifle-meets-cute-and.aspx

Sorry but would never work. The amount of exhaust from a helicopter is quite low. It's nowhere near the sort of pressure that you see on turbofans/turbojets and so i doubt you'd see much more thrust then your car gets out of its exhaust pipe!

Nice thought, but wont happen.

The exhaust on jet turbine helicopters is quite low energy because they have designed the engine to extract maximum power out of the exhaust gas to drive the blades.

By changing the efficiency of the engine they could get quite energetic exhausts but the problem is that there would be less overall power and more importantly the overall efficiency would drop. Simple mass hot gas flow has about 1/4 of the thrust of the same gas driving a turbine / gearbox / propeller, so you would use 4 times as much fuel for azimuth control with hot gas thrusters.

There is a possibly more efficinet alternative with using a ducted fan driven by the gearbox or perhaps a turbofan element in the basic engine design.

http://www.deheli.ch/Bilder/Notar05.jpg

The hughes NOTAR tail-rotorless helicopter. Definately fitted on the MD500 (I saw it about 10 years ago at Farnborough airshow) and the Explorer. So not only can it be done, but it already has been.

Humbly suggests you checkout the MD Explorer "http://www.mdhelicopters.com/products.php?id=MD_EXPLORER" which doesn't appear to have a tail rotor! The local plod use one for traffic work and I can confirm is the quietest chopper I've ever heard, it's black but they've spoilt the look with a yellow roof :(

Yep. None of those kiddie colours prohibited by California law. We can't have wanted posters of "gang-owned choppers" in every redneck cop stop. They would only confuse and frighten plods everywhere.

It depends on what engines are being used on the helicopter, most of the ones I see are jet engine powered so their exhaust is substantial so maybe that would work.

More important consideration is are we happy about these unmanned helicopters or any plane for that matter flying over populated areas, (not in war zones). I'm a glider pilot and in the UK the CAA has proposed that all light aircraft, gliders included, should carry a Mode S transponder so that collision avoidance systems on commercial aircraft and unmanned aerial vehicles can detect and avoid us when flying in uncontrolled airspace. It's a worrying trend.

Especially worrying for Glider pilots as the equipment costs nearly as much as some gliders, will need much more electrical power. It provides no benefit at all to us so we end up paying to help make Commercial Aviation more profitable.

BTW - Us Brits are some of the best competition glider pilots in the world, judging by the gold medals we win every year (just thought I'd say that :-)

Actually, it's got nothing to do with increasing forward thrust - you don't vent the air backwards, you vent it sideways and down to stop the heli spinning in place

The slap of the rotors comes from the air moving down from the main rotor hitting the air moving across from the tail rotor; it's hard to explain without going into the physics of it, but by replacing the tail rotor with the constant stream of ducted air you do get a much quieter heli.

Several police and Air Ambulance services use either the (McDonnel Douglas Helicopter Co) MD520 or MD92 Explorer as both have the 'NOTAR' - NO TAil Rotor - system and are much quieter than helis with a conventional tail rotor. They are also safer - the air is hot enough to give you a burn if you get too close, but it won't chop your head off as can happen with rotors.

Black heli? Well, there ain't one painted like an air amubulance so...

You mean like the MD 902 explorer? It uses a fan to blow air out of slots on the tail boom to generate anti-torque pressure (supplemented by a little blower on the tai). They use this for the London air ambulance. It flies over my back garden regularly. It does sound distinctly different from other helicopters, but not especially quieter. I expect that the main advantage is that there is one less blade flying about to dismember people when landing in highly populated areas.

Isn't that the better solution all around? Variable speed, pitch, contra rotating main rotors, no tail rotor, quieter, higher forward speed, what's not to like?

"Four times as quiet" makes no sense unless it refers to one-forth the db level of a "normal helicopter" and the loudest possible sound or to the loudest possible sound that a "normal helicopter" generates. And if the latter, the A160T would be 4x as [loud] as a "normal helicopter". It's sad that we have twisted and mangled so badly the English language that it has in so many ways become senseless.