The prototype was first flown in 1981, and I’m sure has been improved since. The design seems to make so much sense, so why aren’t we seeing more of them?
Boeing is currently manufacturing the MD 600N, which is a NOTAR chopper.
I don’t know, so I’ll guess.
Helicopters have been built using Sikorsy’s layout for 60 years. Aircraft makers are incredibly conservative and do not make changes unless they have to. For example, the boxer engine design has been around since before WWII. Flat, horizontally-opposed, air-cooled engines are light and develop sufficient power; why change them? The market is rather small and engines have to be certified (which takes years). Another example is the typical general aviation aircraft. The Cessna 172 was designed in the 1950s and the Piper PA-28 series came out in the 1960s. Again, certification of new designs takes a long time and it enormously expensive. And then there are the lawsuits.
In the late-1970s American aircraft manufacturers were building about 15,000 planes per year. In the 1980s that number dropped to 2,000 or less per year. Until rather recently, aircraft makers were liable for “design flaws” or “manufacturing defects” for every airplane they’ve every made. Theoretically they could be sued if corrosion protection that was not applied to an aircraft made in 1950 was not applied to it, even though the corrosion protection did not exist until years or decades later. So manufacturers had to think twice before changing a successful design, because a design change might result in lawsuits. It’s been said that one-half of the cost of a new aircraft was the cost of insurance the maker had to pay. Congress passed a law in the 1990s that limit such liability to 18 years. (Still, can you imagine if car manufacturers were held to such a standard? If your 15-year-old car was not equipped with airbags, you could sue if you were injured because airbags were not common or required back then, but the automaker didn’t install them.)
So the tail-rotor is a safe, proven design. The tooling is already there. Helicopters are designed to use them. The NOTAR has a different tail boom from the Hughes/MD 500. It uses the “coanda effect” to provide anti-torque. It’s not suited to many or most helicopter designs.
My other guess is that it’s proprietary technology. I presume it’s been patented, and any company that wants to use it would have to pay royalties. Or, if it’s proprietary, Boeing might not want to share it. I’m seeing more and more MD-500 NOTARs in the air, so I’m guessing that they don’t want other companies to cut into their sales.