There is no such thing as a stupid question - stupid answer maybe, but not the query!
The main reasons for the development of the tandem rotor system, was the ability to counteract torque whilst providing all the power solely to provide lift. A tail rotor uses a considerable amount of power, detracting from the available horsepower for main rotor lift performance.
The designs that evolved coupled a compact airframe with an excellent lifting capability. The drawback, was that in order to achieve both goals, the rotor systems would have to intermesh. In the instance of the Chinook, the rotor system is 60 feet in diameter (no metric crap here!), but the distance between rotor centres is 39.17 feet. The Chinook is hardly a compact helicopter to start with, but if it were to be built with the rotor systems not intermeshing, the distance between rotor centres would have to be at least 60.1 feet. If you now combine all the additional airframe thay you would require (say, 50% stretch) you are starting to look at a massive increase in empty weight, hence payload reduction and useability.
Like most things in life, the result is a compromise between risk, performance and design.
The K-Max is actually quite an efficient design, in so far that it is a compact, efficient little single seat airframe. Generates a lot of lift for that T-53!
There were many other experiments with dual rotor system, the Bristol Belvedere was an interesting machine.
The Russians also built a large number of intermeshing and non-intermeshing tandem designs. The ultimate was the the Mil V-12. If you look at these photo's you will see the physical scale of separating the rotor systems. It takes a lot of horsepower to run one of these!
http://www.duffeyk.freeserve.co.uk/mi-v12.htm
http://www.royfc.com/mi12001107-3.html
Of course, like so many great innovations in the helicopter world, Igor Sikorsky was the leader. Here is Igor's early attempts at solving the problems of helicopter design, forerunner of everything in the rotary field! Don't forget the ABC, Sikorsky's more recent venture into this realm.
http://www.russian.ee/~star/vertigo/sikorsky.html
The Yak-24 kept up the development work;
http://www.russian.ee/~star/vertigo/jak-24-r.html
All the Kamov products are here:
http://www.russian.ee/~star/vertigo/kamov.html
All the Mil's:
http://www.russian.ee/~star/vertigo/mil.html
Not to be outdone, that famous manufacturer of chainsaws McCulloch got in on the act with a couple of small tandems!
http://www.russian.ee/~star/vertigo/jov.html
http://www.pimaair.org/mcc_mc4c.htm
There are many more examples, including a number on the website below. Just another interesting topic relative to overcoming the practicalities of building helicopters.
Lots of credit to whoever put this website together. It is really quite excellent:
http://www.russian.ee/~star/vertigo/helicopters.html
