If I may anticipate another question:
Why have intermeshing rotors, with their difficulties involving slope landings and danger of approaching the aircraft when the rotors are turning, when these problems are alleviated in a tandem-rotor design that does not require tilting the rotors and, indeed, tend to have the rotors mounted very high?
IANA Aeronautical Engineer, but I’ll offer this non-expert theory: Tandem-rotor helicopters such as the CH-46 Sea Knight and the CH-47 Chinook have a wider CG range than helicopters that have their lift rotor(s) at the CG point. This makes them a little less problematic to load, and also allows for a ramp aft. It also makes them long.
Intermeshing-rotor aircraft like the HH-43 Huskie and the K-MAX (K-1200) do not have the CG range of the Boeing/Vertol offerings, and do not have the interior volume. They are, however, more compact. Given that their mission is air rescue and firefighting, the smaller design can get into places the larger helicopters can’t.
One thing a helicopter pilot has to be careful of is the tail rotor. In confined areas it is easy to knock it against something. This would be suboptimal. Break the tail rotor, and you’re no longer counteracting torque and you start spinning like a top. The intermeshing-rotor design alleviates this problem. The MD 520N, MD 600, and MD Explorer use the NOTAR (NO TAil Rotor) system to reduce the danger of getting the tail into the trees. The MD Explorer has a maximum payload of about 2,500 pounds, less the occupants. I think the HH-43 had a maximum payload capacity of around 4,000 pounds, but I’m not sure. I don’t know how much of the difference in payload is a function of the size of the helicopters, or the efficiency of using all of the power for lift vs. using some of the power to counteract torque.
In any case, ISTM that the intermeshing-rotor design was better suited for rescue operations than tandem-rotor designs, and that they are safer in confined areas since they do not have tail rotors. So why don’t we see more of them? I’m guessing because aerial rescue and firefighting are pretty narrow niches, and the more conventional designs perform other missions just as well or better.