why aren’t all helicopters quadcopters?


So – clearly quadcopters are more stable (see all the drones), so why aren’t actual helicopters all quad copters?

In: 5

Drones are much lighter and don’t require as much power to lift up. Personal use drones also don’t go anywhere near as fast as larger scale helicopters. All this is to say that a standard helicopter generally has much more powerful fuel-based engines that cost more money to build, maintain and operate. It is just not practical to build *all* helicopters as quadcopters because of this.

You have to remember that in physics things change along with size. The design which works best for something small will be far worse for something large. Just look at how different the bodies of different sized animals are.

A single large rotor doesn’t have to spin as fast as 4 smaller ones to provide the same amount of lift. Quad copters that need to move significant mass would be extraordinarily loud even by helicopter standards

Four small rotors are also very complicated to control without computer assistance to ensure all the torques and thrust levels are balanced. On a drone with a fancy computer this is easy because the software can tweak the power to each motor thousands of times per second and you have no idea. In the late 1940s none of that existed, you needed to be able to control the aircraft with levels that pushed rods and levers which pushed through a hydraulic system to push on other rods and levers that do the controlling. Helicopters existed and were in combat service for over a decade before the first plane to use electrical (fly by wire) controls

There’s still a lot of industry and experience around building single rotor helicopters so they’re going to keep making them until someone builds the industry and experience to make powerful, cost effective, reliable, and safe quad copters of a usable size.

The biggest advantage of a quadcopter is stability. For a cheap (or expensive) toy, it makes sense to quadruple the parts so users can enjoy it out of the box with little to no training. With a very expensive functional tool, you can expect serious training for the operator and can get the same stability with lower costs of production and maintenance in addition to fewer points of failure.

1) Helicopters have variable pitch. That’s how change direction, speed up, and basically fly. Drone quadcopters don’t. Variable pitch allows the helicopter to autorotate in the event of an engine failure, instead of crash like a drone.

2) Four rotors isn’t four times the redundancy, it’s four times the chance for failure. Quadcopters don’t fly well on 3 rotors.

3) The ‘heavy lifting’ is done by the outer parts of the rotor, because they’re moving faster than the inner part of the rotor. This favors one (CH-53) or two (CH-47) large rotors over four smaller rotors.

4) Likewise, to compensate for the smaller rotor diameter, quadcopter blades spin faster. This has the advantage of helping with retreating blade stall (the retreating blade is also going forward into the relative wind as the aircraft goes faster, until it’s not going fast enough to work). But it also means the advancing blade is going faster and is limited by the speed of sound (blade tips going supersonic causes a host of problems). And the blade has to be stronger (and hence heavier) to compensate for the higher forces that come with higher RPM.