Hacker News Reader

Comment by m463 | Hacker News Reader

I wonder if the idea of the balance required for two wheels was an impediment to invention and use.

for example, I think one-wheeled devices / unicycles are crazy and only someone with a lot of time, energy and motivation will to learn to balance and use one.

But nowadays computers make it possible for normal people to use them without as much skill.

We might have a "why did we wait so long for simple one-wheeled transportation?"

---

another analogous musing -- why did we start with main+tail rotor helicopters?

Nowadays 4-rotor quadcopters appeared and have taken over.

View on HN

why did we start with main+tail rotor helicopters? Nowadays 4-rotor quadcopters appeared and have taken over

The quadcopter advantage is in it's mechanical simplicity, but having fewer longer blades is better for aerodynamic efficiency(at the expense of max airspeed). This matters less at RC scale, but at full size, even an all-electric helicopter will likely have more range than a quadcopter with the same batteries.

4 rotors is also a much more difficult “controls” problem. Helicopters actually glide reasonably well if their engine cuts off. They’re not super insanely unstable.

Quadcopters are basically obligate fly-by-wire vehicles which necessitate at least pneumatic PID controllers if not computer chips to fly.

You can make a helicopter work reasonably well a lot earlier in a pre-computer “tech tree” than you can a quadcopter.

A helicopter with a broken engine glides well enough to avoid instantly killing everyone on board if the pilot knows what he's doing. I wouldn't call it "reasonably well".

Here you go - drops slightly slower than a brick. The pilot has to speed up the descent on purpose so that he can use that stored energy to slow it down just before the crash, thus converting the crash into merely a hard landing. https://youtu.be/05_WFvh9ISk

That was a shockingly controlled landing for an unpowered vehicle. Very impressive!

> Here you go - drops slightly slower than a brick.

The glide ratio of a brick, even if it is initially traveling at 80 KIAS is ... 0:1. This is the same glide ratio that an unpowered quadcopter would have. Bell 206B, Robinson R44, and R22 all list their unpowered autorotation glide ratios at 4:1 - that is a mathematically infinite multiplier of performance vs. a brick.

https://robinsonstrapistorprod.blob.core.windows.net/uploads...

The Space Shuttle orbiter was nicknamed “Flying Brick” in its landing configuration by the astronauts and test pilots, because even for a glider, it had the worst maneuverability they had ever experienced, not to mention the highest approach velocity and catastrophic failure modes.

https://en.wikipedia.org/wiki/Shuttle_Training_Aircraft

Upgrade that 'maybe' to 'definitely'. The disc loading on a helicopter is typically much lower than on a quad (excepting crazy designs like the giant human-powered quad) which makes it significantly more efficient for the same overall size.

what works in 100g - 5kg drone does not work for much heavier machines.

- Small UAVs are mainly controlled by varying RPM of each rotor

- Full-scale machines keep ~constant RPM optimal for rotor aerodynamics and change angle of attack for each blade for control (collective and cyclic changes).

With big inertia and no alien materials technology, it isn't possible to apply 'quad' design for your average SAR helicopter.

Also, four points of failure isn't a particularly enticing feature for an already slightly terrifying aircraft if you're actually going to be in it.

There is quadcopter with variable pitch blade.

>another analogous musing -- why did we start with main+tail rotor helicopters?

In fact we started with autogyros.

Also the Fw 61 ("the first successful, practical, and fully controllable helicopter" though I don't know the history in detail) has two equal-size counter-rotating rotors similar to a quadcopter.

Reply on news.ycombinator.com