Australian built Hoverbike prepares for takeoff | Hacker News Reader

Australian built Hoverbike prepares for takeoff

gizmag.com

94 pointsyock43 comments

On the one hand, do want. On the other hand, if I remember correctly the only people that survived the Endor speeder bike chase were Jedi. On the other other hand, maybe this would finally fix the "drunk driving" problem, one way or another.

It's been a while since I've seen RotJ, but I believe an Ewok survived his ride, too.

It's a damn shame all the Ewoks perished after the Death Star explosion poisoned their planet.

Depends how you define "shame".

That reminds me of one my favorite moments in all of the video games I have played: the deeply satisfying noise Ewoks made when you shot them in Star Wars Battlefront II.

Were you hoping for it to happen before?

It is well known that some Tagalog (language of the Philippines) was spoken by the Ewoks. No doubt the surviving Ewok was familiar with Manila traffic...

Bad places to use a speeder bike:

1. In a dense forest

Good places to use a speeder bike:

1. Most other places

The Empire was not big on picking the right tool for the right job.

Using a speeder bike in a forest is fine if you drive at a safe and comfortable speed. It's when chasing jedi that things go sour.

You will have to become a Jedi.

I was unconvinced, until I read this bit:

Possible applications include aerial cattle mustering

Now I have a new dream job: hoverbike cowboy.

Large farms in Australia use trail bikes and helicopters to muster cattle already.

For refernce -- Anna Creek Station is slightly larger than Vermont or Isreal. http://en.wikipedia.org/wiki/Anna_Creek_station

Looking at http://www.gizmag.com/hoverbike/18813/picture/135534/ , I'd like to see the protective grille extend over the entire front fan duct, with holes small enough that not even your hands can get through. Suppose you have a small collision with an object, which could throw you over the handlebars and into the front propeller...

I'd like to see one that's not a first-shot prototype :-)

Curious why they decided to only put an apparently safety cage over part of the propellers, that's fine if you don't fall off and never wreck, but I could easily see a mishap exposing a limb to the unprotected region.

In the article he states that he will be fully covering the rotors.

"The propellers, which are currently largely exposed, will also be fully covered in a mesh to ensure limbs don't get too near the blades."

It's too bad he couldn't have an simply automatic grid at low speeds and once going the grid pulls or rotates out of the way for better efficiency.

Actually a rotating grid may work using the air as its triggering force, once the air speeds up some sort of venturi force enables/disables a safety mesh across the opening.

What about hair?

Saves the cost for a haircut?

"...there will be room for a computer override of sorts to stop amateur pilots tipping over"

I don't know. I still think there's too much of a risk in the whole thing being top heavy due to the blades being below the rider. Envisioning being at 5,000 ft. and all of the sudden looking at the world upside down while rocketing to the ground.

Most high-performance combat aircraft these days are rather aerodynamically unstable and only stay in the air because their computers are constantly correcting, and they do it all with thirty-year-old technology. Plus, remember those quadrotor drones. This thing will only crash if its computer does, and the government is going to force them to make their software so bulletproof that that's not going to happen.

…and by the time that software is so bulletproof, this technology will be 30 years old, too.

That is a bit of an exaggeration, but with modern designs, you need wind tunnel data, you have to program a simulator, so that you can test control software without crashing a zillion expensive hardware systems, you need ejection seats and an array of test pilots trained in a flight simulator that behaves exactly like the hardware is thought to behave, etc.

The advantage here is that you could program the software so that it always stays far, far away from danger zones. With fighter aircraft, that is not an option. However, if you do that, the thing will not sell.

True, but this is also several orders of magnitude simpler than a modern combat aircraft. It has vastly simpler dynamics, it doesn't have to deal with control surfaces, it doesn't have to be stable with irregular patches of supersonic flow on its wings, and so on. It'll probably only take three or six years, I bet.

How does it work - can both rotors be adjusted by computer? In which dimensions?

Just wondering if it would be an interesting project to try to create a drone with two rotors instead of the current crop with four. Might be a nice playground for genetic algorithms.

Then again, of course there are already helicopters. Why do these drones need four rotors anyway? Because it is that much easier to stabilize?

The rotors are fixed. My guess with this is that each fan has a blade running forward and backward underneath it that can be rotated by a computer (thrust vectoring: [1]). You can exert a torque on the vehicle by pushing some of the thrust to the left or right instead of straight down. You can exert a torque forward or backward by adjusting the power going to the forward and backward rotors. So, turning left means vectoring forward thrust to the right and vectoring backward thrust to to the left, giving you a net CCW torque. Sliding left means vectoring both thrusts to the right, accelerating you sideways. Forward and backward are handled by increasing and decreasing power to the fans.

The quadrotor drones are easier to control than helicopters because they don't need any control surfaces at all. You can exert a torque in any direction by adjusting the power to the rotors. Need to go forward? More power to the back, less power in front; the front of the drone dips and the thing drifts forward. Controlling the power to each engine is trivial and the dynamics are easy, so the math is pretty easy to do.

[1]: http://en.wikipedia.org/wiki/Thrust_vectoring

Having the center of mass under the blades is fundamental to helicopter stability. There's no mention of how he made this bike stable. I'm guessing, he didn't. Thinks he can work out the bugs by testing. It will work as well as software that's been 'tested to correctness' - after a lot of crashes and hacks, it will limp along.

This is only true for teetering rotor heads (eg: Bell, Robinson) where the fuselage hangs freely by the mast from the centre of the rotor disk. (Under -ve G the rotor and fuselage don't stay nicely aligned, and mast bumping happens - not good).

If there is a rigid/semirigid rotor head like on models, then there is no problem having the center of mass above the rotor. I have sometimes found models to be more stable and perform better when flying inverted.

For soemthing like this 'bike' - the thrust vector rotates with the vehicle - it will stay lined up with the CoG. Like rockets - it may appear unstable to have the motor at the bottom, but it is actually stable.

> If there is a rigid/semirigid rotor head like on [sic] models

Like on what models?

Not sic. I believe he was referring to model helicopters, not a specific model of helicopter.

It's a cool idea but I expect it will have a serious dead man zone between about 40 - 200ft altitude. In that range you're too low to use a parachute but too high to survive a crash.

This didn't work in the 50s:

http://www.aviastar.org/helicopters_eng/bensen_b-10.php

but it may work today with fly-by-wire

I like the concept but, can we replace a huge propeller with three or four inline and directionable small propellers for better stability?

You get less thrust that way.

Also worse efficiency, more complexity, more expense, and more things to go wrong.

And, since this is already being steered by a computer-controlled vectored thrust system, giving it more fans won't make it any more stable in the first place. This system is plenty actuated.

More complexity but more redundancy too.

Want this so badly.

Google 'Ground effect'. Floating on an air cushion 2 feet off the ground just proves that he can strap two overpowered fans together -- it's not actually generating much lift like a helicopter would. He'll definitely make it to 10,000 feet... when he has two fans that are each two miles wide.

I don't think that ducted fans get a lot of wing in ground effect, given that ducts already prevent the formation of wingtip vortices.

I don't think ground effect while hovering involves wingtip vortices at all. His 'flying' figures are only speculation, and all he's proven is that he can hover.

His 'official' specifications: "Hover (out of ground effect) – >10,000ft (estimated)"

"Assuming mass moved is constant then a helicopter hovering in free air will be required to produce a force equivalent to V2 (speed after passing through the rotor) - V1 (starting speed of air) where V1 is some value above 0 given that the air is already moving downwards before reaching the rotor.

When close to the surface (generally considered 1/3-2/3 of the rotor diameter), air forced downwards through the rotor disc is restricted in its flow by the ground. This produces an area of high pressure below the disc and in turn, reduces the duct effect and hence the downwards velocity of the air above the disc. This reduces V1 while V2 remains relatively static, so the value of V2 - V1 increases. From the equation F = M x A we can see that the 'lift' of the rotor disc is greater when in ground effect."

http://en.wikipedia.org/wiki/Ground_effect_(aircraft)#Wing_i...

Also from the ground effect page:

  Wingtip vortices are a major cause of induced drag,
  which refers to any drag created as a side effect of
  generating lift.

Less drag -> more efficiency -> less power required to maintain altitude. I don't know how much of a factor this would be compared to the cushion, though, so we'll just have to wait and see. Given that he's already bought and engine and molded a nice, shiny shell, my guess is that he has plenty of power.

Roll up to the club with this and accidentally put out the windows of the cars next to you when a rock gets lifted up and hurled at 250 mph.

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