I stumbled upon these micro turbines online. They are mainly used in radio-control aircraft.
I noticed that this one, the “Nike” model, has a max thrust of 175 lbs yet weighs only 24 lbs. it’s only 21 inches long and 8 inches wide. Here’s an awesome bench test video of the same model. That thing really gets going!
I thought, jokingly, ‘Wow, that’s an amazing thrust to weight ratio. And it’s so small. You could strap one to each end of a snowboard-sized platform and fly around!’ And then I thought, ‘Wait. Could you?’
I know there was a lot of experimentation with single-person VTOL several decades ago and it seems that such craft are extremely difficult (or impossible) to fly, and suffer massive control and stability issues. I assume the craft I’ve described would be no different and I want to make it clear that I don’t have naive visions of dropping $50,000, whipping this thing up in my garage and zipping around the sky like the Silver Surfer. I’m just curious as to the physics theory and the feasibility. My question is: Could this thing fly in a controllable fashion or would it literally be impossible irrespective of any level of piloting skill?" Is the basic design inherently flawed?
Let’s assume:
Perfect engineering, materials, and construction.
The pilot is as skilled as humanly possible, maybe a bit more if that helps us (Maybe he’s Chuck Norris!).
The basic structure is a rigid, snowboard-sized and shaped platform with a turbine at each end, together producing 350 lbs total thrust. This seems more than enough to lift an average person, airframe, engines, fuel, etc… Let’s assume we have more than enough thrust. Let’s assume thrust between turbines is perfectly balanced and/or adjustable between them, if necessary.
The pilot would assume a snowboard-riding stance and would be attached with, say, ski boots and bindings. The fuel would be in a container between his feet. Let’s assume the positions of the center of thrust and the center of mass share a vertical axis that runs through the pilot’s body and the center of the fuel container. I suppose the COM would be above the COT.
My assumption is that the pilot would impart lateral movement and control by leaning left/right and fore/aft (I’m sure I’m being woefully naive here. Would the pilot instantly flip over once he leaned left or right?). Yaw would be controlled by some mechanism that slightly counter-rotates the turbines on the axis between them. Overall thrust would be managed with a handheld control. All of this would be simultaneously managed by our wizardly pilot.
Let’s assume we aren’t concerned with costs, safety, legalities, broken ear drums, supersonic flaming exhaust jets roasting the gardenias, enraged neighbors, or any other such pesky annoyances.
So, could a pilot at least hover this thing? How about perfectly vertical acceleration? How about controlled, stable forward flight? Level turns? Complex maneuvers? If not, why not? What would be the predominant condition or force that would damn the pilot to a flaming, spiraling death? Would there be some sort of instability negative feedback loop?
The only jet power flying platform I’m familiar with that actually worked was the “Flying Bedstead” NASA used to train Apollo lunar landing mission commanders on how to land a LM on the Moon. And they used ‘out rigger’ thrusters for attitude control. I don’t believe you could manage controlled flight on a snowboard with only 2 jet engines. Not if you were going to control it by leaning. The Center of Gravity would shift drastically when the [del]victim[/del] operator leaned.
I don’t see why not. It isn’t a massive step up fromone of these. It is astounding what people are able to adapt to controlling. Learning to fly the jet board would be hard - no soft water landing - but probably no harder than Igor Sikorsky teaching himself how to fly a helicopter.
Francis : that “flyboard” has 2 major things the turbines don’t.
RCS thrusters. Notice the sideways pointing water jets? Those are under operating control.
The harrier has an RCS system that it uses when the aircraft is in hover mode. It’s bleed air from the engines that is sent through internal pipes and valves to outlet ports.
It’s over water. Notice how the best pilot can only hover for a few seconds before they end up back in the drink? The problem with this jet hoverboard is that you cannot do that - turbine engines aren’t very water friendly.
Could you make a working hoverboard by adding on to this idea? Yes, I think so. You would probably need more engines, a computer controlled RCS system, and so on.
I thought about three engines, but I decided I preferred the streamlined profile of two.
Wow, that’s amazing! It’s very similar to what I’m describing in that the jets are venting fairly close to the center line of the body and entirely below it.
I did come across that in my web surfing and it is a pretty cool design. I think it’s a bit too big and it seems to react relatively slowly.
Check out this picture. It’s called the Bensen B-10 and the layout resembles what I describing.
And then I found this video of the Piasecki VZ 8 Airgeep, also similar.
Mythbusters season 10, episode 4 they revisit fireworks man. WHen they’re testing their new design (around 10:00 in my version) you see what happens with a platform is not aerodynamically stable. If you get the slightest bit of deviation (say from a stray breeze, or uneven terrain) you end up flying all over the place.
I think so. As soon as the operator leaned to one side (even a teeny tiny bit), their center of gravity would be to one side of the thrust supporting them. So now you’ve got gravity pulling down one side, and the thrust pushing up the other side, which makes everything rotate to that side, making the situation worse, and pretty soon the [del]operator[/del] victim is directly underneath the upside-down hoverboard being driven into the ground.
In other words,
– Yes.
The only way to avoid the same issue with tipping over front or back is by making the two fans go at different speeds when things tip, which is actually pretty doable with modern electronics (I think you specified that in the OP). Now, three fans would make dynamic stability possible in both directions.
This will only be true if the thrust is always pushing upwards relative to the ground, rather than relative to the board. Which will only happen if the engines are actively steered to always push downward regardless of the orientation of the board. If the engines are fixed in orientation relative to the structure of the board, it makes no difference whether the thrust provided by the engines is above or below the center of gravity of the platform. It’s the old pendulum rocket fallacy to think that having the engines underneath the load automatically makes the platform unstable.
It’s likely that this kind of platform would be unstable, but more due to ground effect and other aerodynamic effects than due to intrinsic instability.
Easy to do with modern high-power, low-inertia brushless electric motors, which is what makes all those little quadcopters able to work. Harder to do with jet turbines, which don’t respond to throttle inputs nearly as fast. For a jet-powered platform like the OP was thinking of, you’d probably need thrust-deflecting vanes or just pivot the entire engine with servos to keep the platform stable rather than using differential throttling.
Well, I’ll grant you that to the degree the thrust is always relative to the board directly in line with the center of mass, the thrust itself won’t be contributing torque to increase the tipping. But, first of all, if the thrust was perfectly aligned with the center of mass, it wouldn’t have tipped yet (the pencil would still be balanced on it’s point), and second even if it was pefectly aligned, once there was a tiny tip, gravity pulling down the center of mass will still be pulling everything over, and there’s still no mechanism for reversing the tip.
As the linked wiki page on the ‘pendulum rocket fallacy’ makes it clear, there’s little difference between the thrust under or over the center of mass: they’re both unstable.
Now, I suppose, in theory the rider could lean back over the other way to reverse the tip. Good luck with that: it’s exactly the same as trying to ride a bicycle with the handlebars frozen, so the front wheel can’t turn side to side, and that’s basically impossible for normal humans.
Gravity won’t pull anything ‘over’. Gravity alone doesn’t impart torque, it pulls down on the entire object evenly. The only torque will be due to the engine thrust being misaligned with the center of mass of the board and rider. That torque will be the same no matter which way the entire stack is aligned relative to the direction gravity is pulling. It won’t tend to rotate downward unless the torque generated by the misalignment is continuing to push it that way.
Not impossible at all. Balancing on a stationary bicycle with the steering locked is difficult but not impossible. Balancing on a unicycle, where you don’t even have a steering wheel, is also difficult but not impossible. It should be possible for someone riding a jet-powered board to balance by shifting their weight relative to the direction of thrust of the jets - or, if you prefer, shifting the direction of the jets relative to their center of mass, which amounts to the same thing. I wouldn’t want to be the one to try it, but there’s no physical reason why it should be impossible.
Thanks for your input everyone, very interesting stuff.
I agree, if it was possible to fly, it would take an incredible amount of practice.
I believe that the guys who fly these jet packs practice near the ground while attached to an overhead gantry. The same would make sense in this case.
Also, the water jet platform video linked in post #4 is a very similar idea to mine and those guys seem to be doing well riding that thing. It’s encouraging!
Futaba makes a 3-axis gyro stabilizer for the RC aircraft market and I’m under the impression it is an impressive, sophisticated device. Maybe this thing could be incorporated into the design somehow. Of course, now we are getting into added complexity, with servos and complex programming…
Computer control is the way to go here. The hardware you need is almost trivial these days, though the software effort would be fairly involved.
I would put a servo-controlled fin system in the jet exhaust (AndrewL mentioned this too). Four fins in the exhaust stream of each jet, each with independent control.
Not only does this allow thrust vectoring control (pretty much required), it allows bleeding off a portion of the thrust by angling fins on the same axis opposite each other (this would create a small net torque, but that could be counteracted).
This is fairly crucial since turbine engines have a slow response time (they have to spin up and down) and you need extra control authority for a system like this. In practice, you would run at perhaps 10-20% extra thrust and bleed off the excess. This way, when you do need extra for stabilization purposes, it’s there instantly.
Yeah, as Strangelove pointed out, why would you assume it’d be manually controlled? I’d imagine it’d use stabilizing sensors like the Segway and adjust thrust accordingly. There are already electronic skateboard that operate on similar principles, sensing the user’s shifting balance (like a Wii Fit board) and adjusting the mechanics accordingly. It’s not 1903 anymore…