Can a rope thrower act as a propulsion method for land based craft?

Question

Could accelerator devices throwing elastic strings/ropes at the surface (and then pulling them back in) be used to effectively hover over the ground and accelerate by changing the direction of the ropes thrown or the number?

What I imagine is throwing the rope directly at the ground, where it would briefly come to rest/bouncing slightly, before being pulled back up by the other end/both ends if the thrower 'flicks' it like a whip. If the thrown direction is oscillating in the near vertical direction then it would remain stationary (and wasting energy), but the engine would have the potential to keep a group of string spinning at high speed within, whereafter they could be deployed in a near-horizontal direction, allowing for extremely high acceleration of the vehicle, potentially in any direction.

Specifically I'm asking if such a drive could be constructed with near-modern technology, or at all within limits of known materials, and whether it would be powerful enough for it to be built (capable of high acceleration, "all-terrain" movement, structural integrity for at least hundreds of km without maintenance, capacity to hold the power source for itself and some extra weight; efficiency is not a concern outside of the power source being able to push out that much at all; the vehicle is supposed to be autonomous and controlled by an internal computer).

Potential concerns:

• Rope material - whether the stresses experienced by the rope would require unrealistically strong materials, as well as the need for its maintenance. I'm imagining some sort of fluid, possibly organic, that binds with itself when under strong external forces. Such a fluid would allow maintenance via filtration, and the impact forces are not a concern, though I have no clue what can be realistically expected regarding possible tensile strength for such quasi-fluids.

• Engine structure - whether an engine could realistically reach necessary speeds, contain the forces exerted on it during various modes of operation. Though based on law of equal reaction, I don't think it would be significantly more than what car wheels experience, and unlike those, there's no fear of cutting into the ground.

• Ground dust - on one hand the fast rotation of the string should prevent significant dirt from falling onto it, and rest would be flung away during liftoff. On the other hand hard particles could embed into it during impact and then grind the machinery from within. Could this be countered by constantly spraying new layers of material over strings/having strings be very hard and thin?

• Power - just how powerful of an engine would be needed for simple hover, relative to the mass of the potential vehicle?

• Strings intertwining - unless externally induced, the active controls should be able to prevent that from happening.

• Coverable terrain types - I actually do expect it to be able to cover rough terrains and cliffs up to a certain inclination/height. Would the roughness of the terrain unmanageably misdirect strings? Could they be launched with extra force for a jump? Precisely directed into crevices to climb vertical surfaces? A thin and fast string array to drive over water?

• Speed, acceleration, weight capacity - Whether it is possible to achieve high enough values that would make such a drive useful.

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To be clear, I meant the rope to be a loop (multiple loops for better control, energy/momentum ratio), thrown on one side and pulled on the other. Though the thought of spewing a string and sucking it back up is funny, but I think shouldn't have much of a difference, other than thrower operation.

Answer 1

The idea is in theory possible.

A version that technically what is described and possible to build would be very stiff rope and shorter lengths where the vehicle would essentially have wheels without the rims. Linear motors propelling the rope would enable motion.

some real world analogues

A real world similar implementation is tracked vehicles.

Snow chains are more floppy but aren't propelling the vehicle.

so many problems.

A system that uses loose floppy rope? The problems of keeping it from tangling/catching would be very hard. If using rope that can kink. It will kink eventually, and that will be very bad.

Different height terrain will make balancing hard possibly requiring some excess rope to be in vehicle making another source of tangled rope

fraying, gripping of rope etc.

For the challenge only.

Such a vehicle/propulsion system would only be done for the pure challenge not for any sort of practicality.

Answer 2

Here's an idea that isn't a rope-thrower, but may be rope-thrower-adjacent. I remember it as one of the proposals for a wheel for the Lunar Rover. I can find nothing to back this up, so just take the idea on its own merits, if it has any.

Suppose you have a wheel with a rubber rim made of overlapping strips of material. At low speeds, the sheets of material lie coiled. Friction and the set of the strips ensures the rim acts as a solid tyre at low speeds. At higher speeds, the strips progressively straighten out under centripetal action, until you eventually have a set of nearly straight strips that support the vehicle by slapping the ground with their tips. This wheel acts as suspension and gearing as the wheel gets larger at speed. When you slow down, the original shape of the strips will wind them back into their original state.

This is a bit like your rope thrower. It is slapping the surface with a non-rigid body to lift the vehicle and push it along, and then hauling in the that body so we can use it again. In this case it is a set of strips rather than a continuous rope.

Answer 3

Yes - you've just reinvented the leg.

The lower limbs of humans and other animals are, shall we say, optimized ropes. If the animal crawls on its entire body, then the whole body can be considered as a rope. Just ask Indiana Jones! By throwing our legs at the ground and letting them rebound back at us, we can move along reasonably well.

Answer 4

No, this will not work

If a vehicle throws reaction mass away then the same force that was used to throw it will operate on the vehicle in the opposite direction - this is how rocket engines work. However, as soon as the reaction mass is retracted/rebounds by virtue of being attached by a tether then it reverses the propulsive force, giving a net movement of zero. If it were possible to throw reaction mass away and then retrieve it without losing the energy gained by throwing it away in the first place then space travel would not be limited by the tyranny of the rocket equation.

Note that it does not matter how advanced the materials used for the "strings" are or the sophistication of the motors that manipulate them, basic physics prevent this concept from ever working.

(The title suggested to me that this was an idea for throwing out grappling hooks and then retracting them to pull a craft along the ground - that would probably be an extremely impractical method of propulsion, but it could work on the correct ground type.)

Answer 5

I doubt it, assuming I have understood the layout you have in mind, but something similar is possible. The material and engineering challenges aren't overwhelmingly problematic I can think of several options that would work, the energy equation isn't on your side if the motion is purely vertical though. The workable alternative is something like a skipping rope where the rotation of a cable at a set tension striking the ground propels the vehicle upwards and forward. Such a system is likely to be quite heavy but possibly not prohibitively so, you're effectively replacing the tyres on something that could otherwise be a fairly standard all terrain vehicle. Such a system will only work at a very high rate of rotation, at lower speeds, such as when starting and stopping, the vehicle will shake abominably. Also you need landing struts that raise the vehicle off the ground, creating space for the cable(s) to start rotating.

Answer 6

I believe this is theoretically possible.

If a vehicle hovering above ground level is carrying a Mass on a wire. It would be able to 'throw' the mass downwards with as much force as its motor and energy source permitted.

The more energy the mass was thrown downwards with, the greater the upward force on the vehicle.

However, because it would be the ground and not vehicle arresting the motion of the mass. The upward motion is essentially free.

There is still the downward force from the weight of the vehicle and the extra downward force required to hoist the mass back into the vehicle so it could be used again for the next 'fling', but both of those forces would always be the same whereas the upward force generated from flinging the mass downwards is essentially unlimited (given the perfect energy source and motor)

Answer 7

It would rip itself to pieces. We don't know of any materials that would handle such abuse long term. It seems doubtful that you could achieve constant acceleration as it would depend on the ground composition. Uneven terrain would be unmanageable for any length of time.

So, in answer to the question.... no.