[nxcho]

When I took control theory at university, in the last lecture, the lecturer took out a bike with rear wheel steering and challenged us to ride it in the hallway outside the lecture hall in the break. No one could get it to roll more than a couple of meters. The second half of the lecture was spent proving that a rear wheel steered bike is in fact (almost) impossible to control.

[Nevermark]

And in opposite world: Rockets with steering thrusters near their top are highly unstable.

[roelschroeven]

At some point (some) people though rockets with the thrusters near the top would be more stable. See e.g. this rocket by Robert H. Goddard: https://en.wikipedia.org/wiki/Robert_H._Goddard#/media/File:...

But it turns out that it doesn't matter whether you place the thrusters high or low, stability-wise. What matters is that the center of mass is in front of the center of the center of pressure.

[hoseja]

Aren't they just as stable as regular rockets, but it's very inconvenient to put the thrusters on top? It's called pendulum rocket fallacy and from what I can tell that's the case.

[kqr]

Huh, wouldn't this be similar to riding a regular bike backwards, which a lot of people (although not myself) are able to do?

[nxcho]

Yes, it was pretty much a reverse bike with the saddle on the frame and a handle bar just behind where the seat post should be, connected to the steering axle. The details is a little bit fuzzy since it was a couple of years ago but iirc it is actually possible bike backwards at slow speeds but require a lot more active balancing from the rider, and at some point it becomes impossible as the speed increases. Also it concerned the case where the bike is riding straight ahead, it is possible that it is easier to control if riding in a curve.

[Groxx]

In the extreme, it's also equivalent to a unicycle - just lean back to put all your weight on the steering back tire. Unicycles can be controlled.

Both are undeniably less easy than a normal bicycle though.