You are exactly right. This article suffers the common misconception that two wheels spinning in opposite directions and same speed cancel out the gyroscopic stability. And this is simply not true. In fact two wheels spinning in opposite directions and same speeds will actually double the gyroscopic stability (as opposed to one wheel of the same speed).
However, two wheels spinning in opposite directions may cancel out other spinning wheel effects.
It is a common belief that two identical wheels spinning in opposite directions and the same speed have a net zero gyroscopic stability. The basis for this belief is usually false, but the assertion is true.
I've done both the math and the experiment - it's in one of the lectures I give on "Spinning Things".
In short, I believe you to be wrong, and this is based on my personal experiments and calculations. I would be interested to know the basis of your claim.
When computed in detail, gyroscopic stability is really the effect that torque applied in one plane manifests itself as movement in another. The direction of this movement depends on the direction of spin, and they cancel each other out when you have two wheels spinning in opposite directions.
My independent experiments and calculations were done before I read anything formal about it, and it agrees with the work of people who design devices that run on satellites and the ISS. I'd need a lot of convincing that I'm wrong.
This is independent of the other effects that help to keep a bike upright, such as the steering geometry. I have experience of that too, having raced bikes with very small rake, and toured on bikes with a larger rake. The difference is unmistakeable, and unrelated to the gyroscopic issues.
And it sure seemed to have a lot of rotational inertia. If you were right, then I could touch one side of the helicopter slightly and since it has no rotational inertia it would tilt to the side and completely change direction and fly off somewhere into the wall or the floor. This did not happen however, even when I tried to tilt it the helicopter remained horizontal. And please do not tell me that a $50 toy has an active stability system with internal gyros and all the required electronics and super fast servos.
And now that I think of it, I remember that the russians have been making counter rotational helicopters for ages. See for example this one:
How does this helicopter stay horizontally stable in the air and does not fly off on a tangent when tilted by the slightest cross wind? Note that this one was designed in the late 50's before any electronic active stability systems could have been invented.
I have limited personal knowledge of RC helicopters, but a great deal of experience with rotational systems. Colleagues tell me that the counter-rotational systemson helicoptors are stable because the CoG is hanging from a point quite a long way above, and cross winds are applied more-or-less at the CoG because of the cross-sectional area distribution.
I don't doubt that your experience of a toy double blade helicopter is that it seems to have a lot of rotational inertia. I am certain that it's not due to the gyroscopic stability of exactly matched counter-rotating blades.
If you think about it, this explanation cannot be true. The main force the helicopter exerts on its surroundings is along the axis of rotation. If you tilt the axis of rotation significantly in any direction, the direction of the force will change significantly and the motion of the helicopter will also change significantly. Again, this does not happen.
It's unclear what you mean by the "this" in the "this does not happen"
However ...
A helicopter changes direction by using the cyclic setting on its rotors. Then you get more lift from one part of the rotor cycle and less from another. That causes the plane of the rotors to tilt, and then the helicopter goes off in the appropriate direction.
For example, having more lift in the rear portion of the cycle and less in the front means the helicopter gets tipped forward, effectively like lifting one part of a plate. The down-draft now has a significant rearwards component, so the rotors get pushed forward, taking the helicopter with it.
If you then change the cyclic to "flat" so there is identical lift everywhere, the weight of the helicopter dangling from the rotors causes it come come back upright (after swinging a bit)
It's a weird experience sitting in a helicopter when it's doing this, especially if you're mostly accustomed to ordinary aeroplanes.
I don't see any contradiction in any of this, and it really doesn't seem to have any bearing on the fact that contra-rotating disks have no net gyroscopic effect.
When you say "this" you mean the translation of the pilot's controls into the angles of the blades at the various stages of their journey, mixing collective (giving overall lift) and cyclic (giving pitch and roll)
Another effect is the tendency to tilt to the side if you accelerate or decelerate the rate of spin. This effect will be canceled by counter spinning wheels.
Wait, so if you have two identical wheels on one axis, spinning in opposite directions, and you rotate the axis, are you saying you'll experience precession or you won't? My intuition (and physics understanding) says you won't. But the top-level post is saying you will still experience "gyroscopic stability". Is that true?
You don't. That's because the gyroscopic effect cancels out in that case. But if you use a single spinning wheel you will. I'm just saying that precession isn't a different effect than the gyroscopic effect; it's a specific case of it. The same forces that cause a wheel to feel like it's hard to turn (i.e. the "gyroscopic effect") cause precession.
I asked:
> Which other spinning wheel effects? [other than the gyroscopic effect]
And he replied:
> Precession
To which I replied that precession is not a different effect. I did not mean to imply that precession happens when you have two wheels spinning in opposite directions, in fact I believe it does not because the forces that cause a single spinning wheel to precess cancel out if you have two wheels spinning in opposite directions.
You're right, your understand is right, you won't experience "gyroscopic stability." I've done it. You don't.
I believe that people who believe otherwise are working on misunderstandings of perceptions. It's nototiously easy to confuse several effects in this. Careful experiments are required with tight controls on error bars, etc.
It's easy to be fooled. Eric Laithwaite is a classic and high profile example:
However, two wheels spinning in opposite directions may cancel out other spinning wheel effects.