Gyroscopic effects on handling

[Ted68]

Well I had to take my Aprilia dirt bike to the doctor this week. While there I was bombarded with propaganda on their '09 models

From the Aprilia website:
Reduced unitary displacement has allowed Aprilia to develop an extremely compact and lightweight crankshaft. The engine is more responsive to variations in throttle opening as a result, and the bike as a whole is faster and more maneuverable thanks to the reduced gyroscopic effect from the crankshaft.

So my question is what effects do the gyroscopics of rotating parts such as wheels/tyres, the gears/clutch and the engine internals have on the chassis if any?

[ReubenG]

Gyroscopic torque occurs when an object, which is already rotating about one axis, begins to rotate about another axis (which is not parallel to the original axis). In vector form:


The gyroscopic torque is always perpendicular to both axes of the applied rotations. I is the second moment of inertia and are vectors describing the angular velocity (rotation)

So with reference to the motorcycle example (which I am assuming has a crankshaft spinning in the same direction as the wheels). The axis of rotation of the crank is the same as the wheels' axis, and if it spins in the same direction as the wheels then it's rotation vector points to the left. If the cycle enters a left hand turn, then it must rotate (yaw) to the left - effectively rotating about its own vertical axis. Hence the axis of rotation (for the left turn) is the vertical axis and the rotation vector points up.

These simultaneous rotations (about two different axes) cause a gyroscopic torque acting about an axis perpendicular to both - which in this case is the same as looking straight forward from the bike. Because of the direction of the other two rotations, this torque will try to lean the bike to the right i.e. away from the direction of the turn. A rider will just lean more into the turn to counter this.

Conversely, a motorcycle with a crank that spins opposite to the sense of the wheels will experience a gyroscopic torque in the opposite direction - the gyro torque will try to lean the bike into the corner, counteracting some of the normal cornering effect.

A similar process applies with an F1 car (or any other race car) - just in F1 the crankshaft rotation axis is down the centerline, rather than parallel to the wheels. The difference is that the torque (moment) manifests as weight transfer between the wheels, with some consequent body roll / pitch, rather than the big lean angles we see on bikes. On an F1 car the gyro torque due to the crankshaft, and rotation into a corner, will cause weight transfer either from front to back axle, or the other way, depending on whether the crank spins clockwise or anti-clockwise when viewed from the back.

[Jersey Tom]

Gyro effects are non-trivial at high speed. Doubt the crank contributes much, but wheels certainly.

I've been told you can feel the difference in a high speed open wheeler, between an iron and carbon rotor, on turn in.

[Ian P.]

In the case of the Aprilia, I suspect the crank truns opposite to the wheels (geared primary drive). Old flat-track bikes had chain primary so the engine turned in the same direction as the wheels.
The place you feel this most is pitching the bike over into a sliding turn. Same direction rotation engines will step the rear wheel out easier than the opposite rotating engines will. Speedway bikes are a classic example.
For any 4-wheeled vehicle, the gyroscopic forces from the rotating wheels will cause the outside wheels to be loaded up more than the inner wheels. All this is related to the moment of inertia of the rotating mass. Lighter is much better than heavier.
Something to try on any bike.....carefully mind you..... with the bike rolling along at a decent speed, apply a slight pull on the righ handlebar. The bars and the bike will turn left. There will be all manner of explanations of counter steer, trail and steering angles but it comes down to gyroscopic forces and reactions. Long wheelbase land speed stream-liners have an inherrent steering problem since they steer like a car up to a certain speed before they start to steer like a "normal" motorcycle. Effectively a steering input reversal. Makes for loads of embarassed drivers that crash them at low speed.
It will be interesting to see how the flywheel-KERS systems get utilized as there is a real potential for having the gyroscopic forces provide a beneficial effect on the handling of the car.

[countersteer]

Two comments here... Both bike related but interesting nonetheless.

I watched a program on Discovery HD about a renegade outfit developing a MotoGP bike starting with a clean sheet design. From what I understood of it, they had developed an inline, twin crank 4 cylinder which resulted in the cancellation of all gyroscopic effects caused by the crank. Test riders said it turned like nothing they had ever ridden before. Check out www.motoczysz.com

check out www.reverserotatingrotors.com They are developing a system using gears that will rotate the front brake rotors in reverse, that is opposiste the rotation of the tire, with the intent of eliminating (or reducing greatly) the gyroscopic effect of the front wheel/rotor assembly.

The gyroscopic effects must be significant on a bike to go to such lengths to control it. The affect on cars (much lower percentage of rotating mass vs. total mass) would be significantly less.

[TheChad]

You will notice the Gyroscopic effect most when your in the air!
Next time your in the air on your aprilia dirt bike, give it a boot full of throttle and see what happens!

[PlatinumZealot]

Gyro effects will cause the wheel to want to roll inward or outward (in the camber direction) but from the wheel bearings and the reaction force from the wheels cancel it out i don't think there is much of an issue with a car.... or is there?

[avatar]

In terms of cars, I think you might be right about the wheels themselves not having as much overall gyroscopic impact, but their gyro could affect tyre wear.

Any gyro's included in the sprung weight however, will have a high impact on a combo of balance/weight dist/body roll

[avatar]

A few years back, I dreamt up a flywheel breaking energy storage system,
that would use quite a large mass & high energy on the flywheel.

I came to the conclusion that a single flywheel could be detrimental to
car handling (e.g. a forwad rotating, vertical, front to rear mount
could decrease body roll, but would encourage understeer on adverse camber
surfaces, and overersteer on positive camber surfaces)...

...But I figure that 2 or more, could be tuned (by altering the angle or
direction of spin) & with opposing angles could be used to reduce body
roll without the balance shifting so much on cambered surface, or when
curb riding.

Anyone know how the flybrid KERS are being laid out?

[scarbs]

Anyone know how the flybrid KERS are being laid out?

John Hilton of Flybrid said that the 5kg flywheel at maximum RPM going through 130r contributes less than 1% of the force the car carries through that corner, thus the KERS gyroscopic effect is so minimal as to be discounted...

[avatar]

Cool.

I hadn't really thought through the flywheel energy for F1, which is of
course restricted, putting a ceiling on any gyro effect from KERS.

Could gyro still be used to positive effect though?

Might that 1% still be exploitable by mounting it in more sensitive areas,
or to various change chassis/suspension stresses. After all, it is a
force that changes in line with the turning moment.

Or would this be illegal on the same grounds as the swing-in-lock mechanisms?

Av.

[Gecko]

Could gyro still be used to positive effect though?

It certainly could. By mounting the flywheel such that it rotates just in the opposite sense to the wheels, you can get some weight transfer towards the inside wheels when cornering, for example.