Rear wheel steering for yaw correction

[roon]

If a downforce-reliant racecar could steer its rear wheels (in addition the front) then it could orient itself optimally into crosswinds and/or the change of airflow direction when cornering. Whether this would be achieved via computer or via driver heroics & a second steering control is up for debate.

The yaw angle change would probably be small for most corners, high speed ones at least.

[cramr]

I think the benefit would be much bigger in terms of dynamics of the car and suspension design rather than in terms of Aero. Ok you would be able to probably reduce a bit the yaw angles but they still will be there.
Don't forger the increase in weight and complexity that this will add to the car

[Jersey Tom]

This has been a big thing in NASCAR for some time now, actually. Big aero advantage to getting as much rear steer as you can.

[godlameroso]

Passive toe curves for ya.

[Greg Locock]

You could get a top speed advantage if you could crab down the straights if there was a crosswind. Trying to do it round corners is interesting, does anybody have plots of Cd and Cl vs yaw angle to hand? I vaguely remember they don't change much for the first few degrees. https://books.google.com/books?id=kKhnC ... aw&f=false


suggests there could be a worthwhile bit in it. i wonder what sideslip angle F1 cars manage? I'm guessing a few degrees.

[gruntguru]

If you assume optimum tyre slip angle of 6 degrees and no rear roll or compliance steer you get . . . 6 degrees?

Is four wheel steering permitted?

[Greg Locock]

Of course not - the regs summary says "Four-wheel steering is forbidden.". The pinnacle of technology only operates within tightly specified design spaces.

[gruntguru]

So you would have to try to do it with roll/compliance steer. I wonder to what extent these parameters are influenced by in-corner aero considerations.

[Jersey Tom]

Trying to do it round corners is interesting, does anybody have plots of Cd and Cl vs yaw angle to hand?

Don't forget side force...

[Tommy Cookers]

maybe that was the reason for the slab-sided shape of the Lotus 18 ?

rear slip angle/body 'yaw'angle (often called Beta angle of attack) was 12-15 deg
how much side force was that at 150 mph ?

some planes fly easily in 'knife-edge' ie they get 'side force' of about 80% of their weight
(ok, the prop boosts the slipstream)

[Jersey Tom]

I'd wager that "shark fins" - be they on LMP or F1 cars - create an appreciable amount of sideforce. Though on those platforms I'm sure there's also significant interaction with other aero elements.

Open wheel and sportscar aero isn't in my world of experience.

[Greg Locock]

Don't forget side force...

I forgot side force. Well that's different. To get more side force you'd need vehicle oversteer, ie nose in. To get that from the rear axle via roll or compliance steer is exactly the most horrible thing you can do to the stability of the vehicle, and steering feel.

[Jersey Tom]

Don't forget side force...

I forgot side force. Well that's different. To get more side force you'd need vehicle oversteer, ie nose in. To get that from the rear axle via roll or compliance steer is exactly the most horrible thing you can do to the stability of the vehicle, and steering feel.

And it wins championships

[roon]

I'd wager that "shark fins" - be they on LMP or F1 cars - create an appreciable amount of sideforce. Though on those platforms I'm sure there's also significant interaction with other aero elements.

Open wheel and sportscar aero isn't in my world of experience.

Seems like it would be the case. The net effect, whether it increases downforce or cornering speed, is an open question for me. Intuitively, the prevailing airflow will be pushing outward on the fin (unless surficient yaw angle is achieved) while driving through the corner, which seems like the opposite direction of the sideforce you'd want.

I forgot side force. Well that's different. To get more side force you'd need vehicle oversteer, ie nose in. To get that from the rear axle via roll or compliance steer is exactly the most horrible thing you can do to the stability of the vehicle, and steering feel.

And it wins championships

All at or near 200mph. Seems like steering the rear this way would be detrimental to the tires. Yes/no? But manageable obviously if people are winning with the strategy.

[Jersey Tom]

Seems like steering the rear this way would be detrimental to the tires. Yes/no?

Not the case. The tires will basically get back to the same sideslip regardless. It's more that the chassis is what gets steered.