Rear wheel steering for yaw correction

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.
roon
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Rear wheel steering for yaw correction

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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.


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cramr
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Re: Rear wheel steering for yaw correction

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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
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Re: Rear wheel steering for yaw correction

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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.
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Re: Rear wheel steering for yaw correction

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Passive toe curves for ya.
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Greg Locock
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Re: Rear wheel steering for yaw correction

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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
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Re: Rear wheel steering for yaw correction

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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?
je suis charlie

Greg Locock
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Re: Rear wheel steering for yaw correction

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

gruntguru
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Re: Rear wheel steering for yaw correction

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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.
je suis charlie

Jersey Tom
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Re: Rear wheel steering for yaw correction

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Greg Locock wrote:
Thu Jun 08, 2017 4:14 am
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...
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Tommy Cookers
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Re: Rear wheel steering for yaw correction

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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
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Re: Rear wheel steering for yaw correction

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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.
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Greg Locock
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Re: Rear wheel steering for yaw correction

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Jersey Tom wrote:
Thu Jun 08, 2017 10:45 am

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
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Re: Rear wheel steering for yaw correction

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Greg Locock wrote:
Fri Jun 09, 2017 1:48 am
Jersey Tom wrote:
Thu Jun 08, 2017 10:45 am

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 :)
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roon
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Re: Rear wheel steering for yaw correction

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Jersey Tom wrote:
Thu Jun 08, 2017 6:51 pm
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.
Jersey Tom wrote:
Fri Jun 09, 2017 3:23 am
Greg Locock wrote:
Fri Jun 09, 2017 1:48 am


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.
Last edited by roon on Fri Jun 09, 2017 7:00 pm, edited 1 time in total.

Jersey Tom
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Re: Rear wheel steering for yaw correction

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roon wrote:
Fri Jun 09, 2017 5:37 pm
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.
Grip is a four letter word. All opinions are my own and not those of current or previous employers.