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G Forces on banked bends


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#1 Perruqueporte

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Posted 22 February 2020 - 17:52

This may appear to be off topic, but there is a connection.

I was walking along the curved hedgerow towards my shed the other morning when a sparrow hawk flew towards me at a tremendous speed. It banked left to avoid me, in an impossibly tight turn, before jinxing right to resume its course. It was a breathtaking bit of flying and it occurred to me that had that been an aircraft, the human pilot would have surely blacked out. Which led to thoughts of cornering forces on four wheels, and in particular, on circuits with banked corners.

Were there ever accounts of G forces affecting drivers’ thought processes on banked bends at circuits like Brooklands and Monza back in the day?

Christopher W.

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#2 Tom Glowacki

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Posted 22 February 2020 - 18:09

This may appear to be off topic, but there is a connection.

I was walking along the curved hedgerow towards my shed the other morning when a sparrow hawk flew towards me at a tremendous speed. It banked left to avoid me, in an impossibly tight turn, before jinxing right to resume its course. It was a breathtaking bit of flying and it occurred to me that had that been an aircraft, the human pilot would have surely blacked out. Which led to thoughts of cornering forces on four wheels, and in particular, on circuits with banked corners.

Were there ever accounts of G forces affecting drivers’ thought processes on banked bends at circuits like Brooklands and Monza back in the day?

Christopher W.

 

And then there are the woodpeckers . . .



#3 PayasYouRace

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Posted 22 February 2020 - 18:42

Speeds at Brooklands and Monza were never high enough for G-forces big enough to cause a driver to black out. Their curves were way too large radius and the cars simply couldn't go round them fast enough.

 

The acceleration experienced is given by the formula a = v2/r where

 

v = your speed round the turn and

r  = the radius of the corner.

 

Using a rough google maps measurement, the radius of the banking at Monza was about 400 m. Take a car going round at quite reasonable for the time 156.6 mph which is 70 m/s. That gives an acceleration of 12.25 m/s2.

 

1G is 9.81 m/s2 . So you're looking at just slightly over normal. Then consider that the driver wasn't at 90 degrees to the ground so the blood isn't being pushed down from his head as much. For reference, 5G is about where most people would start blacking out unaided.

 

The only time this was close to happening was the CART Texas race in 2001 which was cancelled. That circuit had turns closer to 250 m radius. The cars were easily capable of cornering above 200 mph so we'll say 90 m/s. That gives us 32 m/s2 which is over 3.3G. I'm sure higher forces were actually recorded but this is just a back of the envelope calculation.



#4 D-Type

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Posted 22 February 2020 - 22:10

I wonder about Avus?  The North Curve had a very tight radius and also very steeply banked.


Edited by D-Type, 22 February 2020 - 22:19.


#5 Allan Lupton

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Posted 23 February 2020 - 08:49

If one is travelling at the correct banking angle for the speed one has (often referred to as the "hands-off speed") the car and occupants experience no sideways force as the resultant of gravity and centripetal accelerations is aligned with what would be the vertical axis of the car/occupants. Without looking it up I expect the AVUS didn't have a high hands-off speed.

 

Of course a car can be driven round a banked corner faster than the hands-off speed, in which case the occupants will experience side-loads and observers may be able to see the slip angle that is part of reacting those side-loads. When Stanley Mann and his friends were breaking records on the Millbrook High Speed track, the visible slip angle was pretty evident as the fastest lane's hands-off speed is 100 m.p.h. and many of the shorter records were set in the 120-130 m.p.h. range.


Edited by Allan Lupton, 23 February 2020 - 08:50.


#6 Perruqueporte

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Posted 24 February 2020 - 22:16

Thank you for the learned replies. That was very kind.

And with regard to the woodpecker comment - it is probably the least likely avian to have to worry about blacking out when you consider what must be happening to its brain when excavating a nest.

Christopher W.

#7 D-Type

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Posted 25 February 2020 - 15:24

As Allan Lupton has pointed out, at the "hands off" speed all the cornering force (centripetal or centrifugal depending on your reference point) is acting normal to the car's wheels, ie it compresses the springs equally.  It also pushes the driver's blood against the heart's flow, ie if it's high enough it leads to blackouts.  Hence, this is the speed to calculate the effective 'g' at.  At higher speeds a component lateral to the car comes ito the equations but as it's also lateral to the driver it doesn't add to the effective 'g' or blackout effect.
Incidentally, if I remember correctly, in his autobiography Jim Clark refers to being surprised to find he was experiencing a 4-wheel drift at 140mph when he tried a NASCAR car.



#8 vactrac

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Posted 25 February 2020 - 19:33

Yes. CART at Texas Motor Speedway in Fort Worth TX in 2001.

 

The Firestone 600 was cancelled after drivers reported various G-LOC symptoms, including misidentifying Turn 1 as Turn 3 and going off to the inside of the backstretch trying to pit. Qualifying speed on a 1.5 mile oval was >236 MPH.



#9 Perruqueporte

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Posted 25 February 2020 - 20:41

Yes. CART at Texas Motor Speedway in Fort Worth TX in 2001.
 
The Firestone 600 was cancelled after drivers reported various G-LOC symptoms, including misidentifying Turn 1 as Turn 3 and going off to the inside of the backstretch trying to pit. Qualifying speed on a 1.5 mile oval was >236 MPH.


I had forgotten about that. When you consider that those drivers were highly competent, it must have been truly alarming.

Christopher W.

#10 Izzyeviel

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Posted 27 February 2020 - 15:16

How can Indycar manage Texas when CART failed? Are they simply not as quick?



#11 Collombin

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Posted 27 February 2020 - 20:43

Exactly - a relatively small difference in speed makes a big difference to g forces.