2022 cars 'porpoising' at high speed

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Just_a_fan
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Re: 2022 cars 'porpoising' at high speed

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vorticism wrote:
Mon Mar 07, 2022 11:50 pm
Happens to aircraft as well:

https://www.youtube.com/watch?v=x5ZzktAFJK4

"Porpoising (runaway bounced landing) - repeated bouncing with bouncing amplitude increasing with each touchdown. This is most dangerous bounced landing type typically resulting in severe damage or destruction of airframe."

Q's: Is porpoising a pitching motion over the a particular center of pressure (f.e. tunnel waist, diffuser entry)? Is porpoising a more linear vertical motion? Is one axle affected more than the other?
That's pilot induced, however. What happens with the cars isn't induced by the drivers.
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101FlyingDutchman
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Re: 2022 cars 'porpoising' at high speed

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djos wrote:
Tue Mar 08, 2022 12:23 am
vorticism wrote:
Mon Mar 07, 2022 11:50 pm
Happens to aircraft as well:

https://www.youtube.com/watch?v=x5ZzktAFJK4

"Porpoising (runaway bounced landing) - repeated bouncing with bouncing amplitude increasing with each touchdown. This is most dangerous bounced landing type typically resulting in severe damage or destruction of airframe."

Q's: Is porpoising a pitching motion over the a particular center of pressure (f.e. tunnel waist, diffuser entry)? Is porpoising a more linear vertical motion? Is one axle affected more than the other?
That pilot looks like he came in way too fast and that caused the Porpoising.
From a pilots objective, that's about as poor as one can land an airplane. Looks like the initial "snatch" was way too aggressive. Then leaving thrust on, not assuming any sort of landing config. Does look like high energy initially but that in itself shouldn't have been such an issue if the initial "checK" wasn't so aggressive. Then it should have been binned for obvious reasons. Seems input severely lags the aircraft due to being clueless!

maxxer
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Re: 2022 cars 'porpoising' at high speed

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101FlyingDutchman wrote:
Tue Mar 08, 2022 3:33 pm
djos wrote:
Tue Mar 08, 2022 12:23 am
vorticism wrote:
Mon Mar 07, 2022 11:50 pm
Happens to aircraft as well:

https://www.youtube.com/watch?v=x5ZzktAFJK4

"Porpoising (runaway bounced landing) - repeated bouncing with bouncing amplitude increasing with each touchdown. This is most dangerous bounced landing type typically resulting in severe damage or destruction of airframe."

Q's: Is porpoising a pitching motion over the a particular center of pressure (f.e. tunnel waist, diffuser entry)? Is porpoising a more linear vertical motion? Is one axle affected more than the other?
That pilot looks like he came in way too fast and that caused the Porpoising.
From a pilots objective, that's about as poor as one can land an airplane. Looks like the initial "snatch" was way too aggressive. Then leaving thrust on, not assuming any sort of landing config. Does look like high energy initially but that in itself shouldn't have been such an issue if the initial "checK" wasn't so aggressive. Then it should have been binned for obvious reasons. Seems input severely lags the aircraft due to being clueless!
Pretty clear he went nose down and from then it was just bouncing

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vorticism
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Re: 2022 cars 'porpoising' at high speed

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Doesn't matter if it's pilot induced (though it sometimes isn't). Point was: ground effect + undampened spring force creates a feedback loop known as porpoising. Alternating pressure gradients beneath aero surfaces. Both vehicle types have at least one way of curing it: slowing down.
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Hoffman900
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Re: 2022 cars 'porpoising' at high speed

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vorticism wrote:
Tue Mar 08, 2022 6:16 pm
Doesn't matter if it's pilot induced (though it sometimes isn't). Point was: ground effect + undampened spring force creates a feedback loop known as porpoising. Alternating pressure gradients beneath aero surfaces. Both vehicle types have at least one way of curing it: slowing down.
Porpoising on landing isn’t from this.

A PhD aerodynamicist friend said from the first day of testing to me that a possible cause was vortex shedding inducing oscillations that resonate at the same frequency as the suspension. He had experience with this in aircraft and the tools they had at their disposal were greater than the entire F1 grid combined. You can find my old posts from the first day of testing repeating this.

It could be a combination of things, but it was funny to read Jean-Claude Migeot mention this in an op-ed recently about this being a potential cause and how hard that is to fix.
Migeot explained that the cause of porpoising was not in a cyclical stall function, but down to the aerodynamic forces within the underbody at high speed inducing movement in the car close to its natural heave frequency.
This won’t show up in the wind tunnel because those are often rigid models and a scale suspension won’t oscillate the same and Cfd isn’t good enough (plus you would have to run a chassis / tire model at the same time, good luck). Complex shapes with turbulence requires a ton of computing power and nearly impossible to model accurately.

This vortex shedding is actually what causes skyscrapers to resonate and why they have tuned mass dampers.

Von Karmann Vortex’s are a bitch and it’s arrogant to think F1 cars are insensitive to flutter and structural mode interactions.
Last edited by Hoffman900 on Tue Mar 08, 2022 7:09 pm, edited 1 time in total.

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vorticism
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Re: 2022 cars 'porpoising' at high speed

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Hoffman900 wrote:
Tue Mar 08, 2022 6:51 pm
Porpoising on landing isn’t from this.
Excessive compression of tires/stays/airframe while traveling fast enough to re-propel upward (aided by ground effect); repeat.

Hoffman900 wrote:
Tue Mar 08, 2022 6:51 pm
A PhD aerodynamicist friend said from the first day of testing to me that a possible cause was vortex shedding inducing oscillations that resonate at the same frequency as the suspension.
That's one option I've been considering. As the strakes get closer to the ground, the vortex they shed gets smaller and smaller. Stu brought this up in the AT thread, how the strakes could essentially act like a shutter.

Stu wrote:
Sun Mar 06, 2022 6:04 pm
When you look at that strake set-up, the tunnel entry is incredibly narrow; it looks like a recipe for choking the underfloor flow.
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Hoffman900
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Re: Alpine A522

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Hoffman900 wrote:
Thu Feb 24, 2022 4:29 pm
AR3-GP wrote:
Thu Feb 24, 2022 4:18 pm
chlebekf1 wrote:
Thu Feb 24, 2022 7:26 am
If the floor is not touching the asphalt, bouncing like this is decent
The floor touching the asphalt is what causes the venturi to choke, which triggers the porpoising. You cannot porpoise without first contacting the asphalt.
Not true. Vortex shedding can cause it as well, especially if the car is resonating at the same frequency of the now required mechanical springs or causing wing supports to flutter on some small level.

In my little world, we were joking about running a shaker rig in the wind tunnel, but it's not going to tell you much with the rules required 60% model.
Here is my quote from the 24th. Obviously that joking idea is near impossible to do.

The only place with the computing power , that I know of, to model an F1 car, traveling down a track (which are never perfectly smooth), and with a suspension / chassis / tire model to even an acceptable resolution, is Los Alamos, and even then, it would still be wrong.

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vorticism
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Re: Alpine A522

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Hoffman900 wrote:
Tue Mar 08, 2022 7:12 pm
The only place with the computing power , that I know of, to model an F1 car, traveling down a track (which are never perfectly smooth), and with a suspension / chassis / tire model to even an acceptable resolution, is Los Alamos, and even then, it would still be wrong.
That or just buy Adrian Newey a cup of coffee.

(It's an Adrian Newey joke.)
Last edited by vorticism on Tue Mar 08, 2022 9:26 pm, edited 1 time in total.
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Hoffman900
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Re: Alpine A522

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vorticism wrote:
Tue Mar 08, 2022 8:34 pm
Hoffman900 wrote:
Tue Mar 08, 2022 7:12 pm
The only place with the computing power , that I know of, to model an F1 car, traveling down a track (which are never perfectly smooth), and with a suspension / chassis / tire model to even an acceptable resolution, is Los Alamos, and even then, it would still be wrong.
That or just buy Adrian Newey a cup of coffee.
Adrian is many time ls the genius I am, but he’s just one guy. He reminds me of Smokey Yunick. Genius for sure, but there are others who were / are just as smart or smarter, but without the hype.

I know this will probably upset people, but being around motorsports and other engineering disciplines has made this apparent. No one person is all knowing.

That said, I would love to have many coffees and chat with him.

Just_a_fan
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Re: 2022 cars 'porpoising' at high speed

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vorticism wrote:
Tue Mar 08, 2022 6:16 pm
Doesn't matter if it's pilot induced (though it sometimes isn't). Point was: ground effect + undampened spring force creates a feedback loop known as porpoising. Alternating pressure gradients beneath aero surfaces. Both vehicle types have at least one way of curing it: slowing down.
A "pilot induced oscillation" (to give it the correct term) is not aerodynamic porpoising as exhibited by the cars because it's not inherent in the aircraft but rather in how the aircraft is flown by the pilot. The cars will porpoise at a given speed for any driver because it's inherent in the car's design/setup.
If you are more fortunate than others, build a larger table not a taller fence.

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vorticism
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Re: 2022 cars 'porpoising' at high speed

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Just_a_fan wrote:
Tue Mar 08, 2022 10:21 pm
vorticism wrote:
Tue Mar 08, 2022 6:16 pm
Doesn't matter if it's pilot induced (though it sometimes isn't). Point was: ground effect + undampened spring force creates a feedback loop known as porpoising. Alternating pressure gradients beneath aero surfaces. Both vehicle types have at least one way of curing it: slowing down.
A "pilot induced oscillation" (to give it the correct term) is not aerodynamic porpoising as exhibited by the cars because it's not inherent in the aircraft but rather in how the aircraft is flown by the pilot. The cars will porpoise at a given speed for any driver because it's inherent in the car's design/setup.
Wrong again. See my other prev posts. The agency of the pilot/driver is irrelevant. The physical phenomenon is governed by the same forces. What's known as a type of bounced landing. PIO is a general term and could happen at various altitude, be applied to numerous types of faults.

https://en.wikipedia.org/wiki/Bounced_landing
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Just_a_fan
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Re: 2022 cars 'porpoising' at high speed

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vorticism wrote:
Wed Mar 09, 2022 5:03 pm
Just_a_fan wrote:
Tue Mar 08, 2022 10:21 pm
vorticism wrote:
Tue Mar 08, 2022 6:16 pm
Doesn't matter if it's pilot induced (though it sometimes isn't). Point was: ground effect + undampened spring force creates a feedback loop known as porpoising. Alternating pressure gradients beneath aero surfaces. Both vehicle types have at least one way of curing it: slowing down.
A "pilot induced oscillation" (to give it the correct term) is not aerodynamic porpoising as exhibited by the cars because it's not inherent in the aircraft but rather in how the aircraft is flown by the pilot. The cars will porpoise at a given speed for any driver because it's inherent in the car's design/setup.
Wrong again. See my other prev posts. The agency of the pilot/driver is irrelevant. The physical phenomenon is governed by the same forces. What's known as a type of bounced landing. PIO is a general term and could happen at various altitude, be applied to numerous types of faults.

https://en.wikipedia.org/wiki/Bounced_landing
The increasing and decreasing angle of attack of the aircraft on approach and as they approach touchdown is classic POI. The issue started well before the wheels first touched the ground. Then the pilot tried to correct the situation with control inputs.

Even the Shuttle pilots had an issue with PIO during the early test flights. The control logic was altered to add some damping of the pilots' control inputs to help prevent PIO in future by slowing the response of the controls to inputs.



You can see the PIO starting before the wheels touch the runway. Once they do, the pilot then over controls and the vehicle under goes further oscillations in the air.

Anyway, aircraft PIOs or undercarriage bounces are off topic for the aero-created porpoising of the current F1 cars.
If you are more fortunate than others, build a larger table not a taller fence.

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vorticism
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Re: 2022 cars 'porpoising' at high speed

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Why belabor this? POI is a more general term; bounced landing, 'porpoising,' a more specific one (I used the more specific one.) Third time: the phenomenon is governed by. the same physics, hence why I posted it
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Just_a_fan
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Re: 2022 cars 'porpoising' at high speed

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vorticism wrote:
Wed Mar 09, 2022 5:37 pm
Why belabor this? POI is a more general term; bounced landing, 'porpoising,' a more specific one (I used the more specific one.) Third time: the phenomenon is governed by. the same physics, hence why I posted it
The clue is in the name: Pilot Induced Oscillation. The pilot creates the problem by over controlling and then exacerbates it by adding control inputs that are too late and thus cause an increasing change in attitude in a positive feedback loop. The aircraft doesn't do this inherently (except where the aircraft is deliberately unstable and the control laws aren't correctly implemented) - it's caused by the pilot. Hence Pilot Induced .

The car bouncing along the track is not caused by the driver. It's not a DIO.

Anyway, there's no point going over this further.
If you are more fortunate than others, build a larger table not a taller fence.

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Postmoe
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Re: 2022 cars 'porpoising' at high speed

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Just_a_fan wrote:
Wed Mar 09, 2022 5:21 pm
vorticism wrote:
Wed Mar 09, 2022 5:03 pm
Just_a_fan wrote:
Tue Mar 08, 2022 10:21 pm

A "pilot induced oscillation" (to give it the correct term) is not aerodynamic porpoising as exhibited by the cars because it's not inherent in the aircraft but rather in how the aircraft is flown by the pilot. The cars will porpoise at a given speed for any driver because it's inherent in the car's design/setup.
Wrong again. See my other prev posts. The agency of the pilot/driver is irrelevant. The physical phenomenon is governed by the same forces. What's known as a type of bounced landing. PIO is a general term and could happen at various altitude, be applied to numerous types of faults.

https://en.wikipedia.org/wiki/Bounced_landing
The increasing and decreasing angle of attack of the aircraft on approach and as they approach touchdown is classic POI. The issue started well before the wheels first touched the ground. Then the pilot tried to correct the situation with control inputs.

Even the Shuttle pilots had an issue with PIO during the early test flights. The control logic was altered to add some damping of the pilots' control inputs to help prevent PIO in future by slowing the response of the controls to inputs.



You can see the PIO starting before the wheels touch the runway. Once they do, the pilot then over controls and the vehicle under goes further oscillations in the air.

Anyway, aircraft PIOs or undercarriage bounces are off topic for the aero-created porpoising of the current F1 cars.
I don't know if it's related but motorcycle wobble can be driver induced but is determined by the motorbike's characteristics AND aero. Specially if the wavelength surpasses normal human reaction times.

BTW, I experienced it in a very drastic way at "not so high" speeds, and suspected the unusual positioning of the bmwF800R fuel tank (rear). It stopped when I changed my backpack: I think it acted as a moving shark fin.