Pitch sensitivity and effect on aero.

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FoxHound
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Joined: 23 Aug 2012, 16:50

Pitch sensitivity and effect on aero.

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Reading through an AMuS article earlier and came to some interesting points.

Apparently, an unnamed Mercedes engineer has spoke to Schmidt, saying Mercedes' pitch is 1.0 in comparison to Red Bull's 1.9, which means it carries less drag.
All things being equal(PU wise) Red Bull would need to cut more wing to achieve the same top speeds as Mercedes. Given the draggy set up, it's a hit Red Bull take knowing the higher pitch provides more DF through corners.

Ferrari's pitch is set at 1.4.

What interests me here, is how wing cutting can affect the overall pitch of the car, why not just reduce the pitch to 1.0 and keep comparable wing angle? Is pitch related to rake? And can suspension setup not even out pitch to a lower denomination?
What effects of high pitch/low wing angle to tyre usage?

Obrigado amigos!

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domh245
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Joined: 12 Mar 2015, 21:55
Location: Nottingham

Re: Pitch sensitivity and effect on aero.

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Sounds to me as if that is just the rake angle.

AMuS' own information on car rakes seems remarkably familiar to your 'pitch' values
Image

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DiogoBrand
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Joined: 14 May 2015, 19:02
Location: Brazil

Re: Pitch sensitivity and effect on aero.

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As far as I knew, rake was a low-drag way of getting downforce, because a high rake angle would basically give the same amount of lift as a "big" rear wing, while at the same time having lower drag. But I'm not entirely sure this is correct.

A good explanation for those statements is that Mercedes is constantly trying to state that the other Power Units are as good as their own, in order not to make the rule makers try to take away Mercedes' advantage. Maybe that's not the case on this matter, but it would make perfect sense.

Maybe Red Bull has such a good DF/Drag ratio that even having more drag they can make up for it in the corners, but that wouldn't make any sense, because on this case they'd probably want to have the same DF as everyone else while having lower drag instead of having maybe a lot more DF for a little more drag.

Knowing Red Bull's quality on the aero department I really doubt they'd need more drag to achieve the same levels of downforce as Mercedes. To me my second scenario seems the most likely of the three.

bhall II
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Joined: 19 Jun 2014, 20:15

Re: Pitch sensitivity and effect on aero.

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In broad terms...

Because the regulations revolve around a car's reference plane and not an arbitrary reference point outside the car, e.g. the track, there's no enforced minimum ride height beyond that which results in permissible plank wear. As such, it's my belief that rake is a consequence of lowering the ride height of the front wing in order to increase downforce. Since doing so enhances ground effect, the increase in downforce is accompanied primarily by increased induced drag. Adding the same amount of downforce through higher AoA alone would add both induced drag and parasitic drag. (It's also not always possible, because there's a practical limit to AoA, and it tends to be lower at higher ride heights.)

The drawback is increased pitch/ride height sensitivity, as the distance between a component and the ground is more critical at lower ride heights. That means downforce is subject to greater variation during transient events such as those encountered on an undulating track. In other words, downforce fluctuates more given a change in ride height from 20mm to 10mm than it does given a change from 30mm to 20mm. Additionally, to avoid undue wear of the plank, lowering the front wing requires raising the diffuser, which ultimately means it has to be designed with a higher AoA than would otherwise be necessary, and the higher AoA makes it just as sensitive to ride height variations.

Make sense?

Image
from Ground Effect Aerodynamics of Race Cars

The graphs above depict downforce as a function of ride height. We can see that front downforce coefficient grows to ~1.99 from ~1.83 if the front of the car is lowered to 10mm from 20mm (h) concurrent with the rear being raised to 60mm from 40mm (h ). The same adjustment reduces rear downforce coefficient to ~2.43 from ~2.63; hence the need to increase the diffuser's AoA when adding rake.

Combine all of those factors with the need for all aero elements to work together across a wide range of conditions, and you're left with a very difficult task that presents quite a few unusual problems. But, if you can make it work, it's the ideal aero strategy for the current rules.

(I --- love aero.)

Greg Locock
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Joined: 30 Jun 2012, 00:48

Re: Pitch sensitivity and effect on aero.

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There's some interesting details in those graphs. The sweet spot for rear wing is at a constant pitch.

SameSame
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Joined: 16 Jun 2016, 18:44

Re: Pitch sensitivity and effect on aero.

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bhall II wrote: The graphs above depict downforce as a function of ride height. We can see that front downforce coefficient grows to ~1.99 from ~1.83 if the front of the car is lowered to 10mm from 20mm (h) concurrent with the rear being raised to 60mm from 40mm (h ). The same adjustment reduces rear downforce coefficient to ~2.43 from ~2.63; hence the need to increase the diffuser's AoA when adding rake.
Why would you need to increase the diffusers AoA? Sorry I know this is a bit off topic, and I've searched but could not find a definitve answer, but how would that result in improved rear downforce? Would a higher AoA not decrease the dynamic head and increase the static head of the diffuser at a much faster rate, thereby producing less drag but less downforce too?

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FoxHound
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Joined: 23 Aug 2012, 16:50

Re: Pitch sensitivity and effect on aero.

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Ben,

I'm getting bits of what you described, incidentally very well described I'll add.

From what you've mentioned, I'm getting the high arse rear end of the Red Bull being softly sprung up to the point of a (relative) flat floor?
Higher rear side floor in the slow stuff, lower when the force of air pushes down at speed.
All very well and it makes sense if correct?

But why is there such variance in the philosophies of the front running teams?

Straight off the bat I'm getting that Red Bull would have higher drag/DF in comparison to either Merc/Fezza.

Then with Baku, you have a situation where the engine in the Red Bull is not on par with either Merc/Fezza, and the team is cuts wing to attain good top speed.
The repercussions here are that the arse end be higher and only lower at a higher speed than average, unless softly sprung.
If softly sprung, you are reaching into a dark recess of tyre woes, which we clearly saw for them on some compounds.
bhall II wrote:(I --- love aero.)
You'd never tell.... :D
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