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nocones GRM+ Memberand PowerDork
11/17/22 10:46 a.m.

I've seen several cars on the IG that have INCREDIBLE engineering, fabrication, and $$ in them with incredibly large front elements.  

That's not unusual, large 15-20" cord wings or splitters with diffusers are pretty common.  Even for cars with more "modest" depth front splitters the actual splitter length when including the part under the bodywork can be quite large.  

But what seems to be different about these is they are entirely in front of the body work and are incredibly flat. 

An example (Not picking on it, this car is incredible and I am sure it will be insanely fast) is the Nuked Performance M4. 

The front element is massive, and protrudes in front of the car completely.   It appears to have some amount of curvature to it's underside, but it is not massively "wingshaped".    They posted some pictures in the last few days of it's shakedown and it is incredibly low and very thin and very paralell to the ground. 

It looks like it's an Airfoil with almost 0 Camber, 0 AOA, and something like a ~20:1 chord to thickness ratio

So whats going on here?  I'm assuming it's Aerodynamically correct because again given the rest of the car they are doing things right.  

Is it an efficiency thing?   Very small delta P generated over HUGE area so the front element doesn't have to be more aggressive?  

I am an Aero novice, but when things are explained to me I am capable of understanding them so I am curious.  This seems to be the way Time Attack Cars are moving.  Feras Qartomy's Gridlife Unlimited wining Corvette is similar, but doesn't seem to have as large of a Chord to thickness ratio.

The LMP360 front element that I currently have is a "prototype" placeholder.  My plan has always been to re-build it more "correct".  I had assumed that would be basically the same shape  but with a properly designed multi element Airfoil section in the middle, with diveplanes outboard and above the foglights.   However these elements people are using make me think I can gain some more advantage to the area outboard of the inner element if I understand what they are doing.    I realize my car is a little unique compared to these in that I can do more with the area between the wheels and the nose, but Learning new things never hurt.  

¯\_(ツ)_/¯ UltimaDork
11/17/22 10:50 a.m.

In for learning.  You also see these on Pikes Peak cars:

Monster' Tajima Breaks 10-Minute Pikes Peak Record: Video

nocones GRM+ Memberand PowerDork
11/17/22 10:56 a.m.

One more for reference, and because who doesn't like looking at over the top Aero cars?

stafford1500 GRM+ Memberand Dork
11/17/22 11:15 a.m.

Flat-ish splitters are the direction due to the pressure signature around the leading edge. There is a very deep pressure (suction) spike near the leading edge as the air is turned around that relatively sharp radius. Keeping the surface aft of that fairly flat and not too much angle of attack is the primary means of not stalling the flow. It does require some pretty massive effort to maintain ground clearances over the operational envelope of the car (really stiff wheel rates).

Your car, with slot gapped elements can get away with more curvature and shape due to the energy injection at the slot gaps. Same reason multi-element rear wings can be run at ridiculous final element angles.

Also, more area ahead of the car is more leverage.But it comes at the cost of having to control attitude so you dont grind off all that pretty splitter structure. The top facing surface has some impact on the total downforce generated (~1 magnitude less than the underside), but more importantly it conditions the flow direction before the other aero items like end plates and dive planes.

sleepyhead the buffalo
sleepyhead the buffalo GRM+ Memberand PowerDork
11/17/22 4:33 p.m.

is the Nuke Performance M4 being built for Global Time Attack, Super Lap Battle, World Time Attack... or D) some combination of the first three?

I reckon some of this has to do with Feras and the Nuke M4 being front engine, and built to a certain ruleset.  Plus, them and the Hoonipig are built on "existing Production car chassis"... which tend to limit what how high up you can bring the front element (plus there are significant benefits to brining the front element as far into Ground Effect {GE} as possible)... and what you can "do" with air that you've accelerated under their front flaps... compared to LMP360.

on the other hand, as Stafford pointed out (and we've seen in F1 this year?)... there's pretty significant drawbacks from relying on GE for your aerodynamic downforce.

TPlesmid New Reader
12/5/22 2:18 p.m.

First off, apologies if I underestimate anybodies knowledge here, I'm just breaking down my understanding.

From what I understand, the majority of the downforce created by splitters is mostly unrelated to any kind of aerofoil effects (F1 front wings are different, they literally are wings on the front that utilize their aerofoil shape to create downforce). On more "normal" cars what happens is you get a big high pressure zone at the bumper anywhere there isn't a duct because the air is all smushed up against the bumper or air dam being pushed through space. This high pressure air can either go over, under, or around the sides of the car. Splitters basically act as a shelf for this air to push down against, which obviously creates downforce. Once the pressure in this zone gets high enough, "new" air coming in somewhat goes around it, so it's effectively like the area is filled in solid (this effect is not as intense as it sounds from my understanding but does still exist). This can effectively "soften" the front shape of the car from an aerodynamic perspective. This is just a random pic I found but it kind of shows off this idea.

Splitter and air dam

The pikes peak escuido has huge end plates which stop the air from going around the sides, maximising this effect and forcing all the air in that high pressure zone through their duct, and forcing new air that's not filling in the high pressure zone over the car. Elements on the side like the M4 are just another way to maximize the extra air if you don't go the huge end plate route.

So you're right, from an aerofoil element perspective they are not effective, but that's because they're taking advantage of a different concept. It's worth noting that this is all in front of the bumper, so any ground effect is a whole different story. It's been mentioned that it can be hard to keep these splitters off the ground which stalls airflow under the car ruining GE, but it's doable.

pres589 (djronnebaum)
pres589 (djronnebaum) UltimaDork
12/5/22 2:52 p.m.

That was my understanding as well, that these large front splitters are basically a shelf that air which has stacked up against the front of the car uses as a lever to press the front of the car down.  They're not really an aerofoil as such.

stafford1500 GRM+ Memberand Dork
12/5/22 3:20 p.m.

For TPlesmid and pres589:

There is a measurable amount of downward force generated on the top surface of an exposed splitter. However the majority of the load comes from the bottom surface. The way to think of any aero device is the differential pressure between opposing surfaces (top and bottom in this case). If the car/splitter were very high off the ground the method you are describing is approaching reality. Once the car is down near the ground the effect of the air pressure on the ground is magnified. This is the ground effect, exactly.

The air that is redirected from the front of the car to the underside of the splitter  (this actually starts to happen several feet to many feet in front of the car, depending on the frontal area and speed) accelerates and results in very high speeds over a very small area as it turns under the leading edge of the splitter. This results in a very low pressure on the bottom surface of the splitter. The air that "stagnates" near the nose has the same pressure as the air at a distance from the car (1 atmosphere). The relative low pressure under the splitter compared to this stagnation pressure results in a downward force on the exposed surface of the splitter. The bottom side low pressure does not stop at the same location as the vertical nose, it extends back along the car and gradually rises back to the pressure at or near the back of the car.

The extended area that the low pressure works on is the primary downforce producer. The top exposed edge may only produce ~10% of the splitter downforce. See my notes in an earlier post about the difference between flat splitters and slotted (wing-like) designs.

stafford1500 GRM+ Memberand Dork
12/5/22 3:23 p.m.

The reason some cars wind up with very long overhangs is to take advantage of the leverage of putting the low pressure spike at the bottom leading edge of the splitter to work and to provide as much length as possible for it to work harder on the car. The long overhangs are generally a function of rules or bodywork limitations. If you had complete freedom, the splitter would not be so exposed and the underside would be more shaped to keep the low pressure working as hard as possible for as long as possible.

Cedricn New Reader
12/22/22 12:01 p.m.

The M4 is a space frame car, built for time attack 'unlimited', with almost no rules at all. Hope to see it on track somewhere around here next year :)

Ask the guy here, he is friendly. Verusengineering did the aero CFD on it, So he have lots of details. The splitter is not all flat, there are some tunnels under it.

sleepyhead the buffalo
sleepyhead the buffalo GRM+ Memberand PowerDork
12/22/22 1:52 p.m.
Cedricn said:

The M4 is a space frame car, built for time attack 'unlimited', with almost no rules at all.

That's interesting.  I would have guessed GTA "limited"... since the it "looks" like the main plane element fits about the dimensions restriction required of limited (10in forward, 14in sidewards).  And the two outer elements "look" like they're cheekily taking advantage of a "limit two canards per side" requirement... although, refreshing my familiarity of the GTA rules, I see that the canard limit is a "street" rules restriction... and with the added complication of only 7" sidewards for those.  Which is odd, since the "splitters" and "diffusers" (among other things) are limited to 5inch extension in any direction.  Seems like theres an argument to be made that those dimensional restrictions could/should be harmonized.

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