Technical Analysis: 2018 Barcelona McLaren Nosecone, pt. 1 regulatory framework

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In this series of 3 articles we will discuss what the new McLaren nose cone does and what the team had to do to achieve this radical piece, as there were a lot of regulatory and structural barriers in place that made it difficult to bring out this solution.

The first article will talk about the regulatory side, the second one will debate its influence on the airflow and finally we will discuss the crash impact structure & elaborating on the crash test specifically, in a third article.

How did McLaren succeed getting the nose cone legal

At first glance the 3 holes in front and the slats at the sides look to be contravening the rules if we assume (falsely) for a moment they go straight through the nose and exit in a straight line at the back. The rules specifically state that the nose cone has to be one single, open piece in cross-section:

3.4.1 Nose Shape
Only a single section, which must be open, may be contained within any longitudinal vertical cross section taken parallel to the car centre line forward of a point 150mm ahead of the front wheel centre line, less than 250mm from the car centre line and more than 125mm above the reference plane.

The best way to envision this, is to take the nose in iso view and imagine a geometric plane running parallel to the car centre line, moving from one side of the nose cone to the other. Should the moving plane be able to create 2 separate pieces at any point along its path, the nose cone will not be deemed legal. Also, just looking straight at the nose cone from the front, if any holes are visible, than that would mean it's illegal as well. Visualising this, let's take some cross sections at all contested areas:

So what we see here, at first glance, is that the cross sections create 2 separate pieces at each cross section plane. The holes (blue and green stripes) are quite obvious in that regard -again, falsely assuming these are straight holes running parallel to the car centre line- but the slats seemingly fall foul of the cross section because of the upper support strut (yellow encircled) together with the strut connection to the snow plow (yellow stripe).

So each one of those cross sections would seemingly be an infringement on 3.4.1 and would result in a disqualification based on technical grounds. It doesn't matter if it is a small or big infringement; any visible and proven violation of the technical rule book results in a disqualification. However, McLaren are of course no fools and made sure to implement solutions that actually defeat the literal interpretation of the rule book and thus are technically legal:

The support strut is located just inside the bulkhead area and therefore technically placed outside, barely, the actual nose cone area. There's an area 150mm in front of the front wheel centre line that is excempt of (most) rules. With the strut being placed there, it isn't counted toward the cross section and with only the foot of the slats connected to the flat snow plow, the slats and indeed the nose cone in that area are atleast already considered being one single part.

On a side note, the slats can't be placed (much) wider. 3.4.4 further limits the effective nose cone area:

3.4.4 Exclusion volume around the front wheels
With the exception of the mirrors described in Article 3.5.2, in plan view, there must be no bodywork in the area enclosed by the intersection of the following lines:
a) A longitudinal line parallel to and 1000mm from the car centre line.
b) A transverse line 450mm forward of the front wheel centre line.
c) A diagonal line running rearwards and outwards, from a point 875mm forward of the front wheel centre line and 250mm from the car centre line, at an angle of 28° to the car centre line.
d) A transverse line 875mm forward of the front wheel centre line.
e) A longitudinal line parallel to and 165mm from the car centre line.
f) A diagonal line running forwards and inwards, from a point 430mm rearward of the front wheel centre line and 240mm from the car centre line, at an angle of 4.5° to the car centre line.
g) A diagonal line from 430mm rearward of the front wheel centre line and 240mm from the car centre line to 550mm forward

The reason why McLaren was able to place these slats there is because they designed a slimmer nose than the maximum allowances, which gave them the regulatory space to put down the slats. The slats don't fully touch the max allowed limit, but the snow plow underneath does. Infact, the snow plow can be seen as a blue print of the max allowed dimensions in bird view.

Now regarding the holes: McLaren took a long look at what the competition did and assumingly combined ideas from both Red Bull and Force India/Sauber. At the present moment we aren't fully sure of the exact solutions McLaren has in place, but we can speculate on them and discuss several likely ways mclaren ducts these holes.

The middle hole could be made legal by placing a series of small vanes inside the hole in such a way that air can still pass through, while technically staying true to the cross sectional rule. This solution is copied from Red Bull, and can be put to good use for McLaren's middle hole:

As one can see, the vanes are stacked in such a way that the cross section will always cut one vane and at the edges inbetween 2 vanes it will cut 2 vanes in an overlap. Because both vanes are connected to the bottom and roof of the innards of the nose cone, it effectively means you still have a single section on the cross sectional plane, just with a cavity inside. There's quite some variation possible with this set up; Red Bull definitely had or even has a set up shown in yellow. Looking inside the middle inlet of the McLaren nosecone however, we detect only a single vane, which could indicate a solution close to what is shown by the blue outline around the vanes, indicating a large middle vane and a narrowing of the sidewalls. This is how that would look in iso view:

There is a different possibility however, one that Force India has been using since 2015 for its side inlets. They figured out that if they camber the duct enough going through the nose and exiting on the underside of the nose, you actually can't get 2 seperate parts anywhere with your cross sectional slice. They use this solution for their side inlets. A video to demonstrate:

Basically, 3.4.1 is a 2 dimensional rule which can be worked around when looking at it 3 dimensional. The trick is to camber the duct diagonal.

Sauber has been using this solution too for the side inlets, and teams up and down the grid have been inspired by this idea to create the smaller, so called, NACA ducts to get legal holes in their nose cones to feed for instance the S-ducts. In the cases of McLaren, Force India and Sauber, the holes are intended to vent airflow undeneath the nose. That same principle can be used for a middle hole:

What they can do is split the inlet in 2 and duct them sidewards and downwards. The advantage over the solution with the vanes, is that it creates less blockage for the flow. However, it also forces the flow to bend more and lose energy. We don't believe they are doing this, but it is possible.

This concept of circumventing 3.4.1 is definitely used for the side inlets as well. Ultimately, the overall layout can differ a huge lot however. 2 examples below:

Ultimately, after a lot of consulting (special thanks to jjn9128) and asking around and deducting what we see on pictures, we believe the McLaren internal layout of the nose cone will look something like this:

As mentioned, the middle inlet is made legal by placing bodywork inside the duct to get it cross sectional legal. Through observing, we deducted that it has to be a single piece instead of several vanes with a shape roughly like that. It's crucial to note that we have observed small trailing edges (not shown on the iso view illustration) inside the outlet for the middle duct. It's guessing if these are the trailling edges of small vanes to clear up high energy flow inside the ducts, or that they are effectively creating more ducts somewhere inside the middle hole. We choose for small vanes on our illustrations to keeps things from getting overly complicated, but these small trailling edges could just as well be indicative of more ducts. We simply don't know. Either way, it will help clean up the flow.

The outer ducts are very specifically made to get by the cross section rule, running downwards and inwards the pylon to exit below at the sides of the middle duct outlet. It has to narrow quite radically in order to comply with 3.4.1, but this narrow passage should not immediately create an obstruction for the flow. Again, we observe a leading edge inside the inlet, which either is a small winglet or a panel effectively splitting the duct in 2. It's always guessing, but we went for the vane solution to help steer flow through the narrow legality gap. We also placed these vanes in the back near the outlets of the side ducts. You want to have the flow exit as straight as possible as this flow goes to the splitter.