Technical Where/What, is the Reference Plane in F1??

After having a rather in depth discussion about the legality of the flexible wings, the pitfalls of proving if they are legal or illegal, and the definition of the reference plane with Galahad, I have been prompted to write the following article. Hopefully, by the end of it we can try and get a common consensus on what exactly the reference plane is, and how it is related to the flexibility of the front wing.

I hasten to add, that the following is purely my interpretation, and as such may well be incorrect, so please do not hesitate to put your point across if you disagree with me.

I'll start by saying that the reference plane is not a fixed distance in relation to the car and the floor. The reference plane is constantly changing be it through the change of ride height of the car, the change due to suspension effects, or even the ground, which obviously is never perfectly flat.

So where to begin? I guess the first place will be a schematic or two from the FIA Technical Regulations





For more detailed drawings please click here (BIG pdf file)

To start to define the reference plane, first we must define a plane. In mathematics, a plane is any flat, two-dimensional surface. A plane is the two dimensional analogue of a point (zero-dimensions), a line (one-dimension) and a space (three-dimensions).

Therefore the reference plane, in the case of F1, is an imaginary plane, of infinitesimal thickness, that all other measurements defined in the technical regulations are based on. As the reference plane is undefinable in relation to the ground, it is essentially imaginary. Instead all other measurements are based in relation to this imaginary plane.

The easiest way to think about it, is that it is the lowest area of the car, the area closest to the ground of the sprung area of the car (the chassis). As defined in the technical regulations, the skid block is attached to the reference plane, and as such is the only part of the chassis that is allowed to lie below the reference plane:

"When the skid block is new, ten of the fasteners may be flush with its lower surface but the remainder may be no more than 8mm below the reference plane."

Therefore we have all the design constraints/measurements for the design of the car based on the reference plane (in the vertical direction) and the centre lines of the wheels, a more understandable concept (in the lateral directions), all based around the car centre line.

In effect the exact dimensions of the reference plane, are the dimensions of the skid block and extends from 33cm rear of the front tyres all the way back to the rear tyres, and must be between 30cm and 50cm wide.

From 1994, with the FIA becoming increasingly concerned with the faster speeds of cars, a further plane was defined, the 'step plane'. Lying 5cm above the reference plane, this step plane runs from a line level with the front of the plank to one 33cm in front of the rear wheels, and is the level at which any bodywork viewed from the underside which is not on the reference plane must stop. This takes in the three main areas of bargeboards, sidepods, and diffuser. In effect banning teams from building bodywork closer to the ground to gain a significant aerodynamic advantage (skirts anyone?).

So how does this explain the illegality of the new flexible wings?

Well the allowed dimensions for the front bodywork (i.e. the wings) is defined in the various parts of article 3.

Article 3.7.1: All bodywork situated forward of a point lying 330mm behind the front wheel centre line, and more than 250mm from the car centre line, must be no less than 75mm and no more than 275mm above the reference plane.

In effect, the wings have to lie within 75 mm and 275 mm above the reference plane. Many people (media) have been quoting the regulations as saying that the wings can lie no more than 85 mm from the ground. I believe this has been worked out as an approximation of the average ride height of the car plus the 75 mm, although I am not sure on this point.

The wings are further defined (and in my opinion it is the following regulation that really defines the flexible wings as being illegal) in article 3.15

Article 3.15: Aerodynamic influence :
With the exception of the cover described in Article 6.5.2 (when used in the pit lane), the driver adjustable bodywork described in Article 3.18 and the ducts described in Article 11.4, any specific part of the car influencing its aerodynamic performance :
- must comply with the rules relating to bodywork ;
- must be rigidly secured to the entirely sprung part of the car (rigidly secured means not having any degree of freedom) ;
- must remain immobile in relation to the sprung part of the car.
Any device or construction that is designed to bridge the gap between the sprung part of the car and the ground is prohibited under all circumstances.
No part having an aerodynamic influence and no part of the bodywork, with the exception of the skid block in 3.13 above, may under any circumstances be located below the reference plane.

Understanding that the teams are very clever, and that current testing methods may be insufficient to enforce the regulations. The FIA also cover their own backs by the following declaration in article 3.17.8

Article 3.17.8: In order to ensure that the requirements of Article 3.15 are respected, the FIA reserves the right to introduce further load/deflection tests on any part of the bodywork which appears to be (or is suspected of), moving whilst the car is in motion.

The difficulty, as Galahad and I have discussed in detail, is proving that any regulations have been broken, when the car is in motion. A very difficult prospect at best, with video evidence normally being seen as circumstantial, in ideal conditions.

I'd appreciate any thoughts you might have on the matter.

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Cheers G, you'll be pleased to know that I finally understand what you are saying! Forgive me, I was a trifle slow earlier on

I fully take you point on not assuming that the reference plane is at all times parallel to the ground. Indeed like you say is probably more likely than not that, that teams will run different ride heights front and rear, and so will rarely be parallel to the floor. I'm inclined to agree, however, that although technically (and legally) possible for the teams to run with a high degree of rake, there would be no overall advantage for the teams to do so.

You've also brought me round to the idea that the actual effect we are seeing, with regards to the flexing front wing, is yawing of the whole nose cone assembly, as well as some clever load checked design of the carbon fibre composites in the front wing.

For the entire nosecone area to flex down, it would have to be hinged from somewhere near the leading edge of the skid block, hence the new regulations stating that the skid block can now be compromised of no more than 2 separate pieces, no less than 1m in length.

Really enjoyed this discussion

Its times like these that make you wish the teams had to declare all of their technical secrets at the end of the season

I've done quite a lot of work with carbon fibre, so I can understand (purely on a materials aspect) how you can design the composites to deflect past a critical load, however I am not so sure that is all there is going. As for the flexing aspect of the floor that has been suggested, I have to admit I can't really get my head around how that would work. The only reason that it is being considered is because of the new tests being introduced by the FIA.

After all this flexing wing business, I'm starting to think that only RBR and Ferrari really knows whats going on, and that not even the FIA are really that sure. Maybe just trying to introduce tests to cover all bases.

There is no doubt that the guy who designed the system is sitting in his garden shed somewhere laughing quietly at all the trouble he has caused

Major Dude,

Good work. I have just finished a 12 hour day at the college (I teach a night class 2 nights a week and take Fridays off) and have read your article but have not yet digested it. It will be sometime tomorrow before I can think this through, but I want to say that I have a great interest in this type of article and appreciate that you have brought this forward.

Some initial thoughts: The reference plane is in fact a line one draws on a clean sheet of paper. It provides the point of measurement for all things above and below that line. The "X" can only be "Y' distance above it, and the "A" can only be "B" distance below it. It is a point of reference and does not, as you have said, refer to the ground at all.

What can be said is that the reference plane is never closer than 10mm to the ground because of the minimum thickness of the plank. But it could be any distance above the ground as no demensions are specified except from the reference plane.

The next step is to determine the relative position of the wings as compared to the reference plane, and then see this: if the plane were only 10 mm above the deck, the minimum distance, where would the wing be relative to the ground?

I haven't worked this out, and you may already have done so, but that is a subject that is different from the deflection tests. I'll get back to you after I have had time tomorrow to do the maths.

The deflection tests measure the movement relative to the plane in static tests. But, it the reference plane is above the minimum during testing, and the deflection is within the allowable perameters, the wing passes. But, the reference plane may be, in static tests, well above the minimum of 10 mm enforced by the plank. You can see what I'm thinking, but I haven't run the numbers.

PM me if you want to talk via Skype or MSM or whatever. I would welcome that, but our time zone differences llimits the opportunities. I am -6 hours BST. This offer is also open to anyone else. I love to talk as it sharpens my understanding.

Good show to everyone here!

Could they pitch the car forward, through the flexing not of the floor but through the support bar that connects the front of the car floor with the underside of the drivers pod? If this bows left or right even just a few mm could this not cause the car to pitch forward, lowing the front wings and starting the ground effect?

I may be out of my depth with an understanding, just I know the boffins in F1 have some imagination. Is it true one team developed traction control by using a LED transmitter that corrected the cars acceleration by picking up the sunlight flashing through the spokes of the rear wheels?

What reference in the regulations keeps the reference plane on or near the horizontal?

If the reference plane is an imaginary plane and doesn't have a constant relationship to the ground would it not be possible to rotate it 90°? You could build the car above the reference plane effectively stretching out in front of it and in contact with the ground. Admittedly you'd have a ruddy great plank sticking up at the rear of the car but a few aero devices and an F-Duct could significantly reduce any drag...

Cheers Flood, that is a much more eloquent way of putting it, rather than my ramblings, totally agree!

And yes, this is where the arbitrary 85mm has come from. 10mm, the minimum distance the r.p. can be from the ground, plus the 75mm that the front bodywork has to be above the r.p! (Article 3.7.1)

As for the legality of the wing, despite video footage showing that the wing deflect a lot during running, as you say they stand up perfectly to the deflection tests. Simply I think because the loads experienced by the wing at high speed are at least 5 time more extreme than the loads applied in the deflection tests. Some of the flexing may well appear to be exaggerated however as the downforce will also push the chassis closer to the ground.

Cheers for your input

I don't think so, as this flexing would still take the bodywork below the arbitrary reference plane.

Where as I don't believe there are any regulations that keep it in the standard orientation per say, there are regulations on how everything is built up from the r.p. by this I mean things like the orientation of tyres and bodywork (i.e as all the tyre must be in contact with the ground etc.). These effects help to pin down the orientation of the reference plane.

There are a whole stack of drawings on here that answer most of the questions.They help to work out the what the appoximate height of the reference plane is likely to be.
Being a bit of a techophobe I just put the link.

http://argent.fia.com/web/fia-public.ns ... 2-2010.pdf

Cheers for that link sportsman.

I'm going to update the main body of the article with the link, as well as use one of the extra drawings in that document. One of them rather nicely shows how, even though the reference plane is arbitrary, every major part is based upon that plane (including the wheel axles lying 200 mm above the r.p.) which most readers will be able to use as a point of reference. Many thanks.

Great Article Major!

This is why the closeness of the wings to the ground is something of an irrelevance, I believe. As I understand it, all measurements are to be taken assuming the reference plane to be horizontal. There is nothing in the rules to say that the reference plane (being imaginary) must then remain horizontal, or even parallel to the track surface, during the race (clearly, that would be impossible anyway); it is merely a device against which to measure the stipulated dimensions.
So if the car in race trim were tipped forwards, by lowering the front suspension settings and raising the rear, the wing (even if perfectly stiff) would automatically tip closer to the track surface while still being the correct design distance above the reference plane. The issue of wings flexing is of course a different matter again.

Brogan, what I don't understand about that article, which I saw from a link on another forum, is this:

I thought at first that the test had been revised simply to double the load from 50 to 100kg; I hadn't realised that the point at which the load is to be applied had also moved inboard.

To explain my confusion I will use this analogy; if an olympic diver weighing 80kg stood on the tip of the springboard, the tip of the board (it being by definition quite flexible) would obviously deflect by a certain distance relative to the water surface (which we could call the reference plane). Now, if that diver were to be replaced by a bigger diver weighing 160kg, the tip of the board would clearly deflect more. So if that diver, twice as heavy as the first one, moved back from the tip of the board to the middle, the tip would deflect less again. So if the deflection were roughly the same between the 80kg diver stood at the tip, and the 160kg diver stood in the middle, the end result would be the same.

Now, if the FIA want to increase the severity of the test, have they not defeated their own object by simultaneously doubling the load and moving its point of application inboard?

Yes, I saw that article; a very interesting read. But my issue is, even ignoring torsional flexing, the applying of the static load nearer the support posts could be completely negating the effect of doubling the load. Surely, if they are going to apply the load further inboard, they should increase it much more than simply doubling it, for the reasons I stated earlier.

Anyway, just to add further to the debate about the reference plane and measurements, here are a couple of relevant extracts from the technical regulations:

3.2 Height measurements : All height measurements will be taken normal to and from the reference plane.
and:
3.14.3 All overhang measurements will be taken parallel to the reference plane.

So, as I was alluding to before, it really doesn't matter what position the reference plane is in, as all measurements are simply taken parallel or normal to it. So it could be hanging vertically, it really doesn't matter.

Finally, apologies to Galahad; I had failed to read your first post, and didn't realise that I was more or less repeating (though less eloquently) what you'd suggested about the use of rake to lower the front wing. But I am sure I read an article somewhere recently claiming that Red Bull were able to run a much higher rear end, to help in this, due to the efficiency of their EBD.

So although the reference plane doesn't have to be parrelell to the ground, it must be straight? If so then any wing that ends up shaped like that smiley face's mouth can't go that far before it reaches the reference plane?