Interpretation of Feb 2013 GCR concerning FC Diffusers

[Purple Frog]

Hopefully this thread will be taken serious and not become a flame fest.

In preparation for the 2013 season i have been pouring over the 2013 February GCR for a few days. I keep reading on Apexspeed that diffusers allowed in 2012 F2kCS will not be legal in SCCA Club in 2013.

Seriously, can somebody elaborate?

Is it 9.1.1.4.c the language i colored red?

Based on the language in 9.1.1.6.e., it would appear that all diffusers as we know them are illegal. SInce it doesn't exempt FC diffusers...

If you answer, please include page number, section number, etc. so it will be clear and concise. Please, no opinions, without reference to applicable rule and verse.

Below are all the rules i could find that apply to FC diffusers:



9.1.1.4. Bodywork (page 260)
9.1.1.4.c Bodywork and rear spoiler(s) and any attached components except for suspension components shall not exceed a maximum width of 95cm (37.40 inches). No part of the bodywork, rear spoiler or exhaust system shall extend more than 100cm (39.37 inches) FF; 80cm (31.50 inches) FC behind the centerline of the rear axle nor exceed in height a horizontal plane 90cm (35.43 inches) above the ground with the car as qualified or raced with the driver on board. The safety roll bar/roll cage, fairings, and engine air box are not included in these restrictions. Bodywork shall not increase in width behind the centerline of the rear axle in any horizontal plane. Allowances shall be made for radius of bodywork along primarily horizontal surfaces in this area. Undertrays and floorpans may extend laterally past cockpit sides, sidepods, and engine compart­ment enclosures,

9.1.1.4.d. Diffusers and undertrays shall not exceed a maximum width of 95 cm (37.40 inches). No part of the diffuser or undertray shall extend more than 80 cm (31.50 inches) behind the centerline of the rear axle nor exceed in height a horizontal plane 90cm (35.43 inches) above the ground with the car as qualified or raced with the driver on board. (page 260)

9.1.1.5. Control of Undersides Shaping (page 261)
It is the intent of these rules to minimize (not eliminate) the use of “ground effects.”
a. A reference area is defined
Formula F: by the full width of the lowest surfaces of the car licked by the air stream between the front bulkhead as described in B.3.a above and the rear of the rear tires.
Formula Continental: by the full width of the lowest surfaces of the car licked by the air stream between the front bulkhead as described in B.3.a above and the front edge of the rear tires.
These surfaces may include the floor pan, undertrays, diffusers, side pod bottoms and any essentially horizontal bodywork that is included in the lowest surfaces licked by the air stream. Within this reference area, the lowest surfaces licked by the air stream must be flat with a total vertical tolerance of 25.4mm. An undertray beneath the engine, bell housing and/ or gearbox is not required.
1. Mirrors and any primarily vertical bodywork (e.g., cockpit/radi­ator sides that are oriented 45 degrees or greater relative to the ground) that extend laterally past the outer edges of the floor pan and/or undertrays are not subject to the reference area restrictions.
2. Fairings for streamlining suspension pickups are not subject to the reference area restrictions; however, such fairings shall be symmetrical about their horizontal axis.
3. The perimeter of any reference area surface that transitions upward to any bodywork may use a maximum 1 inch radius and shall be included in the reference surface measurement.
b. Measurement for compliance of the defined area shall be performed as follows:
1. A non-flexible straight-edge bar shall be placed against the lower surface of the reference area in a suitable section (unworn and flat enough to prevent rocking of the bar) from which the bar can be oriented to measure all parts of the refer­ence area. The competitor shall be responsible for the avail­ability and condition of such a surface. The bar shall be of sufficient length to reach all portions of the reference area from that surface.
2. All measurements shall be taken vertically from the bar to the reference area surfaces. The total maximum vertical distance (additive upward and downward) from the bar to any part of the reference area surfaces shall be 2.54 cm. Skid blocks and or rub strips are not included in this measurement.
c. No aerodynamic devices (e.g., skirts, body sides, skid “planks”, undertrays, skid blocks, etc.) may extend more than 1 cm (.394 inches) below the reference area.


6. Aerodynamic Aids (page 262)

9.1.1.6.e. Shaping of the lower surfaces to create “venturi” type tunnels is prohibited. An example of venturi tunnels is shown in the following figure. (page 262)

***** a picture I can’t attach to a post ****


9.1.1.6.j. (FC only) Diffuser undertrays, to the maximum allowed bodywork width are permitted, but any portion within the reference area (B.5) must comply with the reference area measurement rules. (page 263)

[Purple Frog]

For the sake of full disclosure in 2012 i ruled on diffusers based on one basic criteria. That being that from the rear axle centerline rearward the diffuser would have to fit in a box that was 80cm long, 95cm wide, and 90cm high from the ground.

If your diffuser fit in that box it was legal. No matter what shape it was. Thus making the Clayton/Dauntless diffuser legal.

[Wren]

Yes, it is because of the letters in red. The Dauntless and Radon diffusers run afoul of this rule.

9.1.1.6.e does not make diffusers illegal as they are specifically allowed.

[R. Pare]

If I understand your question correctly, you are basing it on the fact that the "venturi tunnel' picture includes in part what looks like what we call a diffuser?

It is a picture of a "venturi tunnel" as has been understood since tunnel-type ground effects came into being. Yes, the tunnel does indeed have a diffuser section ( a divergent nozzle), BUT it also has the raised tunnel section and the raised inlet (a convergent nozzle). It is the presence of all three, not just one, that makes it a "venturi tunnel". That picture has also been in the books since the 2010 re-write, so it is nothing new.

The fact that a diffuser looks like the rear section of a 'venturi tunnel" does not make it a venturi tunnel - with the reason being that it does not have the other two defining characteristics as well.

Hope that answers your question!

And yes, the red lettering about increasing in width behind the axle centerline would, according to the ruling that was just published, make the Dauntless diffusers illegal - as it would have in the old rules.

PS: Remember - the fact that something has been ignored/allowed (or at least not disallowed through a protest action) does not make it legal!

[Purple Frog]

Hum...
I happen to have 3 Pennon diffusers in the shop. Measuring the inside uptake chamber, once across the area around the axle centerline, and once at the rear ...

Two are between 1/64 and 1/32" wider to the rear. So... how picky is the SCCA going to get? I see no allowance for slight variances. The rule seems to black or white.

Since the majority of our F2kCS field runs Pennon equipment, i don't want to go tossing 2/3 of the field at VIR.

Food for thought.

Rules should be written that are easy for scrutineers to enforce...

[racerdad2]

Perhaps having a belt sander on standby....does put you in a tight spot...I do wish I was close enough to race in your series j pretty slim pickins up here... not really looking forward to mixed fields from FV to FA

[Wren]

There are several ways to deal with the measurement issue.

One would be to reference the part of the GCR that deals with measuring things. Bodywork is not specifically mentioned, but you are not going to go wrong applying those standards. In general the rule is that the tolerance is +/- half the final digit of the specification. The bodywork rule is 95cm(37.4 in). If the metric rule is taken as the primary measurement, then the tolerance would be +/-.5cm, which is pretty close to the bodywork tolerance rule in FA.

The other way to deal with the measurement issue is to re-read GCR 1.2.3.

[R Nicholas]

Yes, it is because of the letters in red. The Dauntless and Radon diffusers run afoul of this rule.

9.1.1.6.e does not make diffusers illegal as they are specifically allowed.

Hang on here a sec, I have one of these things.

It measures 95cm as it crosses the rear centerline reference. Then it reduces in width and returns to 95cm. The starting point is 95cm and the ending point is 95cm all behind the point of reference. It would have to increase to over 95 cm to increase behind the centerline on the rear axel. The Dauntless diffuser does not increase based on the GCR point of reference and is under the max width.


Rob,

[R. Pare]

Hum...
I happen to have 3 Pennon diffusers in the shop. Measuring the inside uptake chamber, once across the area around the axle centerline, and once at the rear ...

Two are between 1/64 and 1/32" wider to the rear. So... how picky is the SCCA going to get? I see no allowance for slight variances. The rule seems to black or white.

Since the majority of our F2kCS field runs Pennon equipment, i don't want to go tossing 2/3 of the field at VIR.

Food for thought.

Rules should be written that are easy for scrutineers to enforce...

The rule IS easy to enforce - either they measure correctly, or they don't!

You can handle it in a variety of ways:

1 - Enforce it strictly. Might piss some people off, but a rule is a rule.

2 - Measure everybody at VIR, and give warnings to those who are illegal that it has to be fixed by the next race they attend. Will still piss some off, but at least this way they have been notified and given a chance to fix things without being penalized immediately.

3 - Use the discretionary capability you seem to have in the Pro series to set your own tolerance that you will allow. Everybody goes home happy.

[Purple Frog]

So i went back and read the September 2012 GCR, the one used at the 2012 Runoffs.

I can't find any such FC rule about diffusers widening rear of the rear axle centerline.

That said the club has decided some diffusers legal at the 2012 Runoffs will not be legal in 2013 club.

While F2kCS is getting trash talked on Apexspeed about supposedly allowing things that are illegal in club in 2013, and folks are complaining about having to have two different diffusers... (#209 and #210 in another thread)

In reality F2kCS didn't change the rule to make club member's 2012 gear illegal in 2013. So... why should we change our rules to force our customers to throw out their 2012 gear? Doesn't sound customer friendly.

Just setting that part of the record straight.

[R. Pare]

Froggie, froggie, froggie....... FC bodywork in the old rules is also controlled by the FF bodywork rules.

This sort of confusion is why the rules were combined into one set.........

[RobLav]

My Citation diffuser would probably go afoul of the wording as well because it narrows then gets wider. And I signed up for the F2KCS hoping I would not run into issues like this!!

[Wren]

Hang on here a sec, I have one of these things.

It measures 95cm as it crosses the rear centerline reference. Then it reduces in width and returns to 95cm. The starting point is 95cm and the ending point is 95cm all behind the point of reference. It would have to increase to over 95 cm to increase behind the centerline on the rear axel. The Dauntless diffuser does not increase based on the GCR point of reference and is under the max width.

Rob,

I guess that I would have to see a picture of it. The rule is for any horizontal section. For instance 3" above the bottom of the car, is it still 95cm wide at the rear axle centerline?

The last time that the Dauntless diffuser was discussed here it was not in compliance with this rule and I was assuming that was still the same.

So i went back and read the September 2012 GCR, the one used at the 2012 Runoffs.

I can't find any such FC rule about diffusers widening rear of the rear axle centerline.

The FC rules say to look at the FF rules. Inconvenient, but still binding.

FF rules 9.1.1.D.8.c says: Bodywork shall not increase in width behind the
centerline of the rear axle in any horizontal section

That said the club has decided some diffusers legal at the 2012 Runoffs will not be legal in 2013 club.

It has not.

In reality F2kCS didn't change the rule to make club member's 2012 gear illegal in 2013. So... why should we change our rules to force our customers to throw out their 2012 gear? Doesn't sound customer friendly.

Just setting that part of the record straight.

For me, the single most important part of the record to set straight is that the club did not change any rules in the 2013 rules change that made any gear illegal that was legal in the 2012 rules. What parts were you thinking of? The 2013 rules are more permissive than the 2012 rules.

[R. Pare]

As far as a diffuser that measures 95 at the axle centerline, then get narrower as you go back, but then ends up back at 95 cm at the end, i would personally say that the bodywork has not increased in width - with the width the same at both ends of the measurement envelope, there has been NO increase in width in that envelope when taken as a whole.

In reality F2kCS didn't change the rule to make club member's 2012 gear illegal in 2013. So... why should we change our rules to force our customers to throw out their 2012 gear? Doesn't sound customer friendly.

Just setting that part of the record straight.

Neither did the Club.

[RobLav]

I would obviously agree with Richard... However, I could also argue that diffusers are not bodywork. Since a venturi consists of a convergent/divergant nozzle, the diffuser, being the divergent end, is merely part of and an extension to the floor.

But then venturis are not legal in FC? How silly.... when that is is exactly what is going on!

Frog - why not just say a diffuser is legal as long as it sits inside your box within a tolerance level of 1/16" or so?

[R. Pare]

However, I could also argue that diffusers are not bodywork. Since a venturi consists of a convergent/divergant nozzle, the diffuser, being the divergent end, is merely part of and an extension to the floor.

And you would lose that argument, since diffusers are defined as bodywork in the bodywork section of the rules, nevermind that the Glossary definition also includes them by direct inference.

And no, the rules do not say that venturies are not legal - it states that venturi tunnels are not legal.

[Purple Frog]

The old D.8.c rule in Formula Ford. Got it. Understand.

Good discussion. I re-learned some things.

Now... whether to include that red sentence in F2kCS rules....

[RobLav]

I know I'd lose that argument Richard... but was being upfront with the "non" venturi thing!

[Cblough]

Noob's POV:

After thumbing through the GCR and reading this thread, I literally now have no idea if my 97 VD is compliance or not at a Club level.

How does this help drive FC participation, again?

[R. Pare]

Now... whether to include that red sentence in F2kCS rules....

Personally, I was hoping that they would get rid of it in the rewrite - I've yet to find an old codger that remembers exactly what it was supposed to address in the first place!

If a version of it is to be kept at all, I'd drop out the "in any horizontal section" part so that it is treated as an overall envelope definition.

Whether or not the Club can be persuaded to do the same this year or next is another matter all together......

[R Nicholas]

[Quote Mike E ]
While F2kCS is getting trash talked on Apexspeed about supposedly allowing things that are illegal in club in 2013, and folks are complaining about having to have two different diffusers... (#209 and #210 in another thread)


You getting a little thin skinned on us ?

Everything I have been reading has a ton of praise for the F2KCS.
You guys have one hellva good run going !



Rob N

[Wren]

Noob's POV:

After thumbing through the GCR and reading this thread, I literally now have no idea if my 97 VD is compliance or not at a Club level.

How does this help drive FC participation, again?

You have to have some faith in your chassis constructor. Also realize that it is not going to be a big deal until you are running up front at nationals.

What part of the GCR is giving you trouble specifically? The rules re-write has at least centralized things to one location. There is lots of good information here on apexspeed and lots of people willing to help.

The arms race that would come with a loosening of the rules would be even worse for participation.

[Northwind]

Rob,

Add two vertical planes 95cm apart that run parallel front to rear along the sides of your diffuser. Fill in the gaps between with foam and cover the top with a thin skin. The max body width that will be measured is on the ouside and top of the diffuser. The bottom side and convergent/divergent zones fall outside the measurable definition. I may be off base here though as I have not disected all the rules that might also apply.

[Wren]

Rob,

Add two vertical planes 95cm apart that run parallel front to rear along the sides of your diffuser. Fill in the gaps between with foam and cover the top with a thin skin. The max body width that will be measured is on the ouside and top of the diffuser. The bottom side and convergent/divergent zones fall outside the measurable definition. I may be off base here though as I have not disected all the rules that might also apply.

That is very similar to what I proposed in my compliance review and I was told it was not compliant with the 2012 GCR.

[Reddog]

Hum...
I happen to have 3 Pennon diffusers in the shop. Measuring the inside uptake chamber, once across the area around the axle centerline, and once at the rear ...

Two are between 1/64 and 1/32" wider to the rear. So... how picky is the SCCA going to get? I see no allowance for slight variances. The rule seems to black or white.

Since the majority of our F2kCS field runs Pennon equipment, i don't want to go tossing 2/3 of the field at VIR.

Food for thought.

Rules should be written that are easy for scrutineers to enforce...

At what temperature was your tape measure calibrated? ... and was it a hot day? Just kidding

[R. Pare]

At what temperature was your tape measure calibrated? ...

You could always remeasure using a regular ruler at the axle centerline and a shrink rule for the rest of the length..........

[Purple Frog]

Funny thing about this. The FB guys got it correct, and thus have sexy diffusers. Having sat on the original FB committee for a while, i can say it may not have been intentional. It might have been a case that we were just using the FC rules in the old GCR without any of the FF rules. So, all that bodywork language just got sort of left out, especially about widening rear of the rear axles.

Philosophically, i think it would be better for the future of the class if we eliminated the Bodywork shall not increase in width behind the centerline of the rear axle in any horizontal plane sentence. Can't for the life of me see what good it does.* But then I think its time for 6 speed sequential boxes in FC. Things like that would keep it from being "vintage". What do i know?

* i think originally it was written to prevent huge "whale tail" bodies on FFs.

[Cblough]

You have to have some faith in your chassis constructor. Also realize that it is not going to be a big deal until you are running up front at nationals.

What part of the GCR is giving you trouble specifically? The rules re-write has at least centralized things to one location. There is lots of good information here on apexspeed and lots of people willing to help.

The arms race that would come with a loosening of the rules would be even worse for participation.

I seriously doubt that I'm in trouble -- the diffuser is the stock one that came with the car, and it's pretty narrow -- but I don't get how that interacts with the reference area. Am I correct in thinking that so long as the diffuser doesn't extend in past the front edge of the tires, I'm not worried about the one inch rule?

And, if it meets this section:

"Diffusers and undertrays shall not exceed a maximum width of 95 cm (37.40 inches). No part of the diffuser or undertray shall extend more than 80 cm (31.50 inches) behind the centerline of the rear axle nor exceed in height a horizontal plane 90cm (35.43 inches) above the ground with the car as qualified or raced with the driver on board. "

I'm good to go? I'm probably making this too complicated in my mind.

[Purple Frog]

Cblough, your car was legal when it ran in the pro series 15 years ago. Trust me, its still legal.

[RobLav]

Dan, my thought is the same as yours... although I think I'd start with two aluminum angles screwed to the top of the diffuser - sort of like a couple of diffuser tailfins, which might actually help with downforce.

Silly rule.... and Frog is right - this sort of thing completely escaped me in the FB rules. Law of unintended consequences? Maybe it's good we did not have Richard on the rules committee! He knows too much...

[Stan Clayton]

Yes, it is because of the letters in red. The Dauntless and Radon diffusers run afoul of this rule.

9.1.1.6.e does not make diffusers illegal as they are specifically allowed.

I disagree. If this sentence (Bodywork shall not increase in width behind the centerline of the rear axle in any horizontal plane.) applies to diffusers then all FCs with diffusers are noncompliant. Here's why: A horizontal plane projected through the car and extending aft of the rear axle that is below any part of the diffuser encounters the diffuser at some point as it goes back. At that point the bodywork width suddenly goes from zero if there is no bodywork next to the gearbox to 95cm, or perhaps from as much as 10" wide if there is lower rear bodywork wrapping the gearbox to approximately 95cm wide. BUT IN ALL CASES THE BODYWORK IS INCREASING IN WIDTH.

To help illustrate the concept consider the image below. To the sideview of an FC I have added a solid yellow line representing a hypothetical horizontal plane. You will have to mentally project it through the car, as my MP Paint skills don't extend far enough to draw the plane. If you imagine the wheel and tire out of the way you can see that as the horizontal plane goes aft it suddenly encounters the rising rear diffuser (at about the point the white vertical line bisects the yellow line) and the bodywork suddenly gets wider.

http://flic.kr/p/dY7d7n

If the rule above applies to diffusers, then all FCs are noncompliant, as all FCs have diffusers.

BTW, after all the complaining about our diffuser design we went back to CFD and came up with a Mk2 design that not only has the parallel sides everyone seems to think the rules call for, but it makes even more downforce than before.

[Wren]

That is the bodywork starting. That is not the same thing as increasing.

GCR 1.2.3

[RobLav]

Ha Ha! I see Stan's point in the extreme case. Better to fix the rule.

[Purple Frog]

Stan,
I totally understood your explanation when you first presented it about two years ago. Didn't Linc even have a better picture?

And, based on that very logical explanation, all FC diffusers as we know them are illegal. The rule as written is very black and white, with no allowances for even slight variances, thus almost crazy to try to enforce.

So, thats why i went to the test: "if it fits in the box, its legal."

If you accurately slice a horizontal section out of a Pennon diffuser at a point behind the rear axle, then along that slice where it turns from going across the diffuser to running back along the outside vertical fence... there is like a 1/4"radius, and ...taa da... the section gets wider by 1/4" on each side. Splitting hairs, yes... but the rule is black and white.

[RobLav]

The other argument is that since the (most) diffuser is one piece, and the bottom is 95cm constant width, then the width is NOT increasing. If you take into account the upslope plane, then all of them in FC are wider than the other bodywork (the engine cover) on the car and therefore illegal.

Silly roundabout arguments that can easily be rectified with Frog's in the box definition.

[Wren]

By Stan's argument, if I were to draw a section drawing of a 2"x2" solid bar, it would not have a constant cross section as it increasing from zero to 2 inches. That does not pass the sniff test that is required whenever anyone interprets the GCR.

Rob, How many cars have bodywork behind the rear axle and in line with the diffuser? No modern car that I know of. It is certainly not in Stan's picture.

These are silly roundabout arguments to avoid something fairly straightforward in the GCR.

[Purple Frog]

Where is that "sniff test" spelled out in the GCR?

[Wren]

GCR 1.2.3

[RobLav]

Wren - I hear what you're saying. Engine covers on Van Diemen's (and my Citation) are behind the rear axle centerline. They are in different horizontal planes and higher off the ground. Since the diffuser upslope is wider than the engine / box cover in horizontal planes, then almost all diffusers are illegal!

So... does the width of the bodywork in one horizontal plane apply to other horizontal planes?

I still go back to the argument that the diffuser at a constant 95cm width does not increase in width - and back to Frog's box. Frog - you have a box?

The way I read this now... is that almost all diffusers are illegal. If you take a horizontal plane approx 2" above the floor, then most sidepods are at the max width, then those sidepods decrease in width, but then the diffuser upslope at that plane causes an increase in width. This rule is bogus and needs fixed.

[Wren]

Since the diffuser upslope is wider than the engine / box cover in horizontal planes, then almost all diffusers are illegal!

No, it says nothing like that. If the bodywork pieces are not in the same horizontal section, then they cannot have any bearing on each other.

So... does the width of the bodywork in one horizontal plane apply to other horizontal planes?

Of course not.

I still go back to the argument that the diffuser at a constant 95cm width does not increase in width

You can go back to it all that you want, but that doesn't change the published ruling from the COA. If you are protested at a club event, you will lose.