notch back rear wing question

[quadzjr]

So I looking to build an first gen MR2. If any car is a notch back this is one of them. Now the rules are written as such.

"Cars with a wagonback/notchback/
hatchback style body may have the rear wing assembly,
including the end plates and any wicker, mounted a maximum
of 4.0 inches above the highest point of the roof. For this
subsection, a wagonback/notchback/hatchback style body
(or variations of these) is a car in which the rear edge of the
roofline is no more than 28.0 inches forward of the rearmost
bodywork as measured along the vehicle longitudinal centerline"

my question is where did 28" come from?

where is the the rear edge of the roofline? above the rear glass? where the pillars meet the body work? does rear most body work include bumper?

thanks.

 

[Greg Amy]

my question is where did 28" come from?

GT regs.

where is the the rear edge of the roofline?

Que? Put a marble on the roof and let it roll backwards. When it falls off something, you've found the aft edge.

does rear most body work include bumper?

Yup, 'cause that's the reference plane for where you can locate the wing. (see edit below)

Maybe a photo would be helpful?

- GA

Edit: "...does rear most body work include bumper? Actually, I'd say "no". The intent of the rule is to clarify the characteristics of a hatchback (letting you put the wing higher, thus out of the turbulence of the roof). So IMO -- and I wrote the rule, but please read my sig -- that measurement does NOT include the rear bumper cover.

 

[quadzjr]

I am trying to think of a notch back that has the rear of the body work within the 28". I know all mid engine cars have and the engine lid itself eats up the majority of the 28".

since the pillars of the cars come back and the rear window is vertical.. this creates a large high pressure area thus making it worthless for any wing on the car.

as you can see here.. Air becomes turbulent at low speed.. at high speeds it is even worse. The wind tunnel testing from I have found was performed at 60 kph (~37mph)

The CFD picture is the data from a I believe 100nph.. you can see that the air does not recover.

So for all the mid engine notch back cars they would need to have the rear wing to be above the roofline as well to be effective. Which I think was the point of adding notch backs to the list in the ruling.

 

[Chip42]

the 28" rule is a bit wonky, I'll agree - especially the marble concept. "falls" or "veers downhill"? Many cars cars have a smooth flow from "roof" to rear glass (integra, S14, RSX). the MR2, del sol, X1/9, proper hatchbacks and wagons and pickup trucks have a pretty sudden drop off, though that is at various points along the length of the car. the notchback term is very subjective, as is the 28" method of determination (and I'll even offer that a reasonable definition would hold that the end of the roof is a point of, or within a small region of, inflection from the highest region of the car to that which connects it to the rest of the vehicle, but I know that's not going to be universally accepted)

as for the bumper = body: IT rules would include an integrated bumper (all cars today) and exclude a separate bumper (early A2 VW, E30, etc...) from the "body". the GCR definition uses "licked by the airstream" and I'll argue the bumper is that in either case.

I'd think the MR2 would NOT be a notchback, but it is an interesting question.

 

[quadzjr]

according to the all knowing wiki the MR2 is a notchback. It also lists examples of notchbacks and it falls in line with what I assumed was a notchback. Not a single one I think would fall within the 28" rule. If measured from the top off the roof top of the glass to rear of trunk.

 

[Greg Amy]

Remember the goal for the rule is to allow cars that have stubby back ends - VW Rabbits, Honda Civics, Dodge Omin - to have a way to mount the rear wing reasonably within the airflow. Also note that the regs require mounting the wing on "trunk/decklid" which really don't exist within a hatchback.

The reg as presented was already established (exists in the GT regs) and is reasonably easy to measure (I don't think we want to get into scrutineers measuring "inflection". I think the GT verbiage was a pretty good compromise. Yet, as always, some cars win, some cars lose*.

If you believe that your car does not get equitable treatment by the current regs, and you can support that contention via good data (say, photos of wind tunnel testing showing no airflow within the region the wing has to reside) then by all means submit a request to the CRB for line-item consideration. No promises, but can't hurt to ask (but don't expect wings hanging up well over the roof on MR-2s...)

- GA

* My Integra, for instance, got a nice shaft on this reg. Ignore the fact that the car is actually a hatchback by the true meaning of the word...while airflow is likely relatively smooth back there, because of the reduced height between the hatch and the roofline the underside of my wing is about 4 inches off the hatch. Decisively sub-optimal and in practice feels like it's not doing diddly-squat between full up and full flat.

Looks cool, though.

 

[quadzjr]

I would make a request for clarification on notchbacks as all stubby cars (not hatchbacks) seem to fall outside the 28" rule as written. So for the Fiero, X1-9, MR2 (all versions), Del-Sol. and any other true notchback could be ruled to have the wing 4" above the roofline. Right now as written I cannot think of any notchback cars that fit.

As a note on the integra.. I just looked it up and it looked like realtime was using wing similiar to the STL rule set and they were angled the traditional down. Though I do remember when they went to the RSX especially in the later years they were angling the wings up but the way the air hit them was in line with the air stream that way. But strickly form looking at them you would think they were creating lift. Might be something you can look into.

Wait your a FWD.. why do you need RWD traction? haha just kidding.

 

[Z3_GoCar]

I'd need to look this up in the GT-CS, but doesn't GT allow convertible cars the allowance to "Hershey Bar" or cut the windshield off and run with a half width cage? In that case the distance from end of roof to wing may not be applicable for cars with the long hood short trunk archetecture. Also, when you roll a marble down my roof, it never falls off

 

[Matt93SE]

As a note on the integra.. I just looked it up and it looked like realtime was using wing similiar to the STL rule set and they were angled the traditional down.

The STU/STL wing rules are a carryover from WC-TC. (The APR GTC-200 wing in 48" length was made specifically for the class). So yeah, you'll probably see a little bit of carryover.

 

[JS154]

Edit: "...does rear most body work include bumper? Actually, I'd say "no". The intent of the rule is to clarify the characteristics of a hatchback (letting you put the wing higher, thus out of the turbulence of the roof). So IMO -- and I wrote the rule, but please read my sig -- that measurement does NOT include the rear bumper cover.

Disagree. Body is separate from chassis. just as a fender and door is part of the bodywork, so is a trunklid, front bumper or rear bumper.

Splitter rules for ST I believe refernce limiting forward protrusion as refernced by the bodywork - which would be the front bumper, not the hood or unit body underpinnings.

 

[CRallo]

Did someone say notchback?