IMSA DPi Discussion

[carbsmith]

Originally Posted by canaglia

Guess it's just about eyes get used to that.
It became a so distinctive part of modern sportscars that is actually weird to watch a finless 908 HDi or lola-aston.

Anyway, by the pics, to me is quite clear that is a standard oreca 07 with a customized acura front section.

Wonder if a nissan dpi developes more or less front downforce compared to a standard ligier. The same about cadillac dpi that however has a more revised aero compared to a standard dallara.

Cadillac is definitely higher downforce, this probably is as well, and I imagine the Nissan is roughly neutral. Nothing to do with the dumb panel, they just have what would tend to be interpreted as a higher downforce fender shape. (that's about all they have, either) Probably not a major R&D project so much as the manufacturers pulling out a fender shape they already ran in the wind tunnel and rejected for WEC/ELMS tracks.

[joeb]

Originally Posted by Matt

Acura at least changed the headlights.

I love it from the front 3/4 angle.

That is my favorite angle so far as well. It still looks weird from straight on to me. But I don't care, it will look great in person!

I wonder what they will run for a livery on the Oreca at Petit? Will they have Acura sponsorship?

[Damian Baldi]

Like the Cadillac and Nissan, it's 95% the original car, but I like the result in all cases. That front "wing"? remembers me the one used on the Porsche 962 on mid 80s. the only thing I don't like are the new rims

[AoB Special Stage]

Except unlike the Porsche, this wing doesn't look ready to fly off and kill someone.

[BSchneiderFan]

Sorry, but I still hate the fins. They seem to me a huge overreaction to a couple of incidents and are dog ugly. I don't remember the Group C days being littered with airborne crashes.

[Akrapovic]

Originally Posted by BSchneiderFan

Sorry, but I still hate the fins. They seem to me a huge overreaction to a couple of incidents and are dog ugly. I don't remember the Group C days being littered with airborne crashes.

I agree they aren't pretty but they certainly were not a huge over reaction to a couple of incidents.

In 2008 alone -

Ben Devlin - https://www.youtube.com/watch?v=qjddG3OC03I
Jamie Campbell-Walter - https://www.youtube.com/watch?v=dnLBf6N3xPA
Stephane Ortelli - https://www.youtube.com/watch?v=lNkySVNNpog
Dindo Capello - https://www.youtube.com/watch?v=biUwr2g7txA
Marc Gene - https://www.youtube.com/watch?v=3KfdRTQEiyw
Hideki Noda - https://www.youtube.com/watch?v=GkjOv2HJeZM
RML - https://www.youtube.com/watch?v=TyXYnGv6y1U (Can't remember who was driving that one, sorry)

This is just off the top of my head. There may be more. But all of that happened within 2-3 months. This was the point where fins, holes and thinner cars started being looked at.

[chernaudi]

And how many of those accidents were caused by either hitting something or a mechanical failure? Most of them. But also, how many of them happened in a corner or near one? Almost all of them.

The fin and fender holes and narrower cars (I especially hate the latter point) aren't cure alls, either. But what else did you expect the ACO to do? DPs rarely flipped because they were too slow in corners to do so. But that was because they lacked aero, and ran on rock hard spec tires.

What would you rather have? Fins and holes that do at least work a lot of the time, or crap spec tires and aero limits?

[Akrapovic]

It doesn't matter why the car was sideways, whether it be mechanical failure or hitting something, or if a corner was near it. That part really doesn't matter - it's about how the car acts once it is sideways.

Remember that Daytona Prototypes did suffer from it too, once they added more power and aero.

https://www.youtube.com/watch?v=WTq4qFelmvc

Fins and holes are necessary when you have these big aero dependant cars. And honestly, they really aren't that bad.

[TF110]

They didn't stop Anthony Davidson from flipping. There's other solutions they could have done but they did a stop-gap one in the name of 'safety'. Just like the stupid halo. It's a rush to appear they did something when in actuality it's hardly worth it because it doesn't do that big of a difference in incidents where cars get airborne. Imo, Nascar's roof flaps do a better job at keeping a car planted.

[Akrapovic]

Originally Posted by TF110

They didn't stop Anthony Davidson from flipping. There's other solutions they could have done but they did a stop-gap one in the name of 'safety'. Just like the stupid halo. It's a rush to appear they did something when in actuality it's hardly worth it because it doesn't do that big of a difference in incidents where cars get airborne. Imo, Nascar's roof flaps do a better job at keeping a car planted.

They didn't stop Davidson flipping, but that was worst case scenario, where as in 2008, cars were flipping just from regular spins and offs. Fins and holes are not perfect, but no matter how you measure it and with what metric, that's still a huge improvement.

I also like the NASCAR solution and think it should be incorporated to the engine covers of LMPs, but there is no doubt the current solutions have helped the situation, even if they have not cured it.

[AoB Special Stage]

I think Indycar is/was trying to integrate those sort of flaps on the diffuser.

[chernaudi]

Other than blow overs, why weren't LMP900/675s flipping when they got sideways? Probably the same reason why GTPs/Group Cs weren't and why DPs didn't until they were sped up. The cars cornered too slow.

We have to remember that the 2004 ACO regs increased the volume of the front and rear diffusers, because of that 1000mm wide/50mm tall lip on the front diffuser and the rear diffuser especially had a much bigger exit (200mm vs 150mm on LMP 900s and on the current LMP1 factory cars). The cars generated so much more downforce from the underbody than the earlier cars did.

Also, tire technology got much better, which is why even LMP900s were able to go faster than Group C and IMSA GTP cars.

Are there better solutions to prevent flips? Probably, but they'd probably be more expensive than the fin (not a big deal), fender holes (valid concept, but why do that when the previous 20 years the ACO mandated that you couldn't at least start the race with big holes in the fenders for aero reasons?), or the narrower cars (probably the dumbest thing of all--surface area of the floor wouldn't matter if the cars stayed on the ground in the first place).

Why not take advantage of the chamfered floor and just run an air dam a certain distance inboard of the outer edge of the car? Or a crescent profile on the fin when viewed from the front to funnel air onto the engine cover?

Probably a better idea, or find some way of creating a low pressure area under the car when it's sideways (the chamfered floor, but I don't think it's that efficient), like finding a way to vent air more effectively when the car's sideways (again, the fender holes IMO are of questionable efficiency when the car's sideways).

Unfortunately, the aero genie, like so many genies in racing, are out of the bottle and trying to take downforce of these cars to make them less aero sensitive/prone to certain behaviors will be seen as going backwards. Same thing with trying to reduce tire grip (unless we want these cars to triple or quadruple stint in sprint races, which would equal 5-6 stints at LM).

[TF110]

Some high quality shots of the Acura DPi on autoblog, this one in particular caught my eye because the exhaust exit location was kept. But were these air flow guides (in black in front of the rear wheel) on the original Oreca?

[FormulaFox]

Originally Posted by TF110

They didn't stop Anthony Davidson from flipping.

One incident does not prove an entire concept is pointless. Considerably when in the big picture it's a piece of evidence about how effective the peices actually are.

Anthony Davison's flip was the result of the aerodynamics being compromised from an impact - as has every LMP flip that has occurred since the fins and fender holes were implemented.

There is no way to prevent flips from occurring when the aerodynamics are compromised. Even the flaps in NASCAR/IndyCar won't help if the aero is broken in just the wrong way.

IndyCar has still had a couple of flips during wrecks since adding the flaps. The flaps work in NASCAR far better because it's so much harder to break the aero in a way that the falps can't manage due in no small part to the fact that NASCAR is considerably less aero dependent.

The fins in LMP are MORE than sufficiently effective.

[Akrapovic]

Originally Posted by TF110

Some high quality shots of the Acura DPi on autoblog, this one in particular caught my eye because the exhaust exit location was kept. But were these air flow guides (in black in front of the rear wheel) on the original Oreca?

Yeah those vortex generators are on the original Oreca, but only in high downforce kit. The low downforce kit doesn't have them.




Images from an absolutely brilliant Racecar Engineering page here:
http://www.racecar-engineering.com/cars/rebellion-r1/

Looking at the exhaust exits and the bulging around that area, I think the exhaust and rear bodywork will change.

[TF110]

Originally Posted by FormulaFox

One incident does not prove an entire concept is pointless. Considerably when in the big picture it's a piece of evidence about how effective the peices actually are.

Anthony Davison's flip was the result of the aerodynamics being compromised from an impact - as has every LMP flip that has occurred since the fins and fender holes were implemented.

There is no way to prevent flips from occurring when the aerodynamics are compromised. Even the flaps in NASCAR/IndyCar won't help if the aero is broken in just the wrong way.

IndyCar has still had a couple of flips during wrecks since adding the flaps. The flaps work in NASCAR far better because it's so much harder to break the aero in a way that the falps can't manage due in no small part to the fact that NASCAR is considerably less aero dependent.

The fins in LMP are MORE than sufficiently effective.

One incident? What about Audi's 2014 incident? What about crashes with lmp2 cars all with fins? There were a handful of crashes and flips before the fins, and most of those were from contact, just like with the Toyota. The fins and holes help, only somewhat. F1 is getting rid of the fins next year. I think it's apparent they are marginal at impacting safety. Nascar has more cars on their roof than lmp does. Their speeds are higher and you see that at the super speedways when cars go sideways. A lot of the time, roof flaps put them back down. It's not because of aero dependency... cars get sideways, air goes under the car, car goes up. Maybe they could fix that with the shape of the car. But you can't cure all crashes and lifts. The fins look like an afterthought to a lot of people and there's good enough evidence that they aren't the big fix they're supposed to be. I wouldn't be surprised if there isn't one unless you redo the entire car.

[Akrapovic]

F1 doesn't use fins for safety issues, as those cars rarely have issues like blowing over because the surface area of the floor is quite small. The large surface area of the LMP floor is one of the reasons they are more prone to blowing over (and why thinner cars are less likely too).

F1 cars use the fin to stabilise airflow to the rear wing and helps stablise the car. The downside is they are vulnerable to cross winds. F1 is getting rid of them purely on visuals, which is what has driven a lot of the aero changes in F1 recently.

[AoB Special Stage]

[TF110]

Originally Posted by Akrapovic

F1 doesn't use fins for safety issues, as those cars rarely have issues like blowing over because the surface area of the floor is quite small. The large surface area of the LMP floor is one of the reasons they are more prone to blowing over (and why thinner cars are less likely too).

F1 cars use the fin to stabilise airflow to the rear wing and helps stablise the car. The downside is they are vulnerable to cross winds. F1 is getting rid of them purely on visuals, which is what has driven a lot of the aero changes in F1 recently.

No, I never said f1 used fins for safety. I said they're getting rid of them. If they aren't a safety feature in a faster series, why should they be on cars slower? The surface area of the floor on f1 cars isn't as big, but it's still the majority of the bottom of it, just like lmp's. My argument pretty much says the same thing. The cars need a major redesign to stop blowovers, not just holes and fins.

[Akrapovic]

F1 cars have about half the flat floor area of an LMP. Everything around the nose is discounted because it's thin (and not flat) which allows air to flow around it. Its like having mega massive holes. Yes the cars do need a major redesign if they're going to address that, and there is more they can do, but the fins and holes do have a positive effect and comparing it to a single seater (no matter how fast it is) is like comparing apples and tennis rackets.

The fins create a high pressure zone above the car which helps force it down when going sideways. F1 doesn't have this because there is no significant lift produced when the car is moving sideways. There is also very little place for F1 cars to trap air, where as wheel arches are traditionally high pressure areas that produce lift. The reason it's a safety feature on a slower car is simply because the profile and shapes of LMPs are more prone to it than single seater are.

Single seaters can blow over (Indycar), but F1 cars aren't doing 230mph much so don't need safety features to deal with a situation that won't occur under normal parameters. I think the only time F1 cars get that sort of speed is Mexico, where the air is thinner and would produce less lift anyway.

[FormulaFox]

Originally Posted by TF110

One incident? What about Audi's 2014 incident? What about crashes with lmp2 cars all with fins?

You referred to only one incident in your original post, and I responded to that.

That said, I DID note that all of the major flips since the fin was introduced involved compromised aerodynamics - and that includes the 2014 Audi incident. The majority of the flips that raised concerns before the fins did not involve compromised aero.

The only exceptions to the involvement compromised aerodynamics in flips with the fins were matters where the flip wasn't induced by aerodynamics at all - such as the Ligier LMP2 last month at CTMP.

F1 is getting rid of the fins next year.

And this is relevant how...? The F1 fins aren't mandated safety components - they were put in by the designers for performance reasons. We've no idea if they actually help in F1 the same way they have in LMP(the aerodynamics in the two are so different there's a very strong possibility the fins won't do jack in this regard for F1).

The fins look like an afterthought to a lot of people

Only to people who don't bother to actually look into things. If you actually look closely at the matter it is VERY clear that the fins have helped considerably.

and there's good enough evidence that they aren't the big fix they're supposed to be.

Show me evidence that there have been just as many flips withOUT compromised aerodynamics as there were before the fins were implemented.

The evidence is that they have produced a great reduction in the number of flips there have been.

This is only one example, of course, but it is quite relevant. Prior to the fins, incidents like this caused flips with unnerving frequency, but this is one of many cases since the fins were implemented where the cars stayed firmly planted to the ground:
https://www.youtube.com/watch?v=bmuVZrR53v0

[AoB Special Stage]

What is this bizarro world wherein I agree with Fox?

[joeb]

Great discussion, but this isn't DPI talk is it?

[FormulaFox]

Originally Posted by joeb

Great discussion, but this isn't DPI talk is it?

Well, I think it's at least fair to say that it's at least RELEVANT - DPis are using the same safety components we're debating the merits of, after all.

[joeb]

Originally Posted by FormulaFox

Well, I think it's at least fair to say that it's at least RELEVANT - DPis are using the same safety components we're debating the merits of, after all.

But there are more F1 and Group C references than dpi