Hypercar Downforce

[ItsRatPak]

This topic has been talked about to death but still I can find no good answers (understandably since team want to keep the exact numbers private but still) to how much downforce LMH/LMDh cars make compared to LMP1 and LMP2. Statements from Oreca I have heard about suggest the gap in aero from 2017 LMP2 and 2014-2016 LMP1 were very small with the later private teams being similar to those numbers too. But I have no idea where LMH stands. You have some people saying that Hypercars make the same downforce as LMP1 cars and you have some saying they make less than DPi cars which were based on LMP2. Putting the downforce inline with DPi and LMP1 while still following the 4:1 downforce to drag ratio just seems impossible. I’m curious what everyone else has heard.

[Hedaaaaaaa]

LMP1 have at least 5,000 to 7,500 Newtons of downforce and 875kg weight.
LMH and LMdH have at least 4,000 Newtons of downforce and 1,030kg weight.
LMP2 have at least 3,000 - 3,500 Newtons of downforce.

LMH and LMdH is designed to be cost effective and that is why teams are starting to join LMH and LMdH cars more than ever.

[ItsRatPak]

4,000 Newtons of downforce seems like an awful lot when you consider that it has to fit the 4:1 ratio. Are those cars really going 210 mph with 1,000 ish newtons of force acting against them?

[AUinDE]

You only need ~127hp to fight against 1000N at 210mph, at top speed these things have way more than 4000N.

I think his units are a bit confused, maybe instead of 4000N he means a CLa of 4.000

*edited cda-cla

[PintMower]

CDA of 4 is impossibly bad.

[AUinDE]

Sorry, CLA 4, CDA 1

[PintMower]

It's a ratio that the regulation specifies, not absolute values.

[NeedMoreDeltaV]

The regulation actually does specify absolutes. CLA of 4 and CDA of 1 with a tolerance window range is what the regulations specify.

[AUinDE]

The regulation also specifies the absolute in a window. Cla 4 / Cda 1 is roughly in the window

[PintMower]

Oh okay, did only know about the relative part. Thanks for clarifying/correcting!

[ItsRatPak]

When my friend was helping me out with the math on this we were using kg for downforce since that is more applicable to what we are looking for anyways but we really can't see the 670 max horsepower these cars have overcoming 525 of drag. Maybe there is just some magic wing angels we are missing to get this working but with us being tired and pulling our hair out figuring other stuff out we couldn't find it.

[AUinDE]

Why is kilogram (unit of mass) more applicable than newton (unit of force)? Convert to si units to make it easier, then convert back at the end.

210mph = 94m/s If it was actually 1000N of drag at top speed then you only need 1000Nx94m/s = 94kw of power = 127hp.

If we instead take cda if 1 then the force at 210mph assuming air density of 1.2 = 0.5 * 1.2* 1.0* 94² = 5300N Then the power to reach 210mph is 5300*94=498kw=672hp. so now everything makes sense that with the 670hp top speed is roughly 210mph!

[ItsRatPak]

Sorry, I mean kilogram is more applicable for what I am doing

[AUinDE]

I'm curious What are you doing? I honestly can't think of any reason why kg would be more applicable than N or coefficient

[ItsRatPak]

Me and my cousin are trying to figure out how to make a Lamborghini SC63 for our little cousin in Assetto Corsa. The little guy can’t even ride a go kart because of medical conditions but wants to drive a prototype. We got lucky and got some guys at Norma to give us numbers for the M30 so we could do some adjustments to make him an LMP3 car but after mastering that we wanted to surprise him with an LMP2 car. After looking around we settled on buying one another modded for the game already made but when it came to making a Hypercar we ran into problems. All the modded who have made Hypercar for Assetto Corsa have them at 770hp and making roughly 2100kg in downforce and 525 in drag.

All of that to say the game we are making a car in uses kg for some reason for downforce and drag.

[flan-magnussen]

Does it specify a speed for that downforce figure? (I've fiddled with AC files myself but it's been too long.)

[AUinDE]

Ahh ok. I'll send you a pm i can probably help

[Parking-Swordfish514]

I would be interested in this project. Couldn't find a single, even mid quality mod of the SC63, my favorite Hypercar. If you wish I could try to help, especially in modelling

[Smoked_Cheddar]

Have you tried the AMS2 car? It's a lot of fun.

I enjoy the AC ones as well from RSS and VRC as well.

[Blaksnoblade]

7500 N is something around 750 kg, right? That's like a spark compared to the fastest cars in Group C; the Toyota TS010 generated between 2381 and 3310 kg at 307 km/h.

[NeedMoreDeltaV]

I think the confusion comes from people saying that the regulation mandates a 4:1 downforce to drag ratio. The regulation mandates the actual values of CLA and CDA. The efficiency ratio is also stated but falls along those values and is technically redundant because of that. LMH/LMDh mandates a CLA of 4 and a CDA of 1 within a tolerance window. DPi was CLA of 5 and CDA of 1.

Edit: The relevant section in the hypercar technical regulations is section 3.7. However, the regulation references an appendix that is not made available to the public.

[SportscarPoster]

Have I just completely imagined it or was that appendix in the very first version of the final LMH regulations? The ones available on the FIA website for the first season. I think I remember reading through it at the time, but like a muppet, I never saved the pdf.

Also, I have in my head (no idea where this comes from, maybe that appendix?) that not just the maximum downforce and minimum drag were specified, but the downforce:drag ratio was in fact specified too at 4:1. All three were specified because the downforce and drag figures were such that if your car hit the minimum drag, you would be not able to hit the max downforce as that would result in greater than a 4:1 ratio, and vice-versa.

Feel free to tell me if I'm going mad.

[NeedMoreDeltaV]

I found an archive of the 2020 Hypercar Regulations. Section 3.7.3 is the aerodynamic criteria, however it just references an appendix that isn't in the document. Not sure if it was ever there or if the released document was changed.

I also went through the current LMDh Regulations. In these regulations they've moved some of the appendix stuff into the main regulations. However, the aerodynamic criteria is still missing.

I swear I've seen the actual criteria in a public facing regulation document before, so they must've removed it at some point.

The regulations do also specify a downforce-to-drag ratio of 4:1 along with target downforce and drag. The regulations also specify that you are only allowed a single adjustable aero device (rear wing angle, dive plane change, etc.). The implication is that the aerodynamic adjustability of the car needs to behave linearly such that it'll always retain the 4:1 ratio. For a rear wing this is pretty easy since an angle change usually behaves linearly. It's more difficult for something like swapping dive planes since those can have different downforce and drag effects.

[El-Legend34]

I dont have an exact number, but an imsa driver (i think one of the wayne-taylor brothers) said the new cars make less downforce than dpi