Lotus E22 Renault

[timbo]

This is F1, aero trumps everything.

Unfortunately.

Yeah, almost each car has something on its suspension which looks questionable from the mechanical point of view.

[Lycoming]

What strikes me on that pic is the mechanical design of the upper wishbone. At FSAE, design judges would never stop telling students that there is absolutely NO excuse for having suspension rods in bending.

So were the FSAE judges exaggerating or have Lotus come up with a poor design?

https://dl.dropboxusercontent.com/u/200665/REIB.png

What they don't want in FSAE is threaded rod ends in bending because loading threads in bending is a terrible idea. There are no threads in bending here, the bearing is staked into an insert which is bonded to the carbon fiber. So it's not as bad. Still pretty bad mechanically for the arm, but they use carbon fiber, which can help make up for it a bit, and they have aero considerations that, frankly, don't matter in FSAE.

But it is true that F1 suspension designs are pretty much universally terrible from a purely mechanical perspective for a multitude of reasons. Just try tracing the load path through their suspension geometry and you'll see why.

[Per]

Your point on threads is a good one, but "using carbon fibre to make up for it a bit" really isn't a valid argument. CFRP doesn't magically make the bending load disappear nor does it cope better in bending than metal (I mean, when compared to their respective tensile/compressive properties). Applying bending on a rod simply makes it a structurally less efficient design no matter what material is used.

What is even worse is the pullrod is also attached to the point where the two wishbone elements meet. So the part that is in bending is also carrying virtually all of the vertical load, which makes things even a lot worse. Imagine the load this thing sees when braking at 300+ kph, or accelerating out of a fast corner.

Anyway, I guess my remarks show why I'm a structures/materials guy and not an aero guy, and why I chose not to apply for a position in F1 in the end...

[FrukostScones]

[iotar__]

RG interview, Googlish but mostly understandable. http://translate.google.com/translate?h ... tory.shtml

If it's not clear after Silverstone and team releases car will stay where it is in terms of performance. Problem is aero and understanding of the new rules (what else?). Merc engine in 2015 not enough; new nose might be different again(?).

[techF1LES]

https://twitter.com/techF1LES/status/507855945842434049

[Per]

http://www.f1technical.net/news/19629

Any ideas what Lotus's crucial chassis mistake has been? The article hints to something leading to "inherent instability under braking" but I thought that was more drivetrain-related (problems with ERS-K harvesting and brake-by-wire).

[turbof1]

It could perhaps something be like wrong overall packaging. Local faults in the weight distribution could easily cause this. Because Lotus deems it unfixable this season, it has to be something like the engine placement, gearbox, tank,... which would require a completely new car to built to fix it.

It's guessing though.

[iotar__]

http://www.f1technical.net/news/19629
Any ideas what Lotus's crucial chassis mistake has been? The article hints to something leading to "inherent instability under braking" but I thought that was more drivetrain-related (problems with ERS-K harvesting and brake-by-wire).

AFAIR from some previous interview (memory) they had same or similar miscalculation last season and the new rules exposed it so result aren't in one direction. Based on nothing - maybe that's why they couldn't make "device" work , one more variable and everything changes.

Found it c/p: http://en.espnf1.com/italy/motorsport/s ... MP=OTC-RSS:
"We have some problems with the consistency of the aerodynamics of the car. Sometimes you lose 2% of aero balance, sometimes you lose the floor and with Monza levels of downforce it is even harder to predict. It's basically the problem that we've had since day one and here it is just worse because there is less downforce on the car.

"It's something we cannot 100% solve for this year. But it's something we have been aware since not a very long time. At least we have the tools to measure the problems and from there we can get better. It came in Spa that we realised we had a correlation between wind tunnel, track and driver's comments with some areas that were not very good."
Grosjean said the problem had gone undetected in recent years because it was masked by the additional downforce from the car's blown diffuser, which was banned this year.

"No offence to the team because it has been the case for three years, but with the blown diffuser on the car and more downforce on the car we had before it was invisible to everyone. When it is invisible you don't know it, but with the new regulations and harder tyres and less downforce and the loss of the blown diffuser - everything that made us strong in the past - it is now our weakness. It's unfortunate that it happened at that time.

"I think we are behind schedule in terms of development of the car. We had to focus a lot on the power unit and the cooling, and all that put us on the back foot in terms of developing the performance when you focus on other stuff. The car wasn't well born, after three laps in Bahrain I asked if I had a puncture at the rear of the car and they said 'No, everything looks okay'.

[Per]

Thanks iotar, that's interesting. If they sometimes lose aero balance (probably loss of a bit a rear downforce), and sometimes "lose the floor" they must be suffering with unstable flow. I was thinking about a problem with the outwash front wing in yaw (or in side wind) but it should be possible to fix with a new wing. Same for a tea tray / splitter acting strange in yaw.

"Losing the floor" sounds an awful lot like stalling it, but surely it can be fixed by using less rake? That would reduce rear downforce but at least the car would be predictable. Well, maybe this is what they chose to do in the end but it throws their performance back too much.

Any more insights, anyone?

Edit: just realized that if it is related to instability under braking as the article suggested, it can still be a matter of stalling the floor or loss of sealing the diffuser as the driver hits the brakes and the car pitches - perhaps combined with unexpected behaviour when there is a side wind. In that case the loss of FRIC should have hit Lotus even harder than some other teams, which perhaps indeed it has.

[theWPTformula]

Generally teams only model one half of the car in CFD to save time and money, assuming that the other half will work in almost identical fashion. This could be where Lotus have been a bit short sighted, and not realised how much the 50mm offset of the twin tusk nose design has affected them.

I've expressed my views on this, although I forgot to mention the point about CFD - http://richlandf1.com/?p=28231

[Per]

I do not agree at all with that analysis. The nose tips arrive in a more or less steady and undisturbed flow. They are both nicely rounded, smooth and symmetric about the XZ plane (I mean each individual tusk is symmetric and does not deflect airflow left or right). Consequently, their influence on the airflow is quasi-equal in a straight line. No vortices or separation are ever expected off this nose, under normal driving conditions. So even in cornering the difference between left and right is negligible.

The internal asymmetry of an F1 car has a way bigger influence on the airflow in my opinion, especially since this year with the large intercooler. It is much safer to assume that Lotus' asymmetric rear end has to do with that rather than with a few centimeters of blunt nose at the front of the car.

Also, I'm sure Lotus has run sufficient CFD simulations of the full nose to verify its behaviour in sideslip before actually giving the design the OK, taking into consideration how much resources teams reportedly spent on asymmetric cornering aerodynamics in recent years.

As your analysis says, there are dozens if not hundreds of 'critical' areas in the chassis, the asymmetric nose probably being one of the simpler of them all.

[trinidefender]

Generally teams only model one half of the car in CFD to save time and money, assuming that the other half will work in almost identical fashion. This could be where Lotus have been a bit short sighted, and not realised how much the 50mm offset of the twin tusk nose design has affected them.

I've expressed my views on this, although I forgot to mention the point about CFD - http://richlandf1.com/?p=28231

My understanding is that teams model half the car in CFD to start off with and then switch over to a full model to get more refined results. Especially when running the car in yaw. For a CFD model to be at least somewhat accurate in yaw you have to present the whole model.

It also isn't only the twin tusk nose. The exhaust gases at the rear doesn't exit on centreline. The rear wing support isn't on the centreline. The sidepods, especially at the back are vastly different shaped. The internal aero on each side of the car is quite different. Not to mention I wonder if all the asymmetric placement of parts has caused them to run a compromised centre of gravity placement.

[theWPTformula]

As your analysis says, there are dozens if not hundreds of 'critical' areas in the chassis, the asymmetric nose probably being one of the simpler of them all.

I'd have to disagree with you here. I think it was Gary Anderson who commented on the fact that Mercedes have gone through multiple crash tests to produce 3 iterations of their nose this year. Why put in all that effort if it isn't important? Perhaps we might not think they are that important because they are not changed too much during the season, but the whole car is designed around the nose and front wing so changing them drastically during the year would actually be detrimental.

[wesley123]

I do not agree at all with that analysis. The nose tips arrive in a more or less steady and undisturbed flow. They are both nicely rounded, smooth and symmetric about the XZ plane (I mean each individual tusk is symmetric and does not deflect airflow left or right). Consequently, their influence on the airflow is quasi-equal in a straight line. No vortices or separation are ever expected off this nose, under normal driving conditions. So even in cornering the difference between left and right is negligible.

The issue with cornering is that the tusk completely blocks off the area between the tunnel. Lotus nose works by getting air in between the tusks. This is different to the dong, where air is grabbed from the side of it.

When the dong nose is in yaw, one side isn't blocked off. With the tusks, the area where air is supposed to flow is blocked off. And seeing the importance of getting air there to make the floor work, this is quite an issue. The 50mm(or how much it is) thus makes quite a significant difference in left or right corners.

The area of the tusks also have to be pushed through the air when turning in, which also could be an issue.

The internal asymmetry of an F1 car has a way bigger influence on the airflow in my opinion, especially since this year with the large intercooler. It is much safer to assume that Lotus' asymmetric rear end has to do with that rather than with a few centimeters of blunt nose at the front of the car.

Teams pretty much always run assymetric cooling. It's not much of an issue. Yes, it gives a bit of balance to one side, but that's not that much of an issue, the cooling outlets are mostly in an area of nothing anyways. this balance to the side could very well be balanced out as well via the setup.

I'd have to disagree with you here. I think it was Gary Anderson who commented on the fact that Mercedes have gone through multiple crash tests to produce 3 iterations of their nose this year. Why put in all that effort if it isn't important? Perhaps we might not think they are that important because they are not changed too much during the season, but the whole car is designed around the nose and front wing so changing them drastically during the year would actually be detrimental.

Compared to previous years, the nose now is on the hieight of the front wing. Thus, it's position would have much more effect on front wing performance under yaw. Imo that raises the importance of the nose for this year, to prevent negative interaction from the nose on the front wing.