Aerodynamic Efficiency of F1 Cars

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xpensive
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Re: Aerodynamic Efficiency of F1 Cars

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WhiteBlue wrote:According to Charlie Whiting F1 cars exceed 2.5 tons of downforce. The aerodynamic braking effect is approximately 1g which compares to 640 kg. So you would never be able to glide the thing. Considering that the car only weights 640 kg with driver you cannot reach a glide angle even with 100% negative incline.
...
I'm afraid that our absent friend is mixing things up, as long as the car is rolling free, downforce is not stopping it from rolling down the slope.

If the 650 kg car needs 60 m/s, 216 km/h to balance gravity with downforce to run upside down and it takes 200 kW to move it through the air;

Power = Force * Speed.
Energy = Force * Distance
Potential energy = Mass * g * level

Conclusively;
- Air resistance is then 3333 N and energy consumed over a 100 meter length is 333 kJ
- At the same time, potential energy for 650 kg will balance 333 kJ at 52 meters level.

Pretty steep in other words, but it will work actually.
Last edited by xpensive on 20 Jun 2012, 07:23, edited 1 time in total.
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gixxer_drew
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Re: Aerodynamic Efficiency of F1 Cars

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strad wrote:Wouldn't Aerodynamic Efficiency imply something that slips thru the air? An F1 car with drag the equivalent of at least 1G is not very efficient. I think efficiency would imply little drag. Wouldn't it? A bullet has fair aerodynamic efficiency not an F1 car.
L/D is the commonly used benchmark of aerodynamic efficiency for racing purposes. Both downforce and drag reduction improve performance.

Lycoming
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Joined: 25 Aug 2011, 22:58

Re: Aerodynamic Efficiency of F1 Cars

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In formula one, we typically define aero efficiency as the ratio of lift to drag. you can define efficiency however you like depending on the situation; If I was trying to build a hypermiler then yes, I would consider something that slips through air easily to be more efficient than an F1 car, even if it generates lift (and therefore has negative L/D). But in F1, downforce is king because high cornering speeds are much more important, and lift to drag is a good measure of how good your aero package is. Obviously not the only important metric; high L/D is no good if you have pitch sensitivity, a badly placed center of gravity, or your wings weigh 500 kg. But its an important one, because both of those parameters are important to the car's performance.

It's all about understanding what you are trying to do.

Also, drag isn't all bad; it helps you under braking. Of course, with a typical grand prix circuit, you still want the least drag possible. However, situations do exist where to an extent, higher drag will theoretically improve lap times.

bhall
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Joined: 28 Feb 2006, 21:26

Re: Aerodynamic Efficiency of F1 Cars

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xpensive wrote:I'm afraid that our absent friend is mixing things up, as long as the car is rolling free, down force is not stopping it from rolling down the slope.
Did Mr. Doe really think an F1 car wouldn't freely roll down a hill because of drag?

Would that even be true on Venus?

myurr
9
Joined: 20 Mar 2008, 21:58

Re: Aerodynamic Efficiency of F1 Cars

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Actually I think he was saying that you couldn't have a slope steep enough for the car to roll to a speed great enough to then support its own weight (i.e. drive on the roof of the tunnel). That's how I read it, but his phrasing is poor.

xpensive
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Re: Aerodynamic Efficiency of F1 Cars

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myurr wrote:Actually I think he was saying that you couldn't have a slope steep enough for the car to roll to a speed great enough to then support its own weight (i.e. drive on the roof of the tunnel). That's how I read it, but his phrasing is poor.
My analysis was based on the assumption that an F1 car will have downforce enough already at 216 km/h to run upside down, at which speed the air-resistance wouldn't be more than 3333 N if 200 kW of power was used, why the "aerodynamic braking effect mentioned would not be more than 3333N/650 kg or 0.5 g.

It would be somewhat difficult to find a 50% steep tunnel however.
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xpensive
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Re: Aerodynamic Efficiency of F1 Cars

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Now that I had the time to consider my own numbers and they seem accurate, an F1 car with enough downforce to support its own weight at 216 km/h, could actually free-roll upside-down through a tunnel with a 27 degree angle, amazing.

Never thought about it that way, thanks for bringing it up TC!
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Reca
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Re: Aerodynamic Efficiency of F1 Cars

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In the transcript of the court case F.India vs Fondtech there are couple of data about the target parameters they were aiming to for the (back then) Lotus, in particular target efficiency for start of season 2010 was 3.25, with a target SCz of 4.56 m2. (that being the target for an end of grid team, based on data from a mid-low grid team, we can presume top teams achieved better values, at least for SCz)

If we consider the target downforce needed to stay on the roof as 6500 Nm and assume SCz constant (not necessarily it is but the data coming from wind tunnel they should be good for the mid Re/speed range), that means minimum speed needed about 180km/h.

Another thing, this is part of speed vs time from a video of Schumacher in FP in Malaysia (I love these FP videos, drivers often do "odd" things...):
Image

For a while, travelling in the opposite straight, MS lifts the throttle and coasts (DRS off) before touching the brakes, and in particular (red part) he goes from 288km/h to 237 (80m/s to 66) in 2 seconds, which means average deceleration of about 0.7g.
After that he starts to brake and as visible in the graph, the deceleration rate increases.
strad wrote: I guess it depends on what you call efficiency...to me a lot of drag isn't very efficient
Aerodynamic efficiency is by definition ratio of modulus of aero force component perpendicular to speed (lift) vs modulus of component parallel to speed (drag), if then that number is high or low doesn't change the name of the property, it's still efficiency also if it's close to 0, as typically happens for road cars...

That then for specific purposes the thing you mainly care about is not maximizing efficiency but can be maximizing downforce or minimize drag, that's another matter which doesn't change the definition of aero efficiency.

For example in a track like Montecarlo you can increase downforce as much as possible even if it means increasing drag proportionally more (so reducing efficiency) because that brings laptime benefit and increment of drag has no meaningful impact.

In a track with characteristics more like Spa/Suzuka, an increment of downforce that comes with a proportionally higher increment of drag isn't as helpful, so you likely tend to favor more the efficiency.

In a track like Le Mans (or an oval) on the contrary reducing drag is paramount, even if it costs proportionally bit more on downforce, thus a loss of efficiency, because the time gained in the long straights more than compensates the small loss in corners.

So you have that probably a setup aimed for track like Spa/Suzuka is, according to definition, the most efficient, but certainly would be less suited to Monaco or Le Mans than the, by definition, less efficient setups aimed specifically at these tracks.

The above guidelines then can vary depending by car specific characteristics, starting with how downforce and drag effectively change for different trims of your car (summarized by the polar curve) or with engine power.

The more power is available, the more adding downforce gives a benefit to laptime as even with added drag it's possible to reach a straight line speed level so high that further increasing it brings very little.

For instance, for a F3 car with 210-220hp Montmelò with its long straight will likely demand a rather low rear wing trim as otherwise the time lost in the straight would be way more than what can be gained with the added grip in corners.

In the same track a F1 car with >750hp will on the contrary use wings in a trim very close to max downforce, hardly distinguishable from Monaco's, as even with that level of drag the top speed can get in the range of 300km/h and further increasing it would give little benefit on laptime.

Look for example at this plot, speed in Montmelò from LH's "pole" lap:
Image


The red line is the original velocity, while the green and blue lines indicate artificial velocity plots I made limiting top speed to 310 and 300km/h respectively (instead of the 317-318 effectively reached), and leaving speed equal everywhere else; that change of velocity profile causes an increment of laptime by 0.12s and 0.37s respectively.
Not much for a loss of close to 10 or 20 km/h along a >700m long straight.

It's quite natural, based on that, that F1 designers will tend to focus more on downforce generation at cost of sacrificing a bit the drag and possibly also efficiency, with the power they have available, in almost totality of F1 tracks even with an high drag setup they'll reach a peak speed so high that further increasing it gives little gain so gaining downforce brings more benefit to laptime.

Tommy Cookers
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Re: Aerodynamic Efficiency of F1 Cars

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We (you posters) seem to have established the aerodynamic efficiency of F1 cars in aeronautically conventional terms ie Lift:Drag ratio (as related to the angle of our hypothetical tunnel), and emphasised that 'other measures of aerodynamic efficiency are available' ie those relating closer to lap time.
I thank you for this.

Another issue (which could also be illustrated with similar facilities) ?

I appreciate the difference between a wing with a higher lift coefficient and a wing with a lower lift coefficient, the 'man in the street' might not .........

Which F1 race achieves the higher peak actual downforce, Monte Carlo or Monza (or which other) ?

Which achieves the higher DF in DF-limited cornering ?

Which do we call a high-downforce circuit (and why) ?

Just_a_fan
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Joined: 31 Jan 2010, 20:37

Re: Aerodynamic Efficiency of F1 Cars

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I think Silverstone might be the sort of track that you're looking for. They hit approx 300kph 5 times in the lap and have a number of high speed, high-g corners (Copse: 287kph/5g; The Becketts complex: 1.5g, -3.7g, 5g, -3.9g all whilst cornering at between 297kph and 211kph; Stowe: 200kph/2.9g; Club: 226kph/3.2g; Abbey (no idea but it's 250kph+ and probably 3g+)).

Image

It's a high downforce circuit if ever there was one - you don't take a corner at 250kph and 5g without a lot of downforce. Monaco isn't a high downforce circuit because, although they put a lot of wing on the cars, they never go that quickly so the downforce figures aren't huge.
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strad
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Re: Aerodynamic Efficiency of F1 Cars

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Reca, You've confused me...Are you saying that an F1 car with a ton of drag is aero efficient?
That doesn't make sense to me.
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I found this in a discussion on this subject discussing the Williams FW07
The ultimate aerodynamic Grand Prix machine to ever be raced.
2.278 Kgs @ 150mph/240 kmh with 285 Kgs of drag
Lift-to-drag ratio: 8:1

A modern F1 car has an Lift to Drag ratio of 3.5 to 1.
In other words a lot less downforce combined with a lot more drag to prevent the cars from going fast.
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strad
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Re: Aerodynamic Efficiency of F1 Cars

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BTW...I ain't trying to argue, but to understand the definitions...Not to get in a separate discussion but I would think something like a .308 would be efficient. To me an F1 car is very inefficient.
To achieve anything, you must be prepared to dabble on the boundary of disaster.”
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flynfrog
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Re: Aerodynamic Efficiency of F1 Cars

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strad wrote:Reca, You've confused me...Are you saying that an F1 car with a ton of drag is aero efficient?
That doesn't make sense to me.....
They are as efficient as they can be within the regs.

I have posted in an this older thread but I will repeat it here. Not responding directly to you strad just propping up my soap box

F1 aero for non aero people warning no math or numbers below.

F1 cars are trading engine hp for down force or top speed for corner speed. While the L-D ratio might seem poor compared to an airplane they are not trying to fly as fast as possible or fly heavy loads they are trying to go around a circuit in the fastest amount of time. This does not mean a car has to be the fastest on the strait or the corner. The engineers find the best balance of corner speed and strait line speed to turn an optimal lap for the given HP of the car.

An F1 car makes more power than it could ever hope to use accelerating the car. Lets imagine the car makes no downforce. The driver would have to wait until the end of the strait to put the pedal to the floor only to have to tip toe around the corner with an angry engine trying to light the rear tires into awesome balls of smoke and noise. The car is very aerodynamic with low drag and low lift but is still slow.

Lets take the same car and bolt a flat piece of ply wood above the drivers head at an angle. The car now creates down force. Its top speed is slower (maybe*) but it can now go around a corner faster. The driver can also apply more throttle sooner on the strait. *This make make the car faster at the end of the strait than before. This is resulting in a faster lap time. The car now has the aerodynamics of the barn door (like the one strapped to the roof) but barn doors with enough thrust and AoA can produce lift (or downforce depending on the angle)

How F1 engineers earn the big bucks (or why f1 focuses so much on wings and winglets and tunnels and tunnelets...) If we replace the barn door with a curved barn door we have now created a better airfoil. Our car is gaining downforce and losing drag. It is becoming more and more efficient. With f1 now having spec engines spec tires spec CoG ect. this is leaving a pretty restricted aero package to be the main place to make gains in lap times. A spec engine fixes the max amount of energy we can use. This means all cars will have about the same amount of drag. The gains are now going to be made by getting more lift for this drag. If we get to a point where we are going fast enough around a corner we can now back off some of that lift in favor of slightly lower drag. With F1 being as close as it is currently we see the birth of tiny winglets hoping to get .002% more lift or drag reduction.

So the moral of the story or something (I drank way to much coffee today) If you want to see more efficient F1 cars give them longer straits, less power or open up the rules on the under body of the car to allow tunnels instead of bigger wings.

If you want to see development in something other than aero open the rules on everything there are no gains to be made in frozen engines.
Last edited by flynfrog on 29 Jun 2012, 18:30, edited 3 times in total.

Lycoming
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Re: Aerodynamic Efficiency of F1 Cars

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You can define "efficiency" many different ways depending on what you are doing. For example, you could define the fuel efficiency of a racecar as the amount of fuel required to race a certain distance, or you could factor in how quickly it traverses a certain distance.

efficiency in this case is typically defined as a ratio. If I generate a ton of drag but a kilo of downforce, thats very inneficient. But, if I generate a ton of drag but 10 tons of downforce, thats very good (L/D is 10:1). An F1 car has terrible aerodynamic efficiency compared to this:

Image

But it wouldn't generate anywhere near an adequate amount of lifting force at F1 car speeds. Which is Ok, because it need only generate its weight in lift, and not including pilot, its about half what an F1 car weighs. Low drag is far more important to its performance.

Indeed compared to most things, by L/D, F1 cars are horribly inneficient. However, you should realize that its pointless to compare a competition sailplane and an F1 car. They have different goals and they do different things. We consider the F1 car built by constructor X as being more efficient than the car built by constructor Y because X generates more DF for the same drag as Y, NOT because it does so when compared to the brabham fan car, because it was built under a different set of regulations and is therefore incomparable in that sense.

Its about understanding what you are trying to do. a .308 theoretically has an efficiency of 0 since it doesn't generate lift. Thats fine, because it doesn't need to generate its weight in lift. It just needs to retain its kinetic energy over long distances. It does that spectacularly well, and so is considered efficient for its purpose. Its possible to build an F1 car shaped like that. It would have very little drag and excellent performance on high speed straights. But over the lap, it will be slow; it can't corner or brake very well, and will probably tend to wander at high speed.

The bottom line or tl;dr version is that we define efficiency based on the situation. This is defined by the rules and what we are trying to accomplish. A mclaren is efficient compared to an HRT. This is a reasonable comparision within this context. Said mclaren has nowhere near the efficiency of a glider. But they're incomparable. A mclaren is efficient in the context of a 2012 F1 car. This is not necessarily true in other contexts. This is why one can say an F1 car with a ton of drag is aero efficient, because they are saying so in comparison to other F1 cars.

xxChrisxx
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Re: Aerodynamic Efficiency of F1 Cars

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^^ Good post that.

It's the age old adage that 'everything is a compromise'.
And everything really depends on the situation.

Really the limiting factor for car aero design is engine power available. More power makes less efficient solutions viable.
Last edited by xxChrisxx on 28 Jun 2012, 23:35, edited 2 times in total.