Thursday, December 13, 2012

Inside wind tunnels

In Formula 1 world there are three types of testing validation for new parts: CFD, on the track (free practices or tests) and Wind Tunnel installations.
Lot has been said about the latter, so I'm not going into details about rolling floors or boundary layer suction, but instead I'm going to focus on what and how specifically is being measured in a Wind tunnel and why is that of paramount importance for F1 teams.

One of them has recently been all over the specialized news feeds, namely Ferrari, with their Wind Tunnel struggles, failing to produce correct correlation between tested parts and what's actually being measured on the track as results.
Various sources have been suggesting that Ferrari F1 Team will shut the tunnel down and make re-calibration, system checks, improvements, even calling external consultants, presumably from aerospace industry to check what's wrong. Just how much of all these is true is unknown to the general public, but talks about new wind tunnel construction have also appeared. It is perhaps worth saying that this is large investment and its rough estimated cost is about 40 to 50 million US dollars, besides it takes a lot of time for pure construction and realization.
UPDATE [20.Dec.2012]: Stefano Domenicali confirmed that Ferrari's wind tunnel will be undergoing major overhaul, will remain closed until August and Ferrari's 2013 car will be developed exclusively in TMG facility - see details below.

Apart from the economic outlook, teams are allowed to test with scaled model, up to 60% of the real size, and use speed of up to 50 m/s, which is 180 km/h max or 111.8 mp/h if you prefer imperial units.

Since the model parts do not represent the real world car size, Reynolds number is, for example, used to make coefficient correlation between the 60% model parts and 100% model. However, it is important what the source data shows.

Below you may find a sample spreadsheet with totally bogus and unrelated data, which is there to simply demonstrate the various parameters being measured in a wind tunnel session. Time spent inside the installation is also precious, as teams are having certain time frames allowed.

 Let's break down the data sheet into details:
  1. Cell B holds the value for Lift, in our case there is downforce generated, hence the negative sign. It's usually being measured in Nm, but it may vary in different wind tunnels implementation (Kilograms are often seen, too). 
  2. Next we have Drag, which is pretty obvious.
  3. L:D is lift-to-drag ratio - one of the most used measures for aerodynamic efficiency - sure, you can add more downforce via Angle of attack settings, but this comes at the expense of added drag, too, so balance is important. 
  4. Drag power - this is the consumed horse power, the power required to overcome aerodynamic drag.
    Note: this is a velocity-sensitive parameter, and the formula is simple:
    DRAG HP = ( Drag coefficient (0.9 or 1 for F1 car) * Frontal Area in square meters (assume 1.35) * current velocity (200 km/h = 55 m/s) cubed ) / air density (1225 kg/m3) = ~ 124 HP to overcome aero drag. The same formula gives about 380 HP at 250 km/h, etc.
  5. The next three columns, FY, FX and FZ are moments, measured as distribution of aerodynamic forces around Center of gravity, aligned with the three axes:
    Copyright: F1 Framework
  6. Next, in columns I and J we have vertical loads on the front and the rear, which is very important parameter measured from suspension point of view. While measures here differ, these are usually Newton meters, in this sample sheet the values are in kilograms.
These are some of the most common parameters that teams are measuring in a wind tunnel. Apart from those numbers, more can be crunched as a mathematical representation of the measurements taken, namely calculating coefficients. All of those numbers and their values are carrying certain amount of knowledge in regards to how your car will supposedly behave and that's why it is very important that the output is correct, as this decides what configuration and parts to put on the car.


The next chunk of details goes directly into the heart of Toyota Motorsport GmbH wind tunnel facility in Cologne. F1 fans have heard a lot about it, especially when it comes to Ferrari, but first, I, with "no wax", like to thank their staff for being gracious enough to release those images and data for the public and being patient enough to explain everything. Below you may find some exclusive images from the tunnel.

Outside look of the tunnel's diffuser section
The instrumentation of this state-of-art facility consists of two wind tunnels : one full size and one 60% scales.
Both wind tunnels use a continuous steel belt rolling road which has a maximum speed of 70 m/s. What can really describe those installations is accuracy and high quality - 512 pressure measurement channels are available. The tunnels are also equipped with Particle Image Velocimetry system (PIV) - an optical method of flow visualization used to obtain local flow velocities. The PIV system is usually used to validate CFD predictions and thus better calibrate the setup.
One of the advantages of such PIV system is that its preparation time is almost zero, due to the seeding technology used. That means that the local air is filled with tracer particles and there's no cleanup needed after that. During the process of measurement, cameras are used to obtain images and samples, which are then processed by computer software.
A laser is used to illuminate the flow field around the car’s front wheel to take particle image velocimetry (PIV) measurements (see below).

One of the main advantages of this method, just as well as the PSP method, is that it's non-intrusive, as opposed to the traditional pressure taps.
"Many of today’s motorsports cars are based on existing, commercially-available cars." Frank Michaux, a researcher at TMG, reveals.
"If researchers can identify a way to reduce drag on a motorsports car, it’s reasonable to assume that this information also may apply to future versions of a normal road car." Frank continues: "We need to deliver data quickly. If you see that you are not capturing the flow correctly, then you need to adjust your CFD methodology until you get it right".

After gathering the raw data from the PIV measurements of the “separation point” on the front tires, engineers post-process the data using Tecplot software, which allowes them to see and measure the exact position of separation. Each of Toyota’s PIV measurements consist of 300 datasets, with each dataset containing two images taken 10–20 microseconds apart.

The Tecplot software package itself is widely recognized and used throughout the industry.


During the 2009 season, F1 engineers wanted to carefully study the flow wake behind the front wheels. Since this is critical part of overall car performance, the goal was to push this flow as outboard as possible. Engineers have realized that they need precise back-to-back correlation, and here's a direct comparison between CFG and PIV images: 

In order to get to those precise points, the CFD methodology has to be optimized, and here's a real case:

The next thing about Toyota Motorsport GmbH is its Continuous Motion System.

In CMS mode, a user-defined programme of ride height, yaw, roll, steer and individual pre-load changes provides continuous motion on a predefined trajectory while the HSDA system is continuously acquiring data at high frequency.
This allows realistic road or track analysis and increasing the amount of useful data from each individual test compared to standard motion and acquisition systems.
The typical "Wind-On" time is reduced by 70 to 100%  with CMS, which allows more time to be dedicated to, for example, changing parts. This Wind-On time is extremely precious for F1 teams, which we all know run under certain restrictions when it comes to wind tunnel time. 

Below you may find some exclusive images from inside the tunnel (full sizes available upon click): 
Very good representation of scaled model compared to a man

Toyota TS030 early prototype version

The control and monitoring room

Testing preparation - Toyota TF110
Front wing flap angle at 27 degrees
Surveillance and monitoring  
Glad you have reached this point - I assume you were very interested or your scroll button was stuck :)
As usual, comments and questions are welcome.

Tuesday, December 4, 2012

The evolution of pitstops

The following article is originally posted by Marc Priestley (ex-Mclaren mechanic) at his blog and I have his written permission to repost it here, which I'm very grateful for. His, Marc's website is here - F1 Elvis.
Also, you can follow his Twitter account.

Fangio, British GP, 1950
If you look back at footage of pitstops in Formula One from the early days of the championship in the 1950′s, they’re an all together different spectacle than those of 2012. They appeared leisurely, disorganized and, in the case of refueling, downright terrifying.

Drivers got out of cars while tyres were changed using large copper hammers and fuel was poured into, and often over, the back of the vehicle. Well over a minute later he’d hop back into the moving car as it was pushed away by mechanics and rejoin the race. All this took place at the edge of the track, circuits had no such thing as a separate pitlanes and there were certainly no speed limits.
Now I’ve stood with a front jack in pitlane as a modern F1 car brakes from 100kph to a stop at my feet and it raises the heart rate I can assure you. Mechanics of the 50′s and 60′s faced a series of dangers that would put today’s health and safety officers into an uncontrollable frenzy and have the sport shut down for good. Thankfully Formula One’s moved on in every area and pitstops are no exception. Today’s world record breaking stops to change four wheels in under 2.5 seconds are impressive to say the least, but they’re the culmination of years of development, learning, and improvements in technology. Here’s how they have done it.

For many years we’ve had pitstops becoming faster and faster as the sport woke up to the reality that the pitstop or stops can play a real part in a Grand Prix outcome. Teams initially threw more and more people at the process and gradually, over time, made improvements to their equipment used for the job too.
Just as competitors will always find innovative ways to make their cars faster on track, teams from every era and every formula have found ingenious ways to shave time from their pitstops. Some have done it legally, some questionably and some downright illegally, but the fact that it’s an area where time can be gained over rivals means it’s also an area where they’ll use resources and expertise to minimize the time it takes to service their cars.

1983 saw a number of fires as teams tried all means possible to shove as much fuel into their cars as quickly as possible at a pitstop and back then it was often a form of highly volatile rocket fuel, making it perilously dangerous. Refueling was banned the following year and this brought the focus away from pitstops and into the ability to conserve fuel and tyres during a race.
1983, Keke Rosberg is on fire

In an effort to spice up the show after a ten year break, 1994 saw the reintroduction of mid-race refueling and inevitably teams very quickly began to look at ways of speeding up their stops once more.
Perhaps the most infamous example was the Benetton pitstop fire of the same season, which allegedly uncovered that the team had removed a filter in the standard fuel rig, designed to restrict the flow rate of fuel from rig to car. The increased flow rate would mean the required amount of fuel could be pumped into the car faster than their rivals and of course reduce the time spent in pitlane.
During my early years at McLaren we developed a system to shave tenths of a second off the refueler’s reaction time once the fuel rig had delivered it’s required quantity.
Where normally the ‘nozzle man’ would react to a standard set of lights on the rig telling him to pull off the hose when the fuel was in, we used a stethoscope type device to listen for the valve closing inside the nozzle itself.

Just before the required amount of fuel was delivered, the motorized valve would begin to ‘whir’ and close, a process which took a couple of tenths, and once shut, the lights on the nozzle would illuminate to alert the fuel man he could begin detaching from the car. With the operator listening through an earpiece for the ‘whirring’ of the valve starting to close, he could start to react and be pulling the nozzle off the car by the time the lights switched on, therefore saving valuable time.
In those days of course, refueling was almost always the limiting factor in a pitstop. Time was saved or lost in connecting and disconnecting the rig from the car and the reactions of the lollipop man and the driver in getting away from the box. Although everyone had to use the same refueling rig, pumping at the same rate of 12 litres per second, the same hose, nozzle and valve in the side of the car, teams tried simple ways to make the operation smoother, more reliable and ultimately faster. Extra handles were welded onto the nozzle for someone to assist in pulling it off, fluorescent strips stuck on the nozzle end for the lollipop man to spot when it was completely detached from the car and the same hi visibility vinyl stuck onto the car valve to aid the refueler in lining himself up.
The sport’s always pushing the envelope in terms of technology in all areas, but whereas groundbreaking developments of ten years ago in the ‘real world’ may now seem a little dated, Grand Prix racing moves at a considerably faster pace. Technology in Formula One supersedes itself often before new parts even make it onto a car, such is the rate of R & D, but until now pitstop equipment has been something which got attention only when time permitted within the busy schedule.

Today the focus is different. With refueling gone once more, pitstops are all about replacing four wheels and tyres as fast as physically possible. For the first time in years, F1 teams have a relatively blank canvass with which to create equipment and systems to complete the operation in the shortest time. Wheel changing technology was almost an untapped market if you like, there was no desperate need to change them in 3 seconds when refueling would always take at least another 4 or so. With FIA rules being comparatively open when it comes to pit equipment and procedures, it’s been a case of micro-analyzing every element of the stop to see what can be done to save time. In the past that might have meant finding the fastest way to work with the car and equipment they had, but today there’s considerable resource allocated to the project and so the car and any new equipment can be designed from the ground up around the necessity for the ultimate stop.
Many years ago, frustrated at the difficulty of working on one of Adrian Newey’s complexly designed McLarens, I asked him one day how much of the design brief is about making the car practical and easy to work on? His answer was simply “None”. For the first time in modern F1 designers have had to think, not just about making the car light and fast, but about how they can improve the way wheels are changed during the race, with the realisation that it now has a direct impact on the outcome of a Grand Prix.
Stub axles on the car have as little as three threads of engagement for the wheel nut, to minimise the number of revolutions it has to do in tightening or releasing the wheel and the axle tip’s rounded to guide the wheel into place. Wheel nuts themselves are retained within the rims to reduce the opportunity for cross threading and take away the possibility of one falling out of the socket. In days gone by it wasn’t an uncommon occurrence to see wheel nuts spinning off down pitlane during pitstops or pitstop practice as they popped out of the gun as the wheel was removed. Of course it was hardly ever an issue as a spare nut could be picked up and fitted long before the fuel man had finished his part of the job.
Like the stub axles, drive pegs on the car’s uprights and the wheels themselves are designed to guide them seamlessly together and avoid ‘pegging’, where the two butt up against each other and fail to engage.
The jacking points, particularly at the rear of the car, are specifically made to make it easy to slot the jack into place. Whereas it used to be quite easy to ‘miss’ the old, relatively small, lifting hook with the jack when doing at speed, now things are designed differently. Most don’t even use a ‘lifting hook’ as such and a large carbon ‘splash’ on the jack can be thrown in anywhere under the rear crash structure to avoid the need for two bites at positioning it.

When it comes to the equipment and tools used in today’s pitstops, the advances are somewhat staggering.
The days of four ‘standard’ wheel guns, a couple of compressed air bottles, two basic steel jacks and a lollipop seem like a distant memory in 2012. In car terms, that level of technology would equate to the F1 cars of perhaps twenty years ago, but that basic layout of the pitstop area was still in use by almost every team just three or four seasons back. If you walk down pitlane now, it’s all very different.
The gantries carrying air lines overhead to the outside of the box are complex and beautiful. Huge moulded carbon structures house lightweight, super flexible airlines, ‘traffic light’ systems to release the driver, cameras and electronic cabling connecting almost everyone involved in the stop. As each operation’s completed, the ‘system’s’ notified through either mechanics pushing a button, or an automatic switch. Once all four wheels are on tight and the car’s on the ground, the chief mechanic gets a light and once he’s happy, he pushes a button to give the green light to the driver to pull away.

Wheel gun men now use heavily modified guns from the originals. ‘High flow’ gun backs allow greater air flow through the gun itself and effectively spin the socket faster, around 9000 rpm. Until 2012, when it was banned on environmental grounds, teams used compressed helium instead of air to power the guns. It’s extremely low density again allowed guns to spin faster and therefore remove and replace nuts quicker. The guns of today have bespoke sockets to match the team’s own nut designs, lights to indicate to the user when the nut’s done up to the correct torque and buttons to signify to the jack man that the operation’s complete. Before the recent focus on pitstop speed, gun men would signify they were done by raising a hand in the air and when the jack men saw the two hands at their end of the car, it would be dropped back onto the floor. When the chief mechanic saw four hands and both jacks out of the way, he’d release it. Now the action of raising a hand 50 cm in the air is considered to take too long and so the flick of a switch or button on the side of the gun shaves off valuable hundredths, that’s how thoroughly things are analysed.
One of the very latest developments in wheel gun technology is an automatic direction change. Up to now mechanics slide across a ‘shuttle’ on the back of the gun once the nut’s undone to change it’s direction of rotation, before doing the new wheel back up again. But Rhodri Griffiths of Palindrome Sports, the man credited with most advances in F1 wheel gun technology, has devised a new system which switches direction automatically as the gun’s removed from the first wheel. Whilst it may not directly save time in a standard stop, it’s a device which removes the need for a human operation and therefore one less thing to think about during the two and a half seconds or so that the car’s waiting in the box. Teams carefully study human performance in pitstops as well as that of the equipment, so anything which can simplify an action as well as speed it up, is worth looking at.

There’re teams who have lasers mounted in the overhead gantry which direct two beams incredibly accurately towards each wheel position. The beams cross each other at the exact height from the floor and for and aft position of the wheel nut when the car’s stopped on it’s marks. It enables the gun man to hold the gun ready at the exact height, avoiding any vertical adjustment to his position as the car comes in and hopefully the driver stops right on his marks to avoid having to move left or right.
Front and rear jacks have had a lot of thought put into them recently too. Often now made from carbon fibre to make them light and quick to move into position, they all have a quick release mechanism operated by a lever on the handle. It’s quicker than the motion of raising the jack handle to drop the car on the floor. When the lever’s pulled, the lifting arm of the jack simply breaks away, dropping the car instantly and it’s ‘reset’ ready for the next use. As someone who’s sat in a car for pitstop practice before, I can tell you it’s not a comfortable experience being dropped off the jacks with no comfy cushioned chair and very little in the way of suspension, but ultimately its faster and that’s what counts.
The jack men are looking for two lights from each of their respective gun men in order to dump the car on the floor and teams house those lights in various positions on the gantry, on the jack, or in some cases now, in ‘heads up’ displays inside the jack man’s crash helmet visor. Another example of trying to minimise human reaction times and remove opportunity for error wherever possible.
When the jacks drop they trigger another light for the chief mechanic and if pitlane is clear, he can illuminate the final light for the driver to pull away. Some teams now use a separate spotter to keep an eye on the pitlane, so that the chief mechanic can simply watch his own car and only when the system sees the ‘pitstop complete’ light AND the ‘pitlane clear’ light, does it release the driver.

When the whole procedure’s written down it seems a vast operation and although the bottom line is that it’s just a case of changing four wheels, when you look at it more closely, it is indeed complex. Each of the individual elements are studied using video analysis, onboard car data and of course the good old fashioned stop watch, although these days most teams use their own computer based systems for timing and so even the stopwatch has been replaced to a degree.

One interesting development in the pipeline is an automated jack release system. McLaren have been evaluating for some time, but are yet to race, a jack which drops the car upon receiving an electronic signal from both wheel guns, removing yet another human reaction delay and perhaps saving another tenth or two.

Crews practice over and over and over to the point where, whatever your role in the stop, it becomes literally second nature. Drivers don’t get the chance to rehearse so much and we do still see car’s over shooting, coming in too slowly or too far off center  but mechanics practice for those situations too and normally deal with it without most people noticing.

Throughout F1′s pitstop history they have always played a direct role in the outcome of races and as such, the speed with which they’re completed is crucial. For the ultimate stop, whether it’s tyre changes or refueling, each consecutive action has to preempt the smooth completion of the previous one and that’s where things normally come undone. We’ve all seen lollipops lifted as the fuel nozzle begins to detach from the car, only for it to stick slightly and end in disaster. Today, with stops lasting less than two and a half seconds, there is no room for error or glitch. Everything happens so fast that there isn’t often time to react to anything out of the ordinary, and just as through practice everything’s second nature, you’re conditioned for perfect stops and perfect stops only. Add to that, the pressure that I know only too well and that each of those guys feel when the spotlight’s on them and there’s an incredibly fine line between the perfect stop where all four guns operate perfectly in unison, and complete disaster. Talk of automated jacks, guns and lights is fascinating in terms of the technological advance and perhaps even the ‘show’, but it’ll undoubtedly have many squirming with discomfort at the prospect of the pitstop becoming too fast for humans to react to a problem and the potential safety issues that may cause. At the moment FIA regs are fairly open in this area, but just as with the cars, surely it’s only a matter of time before they step in to restrict spending, close up the field and safeguard everyone involved.