Эффект земли или граунд-эффект (1977-1982)

[Владимир Коваленко]

Из книги Найджела Мэнселла "Верен себе" (Staying on Track).

As I was trying to establish myself as a top driver, one of the most exhilarating aspects of the amazing technology on these cars that I had to learn was the so-called ground effect. This was perhaps the most brutal, dangerous and yet hugely exciting technical development to appear during my career, and it was Colin Chapman who first introduced the concept in Formula 1, with devastating performance effects.

To be there at the time when this technology was evolving in Formula 1 was a great privilege and a real thrill. As savage and unpredictable as the cars with full ground effect could be, I loved the challenge and the adrenaline rush, but at the same time it could occasionally be genuinely frightening. Proper frightening. For those of you who do not spend hours poring over the history books of motorsport engineering and evolution, here is a basic explanation of how ground effect worked. It is well known that designers use wings and aerofoils on the top of cars to control the flow of air and therefore the amount of drag and downforce. Formula 1 cars had utilised wings on the cars body for many years by the time I was racing, of course. What ground effect did was to exploit the fact that the ground itself was a part of that equation. By that, I mean the air between the underbody of the car and the ground plays a crucial part in the amount of downforce that the car generates. When the genius minds of people like Colin Chapman and his team dug further into this principle, it became apparent that by forming tunnels - known as venturis - along the underside of the body (and later the introduction of side brushes then skirts), the ground effect could be controlled, thus generating massive downforce, which in turn allowed cars to take corners far quicker. By using skirts and venturis, the gap could be controlled — like a very precise wind tunnel under the car - and therefore the air underneath could be manipulated to accelerate. Consequently, the pressure in that space would drop, while the pressure on the top of the car was unaffected, thus creating a downforce pushing the car on to the track. If you take an airplane, the principle is that the air pressure under the wing is greater than the air pressure above the wing, which creates lift and forces the plane into the air. Put very simply, ground effect is the opposite of that. Essentially, the presence of ground effect sucks a car down on to the track. The amazing thing was that the faster you went, the more the car was sucked down! In some cases, it was thought the massive ground effect was estimated to be as much as ten times more powerful than the downforce created by the wings on top of the car. Easily enough to drive the car upside down along a tunnel.

This all sounds extremely clever, and it was. Speaking as someone who helped test the principle at high speed on many hundreds of breath takingly fast laps, I can also say that in terms of grip and downforce, when ground effect worked correctly it was absolutely astonishing. You could head towards a corner at 200mph, then brake no more than about 50 metres away from the entrance and still carry an incredible amount of speed through that corner. For a very fast corner, you could fly in at a staggeringly high speed and yet maintain that velocity, it was that stunning. The cars were glued to the track and you were just doing these ridiculous speeds. It was so violent, so staggeringly incredible, so amazing.

The science of ground effect kept evolving, too. The people developing the system were so brilliant they were quickly able to tweak and tune the way ground effect worked depending on which circuit you were at and the demands on the car. For example, they were able to alter the angle of the tunnels underneath. They used what were called shims’, which helped to move the centre of pressure backwards or forwards along the bottom of the car. If you were on a slow circuit and wanted better turn into the corners, you’d move the centre of pressure to the front of the car by altering the tunnels, or by altering the rake of the car, which also adjusts the angle. On very fast circuits, where you wanted a stable rear end, you could move the centre of pressure backwards a little bit and carry more front wing to get the car to turn in and then to keep the stability so that you could go round the corners flat out. You could tweak it; you could move the main centre of pressure of the car depending on how you set the ride height and the angle of the wings, so it was a very complex science indeed, tuning these cars in a completely different way. To complicate matters, every time a car compressed - namely, when it braked and the underbody tilted, even minutely - the centre of pressure moved up and down the length of the car. So the challenge of regulating ground effect was a constantly moving target. Some of the brains behind the science were just legendary and they were able to manipulate where that centre of pressure was located, and in so doing they could make the car more driveable.

Of course, there was a price to pay for ground effect, on a number of levels. Firstly and perhaps most obviously, the sheer savagery of the cornering speed massively increased the amount of lateral G experienced by the drivers. Lateral G is the most toxic kind of G-force. You could be pulling around 5G through corners and it was just totally brutal on the body. There were corners on some tracks that drivers were used to going around at a speed they were familiar with from the days before ground effect. Now we were heading into and through these same corners at substantially quicker speeds. On certain tracks, it was almost like having to relearn the entire circuit. I have to say I always enjoyed that part; in my opinion, I was one of the fastest learners on the grid, so I personally felt I could quickly absorb the changes that ground effect created in terms of driving lines and the altered subtleties of each track.

The perfect ground effect set-up led to such colossal G-force that it was rumoured that some drivers were blacking out. The problem with G-force is that it is rarely constant. It changes from one moment to another. Also, linear G and lateral G are two very different experiences. The linear G-force in a straight line was massive; when you are loading up into a corner, heading straight towards the bend under deceleration, you just have acceleration or deceleration G. That is pretty immense at times.

However, the really vicious manifestation of this phenomenon is so-called lateral G - that is, the G you experience when you are cornering. This is the most dangerous G-force in the world. We were experiencing more G-forces than an astronaut might be faced with and yet we were not even wearing G-suits. Even fighter pilots who experience considerable positive and negative G do not experience the lateral G that an FI driver does. To give you real-world context to that statistic: if you corner at 5G then you are experiencing the equivalent of five people of your own body weight pushing against your head.

It gets worse, much worse. It has been shown that when an FI car bottoms out in the middle of a corner, for that split second the G-force shoots up to somewhere in the region of pulling 25 positive G. That’s 25 people pressing down on your body, all while you are driving at very high speed and trying to race other drivers, think about lap times, track position, strategy and so on. If that sounds extreme, that’s because it is. So when you see a car fly round a corner and sparks briefly fly up from underneath the body as the car bottoms out, you probably think that looks rather dramatic. Let me tell you, it’s absolutely dramatic for the driver!

Dealing with G is an absolutely pivotal part of being a great FI driver. Understanding when the G will hit you, in what direction, how severe, how that will affect your driving and so on are crucial parts of the jigsaw. G-force is such a massive force, so powerful, that you have to find a way to cope with it. The best way in my opinion is actually counterintuitive, in that you have to learn to relax into the G, otherwise your own body’s tension works against you. Easier said than done when you are cornering at 150mph and your body is being battered and smashed inside the cockpit. The downside of relaxing into G-force is that when you learn to do that successfully, your muscle and skin and bone are literally forced into every tiny crevice and corner of the steel cockpit, and that can be really painful. That is when you feel every corner of the car, especially if you have got no foam or seat in the cockpit. Yet if you tense up in anticipation of that pain, you will negatively affect your performance. So it is quite an acquired skill, absolutely mind over matter, and really quite hard to do successfully for long periods of time.

Another crucial development that ground effect created was the need for far harder suspensions. The reason for this was simple: given that ground effect worked by precisely controlling the gap and airflow under a car, you could no longer have nice, soft suspensions that absorbed all the bumps and lumps in a track, cushioning you as you drove. That movement up and down would, of course, dramatically alter the air pressure under the car and either dilute or possibly completely destroy the ground effect. Therefore, the optimum aim was to maintain a specific ride height where ground effect could operate consistently. Consequently, the ground-effect cars were fitted with much harder suspensions. In terms of ride quality, you went from the soft springs that provided a not unpleasant ride to what was essentially a rock-hard, super-powerful go-kart travelling at lunatic speeds around corners. In terms of your day-to-day experience out on the track, the enormous change in ride quality was really quite dramatic. And I can tell you from very painful experience over thousands and thousands of laps of having my arse and pretty much every bone in my body completely battered that ground-effect suspensions were much harder.

There were many cost implications of ground effect, too. For example, the soft springs on cars cost several hundred pounds, but the much firmer and more precise ground-effect springs cost thousands of pounds. For other teams playing catch-up with Lotus, it was far worse, because the cost of developing ground effect from scratch was potentially enormous.

As a driver, you could learn to live with the severe lateral G created. You could train your body to absorb those new extreme forces. You could relearn tracks and understand where the ground effect worked and where it was less powerful. You could get used to the harsher ride. However, the most chronic downside of ground effect was the fact that at times it was inconsistent. When you are travelling into a corner at speeds in the region of 200mph, inconsistency can be lethal. Literally. This was the ultimate price you risked having to pay for using ground effect - if a car bottomed out for some reason and that crucial ride height altered, the ground-effect system could fail and if that happened then you were nothing more than a helpless passenger in the lap of a monster.

Why was ground effect inconsistent and therefore at times highly dangerous? Well, let me explain. If you were able to maintain a consistent ride height and the skirts at the side of the car stayed in their correct position, with the predicted airflow under the car precisely as expected, then it was just the most beautifully powerful, savagely exhilarating system. There was a perfect window of ride height whereby the car was amazingly driveable, incredibly so. The tremendous downforce was just a joy when it was there. But then suddenly ... BOOM! ... it could be gone. At that instant, if you are halfway through a corner at I60mph, then you are in big, big trouble.

Usable ground effect could literally disappear in an instant. This could happen if one or both of the side skirts moved or became stuck, and also if the ride height altered for some reason. In those situations, the positive air pressure you had generated would stall and that incredible suction would dissipate instantly. You could go from having several thousand pounds of downforce to almost nothing in a heartbeat. To use the technical terms, the ground effect could ‘attach’ and ‘detach’ at times very unpredictably.

When ground effect disappears, the car becomes almost undriveable. If you were in the middle of a corner when that happened, there would be absolutely nothing you could do to save the car, and more than likely you would fly straight off and have a massive accident because, by definition, you are cornering at high speed. If that happened ... you’d better hold on tight. Certain corners you would enter and be thinking, I might not actually come out of this corner at all, finito.

The scariest part of ground effect was that you didn’t know when it was going to fail. That’s not strictly true; there were times when the car would start to do what was termed ‘porpoising’ - that is, bouncing up and down. This happened when the ground effect was detaching, reattaching, detaching, reattaching and so on. Maybe the skirt was partially stuck; there were a number of other possibilities, too, but the manifestation of the problem was this porpoising - which, I can tell you from personal experience, when it happens at nearly 200mph is very unsettling indeed.

The window of operation was so small, and the consequences of failure so vast. Ground effect was such a poisoned chalice. If you can imagine a car’s performance is like the tip of a needle, and balancing perfectly on that tip is the optimum performance. The danger of going off line even a tiny fraction spells disaster. The aim was to make a ground-effect car’s optimum performance more akin to an oblique curve, so that in the event of a failure you would still have a bigger window of working opportunity for that car before it flew off the track. However, at times, ground effect was all or nothing. It was very hard to harness the incredible energy and downforce and maintain it in a stable fashion. Everybody could get massive downforce using this idea; the trick was creating usable massive downforce.

The engineers, aerodynamicists and brains behind the system worked tirelessly for months and indeed years on end to try to solve the problem. They battled to try to regulate the ground effect, to make it ‘solid’ so that it did not compress -this prevented the centre of pressure under the car moving about unpredictably and therefore made the system consistent. They tried fixed skirts and other ideas to try to control the beast.

Ground effect suited my driving style. It suited a strong racer, a driver who would go into a corner and hang on for dear life. You almost had to have a suicidal trait, where you were willing to risk everything to try to do the job. Ultimately, the limitation of ground-effect technology (if it was working perfectly) was the human being driving the car. It was a case of how brave, how stupid, how talented are you? And how prepared are you to put it out there and risk everything? Literally everything.

Tragically, there were fatalities that some experts speculated ground effect may have contributed to. Patrick Depailler lost his life testing in Hockenheim in 1980. To be absolutely accurate, it was never actually certain if ground effect contributed to his fatal accident, which was attributed to a suspension failure. tie went into a corner and the car appeared to simply fly off the track. Even if that fatality was not related to ground effect, there was much conjecture that the system could be very dangerous.

Ground effect was used between 1977 and 1982. As I mentioned, there were efforts to tame the idea to a degree, but it remained an essentially risky science. The FI authorities eventually banned ground effect due to very justifiable safety concerns. I think if it had been left to continue and evolve unfettered, it could easily have killed many drivers. So they banned it, for all the correct reasons.

Despite all the negatives I have detailed, from a purely technical point of view ground effect was a truly phenomenal invention, and it was simply amazing to be involved right at the point when it was introduced into Formula 1 with Colin and then to see the evolution of that dark art.

From a driver’s perspective, perhaps the single most damaging consequence of ground effect was the shattering of your confidence if it failed in a corner and you flew off the track.

[Роман Семёнов]

Насколько я понимаю, в русскоязычной науке это же явление называется экранным эффектом, эффектом влияния земли, эффектом экранирования земли.
Конечно же, его сознательное применение в гоночной практике не ограничивается постройкой машин с днищем особой формы и боковыми юбками. В книге Райта в приложении А пишется, что получить преимущество с помощью данного эффекта пытались начиная с 1960-х. И сейчас посредством гибких передних крыльев в Ф-1 стараются максимально использовать данный эффект, а в случаях, когда профилированное днище и диффузоры запрещены правилами, площадь плоского днища максимизируют, чтобы генерировать как можно больше прижимной силы с помощью того же экранного эффекта. И этот же эффект используют в дорожных легковых машинах, делая максимально плоское днище без выступающих частей.

[Владимир Коваленко]

Video: Clive Chapman on the discovery of ground-effect aerodynamics at Lotus