News on the black stuff
Carbon brakes slashed F1 braking distances – once many dramas were resolved
Aerospace engineering and Formula 1 design are inextricably entwined. To some extent one of these frontier technologies has benefited from developments fostered by the other, way back into the mists of time. There are many examples. The Daimler company’s Mercedes GP car for the 1914 season featured lightweight engine construction. Almost immediately more pressing global concerns than mere motor cars chasing one another around in circles led to the technology literally taking off in the Great War’s military aero-engine race.
Back in the mid-1970s one of Formula 1’s greatest forward leaps came in the development of carbon brakes. Gordon Murray of Bernie Ecclestone’s Brabham team was reading about the technology featured in the Concorde supersonic airliner project. Just a passing reference to its carbon braking system really caught his eye. It claimed a weight saving of “about 1100lb” compared to a then-conventional metal disc/friction pad system.
Now a Concorde’s under-swingings featured a lot of brakes, but it was the weight-saving prospect that riveted Gordon’s attention. He contacted Dunlop – who made the Concorde brakes – and met their specialist engineers to discuss the possible application of carbon brakes to Formula 1. Dunlop began development of a suitable set.
Everyone was worried about using full ‘plastic’ brakes because little was known about the material’s behaviour in extremis. Consequently what emerged was a steel disc drilled to carry ten carbon ‘puck’ inserts on each side. Each puck had matching radii machined into it, apart from the final one to be installed which had a flat on one side – you fitted them all around the disc and then twisted the last one and it locked them all into place like a Chinese puzzle. This was a neat way of combining the lightweight, frictional and high-temperature-resistance properties of the carbon material with the known stability of a metal disc.
Those brakes were raced during 1976 on the works Brabham-Alfa BT45s driven by Carlos Reutemann and Carlos Pace. The South Americans needed patience. Pace wrote off one of the cars in Austria when he tramped on the brake pedal to find nothing at home and promptly creamed at high speed into a trackside barrier. It was found the disc diameter had grown, the disc touched the caliper and the heat then generated had boiled the brake fluid, so when he hit the brake pedal it simply compressed the vapour in the system and the pedal went straight to the bulkhead without applying his brakes at all…
Scary stuff indeed.
By the late 1970s carbon brakes were gaining widespread acceptance throughout the aircraft industry. A landing aircraft only needs one major braking application, after which taxiing needs are relatively intermittent and mild. Operational demands in racing cars could hardly be more different; ferocious, frequent, repeated many times.
In Brabham’s pioneering case Gordon heard of a specialist Californian company named Hitco – a division of Armco steel – which manufactured carbon brakes for the aircraft industry, not only for undercarriage wheels but also as rotor brakes in helicopters. Gordon struck up a productive working relationship with Dave Gibson of Hitco and they reached an exclusive co-development agreement for F1 to perfect an ‘all-plastic’ disc brake rotor that would replace the Dunlop puck-type halfway-house system.
Initially, in 1980, Brabham used 0.7in-thick solid carbon-carbon Hitco discs. Theoretically, carbon pads on carbon discs should have been good for 2500deg C without degrading but as Gordon recalled: “We found in practice if we ran the material to just barely above 850C in racing it would become oxidised in the cooling airstream we had provided.
“This had the weirdest effect. We could run 60 or 70 laps with negligible brake wear and perfectly adequate performance and then in just two qualifying laps the driver might exceed that critical temperature and the material would simply dissolve! The brake would end up like a piece of ragged, floppy cloth – total scrap!
“That triggered a lot of development work with Hitco, including anti-oxidant coatings for the carbon material, but we eventually found that cooling was the real key – you had to control that temperature build-up, and attention to cooling in the finest detail really paid off. Unusual wear, too much bite in one application, not enough in the next – uneven temperatures producing a similar effect, with carbon-carbon capable of generating such terrific heat so rapidly, and then capable of cooling just as rapidly, we had real headaches with differential expansion of materials…”. They eventually adopted silver-plated aerospace nuts which could withstand the temperature range ramping up and down so rapidly around a circuit without working loose, chattering and eventually letting something vital come adrift.
“For some time we took the conservative option and ran conventional cast-iron brakes on circuits like Monaco, Montréal and Detroit, and only used carbon-carbon on ‘light demand’ circuits like Silverstone, Hockenheim and Monza. But the system developed quite rapidly, and by the end of 1983 we were sufficiently confident to rely exclusively upon carbon brakes.”
As also, by that time, were McLaren with rival French-made SEP carbon brakes. Contemporary McLaren designer John Barnard worked initially with Goodrich in California “…and I vividly remember organising a test at Donington with Niki Lauda driving. We had one set of each alternative to try. We were using the standard small twin AP caliper, and there was a set of Goodrich solid, non-ventilated discs, a set of new SEP discs from France and our normal iron disc as a baseline.
“We set up the car with the carbon discs, ran it and it was just stunning! It instantly shortened the braking distance at the end of the Donington Park straight from about 100 yards on the iron brake down to 60 yards on carbon.” With their contemporary ground-effect car “Niki could just stand on the pedal at the last possible moment, and the thing would just stop. That test really drilled it home, carbon was the way to go.” While the Goodrich system was basically a helicopter rotor brake, SEP was committed to developing specialised carbon brakes for racing cars, and so JB worked with them and ran their brakes through 1983.
But what he recalled of development was how, “With the conventional iron disc, once it was soaked with heat you then had to get rid of it. You could see it while testing near dusk. You’d see the car coming down into the braking area, and with iron discs you’d just see a dull glow slowly build up, then dim down slowly after the brakes had come off as the heat was slowly dissipated.”
In vivid contrast, “With the carbon brakes you’d suddenly see this orange light bulb switched on inside the wheel…. It literally looked like that, the heat would build up so rapidly. And then they’d come off the pedal and boomp – literally just like that – the light bulb was switched out.”
I vividly remember one of the Carloses’ Brabham BT45s having just flurried into the pits during practice at the Nürburgring, front hubs apparently bursting into flame as it stopped. Gordon: “The carbon disc would heat up to a surface temperature of 1000 deg C – and at that level anything that could see it would suffer. Heat radiation alone would ignite bearing seals, melt the hub grease, boil fluid in the calipers, heat up the wheels and cause the tyres distress…”
And the most vivid report I have ever heard of carbon-brake heat radiation is of the wind-blown summer butterfly that came innocently fluttering by only to be blown too close to the just-parked Brabham with its incandescent prototype brakes. And in mid-air, mid-flutter – pooph! – mother nature’s most delicate and fragile beauty just burst into flame…and was gone.