Features - Technical
MARCH 8, 1998
The 1998 Formula 1 cars
BY PETER WRIGHT
McLaren produced the MP4/13 among the last of the new cars to be launched, as is their usual practice, relying on thorough preparation and testing of the narrow 1997 mule car to produce a new car that would not need too much sorting out prior to the first race. When Mika Hakkinen set the fastest Barcelona test time on only his third flying lap in the car, the previous two laps must have given them the feedback and confidence to drive the car at that speed. That says that the basics of the car were right: weight distribution, wheelbase/track ratio, aerodynamic balance, suspension geometries, stiffness and set-up, and of course, tyres.
Matching the three magic numbers:
· Weight distribution
· Aerodynamic downforce distribution
· Roll stiffness distribution
to the tyre cornering stiffness distribution throughout the speed range, is the secret to a well balanced car and inspiring driver-confidence. The 1998 Technical Regulation changes - narrow track and grooved tyres - have jumbled up the established solutions. From the way the other cars twitched about trying to keep up with the McLarens, only the latter has the secret combination at the moment.
Grooving the tyres has done many things to them, demanding big changes in compounds and construction to enable them to survive 20 or so laps. Because they are solely circumferential grooves, they affect cornering performance more than braking and traction (it is loading up the edges of the grooves that destroys them). As a result the tyres will have been re-optimised for lateral loading, perhaps at some expense to longitudinal loading. It is likely that the relative cornering stiffness and peak performance front to rear, will have changed compared to the 1997 slicks.
Narrowing the track by 12%, also has a number of effects. Firstly the track to wheelbase ratio changes, affecting the ratio of longitudinal weight transfer to lateral weight transfer, and hence stability and control. It is not possible to reduce the wheelbase by the same ratio, as firstly it is not possible to get everything packaged into the smaller space, and secondly a 12% narrower and shorter car would have an undertray that is 23% smaller in area and hence has lower downforce potential.
Secondly, the magnitude of the lateral weight transfer per g increases, as it is not possible to reduce the CG height by the 12% that would be needed to keep everything equal.
Thirdly the aerodynamics are all messed up. Bringing the front and rear tyres inboard affects the flow of the front wing, the rear wing and everything in between. The best aerodynamicists with the biggest wind tunnels may have been able to reclaim the lost downforce, but they may not all have been able to get the distribution they want.
Those teams that built narrow '97 test cars, early last year, will have had the most time to find out about the new requirements and help define the major layout parameters of their new cars. Producing a well balanced car was one of Adrian Newey's fortes while at Williams, and it would seem that he is the first to get it right. There is no way we can find out what those magic numbers are, but it probably won't take long for Williams, Ferrari and Goodyear to discover them.
Obviously the numbers for a Bridgestone car may be different to those for a car running on Goodyear's, but there is one other complication: the McLarens may be able to run different numbers to everyone else! During 1997 they developed a lateral-biasing rear brake system, designed to enable the driver to steer the car using one or other rear brake, in much the same way as Yaw Stability/Anti-skid systems on some road cars use the ABS system to apply a rear brake and control a skid. On the McLaren, the clutch pedal is replaced by a second pedal (the clutch being operated by a lever behind the steering wheel). The driver selects the inner rear brake for the approaching corner and when the car begins to understeer into the corner, as most Formula1 cars do, he applies braking effort to this second pedal to brake the inner rear wheel. The resulting yawing moment generated turns the car into the corner. He may apply power at the same time and use both feet, on throttle and brake pedal, to assist with the steering control of the car. On exit from the corner it is this same inner rear wheel that will tend to spin as power is applied, and so a further application of the pedal will brake it, helping the differential transfer torque to the loaded outer wheel and prevent the inner wheel spinning.
McLaren ran this system late in 1997, which was probably a contributor to their late season performance improvement. More important is that both drivers gained experience of the system and had all winter to develop new driving techniques - it must, after all, take some practice to learn to steer the car with hands and both feet - although drivers brought up on Karts will have the right tendencies. - Perhaps equally important, McLaren were able to investigate whether this system allowed them to change the weight distribution. Having greater steering control would permit a more forward weight for greater stability i.e. different magic numbers.
Although it is rumoured that Williams and a couple of other teams have tried similar systems, it would appear that none have yet refined them to the same level as McLaren. Once the other teams stop trying to get the system banned, on the grounds of it being a 4- (or is it 3-?) wheel steer system, they will have to get on and develop similar systems. Then they will have to train their drivers to use them. Then they may find out that they need different cars.......
The long lead-time components of a Formula1 car, those whose design must be frozen six months or more before launch, are the engine, the gearbox and the monocoque. For 1998, every monocoque is entirely new to meet revised regulations aimed at enhancing the security of the driver's safety cell. Cockpit aperture size is increased; the side impact test point of contact has been moved forward 200mm and the velocity of the impactor increased 40% (equivalent to 96% more energy, which is why there has been so much trouble passing the new test); and the area around the driver's legs is increased in both internal and external cross-section. In spite of the safety features being agreed by the Technical Directors, some have chosen to interpret them literally: McLaren have produced a monocoque that meets the exterior dimensions only where the dimensions are exactly specified on the drawing, using 4 "horns", narrowing it in between. Benetton and Minardi have retained short side-pods, relying on streamlined "prongs" to absorb the side impact load.
The other area of the monocoque to come under scrutiny is the fuel tank. The compromise between a short tank, to allow the driver and engine to be placed as close together as possible for a short wheelbase and lower polar inertia, must be weighed against the higher CG of the fuel in a short tank. Stewart and Arrows have also chosen to place the engine oil tank recessed into the rear of the monocoque, to move weight forward and permit the engine auxiliaries to be moved from the sides of the engine to the front.
Amazingly, engines continue to become smaller, lighter and yet higher revving. The Illmor probably leads the field in size and weight as well as power - but not necessarily RPM. Clear comparisons are not possible as figures for these parameters are well guarded. A new feature, introduced on the Peugeot and one or two other engines last year and now adopted by all the leading engines, is to run the water cooling system hotter and therefore at higher pressure, to suppress boiling. Higher temperatures and pressures are not beneficial to the engine, detonation being very sensitive to temperature, but it does allow the use of smaller radiators for the same heat rejection. This is an excellent example of true systems engineering: the trade-off has been calculated and the optimum overall solution for the car has been adopted. There has been some discussion about the safety of a hotter, higher pressure water system in an accident, but they are no worse than oil and hydraulic systems.
Ferrari had been unique in deviating from cast magnesium or aluminium for gearbox cases. John Barnard started the trend by designing a fabricated titanium case for the 1995 Ferrari, and graduated to a titanium centre gear-case with CFRP front case (plus oil tank), and differential housing (plus wing mounting and rear impact structure). It is therefore not surprising that he has now designed an all-CFRP gearbox for the Arrows A19, but it is perhaps ambitious of Alan Jenkins to have committed the Stewart SF2 to one in only their second GP season. Both are longitudinal, 6-speed boxes (as are all except Williams, who are still happy with their compact transverse unit) and reputedly very small.
Apart from the greater specific stiffness and strength of CFRP, compared to the cast alloys used by others, it is the manufacturing process that offers additional benefits. Casting tolerances and potential impurities in the molten metal mean that many parts of the casting must have a greater than optimum wall thickness. CFRP can be laid-up to exactly the thickness required, with the fibres running in the optimum direction for carrying the design loads. As a result the gearbox will be smaller and lighter. With the rear wheels coming in 100mm per side, encroaching on the aerodynamically important space between wheels and gearbox, size is everything.
It would be unfair to judge whether the cost, complexity and potential unreliability outweighs the benefits of such risky designs, until these two mid-field teams have had the time to sort out and refine their new gearboxes. However I have my doubts.
The new monocoque cross-section regulations have put the squeeze on front suspension design. With the move to torsion-bars almost complete, there is now little room to package them either side of the required leg space, and designers are loath to widen the monocoque. Likewise there is little room on top of the monocoque for dampers and linkages. Teams are not being very revealing about how they have re-packaged all the hardware, but it seems that they have used the space forward of the driver's feet, inside the 150mm of strong survival cell that is mandatory, forward of the front axle centre-line. The suspension rockers are now vertical instead of horizontal, with the torsion bars, doubling as their pivot axes, horizontal instead of vertical. McLaren, Ferrari and Arrows have all made the change, but it may be a while before photographs appear that reveal exactly what the new arrangements are.
Tyrrell have reverted to a new version of their hydraulic suspension. The mechanical linkage is replaced by hydraulic cylinders and connecting pipes, giving complete freedom in mounting the springs and dampers. It also allows various forms of cross coupling of suspension units, to replicate 2- and 3- spring arrangements. Strategically placed valves in the system would also permit all sorts of damping combinations. Wouldn't it be interesting if Tyrrell would only publish a hydraulic circuit diagram...! Tyrrell have also mounted their rear suspension units on the side, instead of on top of the gearbox - all in the interest of lowering the CG.
The flexure-pivot bearing for the inboard mounting of wishbones is also gaining popularity. Offering zero friction and free play, and lighter and stiffer than a rod-end, they are formed unto the ends of wishbones as a continuous extension of the carbon fibres from which the wishbones are made (steel wishbones have welded-in high tensile steel flexure pivots). Pioneered by John Barnard on the 1994 Ferrari, they offer a small gain in suspension performance, but are an extremely elegant design detail.
Narrowing the track front and rear has meant that some parts of the bodywork and wings have been subject to intensive development in wind tunnels and on the track using narrow 1997 cars. There is a wide variety of solutions and it is not yet clear who is right. By the end of the year one would expect there to be some signs of agreement as the aerodynamic details converge towards the optimum design. Probably all the cars will begin to look more and more like the McLarens!
An obvious area that has been influenced by the front track is the front wing, still the most critical component for the aerodynamic performance. Pulling in the wheel and tyre so that it shadows the front wing tip by a further 100mm per side, has led most aeodynamicists - notable exceptions are Ferrari's, Benetton's and Sauber's - to sacrifice wing span for space to put a variety of vanes, both horizontal and vertical, on to the outside of the wing end-plates. With the job of controlling the flow around the tip of the wing, from high pressure top surface to low pressure underside, and influencing the resultant tip vortex. These devices will undoubtedly change regularly throughout the season.
The same problem exists at the rear, only this time the wing is behind the tyre. There are a number of solutions to controlling the airflow, both ahead of the wheels and in the design of the rear wing endplates - notably on the McLaren. It may be that the turbulent wake of the rear wheels, impinging more on the wing endplates, has led to the spate of rear wing failures in testing and in Melbourne. The Arrows has the most unusual arrangement ahead of the rear wheels. Barnard has abandoned the usual "coke-bottle" shape around the rear wheel, with radiator air ducted through the narrow confines of the engine and gearbox, even though he pioneered it on the 1984 McLaren MP4/2. On the Arrows A19 he has cut back the side pods ahead of the rear wheels and exhausted the hot radiator air through the resulting aperture. This arrangement will certainly avoid the hot air exhausting under the rear wing.
Otherwise the aerodynamic development of this year's Formula1 cars continues along the path of previous years, with continuous development of the details of diffusers, exhaust pipes, engine intakes, barge-boards and radiator duct shapes. The differences cannot be major or the designs would have converged by now. Far more important is the characteristic of the front wing - how it's downforce changes as it approaches the ground when the car pitches. Herein lie the stability of the car under braking, and its ability to turn in lie. Newey is the expert, having learnt the hard way on the ultra low Leyton House March's, that were blindingly fast on smooth tracks and pretty awful over bumps. It is not surprising that the pale grey front wing covers of the McLarens are fitted as soon as the wheels stop turning.
How will the season develop? Once McLaren's competitors get their acts together, and sort their cars out, I would expect it to become a tyre race first and an engine race second. However, it just may be that those extra pedals on the McLarens are more significant than they may appear, in which case the other team's drivers have got a lot of practising to do.