Chapman’s file
In his dossier, Chapman had also tackled chassis problems, with operational indications and constructive solutions. Here are some areas of intervention: roadway widening, body stiffening, reduction of sliding friction on the suspension joints, barycentric positioning of the tanks…etc. Returning to chassisthe growing stresses due to the evolution of the aerodynamic-tyre combination and the smaller sections envisaged for the 78 had in fact prompted the Lotus designers to experiment with new technologies, such as sandwich panels: 2 light alloy plates glued to a honeycomb structure spacer of the same material (Cellite); they were innovative materials in use in the aeronautical industry.
Previously, similar panels (Mallite) had made their F1 debut on the ’66 McLaren M2B by Robin Herd, but in this case the internal spacer was a lightweight balsa wood. The experiment was not followed up because the panels, being pre-packaged, were flat and therefore not suitable for building curved and rounded surfaces in vogue at the time. Now, with the frame narrow and free from the shape of the bodywork, all this was no longer a limit. With the considerable stresses induced by the ground effect, these materials then became indispensable for everyone. Bellamy did not have specific experience with this technique, so, in addition to a basis for calculations, he pragmatically relied on Mike Cooke who set up a desk for a series of practical tests aimed at verifying the actual performance of the various solutions. In the end, a main load-bearing structure was chosen consisting of 2 sandwich panels placed on the sides, as long as the whole body (a sort of pair of beams) and closed above and below by single riveted plates.
To complete it, a series of shaped steel reinforcements, positioned both to contribute to the overall stiffness and to provide attachment points for the suspensions and the supporting engine, thus distributing the concentrated loads. It is therefore the central part of the body, which resembles a truncated pyramid, which essentially provides the torsional resistance. The 2 petrol tanks that protrude at the rear, one on each side, instead have the role of supporting part of the pontoon-bellies. There are a total of 3 tanks, the 2 mentioned and a central one between the passenger compartment and the engine. Their aligned and barycentric position is important, a choice made to limit as much as possible the variation of the longitudinal balance with emptying. On the other hand, the transversal one could be modified as a manual valve had been adopted capable of selecting the draft in the 3 tanks: an unusual practice in F1, which can only be used in circuits with a prevalent type of curve. Moving on to suspensions, these were designed by Martin Ogilvie, naturally all with a transversal deformable parallelogram scheme, very similar to those of the coeval type 77. Among the specifications was the objective of exploring the widening of the carriageways to limit load transfers when cornering , but the need to reach the maximum regulatory limits, especially in front, became evident when the aerodynamic potential of the Venturi channels was discovered. Then the question of sliding friction on joints: it was born from Chapman’s (true) intuition that, to favor tire grip, it was more profitable to limit them and rely on the viscous damping of the shock absorber. Going into the construction details, at the front: a tubular trellis supports the balance wheel with the external spring-shock absorber of the body; the rocker arm is articulated on needle bearings and has the ball joint on the hub carrier oriented vertically to better support the large aerodynamic loads induced (a standard for subsequent ground effect cars); the lower triangle is in shaped sheet steel (for years like this at Lotus) to better position the material according to the stresses; the joints, on the chassis side, are on needle bearings; external brakes.
Posteriorly: the lower triangle is completely similar to the front one; above there is the scheme of the double connecting rod, to keep the toe constant during the excursion, a single strut-reaction rod; the peculiarity lies in the fact that the connecting rods are fixed directly on the double inboard brake caliper, a legacy of the 77; the simple diagonal position was chosen for the spring-shock absorber.
Naturally, as soon as the importance of aerodynamically freeing the divergent channels (diffuser) was understood, on the following type 79, both the springs-shock absorbers and the brakes were moved: the former in adherence to the gearbox, adopting a rocker arm linkage, while the latter all inside the rims, then outboard. Finally the engine-gearbox and its installation. Being the usual Cosworth 8V DFV and its bearing assembly, little to add being all according to the standards of the time (already described), the only change is the position of the oil tank. After being banned by regulation from the position astride the gearbox (cantilever), many, including Lotus, had moved it to the driver’s shoulders, however complicating the shape of the last rear frame. On the type 78, Chapman and his friends thought of obtaining it from the fusion-spacer placed between the engine and gearbox, which had already been in use for some years. A solution that saved something in terms of weight but above all allowed the engine to be mounted in a more barycentric position and to be able to fix it more rigidly to the frame, being able to adhere to the last frame (flat) of the latter. Also for the gearbox there was a desire to continue experimenting in the wake of the type 76, this time recovering the sequential queerbox developed by Lotus in the 60s. The goal was always to speed up shift times. The design and construction of the prototypes were carried out with the American Getrag, but in the end nothing came of it, on the 78 the usual FGA Hewland was always used.
Data sheet
Builder: lotus; site: Hethel;
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model: 78 or JPS MKIII; year: 1977 debut;
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examples built: 4 +1 prototype with wheelbase 110 in (78/4 the photos of the article)
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designers: Colin Chapman Ralph Bellamy, Martin Ogilvie, Peter Wright;
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frame type: light alloy monocoque, Cellite honeycomb sandwich panels, bearing engine;
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tanks: 3, in rubber, total capacity about 200 L.;
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front suspension: upper rocker lower triangle;
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rear suspension: upper double connecting rod, lower triangle; spring/suspension on the diagonal;
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hub carriers: ant. cast in light alloy, post. welded steel sheet;
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anti roll bars: ant. fixed, post, reg. manually from the passenger compartment;
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you look for: magnesium alloy, decomposable, Speedline, 13″;
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brakes: vented discs and dual calipers, Lockheed;
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step: 107.9in, 2741mm; front carriageway: 67in, 1702mm; carr. post: 63-in, 1600mm;
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tyres: GoodYear;
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car body: set off removable in glass fiber composite;
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total mass: 578 kg;
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motor: Cosworth DFV 8V 2993cc 480hp @ 10600rpm;
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transmission: FGA Hewland, 5-speed.
In the next and last episode we will talk about sports results.
Technique of historic Formula 1 cars: Lotus 78 (1977) – First part
Technique of historic Formula 1 cars: Lotus 78 (1977) – Second part
#Technical #analysis #Lotus #chassis #FormulaPassion