Formula One trend of design
Safety roll-over bars
I think the safety roll-over bar came to us from the USA, and when it first appeared it was a bit of a joke. The idea was to provide a tubular structure projecting higher than the driver’s head, which would protect him if the car crashed and landed upside down. In the early days roll-over bars consisted of a simple tubular hoop welded to the chassis frame that often was not tall enough and, more often, not strong enough to support the weight of the car even if it had been turned gently over. The whole business seemed a bit stupid and a sop to the safety-gods who seemed incapable of rational thinking and copied USA ideas blindly. I saw roll-over bars measured with a mechanic sitting in the car and not wearing a crash-hat, so that when the driver was in the car his crash-hat was inches higher than the tubular hoop. I saw these hoops flatten completely when a car skated along upside down and I saw hoops with no fore and aft strength other than the quality of welding. It is not surprising that I could not take them seriously.
In those early days of the safety parade one well-known foreign driver, who drove for an English team, did not have a great command of technical knowledge and from his visits to the USA he had learnt the term “roll-bar” referring to the tubular hoop behind his head. At the time it was the beginning of the technique of adjusting the suspension roll, or roll-stiffness, by means of different anti-roll torsion bars; the solid steel bar joining the two suspensions and operating in twist. Engineers called these “roll-bars” in loose talk and when the driver in question heard the team’s chief engineer say “We’ll change the roll-bar and see how it affects the handling,” our foreign driver was very puzzled, because “roll-bar” to him was the tubular hoop behind his head and he couldn’t see how changing it could affect the handling, Fortunately we have progressed since those days, both in knowledge and design and today the roll-over bar is a very functional piece of equipment.
We went through a bad period when the Formula One car became an aluminium monocoque with the engine bolted to the rear bulkhead, for designs were made which allowed the engine/gearbox/rear suspension assembly to break away from the monocoque under severe and terminal impact loads, leaving the driver in the security of the monocoque. Roll-over bars and structures were being attached to the engine, until someone realised what they were doing. Gradually a uniformity of thinking evolved among the constructors and the FIA Technical Commission and today there are a number of pages in the Yellow Book on the requirements and suggestions on design. The structure has to be able to withstand three simultaneously applied loads, lateral, fore and aft and vertical and they are a function of the weight of the car, complete with driver and full petrol tanks (i.e. starting lane weight). This weight is W and the calculated lateral load is 1½ x W, the fore and aft load is 5½ x W and the vertical load is 7½ x W. so it can be seen that the roll-over structure today is a pretty serious design study. Specifications are laid down for the quality of material used, whether steel or aluminium, but the basic design is left to the individual designer. However, he has to have available at Scrutineering drawings of the construction and calculations to prove that the structure complies with the strength requirements. As far as I can find out nobody has tested a roll-over structure physically and all designers hope that their structure will never be tested in a practical manner, in the form of an end-over-end accident.
The general trend of design is to use one large diameter hoop with two tubular bracing struts running rearwards, and this layout is used by Lotus, Tyrrell, McLaren, ATS, Lotus, Ensign, Alfa Romeo, Ligier, Williams and Arrows. In such cases the rules require the bracing struts to join the main hoop at not less than threequarters of its height and the struts must be of the same material and dimensions as the main hoop. While most teams use steel tubing, Williams, Ensign and Tyrrell use titanium, and Lotus use aluminium. Attachment to the monocoque varies from the frame being bolted to anchor plates riveted to the monocoque, as on Williams, Tyrrell and Ensign to the structure being welded to steel plates which are in turn riveted to the monocoque, as on the Arrows and the ATS.
Fittipaldi (née Wolf) and Shadow use a tubular hoop and another rearward running hoop welded to it with gusset plates welded to both hoops to form a rigid box-section. Brabham use a somewhat similar construction. Ferrari have a variation on the hoop and double bracing struts, by having aluminium sheet riveted to the tubes to fill in the triangles formed at the sides of the structure. Osella are alone in using a hoop with a single rearward bracing strut joined to a cross tube in the main hoop. Renault are completely on their own in using a fabricated structure of welded steel sheet, to form a single vertical hoop which is riveted permanently to the monocoque.
We have come a long way since the appearance of the first tubular roll-over bars that you could almost bend with your hand, in the days of the 1½-litre Formula in 1961. Now the roll-over bar is a carefully stressed part of the car and an important part of the monocoque now that the driver is strapped firmly within his capsule so that he stays with the strongest part of the car throughout any accident, even though wheels, suspensions, gearbox, engine and sidepods may break away while the kinetic energy of 150 m.p.h. is being dissipated in a short space of time.
D.S.J.