Blade Roll Structures – Legality (Lotus & Force India)

Last year Mercedes GP surprised many with their blade style roll hoop. Rather than the rounded hoop with the engine air inlet snorkel formed in the centre, the structure was a single thin blade and the inlet split into two either side of the blade. There are several benefits to such a solution, the primary one being better airflow to the rear wing, but also weight and inlet tract length are likely secondary benefits.

Although meeting the various load and impact tests, many thought the set up was marginal on safety, primarily thought the narrow structure being likely to dig into soft surfaces such as gravel traps, reducing the effective height of the structure, with obvious consequences for the drivers head. When the new rules for 2011 were introduced, I immediately thought the regulation 15.2.4 intended to ban these structures, but the wording does not go as far as that. What the rule requires is that there is a minimum cross section for the structure. It transpires that the rules intent was not to outright ban these blades, but to ensure they had a reasonable cross section, to allay fears of a ‘digging in’ problem.

15.2.4 “The principal roll structure must have a minimum enclosed structural cross section of 10000mm², in vertical projection, across a horizontal plane 50mm below its highest point. The area thus established must not exceed 200mm in length or width and may not be less than 10000mm2 below this point.”

The rules mean when looking from above (vertical projection) a horizontal projection 50mm below the top of roll hoop must have a cross sectional area of 10000mm2. Which for a rectangular cross section, the blade would to be a minimum of 50mm wide, which isn’t too difficult to achieve. The effect of this rule is that the long very thin blade of the Mercedes is outlawed, but shorter and wider structures are still allowed.

Roll hoops have a series of load and impact tests to ensure they are strong enough to survive an accident. Historically a roll hoop has been a metal tubular fabrication, bolted\riveted to the top of the fuel tank area of the tub. As carbon fibre became the choice for monocoques teams started to simplify the roll hoops, making a point or blade structures moulded into the top of the tank. Gordon Murray’s BT53 is the first example I can recall. Over subsequent years, Arrows and Benetton have tried pointed hoops, but since the advent of normally aspirated engines the roll structure has also formed the inlet snorkel for the engine, making blades less desirable. Rules initially mandated a maximum cross section to prevent huge inlets seen in the seventies. These rules appear to have been dropped from the regulations and there have been few regulatory requirements for size and shape of the structure. Aside from the demand for a slot to pass a sling through, should the car need to be craned away. As Monocoques are now homologated, the structural shape of the roll hoop cannot be altered during the season. Mercedes achieved this last year, by homologating the blade and later adding non structural bodywork to form the inlet snorkel. This add-on section being later removed to expose the blade. The blade used to be visible inside the inlet snorkel, even at its launch. A point to note is that although the roll protection has to absorb massive loads to pass the crash tests, it is not in itself an initial part of the monocoque. The carbon fibre tub is made up of several major parts, the top and bottom of the main shape, bulkheads and cockpit surround. But the roll structure is a separate bonded on part. Laid up separately and attached at the later part of the monocoques completion.

This year Both Lotus and Force India have adopted blade style roll over protection, both adopting similar layouts albeit different structural solutions. Mike Gascoyne was clear that the benefit on aero was marginal, but he insisted the prime benefit is also CofG height. Lotus have engineered their structure from composites, this in itself is quite unique, as even conventional roll hoops are made of metal to create the slim undercut shapes to meet the impact\load tests. Albeit they are subsequently wrapped in carbon fibre, acting as both streamlining and structural reinforcement. As the blade shape is simpler, Lotus have been able to make the protection from carbon, this saving a weight and significantly removing weight from about the highest point on the car. Force India meanwhile went a similar route but their structure is a metal part, clad with carbon, although the weight comparison to the lotus is impossible, it would be fair to assume it is slightly heavier.

As Mercedes have moved away from this solution, it will remain to be seen if the blade will be a more permanent solution in F1 or just a passing fad.

25 thoughts on “Blade Roll Structures – Legality (Lotus & Force India)

  1. Why have they chosen to position the air intakes only marginally lower than traditional intakes? Surely they could have been even more radical with this design and moved the intakes even further down thus increasing the aero and COG benefits further.

    • I’m going to guess it’s down to balancing the aero benefits against the engine aspiration requirements. I guess lowering the intakes reduces the ram-air effect that provides a bit of extra power at high speed.

  2. Well done, good post – interesting to learn a bit more about the roll hoop structure. Is McLarens ‘double’ air intake a way to clean up aero or just because they need more cooling for KERS, etc?

      • McLaren, as far as I know (just a simple fan, not an engineer!) announced at their launch that the first air intake was for the engine etc and the second was for kers and the gear box oil cooling – but if you read up on their launch speeches, it is in there somewhere. I dont think its hugely technical, just a way of separating the air in a clean way to get it to its destination.

      • Mac have in fact three inlets! I’ll write and draw it for another blog post, but in summary…
        1) a conventional inlet snorkel for the engine
        2) an inlet further back on the engine cover which is for gearbox\hydraulic cooling
        3) an inlet below the roll hoop snorkel is for KERS.

  3. Thanks for the article, scarbs. Was the W01 blade also a metal structure wrapped in composites like that of the VJM04? And do you know if Mercedes opted for it mainly because of CoG or aero reasons?

    • Sorry, Merc never granted me any interviews or responses to my q’s, so I dont have info on that. My understanding is that most roll structures are part metallic, so I expect the W01 is too. I did hear it was an aero lead design.

  4. but i feel that the COG benefit of VJM04 would be offset by the higher than usual side-pods. i don’t really understand what will be benefit for using such high side-pods. pls throw some light behind the logic of such design. thanks

      • When you say sidepods you mean coke. The sidepods have a regulated height but after the radiator is the coke and teams can shape this is almost anyway they like. Force India appear to have larger sidepods from a front point of view because the inlet is lower than most because of the way the air is channeled to the radiators and then exited from the car – but the sidepod is the same height, it jjust appears like that as it seems chunkier. Force India often use a slot to the right of the drivers cockpit – like he McLaren did in 2010 because the airflow over that part of the car is of very low pressure due to the curvature of the sidepod and therefore the airflow helps withdraw the air efficiently from the radiators. The reason why teams sculpture the lower part of the sidepod – and therefore have high radiator intakes is the increase the airflow to the diffuser and increase downforce – Force India haven’t done this as much as other teams because of their efficiency they are designing to. The Toro Rosso STR6 ran sidepods that left a gap from the bottom of the sidepods to the floor – like the Ferrari F92A of 1992. This was actually an idea I came up with independently of Toro Rosso in summer 2010. The benefits of this are much greater flow to he diffuser but also with the ‘wing-like’ shape on the underside of the sidepod, some load can actually be created here and it being very central to the car is quite benefitical. Not to mention the improvement in cooling as the fast flowing low pressure air can withdraw the flow from the radiators much more easily. The disadvantages are an increase on CofG. Red Bull appear to have much more sculptured coke. This is because they do not exit the cooling around the sidepod/coke area so can package this area much tighter. Red Bull have a cooling outlet at the back of the engine cover infront of the beam wing. This gives great load gains as much more airflow is channeled to the diffuser. If you notice from race to race, the Red Bull radiator inlet doesn’t change (and the roll hoop doesn’t becuse that is homologated) but the cooling outlet increases or decreases dependant upon the cooling required from that climate. So the height of the sidepod (directly beside the drivers’ cockpit) is the same height. What you mean is the shape of the sidepod from a front point of view and the coke which is from the front of the sidepod to the back of the sidepod.

  5. Great article! Definitely learnt something. Actually surprised that humble steel was still used in hoops….

    As for the Force India, anytime you can pull weight away from that high in the car, you will always get a benefit. The ‘high sidepods’ aren’t really so. It’s only the bodywork that makes it appear that way. The masses that really count, like exhausts, rads, coolers electrics etc, are relatively low, and thats what counts. In some cases higher sided pods can be a benefit. The IRL cars of a few years back found aero benefits from it……

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  7. Good Explanation, Thanks

    Slightly off topic I noticed something I didn’t realise till now – the gearbox is chalked as RB5, which on searching turns out to be the case. It’s Red Bulls ’09 spec which was not designed for last years double diffuser & is also lighter.

    I would post a link but not sure of the site rules

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  9. Are you 100% sure McLaren’s solution is all about thermal management?

    Dual air intakes are all very good as well but I’m sure you’d encounter differential pressures when the car is experiencing yaw, which could be problematic?

    Loving the Lotus, looks like they’ve really innovated this year.

    • Yes, I have a post demonstrating the purposes of each of McLarens inlets coming up today!
      There may be an aero element to it, but fundementally this is their most efficient way to package the inlet requirements.

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