Evaluating FSAE aerodynamics 2013 event report Alternatives for a ...

TECHNOLOGY – TUBULAR FRAMESEQUATIONS!"#$%"&' !"#$%&' !"#$ (!! ! ) = 32! ! !"#$%h(!!) !"#$%&'( !"#$%&' !"#$ !! !∴ !"#$% !"#$ !! != 36.8! ! !"#$%h (!!) = !"#$%"&' !"#$%&' !"#$ + !"#$%&'( !"#$%&' !"#$ !"h!"#$! !"#$% !h!"# !"#$% = !"#$% !"#$ ! !"h!"#$! !h!"# !"#$%&"h!!! ! The required Joint Shear Force was to be equal to the force required to take a baseline steel tube beyond its elastic limit. This force was calculated, using the below formula, as 18.8KN. !"#$$ !"#$%&'() !"#$ (!! ! ) = !! ! ! − !! ! ! = 62!! ! !"#$% !"#$% ! = !"#$% !"#$!"#h= 18.8!" Figure 1: FSAE chassic comparison!!! ! ! !"#$$ !"#$%&'() !"#$ (!!! )tubes were 68 and 75 per centrespectively. These savings,however, don’t include the massof a metallic node.‘Due to the sponsor onlyoffering us a specific type oftube with 36.8mm OD and32mm ID, we were a bit limited inthe real world,’ says Demetriou.‘This tube only provided a 46and 45 per cent weight savingand was over-specified by afactor of 3-4 in terms of strength.The other major impact of theincreased tube diameter wasthat the floor thickness wouldconsequently change. Thatwould have a big impact onthe damper mounts on theCoventry car which areincorporated into the floor.With an increased diameter ofthe floor rails, it would not havebeen possible to use the samemounts or floor.’loads directly into nodes anddistribute these throughoutthe chassis, causing minimaldistortion to any of the members.’The ethos of the CoventryUniversity 2012 FS Vehiclewas ‘lightweightness’, whichrestricted the quantity oftubing that could be used toconstruct the chassis. Therewas a balance to be foundbetween torsional rigidity andmass. Collected data for variousFormula Student vehicles can beseen in Figure 1 above, whichshows mass vs rigidity.Demetriou wondered ifthe same stiffness could beachieved for less mass by usingoff the shelf carbon fibretubes, which are relatively lowcost and readily available. Herealised that he would haveto overcome the metal-tocompositebonding challenge,and went on to investigate howthe concept would impact the2012 Coventry car.The Carbon Fibre tubes weresponsored by Exel Compositeswww.racecar-engineering.com • Formula Student supplementUK and were to be from theirExelite range of high strengthtubes. A spreadsheet wascreated which utilised macrosto derive wall thickness. Thisallowed the outside diameterof a tube to be specified,due to compact packagingconstraints, while the wallthickness was varied. Thespreadsheet also had the abilityto display the mass of each tubeand thus derive the percentageweight saving between the twotubes. Savings for equivalentSTEEL OR COMPOSITE?Despite this, Demetriou managedto complete the modified hybriddesign, which can be seen(see Table 1, p61) showing thatwhile some steel memberscould be replaced by compositetubes, not all of them could be.However, in many cases, thiswas due to the lack of choicein carbon tube availability toCoventry, and in reality wouldnot be a major concern.The bulkhead needed toremain in steel to accommodatethe mandatory FSAE crashbox.The design of the Coventrycrashbox was such that itrequired the anti-intrusionplate to be welded, around itsperimeter, to the frame. Witha carbon frame an alternativemethod of attaching the platewould be required.As previously explained, anyincrease in the diameter of thetubing would not accommodatethe existing hardware for thedamper mounts. There would alsohave been an issue regardingground clearance – the bottom ofthe spaceframe would be 11mmlower, plus the depth of a nodecausing the vehicle to groundout when experiencing heave orsingle-wheel bump.The pull rod used for the'A good spaceframe will receive loads directly into nodes anddistribute them throughout the chassis with minimal distortion'