1991-1992 Jaguar XJR-14

Images copyright Bob Chapman @ Autosport Image and Michael J. Fuller

Text copyright Michael J. Fuller

Jaguar XJR-14The rear wing is easily the most notable detail on the XJR-14.  Rival teams initially protested the concept saying that the lower tier was merely an extension of the diffuser and thus should be regulated as such.  But in spite of all their noise, the Jaguar's competitors never officially took the matter to FISA.    

At the XJR-14's debut at Suzuka, the #4 Brundle Jaguar fell afoul the scrutineers and had it's initial Thursday qualifying times thrown out over an issue with the rear wing's height and how that measurement should be taken.  FISA contented height measurements were taken from the lowest point on the reference plane.  TWR contented that this didn't make any sense as this method didn't take chassis rake into account and that height measurements should actually be measured perpendicular to the reference plane itself.

The end result was that the stewards made the #4 car lower the upper tier by 70 mm.  This had precious little effect on the car's performance, much to TWR's competitor's consternation.

The long chord twin element lower wing worked to enhance the flow through the underbody while the short chord twin element upper tier was essentially a trim device used to alter balance and increase overall downforce as needed.  
Jaguar XJR-14Rival team's primary focus of protest was the relationship between the trailing edge of the underfloor and the lower mainplane.  As you can see there is but a few inches in height separation between the two and the thought was the FISA should deem the lower wing an extension of the diffuser.  Ultimately nothing materialized from the rival rumblings, after all, the XJR-14 was little different in execution than what Southgate had been doing for years on the V12 Le Mans Jaguars.
Jaguar XJR-14 chassis #591The XJR-14’s tunnel exits are free from obstructions but for the lower A-arms.  Here we can see the proximity of the lower-tier of the rear wing to the tunnel exit.  The XJR-14 raced to Group C underfloor regulations and hence the tunnel exit height was to the regulated 280 mm and comparatively low.  The outer corners of the tunnels are chamfered to provide clearance for the rear pushrods and taking them out of the airflow.
Jaguar XJR-14The aerodynamic advantages of the twin tier rear wing set up were rather significant.  The long chord lower tier helped "excite" the airflow going through the diffuser, improving efficiency.  In conjunction with the adjustable front wing, the short chord upper tier mainplane and flap allowed for increased overall down force levels and maintained balance with increasing front flap angle.

Ultimately the origins of the concept lays within the work done by Southgate.  Consider that Brawn would have been hard pressed to have ignored contemporary sportscars up to the point of his tenure at TWR, not to mention the reams of data at his disposal (naturally generated by Southgate).

The flick up feature on the XJR-14's tail (the Duck's Arse or DA) was a late addition.  Wind tunnel development was ongoing while the manufacture of the car was in process and a story is relayed that tells of wet gel coat being scrapped off the engine cover pattern in order to include this last minute change.  

The end result was 
the XJR-14 generated 5880 lbs. of downforce for 1400 lbs. drag (figures quoted at 200 mph).  Brawn et al effectively matched Tony Southgate on their first attempt.  

Absolute downforce numbers increased substantially when the XJR-14 was brought to IMSA simply because downforce was the only thing that mattered.  In typical IMSA configuration the XJR-14’s downforce could be increased to 7800 lbs. with 1700 lbs. drag.  Though when the situation called for it, amazingly even more downforce could be extracted; Ian Reed, TWR USA Technical Director, “We did some aero development at Manchester, UK, for a ‘Street Fighter’ version.  We put on absolute maximum rear wing and added a long front flap extension. We got over 10,000 lbs at 200 mph but at huge drag. This worked well on street circuits.”  Naturally in such a configuration the drag was so high top speeds wouldn’t creep much beyond 150 mph and would have only been relevant at venues such as New Orleans.

ęCopyright 2009, Michael J. Fuller