Analyzing Possible Aerodynamic Secrets Of The Nissan GT-R LMP1 Car


When it rains it pours — about 24 hours after our little amoeba friend appeared on the 'Net showing the Nissan GT-R LM LMP1 going through its testing cycle at the Circuit Of The Americas, thanks to diligence on Jalopnik's behalf, more images, vastly more descriptive ones at that, pop up. It's an information bonanza!


[Editor's Note: Mulsanne's Corner is one of the best sites on prototype racing history, design, construction, and aerodynamics. I recommend you visit the site right here. I'm happy to have him here on Jalopnik, because nobody else writes so clearly about not only the technical side of these groundbreaking cars, but also the very political background from which they spring. Here is his analysis of our spy photos of Nissan's undisguised prototype. - R.O.]

So I've been reporting on the Nissan for over a month now with my first articles going on mid-December. No other outlets are writing about the program at the moment, instead they are presumably waiting for the official launch.

Thus it puts me in the tight spot of being the only one willing to stick my neck out, and as has been seen, I've had to rely on a fair bit of speculation. That's nothing new to those who frequent my site. This process is about homing towards the truth so at times, to some, it seems as though I'm grasping at straws. The reality is the information is evolving and I'm adjusting my viewpoint with those updates. I'm augmenting source information with speculation as I don't have a clear picture; it's very obscured. But have I been so wrong? I'll argue the speculation has simply become more nuanced. And while I'll never talk about who my sources are, I will say this: Nissan's NDAs have been pretty effective and frustrating. That I've been able to dig up as much information as I have speaks to connecting the dots, from Delta Wing and ZEOD, to scraps of information here and there, to my always reliable cadre of sounding boards (you all know who you are). And once you piece all that information and references together, at the end of the day the car begins to draw itself and it actually makes quite a lot of sense. Yes, I might miss on some of the specific details, but I feel I've been providing a pretty clear picture into the concept phase.


A rear wing has appeared! For starters, I've always felt that the rear wing delete would be a Le Mans-only configuration, if I didn't make that clear. However, note that from the images it doesn't appear the Nissan is carrying much rear wing angle, and these shots were taken at COTA; a high downforce circuit. That should tell you something about design intent regarding the rear wing and it's overall importance. As to why it appeared, I've been told that the drivers felt the car was "dangerous" and needed a touch more rear downforce. The rear wing was then added based on that feedback. However, I still feel very confident that Nissan will run without the rear wing at Le Mans and that its addition was only necessary with the increased total downforce demands of higher downforce tracks.

Very early on in this process I was informed of the detail regarding the drop gear on the upright and raised half-shafts that I mentioned back on January 7. I was told this was because the Nissan had "huge tunnels" at the rear. I really didn't know if I should take that literally or not, and after confirming Nissan hadn't been given any dispensation regarding the underfloor from the ACO I tucked the "huge tunnels" thought away. Though I still didn't know what to make of the raised half shafts. So I came to the conclusion of the diameter discrepancy front to rear and that Nissan must be compensating for extreme halfshaft angles. It fit the rumor narrative at the time coming from AutoHebdo about smaller rear tires. But seeing the tires now, the front to rear diameter difference is small. So I don't think Nissan is compensating for halfshaft angle at the rear. But why the raised halfshaft? Back to the "huge tunnels" comment. Upon seeing the rear end of the car I'm struck by the very tall rear deck height and the complete lack of any sort of obvious front diffuser exit. The rear deck height is monstrous; for 2015 the ACO has mandated a minimum rear body trailing edge height of 50 mm above the diffuser. So one would expect to see the minimum (50mm), or thereabouts, given the trend towards zero heights the past couple of seasons. 50mm is 2", and as a reference the diffuser exit height is a maximum of 200 mm tall. It's pretty obvious that the rear deck height is greater than 200 mm above the rear diffuser trailing edge.


So clearly something is going on there. Now the at the rear of the car, in the base area, is a very nice source of low pressure. Could there be some sort of tunnel, or ducting, projecting rearwards from the front of the car, through the side pods and along side the tub, and out the back? But what could the low pressure feed from the car's base area be activating? Regardless, this starts to perhaps better explain the raised rear halfshaft. Recall the Audi R15 ran into issues with their flow-through concept when it came to the rear suspension and half shaft, these elements increased the induced drag and made the overall concept a very tough argument in Le Mans spec. Thus I think Bowlby has raised the half shaft and incorporated a drop gear on the upright not to compensate for reducing tire diameter, but to pick that element up out of the air flowing through the duct, allowing for more effective flow-through. Presumably the upper A-arm is out of the flow to begin with and the lower A-arm intrudes into the diffuser tunnel more than likely. But what is the purpose? Could the low pressure wake behind the car lend a hoovering effect to the front diffuser? This would explain the lack of any exits at all past the front wheel centerline as any interruptions, changes in direction, in the ducting would reduce pressure recovery. But is the trailing edge exit too far away to have any influence on the front diffuser? So is it only for cooling? Surely the two exit ducts towards the leading edge of the nose (the only two that can be seen on the entire car) are related to that. Though that doesn't seem to be enough for the presumed cooling needs of the car (water, oil, intercoolers). But there are also no obvious means of generating front downforce. No diveplanes even (remember these images are shot at COTA). And there are certainly no exit ducts of any kind related to obvious downforce generation. This car will need front downforce and the mandatory cutouts (Big Honking Holes, note Nissan has gone for the top location option) in the front wheel arches certainly aren't enough to feed the front diffuser creating the necessary front downforce.We've seen similar details in the past, recall the boundary layer suction developed for the Nissan P35's large side pod oil cooler inlets. Utilizing the large area of low pressure situated behind the car, a slit in the leading edge of the duct drew off the thickened boundary layer ahead of the main intake. It was a simple and small detail on a mid-rear engined car which utilized the rear wake to also draw out the heated oil cooler air through the engine bay, past the engine, gearbox, and suspension, and out the back of the car. And it worked, even in that comparatively dirty environment. How much more effective would the low pressure draw of the base area be if the car design was optimized for this purpose and the rear end didn't have all the complications of a engine being in the way? So with that, what do you do with it? The answer could be very interesting. Watch this space.


Looking at the side view and focusing on the wheels, it seems pretty clear the rear tire diameter is smaller than the front but that the wheel diameter is the same or very similar. Therefore I think there's less of a need to compensate for half shaft angle and the real reason for the upright drop gear is what I mentioned above and simply for aero reasons; to clear the full length ducts/tunnels that provide front diffuser activation. The front view affords a look at rear tire widths, based on the width of the rear fenders, and it does appear that the rear tires are narrower than the fronts.At the front we can see what looks like the crash structure protruding forward out of the primary radiator inlet. It seems a bit awkward looking and I can't think of any reason why it wasn't better integrated into the design, assuming I'm right that it is indeed the crash structure.These images unfortunately don't provide any corresponding visual evidence to the location of the engine exhaust exit. I was told they poked out the engine cover ahead of the windscreen, but the limited views available don't reveal that, or much of anything really, just lots of reflections in that area. The side view mirrors are positioned just aft of the mandatory fender holes, presumably riding in part of the low pressure wake created by those holes.


At this point all there is left to do is to but wait for the official launch as these images certainly have satisfied a portion of my curiosity until then.

Photo Credits: Stef Schrader/Jalopnik

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