this is the aerodynamics of the 1996 Subaru WRX STI impressor one of the most successful rally cars ever and it was a super car for yobs one of my friends had one but it had a problem with this down Force which is why they added a rear wing so in the second half of this video we're going to look at the aerodynamics of this car without the rear wing to see how it was affected but first with the rear wing the front lip is pretty decent because while the small lip isn't as large as what it should be it still helps accelerate the float under the front of the car to help keep it St at higher speeds the flo under the rest of the car is pretty good too and so is the diffuser which is a little surprising considering the app menion downforce problems this car had but if we look at the rear window we get a clear idea as to what the major problem was and that was the rear sloping down way too sharply which resulted in the flow greatly separating this was also a problem that this car's main rival the Mitsubishi Evo had and that is why later versions featur Vortex generators the Wake from this rear window is even worse than it looks because while yes it does dramatically increase the drag of this car look at how low the rear wing is it is very much in the Wake which renders it far less effective than if they moved it up higher which is what they ended up doing in later versions so while they tried to help the Rex reduce its lift with this rear wing it wasn't well positioned the front windshield is a little flat too which also causes a lot of quite fast moving flow to hit it decelerate and increase the drag the re's Wake looks much worse than it is because of the Wake from the rear window to too but if you look at how long it takes to die out Downstream it's actually pretty decent and comparable to Modern cars 30 years later from this pressure plot we can clearly see what is causing the lift problem with this car there is very low pressure over the roof and even though the underbody is producing good low pressure at the front and back the middle isn't even close to producing the pressure the roof is seeing so naturally the roof is acting like a wing and producing a lot of lift the typical way of overcoming this problem is by making the roof sleeker which would probably have made the car longer which for rallies isn't good because that would increase the car's second moment of inertia and make it harder to change directions alternatively if they made the hood more sloped they probably would have reduced some of this low pressure while also reducing the high pressure on the front windshield which would have reduced the drag at the same time then you could add more downforce elements around the car and still not exceed the drag you originally had like we saw with the Audi R8 the front is very blunt and blocky which comes with a very high pressure and hence drag penalty despite being in a wake the rear wing still seems to be generating a little bit of down Force there is high pressure over the top and low pressure underneath so at least it is having some positive effect still but we can see the Wake from the rear window is unsteady so this rear wing is constantly having to fight different conditions just to do his job from on top the aerodynamics is much better than what we saw in the side planes here the wake is very small as it follows the gentle curves around the back the Wake then dies out half a car length Downstream which is very good for for a car of this time period there is no flow separation around the front edges and the rules don't create big wakes either all of that is really good for the rexs looking at the vores created there are quite a few strong ones coming from the tires but also the a pillars again because the roof is too boxy and even the side mirrors are producing a lot of vortices the rear window is of course producing vortices as the flow separates the rear wing kicks the flow up and the rear is accompanied by familiar vortices we usually see these streamlines show that the flow hitting the car are forced to change direction dramatically as they jump over the hood many of them are then forced around the a pillars which is not great for the drag either an alternative would be to direct more of the float around the sides of the car to reduce the impact of the a pillars and even the C pillars further Downstream none of these streamlines flow behind the rear window which shows us that the flow behind the rear window is in a microcosm of its own a lot of the streamlines were directed under the car which is great for producing downfalls and imagine if this car didn't prod produ much downforce through the under body it would have been way too unstable looking at the drag ISO surfaces the side mirrors are producing so much drag I don't remember ever seeing side mirrors producing this much before and apart from the rear window the drag of this car is pretty comparable to other cars in fact in the '90s many cars had terrible rear window aerodynamics so this wasn't that bad the draag coefficient is 0.36 which which is better than a kick in the pad that is for the original car with the rear wing what about without the rear wing how was this car's aerodynamics then much of the car is behaving the same way for example the front under body the float over the windshield and the roof and of course the float over the rear window still separates but looking at the Wake without the wing the flow doesn't kick up as much now this difference isn't as large as what it would be if the wing was in clean flow to begin with but there is still some difference looking at the pressure plot there is a little less high pressure around the rear but it is marginal and in fact looking at the lift coefficients produced by each car the one with the wing had a lift coefficient of just 0.01 which given the uncertainty of the simulation is pretty much zero without the rear wing the lift coefficient was 0.05 so the wing was enough to make this car neutral comparing a top view slicing through the rear wing the wake is very different here and I might even say that the rear wing is helping stabilize the flow and reducing the wake in the plane I still can't get over how big the wake's from the mirrors are though L from the vortices without the rear wing they're not being kicked up as much and there seems to be slightly few vortices around the rear back probably because the rear wing itself produced vortices as well because it is generating downforce without the rear wing the drag structures from the rear window are much more distinct and allowed to develop unhindered with the rear wing these structures are chopped in half and that is what I meant earlier about the rear wing stabilizing the flow these streamlines show that without the rear wing the flow wraps around the SE pillars a a little more which isn't that good for this car considering how pronounced these pillars are overall the draag conf of this car without the rear wing came in at 0.37 which I can see given the minor benefits the rear Wing produced in the rear wake finally I mentioned that the original Rex had lift problems we also did a simulation with a decent sized front splitter plate to see just how much better it made the Rex's aerodynamics or if it did at all we made a video about it and you can find it on our patreon so check that out peace ad Amigos