1990's Exhaust Blown Diffusers

[alesifan]

In Adrian Newey’s new book he said exhausts blown diffusers were last used in 1994 prior to red bull in 2010. In 1994 Newey asked Bernard Dudot if there was a way to keep the throttle open around the lap and regulate power another way – spark cuts ignition timing etc. Then Imola happened and blown diffusers were banned but Newey doesn't specific exactly when.

Does anyone know for certain exactly when? I think it may have been at the start of 1995 but can't be sure.

[Blackout]

This article says they were key in 1995 https://news.sportauto.fr/news/1498218/ ... 95-Renault

[OO7]

Exhaust blown diffusers were banned for 2012, with the location of the exhaust pipes now prescribed in the technical regulation, however teams found a way to continue with the function in a more limited fashion with the Coandă side pods.

Prior to 2010 and Red Bull's RB6, exhaust blown diffuser had fallen out of favour with teams, due to the cars sensitivity to throttle changes.

[jjn9128]

The application of the exhaust blowing between the 1990's and 2010's was very different. In the 90's the exhausts exited directly into the diffuser, just downstream of the kick with the purpose of 'energising' the air flow. The cars with this sort of diffuser required a very particular style to drive - to get rear downforce and stability they'd have to get hard on the throttle earlier in the corner than was previously normal. Maybe it's apocryphal but there's the story of Mansell and Piquet/Patrese getting the first EBD car and finding it hard going, when the car slid the natural reaction was to come off the gas, which lost downforce so made the slide worse. When told to stay on the gas to increase rear downforce Mansell trusted the engineers and instantly went 1.5-2 seconds faster, while his team-mate took longer to adapt. Could be one of Mansell's self-aggrandizing stories, but I think it was one of Frank Dernie's stories.

The 2010's EBD was different in that it exited on the 'top' of the car to the sides of the diffuser - the rule being that floor had to form 2 solid surfaces (step and reference planes) when viewed from below - which was added to the regulations somewhere between 1994 and 1997. The function was different too, as the diffuser kick started at the rear axle line the squirt from the tyres would end up in the diffuser flow, so the high energy gas from the exhaust was used to 'seal' the edges of the diffuser, kind of like an air curtain pushing the tyre wake away from the diffuser. At this point they were cleverer about advancing or retarding timings or cutting cylinders to maintain mass flow, so it was more automated without the driver needing to be on the gas.

[OO7]

Nice post jjn9128.

[krisfx]

IIRC they were phased out around 98.

I think Ferrari were the first to go to persicope style exhausts. I read that it's because the rear tyres got narrower and the V10 also sat further forward, so the exhausts got shorter for power/RPM tuning. Another issue was that they cars suffered on/off downforce, probably because tech for off throttle blowing wasn't available at the time.

[megz]

The 2000 McLaren MP4-15 was still running a low exhaust exit into the diffuser, I think this carried into 2002 on the MP4 - 17. A picture below claims to be the MP4-17.

[alesifan]

Thanks everyone for the replies.

[zac510]

Maybe it's apocryphal but there's the story of Mansell and Piquet/Patrese getting the first EBD car and finding it hard going, when the car slid the natural reaction was to come off the gas, which lost downforce so made the slide worse. When told to stay on the gas to increase rear downforce Mansell trusted the engineers and instantly went 1.5-2 seconds faster, while his team-mate took longer to adapt. Could be one of Mansell's self-aggrandizing stories, but I think it was one of Frank Dernie's stories.

Well I read that story in Newey's biography and in reference to the active suspension, not the diffuser.

[jjn9128]

The 2000 McLaren MP4-15 was still running a low exhaust exit into the diffuser, I think this carried into 2002 on the MP4 - 17. A picture below claims to be the MP4-17.

Low maybe, but exiting through the diffuser surface, no. Maybe exiting into the centre channel was possible, but the important point is no longer visible from below the car and not as effective as the late 80's, early 90's EBD.

Well I read that story in Newey's biography and in reference to the active suspension, not the diffuser.

Yeah there are a few stories like that about Mansell, maybe the blown diffuser was Piquet (86?) then and the suspension was Patrese (88). My recollection is that Mansell initially wouldn't drive the active suspension car because of previous experience at Lotus, but upon seeing how Patrese was quicker with it he then wanted it. He's supposed to have said "the b*****ds are finally putting it on my car" or something to another driver (Lehto?) outside the garage, which caused the mechanics to down tools and go for a long lunch. He was not well liked by the team, albeit very much respected for his skill and bravery.

[Just_a_fan]

Maybe it's apocryphal but there's the story of Mansell and Piquet/Patrese getting the first EBD car and finding it hard going, when the car slid the natural reaction was to come off the gas, which lost downforce so made the slide worse. When told to stay on the gas to increase rear downforce Mansell trusted the engineers and instantly went 1.5-2 seconds faster, while his team-mate took longer to adapt. Could be one of Mansell's self-aggrandizing stories, but I think it was one of Frank Dernie's stories.

Well I read that story in Newey's biography and in reference to the active suspension, not the diffuser.

I remember it being the active suspension too. Patrese struggled with the active to start with because the suspension didn't give the usual roll response on turn in which drivers use as part of their feedback from the car. Mansell was told to trust that the car would grip so he did. Patrese never really felt comfortable doing so.

[OO7]

Low maybe, but exiting through the diffuser surface, no. Maybe exiting into the centre channel was possible, but the important point is no longer visible from below the car and not as effective as the late 80's, early 90's EBD.
http://www.ultimatecarpage.com/images/l ... des_16.jpg

That's exactly how McLaren did it with the MP4/15 and MP4-16:

[alesifan]

In the 90's the exhausts exited directly into the diffuser, just downstream of the kick with the purpose of 'energising' the air flow. The cars with this sort of diffuser required a very particular style to drive - to get rear downforce and stability they'd have to get hard on the throttle earlier in the corner than was previously normal.

Great post & thanks for that!

I'm told by a Williams mechanic from the time that the EBD was on the Fw17, but not the FW17b where the the exhaust went over the top of the diffuser. This was possibly because the drivers not liking how the engine "felt" and the EBD making the car nervous off throttle as you eluded to above. However in that great article posted above about the B195, it states that;

The blowing required some adaptation work on the part of the pilot. Michael Schumacher, still in our interview in 2010, noted: "the difference in aero support between the phases where I accelerated and where I released the pedal was very significant. We worked to reduce this effect. Renault brought several solutions: "butterflies always open, ignition delayed ... We focused mainly on partial loads. Michael was excellent at keeping an identical throttle position throughout a turn. I used his skills to show Olivier Panis what to do. "

So I suspect that is the difference between whether teams used it beyond 1995 or not was the skill of the drivers, not any reg changes. I know there were changes to the diffuser at Barcelona 94 and Hockenheim, but Autosport seems to suggest that exhaust outlets positions were not changed during these raft of changes. But the diffusers were cut to reduce their effectiveness. So I can only assume the new regs raising of the cars' ride height in 1995 led to EBD being less effective. Thereby meaning that driver skill on making the EBD work for them was even more of the defining factor on whether it was kept on the car or not.

[jjn9128]

I'm told by a Williams mechanic from the time that the EBD was on the Fw17, but not the FW17b where the the exhaust went over the top of the diffuser.

Looks like I'm wrong about the 2 surface floor rule making it impossible. I've been trying to find a pic of the FW17 from behind, but can't, though looking at this diffuser for a 1995 Honda which never emerged, the exhaust still exits through the diffuser surface. Maybe as you say it's the increased ground clearance made it less effective so it fell out of fashion, or a combination of that, clamping down on TC and the loss of active suspension. It's certainly impossible now, where even the starter hole has to have a cover.

I only have the 1994 and 97 rules but my reading of the 97 rules is that this was impossible from at least then. When the design like the McLaren a few posts up would be legal because from below there is no hole visible.

[alesifan]

I've been trying to find a pic of the FW17 from behind,

I'm told the FW18 g/box and arrangement was very similar to the Fw17b. I think Newey also eludes to this in his book.
17B ran a totally different gear box, suspension and rear wing set up to the Fw17. If you compare this to the Fw16 rear end this was a much slimmer arrangement.