New tailpipe regulations (exit holes and loopholes)

[aleks_ader]

(Lotus' DDRS was never raced.)

Kimmi race it once in Britain GP 2013.

[PlatinumZealot]

To entrain air you need a lower pressure fluid stream. Not a lot you say, not a lot is subjective I know. Well the F-duct worked by creating a near vacuum. In the Mclaren car, the driver blocks off a hole cutting off all entrained air flow that was coming from the cabin. This dropped the pressure even more in the "X" shaped junction in the system ducts: The main stream duct, the switching duct, the wing blowing duct and the "vent" duct, thus creating an momentum change diverting the main stream of air away from the duct leading to the Rear wing, stalling it.

With that said, you can see the challenge you will face using the waste gate exhaust to do this without creating a low enough pressure. I am at work but maybe I can do a quick sketch.. or maybe I can do it tomorrow.

I think you need to redo your Homework on the operation of McLaren F Duct. The wastegate switched F Duct is still a realistic concept.

No need to redo any homework I have the CFD simulation file on my computer still. Haven't changed it at all. Check one of Ringo's posts for the video of it switching.

I wrote that the F-duct switching can be done by the waste gate but you have to add a bit more to your annular duct.

Getting the wastegate to switch the F-duct is half the battle: A likely legal way to stall the wing is the Lotus e20 F-duct since slitted wings are not allowed anymore.

It was very tricky to get right for me.

This was one of my attempts at the E20 F-duct some years ago. It was difficult to get it at this point. And even then I was not satisfied that it was working.



(Matt Sommers, I am borrowing one of your images...) This is the first time I am seeing Flo-vis on it, but it shows the fidelity of my CFD simulation:



The Mclaren F-duct was much easier at the way it stalls the wing is totally different. You can say that one is normally open and the other is normally closed...

[bhall II]

Kimmi race it once in Britain GP 2013.

I stand corrected. It was used once over two-year period of development.

Hey, isn't it true that some teams have undertaken a transition to diffuser layouts that direct underbody air flow toward the outside edges in order to utilize the low-pressure wake behind the brake ducts as if they're small beam wings? I mean, just look at those streaklines...



If so, doesn't that mean the diffuser won't necessarily stall if aerodynamically decoupled from the rear wing, or if it does, that the situation isn't as hopeless as you initially stated?

I suppose so.

Even though Lotus' "device" clearly didn't meet expectations, how likely is it that the biggest problem faced by the team was a design that passively relied on difficult-to-tune pressure thresholds to activate and deactivate the system?

That does seem like it would be a significant stumbling block.

So, it's possible a more active switch could have made it a viable solution?

Maybe.

And why is it taken for granted that the utility of a monkey seat is incompatible with a stalling device? Isn't it at least theoretically possible to realize the monkey seat's effect in a different manner, one capable of coexisting with a stalling device?

Shut up.

[PlatinumZealot]

No one stalls the diffuser... You actually don't want to stall the diffuser.. why people talking about stalling the diffuser? The diffuser actually helps pressure transition from under the floor to the rear of the car. Why would you want to stall it?! Crazyness. Anyways carry on.

[bhall II]

Why would you want to stall it?!

Show me where anyone said otherwise.

But, since you brought it up...

At Monza, ride heights have to be set low enough to promote some stall in the diffuser at high speed while maintaining grip at around 130mph as the car pitches, yaws and rolls through the tricky second part of the Ascari chicane. As the DRS is activated on the straight, the stall invoked in the rear wing has to promote a more generalised stall through the beam wing and diffuser and, in so doing, shed the speed-sapping drag that is an inescapable feature of downforce.

[PlatinumZealot]

That is a diffrent kind of stall that, is speed induced in only a local area of the diffuser. The physical diffuser angle connot be changed right. A steeper one works better at low speeds, a shallower one works better at high speeds this is because the air can still "attach" to it. F1 engineers solve the problem by making the diffuser concave in side profile. That makes the air in the concave part right after the throat act as the upper wall of the diffuser. There is always a pocket of slow moving air in there. This pocket of slow moving air changes shape at different speeds so in essence the concave diffuser adapts and can work efficiently at a wide range of speeds. This pocket of air is the stall he is talking about. It is determined by the speed of the car and is pretty much expected. The flow through the diffuser is still fairly laminar flow (below that little pocket). On a whole the diffuser is not stalled. Pat Symmonds chose his words wisely as you see.

In the context of what you guys are talking about;- like you would have a stalled rear wing, wholesale break up of air flow, I am saying that is not wise to do that for the diffuser.

[bhall II]

In the context of what you guys are talking about;- like you would have a stalled rear wing, wholesale break up of air flow, I am saying that is not wise to do that for the diffuser.

Again, show me where anyone has even so much as hinted at something to the contrary.

[PlatinumZealot]

I'm too lazy to.

[bhall II]

I respect your honesty.

[hollus]

Simplyfying my wall of text from last page, it could be set-up without bi-stable switches and totally under driver control:

Set up gears 1 through 6 so that they can cover everything from 0 to 300km/h. Those 6 operate normally. Then set up 7th to operate between, say, 270 and 340km/h and 8th to operate between 200 and 270km/h (so shorter than 6th and 7th). Now make 7th and 8th be gears that always open the second wastegate, which only opens in that case.

Then the driver can activate his f-duct at will at any point above 200km/h (going quickly from 5th to 8th if needed), while always having it on above 300km/h, which should be faster than any real corner in the season (is eau rouge a real corner?). Lifting the throttle before braking deactivates it to avoid performance losses in the initial phases of braking.

You have to stretch gears 1 through 6 (but not much more than Mercedes did in 2014), but it means using the duct for a much longer portion of the lap in almost any circuit, plus a simpler activation mechanism, plus activation (mostly) only on

Note, this was elaborated in response to http://www.somersf1.co.uk/2015/10/in-th ... e-drd.html. Thanks Matt for that (crystal clear) piece.

[dren]

Wouldn't using the waste gate exhaust gasses to stall the rear wing be counter productive towards overall PU performance? I would think the waste gate would be open more than you'd want.

[ian_s]

i was thinking that too, having the wastegate open is just wasting energy

BUT, when they are using the full power modes they have, running the MGU-H to provide boost and opening the wastegate, reducing the drag could well be beneficial too

[PlatinumZealot]

Wouldn't using the waste gate exhaust gasses to stall the rear wing be counter productive towards overall PU performance? I would think the waste gate would be open more than you'd want.

Good point. I think it is a trade off... Stalled wing means you need less power down the straights. Which means you can afford to blow off a bit of exhaust... it has to be analysed some more.

[dren]

I agree. The 'recovery' side of the PU is so vital to overall performance I would think manufacturers would not flirt with the idea of wasting the 'recover' for DRS.

Does anyone have an idea how much or how often the waste gates are used now?

[turbof1]

I think, in case of confusion, it's worth to point out that the wastegate gasses themselves will not stall the wing. Rather, they'll activate the fluid switch which will let normal airflow which flows through roll hoop inlet to the underside of the wing.