85 replies to this topic

[Lee200]

Bob, Tommie, and Martin bring up some very good points.  

We are lucky to have patches to the drafting code that better simulate this effect.  It's certainly not perfect, but is the best we could do given our limited knowledge about how drafting really works.  I remember spending an inordinate amount of time searching for hard factual data on how effective drafting is for the '66 mod, but sadly there is very little information available.  There have been a few scientific studies, but usually these don't give much practical information.  The best I found was for big heavy trucks which are far different from the small and light F1 cars.

If anyone out there can find some scientific info on drafting, I'd love to see it.  The '66 mod (and the sports car) draft is based mostly on anecdotal evidence like Brabham saying he could feel a draft so many feet or seconds back of the car in front, etc.  And there's precious little of even that floating around too.

I do feel though that the draft code from the '66 mod onward is better than what we had before. One could argue that the effect is too strong or too weak, but until someone comes up with some usable data, it's all really a best guess estimate.

Edited by Lee200, Dec 21 2010 - 03:34 PM.

[brr]

TvO, on Dec 21 2010 - 03:27 PM, said:

Would it add fun to the racing? No.

Yes. Overtaking tastes good when you deserve it.

[JohnnyAck]

At 2:30 James Garner says its roughly well enough, and roughly is what is happening with the new slipstream, 10 mph ez. far as distance, I think its a matter of the size of the car and the aerodynamic cleanliness. I think the slipstream is close enough, especially in the gt cars.Thanks mod team.

[SteveC43]

Lee200, on Dec 21 2010 - 03:31 PM, said:

If anyone out there can find some scientific info on drafting, I'd love to see it.  The '66 mod (and the sports car) draft is based mostly on anecdotal evidence like Brabham saying he could feel a draft so many feet or seconds back of the car in front, etc.  And there's precious little of even that floating around too.

I agree. We're all guessing here and I realize you guys are just doing your best with very little resources. So, I started doing some searching.

Quote

For some distance behind a high drag car, such as an open wheeled Formula car, the drag of a following car is reduced. This can be of the order of 30% reduction at 25 metres distance, and depends on the aerodynamic details of the two cars. This reduction in drag means that less power is needed to maintain the top speed and enables the car to accelerate (around 0.2g for a 450bhp car of the late �60's), even though it may be travelling at it's clean air top speed. If the driver accelerates from some 50 metres back behind the car in front, while in it's slipstream (drivers claim that they can feel the effect up to 100 metres behind), he will be travelling around 5 kph faster when he comes right up behind it. Popping out of the slipstream now enables him to use this speed advantage to overtake, but he will still use over 0.25 km to draw alongside and hopefully claim the next corner. Fast corners leading onto long straights were ideal for this manoeuvre."

100 meters is roughly an American football field. I'm not sure how credible this person is and it could be complete B.S., but it is at https://www.grandprix...ft/ft00196.html

There is also a very promising article in "Proceedings of the Institution of Mechanical Engineers. Part D, Journal of automobile engineering."
I have only been able to get page 1 of the article so far though (see attached).

https://archive.pepub...x164r27h746k41/

Attached Files

•  aero.pdf   102.81K   14 downloads

Edited by SteveC43, Dec 21 2010 - 08:41 PM.

[M Needforspeed]

Another intriguing possibility is being developed by Californian architect/racing driver, David Christian. Involved in track design, he is looking at the feasibility of extending the short-track oval principle of multi-line corners to road courses. The 1/4 and 1/2-mile ovals were built with three lanes, banked at around 6�, 9� and 12� from inner lane to outer. The theory was that the longer path in the outer lane was compensated for by the higher speed possible with the increased bank angle. Anyone who has watched the short oval cars will know that they overtake each other! Whether this principle can be applied to road courses, by varying the camber across the track width, remains to be seen. If it can, and there becomes more than one line through any corner, not only will it be possible to overtake round the outside (or down the inside), but by regular use of all the lines, the full width of the corners will be kept clean of "marbles". This is certainly worth investigating for potential application to future tracks.

thanks Steve for the link

imo,this excerpt is the only sustainable solution to see more overtaking, given all the others well described and explained arguments of the review.

[M Needforspeed]

it is only a small info on the distance where the slipstreaming effect began for 1967 F2 cars :
  50 m behind on the Reims long straight.
  source : Beltoise - L' Auto Journal weekly mag

Edited by M Needforspeed, Dec 22 2010 - 05:31 AM.

[M Needforspeed]

period pics, as well at Reims and Monza shows cars that were no more in the 4/5 cars leading pack, but could regain all the gap after 3/4 laps.
Gethin who won the slipstreaming battle at Monza 1971 is a good example : he was well behind the leading pack (more than ten cars length) on the straight going to the Parabolica, but was able to catch them few laps just before the chequered flag.He added the advantage of a multiple cars slipstreaming effect, that isn 't modelled in GPL.

Edited by M Needforspeed, Dec 22 2010 - 05:33 AM.

[brr]

SteveC43, on Dec 21 2010 - 08:35 PM, said:

100 meters is roughly an American football field. I'm not sure how credible this person is and it could be complete B.S., but it is at https://www.grandprix...ft/ft00196.html

If its the same Peter Wright who designed the Lotus 78, then I'd say pretty credible. In any case, Pat Symonds of Renault has said more or less the same thing, i.e. that the slipstream can be felt at distances up to 100 meters, and when much closer than that there can be a speed gain.

[Arturo Pereira]

Interesting topic, even if it was discussed before.

If the effect of slipstream can be felt at 100meters, that is about 20 cars lengths behind. However, at 200mph, 100 meters can be done in 1s.

I guess we could be getting a confusion about the terms. The effects of running behind other car depend on the distance to that car AND on the speed of that car. At some point, we get a bit more speed but not yet a tow. At this point, we do not get enough speed to close the gap, which means the drag of our car is not low enough. From that point on, we start getting a tow, we can close the gap and we can even try a pass.

However, this is not as simple as it shows. When we left the draft to try a pass, we, literally speaking, face a wall of air at, let´s say, 200mph. So the chances to try a safe pass are also related with the relative power of each car.

[Pavel]

Here is scans that were on RSC. Maybe someone didn't see it.

Attached Files

•  slipstream_1.jpg   289.56K   101 downloads
•  slipstream_2.jpg   302.53K   109 downloads
•  slipstream_3.jpg   342.57K   75 downloads

[richard cooke]

brr, on Dec 20 2010 - 02:52 PM, said:

TvO, on Dec 20 2010 - 02:30 PM, said:

Apperantly, teams running a car in the Indy 500 have to take into account that the car can experience a decrease in drag when it's as much as 9 seconds behind the leading car.

What is the source of this information?

In that year's TV coverage one of the race teams told the reporter that their telemetry detected a decrease in drag 9 seconds behind the car in front.

Richard

[Rudy Dingemans]

TvO, on Dec 20 2010 - 04:31 PM, said:

Why should it be weakened? Where does all this sceptisism come from?

Experience in GPL with the later patches (which were partly botched imho) Tommie. Like I said the overall slipstream effect is better than it used to be, but it's definitely too strong at large distances. You start really getting sucked forward with the other car barely in sight yet, instead of getting sucked forward when getting actually near to the car in front.  

I've had 65 and 66 races where guys behind me lost it and spun off (or got off the track) at Monza and then were right back on my tail two laps later.     That's just not realistic, and that's final - no matter what anyone says here.  

Bob Simpson, on Dec 21 2010 - 10:49 AM, said:

The trouble with this GPL simulation is the limitation that it only covers one condition.  There are no side wind factors, nor do the slightly different aerodynamic qualities of the cars within each mod factor in.

Bob's probably on to something here. One of the reasons that the draft is too strong at distance (especially for the smaller/slower 65 and 66 cars) is probably that IRL, it gets "spoiled" after a few seconds by side winds and other aerodynamic factors.

(I still don't buy Bob's reasoning of slipstreaming on bicycles, I don't think that exists (it just reduces the head wind if you tuck in behind the cyclist in front, but front drag reduction is not the same as a slipstream - which "sucks you forward" and bicycles just don't go fast enough to punch such a hole in the air needed to do that). But apart from that, I think he has part of the explanation here.)

Regards, Rudy
(GPLRank: -40)

Edited by Rudy Dingemans, Dec 22 2010 - 02:11 PM.

[M Needforspeed]

Rudy Dingemans, on Dec 22 2010 - 02:10 PM, said:

TvO, on Dec 20 2010 - 04:31 PM, said:

Why should it be weakened? Where does all this sceptisism come from?

Experience in GPL with the later patches (which were partly botched imho) Tommie. Like I said the overall slipstream effect is better than it used to be, but it's definitely too strong at large distances. You start really getting sucked forward with the other car barely in sight yet, instead of getting sucked forward when getting actually near to the car in front.  

I've had 65 and 66 races where guys behind me lost it and spun off (or got off the track) at Monza and then were right back on my tail two laps later.     That's just not realistic, and that's final - no matter what anyone says here.  



Regards, Rudy
(GPLRank: -40)

   Can you give a number in meters, Rudy ? How much car sizes back did you experienced what seems a power like a storm huge slipstream ??

Only thing I can say is I just finished "the Jack brabham story " book, and he gives figures of tow still faraway from the car ahead.

Edited by M Needforspeed, Dec 22 2010 - 02:24 PM.

[Lee200]

Pavel, on Dec 22 2010 - 06:45 AM, said:

Here is scans that were on RSC. Maybe someone didn't see it.

Thanks Pavel or these.  I'd not seen them before.

Do you have the next month's installment which supposedly covered the theory behind slipstreaming?

[richard cooke]

M Needforspeed, on Dec 22 2010 - 02:19 PM, said:

Only thing I can say is I just finished "the Jack brabham story " book, and he gives figures of tow still faraway from the car ahead.

I remember reading an article where Jack Brabham claimed he got a tow 400yards away, but have never been able to find the article again.  What does the book say?

Richard

[John Woods]

Just completed several laps at Indy with average front and back straight times of about 13 seconds, which would mean an effect at 9 seconds would be, for instance, between the exit of turn 2 or 4 to a point about 3/4 of the way down the straight, (as if my experience makes any difference).

Thanks for the article, Pavel.

Anyone know, does the drafting effect apply to wheels independently, or just the tub, or all?

[M Needforspeed]

richard cooke, on Dec 22 2010 - 02:50 PM, said:

M Needforspeed, on Dec 22 2010 - 02:19 PM, said:

Only thing I can say is I just finished "the Jack brabham story " book, and he gives figures of tow still faraway from the car ahead.

I remember reading an article where Jack Brabham claimed he got a tow 400yards away, but have never been able to find the article again.  What does the book say?

Richard

Richard,


that' s precisely in that book ! I will check and post the excerpt

[M Needforspeed]

richard cooke, on Dec 22 2010 - 02:50 PM, said:

M Needforspeed, on Dec 22 2010 - 02:19 PM, said:

Only thing I can say is I just finished "the Jack brabham story " book, and he gives figures of tow still faraway from the car ahead.

I remember reading an article where Jack Brabham claimed he got a tow 400yards away, but have never been able to find the article again.  What does the book say?

Richard

Richard,


that' s precisely in that book, released in 2004, he wrote himself with a little help from Doug Nye! I will check and post the excerpt

Edited by M Needforspeed, Dec 22 2010 - 04:29 PM.

[M Needforspeed]

Got it ! P 213

Brabham describe the Reims Formula 2 1964 race with the BT10 Ford SCA 1000 cc engine  " the fastest part of the Reims circuit was the long downhill straight - actually the main Reims - Soissons road into Thillois corner, down which our little 1 litre cars were hitting 142 mph ( 229 Km/h).Slipstreming effect could be felt at considerable range.To break another car out of your "tow" you had to pull at least 400 yards ( 366 m) ahead of it "

Towards the end of the race Alan Rees, in Roy Winkelmann's private Brabham, and I had managed to break some 500 yards ( 457 m) clear of the pursuing pack and he led into Thillois, the final right-hander entering the long, undulating finish straight.I was hoping to slipstream him out of that corner and slingshot ahead at the line, but he was playing the same game.We both crept unbelievably slowly round Thillois, and when he booted it for the line I couldn 't quite get by and he won by half a length  

what's remarkable is that if you go 400 m back at Reims, there is a good chance your car is still going downhill, and the car towing in front is in a lower position and thus isn't on the same altitude airflow ...How the effect can be so strong or simply felt?    
  
So there seems we can set GPL slipstreaming on a wide range of numbers !

Don't be too conservative Rudy,listen to the "wise quiet silent man" of motor Racing, as Black Jack was also descibed.

Edited by M Needforspeed, Dec 22 2010 - 05:17 PM.