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Drafting


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#16 svenvangent

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Posted Dec 21 2010 - 05:27 AM

You know what I also noticed is ....that the training/race times between 67 and F1 GT mod are so differend .
What I mean is , if you do a training time in the 67 F1 and than you do a race time you will have no significant differences in times but if you do that with the GT mod cars you will have a big differend time .
I know that the slipstream for the GT mod has more effect than the 67 F1 ( I think so :idunno: ) .
So my most respect go's still out for the 67 f1 racecare times but for the GT mod it is the training time where I have the most respect for because you can cheat so easily with the slipstream of the GT mod cars in a race to improve your time .
greets  :hat-tip:

Edited by svenvangent, Dec 21 2010 - 05:28 AM.


#17 MECH

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Posted Dec 21 2010 - 05:56 AM

You know 'Drafting' can be such a 'Drag' so just enjoy it for what it is; ameasily atempt to simulate something, nothin' more nothin' less :P

#18 tdurrett

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Posted Dec 21 2010 - 06:18 AM

I remember a video recently of Franciti driving Jim Clark's Indy Lotus--especially how the car handled in the drive.
The car had such a slight form to the wind...but Clark did use drafting following the big Offys.

#19 Bob Simpson

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Posted Dec 21 2010 - 10:49 AM

Quote

You know 'Drafting' can be such a 'Drag' so just enjoy it for what it is; ameasily atempt to simulate something, nothin' more nothin' less

I agree.  There have been arguments towards both ends of the spectrum.  Like Tommy, I know that the draft at low speeds on a bicycle is a huge factor, but like others, I find it hard to imagine that at 9 seconds behind on an oval the draft will be meaningful.  But for sure the original 67 cars’ draft was absurdly absent.

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.

Bump drafting isn’t much of a factor when you throw in braking for corners like we see on most road circuits and the squared off rear shape of the NASCAR cars are particularly suited to that.

Also to note is (I think) that the draft off of a GPL car follows it straight back, rather than spreading wider as you get further back.  And the draft moves side to side with the car along a trace relative to the car position on the track rather than the more realistic stationary trail (assuming no side wind).

A lot of debate and thought has gone on before and now we have what we have, so enjoy the racing for what it is – a simulation with some flaws.  Just like any other simulation.

#20 TvO - guest

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Posted Dec 21 2010 - 03:27 PM

View PostSteveC43, on Dec 20 2010 - 08:15 PM, said:

View PostTvO, 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.

I tried staying out of this, but that statement is so clearly a case of seeing what you want to see, I have to point it out.

First, you're comparing apples and oranges, i.e. a car that relies heavily on downforce to ones that placed a premium on smooth lines and low drag. What the Indy car guys are talking about is not tow. They are talking about turbulent air. This causes the car to move around and can also take some of the downforce, particularly on the front end of the car, away. They have to add more wing usually to overcome this as well as do some things to increase mechanical grip. It does not necessarily make them any faster. It is also not a good comparison to a smooth car as I'm sure the air behind wouldn't be nearly as turbulent and the car behind may or may not feel it as much as a car relying on the downforce is.

As for how it is in the sim, I'm over it. There are enough known inaccuracies in the GT mod to make them a bit more fun to drive, one more isn't that big a thing. If they did them realistically, I doubt any of us would drive them long as they would steer and brake like tug boats if the Daytona Prototype in iRacing is any indication.

I already have regrets posting that Indy 500 9 seconds drag fact. It's just an anekdote. I'm not implying whether this is true or not and whether or not we can compare it to GPL cars. But I know for a fact someone said this at RSC, and nobody said they knew for a fact that slipstream only comes into play one second back. So, and this is my point, what I don't understand is why people tend to believe shorter slipstream is more realistic, when there's not a single report stating it is, but there are reports stating it isn't. It's not seeing what I want to see as there is only one way of seeing it.

If we put the Papyrus slipstream model back in, would it add realism? No. Would it add fun to the racing? No. So why would you want it then? Obviously the current sipstream model is not perfect, but it's more perfect than Papy's which is why we used it.

#21 Lee200

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Posted Dec 21 2010 - 03:31 PM

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

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.


#22 brr

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Posted Dec 21 2010 - 04:31 PM

View PostTvO, on Dec 21 2010 - 03:27 PM, said:

Would it add fun to the racing? No.

Yes. Overtaking tastes good when you deserve it.

#23 JohnnyAck

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Posted Dec 21 2010 - 05:45 PM

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.

#24 TvO - guest

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Posted Dec 21 2010 - 05:52 PM

View Postbrr, on Dec 21 2010 - 04:31 PM, said:

View PostTvO, on Dec 21 2010 - 03:27 PM, said:

Would it add fun to the racing? No.

Yes. Overtaking tastes good when you deserve it.

View PostTvO, on Dec 20 2010 - 06:36 PM, said:

... The effect of this is rather than getting quite close and then suddenly getting sucked in so you can slingshot past, you gain enough slipstream to catch up to your opponent at high speed tracks usually within two laps, but you can't slingshot past as easily so you have to actually overtake rather than cruise by. This is also what happened at the races I mentioned earlier.

:wave:

#25 SteveC43

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Posted Dec 21 2010 - 08:35 PM

View PostLee200, 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 http://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).

http://archive.pepub...x164r27h746k41/

Attached Files

  • Attached File  aero.pdf   102.81K   13 downloads

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


#26 M Needforspeed

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Posted Dec 22 2010 - 05:13 AM

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.

#27 M Needforspeed

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Posted Dec 22 2010 - 05:17 AM

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.


#28 M Needforspeed

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Posted Dec 22 2010 - 05:32 AM

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.


#29 brr

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Posted Dec 22 2010 - 05:36 AM

View PostSteveC43, 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 http://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.

#30 Arturo Pereira

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Posted Dec 22 2010 - 06:36 AM

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.




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