mark kibort

Now the charts. Dont want to confuse the situation with fact, but here I go........

I like the graphs below because the NACA 4412 is a very similar wing to the cup car wing. (like the Clark Y air foil below as well) the gurney flap size is probably about 1/4" which is the 2% of cord GF. (the bottom two charts are for a higher lift wing Re 110,000 range)
Look at an a lift coeffieint of 0.5 look at the angle of a Gurney flap wing vs a non gurney flap wing. its 1 degrees vs 5 degrees.


NOW, look at the drag when both wings (with and without gurney flap) are making 0.5 Cl. Drag with Gurney Flap vs drag of non- GF. Its .025 vs .04. near 40% difference.

what do you see? I see that there is about a 40% increase in drag for a gurney flap on a wing producing ths same amount of downforce(or lift).
And, if you had a 3% gurney flap, which is pretty common, that increase in drag is DOUBLE over a non gurney flap wing at a Cl of 0.5.


To get 0.5 Cd, you need 5 degrees of AOA for the non-gurney flap wing, and only 1 degrees for the gurney flap wing. (0-1 degrees depending on the height of the GF)
all gurney flaps at 0.5 Cl have an increase of drag over a non GF wing. .

An interesting twist to all this, is that at no lift (0 lift) ..... the gurney flap produces so much drag as that if you wanted to match it with a wing angle, with no gurney flap, you could create enough lift with the non gurney flap wing as to produce .5 Cl with about 5 degrees of AOA, which is huge!!

So, in summary, you don't want a gurney flap on a wing if your AOA is less than putting out near its max lift. as a safety margin, I would install one if I was near 50% or 75% of its max lift capabilities based on its AOA and lift/drag characteristics.

I do like all the papers that had been linked too. I have an emotional attachment ot the cal poly paper because I was Aero there for a while. However what has been quoted was the negligible effect of the increased drag for gurney flaps less than 1.25%, which on a 13" wing cord length, is near 1/8" . most wickers or Gurney flaps are around .25" which is near the 2% of cord.
on that Poly paper, the GF plots don't even go down below lift levels of 1.0, but it's shown below... again, strengthening my case that at low lift settings, drag can be much higher with a GF.

The net net of all this , based on the facts, is that more lift (downforce) is possible with a GF. a normal wing might max out at 17 degrees, with a gurney flap it can create 20% more downforce. This is the point for using the GF. as you get up in the Cl levels, the drag differences for a given Downforce are very small. at the low end, there is a significant difference, and if I was racing at a fast track, I would pull the thing off and use wing angle vs the GF to give the appropriate downforce... in the case of Mikes experience at RA... that GF fell off, I would give the wing 5 degrees and in the end, he would have benefited by having the same downforce and less drag after a pit stop and a wing adjustment without the GF.

And by the way, a cup car wing is 12" wide and most gurney flaps Ive seen are near .5" which is OVER 4% ..... This DOUBLES the drag at low wing angles using a Gurney flap....... just to keep things "real" here.

http://www.aoe.vt.edu/~mason/Mason_f/AIAA2007-4175.pdf

Veloce Raptor

Good stuff, Mike

Nizer

this wing talk is fun and all but how about we get back to driving?

jakermc

Here is a good example of what the differences look like in the data. Example is two different cars, so some differences there, but same driver who improved during the 6 months between the two runs. Track is Homestead with the infield course being utilized.

hf1

mike, thanks for the great posts in this thread. I noticed your left foot permanently positioned over the brake pedal. Is it pretty much a given that with paddle shifters everyone now exclusively uses their left-foot for braking at all times?

ProCoach

Mike, with the push of that left leg, especially into T5 and T12, looks like you could be generating 1700-1800 psi brake pressure! <grin>

I did spend a lot of time looking at the LFB technique of my PDK client this past weekend...

mark kibort

interesting that you can use the left pedal for all braking..... Just like Go Karting?? All that off season experience might come to use someday (when I get my own paddle shifiting 458 race car. I wonder if future cars will have the brake pedal against the left wall of the car so it is like a go kart

fleadh

Nice catch! After working with my Co-Driver Jan Heylen, in the GTC car through 2013 I ended up switching to only left foot braking in the middle of the season (even in the Porsche). I had always used my left foot when I wasn't downshifting (ie: brush of the brakes into sweepers, kinks, etc) so I had good feel.. but I was always taught to drive a Porsche Cup using the clutch for downshifts.

It wasn't until I saw my co-driver doing it consistently and the transmission being perfectly fine half way through the season (i believe we had already done 2 hour based gearbox rebuilds by then). He was trying to help me close the gap to his times and one of the last things left was that little bit of "dead time" between full throttle and maximum brake application... so I switched. And to be honest, it had a big positive effect on my driving. With my foot over the brake I always feel like I can react faster to balancing the car and I use a lot of brake/throttle overlap to help control the balance of the car. On a perfect lap you don't really need it, but in a race you rarely ever find yourself with enough clear space to put together a "perfect" lap.. but it makes me feel much more in control which lets me push harder without getting into the danger zone.

In a Cup if you left foot brake you just have to be extremely precise with the timing of your downshifts/blips. It's not so much that it'll damage the gearbox (it will if it's REALLY off, or way too early), but it'll really upset the car and make it harder to slow down (rear wheels will overdrive the brakes).

The only thing I was worried about when switching to LFB'ing was my brake traces.. I've always had text-book lines (helps to be taught how to drive properly from the first time in a race car!). However, after the first 10 or 12 laps in the car it was clear that my traces were as good as ever, maybe even a little better as without having to heal & toe it gives you a more stable brake pressure.

I don't recommend it for everyone because it's really a tiny effect on overall lap time, but at least for me personally, raised my "comfortable being uncomfortable" point. I'd worry about other stuff before switching to it if RFB'ing is working fine for you...

ProCoach, it's funny you mention that... we were playing with different brake pads throughout the weekend trying to find a good balance that'd let us heavily trail brake the car (which the 458 platform never seems to like, but it's how I drive fast. trying to find the rite pad with the perfect type of "release" on the rear of the car). If you notice I'm off the brakes pretty early in most of the corners... which also meant I had to really attack the pedal at the start of the braking zone in order to give me just enough time to slow the car down and still have enough time/space for a smooth brake release to keep the front of the car (splitter) relatively flat and from bouncing back up. It wasn't my normal style, but worked best for this particular day/setup. The previous day w/ JvO in the car he was about 1 second faster than I was.. and it wasn't until we worked together to see subtle style change he was doing that helped me find the last bit of time (he did it subconsciously, but when we looked at the data together it was pretty clear. since we worked together so much we noticed pretty quickly what was out of the norm).

edit: also, let's not forget the pure GT3 spec car puts out a lot of downforce when you're deep into 6th gear.. like a prototype/openwheel car you can get away with huge initial brake pressure as long as you back off quickly in relation to your ground speed! :-)

And just for the record, on that last lap I over drove the **** out of the entries. I knew it was the last lap of our 2-day test so I went deeper into every corner and hit the brake even harder just trying to overdrive the system to see how it'd behave. It actually went faster... the mistake in Canada cost me 1 second. I had a 2:06 predictive on the dash going into Canada so I was going for it (just to rub it into JvO's even more, that's how we roll!).

ps: sorry for essays and the wing derail. this is a good thread, hopefully we can keep it on topic.

-mike

mark kibort

One more thing on the "Wing Talk"....

so Mike, you have the graphs now of two different wings.
the shape most likely to be like your 458 wing is the second set of graphs. (the flat top wing)

Now, what happened to you , if you had the wing set at 0 angle of incidence. (and lets say that's the same as AOL for the sake of discussion even though it might be 5 degrees difference)
Did you see the lift (downforce ) values?? even at 0, you get a Coefficient of lift of near 0.4 and drag of .04, However, with the gurney flap of about 1/3" in height, you get a lift value of 1.5 and a drag of .12. ..... in order to get 1.5 Coefficient of lift, you need the wing set at 10 degrees without a Gurney flap, but the drag is only .08. at that same Cl with a GF, you need 0 AOL and it produces .12 coefficient of drag. that's 50% more drag to use a GF.

Ok, follow along to where im going here:

In your situation at RA. if you put down 500lbs of downforce (with 50lbs of drag) at 0 AOL with a GF, and it flew off, suddenly your wing was only putting down 250lbs, and 25lbs of drag. (good for the straights, but a problem for you in the turns) the net gain for the straight, was 25lbs of drag, or about 8ft-lbs of torque (near 8hp) at the engine gained. (due to a 3.2:1 gear ratio at 150mph)

The point of all this is that if you (your engineers) decided to use wing angle INSTEAD of a Gurney Flap, the drag would have been 50% less. meaning, instead of making 500lbs of downforce at a cost of 50lbs of drag, you could have made 500lbs of downforce at a cost of 25lbs of drag.
you would save 25lbs of drag, or 8ft-lbs of engine torque or near 8hp.

With gurney flap , L/D 12:5 (Lift 1.5, drag .12)
Without gurney flap L/D 18:1 (Lift 1.5 , drag .08)

(gurney flap at 3-4% of cord or near 1/3-1/2" high on a 12-13" width wing )

SAME DOWNFORCE, LESS DRAG

The same gains you saw down the straight , you would see by not using a GF and using the wing angle to give downforce.

If anyone here doubts this, especially the ones that have taken out of context the summaries in the GF links on the internet..... please speak up and show why you don't agree with this information.

So Mike, you want to gain 8hp, or 8ft-lbs of torque at the engine at road America..... And you like the way the car felt at 0 angle of incident with a Gurney flap when going down the straight??? Lose the gurney flap and put the wing at 10 degrees........

fleadh

Mark, I think you're confusing what I said about the experiences with the Ferrari at Road America and what happened to me with the gurney flap at Sebring in the Porsche. I'm lost with what you're saying and don't really care about those air foil numbers, that's why I hire engineers. I just want to go fast.

-mike

noturavgm

Great contributions to the thread. Learning something new every post.

Since the entire braking sequence seems to be one of if not the most important aspect of track driving, and that there also seems to be more than one theory around, do you have any recommended reading or viewing material that you find especially beneficial and accurate based on your experience? (other than a pro coach and in-car data :-) )

KaiB

...faster...

I've "followed" your progress Mike and absolutely respect what you've done.

You've put time and money, a wide-open attitude and quite a bit of effort into improving. Nobody ever really gets there, but dude you're close.

fleadh

I'm a big fan of Ross Bentley's Speed Secrets book. If I remember correctly, he dedicates a lot of time to braking. I don't have it at my office or I'd verify.. but it's one of the few texts I've read about performance driving and it helped me articulate (in my head and verbally) what I thought I was feeling and/or attempting to do.

And at least for me personally, I learn best by doing and if possible, having someone show me exactly what they're talking about. I'm not comfortable riding with people who want to show me but I'm very comfortable reading the squiggly lines and relating it to how it felt when I was driving.

-mike

fleadh

Thanks KaiB! Sometimes I don't post because I don't want to come off as a know it all or an actual Pro driver.. but I do like to bench race about driving and show people that if *I* can go a certain pace or learn to do something, anyone can!

I was lucky to have some good people around that fostered my desire to get better so it's nice to try and pay it forward -- even if it's over the internet. :-)

-mike

mark kibort

Mike, I like to go fast, and usually don't trust too many people blindly. Figuring things out, helps me. I don't have the cash to pay engineers (or anyone to help) so for me, its a win win, at a cost of more effort on my side. I think many here can appreciate that.

It doest really matter what happened at what track, the point is, you had the Gurney flap fall off and you didn't like the way it drove. (wing angle set at near "0" as you said). makes perfect sense. The point is, you can hire engineers and they are usually generalists. This is something that I used to specialize in.
Hey, they might have missed it. People seem to always go with the herd. even engineers. " Everyones got a GF", "so we need one too".
Look, just trying to help and provide info here.

The bottomline is this
in this study from cal Poly, there was a net net result. Everyone that read it seemed to miss this KEY point.

"If the Cl is greater than 1.4, then and ONLY then does the lift to drag ratios go up". (that's what you want) . Otherwise, at any other time, the drag costs for a wicker (Gurney flap) costs more than wing angle alone with NO gurney flap.
if you don't want to get into the numbers, translation is this 1.4 Cl for the wing that most of us run, is near max lift, PERIOD! So, you might to mention it to your engineers. what could it hurt.... its a free 8hp !

With a low wing angle... you don't want a GF... its that simple.

see page 10 below
"
An added benefit of the Gurney flap
on the NACA 4412 airfoil is an increase in the lift-to-drag ratio for Cl >1.4."

http://api.viglink.com/api/click?for...ext%3Daero_fac

Mark