worf928

It all depends upon the profile of the airfoil. The profiles on which I've done some analysis for the NE Racers are approaching the stall region at 20 degrees. Wings that have good efficiency and high lift through a wide range of attack angles are usually pretty complex profiles - more complex than what I've seen mounted to cars.

Regardless, dragging the wing is not necessarily a bad thing if you have power to spare. On a short twisty track a high-power car might get better lap times by dragging the wing.

mark kibort

yes, thats true. generally, on a short twisty track, the speeds are not sufficient enough to create the down force needed to be effective. so, as you say, with big hp, you can drag a wing around and get some additional downforce from the drag forces in addition to the lift (or downforce) forces. its a vector force on a wing that has a few components.

one of the ways the slats and indy angle iron wings generate lift, is similar to the wings on jets when they take off and land. they come apart and effectively create a higher angle of attack. ( aero cord line changes).

anyway, as i said, the point of max lift for a asymetrical air foil is about 20 degrees. stall usually happens at near 28 degrees. you are always approaching stall after you hit max lift. then, drag continues to go up, as lift will go start going down.

here is a bad copy of the graph for an asymetrical air foil. left side is lift to drag ratio. right side are the lift coeffient and drag coef scales, and at the bottom is angle of attack.

enjoy

MK

Benton

Glen,
If you are referring to my wing, I have it set at the max of 10 degrees, and it can be incrementally adjusted back to 0.

Jim bailey - 928 International

Actually not this simple....."my wing at 100lbs of downforce right above the rear hatch will be 2.5 feet from the axles so, 250lbs of downforce to the axle. Mark attaching to the shock tower, running uprights back 2.5 feet would do the same thing. i think i get it now. is that the idea?" ..... what happens if you add 100lbs 2.5 feet behind the axle is you now have an equal up vector force of 100lbs 2.5 feet IN FRONT of the rear axle however the rear axle was already supporting some of the weight in front of the rear axle as was the front axle. So first you must determine the static front and rear weight % then determine the center of gravity , determine where 2.5 feet in front of the rear axle is relative to the CG and then you can calculate how much weight is being lifted off the front wheel and how much is off the rear wheel from that 100lbs of upward vector 2.5 feet in front of the axle. Now IF just by chance the center of gravity just HAPPENED to be exactly 2.5 feet in front of the rear axle then the up vector of 100lbs will remove 50 lbs from the front axle and 50 lbs from the rear the added down of 100 lbs is 200 lbs at the axle pivot point less the 50 lbs for a net down force of 150 lbs. The only instance where adding 100lbs behind the rear axle can add 200 lbs to the rear axle is if the weight /downforce is EXACTLY as far behind the rear axle as the wheelbase of the car or 98.43 inches for a 928 or 8.2 FEET .

mark kibort

Right again Jim. In that post, i agreed with you also about it mattering ONLY where the wing ended up. mounting to the front, middle or rear alll does the same thing. now the amount of downforce is determined by some slightly more confusing calculations based on CG, fulcum points and distances.
again, i agree.

give my wing a shot. what does my 50 more additional llbs of downforce at the wing, do to my front wheels (statically)? assume 3000lbs car weight, 50/50 weight distribution (before wing forces), 100" wheel base, and 2.5 feet (30") wing center of pressure, position to the rear of rear wheels plane.

Mk

Dennis K

I'm showing 1565 lb at rears, 1485 lb at front.

weight at front wheels = (3000 lb x 50" - 50 lb x 30")/100"
weight at rear wheels = (3000 lb x 50" + 50 lb x 130")/100"

mark kibort

Is that how you calculate it?? sounds about right. i was thinking that the front would be 15lbs lighter , which you indicate and the rear was going to be 50lbs heavier (with downforce) you have 65lbs more in the rear.

i can handle 7.5lbs less per tire up front, shouldnt make any difference. heck, side to side up front has been up to 40lbs difference, but rears are pretty close.

now the question is really what happens if the balance is really 56/44%

Mk

mark kibort

new data for the downforce of the cup car wing on the 928

https://rennlist.com/forums/racing-and-drivers-education-forum/311397-gt3-cup-car-wing-forces.html

jon928se

The starting points for all of this discussion are simple

1 get the wing as high as possible so it isn't affected by the changing airflow off the roof of the car. The length of vortexes off the back edge of the roof change with speed, and the angle off the airflow changes with speed. Unless you have your own wind tunnel or the unadulterated results of somebody elses trsting you can't really start to utilise the differing effects to advantage.

2. Once the wing gets into the region where some of the airflow over it starts to stall you are also getting to the point where drag increases dramatically and lift (downforce) decreases dramatically

3. Use wing fences (vertical plates on the end of the wings) If the width of the wing is limited by the regs using a wing fence (up to 6x the depth of the wing) increases the effective length of the wing by as much as 20% with little extra drag. Or if you have enough lift make the wing smaller thus reducing drag for no loss of negative lift.

4. If the rules allow you to put the wing really high put it right over the centreline of the rear wheels. Any further back than this does add downforce to the rear wheels but the extra gained downforce is balanced by the uplift to the front wheels.

5. A proper aerofoil shape (with longer chord lengths for the DOWN side than the up side because we want DOWN force) will work a lot better than a curved piece of plate.

6. The trailing edge should direct the airflow to resume the same incidence angle that it hit the leading edge.

Go browse the model glider forums because that is where most of the last 50 years advances in aerofoil start from.

Idle musings from an old model glider flier, and a half decent (OK better than half decent) sail trimmer.

And remember most of the advances in slow speed aero and materials science didn't come from the space race, they came from world class radio control yacht racing.

Brett928S2

Hi

Umm...can we reverse this...next year I intend to try some HIGH SPEED runs with my Nitrous...

I have an S2 with the little rear spoiler....now...to get VMAX ,,,,do I remove it....or can a BIG WING like the above,,,be set to INCREASE top speed and lower drag ????

I am not sure I explained that well...lol.....so can the wing INSTEAD of increasing downforce...be set to DECREASE downforce...and so aid top speed on a straight runway ???? (no cornering involved) ??

All the best Brett

928S2 AUTO V8 4.7 LTR 1986 IRIS METALLIC BLUE WITH X-PIPES, RMB, PROMAX CHIPS, KICKDOWN SWITCH, K&N,WIZARDS OF NOS - NITROUS KIT 150 HP - 505 BHP / 500 FT LBS TORQUE.
PCGB - 928 - FORUM - MODERATOR.
EMAIL : managingdirector@pchealthcare.co.uk

mark kibort

Doing imperical tests dont have to be that complicated.

1. we all have roof lines and there will be differences to how the air is deflected, but based on some of my tests, it seems to be deflected at near the same angle as the trailing edge of the roof. also, we have some good aero curves of our car (thanks to those that have posted them) . having the wing as high as possible is not a requirement, we are not talking about boundry layer air here, we are talking about deflected air flow, and it is as effective to be used as the air 3 feet above our car!

2. by measuring down force at different speeds, we can plot the downforce profile of the wing for different speeds. drag/lift curves can be assumed close to the air foil for which i posted its curve right from some aero text

3. generally, we wont be using the wings at stall speed, at the highest angle of incidence (angle of attack) lift to drag ratios are near 10:1. any higher and drag goes up faster than lift and probably isnt worth using the wing at that setting anyway.


mk

ps here is the picture of 160lbs of weights on the wing to calabrate the downforce at speed.