I was just looking at Mark's wing. Man, all that steel ?? i know he mentioned all the flex he has seen on other designes requiring the "X" wires, but with the bracket ive designed, its very stout. very little flex side to side, using the 1/8" sheet aircraft grade aluminum. its mounted to the steel hatch, which obviously is not going anywhere and has little flex. Also, ive put 130lbs of weight on the wing, as i showed pictures of, and it was very stable. as it is , my brakets weigh 6lbs, and so does the weight of the wing. vs the other wing of 8lbs (gts wing) im a little heavier. the wing endplates are 1lbs each.

now, make those brakets like Mark did out of Steel, and you are talking some huge weight as refected to the chassis, all in the very very end of the car. I would have to guess that those brakets are 2 x the size of mine, and steel weighs near 4x that of aluminum, so im thinking 30lbs. in a turn, because the wing and brakets are 2-4 feet off behind the wheel plane, effectively, you could have effectively 120lbs as if it was in your gas tank as far as centrifugal force. this is what wings are trying to get away from! you get the downforce as if you have more weight in the back, but you dont want the weigh in the back, due to the centrifugal force.

Its a pretty cool design though (looks real clean) but you dont need anywhere near the strength that those brakets will have. he could have made it out of entirely aluminum, and bolted it down, inside the car near where those big welds were. Im wondering, as the car is going to paint and he is doing some deep cutting in the chassis, why not just weld the brackets to the rear hatch? its steel and plently strong?

the next point is, howmuch downforce can you use in a 928. sure, ive already shown the drag is not much even at 200lbs of downforce (say 20lbs of drag, through the gear box of 4.5:1, so, 5ftlbs of engine torque loss, NOT a big deal) but, since the wing is near 3-4 feet behind the wheels (mine is 2.5' back) that 200lbs of downforce will create almost 100lbs of fulcrum lift on the front. NOW, you NEED 100lbs of downforce in the front using dive planes, splitters, hood vents, etc. otherwise, it might be really pushy up front.

Be interesting to see how it feels when Mark gets it out on the track.

again, it is a pretty cool set up. just overkill. It does look pretty nice!
are those upright brackets bolted to the 3/16" steel plate, aluminum mouting to the wing?

Mk

 

He didn't seem to like the weight comments, and mentioned he intends to run in a class requiring a certain amount of weight. I agree with you though, and as someone else mentioned, adding weight if needed is easy, and you can put it where you want.

 

He should know, we are all trying to help! Im just wondering if he was confused on how strong those brackets need to be, and if there are any advantages of attaching the wing to the chassis inside, vs the rear hatch. you get betteer leverage of the downforce as it attaches further to the rear of the car. as it is now, you (and most other traditional attachments) have a 1 foot advantage of leverage mounting to the rear hatch.

also, there is a lot of confustion about weight and balance. sure, if you are going to add weight its better you put it low and in the center as you said.

it is a very cool set up. i guess the hatch even clears the wing , and thats the main idea, right? however, many racing series, dont want the wing to break the plane of the rear of the car. good luck trying to move the wing forward on that set up!

MK

 

Mark wasn't confused. Wet and bored maybe. But, not confused. (Mark's probably changed the mounting since...)

The thin hatch metal will flex. If the supports are not big-enough and not installed to eliminate the flex in the hatch you will get a side-to-side (left-right) harmonic vibration once the wing is under load. Some of the Yankee Mouse Motor crew ran the "X" braces to eliminate the left-right vibration IIRC.

 

Kibort.." is 3 ft-lbs lost at the flywheel, really a consideration?? am i missing something here?" Perhaps like the benefit of downforce is only in the turns while drag is 100% of the time plus the benefit of downforce is not linear have 1000lbs on a tire and add 50 lbs you do not gain 5% more stick so much depends on the tire. Like the misperception that adding a heavy front roll bar (anti-swaybar) will make the car corner faster when in fact the unloading of the inside tire takes away more stick than you increase on the outside tire but the car does stay flatterand FEEL more stable ...if the front suspension geometry is poor the lack of roll and subsequent camber change can mean that the bar helps BUT the better solution is heavier springs.

 

The last time Mark Anderson was at Road America, his front mounting point for his wing on his hatch was slightly buckled upwards from the wing pulling on it.

Of course, that's because that boy knows how to drive extra-fast!

 

Finally, someone that agrees with me! Guys, like I said, I'm going to replace the steel outer portions with 1/8" aluminum, I just had some spare steel laying around! I mean spare as in 10 feet of steel, free! I don't have any aluminum laying around, and I need to finish the car soon. In the end, I am guessing I will have about 10 more pounds on the rear of the car. I don't know if anyone here is, but I am not a good enough driver to tell 10 more pounds on the car. Yes, at the very back it does increase the polar moment of inertia (I think that is the way to phrase it), but I'm not going to split hairs.

Like I said before, I wasn't attempting to undermine the importance of weight. My car should weigh under 2800 pounds when completed.

 

Thanks for compliments on the concept, Mark. I don't think the hatch will clear the wing, although I haven't tried it yet. I spent about 20 minutes cutting the mounts out... the aluminum mounts will be a bit better design and fit within certain parameters better.

 

That's all part of my active aero package designed to flatten the wing out at high speed to lower drag. (in my mind)

Actually the hatch is not ideal but much more user friendly than other options.

 

i remember mark's first uprights, they were kind of flimsy. mine are solid as a rock and made from a higher grade aluminum. (also key) you will be surprised as to how expensive the good aluminum is!)

Mark has since upgraded his brackes to a much stiffer set up, but no x bars.

I know the weight is not that huge of a deal, but you will be amazed at what you will do later to save a fraction of what you have put on the car. you have two HUGE plates on each side attaching the wing to the chassis. the hatch isnt the issue with the brackets. its plenty strong, its the brackets being forced backward due to the drag, right?? now, I already went over the forces.
im getting 130lbs of down force right not at 7 degrees of wing tilt plus the 9 degrees that the air is angled down at. pretty close to the max efficient range of a air foil type wing. say you get 200lbs of down force, its only going to be near 10:1 lift (downforce) to drag ratio. thats 20lbs pulling on the structure. you can see, you dont need to get this strength with steel. case in point, look at the GT3 cup cars. they have their aluminum brackets attached to carbon fiber body parts . again, only 20lbs of drag at the most.

sorry about the wet and bored part. sounds like you have had some fun with the project. it does look good and i though the idea was for the wing to clear the hatch. the other issue is you want the wing attaching far back as possible to take advantage of the leverage points. also keep in mind, the fulcrum effect. my 50lbs of additional down force 2.5feet behind the plane of the rear wheels only lifts 15lbs on both front wheels, or 7.5 lbs per wheel. i can live with that. (vs my old 80lb of downforce , tilted GTS wing) you however, should think of the 3-4 feet your wing is to the rear of the car, as that can be half the downforce lifting up on the front wheels.

since the pics below, mark fixed the stiffening issue with the bigger brackets. i show them below

Mk

 

I think it wasnt obvious that i was joking. big deal = not really a big deal!

anyway, but yes, the drag is always there, but if it is measured at the max speed and it is a small value, then it is a real small value at the slower speeds. unfortunately, going a lot faster, increases the downforce quite a bit. at road america, if my measurements are right at 100mph, then at 150mph, i could be looking at 430lbs of downforce, with 43 lbs of drag and through the top of 4th gear at 3.2:1, thats 13ft-lbs of torque lost at the engine or near 17hp! if im drag racing JL at RA, that near 20ftlbs of engine torque loss may cost me a position! (that hopefully you can make up in the sweeper and kink!)

Mk

 

Mark.."thats 20lbs pulling on the structure. you can see, you dont need to get this strength with steel. case in point, look at the GT3 cup cars. they have their aluminum brackets attached to carbon fiber body parts . again, only 20lbs of drag at the most." I think you are over looking leverage 20 lbs pushing rearward on the top of the wing pushes down on the rear of the mount to the hatch BUT big but that becomes an upward force on the front of the mount and is multiplied by the ratio of the height of the wing to the width of the lower mount. So if the wing is 5 times higher than the width of the mount ...

 

yes, it will be more than 20lbs of force at the wing mouts, but i was only talking about the force at the wing itself. try and move the car forward or more importantly backward, by grabbing the wing. it take more than 50lbs or 5x the force the wing will ever see to pull the car backward. you can see the stability of the mounts and give yourself some HUGE safety factor. my aluminum mounts are much smaller than Mark's and works fine. sure you can see it pull up slightly, but again, im using 50lbs of force. since it will be more like 20lbs of force, the mounts are pretty solid and there is no side to side movement any more than you see on a cup car from the porsche factory. i figured if they need it to be more sturdy, they would have made it more sturdy. No one has more cars out there with the same kind of wing than porsche and their GT3.

Mark,, since he was cutting, could have just made slots to the hatch itself and attached it to the side walls of the hatch structure. then, it would look the same, and have even greater f/r stability and strength. it would be a little trickier due to that "box" structure of the hatch in that area.

anyway, the point is, the rearward forces of the wing are not that great. down force is substantial, hence the constuction of the wing itself is important and where you attach it to, near the rear of the car. further in you attach the wing, the less downforce you apply to the wheels do tothe leverage points. (attaching to the rear end of the car, is better than attaching to the shock towers by a factor of 2.5')

mk

 

Where the mounts attach to the car has little to do with the effect ..."further in you attach the wing, the less downforce you apply to the wheels do tothe leverage points."... what matters is where the WING is and the load is plumb bob straight below the wing which is why most sanctioning bodies will not allow the wing to protrude behind the car it also means that the more the uprights angle back the more the lever action of the base pushes down on the rear of the mount and levers up the front. As a gross exaggeration if you put a wing directly above the rear axle but extend the mounts forward and attach them above the FRONT axle....guess what the down force will ALL be on the rear axle ...

 

Worked for the Ferrari F1 team - their recent wing package for 2006 was doing the same thing - FIA put a stop to that a few races ago.



Isn't the best place to mount a wing directly on the axle? Push the tires down without the suspension getting in the way.