[ QUOTE ] How would you adjust the airfoil while going down the track to keep the force as desired? Would it need to be computer controlled or could you do it manually? I can imagine a specific rate spring that changes the angle of the wing at a certain downforce. Now how do you make the whole bellytank change its angle of attack? TZ As I understand the dimples on the underside of my knee-board are ther to stabalize it a little [/ QUOTE ] Cadillacs and Lincolns (and a lot of other new cars I would guess) have "load levelers" that adjust the ride height to level regardless of how many people and their bags you put in the back of the car. but it works "slowly" so it doesnt adjust every time tha car bounces over a bump. It works throung a lever sending a signal, sort of like a gas tank sending unit. and it adjusts to keep the body at a certain level above the axle. To adjust the inverted wing efect I think it would be sensed under the spring load so the wing angle would adjust to keep down force at a level dialied in, and adjustable from the driver's controls. Of course it would be banned from use by new rules because that's what SCTA does when the driving of the cars start going "Robot"
I've owned several dirt track stock cars that the bodywork was "dimpled". Never seemed to make'em faster though.
[ QUOTE ] I saw this do***enary on 'dambusters' one, during WWII the brits planned on busting all these dams that provided Germany with I dunno how many % of all it's electricity, to do that they developed these giant golfballs full of explosives, I think they used the dimples to give 'em spin, so when they would hit the water they'd bounce on the water 'till they hit the dam, then sank till all the way to the bottom where the pressure would sett 'em off, goodbye dam, and 9 months later, hello baby-boom [/ QUOTE ] But the found that the mines were more accurate if they were cyclindrical rather than a sphere.
O.K. I'm not Mr. Wizard or Bill Nye "The Science Guy", but, I'm still gonna contend, that, lift on a high speed automobile would be detriment. We've talked about golf balls, airplanes, boats and CARS. Of them all, cars are the ones you DON'T want lift on. They're ground based vehicles. Boats have rudders for control. Planes also have ailerons and flaps, trim tabs...etc, for control. Golf balls don't have control. If a car leaves the ground, it doesn't have control, either. It's rudders are it's tires, and when you add lift, you subtract control {on a car}. RAY mentioned the vinyl roof thing in NASCAR. I never heard of that, but something that NASCAR has employed, that might apply, is the flaps that open when a car gets turned around. What happens when a 200 mph race car, which relies HEAVILY on downforce, goes backwards? It becomes an airfoil. It LIFTS. Those flaps are designed to reduce the venturi effect. The increase and subsequent decrease of air pressure causes the car to leave the ground. Once it does, it is acted upon by the air that gets underneath it... as in C9's "angle of attack" explaination. Hydroplane boats catch air all the time. However, they are launched upward by hitting waves, not by lift, but the result is the same as the hand out the window. If you add lift to a 200+ mph car, it'll do just that... LIFT.. Without controls to take over when the tires leave the ground... YOU DIE!!! And even if you could control it, it wouldn't be a LAND speed record, would it? The effects of "drag" are felt at the back of the vehicle, opposite of the direction of travel. Adding lift, is the same as a reduction in weight. Weight is downforce... downforce is not drag. If you build lift into a car and run it at very high speed, it just might fly. I hope the ambulance driver knows a shortcut... I'm not a wannabe expert, I just like my car to stay on the ground. JOE
[ QUOTE ] If you build lift into a car and run it at very high speed, it just might fly. [/ QUOTE ] Yes,that's right.But we are talking about reducing drag by influencing the boundry layer.Any airfoil sections suggested were to reduce drag and/or produce downforce. In the first pic,the tufts of yarn show fully separated airflow over the center of the rear window.The steeper the rear window,the worse the problem. Adding vortex generators to the roof improves the airflow over the rear window producing increased downforce AND reduced drag. By encouraging the air to close in behind a shape,any shape,drag will be reduced.Pics from streamlining.com
UNKL IAN- I've been meaning to thank you for posting this topic. I recently bought another house, and have been fixing it up to sell, and this thread has helped me occupy my brain while I've been working over there. All of the aspects of this entire topic are tough enough by themselves, but everything is compounded by so many variables. It's cool. Great thread. I'd like to see the results of the dimple idea in a wind tunnel. BTW- Are those little tufts of yarn TRADITIONAL? JOE
I've actually been studying a couple of aerodynamics books. The key to golf ball dimples is the angle of seperation of the boundry layer as the fluid (or air) p***es over the tumbling sphere. And that angle changes as the air fows from the leading edge of the ball, over or under the ball, and towards the back of the ball. Because it's a spinning sphere, there's no normal "vortex street," or normal trailing wake. A bullet, for example, would leave a seperated wake, just like a land speed car would. But a spinning ball doesn't. Those golf ball dimples are there to create that "vortex street." It's estimated that a 230 yard drive on a dimpled ball would fly around 50 yards on a smooth one. The dimpels also do create lift. But I don't think that a tumbling, lifting car is a good thing on the salt flats. Wingnutz mentioned "riblets," which are similar but different. In biology, they're called denticles, and are tiny V-grooves found in animals like fast swimming sharks. They're not dimples, but long grooves, in line with the flow. Riblets work best at a size that's inverse to the speed. A shark may have bigger ones, but a slow (40 mph) solar car runs best with riblets measuring 0.008" high and wide. A land speed car would need even smaller ones. And that's probably a lot smaller than wet sanded paint. Finally, Unkl had an interesting point about exposed wheels. They created a LOT of disorganized, low-pressure air. But there's something in addition to faired axles and angles of attack. If you could (legally) direct some high pressure air over the the air disrupted by the wheels, you would get some serious downforce... --Matt
[ QUOTE ] The dimpels also do create lift. [/ QUOTE ] Would dimples create lift on a ball that wasn't spinning?And which direction does a Golf ball spin?
[ QUOTE ] Would dimples create lift on a ball that wasn't spinning?And which direction does a Golf ball spin? [/ QUOTE ] A non-spinning ball would be difficult to achieve with the lower lofted clubs - one iron, driver etc. Even so, I'm sure it could happen and if so not much lift would be generated. As viewed from above and ***uming a right handed player, a "normal" shot - straight or with a slice/fade to the right, the ball will spin in a clockwise direction. When the same player hits a hook/draw the ball spins in a counter-clockwise direction. It has to do with the angle the club face hits the ball. For a left handed player, insert mirror image and everything works opposite.
[ QUOTE ] As viewed from above ... the ball will spin in a clockwise direction. [/ QUOTE ] So the ball spins around a vertical axis. NOW I'm confused!I think I could see how a Golf ball could generate some lift spinning around a horizontal axis.But how is it going to create lift spinning around a vertical axis?The relative motion on the top and bottom of the ball is the same.
[ QUOTE ] Would dimples create lift on a ball that wasn't spinning? And which direction does a Golf ball spin? [/ QUOTE ] Good questions. I have no idea if dimples would create lift on a ball that wasn't spinning. I would guess that they would not. I also don't know how significant the lift is, anyway. Doesn't a golf ball always have backspin, meaning it rotates in the opposite direction of a car's wheel. Do open, dimpled wheels provide negative lift? Not if they're actually in contact with the ground.
The winner of the America's Cup Stars and Stripes used riblet tape made by 3M: http://oea.larc.nasa.gov/PAIS/Riblets.html
[ QUOTE ] So the ball spins around a vertical axis. NOW I'm confused!I think I could see how a Golf ball could generate some lift spinning around a horizontal axis.But how is it going to create lift spinning around a vertical axis?The relative motion on the top and bottom of the ball is the same. [/ QUOTE ] There is a small component of spin along the horizontal axis when the ball is struck with a driver or other low-loft club, but for the ball to slice/fade or hook/draw it needs a large component of spin around the vertical axis. Incidentally a fade is simply a mild spin and a draw a mild hook. And to add some confusion, for a right hand player, the draw goes the farthest because it's component of horizontal axis spin is in the correct direction to ***ist in lengthening the rollout. Rollout being after it hits the ground. The fade/slice has the ball spinning in the opposite direction than needed and has the effect of putting the brakes on. (are we getting off topic here? 8^) So - getting back to the fade, - and we're still dealing with a right hander - one side of the ball (left) is spinning against the apparent wind and the other side (right) is rolling along the apparent wind which is what makes for the fade. Or hook as the case may be. Or the curve ball in baseball. Also, due to the loft of the club (angle from vertical) which isn't a whole lot on a driver - ranging from 9 degrees which should be for the pro's or very good amateurs to about 12 degrees for the rest of us - the ball when struck does pick up a small component of horizontal axis spin, but not as much as the vertical component. Loft being one explanation of why not too many average amateurs use a one iron. Going up the loft scale to the steeply lofted nine iron, pitching wedge or sand wedge, the ball when struck correctly will take on a considerable amount of horizontal axis spin and that adds to the launch angle from the steep club face as well as making the ball climb even more. The climb due to the same reason the ball fades or draws. What little vertical component spin comes off a correctly struck steep club face is not too much. Some guys and gals who hit the ball a long ways can fade or draw a nine iron etc., but it's not a real commonly done thing. So here's the part that may confuse you. Getting back to the driver and desiring to say, fade** the ball around a tree so as to be in the proper place for the next shot or perhaps even get on the green on a short 4 par, the driver is swung normally with the feet aligned properly so as to just miss the tree on it's left side. The trick is, when you grip the club, roll the face open a bit. The open face matching exactly the angle of where you want the ball to end up. When the ball is struck properly - which is not always done, ask any golfer - it will it will fly left of the tree and start cranking to the right and end up where you want it. There's no mumbo-jumbo or voodoo with the fade. All you gotta do is aim correctly, open the club face for the fade, swing normally, physics takes over and the ball goes where you want. Sometimes. But that's golf.... **The draw is accomplished by closing the club face and following the same alignment rules. Usually the ball is struck with a square club face, but for most of us the ball is not struck completely square and that's why some are faders and some draw the ball. (My dad used to build custom golf clubs, knew the game well and knew how things worked as well as he carried a single digit handicap when he was younger.)
[ QUOTE ] The winner of the America's Cup Stars and Stripes used riblet tape made by 3M: [/ QUOTE ] When I did sail research for racing sailboats, we experimented with riblets in the sail, small dams that would direct the air. They acted like miniature, skinny long parachutes to provide some loft within the sail to allow it to build a bigger pocket. That failed. They slowed the airflow on the inside surface too much and caused the sail to collapse. We found that using segmented soft battens worked better. On the other hand, using a similar riblet that directed the flow away from problem areas of a sail, like the pocket immediately behind the mast, or the bottom few inches above the boom, and the area immediately in front of any fittings on the sail, smoothed the air flow around those items and gave greater continuous surface pressure on the sail. Having good transitions between the areas of sail pressure prevented sagging or creasing at those areas. That doesnt exactly translate to hard solid car bodies. Sails are two sided, and controlling the speed of the air on each side aids the loft and force transferred to the boat. What does apply to cars is that when its impossible to fare in any protuberances, provide a series of small riblets perpendicular to the air flow that build from a small to a larger size to separate the air flow from the surface before it hits the protuberance. In effect, you are creating a fairing of still air around the riblet that the swift moving air will move around with less drag than the actual car surface will have.
The NASCAR racers that Ray brought up were the Super Birds vinyl tops. NASCAR nixed the whole car including the 426 HEMI the vinyl was designed for that one purpose and not many caught on
[ QUOTE ] SO... How about covering your car in Teflon?! Travis [/ QUOTE ] I can't get that damn stuff to stick to ANYTHING.
I have always wanted a car made out of NERF! I have actually thought about the things that you could do in a nerf car. It would be a blast if ALL the cars on the road were made out of nerf.... HC
The Jalopy Journal
