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Discussion in 'General Tech' started by mcglsr2, Mar 18, 2015.
some create drag and some do not.
after some reading I am just as confused as ever. from what I read most spoilers will create drag but then again most spoilers we see today are mainly for looks.
Pretty much my brain/logic, available resources, diligence and a desire to learn. I am not an avionics engineer or anything like that (though I am a software engineer - so different field for sure but still of the engineering mindset). So I'm sure that doesn't qualify me as an expert - and I freely admit that I am not. Arm-chair quarterback at best. So take that for whatever you want. Feel free to dismiss everything I say. I still think I am right though
And the struggle you are having is that your resources are lumping wings and spoilers together as the same thing. They are not. A wing is an airfoil. Period. End of statement. A spoiler is an air dam. It is NOT an airfoil. In fact, that link you provided basically uses spoilers and wings interchangeably. This is notcorrect, thus your struggle. If you replace the word "spoiler" in that link with the word "wing" - they yes, I agree with it. And wings create drag.
Point of reference: the question on that site is "What exactly is the purpose of the spoiler on a car and how does it work?" And what do they show? A picture of a big ass wing. Not a spoiler. So immediately that article is already off on the wrong foot. Wings and spoilers are two different things. All your previous posts, if you said "wing" instead of "spoiler" - then yes. There will be drag.
Okay, this video is perfect. In the beginning, in the race between the car with the spoiler and the one without, the one with the spoiler won. Why? Let's hold on to that thought. Now, where the video is wrong (which makes it perfect). At 3:30, the dude says the spoiler forces the air upwards, creating drag. This is not true depending on the design of the spoiler. Looking back at our Mercedes example, we saw that the spoiler *leveled* off the air, it didn't force it upwards. If the spoiler is large enough, it could force the air upwards and then one might start to see some drag because the upwards flow does not mingle well with the other laminar air around it. On a properly designed spoiler, it will reduce drag.
So back the beginning of the video - if, at 3:30, he's right in that the spoiler created more drag, then the car with the spoiler would have lost the race. Because more drag means slower. However, it won the race. It winning the race is actually correct, since the car has reduced drag, it can accelerate faster. So unfortunately the video contradicts itself at 3:30. It was correct in the beginning, but messed up when explaining the air over the spoiler.
It's wrong again at 3:40 where it talks about the airfoil (wing) decreasing lift without increasing drag. We know from the real world that this isn't true - if it was, Nascar would all run wings rather than spoilers, since, according to the video "it decreases lift without increasing drag" - in other words, apparently free extra downforce. So they would all run wings and get the downforce. But they don't. Because you don't get more downforce for no extra drag, as the video implies.
Yup, after watching the video again, I do believe they are wrong about the way they describe the spoiler, and airfoil for that matter.
As for their experiment, while I applaud it's creativity, it's not very scientific. The smoke can easily be drastically altered by the fan they used - which has a dead spot right in the middle. Which means the fan will separate the smoke as it passes through the blades. Furthermore, the car is suspended in mid air. Cars do not fly, so the air passing under the car is not affected at all by the proximity to the body and the ground like it should be, which means the air interacting at the rear of the car is highly suspect. However, even with all this, they do get pretty close...and then again get the explanation wrong like they did earlier in the video.
The whole video can be debunked with a simple question: in the very beginning, why did the car with the spoiler beat the car without one?
At 5:25, talking about the spoiler, they say essentially that "the redirected air leads to a low pressure zone behind the car, which can increase drag." They then immediately say "the high pressure air, over the trunk reduces the effect of lift with downforce. In other words, your car will be able to accelerate faster." So tell me - without increasing power, and increasing drag, how in the world can the car be faster? The answer, it can't. This video is just flat out wrong. A perfect example. Back to my question, how did the car in the beginning with the spoiler win? Answer: spoilers reduce drag, which allows cars to accelerate faster.
It's really not hard, once one accepts that Wings and Spoilers are different, and that the vast majority of people that talk about them confuse them as the same thing. They aren't. They work on totally different principles. Once one realizes that, and realizes that most "sources" combine the two incorrectly in the same definition, it will become much clearer. They are different. Wings are not spoilers, and spoilers are not wings.
Think of it this way: an airplane doesn't fly with spoilers. It flies using wings. And they are never called spoilers. Because they are different things.
I just thought of another example: drag cars. Do the vast majority of drag cars run a big ass wing? Nope. Most have a sled-like looking wedge thing hanging off the back - a spoiler. To reduce drag and increase top end speed, which I have to imagine is important in a drag race. Drag racers do NOT want drag. And they don't need downforce, because no corners. What they need is top speed. If spoilers created drag, which would hurt the top speed, why do they use them? Reason: because they actually don't. Spoilers reduce drag and let the car accelerate quicke/have a higher top speed.
The exception here are those skinny things with the massive wing - I imagine they need the downforce because they are so ridiculously fast the tires would never hook. They need the extra weight on the rear tires for traction. And they will reach speeds pretty damn quick where the wing will actually be effective. Remember, that wing ain't doing shit while the car is on the line, or even when it launches. Air has to move over the wing for it create downforce. I suspect that wing is to prevent the rear-end from getting loose and keep the rear tires planted at halfway down the track and beyond.
I watched some more drag videos - there are a number running a wing rather than spoiler. It appears they think the downforce is more important (and it could very well be).
I'm an avionics engineer... kidding, just mechanical.
To my understanding, the content in this thread appears to be correct. That being said... aerodynamics is extremely complicated magic. It can be fairly unpredictable. So I'm not sure if some of the "rules" of wings vs spoilers can always apply.
Totally agree, and it also depends on the setup of the wing and/or spoiler. However, in general, what I described for Wings is (I think) accurate, and what I described for Spoilers is (I think) accurate. Can one make a wing act more like a spoiler and vice versa? I'm sure. One can get it all wrong, or magically get it all right. However, what doesn't change, is the concepts that are applied to each wing and/or spoiler in their ideal configuration. That I will stand behind. Now, whether the thing on the back of one's car is a wing or a spoiler could be totally up in the air. It depends on the body shape of the car, the placement and size of the wing and/or spoiler, and I imagine the phase of the moon thrown in for good measure
What I will maintain is the purpose/job I described for a wing, and the purpose/job I described for a spoiler. Yours, hers, or his actual implementation can certainly vary to different degrees of effectiveness.
Just curious what you aerodynamic experience is mcglsr2? Just trying to get a feel if you do this for a living or just did some reading and cut/paste?
If I am not mistaken isn't there two types of drag going on with a spoiler? There is the drag that is created just from the wind hitting the spoiler(similar to the force you feel from the wind pushing your hand around if you hold it out the window at speed)as well as from the pressure diffrerence it creates behind it? A wing does not have as much of the drag created from the wind hitting it and can reduce drag by guiding the air but a spoiler like on the top fuel rail car is not going to do anything to increase top speed. I think a spoiler like That creates the force pushing down just as much from the drag of the air hitting it as much as it does with the pressure difference between them.
I think to say that spoilers reduce drag and increase top speeds just is not always accurate. The articles I posted above talk about how they control the drag to increase down force but they do not say they reduce drag.
this article talks about the wing creating some major drag but also some major downforce.
Pretty much my brain/logic, available resources, diligence and a desire to learn. I am not an avionics engineer or anything like that (though I am a software engineer - so different field for sure but still of the engineering mindset). So I'm sure that doesn't qualify me as an expert - and I freely admit that I am not. Arm-chair quarterback at best. So take that for whatever you want. Feel free to dismiss everything I say. I still think I am right though And no, I don't just copy/paste. I think things through quite thoroughly. I think the fact that what I am saying here seems to differ from what most folks have said so far shows that I am not copying/pasting. Ultimately, I just feel like I understand the difference between wings and spoilers really well. It doesn't mean I can go out and design a perfect system. That would take a lot of testing and research. I just feel that I have a solid grasp of the concepts involved. Could I be wrong? Sure.
And to an extent on what you are saying - no, it's not quite right. On the articles you refer to, they mix wings and spoilers. They are treating them as the same thing. They are not. A spoiler does NOT create a pressure difference behind the car - it in fact reduces the pressure difference, that's the whole point of a spoiler. It smooths the air passing off the trunk, which reduces the turbulence, which reduces the pressure difference. Thus, a decrease in drag.
A wing has WAY more drag than a spoiler - that is the trade-off for downforce. Downforce is not free - it costs an increase in drag. If a wing did not produce drag, why doesn't EVERYTHING have a wing? Why doesn't Nascar use wings?
From your post, you said: "The articles I posted above talk about how they control the drag to increase down force but they do not say they reduce drag." And this is correct - FOR WINGS. Not for spoilers. They are different. And the articles don't treat them differently. They use wing and spoiler interchangeably, but what they are really talking about are WINGS.
To help you understand, think about and answer these two questions:
Why is a pickup truck more efficient (gets better MPG) with the tailgate up rather than the tailgate down? If you don't believe me, article on it here.
In a drag race between two identical cars, identical roads, setups, everything, but one has a spoiler and the other doesn't - why is the car with the spoiler faster?
Yup, because that is the purpose of a wing. To create downforce. Drag is a by-product of the downforce. The more downforce, the more drag that is created.
Note: that article deals with WINGS. Not SPOILERS. And for wings, it is correct.
I have never seen two identical cars with only a spoiler racing but if you have a link to the vid I would love to see it. again reading the articles I am not sure if they are confused or you are.
"Every time a wing generates lift (or a spoiler generates down force) it also generates drag. Drag is the natural reaction of the fluid (air) to resist motion through it (the car). Drag is bad, because it slows down the car. So, more down force is good... but too much down force = too much drag, which is bad. Very very high performance sports cars, like Le Mans or F1, have a ratio called the 'lift/drag' ratio. The car designers try and maximize this so that the car has just enough force to get around the corners, but not so much that they are too slow. Indy cars, and ones that are designed like that can have down force on the order of 3G's, at 200mph. That means they could hang completely upside down on the track, and as long as they kept going fast enough, they would still stick to the road. "
in the article about the top fuel wings
"At this speed the rear wing alone produces about 5,500 Ibs of
downforce and generates around 1,000 Ibs of drag."
And then I found an article about the drag reduction system that they used in F1. It would open a flap on the wing that reduced the downforce and increased the top speed.
I'm really confused.
Scott, it seems like you're arguing the exact point that mcglrs is making.
Wing creates downforce with a consequence of drag. The idea is that positive of the downforce remains larger than the negative of drag.
yes please ignore me going on 48 hrs with no sleep.... just went back over it and saw the parts I missed.
No worries, I thought that was my issue too.
Yup. In this case, the positive of the downforce is that it allows car to corner much faster. So the trade-off of having to accept the drag is okay because you get to be a lot faster in the corners (and make up for any negatives you will get in the straight because slower acceleration/top speed because drag)
No worries :thumbsup:
You posted the vid, in post #22. Watch from 0:15 to 0:26. They are speaking hypothetically, of course. The one with the spoiler wins. Of course, I suppose we could take this with a grain of salt as they are wrong about pretty much the remainder of the video
If the article talks about wings and spoilers being the same thing, then they are wrong If they talk about wings and downforce and increased drag, then they are right. If they talk about spoilers and reduced drag, then they are right.
Ok, this thread was started because of the spoiler I built for my street/track car. I'm here to say I too was under the impression that a spoiler, at least 6" high, would create large amounts of drag because my thinking was basically the same os so many others in assuming that because there's this wall sticking up from my trunk, that it was acting like a parachute in a way. That it was catching large amounts of air and forcing it upwards, since it can't go downwards, thus creating drag and downforce. After reading everything that MCGLSR2 posted I strongly believe he is dead on. A wing needs to have clean air in order for it to work. Every race car that I've seen that uses a wing has them mounted in a way that puts it almost in line with the roof in order to catch unobstructed airflow. A stock style "wing" on say a SN-95 could never perform as a wing because the cabin of the car is directly in front of it and so actually acts more as a spoiler which can be seen on countless videos that clearly show the affects a spoiler has on airflow in a wind tunnel.
So it would seem that the spoiler I built, which I believed would create large amounts of drag but in turn give me more downforce, actually will reduce drag and although not give me downforce, would instead remove lift. This also would mean that the Shinoda spoiler I had on was doing a great job of reducing drag being it's a 15" whale tail type of spoiler. So now I ask myself which one would work better for me, the nascar type 7.5" high spoiler I have on now that sticks straight up, or the Shinoda 15'' whale tail design that stuck straight outward???? Wish I had a wind tunnel.