Multi-element wings & gurney flaps

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Jake Latham	Multi-element wings & gurney flaps		Lead	[-]
Registered User Posts: 386 06/09/08 10:51:35	Tags : None All - I'm playing with adding a second element to the rear wing of my Radical, although I have one question I haven't been able to find the answer to. The existing Radical wing has a small gurney flap at the rear of it. When adding a second element, should one remove any gurneys on the main element? Or, do you treat the gurney as the top of the trailing edge of the main wing, and set your gaps/overlaps/etc based on that? I'm using McBeath's "Competition Car Downforce" to muddle my way through this experiment. Radicals that come with the two-element wing from the factory seem to have the gurneys still in place, but I didn't want to take that as gospel of a correct approach. Removing the gurney in this case will mean cutting it off, since it is contiguous with the upper surface of the wing - one big sheet of alum. Thanks for any input, -Jake
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matt1racer	wings	#1	[url]	[-]
Registered User Posts: 22 06/09/08 12:44:37	Jake All of the multi element wings i have worked with did not have a gurney between elements and we had as much as 6 elements on the older indycar barn doors at the rear so thats my two cents. Perhaps do to the way they make there elements that fold or integral gurney is how the aluminum is held together at the rear of the element so be cautious of that before cuttting it off. Have fun.... cheers matt
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Charles Warner		#2	[url]	[-]
Registered User Posts: 551 06/09/08 20:24:39	Jake, I am probably preaching to the choir, but if your current wing was designed as a single element a lot is involved in creating a double element wing. A lot more than just adding a second element. They need to be designed and mated from the get-go. For what it's worth - the 1987 March F1 cars had provisions for Gurney flaps on both the main elements and the secondary ones. Charlie Warner fatto gatto racing
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Jake Latham		#3	[url]	[-]
Registered User Posts: 387 06/12/08 11:12:44	Thanks for the tips all. From reading around a bit more, answer seems to be to remove the gurney on the main element. Shouldn't be an issue with the way the Radical wing is constructed - just a careful few minutes with a grinder -Jake
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bdsmith21	Gurney	#4	[url]	[-]
Registered User Posts: 50 06/21/08 12:34:54	Definitely remove the gurney from the main plane. One benefit of adding a wing flap is increasing the air speed on the bottom of the wing. This is accomplished by having a convergent slot gap. The air needs to be funneled into the slot gap and shot out the back. A gurney would ruin this effect. The faster air helps to attach the flow on the back bottom side and prevent stalling. Last Edited By: bdsmith21 06/21/08 12:37:49. Edited 1 time.
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Brownslane.diasio	What's the "flap" about??	#5	[url]	[-]
Registered User Posts: 26 07/07/08 18:59:50	Jake, Charlie is correct. Typically, with a dual (or more) element wing, the main element is deeper and / or shorter in chord (not to be confused with span). This is designed primarily to manage airflow and laminar attachment in a much different way than a single element. Done right, you get much more downforce, with an increase in drag, but not linearly proportional. Simply adding a second element above a single-element design may do little more than increase drag...My Atlantic wings always had a "indent" at the rear of the chord and the placement of the second element was CRITICAL to both downforce and drag...You might look at increasing the height of the rear Gurney flap....you'd be surprised what a difference in 1/8 inch in height will do. I use WD-40 sprayed along the leading edge of the wing before a session. "reading" the oil movements will tell you a lot, and by increasing AOA, you can eventually see when you stall the wing. By increasing the Gurney height at this time, you can "straighten" out the underwing flow, re-attach air, and run a higher AOA... maybe not as sexy as a dual element, but can be quite effective. Not too many biplane airliners out there any more..... Tom in Toronto
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Ren		#6	[url]	[-]
Registered User Posts: 522 07/07/08 20:36:04	Brownslane wrote: Not too many biplane airliners out there any more..... Nah, you just have to catch them at the right time... like takeoff and landing Cheers, Rennie
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ted arken		#7	[url]	[-]
Registered User Posts: 2696 07/07/08 21:45:00	Ren wrote: Nah, you just have to catch them at the right time... like takeoff and landing Priceless
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Jake Latham		#8	[url]	[-]
Registered User Posts: 402 07/07/08 23:51:04	All - Enjoying the input, thank you. I'll go ahead and report my results. Lee ought to be quaking in his Nikes! I removed the Gurney from my Radical wing. Turned out to be for nought, as it had a bend in it, not really visible by eye, that prevented me from using it with a second element. Curses! Tom - the "indent" you mention is what's called an "internal" flap arrangement, instead of the "external" arrangement. McBeath discusses both, but both work fine. So, I bought a pair of el cheapo wings from APR to see what would happen, and fashioned up some endplates and an a-dapter kit (said like Johnny Cash) McBeath's book gave some guidelines for slot gap and overlap, but mentioned that within those rough guidelines, they're not super critical for your home/club racer whose wind tunnel is broken like mine is. The important feature is that the gap converges. So, I obeyed all of these, ending up with approx 3/8 and 5/8 gap and overlap, respectively. Radical wing chord was approx 11", versus the new wings with 7.5" and 5.5", respectively. Span on both 61". Initial result was loss of 6-7mph (!!!!) top speed versus the Radical wing at a moderate AoA, but gain of approx .75 sec laptime. Corner speeds WAY up across the board from the data. AoA's were quite high - ~6* on main plane, and about ~25* on flap, measured with a $25 Sears digital level (my new favorite tool). I kept modifying my endplates throughout the weekend to try and back the flap angle off. Gained back about 3mph of top speed with no reduction in grip. I was under the CSR lap record by .5 sec by the end of the weekend, but drag was still considerable. Oil traces from some unfortunate competitor in front of me revealed separation on the bottom side of the mainplane about 1" from the end, but it's a super-duper wonky shape, so none of us were particularly suprised at that - (see pictures). - But what do you expect from a $100 aluminum extrusion? I do wish I could have used my Radical wing as the main element. If I find a suitable 61" span wing at any point, (anybody have any old Radical wings in their basement?) I will probably replace the 7.5" APR element with that. Total cost of the project was about $300 - two wings, and some aluminum for endplates and adapter mount. Planned on trying a bi-plane setup to see if it helped at all with the diffuser/underbody, but having to use the APR wings up high made that unworkable. Next time, going to continue to reduce the wing angles to see what I can find in terms of grip vs drag. Pueblo rewards a lot of downforce from what I can tell, so I'm really eager to see how it will behave. I'll also do some comparisons against the Radical wing at max AoA's to see what that does in terms of top speed, corner speeds, and laptimes, and see if I've done myself any durned good at all. Directory o' pictures (yes, I'll get thumbnails eventually...) http://www.jakelatham.com/radical/projects/new_wing/ Race writeup results is in the "2008 races" section for La Junta June... Cheers all! -Jake
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Ren		#9	[url]	[-]
Registered User Posts: 523 07/08/08 00:07:49	Jake, Dump your mainplane AoA back down to perfectly flat, you'll get less separation that way. As long as you keep the gap convergent toward the rear, a plain flap as you are using here will work just fine. While the slotted flap wing a short lip arrangement is the most common configuration (that's the "indented" method you mentioned), the reality is that it is only a few percentage points more efficient than an external airfoil flap. There's a long way to go yet for you in terms of finding a good set of airfoils to work with (that part can take quite a while, and CFD helps one hell of a lot...), but your basic test here I think shows promise. Can you do fiberglass work to build new wings? Cheers, Rennie
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Jake Latham		#10	[url]	[-]
Registered User Posts: 403 07/08/08 08:37:48	Ren - I'm just getting started learning how to do fiberglass. A friend just taught me how to repair the @(!* Radical splitters, so I think wings are a ways off for my skillset. One thing I wanted to make sure I was using the right definition on, which I'm basing on the illustration from McBeath's book, is AoA. The Radical wing has essentially no camber, so measuring AoA was as easy as putting the level on the top surface of the wing. However, the APR wing is fairly heavily cambered. So, is the AoA measured from leading edge to trailing edge, (which appears to be the case, illustrated from the book), or along the flat upper surface of the wing? Pic: http://www.jakelatham.com/radical/projects/new_wing/DSC03552.JPG (note goofy profile of these wings too...) If so, then to run at 0* AoA, the lower surface of the wing would actually be inclined somewhat relative to the airflow. Measuring the wing flat surface vs the complete chord (including the cambered section) is about a 4* difference in measurement, IIRC. (I don't have them here to measure right now). Does that seem OK? Cheers, -J
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JLSchuster		#11	[url]	[-]
Registered User Posts: 7 07/08/08 12:19:45	I have the same APR airfoils on my miata. In a nutshell, if you're in clean air and want to minimize drag then the lower element will indeed be at a negative AOA, but the overall AOA will be positive due to the interaction between the airfoils. How to measure exact AOA? I have no idea. I just experimented with various angles and measured top speed and corner speed on a section of track that I'm intimately familiar with. You may want to play with javafoil to give you a better idea where to start. This is a good example of what you can learn (incidentally, using the same airfoils): http://corner-carvers.com/forums/showpost.php?p=559773&postcount=52
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Ren		#12	[url]	[-]
Registered User Posts: 524 07/08/08 12:23:31	Jake, For rough measurements, measure AoA from leading edge to trailing edge. In your case, the wing will take a bit of a nose-up appearance, yes. The reality is a bit more complicated, as what you'd really want to measure there is the point where the camber line intersects the leading edge, to the point where the camber line intersects the trailing edge. In other words, true 0º AoA is a bit more nose-up than just measuring across the upper surfaces of the wing. Properly done, I would expect that carrying as much wing as you mentioned would cause the car to understeer badly - that just points to the "inadequacies" of the wing profiles you're using, so nothing unknown or surprising really. You're making a bit more downforce, sure, but the drag penalty is significant in this test. The right airfoil will make all the difference in the world. For instance, on the development work we are doing for Mark Jaremko, we modeled the full car in CFD and created a custom single element high-camber airfoil to go right down on the deck to activate the rear diffusors, while keeping his upper element intact. We started off with only a few degrees of angle on the lower wing, and it stuck the rear end of the car so hard he felt like the car might do wheelies... we've since backed off on the wing angles to get balance back in the car, but the result is that he's ended up with a car that has massive grip in the corners, and as a bonus he's picked up a MPH or two going down the straights compared to the stock wing setup! And development work continues... Even without going the CFD route, just picking a good solid low speed airfoil from the books would be a huge improvement over the APR wings... Cheers, Rennie
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Jake Latham		#13	[url]	[-]
Registered User Posts: 404 07/08/08 13:28:55	Ren - OK, good, glad I was understanding the diagram correctly, in terms of the camber line and AoA. In practice, I'll just measure from top edge to top edge. Wanted to make sure the "nose up" actually did make sense in that regard. The wing did absolutely stick the back end, which is what I was going for. I had focused so much on front grip (a typical sore point for Radicals), that the car had finally become a bit untrustworthy at the back end. Darn thing is actually pretty darn balanced now. Agreed that the wings have some "inadequacies", but they excel at the primary metric that governs my tinkering: cost. Thanks for the help - eager to see what next time out brings. -Jake
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fokoracer	CFD for mortals....	#14	[url]	[-]
Registered User Posts: 187 07/09/08 01:02:16	While I know some of you make a living doing this stuff, I was wondering if there's anyway a mere mortal like myself could do useful modeling with CFD? In other words, is there a reasonably priced and functional bit of software that would work for us who are not at the bleeding edge of the DSR arms race? I would love to do some of this stuff myself. I like the tinkering anyhow and am technically adept. But I don't have the time or bucks to make part after part and do real world test days. I think a "little" CFD work on the computer might save some wind tunnel time??? Thoughts? Fabian
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Ren		#15	[url]	[-]
Registered User Posts: 525 07/09/08 03:03:34	Fabian, If you're asking about doing full car CFD, then I'm afraid the short answer is "no" to reasonably priced... on the other hand, if you want to do simple airfoil based caculations to play around with airfoils, there is a fairly large selection of freeware and $50 price range desktop software that will do the basic calcs for you for standard airfoil ranges. I feel like we've done about 10 years worth of development effort in the last 3 months, given the number of iterations we've gone through in CFD. Obviously there is no substitute for the real world, but so far we've seen very good correlation to the feedback we're getting from Mark. We're not getting it perfect out of the box, adjustment-wise, but it's been awfully close, and there have certainly been no nasty surprises. Cheers, Rennie P.S. - finally did get around to putting the full Dauntless bodywork & tunnels into CFD. Drop me an email if you'd like me to forward the PDF case study.
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pleonard2000.socalpeeps		#16	[url]	[-]
Registered User Posts: 3 07/09/08 19:47:28	Jake, FYI ... the 9.25" Radical wing (the low downforce wing) DOES have some camber ... about 7%. In order for me to measure proper AoA, I sketched a line on the outside of the end plates that coincides with the leading edge/trailing edge line. I then put my digital camber gauge on this line. Also be sure to take note of any slope of the ground that you might be parked on. Aside ... at the last La Junta event, I mentioned that I had the low downforce wing, and someone asked "Why do they even bother to make one?" I'm looking forward to adding the small 2nd element. Thanks the the guidance on overlap and gap, etc. I'll let you know if I get a hot wire foam cutter ... I, too, was disappointed with the flatness of the APR airfoil, so I might experiment with making my own wings. It's pretty easy, really. We could make a set of wings in an evening. No problem. They'd be lighter than the alum ones, too. We can combine your new f/g skills with some foam cutting and bagging! The hard part would be selecting an airfoil. Oh ... from my freeware airfoil calcs, the 9.25" Radical wing at 0* AoA has 60% of the downforce compared to 5* AoA. Also ... my estimates for adding the 5" upper element will result in twice the downforce of the single 9" wing. Paul Leonard Driving Force Motorsports
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