TimZ Posted April 8, 2011 Share Posted April 8, 2011 (edited) You want to rethink that estimate just a bit? Care to clarify your question a bit? The only estimate that I see was in the change in suspension travel, which would imply an increase in downforce of somewhere between ~400 and 550 lbs, relative between the "tail" and "no tail" tests. Sounds like quite a bit, but doesn't sound like it's out of the realm of possibilities... Edited April 8, 2011 by TimZ Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 8, 2011 Share Posted April 8, 2011 Considering the whale tail spoiler put out 250 lbs at 120 mph in the wind tunnel, and lift is exponential by way of velocity squared, 550 lbs at 70 mph sounds way out of the realm of possibility to me. Quote Link to comment Share on other sites More sharing options...
Leon Posted April 8, 2011 Share Posted April 8, 2011 Considering the whale tail spoiler put out 250 lbs at 120 mph in the wind tunnel, and lift is exponential by way of velocity squared, 550 lbs at 70 mph sounds way out of the realm of possibility to me. Care to explain your math? I calculate about 200lb at 70mph from Tony's numbers. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 8, 2011 Share Posted April 8, 2011 Figure the compression on each spring and how much pressure it takes to get that amount of compression, multiply by the number of springs. Quote Link to comment Share on other sites More sharing options...
Leon Posted April 9, 2011 Share Posted April 9, 2011 Figure the compression on each spring and how much pressure it takes to get that amount of compression, multiply by the number of springs. Doh! There are 2 springs in the back... Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 9, 2011 Share Posted April 9, 2011 "Which Tail" would be one question to ask... Someone says 250 for the one in the wind tunnel at 120mph--'which tail'? (275X2)*.5= 275# (275X2)*.7= 385# So (275+385)/2=330# by a really rough measurement utilizing O-Rings on a strut piston rod, magic marker and string, and well within the realm of 'rough estimate' trying to explain why my car no longer lost traction in 3rd gear under boost in a particular corner (or in a straight line for that matter, I was more concerned at one particular corner I thought I should be able to take flat out without having to lift from traction issues.) It seemed reasonable that the car had somewhere around 300# of downforce generated by the wing as adding 250# of shotgun pellets in bags didn't quite tame the issue in a straight line. Why the 50mph differential? Who knows, maybe it's like dyno numbers. Nobody else I know has problems with traction like I did with only 350HP at the rear wheels. Maybe it was more. I wasn't hung up on sizing up my problem and talking with other people about it, I just concentrated on solving it and trying to get rough estimations on what it took to do so. Not whitepaper presentation to the SAE quantification, but enough rough measurments to get an idea what I had. 275# is a recollection as well. This was 1991 when I was doing all sorts of other pressure-cel tests on the body and it's parts. They may have been 250#, as I remember Eric Messley saying I DEFINATELY needed stiffer springs in the back and at the time he was running 275's so maybe I was running 250 or 225's. They are RSST Springs from Japan one day maybe when I get the time I can take them out and spring scale them to get an exact number. It's not like the Japanese Cartons are extant to read the Kg/Cm numbers any more. They are Red Springs, does that help any? My guess was the downforce added was more than 250# as birdshot didn't cut it. Half and Inch or more of spring compression seems to bear that number out to some extent. Close enough for me. Maybe that's why I put up as much as I did towards the aero tests when I learned about it. Better numbers from a better testing environment than I had available in 1991. When was that again? What? 20 years ago? Here's your boxing gloves John---feel free to remove the flypoop out of the plate of ground black pepper there now. Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 9, 2011 Share Posted April 9, 2011 (edited) Wow, I just went and read my post---that was supposed to be 70% Compression (.7 .5-1") 70% of a 275#/1" is as calculated above. But like I said, they may have been 250's...or maybe 225's. I don't recall the packaging numbers from 19894 1984 when I bought them and installed them. "Tighter than most, not as tight as Messley's" Maybe John Coffee can shed light on how Eric had the back set up when he was running BSP in 1991/1992 seasons. Less than that. That's what my springs were, "less than that" -- and they compressed .5 to .7 of an inch at roughly 70-80mph. Edited April 9, 2011 by Tony D Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 15, 2011 Share Posted April 15, 2011 Discussing this with Frank and Joe in the truck today I remembered that I also had a serious speedometer error. I was recalling spedometer number, when in fact I showed 110mph on the speedo it in reality was 137mph. So this same error might be retroactively applied to my speed numbers. Perhaps me showing 70mph was closer to 90 mpd... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 15, 2011 Share Posted April 15, 2011 (edited) Speed = unknown. Spring rate = unknown. Spring compression = unknown. Result = useless. I did some simple calculations out of Tune to Win, and they make your testing method look even more dubious. Consider that longitudinal weight transfer is acceleration g(weight x cg height/wheelbase). So let's assume that you accelerated relatively slowly, like 0-60 in 10 seconds. That is roughly .3 g according to this caclulator: http://measurespeed....calculator.php. Make a guess at the weight with you in it at 2550, cg height at 21" and wheelbase at 91, and you get 176 lbs of weight transfer to the rear WITHOUT the whale tale. You didn't mention whether you measured the zip ties on the strut or had someone else do it for you while you sat in the car, but that would also skew the numbers by a pretty large margin. Factor in a crack in the pavement anywhere along your test run and the resulting suspension movement, and you really don't have anything useful left. I think what you were trying to do works reasonably well if you have data acquisition and you can monitor the compression of the strut over a period of time and at different speeds, but what you have there is just a maximum displacement measure, not anything useful to calculating downforce. I've been trying to consider the effectiveness of the whale tail vs wings, and I've come to the conclusion that the whale tail is VERY efficient at producing downforce when using the wind tunnel numbers when compared to the APR wing. What I can't say is where that downforce is coming from. I brought it up on another forum and didn't get a satisfactory answer, so then I emailed Simon McBeath again and he showed me the limitations of the wind tunnel: it is easy to see the effect of the tail, but impossible to know what caused it. Quoting doesn't seem to work on this for some reason so here is the email to McBeath: Hello again. I have another question for you, hoping you could help shed some more light on a different aspect of aerodynamics for me if you have the time. I've seen on some Porsche sites where they say that whale tails are only spoiling airflow over the top of the car, and that they cannot make any actual downforce. I've also seen wind tunnel test results on a Z where they were able to make a 253 lb change in rear pressure, with at least 176 lbs of that being “downforce†at 120 mph. Data here: http://forums.hybrid...nnel-test-data/ I was interested in the Coefficient of lift required to make such a change, and how one figures that on a spoiler vs a wing. I have not come across an answer so far, and I’ve been trying all my usual knowledgeable sources to no avail. I've got a rough area of the top side of the whale tail at 6.28 sq ft, and I've plugged that into a downforce calculator (for wings) in a couple different ways. To figure out effectiveness of the tail, I'm plugging the area and the lift desired into a calculator, and just adjusting the Cl until I get the number I want to see. If you figure from the test previous that the tail made 253 lbs downforce, that works out to a Cl of 1.1, which seems VERY impressive for a spoiler. If you figure that the downforce was only 176 and the rest came from spoiling the 76 lbs of lift in the test previous, then you get .76 for the Cl. There was an APR wing tested, I believe it was the 55" span with the 7.5 and 5.5 chord lengths. I don't think this wing is sold anymore, but it was the ubiquitous dual element ricer wing in the States for a couple years. Anyway from the base test before the wing was installed to using it with the highest downforce setting, the change in pressure was 110 lbs @ 120 mph. I've figured that out at about .6 Cl on my calculator. That seems about right by gut feel for a cheap wing that may not have been at the most advantageous angle of attack. There is another whale tail for the 280ZX which was homologated for IMSA racing back in the early 80s which is much smaller and Nissan claimed 370 lbs downforce at 100 mph. http://zhome.com/History/ZXR.htm That claim seems utterly outlandish, it's Cl would have to be in the 3.5 range to get the amount of downforce from my estimate of its size. It was the ZXR whale tail and its wacky numbers piqued my interest and got me wondering about the efficiency of the tail that had been put in the wind tunnel. So what I'm interested in knowing is which is the proper way to use these numbers, and whether I've done my figuring right. I realize that the whale tail might have a significant effect on the flow of air underneath the car as well, so it may be a combination of the spoiling of the airflow on top and some downforce production with speeding up airflow on the bottom, but the numbers look almost too good to be true even out of the wind tunnel tests. These were not flat bottom cars or anything, they were stock underneath, and Z's have lots of edges sticking out to catch air on the bottom, and the wind tunnel did not have a rolling road, just a stationary tunnel. In asking others about this, I’ve gotten a pretty uniform: “Speeding up airflow below the car is the source of the downforce.†I understand why that would seem to be the case, basically they’re assuming that the whale tail acts as a Gurney on a wing and that accelerates the air below the car, creating the downforce. In actual practice though, that seems very unlikely due to the rough underbody. Maybe I’m underestimating the effect of the tail though, I don’t know. My thought is that the whale tail is acting as a kind of parachute, and the leverage of the whale tail sticking out behind the car is what translates this into downforce. The only problem with my theory is that the coefficient of drag actually DROPS .05 from the test previous to the whale tail test. ... Thank you for your time, Jon Mortensen Response: Hi again Jon Time for a quick reply, which is to say that without the benefit of CFD it just isn't possible to figure what the direct contribution from a wing or spoiler is on a car because of all the interactions you mention. All that's possible to say is that all the things you mention will be happening. So there will be raised pressure on the deck ahead of a spoiler, leading to downforce, and reduced pressure behind the spoiler, leading to reduced base pressure in the wake, which in turn will lead to reduced pressure under the car. If you were to CFD a model with a whale tail you could assess the forces on the whale tail itself and those on the car body separately, which is about the only way I know of that allows the various contributions to be evaluated. In the wind tunnel, all you can do is measure the forces at the front and rear axles through the tyre contacts. So whatever 'delta -CL' you measure is related to the car as a whole. And a car's coefficients are calculated using frontal area, not plan area don't forget. Only wings are conventionally referenced to plan area. So this complicates any attempts at factoring out the effect of specific parts too! But like I say, without CFD you can only address the changes to the whole car's coefficients, which the wind tunnel alllows to be split as CLfront and CLrear. I'm ashamed to say we haven't done any rear spoiler evaluations in the wind tunnel for Racecar Engineering... So the only data I can point you at is the CFD study in CC Downforce and its succesor CC Aerodynamics, 2nd edition out now. Hope that helps... Cheers Simon So far my best guess is that it is the top side that produces the downforce, and just as a wing is more effective if you hang it off of the back of the car because it has more leverage there, so too the extended length of the spoiler is what gives it its power. Regardless, I really do think that it is a good option for efficient downforce, but many racing classes won't allow them (nor will they allow wings hanging off the back of the car to get the same increased leverage). Edited April 15, 2011 by JMortensen Quote Link to comment Share on other sites More sharing options...
260DET Posted April 18, 2011 Share Posted April 18, 2011 It may be worth looking at how Gurney flaps make downforce to understand how flush fixed aero devices like whale tails do it. My understanding is that a Gurney makes downforce simply by deflecting air upwards and thereby placing a load (downward pressure) on the surface it is attached to. Look at the S30 bob tail spoiler, it's basically a big Gurney. Then there are the 'bath tub' rear spoilers used on RX7's, Walkinshaw Holden Commodores and some Porsches. They basically seem to deflect a down flowing air stream towards a horizontal flow and then force it up with a Gurney type lip at the back. Anytime you deflect airflow a force is created, its just a matter of harnessing that force for your purposes. A wing had the added advantage of being able to use both sides of its structure to produce an aero effect, plus it is able to be placed wherever it is most effective. So it is potentially a more effective device than its flush fixed aero alternative. You have PM by the way Jon. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 19, 2011 Share Posted April 19, 2011 The Gurney does deflect air upwards, but I think the more important effect is that this creates a vortex behind the Gurney. This vortex in turn sucks the airlflow tight against the low pressure side of a wing, where it is normally liable to separate. This reduces flow separation and allows for a more aggressive angle of attack. Now in the case of the whale tail, the argument seems to be that the whale tail acts like a Gurney which is trying to keep the flow attached to the bottom side of the car. The flow really can't be attached, because the back of the car isn't a smooth surface at all, but creating more low pressure on the bottom side could pull more air out from underneath. I think that this might be happening to some degree, but since the bottoms are not flat and the flow cannot stay attached due to the shape of the rear valance/bumper/whale tail, I think the advantage the whale tail has is more due to leverage. That's pure gut instinct though. Quote Link to comment Share on other sites More sharing options...
260DET Posted April 20, 2011 Share Posted April 20, 2011 Whaletail setups can effect airflow around and under the back of the car for sure, but to get any real benefit would usually have to be combined with something like a rear diffuser. Any air attachment to the bottom of a car due to the effect of a whaletail is a secondary effect at best I think, its primary effect and main benefit is as I have already described. Having said that, the problem with discussing aero is that the effects always depend on the physical shapes and their interactions so it gets complicated very quickly and makes it difficult to be definate about anything. Quote Link to comment Share on other sites More sharing options...
palauoriginal Posted April 26, 2011 Share Posted April 26, 2011 use both. those rauh welt Porsches use them. not that that legitimizes the combo... Quote Link to comment Share on other sites More sharing options...
gnosez Posted April 27, 2011 Share Posted April 27, 2011 So the man who built the 280ZXTT says in no uncertain terms that the reason they put those whale tails on is because they worked, period. Quote Link to comment Share on other sites More sharing options...
Kingbaby Posted September 3, 2012 Share Posted September 3, 2012 Hi all, I'm a newb...I'm looking to visually enhance and aerodynamically increase the role of my wing! I read this link...my head started to hurt, along with my eyes... http://forums.hybridz.org/index.php?/topic/55944-windtunnel-test-data/ picture of wing picture of MCR wing with a more pronounce top blade picture of Amuse wing with different top blade and gurney flap So my question to all the engineers, and forum know it alls...in short what do you think the pros/cons of raising the stock nismo V3 wing? quotes from my thread over on my350z.... any inputs is appreciate it...loving this site so far! Either way removed my wing today in preparation for awesome or complete and utter failure! Pop trunk and remove the six black tape circles covering (6) 10mm bolts and (2) 10mm nuts! A whole bottle of this is required! Not even kidding...floss and plastic knife help! The mess it left? Authentic Nismo 350Z Z33 V3 Wing Spoiler (<---for engine searches) is 10lbs max my house scale is accurate but by myself wasn't able to hold the wing and take picture! (3) 10mm each side (6) total...1 Philips head bolt' date=' didn't size it holds the center blade down [img']http://i276.photobucket.com/albums/kk7/King-Baby/2amR/3346AEF5-F268-407F-9F1B-56C2CD1FD0DB-3796-0000020365BC5476.jpg[/img] Seperated! For the high rising idea, it's not a smooth/flat surface. So the mount gonna have grooves in it. Hey so my mind been racing since I removed the wing! Where are all the engineers at? I'm only good at removing things lol. Couple questions: So the V2 doesn't have a center stanchion' date=' why doesn't the V3? Would rising it to the roof line be too much stress on the wing now that it's 4 pieces? Currently drawing a design for the riser so that is aesthetically pleasing to the eye! Thanks Doodle! [img']http://i276.photobucket.com/albums/kk7/King-Baby/2amR/23851822-31BA-465E-9B3F-5876AC3BD73F-5468-000002AE5141AA97.jpg[/img] Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 3, 2012 Share Posted September 3, 2012 Not sure you you would attach the uprights without it looking really kluged. I'd just go buy a spoiler and get a good wing and install them separately. Quote Link to comment Share on other sites More sharing options...
Kingbaby Posted September 3, 2012 Share Posted September 3, 2012 Not sure you you would attach the uprights without it looking really kluged. I'd just go buy a spoiler and get a good wing and install them separately. Thanks for the input first off... I think I should clarify what I'm envisioning. Take a look at the picture of the wing seperated, the middle stantion/blade will be removed. Therefore leaving just the two wings...with a 4 inch riser. like so I have a APR 300 wing on standby, but would like to see this materialized first. thanks again Quote Link to comment Share on other sites More sharing options...
Mikelly Posted September 3, 2012 Share Posted September 3, 2012 (edited) So the whole purpose of that application on the Porsche 911 is to get the wing into the clean air. the base and wing work together to provide the downforce and stability. It's added to the RSR front bumper/cannards generally to balance the package. These cars tend to see a 12-15 mph increase in speed thru the uphill esses at VIR, but lose straight line speed on the long straights, due to the drag the wings cause. The car that won this year's ultimate track car challenge, a 2008 Z06, was running the LG Motorsports World Challenge splitter/wing conversion and would pull on every single car at the event in the climbing esses. But took a hit in straight line speed for the same reason. So be mindful of the benefits vs. detriments of the wing and what you hope to get from using it. Mike Edited September 3, 2012 by Mikelly Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 3, 2012 Share Posted September 3, 2012 I don't normally link to Facebook, but see if you can view this picture: http://www.facebook.com/photo.php?fbid=403806673001975&set=a.301931639856146.70083.100001179367953&type=1&theater I wouldn't make your uprights anything other than straight vertically. Too much pressure at speed, and if everything is not super stiff you can get cavitation (flutter) which will beat the hell out of the mounts and uprights. If you went with separate mounts for the wing and the spoiler, you wouldn't have this issue. If your uprights fold as you go through a turn at 140 mph or into a braking zone, you might leave the track at very high velocity. There are vids of wings and supports failing on youtube. Get a quality wing and get it mounted securely. I don't know about that APR wing that you have, but I do know that I was at an autox a couple weeks back and a guy with an EVO had their double element aluminum wing and it was cracked pretty badly where the uprights bolted to it. He was aware of the cracks and said that they happened at a track day and he hadn't bothered to replace the wing yet. Quote Link to comment Share on other sites More sharing options...
Kingbaby Posted September 3, 2012 Share Posted September 3, 2012 So the whole purpose of that application on the Porsche 911 is to get the wing into the clean air. Mike That's the same reason for raising this wing. At 4 inches it will be at the roof line just like any other wing I buy and attached to the trunk. Thanks I wouldn't make your uprights anything other than straight vertically. Too much pressure at speed, and if everything is not super stiff you can get cavitation (flutter) which will beat the hell out of the mounts and uprights. If you went with separate mounts for the wing and the spoiler, you wouldn't have this issue. If your uprights fold as you go through a turn at 140 mph or into a braking zone, you might leave the track at very high velocity. There are vids of wings and supports failing on youtube. Get a quality wing and get it mounted securely. I don't know about that APR wing that you have, but I do know that I was at an autox a couple weeks back and a guy with an EVO had their double element aluminum wing and it was cracked pretty badly where the uprights bolted to it. He was aware of the cracks and said that they happened at a track day and he hadn't bothered to replace the wing yet. I couldn't get to that link...I'll try on my desktop, I'm on my phone at the moment. The riser will be straight after reading, anything fancy and not tested will more than likely fail. This is the wing, but it's exactly for the 350Z. I'll be having a shop fab pedestals to the same specs as the apr wing. At 4 inches it would put the wing right below the roof line. So not too much into 'clean air' , but into more of it? Again thanks for the feedback... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.