Z-TARD Posted October 12, 2006 Share Posted October 12, 2006 Is the flow seperation point dependent on speed? If so, I suppose you'd have to tune your vortex generator location to a given vehicle speed? I've pretty much given up on the louver idea anyway, I was thinking about that one day when I was more bored than usual... I would tend to think that the flow seperation point would move futher up the hatch towards the top as speed increases. The air rushing over the car would have less time to displace downwards over the sloping hatch. Following this line of thinking, having the vortex generators located near the top of the hatch would effectively provide coverage for most of the speed range by promoting airflow over the hatch at an early point. The vortex generators coupled with a whale tail set at a moderate angle would probably be very effective at producing downforce, with minimal impact on drag. For my car, I've been seriously considering the vortex generators coupled with an aluminum Cobra Daytona Coupe style spoiler like the one I made for the "Pinks!" car. At the current pace, this will be completed sometime in 2012..... Mike Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted October 12, 2006 Share Posted October 12, 2006 Jon, Very good point, which I had forgotten. I'm sure there is a trade off somewhere along the line. You might also be able to delay the spill around the sides of the car (C-pilar) towards the point of separation and reenergise the flow that way? Dave Quote Link to comment Share on other sites More sharing options...
260DET Posted October 12, 2006 Author Share Posted October 12, 2006 Link to a Missybitchi VG tech paper, last page provides a useful summary. http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf#search=%22vortex%20generators%22 Quote Link to comment Share on other sites More sharing options...
Mikelly Posted October 12, 2006 Share Posted October 12, 2006 With regards to the "BRE" spoiler, I know well the history of that "works" part and how it was developed elsewhere in the world. However, Here in the good ole US of A, which is where fully 90% of our members hail, We'll continue calling it the B-R-E... History lesson over. Mike Quote Link to comment Share on other sites More sharing options...
JIM73240Z Posted October 12, 2006 Share Posted October 12, 2006 point blank, if you want max down force, get a wing and get it up as high as you can to get clean air around it. if you want to negate the up lift by the shape of our cars, i think the air needs to be directed back down the hatch to a spoiler/ tail. the vortex gens allow the air to follow the shape of the car better to be used at the spoilers. jim Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 12, 2006 Share Posted October 12, 2006 Link to a Missybitchi VG tech paper, last page provides a useful summary. http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf#search=%22vortex%20generators%22 That's an interesting read. Apparently a .006 change in the cD was enough for them to put it on a production car. But their wing is so high in the airflow that I think it didn't have as big an effect as it would on our Zs with a spoiler. I never would have thought to angle the outermost VGs to the center like they did there. That would almost have the effect of fences on the sides of the hatch (something else I had considered at one point). The other thing to consider is where to place the VGs. Do you put them at the trailing edge of the roof, or is there already flow separation there? Quote Link to comment Share on other sites More sharing options...
74Adam Posted October 12, 2006 Share Posted October 12, 2006 So, has anyone here actually tried the supra style spoiler? Quote Link to comment Share on other sites More sharing options...
veritech-z Posted October 12, 2006 Share Posted October 12, 2006 Which one is the supra style? Quote Link to comment Share on other sites More sharing options...
JIM73240Z Posted October 12, 2006 Share Posted October 12, 2006 is that like the cal wing or the one that you see a lot on mitsu eclipsiseses. jim Quote Link to comment Share on other sites More sharing options...
74Adam Posted October 12, 2006 Share Posted October 12, 2006 Well, the one I'm thinking of is the one from the old supra's of the early eighties. That was the real angular style. Here ya go: http://cgi.ebay.com/ebaymotors/1985-Toyota-Celica-Supra-Parts-Project-Car-Blue_W0QQitemZ110042409657QQihZ001QQcategoryZ6447QQrdZ1QQcmdZViewItem MSA and VB used to sell a version of this spoiler that fit the S30. I say "used to" because I just looked in my latest MSA catalog and it isn't there. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 12, 2006 Share Posted October 12, 2006 Veritech, the spoiler we're talking about is the one at the top of the hatch on the Supra, not the one at the bottom. I think Mike kZ has one. As far as MSA goes, I just looked online and they aren't selling whale tails either. And they stopped selling their street flares. Bummer. Wonder if it would be possible to track down who the manufacturer for MSA was. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted October 12, 2006 Share Posted October 12, 2006 I know I've seen one in a picture of Mike KZ's car once before, I don't know if he still has it. I was curious about that spoiler as well. What about something like what Toyota offered for the Altezza that looks like the "BRE" spoiler, but at the top of the window? Quote Link to comment Share on other sites More sharing options...
260DET Posted October 13, 2006 Author Share Posted October 13, 2006 That's an interesting read. Apparently a .006 change in the cD was enough for them to put it on a production car. But their wing is so high in the airflow that I think it didn't have as big an effect as it would on our Zs with a spoiler. I never would have thought to angle the outermost VGs to the center like they did there. That would almost have the effect of fences on the sides of the hatch (something else I had considered at one point). The other thing to consider is where to place the VGs. Do you put them at the trailing edge of the roof, or is there already flow separation there? How about referring to one of those airflow over the body illustrations that are around for our cars? Some of them use different colours too eg red to show a high pressure area. Quote Link to comment Share on other sites More sharing options...
denny411 Posted October 13, 2006 Share Posted October 13, 2006 I have two of the supra style spoilers. It is the same one that Mikekz has. I opted to use the whale tail instead. Not neccessarily for aerodynamics,but it seems to flow better with the lines of the car. if someone is interested in one of the spoilers,pm me. i don`t have any specific plans for them. Denny Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 13, 2006 Share Posted October 13, 2006 How about referring to one of those airflow over the body illustrations that are around for our cars? Some of them use different colours too eg red to show a high pressure area. I've seen drawings, but never an actual illustration or test result with pressures in different colors. Can you find one and provide a link? Quote Link to comment Share on other sites More sharing options...
veritech-z Posted October 13, 2006 Share Posted October 13, 2006 I've only seen the 280zx one that proxlamus posted on one of the super long aero threads of days gone by. Driftn280zxt asked for one, so I just reposted it in the vendors forum under the 280zx widebody kit thread, along with a link to the thread it appeared in. It only has one color of smoke. Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted October 13, 2006 Share Posted October 13, 2006 Well I had a honeycomb ready to go in but never did since I needed wind that was going to have to be like 1300mph... I may still make one with a high power fan just to play with different designs. I figure that if I have a powerful enough fan I can see if something creates a huge aerodynamic problem. Mostly for testing out front ends rather than testing the drag of mirrors...In my pics I was just helping the model dry so I did not have any honeycomb in there at the time. I am just now in college and had never heard of the reynolds number before hearing about on hybridz. I wil be taking some fluid dynamics courses in the future since my major is mechanical engineering. Hopefully by then I can be testing my widebody design that I want to implement onto my Z. Yeah, uh....that guy made a circular wind tunnel and didn't even know how to scale the velocity down. You need to use Reynolds equation...and circular test sections create all sorts of issues. The best thing to have is a square or rectangular test section. Plus, he doesn't have any screens or honeycombs to get rid of turbulent or angled air. I don't know wtf they're on about the tunnel being pressurized. Most wind tunnels are below atmospheric pressure when they're running. Anyways, I'm currently trying to do a project in conjunction with Dreyer's Ice cream to save their trucks around 5% gas on the highway. But I'll see if I can get some more time to throw a Z model in there. Quote Link to comment Share on other sites More sharing options...
RedFive Posted October 16, 2006 Share Posted October 16, 2006 Olderthanme: Why 1300mph? Because Re said so? Be careful, Re numbers are nearly impossible to match. Do some reading on it, there are tricks you can pull to match up Re numbers, but it is very much a pain in the ass and sometimes not even possible. Fluid Dynamics is an okay class, but it's mostly pipe flow theory. What you really want is some sort of Experimental Aero class where you get to play with the tunnels or an Aerodynamics class where you have to work Re equations for airfoils and stuff. If you want some tips to improve your tunnel, PM me. Quote Link to comment Share on other sites More sharing options...
260DET Posted October 16, 2006 Author Share Posted October 16, 2006 I've seen drawings, but never an actual illustration or test result with pressures in different colors. Can you find one and provide a link? Can't remember, sorry, it was way back in my S30 development days Quote Link to comment Share on other sites More sharing options...
bjhines Posted October 16, 2006 Share Posted October 16, 2006 I don't want to upset the apple cart... but it would seem that there are some lines of thinking that need to be addressed... correct me if im wrong.... Hatch area: ----------------------------------------------------------------------- The problem: 1. The stock configuration would seem to achieve lift on the upper-middle of the hatch window.... This is due to the fact that air does not detach from the rear deck until very far aft.. ~ 2/3rds the way down the hatch... 2. There is spillover air from the sides... creating vortexes on either side following the top of the sails and hatch seams... these create drag and may further contribute to lift... they may also disrupt air flowing over the rear hatch and negate some lift there by detaching flow a little earlier... 3. Air comming up from underneath the car is turbulent and mixes with semi detached air spilling down the rearmost portion of the hatch and the sides.... this creates drag.... ----------------------------------------------------------------------- The solutions: We have seen a lot of different attempts at aero-bodywork... Obviously there is differentiation between race car and street car bodywork... Lip spoilers: The rear lip spoilers do not attempt to address the problems with rear end lift caused by the very smooth roof and low sloping rear hatch... they use some of that still attched airflow to create downforce at the extreme rear end of the car... So.. the lip spoilers create downforce in the most effective place... in an attempt to negate some of the lift in the upper-middle of the hatch... Obviously there is some air separation that far down the hatch... soo a taller rear lip will grab more smooth flowing air and create even more downforce... this is a good trade off... it is also astheticly pleasing... I doubt that a rear lip spoiler shorter than 3" would have any real effect... shorter spoilers may not even disrupt enough smooth airflow to cause any measurable drag... Upper deck spoilers (Supra type): These were used to separate airflow early to negate some of that rear end lift... I dont know what surprises that approach might hold for drag coefficients... and I imagine that a tall rear lip spoiler would actually create more rear end downforce... I do know that those cars had a high rear clip and the use of a tall lip spoiler would have interfered with rear end visibility... I imagine that the roof lip was a trade off to ensure good visibility... ----------------------------------------------------------------------- As far as small stick-on vortex generators go... the more you do to ensure air stays attached to the rear deck... the more lift you will generate there... they may increase the effectiveness of a shorter rear-lip-spoiler... but that might not actually achieve anything useful considering there is even more lift on the rear hatch window... also consider that the use of a "Supra type" upper lip in conjunction with a "BRE style" rear lip may not be very effective at all... the supra lip separates airflow early causing the BRE spoiler to be less effective... I have seen land speed cars with parallel "dorsal fins" attched to the sides running from the roofline to the rear of the car... these are there to keep the side vortexes from forming and causing instability at high speed in crosswinds... These are probably very effective.. but they look absolutely horrible... no one even considers them because they change the side profile so much... There are many more but I am tired... Quote Link to comment Share on other sites More sharing options...
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