Landracing Forum
Tech Information => Technical Discussion => Topic started by: robfrey on May 27, 2009, 01:03:26 AM
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Hi guys,
I need some tech advise.
Is it better to run the tires of a lakester right against the body or is it better to keep them far enough away not to ruin the laminar airflow down the sides of the body. We will running in the AA/BGL class. Our car currently has some "boat tailing" after the rear wheels but it will have much more next year so please keep that in mind when helping me with decision. This car was Dave Hallers #93 lakester but we have added suspension front and rear for being able to run at Maxton.
(http://i436.photobucket.com/albums/qq89/robfreyvogel/No93%20Lakester/Lakesterreartop52509.jpg)
(http://i436.photobucket.com/albums/qq89/robfreyvogel/No93%20Lakester/Lakesterrear52009.jpg)
(http://i491.photobucket.com/albums/rr280/dhaller-2008/100_6073.jpg)
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my 2 cents says wide.......but I'm biased
(http://www.landracing.com/forum/index.php?action=dlattach;topic=862.0;attach=10971;image)
being a lakester they're out in the wind anyway , we figured the expense of narrowing the track gave us two things , turbulence close to the body(bad) and reduced stability if we got her sideways( bad too).............
The penalty is a bit of extra axle, in our case the frontal area of that is minimal....
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my 2 cents says wide.......but I'm biased
(http://www.landracing.com/forum/index.php?action=dlattach;topic=862.0;attach=10971;image)
being a lakester they're out in the wind anyway , we figured the expense of narrowing the track gave us two things , turbulence close to the body(bad) and reduced stability if we got her sideways( bad too).............
The penalty is a bit of extra axle, in our case the frontal area of that is minimal....
Thats the same conclusion I reasoned. Your car looks mean in that picture. How fast has it been?
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Have to agree with Dr G--------haven't got a clue but I'm biased too!
Years ago someone told me to keep at least 9" between the body and wheel. Another question: On my lakester the rear track is about 6" wider than than the front. I had plans on cutting down the rear to be the same width as the front which is 44" or even put it inside the front a little. It hasn't been in the budget yet. I'm leaving the differential open for now. I'd appreciate advice on this myself. Not tryin to steal this thread but to expand it.
If your lakester is the blue one pictured I would leave the wheels where they are. With the headers and all hanging out, there probably would less turbulence with the wheels close to the body. There are people on this forum that can help you with areo much more than this guesser! I hope they will join in on this thread.
Harvey
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If I were going to run that much power---I would bring them in---for aysmetrical thrust reasons---like a dragster
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The biggest drag contributors (besides the tires themselves) on this one iare the blunt back end and the zoomies-in-the-air headers. JMHO, I would do three things:
1. Put 4-into-ones on both sides with the exhaust pointed aft. Both drag and residual thrust will improve. Zoomies are VERY peaky, www.burnsstainless.com has a great header design service to create the broad powerband needed for LSR without sacrificing the top end.
2. Close out the tail with a proper fairing. Your chute packs face almost vertical anyway, so a tail section/diffuser to fill in the separation will be the biggest drag reduction improvement possible.
3. Leave the wheel track wide. The tires of any lakester are guaranteed to create separated flow, and keeping this away from the body is the best choice. If anything, the rear track should be wider to allow air to cleanly flow between the tires and the body. If this is impractical, look at how Group B and Prototypes use diffuser fences to create vortex flow to fill in the back of the rear tires.
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I have heard very good things about Burns Stainless.
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We run them wide (44 inch) track in the front and narrow against the body (29 inches) in the rear... maybe it could go faster if they were different, just don't know.... never tried anything else after Lynn Yakel told us to do it that way when we converted the liner (he assisted Ben Jordan in the design) to the lakester. Of course we don't have a real high HP application like the fast guys.
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I know this is not the same but when we ran my friends rear engine roadster (lakester with a roadster body) on a CFD program we found that the front wheels liked 6" (each car would be different) away from the body. The rear was pretty much dictated by the trans axle.
3. Leave the wheel track wide. The tires of any lakester are guaranteed to create separated flow, and keeping this away from the body is the best choice. If anything, the rear track should be wider to allow air to cleanly flow between the tires and the body. If this is impractical, look at how Group B and Prototypes use diffuser fences to create vortex flow to fill in the back of the rear tires.
Also what Blue said about filling the back of the tires has a lot of merit. We saw some good gains on the CFD program there. This what we did and you could do the same if you wanted. We have axle fairings with strakes on the bottom of the fairing to direct the flow to the back of the tires.
I think with a rounded nose like the BB1 stream liner you should also see some better flow around the front. Tony
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The biggest drag contributors (besides the tires themselves) on this one iare the blunt back end and the zoomies-in-the-air headers. JMHO, I would do three things:
1. Put 4-into-ones on both sides with the exhaust pointed aft. Both drag and residual thrust will improve. Zoomies are VERY peaky, www.burnsstainless.com has a great header design service to create the broad powerband needed for LSR without sacrificing the top end.
2. Close out the tail with a proper fairing. Your chute packs face almost vertical anyway, so a tail section/diffuser to fill in the separation will be the biggest drag reduction improvement possible.
3. Leave the wheel track wide. The tires of any lakester are guaranteed to create separated flow, and keeping this away from the body is the best choice. If anything, the rear track should be wider to allow air to cleanly flow between the tires and the body. If this is impractical, look at how Group B and Prototypes use diffuser fences to create vortex flow to fill in the back of the rear tires.
The zoomies are gone. Twin turbo BBC is now the plan. Headers will tuck within the chassis and should be much cleaner.
I want to do something with fairing in the rear but we got a late start and are rapidly running out of time. The engine will make over 1800 hp at Bonneville elevation so this year it' going to be the Fast Freddie approach and install a bigger hammer. The trick has been to do enough engineering that allows us to improve the bodywork next year without redoing all we did this year.
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The Reverend and I spent a lot of time discussing exhaust location. An aero engineer told us two things , the first was that it would give us thrust. Now with a tame V6 that's not going to be a lot , but it is thrust. The second was that rapidly cooling gas is going through a vast volume change, thus very hot exhaust may well be reducing in volume many times over as it leaves the tailpipe...this is a very useful thing to add to a turbulent wake.....his contention was that it would have a "calming effect", thus helping to reduce drag.
However the most important aspect is that which Blue( love yer work Blue) mentioned, but I would like to add something.
1. Put 4-into-ones on both sides with the exhaust pointed aft. Both drag and residual thrust will improve. Zoomies are VERY peaky, www.burnsstainless.com has a great header design service to create the broad powerband needed for LSR without sacrificing the top end.
The last thing you want is exhaust gas blasting out through what remnants of attached flow you have down the sides of the body, let alone having zoomies hanging out there.
Hence , the exhaust on our car leaves the very last point of the body pointing straight back into what wake we are leaving.........
(http://www.landracing.com/forum/index.php?action=dlattach;topic=862.0;attach=10957;image)
BTW Robfrey, we haven't gone that fast yet, read about it here
http://www.landracing.com/forum/index.php/topic,862.628.html
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The last thing you want is exhaust gas blasting out through what remnants of attached flow you have down the sides of the body, let alone having zoomies hanging out there.
Hence , the exhaust on our car leaves the very last point of the body pointing straight back into what wake we are leaving.........
(http://www.landracing.com/forum/index.php?action=dlattach;topic=862.0;attach=10957;image)
BTW Robfrey, we haven't gone that fast yet, read about it here
http://www.landracing.com/forum/index.php/topic,862.628.html
That is absolutely the best tail closure I've seen since Bub-7. Where are the chutes?
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The last thing you want is exhaust gas blasting out through what remnants of attached flow you have down the sides of the body, let alone having zoomies hanging out there.
Hence , the exhaust on our car leaves the very last point of the body pointing straight back into what wake we are leaving.........
(http://www.landracing.com/forum/index.php?action=dlattach;topic=862.0;attach=10957;image)
BTW Robfrey, we haven't gone that fast yet, read about it here
http://www.landracing.com/forum/index.php/topic,862.628.html
That is absolutely the best tail closure I've seen since Bub-7. Where are the chutes?
(http://i227.photobucket.com/albums/dd35/Jarman-Stewart/th_P1130174.jpg) (http://s227.photobucket.com/albums/dd35/Jarman-Stewart/?action=view¤t=P1130174.flv)
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It all looks a bit hillbilly in that shot , it was at the time that we were still sorting out a catch for the doors. The anchor point for the chute is just above the centre of gravity and although it doesn't look like it there is a clear straight line back from it out of the car. We haven't yet done the 175 chute run but I did inadvertantly pop it on the test track and from all accounts it launched, filled and flew clear of the bodywork. Another advantage of that tail treatment is the chute deployment . Anyone who has seen exhaust condensate hovering behind a road car on the move will be in no doubt that there are dead spots behind vehicles and they could indeed hinder chute deployment, we won't have that problem. The problem we do have is finding a catch that will hold well enough, and not too well so's the solenoid can't trip it.