Internal Body Aerodynamics
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vette427sbc
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Another McLaren 720s... with some notable bits and pieces compared to the last one...
Under car strakes that move air out from under the car to the side just after the front wheels are very pronounced. Probably around 1.5” tall.
The rear wing is active, and also an air brake I assume, judging by the massive hydraulic rams. The hydraulic feed lines are -4AN, compared to a typical Porsche 911 active spoiler with is -3 or even smaller (im referring to a 996 chassis, don’t know about the newer ones). My guess is to be able to change wing position quicker
Under car strakes that move air out from under the car to the side just after the front wheels are very pronounced. Probably around 1.5” tall.
The rear wing is active, and also an air brake I assume, judging by the massive hydraulic rams. The hydraulic feed lines are -4AN, compared to a typical Porsche 911 active spoiler with is -3 or even smaller (im referring to a 996 chassis, don’t know about the newer ones). My guess is to be able to change wing position quicker
vette427sbc
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I thought the undercar strakes were interesting considering how large and efficient the rear diffuser looks. Is it a general rule that removing as much air out from underneath is best? Even when that air can be used to generate downforce from the diffuser? These cars also have the opposite of a typical rocker panel “skirt”. They are very rounded vs. flat, like the C7Z skirts and most other track oriented super cars
phantomjock
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Yes. Think Chaparral-Sucker car. Lower pressure under body creates downforce.
A diffuser does generate downforce, generally aft of the rear wheels. The undesired-unintended consequence is stiffer springs to counteract the"lifting" of the front end due to a "fulcrum-like effect.
The "hottest" prototype cars (and F1) use tunnels for a similar effect as the strakes seen here. The tunnels help move the low pressure area more forward to get balance in downforce.
The rounded skirts(I think) are being use to shape generated vortex sheet to reduce drag around the wheels/tires.
Hers is my best guess of what the streams might look like:
Yellow are teh streams - sorry takes too long to make curves of vortex! Red arrows downforce; wing, splitter, "rocker/skirts", and blue the very slippery angle of the front wind screen.
Hope this makes sense - can't say its CFD - just one guy's opinion/idea of what might be going on.
Cheers - Jim
BTW - I did run the SR with side skirts (not authorized - but if you ain't cheatin"...) and the car was very well balanced and like riding on rails. Removed them and have ran with splitters and a wing. Now have 2 tunnels cut into the side pods and they work well. Now in the rebuild am adding a spoiler in lieu of wing. We'll see how that all goes. Still considering strakes similar to the M720.
Don't know anything about the aerodynamics but I like that car!
rtj
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That large vertical looking “wing” behind the front wheels is probably responsible for the side skirt area (rocker area) being so different from the c6 or c7.
Jim is right, vortex dominated flow down the sides.
Well it speaks volumes about how much trust your customers have in your work. Big $$$$ there.
Jim is right, vortex dominated flow down the sides.
Well it speaks volumes about how much trust your customers have in your work. Big $$$$ there.
vette427sbc
Well-known member
Your CFD makes total sense! Thank you for the explanation.
Again, this makes much more sense :thumbs:
These are pretty wild cars... I typically like “raw” cars; lots of hp and a well balanced chassis. Not much more. I think this up there with my favorites though! And I definitely get an interesting variety here. I think people find more trust in someone to work on their car when they see that I’m also an enthusiast and not just working a job to pay the bills. This McLaren had just under 400 miles on it :shocking:
rtj
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Teaser vid.
[ame]https://www.youtube.com/watch?v=JttSo9WiiM8&app=desktop[/ame]
First half is aero related.
https://www.motor1.com/news/261384/mclaren-720s-rocket-science-video/
Details much easier to see with white paint.
[ame]https://www.youtube.com/watch?v=LemZQaRs6kU&app=desktop[/ame]
[ame]https://www.youtube.com/watch?v=JttSo9WiiM8&app=desktop[/ame]
First half is aero related.
https://www.motor1.com/news/261384/mclaren-720s-rocket-science-video/
Details much easier to see with white paint.
[ame]https://www.youtube.com/watch?v=LemZQaRs6kU&app=desktop[/ame]
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phantomjock
Well-known member
BTW - both are excellent videos- THX rtj!
Continuing with the underbody areo on the M720.
I sourced the following image showing the vanes and splitter on a 520 - similar underbody thinking.
Note the mini-diffuser built into the splitter in front of the tires. These can be very powerful. One outfit did some downforce testing trackside and found these splitters gave a 200% increase in downforce of the splitter. Nice.
Also note that the "tire diffuser" is located below the duct work -- heaps of downforce I'd bet.
Also note these vanes are made as a single piece and mounted. Similar on the 720? Makes the install easier - one set of fasteners and sets the relationship of one vane to the other. Based on testing-or just smart intuition?
Here is a paint splatter test result. Not all the air leaves - just enough...
There are several great ideas here that can apply to the C3s and keep it "subtle" at the same time.
Cheers - Jim
Continuing with the underbody areo on the M720.
I sourced the following image showing the vanes and splitter on a 520 - similar underbody thinking.
Note the mini-diffuser built into the splitter in front of the tires. These can be very powerful. One outfit did some downforce testing trackside and found these splitters gave a 200% increase in downforce of the splitter. Nice.
Also note that the "tire diffuser" is located below the duct work -- heaps of downforce I'd bet.
Also note these vanes are made as a single piece and mounted. Similar on the 720? Makes the install easier - one set of fasteners and sets the relationship of one vane to the other. Based on testing-or just smart intuition?
Here is a paint splatter test result. Not all the air leaves - just enough...
There are several great ideas here that can apply to the C3s and keep it "subtle" at the same time.
Cheers - Jim
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rtj
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https://www.motor1.com/news/261384/mclaren-720s-rocket-science-video/
This guy claims to be a rocket scientist, but I suspect he may be an actor. Granted he does claim to be an aerodynamicist, but I would think a rocket scientist would not claim “laminar” flow over the front tires. It is a spinning disk! There is no way in hell that can be laminar in the true sense of the word (by definition).
I think they are creating big vortices to keep the flow somewhat attached and go where they want it. Sort of like the F1 cars we’ve been looking at.
Edit
In fact the cfd plots they throw on the screen briefly after he says that, shows the flow rolling up.
Bill Nye science guy maybe?
Yes this was bugging me since yesterday
This guy claims to be a rocket scientist, but I suspect he may be an actor. Granted he does claim to be an aerodynamicist, but I would think a rocket scientist would not claim “laminar” flow over the front tires. It is a spinning disk! There is no way in hell that can be laminar in the true sense of the word (by definition).
I think they are creating big vortices to keep the flow somewhat attached and go where they want it. Sort of like the F1 cars we’ve been looking at.
Edit
In fact the cfd plots they throw on the screen briefly after he says that, shows the flow rolling up.
Bill Nye science guy maybe?
Yes this was bugging me since yesterday
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rtj
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Actually, you could steal a lot of those ideas for a crazy c3. Given a lot of time and ambition (I’m kind of low on those right now). But a set of inter coolers at the back for some rear turbos would not be very big and could grab that rear scoop flow.
phantomjock
Well-known member
Hey you talkin' bout me?
The underbody strakes are a real keeper, like the tire air curtains many posts back, - as is full belly pan. Flow directing with diffusers built into splitter, some cool suction or boost in the rear deck... and on, and on, an on it goes. So many mod possibilities -- so little time/money/ pick one.
Cheers - Jim
The underbody strakes are a real keeper, like the tire air curtains many posts back, - as is full belly pan. Flow directing with diffusers built into splitter, some cool suction or boost in the rear deck... and on, and on, an on it goes. So many mod possibilities -- so little time/money/ pick one.
Cheers - Jim
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69427
The Artist formerly known as Turbo84
BTW - both are excellent videos- THX rtj!
Continuing with the underbody areo on the M720.
I sourced the following image showing the vanes and splitter on a 520 - similar underbody thinking.
Note the mini-diffuser built into the splitter in front of the tires. These can be very powerful. One outfit did some downforce testing trackside and found these splitters gave a 200% increase in downforce of the splitter. Nice.
Also note that the "tire diffuser" is located below the duct work -- heaps of downforce I'd bet.
Also note these vanes are made as a single piece and mounted. Similar on the 720? Makes the install easier - one set of fasteners and sets the relationship of one vane to the other. Based on testing-or just smart intuition?
...................
There are several great ideas here that can apply to the C3s and keep it "subtle" at the same time.
Cheers - Jim
I'm trying to figure out what's the purpose of some items I'm seeing there.
1) Do those small diffusers add any downforce, or are they just shaped that way to feed cooling air to the brake cooling scoop attached to the lower suspension link?
2) What does that J shaped piece do, other than perhaps direct air to the low pressure rearward side of the tire?
Just trying to understand what I'm seeing.
phantomjock
Well-known member
My guess/analysis-estimate, is the design and placement is to: (Front to Rear)
Downforce aft of the front axle is "better" balance than forward, just as forward of the rear is better than aft. Reducing pitching moments is a good thing.
Here is a good graphic you'll enjoy:
Regarding ride height. These mount with the same ground clearance as air curtains, so would get scrapped off at the same time as other underbody enhancements.
Hope that helps. (BTW - I really gotta shout out to Chris for bring this subject in. THANKS Chris! Even though it gives me more ideas to work...)
Cheers - Jim
1. Add some flow/cooling (without adding any ducting) to the brake caliper (very clever vane they've added to the A-Arm - eh?)
2. Move air to the rear of the tire - and out the side (rear-facing) scoop - feeding energy down the side to the rear devices
3. Generate downforce at the area created by the "throat" formed between the left and right vanes. I understand the design was developed by an engineer experienced with CAD, CFD, and worked with engineering for NASA, and others. The flow-vis pattern shows a lot is on the underside of the car on the outside of the vanes. There is a low pressure area that is sucking the flow-vis up. I have read that this was run at 100 mph but have not seen any data from pressure taps. Would really like that!
The McLaren apparently has a lot of High Speed understeer at and above 100 mph. These vanes have been suggested to eliminate that understeer - adding more front wheel grip (downforce enabled). And, the results -- 2 seconds faster on a 2 mile course!2. Move air to the rear of the tire - and out the side (rear-facing) scoop - feeding energy down the side to the rear devices
3. Generate downforce at the area created by the "throat" formed between the left and right vanes. I understand the design was developed by an engineer experienced with CAD, CFD, and worked with engineering for NASA, and others. The flow-vis pattern shows a lot is on the underside of the car on the outside of the vanes. There is a low pressure area that is sucking the flow-vis up. I have read that this was run at 100 mph but have not seen any data from pressure taps. Would really like that!
Downforce aft of the front axle is "better" balance than forward, just as forward of the rear is better than aft. Reducing pitching moments is a good thing.
Here is a good graphic you'll enjoy:
Regarding ride height. These mount with the same ground clearance as air curtains, so would get scrapped off at the same time as other underbody enhancements.
Hope that helps. (BTW - I really gotta shout out to Chris for bring this subject in. THANKS Chris! Even though it gives me more ideas to work...)
Cheers - Jim
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phantomjock
Well-known member
Just had another cup of coffee, and thought I'd add some more.
Here is a graphic of the M720 overlaid with the vane downforce distribution:
When you look back at the comparison graphic, there is about a 200% increase in downforce from those vanes. Wow - that is significant. Also, you'll note the stock underbody sort of balances the front downforce equally around the front axle, the modified aft of the axle.
The "modified" (vanes installed) has a HUGE increase aft of the front axle - with little to no change in the rear - so I'll retract the added energy thoughts to the "rear devices" I posited earlier.
This seems like a very easy and inexpensive (and stealthy) means of generating some significant downforce we can use on our cars. And note there is very little increase in frontal area, certainly less than we see in many "air dams."
If anybody has an idea where the CG is on the M720, I'd like to know that too. Useful to look at center of pressure, center of gravity, and moment of inertia all at once.
I'm going for another coffee.
Cheers - Jim
Here is a graphic of the M720 overlaid with the vane downforce distribution:
When you look back at the comparison graphic, there is about a 200% increase in downforce from those vanes. Wow - that is significant. Also, you'll note the stock underbody sort of balances the front downforce equally around the front axle, the modified aft of the axle.
The "modified" (vanes installed) has a HUGE increase aft of the front axle - with little to no change in the rear - so I'll retract the added energy thoughts to the "rear devices" I posited earlier.
This seems like a very easy and inexpensive (and stealthy) means of generating some significant downforce we can use on our cars. And note there is very little increase in frontal area, certainly less than we see in many "air dams."
If anybody has an idea where the CG is on the M720, I'd like to know that too. Useful to look at center of pressure, center of gravity, and moment of inertia all at once.
I'm going for another coffee.
Cheers - Jim
vette427sbc
Well-known member
Put the next cup on my tab... this is all such valuable and interesting information. Thank you!
