Aerodynamics flow diagram?
12-04-07, 01:14 PM
#2
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Since we are on this subject.
Does anyone knows how the air flows under the hood, IE: the routes it likes to follow, where does most air exit?
Any benefit or drawback to venting air out?
Does anyone knows how the air flows under the hood, IE: the routes it likes to follow, where does most air exit?
Any benefit or drawback to venting air out?
12-04-07, 01:21 PM
#4
CC of L-Squared Shots
I would think the flow of air in the engine bay is very disruptive. It goes past the radiator and then I think it just disperses downward... I could be wrong.
12-04-07, 01:23 PM
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You are awesome, Thanks.
Anyone know about a underhood,undercar airflow diagram.
I wanted to see a flow diagram with the GTU aero parts. To see exactly what they are doing to the air, where it kicks out, draws underneath etc.
Last edited by glhs0867; 12-04-07 at 01:49 PM.
12-04-07, 01:32 PM
#6
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The arrows represent the air pressure on the panels. Where it points in that's more than ambient pressure, where it sticks out that's less than ambient.
The hood is more or less sealed all the way around, so the air exits underneath the car. This isn't a particularly good thing, but propping up the back of the hood will cause air to enter there, not exit (see the high pressure area). Venting closer to the front of the hood will work well and will make the radiator more effective by venting whatever high pressure air builds in the engine bay, causing more airflow.
The hood is more or less sealed all the way around, so the air exits underneath the car. This isn't a particularly good thing, but propping up the back of the hood will cause air to enter there, not exit (see the high pressure area). Venting closer to the front of the hood will work well and will make the radiator more effective by venting whatever high pressure air builds in the engine bay, causing more airflow.
12-04-07, 02:03 PM
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The arrows represent the air pressure on the panels. Where it points in that's more than ambient pressure, where it sticks out that's less than ambient.
Airflow moving up the windshield combinds with the air above causing higher pressure, then the airflow moves toward the back near the hatch glass which releases some of the pressure.
but propping up the back of the hood will cause air to enter there, not exit (see the high pressure area).
The air flowing over the hood which is continuously compressed with the airflow above it, reaches that point and then will release some of the pressure.
How much lower the pressure is at the end of the hood line compaired to the pressure in the engine bay is something I would like to know. This would be the only way to know for sure if the air will enter or exit for the looks of it.
Venting closer to the front of the hood will work well and will make the radiator more effective by venting whatever high pressure air builds in the engine bay, causing more airflow
Last edited by RotaMan99; 12-04-07 at 02:12 PM.
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12-04-07, 02:28 PM
#10
I've been waiting 6 months for my copy to arrive!! Amazon keeps asking me to approve a 2 month wait because they said it was available and now they can't find it. Wouldn't most of the heat escape underneath the tranny, PAST the underbelly tray?
12-04-07, 02:58 PM
#11
The mystery of the prize.
For those arguing how to read the aerodynamic profile, read these:
http://www.dynamicflight.com/aerodyn...pres_patterns/
http://www.grc.nasa.gov/WWW/K-12/airplane/presar.html
http://www.dynamicflight.com/aerodyn...pres_patterns/
http://www.grc.nasa.gov/WWW/K-12/airplane/presar.html
12-04-07, 03:59 PM
#13
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If you read it your way then it's a low pressure area in front of the radiator, so flow will come out of there. Also the car will be making some serious downforce with all that high pressure over the top and there's a high pressure area behind the car pushing it forward (negative Cd?).
The car deflects the air, which is forced to speed up and as it speeds up the pressure drops (that's how a wing works), causing that low pressure area over the top of the car. At the base of the windshield the flow slows and even stagnates, causing higher pressure (that's why they put the HVAC intakes there). American cars often use cowl induction hoods which take the air from that area precisely for the reason that it's at higher pressure. Maybe there'll be some flow out if the engine bay is fairly well sealed, but it's a bad place to try and vent the engine bay.
Vented hoods have been shown to work, othewise why would pro race teams use them? The air gets rammed into the engine bay by the opening in the bumper and has to go through the radiator and around the engine and all that other stuff to get out, a hood vent into a low pressure area will cause air to leave the engine bay by providing it with an easier flow path, helping lower the pressure in there, causing a greater pressure differential across the radiator, causing more flow.
12-04-07, 04:36 PM
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The car deflects the air, which is forced to speed up and as it speeds up the pressure drops (that's how a wing works),
At the front of the car where the gap in the bumper is there is not as much pressure because the air has a place to flow. Its not being redirected or compressed into the airflow above causing high pressure.
12-04-07, 05:54 PM
#15
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Yes, there is higher pressure at the front of a wing, but that's due to stagnation (flow slowing/stopping due to the object directly in its path), as it flows across the top of the wing it speeds up and the pressure drops, as the air proceeds to the trailing edge it slows down and increases in pressure untill it approaches ambient pressure at the trailing edge. The lift is concentrated towards the leading edge because that's where there's the greatest velovity and lowest pressure on the top surface. Lift can be approximated as a force at the quarter chord point (1/4 the distance from the front to the back of the wing).
Bernoulli tells us that as the velocity increases the pressure must drop. That's a well known (well apparently not well enough) fact.
Just look at it, if out was high pressure than it'd have lots of downforce and the high pressure air would push the car down the road, that's not the case.
Seriously though, stop talking out your ***, you'll just confuse people and make yourself look like an idiot.
Bernoulli tells us that as the velocity increases the pressure must drop. That's a well known (well apparently not well enough) fact.
Just look at it, if out was high pressure than it'd have lots of downforce and the high pressure air would push the car down the road, that's not the case.
Seriously though, stop talking out your ***, you'll just confuse people and make yourself look like an idiot.
12-04-07, 06:14 PM
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easy guys.
I only asked for diagrams. Please don't chew this up in the Flamage catagorary.
I know quite a bit about pressure waves and Hi energy piping.
I just needed a flow diagram for the 2nd underneath tray and other aero dynamic additions to the GTU.
No other RX7 offer such aerodynamic values vs compared to weight of other models.
All newer models" post 1988" weight alot more., so how can we determine what the GTU aspects add?
The 88 GTU was designed factory with all kind of goods. for aerodynamic efficency.
Not the Base/SE model. I had one, It didn't have half of the additions the GTU has, for aero.
However my SE 88 had LSD yep on 4 lug... you could pull a hand full from either wheel well. Hand full of nicly shreaded rubber from the fendcer.
I only asked for diagrams. Please don't chew this up in the Flamage catagorary.
I know quite a bit about pressure waves and Hi energy piping.
I just needed a flow diagram for the 2nd underneath tray and other aero dynamic additions to the GTU.
No other RX7 offer such aerodynamic values vs compared to weight of other models.
All newer models" post 1988" weight alot more., so how can we determine what the GTU aspects add?
The 88 GTU was designed factory with all kind of goods. for aerodynamic efficency.
Not the Base/SE model. I had one, It didn't have half of the additions the GTU has, for aero.
However my SE 88 had LSD yep on 4 lug... you could pull a hand full from either wheel well. Hand full of nicly shreaded rubber from the fendcer.
12-04-07, 06:38 PM
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if out was high pressure than it'd have lots of downforce
Last edited by RotaMan99; 12-04-07 at 06:46 PM.
12-04-07, 06:47 PM
#18
Spoilers are plates on the top surface of a wing which can be extended upward into the smooth airflow and spoiling it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section.
12-04-07, 06:53 PM
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easy guys.
I only asked for diagrams. Please don't chew this up in the Flamage catagorary.
I know quite a bit about pressure waves and Hi energy piping.
I just needed a flow diagram for the 2nd underneath tray and other aero dynamic additions to the GTU.
No other RX7 offer such aerodynamic values vs compared to weight of other models.
All newer models" post 1988" weight alot more., so how can we determine what the GTU aspects add?
The 88 GTU was designed factory with all kind of goods. for aerodynamic efficency.
Not the Base/SE model. I had one, It didn't have half of the additions the GTU has, for aero.
However my SE 88 had LSD yep on 4 lug... you could pull a hand full from either wheel well. Hand full of nicly shreaded rubber from the fendcer.
I only asked for diagrams. Please don't chew this up in the Flamage catagorary.
I know quite a bit about pressure waves and Hi energy piping.
I just needed a flow diagram for the 2nd underneath tray and other aero dynamic additions to the GTU.
No other RX7 offer such aerodynamic values vs compared to weight of other models.
All newer models" post 1988" weight alot more., so how can we determine what the GTU aspects add?
The 88 GTU was designed factory with all kind of goods. for aerodynamic efficency.
Not the Base/SE model. I had one, It didn't have half of the additions the GTU has, for aero.
However my SE 88 had LSD yep on 4 lug... you could pull a hand full from either wheel well. Hand full of nicly shreaded rubber from the fendcer.
trust me. My gtu was 5 lug weird...
12-04-07, 07:26 PM
#20
Spoilers are plates on the top surface of a wing which can be extended upward into the smooth airflow and spoiling it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section.
Spoiler = downforce
12-04-07, 07:33 PM
#21
Black91n/a has it right.
I'm digging through some some flying stuff, I know I've seen pictures of wings with the arrows showing the center of lift etc. and the arrows are used as he describes, the length of the arrow shows the amount of pressure differential as well IIRC.
I'm digging through some some flying stuff, I know I've seen pictures of wings with the arrows showing the center of lift etc. and the arrows are used as he describes, the length of the arrow shows the amount of pressure differential as well IIRC.
12-04-07, 07:59 PM
#22
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A spoiler (on a car) causes stagnation and deflects air upwards causing downforce.
I'm not aware of any other diagrams depicting flow. The only significant changes that I'm aware of are the different bumper on the S5, the various spoilers/wings and the rear undertray add on from the Sport models.
The best (least drag anyway) aero kit was the S4 Sports with the aluminum undertray behind the normal plastic one and the small spoiler (not to be confused with the TII and similiar ones). IIRC it gets 0.02 lower CD from that undertray and spoiler.
There's some good reading material linked at the bottom of the page here: http://www.fatcatmotorsports.com/chassis.htm
I'm not aware of any other diagrams depicting flow. The only significant changes that I'm aware of are the different bumper on the S5, the various spoilers/wings and the rear undertray add on from the Sport models.
The best (least drag anyway) aero kit was the S4 Sports with the aluminum undertray behind the normal plastic one and the small spoiler (not to be confused with the TII and similiar ones). IIRC it gets 0.02 lower CD from that undertray and spoiler.
There's some good reading material linked at the bottom of the page here: http://www.fatcatmotorsports.com/chassis.htm
12-04-07, 11:24 PM
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Yes! However, as you see in the diagram, the car has a good natural downforce effect even without the spoiler. This is due to the sloping rear window, and can also be found in "fastback" designs. The FC RX-7 designers originally wanted a longer rear window with a steeper rake, but they opted for the resulting design due to glass production, weight, 2+2, and sunroof issues.
12-04-07, 11:40 PM
#25
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Oh man, not again... 
How can one simple drawing be responsible for so much misinformation posted again and again?
The diagrams represent force vectors, i.e. the direction the air's static pressure is pressing against the car. Arrows pointing away from the car represent pressure lower than ambient; arrows pointing into from the car represent pressure higher than ambient.
No, airflow traveling up the windscreen separates from the body at the sudden change of direction at the top, the reattaches further along. The same thing happen at the top of the rear windscreen and again at the tail.
The bottom of the windscreen is obviously a high pressure area, again because the air is being forced to change direction quickly. This is why nearly every car in the world has the ventilation intake located there, and why air flows into the cabin even if the fan's off.
Sorry, but you really don't understand how aerodynamics work. That's completely wrong.
Here's an Autospeed article that tests just that. The pressure difference above and below the hood at various points was measured to find the ideal location of a vent. The results speak for themselves.
http://www.autospeed.com/cms/A_2162/article.html
If you aren't a member, this pic shows the pressure differences measured. Positive numbers show where the pressure above the hood is greater than the pressure below it. Negative numbers show where the pressure above the hood is less than the pressure below it. See where all the negative numbers are?
http://us1.webpublications.com.au/st...1/2162_7mg.jpg
Venting close to the front of the hood is the proper way to vent the engine bay, and there are hundreds of OEM vented hoods and properly developed race car hoods that do exactly that.
How can one simple drawing be responsible for so much misinformation posted again and again?
Airflow moving up the windshield combinds with the air above causing higher pressure, then the airflow moves toward the back near the hatch glass which releases some of the pressure.
Thats a low pressure zone.
The air flowing over the hood which is continuously compressed with the airflow above it, reaches that point and then will release some of the pressure.
How much lower the pressure is at the end of the hood line compaired to the pressure in the engine bay is something I would like to know. This would be the only way to know for sure if the air will enter or exit for the looks of it.
http://www.autospeed.com/cms/A_2162/article.html
If you aren't a member, this pic shows the pressure differences measured. Positive numbers show where the pressure above the hood is greater than the pressure below it. Negative numbers show where the pressure above the hood is less than the pressure below it. See where all the negative numbers are?
http://us1.webpublications.com.au/st...1/2162_7mg.jpg
That wont work
