Returning to C3 Aerodynamics
Thread Starter
Drifting
Joined: Jul 2002
Posts: 1,254
Likes: 1
From: Edinburgh
I think there is some confusion as to what this splitter is being asked to do. Firstly, if you take the stock air dam as fitted, try getting down on the ground, on your back in front of the car, bracing yourself and put both feet on the bottom of your air dam and see how much flex you get, not a lot! If I get that much additional pressure I will be more than happy. If I am getting too much flex, then I can reduce the depth of the splitter or I can reinforce it with brackets from behind. Remember this is not a wing, merely a lip on the spoiler to turn the air and create a high pressure area, so things like being perfectly parallel to the road are not critical. I probably wont get a chance to give it a significant test until the end of the month when I head up to the north of Scotland where the roads are significantly quieter. 
My idea of tell tales to guage the flexing is by fitting several threads the first being hand tight the second with 1mm slack the third with 2mm etc. then check to see how many are broken or are pulled from the tape fixing. Hopefully that will be a good indicator. All good fun though!
Graeme
My idea of tell tales to guage the flexing is by fitting several threads the first being hand tight the second with 1mm slack the third with 2mm etc. then check to see how many are broken or are pulled from the tape fixing. Hopefully that will be a good indicator. All good fun though!
Graeme
Le Mans Master
Joined: Apr 2007
Posts: 7,353
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From: Graceland in a Not Correctly Restored Stingray
FWIW, my earlier comments regarding the need for bracing were somewhat more targeted at PC dams rather than earlier extensions, as yours may or may not require such, but nevertheless a valid observation which comes from the BTDT school of personal experience with regards to the former.
Innovations such as you're chasing are good for the breed. Best of luck with your tests, and post up with results.
Innovations such as you're chasing are good for the breed. Best of luck with your tests, and post up with results.
Safety Car
Joined: Nov 2005
Posts: 3,961
Likes: 573
From: Lompoc, CA. Santa Barbara County
FWIW, my earlier comments regarding the need for bracing were somewhat more targeted at PC dams rather than earlier extensions, as yours may or may not require such, but nevertheless a valid observation which comes from the BTDT school of personal experience with regards to the former.
Innovations such as you're chasing are good for the breed. Best of luck with your tests, and post up with results.
Innovations such as you're chasing are good for the breed. Best of luck with your tests, and post up with results.
Bee Jay
Burning Brakes
Joined: May 2006
Posts: 893
Likes: 7
From: Hazerswoude-Rijndijk Zuid Holland
I think the fixed headlight idea was to eliminate the problems with the stock lights standing up in the wind as it were when they were racing in the dark, 12 hour races etc. The hood creates a high pressure area immediately infront of the windscreen but that is in the centre of the car. The problem is that the front end which causes the steering becomes 'light' over 120mph or so with increased problems in cornering and in the rain aquaplaning. I have already changed the angle of attack of the front end by lowering it about 1" which helps, if this splitter works I will then need to look at the back end of the car which is becoming increasingly light - for various reasons. I carry no spare wheel so if I get rid of the spare carrier I should add a diffuser, whichy will be an interesting exercise, but, I like my car to look stock! Aarg!
So difficult!
Graeme
So difficult!Graeme
A while ago I came across a cover for the rear bottom the whole area from the back wheels to the rear was one big body panel. It was meant for cars with side pipes. It was on a local "ebay" I never had seen it and never have again, not with the major corvette plastic companies. That would be a good start for a diffuser. I wish I had bought it, just to show you.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
I just bolted on the center section of my Pace Car spoiler last night. Beleive me, that thing is mounted solid and is not going to flex much at all. The center section is bolted flush to the center pan behind the bumper with about ten bolts. It doesn't flap in the breeze, and I have the original urathane version.
Bee Jay
Bee Jay
Burning Brakes
Joined: Oct 2006
Posts: 1,044
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From: Henrico VA
I have been toying with similar ideas recently. I have the stock '69 front air dam and the steering shakes a little more at 85, then goes away around 90, so I was wondering if this would help or if it is a resonance thing, but it doesn't shake anywhere near violently. I was told that it is lift on my front. Anyways, I may copy your design with fiberglass. Thanks!
Le Mans Master
Joined: Aug 2000
Posts: 6,362
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From: Brazos TX
Cruise-In IV Veteran
Cruise-In V Veteran
I've been toying with a front splitter design that integrates with the PC air dam. Someday soon I will build it. Good job, Graeme. That's a nice little piece. Testing will tell you if it works and if it's rigid enough.
For those that haven't seen it here is a chart with real world measurements for a range of Corvette body styles. There can be no arguing that in the configuration tested a C3 generated lift at the front. Other configurations will vary and rake can have a significant impact on lift. I just ask people to not try to simplify things into statements like "I've run mine to 120mph and it doesn't lift so I don't know what you people are talking about, there is no problem".
For those that haven't seen it here is a chart with real world measurements for a range of Corvette body styles. There can be no arguing that in the configuration tested a C3 generated lift at the front. Other configurations will vary and rake can have a significant impact on lift. I just ask people to not try to simplify things into statements like "I've run mine to 120mph and it doesn't lift so I don't know what you people are talking about, there is no problem".
Race Director
Joined: Dec 2007
Posts: 14,345
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From: Hartselle AL
St. Jude Donor '09
burners, interesting data. The two things that jump out at me is the vast improvement with the C4s from the previous gens. Then that the C6 seems to have lost a bit of ground compared to the C5.
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Verdad Gallardo
Team Owner
Joined: Jul 1999
Posts: 65,492
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From: Orange Park Florida
I've been toying with a front splitter design that integrates with the PC air dam. Someday soon I will build it. Good job, Graeme. That's a nice little piece. Testing will tell you if it works and if it's rigid enough.
For those that haven't seen it here is a chart with real world measurements for a range of Corvette body styles. There can be no arguing that in the configuration tested a C3 generated lift at the front. Other configurations will vary and rake can have a significant impact on lift. I just ask people to not try to simplify things into statements like "I've run mine to 120mph and it doesn't lift so I don't know what you people are talking about, there is no problem".
For those that haven't seen it here is a chart with real world measurements for a range of Corvette body styles. There can be no arguing that in the configuration tested a C3 generated lift at the front. Other configurations will vary and rake can have a significant impact on lift. I just ask people to not try to simplify things into statements like "I've run mine to 120mph and it doesn't lift so I don't know what you people are talking about, there is no problem".
also I have to laugh, the C3 has gone from minor REAR lift, lights down to actual DOWN force with lights UP???
cute, wonder how in hell THAT was managed???
also like to know what affect just taking the lights OUT of a C3 does to FE lift....almost what I did, small hole, no/lo frontal area, open in back of trays so no bucket affect until the radiator....still thinking of holes in the back dunno I like that or not....
and where in front is this lift generated at?? not under the hood, that's for sure....so??
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Gene, I don't recall all of the details of the article just now, but these numbers are most likely direct readings from corner weights taken at the tire patches during the various test conditions. Whether or not pressure differentials and/or "simple" leverage is responsible (I'm curious and would like to know more about this), the bottom line is that having the headlights up does effectively change weight distribution at speed.
I'd think having open holes where the headlight buckets reside would primarily increase drag, but would hesitate a guess as to how that would affect the lift/downforce picture.
As I've stated elsewhere, it's too bad they didn't test variations of the C3, given that it evolved somewhat over the course of the generation's run. By '82, aerodynamically the C3 was a considerably different animal than it was in '68.
Maybe Blue71vette will chime in with his take on this...
I'd think having open holes where the headlight buckets reside would primarily increase drag, but would hesitate a guess as to how that would affect the lift/downforce picture.
As I've stated elsewhere, it's too bad they didn't test variations of the C3, given that it evolved somewhat over the course of the generation's run. By '82, aerodynamically the C3 was a considerably different animal than it was in '68.
Maybe Blue71vette will chime in with his take on this...
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
At what speed were those figgers taken???
also I have to laugh, the C3 has gone from minor REAR lift, lights down to actual DOWN force with lights UP???
cute, wonder how in hell THAT was managed???
also like to know what affect just taking the lights OUT of a C3 does to FE lift....almost what I did, small hole, no/lo frontal area, open in back of trays so no bucket affect until the radiator....still thinking of holes in the back dunno I like that or not....
and where in front is this lift generated at?? not under the hood, that's for sure....so??
also I have to laugh, the C3 has gone from minor REAR lift, lights down to actual DOWN force with lights UP???
cute, wonder how in hell THAT was managed???
also like to know what affect just taking the lights OUT of a C3 does to FE lift....almost what I did, small hole, no/lo frontal area, open in back of trays so no bucket affect until the radiator....still thinking of holes in the back dunno I like that or not....
and where in front is this lift generated at?? not under the hood, that's for sure....so??
BTW what year C3 did the chart apply to (early or late?)
Last edited by roscobbc; May 2, 2009 at 04:59 AM. Reason: spelling
Melting Slicks
Joined: Jul 2002
Posts: 3,000
Likes: 22
From: Boulder Creek California
Gene,
The lift comes from high speed air over the top of the hood, an inevitable feature of every car, plus to some degree the high pressure buildup under the nose. The engine bay itself is usually a low pressure area however.
I'd say the weight transfer effect of the front lift caused by the headlights is likely the source of the rear downforce. It could be though that the physical lifting of the front end (put 150 pounds force up on the front up your car and see how much it moves!) could be beneficially affecting the rear downforce but I would expect that to be a negative thing (more air packing under the rear causing high pressure, lower pressure separated flow area over the rear). If this is a fixed-ground wind tunnel test though I wouldn't put much stock in anything going on under the car, and 20lbs could be testing error if these tests were not carefully carried out.
Would be interesting to know what magazine that came out of and what the various test conditions were. It's weird to see L/D stated which is usually efficiency but in this case I guess it's inefficiency?
The lift comes from high speed air over the top of the hood, an inevitable feature of every car, plus to some degree the high pressure buildup under the nose. The engine bay itself is usually a low pressure area however.
I'd say the weight transfer effect of the front lift caused by the headlights is likely the source of the rear downforce. It could be though that the physical lifting of the front end (put 150 pounds force up on the front up your car and see how much it moves!) could be beneficially affecting the rear downforce but I would expect that to be a negative thing (more air packing under the rear causing high pressure, lower pressure separated flow area over the rear). If this is a fixed-ground wind tunnel test though I wouldn't put much stock in anything going on under the car, and 20lbs could be testing error if these tests were not carefully carried out.
Would be interesting to know what magazine that came out of and what the various test conditions were. It's weird to see L/D stated which is usually efficiency but in this case I guess it's inefficiency?
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
I can speak for the early c3s ,at 150 mph,there is so much air force under the car that my hood was tring to pry off the hinges,the hood actually distorted and raised up.The steering gets really lite.So what ever you do to divert the air flow will work.I am going with a l88 front spoiler,from Gregg racing,dont know how effective it will be.
Last edited by Billysvette; May 2, 2009 at 10:32 AM.
Racer
Joined: Mar 2005
Posts: 294
Likes: 1
From: Racine Wisconsin
Live&LetDrive, Article was Corvette Fever May 2009 page 39. The "nose rise" of the stock 1970 C3 at 85 mph was 117 pounds of lift on the front wheels with the headlights down and 150 pounds of lift with the headlights up. With the headlights down the rear lift was 9 pounds. With the headlights up the rear did not lift but 14 pounds of downforce was observed. I agree with you that this probably means that the center of lift (as you state the hood surface) was higher than the center of gravity and the 150 pounds of front lift and 180 pounds of drag acted around the center of gravity to cause the rear downforce. With the headlights up, also above the center of gravity, the CDA (coefficient of drag x frontal area) increased from 8.69 to 9.73. I would think that a chin spoiler of approximate frontal area of the headlights at or below the center of gravity would produce some front downforce. This would be a modest change. I think that radius idea to keep the air attached to the surface is founded on the principle of the Coanda effect but I don't know much beyond that. I wonder if we could get Corvette Fever to run some tests with various C3 chin spoilers and other mods to evaluate lift, downforce and drag.
Team Owner
Joined: Apr 2002
Posts: 62,198
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From: All humans are vermin in the eyes of Guru VA
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Cruise-In V Veteran
Here is another idea.
I have been mulling vortex generators for awhile.
this was the first thing to come up today.
http://autospeed.com/cms/title_Blowi...1/article.html
I have been mulling vortex generators for awhile.
this was the first thing to come up today.
http://autospeed.com/cms/title_Blowi...1/article.html
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
Here is another idea.
I have been mulling vortex generators for awhile.
this was the first thing to come up today.
http://autospeed.com/cms/title_Blowi...1/article.html
I have been mulling vortex generators for awhile.
this was the first thing to come up today.
http://autospeed.com/cms/title_Blowi...1/article.html
Thread Starter
Drifting
Joined: Jul 2002
Posts: 1,254
Likes: 1
From: Edinburgh
I have a slightly lowered front suspension, maybe 3/4" and I find the lightness in steering doesnt come on until 130-140mph, so maybe changing the angle of attack of the car helps.
I had the car up to 70 -80 mph yesterday with no appreciable movement, the taught tell tale had maybe 1 or 2 mm of slack in it after, but I dont expect any big problems until I get into 3 figures. If I dont get another chance tomorrow to run it, I am off salmon fishing for most of next week so the vette will have a rest.
Graeme
I had the car up to 70 -80 mph yesterday with no appreciable movement, the taught tell tale had maybe 1 or 2 mm of slack in it after, but I dont expect any big problems until I get into 3 figures. If I dont get another chance tomorrow to run it, I am off salmon fishing for most of next week so the vette will have a rest.
Graeme
Last edited by Graemeinvette; May 2, 2009 at 03:43 PM. Reason: Adding information
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
I would like to see someone do a test with a Vette body upside-down!
we might then see some positive downforce
- think about it
- a side elevation section of a C3 is probably very similar to a 'Clarke Y' airfoil wing section
we might then see some positive downforce - think about it - a side elevation section of a C3 is probably very similar to a 'Clarke Y' airfoil wing section
Melting Slicks
Joined: Jul 2002
Posts: 3,000
Likes: 22
From: Boulder Creek California
Vortex generators can definitely help keep a flow attached. Could help a '79-82 but I'm not sure where it would be useful on an earlier C3. If a diffuser was added it could find use there.
I find it funny that the headline picture in that article they have VG's right before the 90º edge at the rear of that car! Somehow I don't think they're helping there! (Not to mention screwing up the flow on its way into that car's little wing.)
I find it funny that the headline picture in that article they have VG's right before the 90º edge at the rear of that car! Somehow I don't think they're helping there! (Not to mention screwing up the flow on its way into that car's little wing.)