Drag, Drag and More Drag

[xcarguy]

Thanks for starting another interesting thread..

 

So - my front and rear roll cage hoops have combined frontal area of 210 sq in. For 150 mph and Cd = 1 , theory says that I would have 68 lbs of drag, which would use up 28 WHP. Might be enough to effect balance too. If the center of roll cage pressure was 40 inches off the ground and 18 inches ahead of the rear wheels, cage drag would transfer 29 lbs from the front to the rear tires.

 

Very interesting, ecarte56. And that's a huge WHP deficient. You’ve definitely hit on something with your calculations. In another thread (http://www.usa7s.net/vb/showthread.php?t=9876) I posted an older article pertaining to some wind tunnel testing done on a Caterham. Unfortunately, the article is so pixelated when you try and enlarge it that the text is unreadable. However, here is an excerpt that substantiates your post:

 

“The result is interesting and quite disturbing. At 100mph we're getting 74.1lb of lift at the front of the car and 4.1lb at the rear, which is a pretty big imbalance. . . . . . . . At this stage the drag coefficient measured 0.59Cd, which is about as bad as you’d expect. For the next run we remove the aerodynamic covering from the cage, leaving it a simple rounded tube. The result is that front lift increases to 77.1lb and, surprisingly, to 5.1lb of DOWNFORCE (my emphasis) at the rear.” escart56, there's 'wind tunnel' results of the transfer you calculated. It’s also interesting to note that at the end of 32 wind tunnel runs, those involved in the testing were able to get the car’s downforce fairly well balance with 31.4lb at the front and 31.5lb at the rear.

 

Skip (scannon) if you’re following along, please post the link you have to that article in this thread; thanks in advance.

 

Tom (yellowss7) you getting all this? :jester:

[subtlez28]

subtle,

 

The link is in a post on the first page of this thread. This is what's on the table for consideration:

 

http://www.uflyit.com/streamline_fairings.htm

 

Oh, I guess I just looked at the perty pictures, and did not page down.

 

That is the same idea, but not exactly what I was talking about. The ones I am thinking of come in small sections. Idea being you could use as is, or wrap them and use them as structure.

 

I'll dig around a bit for them later.

[Croc]

I know I am late to this thread but my thoughts on this are:

 

1) Great idea but you are adding more weight.

 

2) When I put my CSR in the wind tunnel a few years back it was clear to the doctoral students who were doing an aero study of various objects (and me as a lay muppet observer) that aero benefit starts to kick in north of 100mph for most aero improvements on my Caterham. How many of us average north of that in a track lap? I know a storker can get some very high speeds but even so does the aero benefit outweigh the weight penalty given the average speed will be lower than where the theoretical benefits kick in?

 

3) Lets say we can prove there is an aero benefit - assuming that, does that mean when you go around a corner you are stalling your "wing shape" since the air flow is not directionally straight which introduces a new amount of drag previously not there? Shane - you are a pilot so you can probably add more intelligent thought to my thinking?

[Kitcat]

Given the Stalker's almost unlimited power, but real world cornering limits, it seems to me (expert that I am:)), that adding grip at the expense of speed isn't much of a concern for that particular car. For our little 4 cyl Caterhams, etc., it is easier to achieve a balance between our above average grip and modest power. And adding grip isn't worth the hit our modest power wld suffer. For them Stokers tho....

[xcarguy]

I know I am late to this thread but my thoughts on this are:

 

1) Great idea but you are adding more weight.

 

2) When I put my CSR in the wind tunnel a few years back it was clear to the doctoral students who were doing an aero study of various objects (and me as a lay muppet observer) that aero benefit starts to kick in north of 100mph for most aero improvements on my Caterham. How many of us average north of that in a track lap? I know a storker can get some very high speeds but even so does the aero benefit outweigh the weight penalty given the average speed will be lower than where the theoretical benefits kick in?

 

3) Lets say we can prove there is an aero benefit - assuming that, does that mean when you go around a corner you are stalling your "wing shape" since the air flow is not directionally straight which introduces a new amount of drag previously not there? Shane - you are a pilot so you can probably add more intelligent thought to my thinking?

 

Hey, Mike,

 

Good points/considerations. However, my being a pilot doesn’t by any means put me ahead on understanding any of this. I simply enjoy, from a layman’s point of view, using aerodynamic theory to try and find ways to make the Storker getyup and go a liittle better. :jester: There are aerodynamicists who aren’t pilots but could answer, in great detail, every question we have about what will work, how well it will/will not work, what the tradeoffs are, etc. And, there are pilots (the majority of them) who aren’t aerodynamicists and cannot explain any of this beyond the simple correlations of lift, drag, thrust and weight (this is me). I really can’t tell you what the effect will be on the car in a turn with airfoils covering the roll cage tubes. I can only ‘theorize’ (again, based on my limited understanding) that the angle of attack of a vertical round roll bar, enclosed with a symmetrical airfoil, would be minimal during a turn and would produce (overall) less drag than the bare round tube. A John Deere moment might be a better indicator.

 

As for adding weight, that’s a given. Any time you add something with mass to a car, whether it weighs an ounce or a pound, you have added weight to the car . . . . period. The small airfoil covering that’s been touched on in this thread weighs 1.45 lbs. per 8' section and the large airfoil weighs 2.3 lbs. per 10' section. I’ve estimated that I will need to use most of two sections of the large airfoil and about 38” of a small section. That’s roughly around 5lb of airfoil.

 

Aside from doing extensive wind tunnel testing, the only means I have available for testing such a mod is to simply install it and try it. I and one other forum member have discussed the idea of adding this product to our roll cage to see if we can cheat the elements and perhaps gain a bit more speed. To borrow from one of our previous conversations, in theory, if you can decrease the drag on any part of your car (using that term collectively for all of us) then, in theory, it should reduce the overall drag which, again in theory, should yield a better top end speed for a given distance (such as the straight on Lightning) as well as reduce the time it takes to reach a certain speed with in a given distance (quicker lap times); yes, I know, there is still the issue of having added additional weight to acheive the outcome.

 

It may be that the actual yield of such a mod is so minor, that it would take a data logger to capture the results. However, someone such as yourself, with lots of experience at a given track (such as NJMP’s Lightning course) with a given car and extremely consistent lap times, might add the airfoils and be able to tell right away if there is any noticeable improvement.

 

If what I have written tonight seems choppy, rushed and sort of thrown together, please forgive me. I’ve had three very long days back-to-back due to our being short on pilots this week and I am a little tired. :nopity:

 

Perhaps someone on here would be willing the test the airfoil during a 'John Deere' moment to see what effect they might have on the dreaded death wobble. :ack:

[xcarguy]

Given the Stalker's almost unlimited power, but real world cornering limits, it seems to me (expert that I am:)), that adding grip at the expense of speed isn't much of a concern for that particular car. For our little 4 cyl Caterhams, etc., it is easier to achieve a balance between our above average grip and modest power. And adding grip isn't worth the hit our modest power wld suffer. For them Stokers tho....

 

There ya' go, Mike, pick'n on Storkers again. :jester: However, when Autocar did the Caterham wind tunnel testing in the 2001 article that's been mentioned on this thread and one other, they did so because of the over steer they were experiencing due largely to the amount of lift generated on the front of the car. The goal of the testing, as I saw it, was not to necessarily add grip (down force) but rather to reduce frontal lift by balancing the existing (available) grip at both the front and rear of the car. At the onset of the testing, front end lift at 100mph was in excess of 70 lbs. By the end of testing, down force for both the front and the rear was just north of 30 lbs.

 

Any of us who have added a full cage (if for no other reason than safety’s sake) to our cars (Storkers or otherwise) know that we’ve added weight, increased drag, increased front end lift and reduced acceleration and decreased top end speed. In the sixties, when Carol Shelby’s Cobra started getting a bit ‘long in the tooth’ and less competitive, he took the car’s chassis and added a fully enclosed body. That car became known as the Daytona Coupe. While that car was substantially heavier than the Cobra, it was also more competitive because of the aerodynamic improvements.

 

Adding the airfoils to the roll cage of an open car should (in theory) decrease the car’s overall drag coefficient and hopefully transfer some weight to the front wheels (decrease front end lift) at speed. A gain in useable rear wheel HP may also be experienced with the weight transfer. In this situation, adding the weight of the roll bar airfoil may be good. Again, this is theory (wearing out that word) and something I’m willing to try. If it doesn’t work :puke: I have space already reserved on my big ‘wall of shame’ for the airfoil. :cheers:

Edited August 29, 2014 by xcarguy

[seschm1234]

I had trouble reading the previously posted article. I found this on the california Caterham club website which is a higher resolution of the above referenced article on reducing drag in a Cat.

 

http://www.californiacaterhamclub.com/aerodynamic/Caterham aero art 1 copy.jpg (http://www.californiacaterhamclub.com/aerodynamic/Caterham%20aero%20art%201%20copy.jpg)

http://www.californiacaterhamclub.com/aerodynamic/Caterham aero art 2 copy.jpg (http://www.californiacaterhamclub.com/aerodynamic/Caterham%20aero%20art%202%20copy.jpg)

http://www.californiacaterhamclub.com/aerodynamic/Caterham aero art 3 copy.jpg (http://www.californiacaterhamclub.com/aerodynamic/Caterham%20aero%20art%203%20copy.jpg)

[xcarguy]

seschm1234,

 

Thanks. Been needing that link in this thread.