Windtunnel testing an RC10L3 (pics) - Page 2

kekekek · #26 02-05-2004, 04:21 PM

ummmmm go KU!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

B4man · #27 02-06-2004, 01:31 AM

Richie: Yea, those uniforms are bright, but I didnt notice sitting 3 miles away in the student section, lol.

Im trying to get some graphs together as I type this. I'm wondering if I should just put a link up so people can download my research paper in PDF format, but I dont know how many people will read 30 pages, lol.

In the meantime, here is a pic of the setup from outside the windtunnel:

B4man · #28 02-06-2004, 02:30 AM

Ok, I have have the graphs setup. I lost a lot of resolution converting them to JPGs, but you get the idea. This graph shows drag force in pounds for the various wing configurations:

B4man · #29 02-06-2004, 02:44 AM

Here is the graph for downforce. Now the important thing to notice here is that the baseline body (no wing or spoiler) created a significant amount of lift, which is bad when youre racing at 70 mph. Also, you'll notice the downforce of the STD wing seems to level off at a certain point. This is due to the immense deformation the wing undergoes at the higher velocities. This causes the wing to become less efficient, thus decreases downforce:

B4man · #30 02-06-2004, 02:58 AM

If you guys want to contact me, my email is:

nmaz@iastate.edu

or

djshortround@msn.com

RichieRich · #31 02-10-2004, 04:32 PM

Amazing. You know, I might want to read your paper. This stuff is very interesting. Then, maybe I can appear intelligent when people talk about this stuff.

The fact that the baseline reading shows body lift without the wing is pretty interesting. You would have to run with a wing no matter what to combat the lifting effect.

-=ADA$=- · #32 02-10-2004, 04:43 PM

so maybe connetcing wing like in 1/8 almost directly to the wheel hubs, it shouldnt deform like this, and be much more efficient

InspGadgt · #33 02-10-2004, 06:43 PM

B4 that's some great data!

ADA...I'm actually surprised 1/8th is still using this method...I think it possibly has more to do with keeping wheel clearance then actual downforce issues though. Real formula 1 racing tried having it's downforce on the rear hubs for awhile and found that it works better to have the downforce applied to the chassis rather then to the wheel hubs. I can't remember the reasons right now so if you want more specifics I'd have to do some reasearch. I've actually been considering experimenting with my 1/8th and mounting the rear body mounts to the chassis rather then the suspension.

InspGadgt · #34 02-10-2004, 09:09 PM

I'd also look at testing with different thicknesses of wing wire for less flex or even a 4 point mount system for better support.

MegaMe · #35 02-11-2004, 12:53 AM

interesting you can see the standard wing becoming less efficent at high velocities compared to the naca wing i assume due to its flexing.

i would imagine that attaching the wing to the body would mean the suspension compresses at high speeds? compared to attaching to the suspension

-=ADA$=- · #36 02-11-2004, 03:47 PM

to be true i dont know that much about this method, just looked if it would help, and my point was to connect wing directly to chassis, cause body is rather flexible, and 1/8 onroads use "similar" thing, wing "bolted" to wheel hubs

InspGadgt · #37 02-11-2004, 05:08 PM

Ah I see...well pan cars like this used to have the wing connected to the rear pod which would make the force effective like that of a 1/8th on the wheel hubs. I think they went to a body mount system to put downforce to the chassis through the body. I had a friend who did something similar and mounted the wing to the body mounts. This would probably be more effective but it's more of a hassle to do.

MobileMikeV · #38 02-11-2004, 08:50 PM

that wing is much much too high on that cars. The affects on a real car would be much different with the wing mounted lower.

InspGadgt · #39 02-12-2004, 05:10 PM

The higher the better...the wings on real street production cars are primarily for asthetics and do little or nothing for the car. Look at the GT class racing cars, they have their wings up very high. The reason being is there is a low pressure area that develops behind the rear windshield which makes the wing less effective. It's better to get the wing up above the roof line or as close as the rules allow to get cleaner air flow over the wing and more downforce.

AudiTT-Quattro · #40 02-12-2004, 06:17 PM

Quote:

Originally posted by InspGadgt
Ah I see...well pan cars like this used to have the wing connected to the rear pod which would make the force effective like that of a 1/8th on the wheel hubs. I think they went to a body mount system to put downforce to the chassis through the body. I had a friend who did something similar and mounted the wing to the body mounts. This would probably be more effective but it's more of a hassle to do.

Either way, the force is still applied to the chassis no matter how you connect the spoiler to the body or rear pod.

B4man · #41 02-12-2004, 07:17 PM

The mounting positions (either mounting the wing on the body or directly to the rear motor pod) I had to think about. I wanted to have the setup that most racers have used on their superspeedway setups. Mounting the the wing on the body does have its disadvatages because it does compress the suspension as downforce is increased on the wing. This might change the handling due to its lower ride height. Mounting the wing on the motor pod through the body has the advantage that the downforce does not compress the supsension and change the suspension settings, but the holes through the body need to be fairly large to allow rear pod movment with the wing wires through the body. This might cause some pressure differences that wouldnt be desirable at speeds. Also, mounting the wing right to the body makes it much easier to remove for maintenance. Thats probabaly the biggest reason racers have the wing attached directly to the body.

B4man · #42 02-12-2004, 07:20 PM

Audi is right, no matter how the wing is connected to the car the downforce is still transferred to the wheels.

InspGadgt · #43 02-12-2004, 07:22 PM

Quote:

Originally posted by AudiTT-Quattro
Either way, the force is still applied to the chassis no matter how you connect the spoiler to the body or rear pod.

Everyone I learned from considered the pod not as part of the chassis but as part of the rear suspension. In the case of the wing being attached to the pod the force is applied pretty much directly to the wheels whereas on the chassis it's applied to the wheels through the suspension.

B4man · #44 02-12-2004, 07:32 PM

Mobile: yes, the wing is very high. One of the tests i wanted to run was to vary the height of the wing relative the the back of the car, that is why i had used the adjustable bolts to allow for an almost infinite amount of adjustments. But due to time restraints i wasnt able to test varying heights of the wing. It does render the wing a little less efficient as a lower wing would place it within the turbulent flow behind the car. BUT, and this is a big but, there is a height that can be attained were the wing will aid the flow underneath the car in a phenomenon called ground effect. And this wing placement might be fairly low, almost counterintuitive. This is why some of the prototype cars or even Indy and F1 cars have multiple levels of wing and some might be fairly low, but these low wings increase this ground effect significantly by helping direct the flow from underneath the car.

KMac · #45 02-12-2004, 07:55 PM

Quote:

Originally posted by InspGadgt
The higher the better...the wings on real street production cars are primarily for asthetics and do little or nothing for the car. Look at the GT class racing cars, they have their wings up very high. The reason being is there is a low pressure area that develops behind the rear windshield which makes the wing less effective. It's better to get the wing up above the roof line or as close as the rules allow to get cleaner air flow over the wing and more downforce.

That's only partially true. The resultant aerodynamic downforce from the wing MUST be directed straight through the centerline of the rear tire or else you get undesired results. If the aerodynamic downforce points behind the centerline of the rear tire you get downforce on the rear PLUS a torque about the rear axle. This torque will actually produce UPWARD force on the front tires causing you to lose grip and understeer.

Try this: get a hotwheels or matchbox car and push downward on it from straight above the rear wheel. You'll notice the rear of the car squats down. Now, put your finger on the very back of the trunk and push down. Notice how the rear end goes down BUT the front end comes up. Not good!!

Now, put your finger on the rear windshield (ahead of the rear tires) of the car and push down. Notice how both the front and the rear of the car squat down.

Now, imagine a wing mounted down on the decklid of the car and it's aerodynamic downforce is directed a couple of inches behind the wheels. No big deal. But, if you begin to raise the wing, that downforce now points further and further behind the wheel producing more and more lifting force on the front wheels. Happy steering!!!! You're on your way to the "Darlington Stripe"

In theory (and only generally) the best wing solution would be a wing mounted just ahead of the rear windshield on the top of the car. At this point it would see a huge amount of airflow and could be reduced in size to get the same downforce as a trunk mounted wing. You could also adjust the pitch of the wing to alter its aeronynamic downforce direction to keep it ahead of the rear tire and produce downforce on both the front and rear tires, and be able to slightly vary the ratio of rear/front downforce.

Class dismissed.

B4man · #46 02-12-2004, 07:59 PM

Now when I was watching some superspeedway racing, almost all the racers cut out the rear of their bodies to completely expose the rear pod. The theory is that this decreases drag. I ran tests to prove this theory. On this graph, I dont have drag measured in pounds, this is how the drag was meaured (in voltage) , and then I converted it to pounds later. Also, there is alot of data here, and some of the lines can be difficult to read. This shows drag with the body fully enclosed (back) and with the rear cut out (no back). This is pretty intersting:

B4man · #47 02-12-2004, 08:11 PM

There is virtually no change in drag from removing the back of the car. The change comes in the form on downforce. There is a large increase in downforce from the removal of the rear of the body. The feeling that racers have of increased speed is actually an increase in downforce, which could translate into better handling. Here is the downforce graph comparing the back vs. no back conditions:

B4man · #48 02-12-2004, 08:28 PM

Quote:

Originally posted by KMac
That's only partially true. The resultant aerodynamic downforce from the wing MUST be directed straight through the centerline of the rear tire or else you get undesired results. If the aerodynamic downforce points behind the centerline of the rear tire you get downforce on the rear PLUS a torque about the rear axle. This torque will actually produce UPWARD force on the front tires causing you to lose grip and understeer.

Try this: get a hotwheels or matchbox car and push downward on it from straight above the rear wheel. You'll notice the rear of the car squats down. Now, put your finger on the very back of the trunk and push down. Notice how the rear end goes down BUT the front end comes up. Not good!!

Now, put your finger on the rear windshield (ahead of the rear tires) of the car and push down. Notice how both the front and the rear of the car squat down.

Now, imagine a wing mounted down on the decklid of the car and it's aerodynamic downforce is directed a couple of inches behind the wheels. No big deal. But, if you begin to raise the wing, that downforce now points further and further behind the wheel producing more and more lifting force on the front wheels. Happy steering!!!! You're on your way to the "Darlington Stripe"

In theory (and only generally) the best wing solution would be a wing mounted just ahead of the rear windshield on the top of the car. At this point it would see a huge amount of airflow and could be reduced in size to get the same downforce as a trunk mounted wing. You could also adjust the pitch of the wing to alter its aeronynamic downforce direction to keep it ahead of the rear tire and produce downforce on both the front and rear tires, and be able to slightly vary the ratio of rear/front downforce.

Class dismissed.

What youre talking about is a balance in downforce between the front and the back. Any correctly aerodynamically engineered race car will have almost the same downforce in the front as in the rear, just as weight distribution is almost 50% front and 50% rear. Your theory of the best solution is somewhat flawed in that it is not a very efficient way to make downforce, it cause a significant amount of drag. Thats why you dont see many race cars with your 'best wing solution'. The most efficient way to create an even amount of downforce is by the use of ground effect. It is sad that this type of design has been banned or limited in many forms of racing and if it is used, its elegance is never seen from outside the vehicle.

InspGadgt · #49 02-12-2004, 08:39 PM

Ah but we're talking about 2 different things here Kmac...one being the effectiveness of the wing in it's placement in the airflow behind the car and the other being the force applied to the rear wheels and how it's leveraged.

True it is better to have the downforce applied directly over the axle or in front of the axle rather then behind to keep the front end from lifting. But lifting the height of the wing straight up does not move the wing more behind the axle. In fact because of the angles involved it applies the force as if it were closer to the axle rather then further away. But what it does to is move the wing up into cleaner air making it more effective thus applying more force behind the axle line. Take a look at my quick drawing...the lower point of the triangle is your axle and where the arrow is is the force applied by the wing. Both triangles have the force from the wing applied the same distance behind the axle but the second one the wing has been raised to twice the height of the first. Given if the wing is in clean air in both scenarios it will apply the same amount of force vertically to the triangle at the point where the arrow is. Because the angle from the wing to the axle in the first triangle is closer to parallel with the chassis it will have more leverage to lift the front of the car then the 2nd triangle with the raised wing. But if you throw this in on a car and say the first wing position is below the roof line of the car in the lower pressure area the wing itself will provide less downforce then the 2nd triangle with the wing higher up and in the higher pressure area.

InspGadgt · #50 02-12-2004, 08:46 PM

Right B4...by using ground effects your reducing drag by having to run less wing for down force and increasing down force by creating somewhat of a vaccuum under the car. However this comes at a cost too though as ground effects are very speed dependant making it a very tricky balancing act indeed.

I should add to my earlier post that front end lift only comes when the downforce applied behind the axle is greater then the downforce and weight of the front of the car combined. Until that point you can easily create more grip out of the back tires by moving the wing back. Early F1 cars ran their wings much further back then today's F1's and only moved those wings foward when they were forced to by the rules.