Wing vibration

[4SQR]

I am seeing a lot of vibration at the ends of the wing at speed. In two places where the strut is attached I am seeing cracking. I am running 5* angle. I would prefer the strut be bolted to the frame, but that would mean a redesign of the back shell for removal. I may run without the wing to see what the drive is like.

Looking for thoughts on all.

 

[RushR.Rentals]

I studied aerodynamics for a few years before I changed my field of study.

I tend to stay way far away from aerodynamic discussions on general automotive forums .

a wing can have some movement side to side with no bad effects on the wings performance.
what you do not want is a wing to move fore and aft as this will tend to also change the wings angle.
this is a problem I'm working on with the rush cars at this time with out having to change the clamshell and still making the clamshell removable quickly.
also there is not enough structor around the wing where they mount to the supports/uprights . the only good fix for the strength around the mounting points of the wing is to add it in during the wings production.

 

[4SQR]

This is what I am observing

 

[RushR.Rentals]

how's the underside look around the mounting area?

 

[4SQR]

how's the underside look around the mounting area?

 

[Bill Wright]

how's the underside look around the mounting area?

@RushR.Rentals I believe this question is asking what the "underside" of the clamshell looks like "around the mounting area" where the wing support mounts to the clamshell?

@4SQR , you write you are " running 5° ". Does this mean you have moved the wing from the "standard/factory" position?

The baseline calls for the wing to be in "Hole A". I can't locate the info showing which hole that is. My car came with the wing running as "flat" as the standard mounts allow.

 

[4SQR]

@RushR.Rentals I believe this question is asking what the "underside" of the clamshell looks like "around the mounting area" where the wing support mounts to the clamshell?

@4SQR , you write you are " running 5° ". Does this mean you have moved the wing from the "standard/factory" position?

The baseline calls for the wing to be in "Hole A". I can't locate the info showing which hole that is. My car came with the wing running as "flat" as the standard mounts allow.

Bill- I misunderstood. Will get a pic.
I did move it one hole but it’s hard to describe without a pic. In any case, I have been educated about airflow dynamics and these wings. Will obey my betters in the future. Lol.

 

[RushR.Rentals]

with our two cars the wing angles at the factory setting was at .5 degrees tilted up in the front.
with a little pressure pulling back on the wing it easily moved to 1. degrees up in the front. pulling the wing back harder it went to 1.5 degrees up angle in the front measuring the wing in the center.
a leading edge of a wing should be facing straight into the flow of air. on many cars this isn't also that a wing angle is at zero angle on a horizontal plane.
on some cars as the airflow over the roof and down the rear glass the airflow is coming down on a downward angle.
I would love to see a better simulation of the rush sr airflow over the car to see just how it's hitting the leading edge of the wing. the best I will be able to do is setup a pitot tube. from the sim it looks like the airflow is hitting the wing straight on a horizontal plane????

by setting the wing at IMO a 5 degree down angle being a twist wing is that the two outside edges acted like cups putting excessive pressure at the weakest spots of the wing. it was also basically putting the wing into a stall having the airflow on the underside lifting off the wing.
all this is a total hypothesis with out having enough data to support anything.

 

[Licklobster]

with our two cars the wing angles at the factory setting was at .5 degrees tilted up in the front.
with a little pressure pulling back on the wing it easily moved to 1. degrees up in the front. pulling the wing back harder it went to 1.5 degrees up angle in the front measuring the wing in the center.
a leading edge of a wing should be facing straight into the flow of air. on many cars this isn't also that a wing angle is at zero angle on a horizontal plane.
on some cars as the airflow over the roof and down the rear glass the airflow is coming down on a downward angle.
I would love to see a better simulation of the rush sr airflow over the car to see just how it's hitting the leading edge of the wing. the best I will be able to do is setup a pitot tube. from the sim it looks like the airflow is hitting the wing straight on a horizontal plane????

by setting the wing at IMO a 5 degree down angle being a twist wing is that the two outside edges acted like cups putting excessive pressure at the weakest spots of the wing. it was also basically putting the wing into a stall having the airflow on the underside lifting off the wing.
all this is a total hypothesis with out having enough data to support anything.

View attachment 547

Long time lurker and future customer when I return to mainland US and wanted to comment here. Wings (well, airfoils) are not necessarily designed in the manner you speak - and often the application on a vehicle is an afterthought compared to their use and design in open space; especially in the case of established NACA profiles and foils.

The foil is going to work within a 10-16* window and stall on both ends of that window, due to reversion (usually -4* to 12* or so, depending on foil - im not sure what NACA profile Rush uses, maybe they'd share). Measuring the AOA with a flat bar and adjusting that AOA to the lift/drag profile you're targeting is the solution here. Downforce isnt made on the top of the wing, it's made on the bottom. The profile will dictate how you measure for AOA. My two cents. Do agree some type of cross bracing is necessary, whether that's cables or otherwise. X cables will cost you almost nothing and almost completely eliminate lateral movement and "shake/shimmy" because they keep the wing structure in constant tension in both directions.

The damage here looks like it's from shake/shimmy and tension cables would eliminate that.

Example (not my page, no affiliation)

Sean Wally - Wing Bracing

My second project from the weekend was to add a set of tension cables to the wing mounts on the Exocet. The problem is that because the wing sits on two steel mounts about twenty four inches away from the chassis, there's a lot of play, vibration, and oscillation that gets amplified. Over time...

wheelwell.com

 

[Bill Wright]

Early RUSH SR's had a cable cross bracing on the wing supports.

 

[Licklobster]

Something that should absolutely be added back.