Chassis mounting wing

[JMortensen]

I picked up an extruded AL wing off of ebay for a surprisingly good price. 65" wing, $379 plus tax. https://www.ebay.com/itm/324563472720 When it shipped it went from FL to WA, then to IL, then back to WA. So it went about 7000 miles to be delivered 3000 miles away. The built in gurney got bent from all the extra traveling, but only a couple inches in from the end and I think I can probably straighten some of it. I talked to the seller and I took a discount and I'll chop the end off. I think I can make it a 63 or 64 inch wing and make that work. They suggested a miter saw, which I have, so shouldn't be too big a deal to cut it (hoping). Actually just looked at it again, now thinking of hacking off the gurney instead and keeping the full width...

Looking at how to do chassis mount. Years ago I had talked to Cary and he had suggested a 1/8" aluminum plate from the hatch to the floor to take the vertical load. I still have the piece that I bought years ago. Thinking I can screw to the hatch area at the top, and just run the plate straight down to a piece of angle aluminum, and then bolt that straight to the frame rails with nutserts. The problem is where it hits the car. There is a natural angle where the outer weatherstrip goes, then a step down to another angle where the main hatch weather strip goes. I can't put the upright on the first ledge. There isn't enough room for a decent sized fastener in there. If I put it down a step, then the upright takes up too much space and I'd have to really hack into my fiberglass hatch to get it on. I think the solution is to cut a slot in the first step and slide the uprights down into the chassis and then bolt through. There is a doubled up piece of metal in the hatch there which will make it harder to get to the back side of the 1/8" sheet. Think I'll weld nuts to the aluminum to solve that problem.

Going to trace the wing profile onto a piece of cardboard and start playing with uprights. 

Plan is 1/4" 6061 for the uprights from the body to the wing. I could probably cut holes to lighten it from there, but I'm not going to worry about it right now. More fixated on getting it installed on the car.
 

Thoughts and feedback appreciated.

[jhm]

Jon, what about reworking that lower bracket in your photo (the red bracket) to tuck up inside the pocket next to the hatch mounting surface?  Finish the top of the red bracket with a nice big flat surface (maybe 2" x 8"?) that buttes up against the inside of the stock sheetmetal.  You can then shape the wing's outer mounting strut panels to use that flat reinforced area as mounting points.  I'm probably not explaining myself very well -- I'll try to sketch something and PM it to you.

 

This concept would likely provide a stronger overall design, and *maybe* less in the way of taking the hatch on & off.

[JMortensen]

I think we're on the same page there. The bracket to floor will be on the outside of the wing support, so the bolts will go through the sheet metal, the wing support, and the 1/8" plate, and then there will be a nut welded to the back of the plate. Hard to draw this stuff well, and helps if you don't change colors... duh.

Should be more like this:

Edited March 21, 2023 by JMortensen

[jhm]

Ah yes…that’s it.  I think I just wasn’t mentally picturing it correctly after reading the original post.

 

Should be a nice setup!

[tube80z]

2 hours ago, JMortensen said:

I think we're on the same page there. The bracket to floor will be on the outside of the wing support, so the bolts will go through the sheet metal, the wing support, and the 1/8" plate, and then there will be a nut welded to the back of the plate. Hard to draw this stuff well, and helps if you don't change colors... duh.

Should be more like this:

 

Looks good to me.  If that ends up being in the way you could always have a small piece that comes above the body and pip pins to the wing's uprights.  You could potentially use that system to shift the wing around if you wanted a track setup vs. an XP/SCCA legal setup.  

 

Personally, I'd not use aluminum up rights and use steel tube.  Then 3d print a a aero shaped cover.  I looked up the cost of alloy and choked a little.  I keep thinking pre-covid prices for things and getting the shock of what they are now.  Keep up the good work!

 

Cary

[JMortensen]

Thought was to have two sets of uprights, one SCCA legal and one not, the not legal setting the wing further back. AL is getting pricey, but this is surprisingly cheap. Still need to get some sheet AL to do under the drivetrain. Might do both and then go pick it up in Seattle and save the shipping cost.

Forgot link: https://www.onlinemetals.com/en/buy/aluminum/0-25-aluminum-plate-6061-t651/pid/1248

Edited March 21, 2023 by JMortensen

[JMortensen]

I like this because it's double shear and easier to fab. Wouldn't have to line up and drill 20 holes. Thoughts on slippage?

Edited March 23, 2023 by JMortensen

[calZ]

I don't see a picture of you meant to post one

[JMortensen]

Now it looks like it's in there twice.

 

[calZ]

Looks good to me. I think rather than a slot, I'd go with overlapping holes like in this picture. It would make replicating setups and matching the left and right mounts a lot easier than with the slots. 

 

[JMortensen]

Got a really strong answer on the slippage question, so I thought I'd spread it around:

"Its been awhile so I may be missing something.

Based on this calculator, its showing that torquing a 1/4-20 bolt to 20in-lb would give a preload of 426 lbs.

https://mechanicalc.com/calculators/...orque-preload/

Then going here https://www.engineeringtoolbox.com/f...nts-d_778.html

and putting in US units (Slugs) and 32ft/s2 plus 1.35 mu for aluminum

I doubled the answer because you have two surfaces sliding against each other in the pictured joint. In reality, you would have 4 because of two sides of the wing. Or only 2 if you did a single-shear joint.

So with 2, it should not slide until 1120 lbs is added to it


Also, you are sharing load with the front bolt as well.
If you slot the rear bolt, if it does slide it will lower the wing angle and reduce the downforce.
If you slot the front bolt, it will increase the wing angle and increase the downforce."

 

[Fridge Gnome]

Definitely interested in what you come up with. I've been thinking about going for this project as well.

 

Just spitballing, but the frame edge around the hatch has never struck me as a particularly weak location, I would think it could handle the ~250lbs each without the 1/8 aluminum?

[JMortensen]

Yeah, for sure the hatch area can take hundreds of lbs of force. there is a reinforcing panel underneath the pillar, and it handles slamming the hatch for decades.

My wing, as delivered, was supposed to make ~600 lbs of downforce at 150 mph. I'm probably going to make a second element for it, so might be closer to 1000. I think it needs some way to transfer that load to the floor. If you're using a wing like the one they tested in the wind tunnel (small) then yeah, just bolt it on and go.

[JMortensen]

2 options, swan and under mount. They're both less than 6" above the roofline. Swan is a lot more complicated, obviously. I think I can get the second element under 6" above roofline with the swan, would have to lower it with the standard pedestal.

Will remove the 10" autox spoiler and probably install a similar spoiler that is 3 or 4" tall.

The wing element is behind the roof in the swan, so less frontal area, although I think a second element would be almost entirely above the roof as viewed from front.

 

Edited March 26, 2023 by JMortensen

[JMortensen]

Here's the de-gurney'd wing: 

[tube80z]

On 3/26/2023 at 4:57 PM, JMortensen said:

2 options, swan and under mount. They're both less than 6" above the roofline. Swan is a lot more complicated, obviously. I think I can get the second element under 6" above roofline with the swan, would have to lower it with the standard pedestal.

Will remove the 10" autox spoiler and probably install a similar spoiler that is 3 or 4" tall.

The wing element is behind the roof in the swan, so less frontal area, although I think a second element would be almost entirely above the roof as viewed from front.

 

 

 

On the swan neck it doesn't need to go up and then down to the top.  You can have it come straight in on the wing nose and mount that way too.  Take a look at all the F1 cars for reference.  This will allow you to get the wing as high as if you mounted under.  XP rules also say wing or spoiler but not both.  Out side of that you can do whatever you want.  I'd keep the 10 incher and drop that angle down to less then 30 or so and see how it change flow on the wing.  You can use oil drops or tufts if you point a camera to see how they are moving.

[JMortensen]

I figured I wanted to straighten the airflow under the wing, but the higher it is the more pressure there will be closer to the bottom of the wing. I think there is a happy spot in there for spoiler height, but I'm doubting that it's 10". Maybe if it were laid out almost flat. Would be interesting to see what effect that would have on a diffuser, but I think to start I'll make a shorter one. This one won't lay all the way down, since the hatch has a little convex curve. Would have to slot the outer holes in the lexan.

Looked for a front mounted swan and can't find it. the F1 cars look like they're mounted to the top front part of the wing.

Edited March 28, 2023 by JMortensen

[Fridge Gnome]

I think he's referring to the arch over the leading edge of the wing, most of them are just flush with the upper surface.

 

[JMortensen]

Yep. That must be it. Thanks.

[tube80z]

On 3/28/2023 at 9:19 PM, JMortensen said:

Yep. That must be it. Thanks.

 

Sorry, I should have included a picture but that is what I meant.