Layers of carbon for a foam core front wing?

[404namenotfound]

I did a search on this but didn't really find anyone with a question like this.

How many layers of twill weave carbon are people running to keep the wing from collapsing in a cone strike? I ran some numbers but it required a lot of assumptions and I don't want to be wrong when one of our drivers hits one of those 10# 3 foot cones.

In the past we have run 3 over a foam core and I feel we just got lucky we never hit one of the big cones.

Any help is appreciated I'd just like to validate what I came up with.

[Luniz]

Why don't you just replace the front lip on the foam core with sth. else like wood? That's what they do in model airplanes...

[404namenotfound]

What is STH? sounds interesting.

I don't think wood would be a good idea as adding more layers of carbon would be a better use of the added mass.

[Luniz]

sth. is an abbreviation for "something" ;-)

Please introduce yourself (who you are, which team etc.)

[Rex]

Why don't you just replace the front lip on the foam core with sth. else like wood? That's what they do in model airplanes...

This is pretty reasonable advice. A thinwall metal tube of appropriate diameter to meet the leading-edge radius requirements, wrapped inside your regular carbon layers, makes tech on leading edge radius rule a stress-free moment, may provide more mounting options than otherwise, and takes a cone hit with relative ease. If I could do FSAE all over again, I think the best use of added mass would be in places that prevented epic failures (i.e. wing shatters upon cone strike in endurance event) and/or reduced the number of things I lost sleep worrying about. Our drivers weren't good enough to notice tenths of pounds (or even pounds, or even 10 pounds for that matter), but a few hard cone hits along the way were almost guaranteed.

Or if you're committed to using more carbon, I can't help with that math. Maybe post your figures and someone can validate or criticize?

[Luniz]

Forget about the math... You'd have to do a non-linear explicit impact simulation (the sort of stuff they do for birdstrike in the aero industry), and you will never get all the required material properties for this sort of calculation. Also, even if you would get the material data, how would you ensure that your lamination process is accurate enough to actually produce a meaningful analysis?

[404namenotfound]

Forget about the math... You'd have to do a non-linear explicit impact simulation (the sort of stuff they do for birdstrike in the aero industry), and you will never get all the required material properties for this sort of calculation. Also, even if you would get the material data, how would you ensure that your lamination process is accurate enough to actually produce a meaningful analysis?

That's what it comes down to. I couldn't accurately model anything and it got to the point where I was measuring the properties of a cone with some weights and a ruler. Also like you said I couldn't model the carbon's properties and I was planning on just doing some test pieces once I got a force figured out. That's why I figured I might just ask what other teams do.

I do like Rex's idea with the pole. I might just do that. It seems like it would be a decent use of the mass, better than wood anyway IMO, and its down low.

[Steve Krug]

Mass of cone, velocity of impact, and elastic collision condition may be good starting parameters.

Building test pieces and attempting to replicate such an event could lead to design conclusions. With our time frame it may be difficult to construct a precise non-linear element analysis via software. It's possible though.

[Charles Kaneb]

They make tiny little cones for autocross trophies. I wonder if you could build a scale-model wing and crash test it a few times to correlate your calculations to results.

[Cunningham]

The equation is pretty simple actually.

Test wing + rigid mount + desired speed + redneck truck = yes/no

Wing Impact Test.jpg

Seriously though, we hit the wing at our target speed and had 0 damage to the leading edge. This method was much quicker and more reliable than the analysis.