Wing Construction

[Wesley]

University of Oklahoma has been running wings for two years now in competition, with a very noticeable effect, but we're still working on refining our construction methods. The wings support themselves adequately on the track, as they haven't broken or fallen off under normal operation, but we've run into quality issues during manufacture.

The first problem is one Claude points out to us every year, as he puts his body weight on our wing and we listen to it crack. We're currently using the "taco-style" manufacturing method (thats the scientific term) which entails forming the wing profile on a mold with an open trailing edge, then bonding the halves together around aluminum ribs to create a closed profile.

With no spar on the rear wing, we're relying on the two wing-shaped thin sheets of carbon for all of our rigidity, but adding a spar that will contribute any actual rigidity will end up weighing a ton.

What we're considering for next years wing design is sandwiched honeycomb - wrapping a wing profiled sheet of honeycomb in carbon, but we're at a loss to find a way to shape the honeycomb without destroying it. Machining in our router may work, but it seems like overkill, and tools may still grab.

Alternatively, hot wired foam with wood ribs and brass tube spars (model airplane style) could work, but would also be moderately heavy.

Does anyone have any useful yet light construction methods they are willing to share that will keep Claude from snapping our wing off at next years competition?

Secondly... we need to work on our build quality. Claude observed the gap difference on each side between the slats on the front wing and commented "It's like having two different girlfriends," much to our amusement. But that just comes down to practice and attention to detail.

[Superfast Matt McCoy]

Originally posted by Wesley:
Secondly... we need to work on our build quality. Claude observed the gap difference on each side between the slats on the front wing and commented "It's like having two different girlfriends," much to our amusement. But that just comes down to practice and attention to detail.

He said it like it's a bad thing? Last year we wrapped electrical tape around the edge up against the end plate to hide the gap. Like having two girlfriends, but being sneaky about it.

You could just find some alternative materials and manufacturing methods, find the weight difference, and argue quantitatively that the very lightweight squeeky-squeeky design is better than the XXlb heavier non-squeeky-squeeky design. Point out that the loading of the wings on track does not include being leaned on by a fat Belgian man. Maybe point a camera at the wing during an acceleration run to show its stiffness in use.

If you think you really need stiffer wings, you might look into three dimensional honeycomb that is advertised as machinable.

[Bullitt]

I've had a lot of experience with wing construction this year. We were attempting to run an aero package at West this year, but it didn't quite pan out. I would start out by suggesting that you not be too concerned about weight for your first iteration. Our entire package came in at under 30 pounds, even though the wing elements were constructed almost entirely out of fiberglass and expanded polystyrene.

I like the "taco" method you are using. We had originally planned to use a similar method to construct our rear wings, but time was running out and it was easier to just wrap the fiberglass around foam instead of building molds. We had not planned to use any internal structure, but since we didn't build them like that I don't know how it would turn out. It seems like it would be easy enough to add an efficient spar if you are already tossing ribs in there. Remember you mechanics of materials classes; most of the mass should be in the spar caps to help with the bending stress, and the spar web should be very thin as it is only there to take the shear stress.

For the front wings, I would recommend wrapping some sort of polystyrene (expanded or extruded) in fiberglass and/or Kevlar. The main concern with the front wings is the ability to withstand cone impacts, and the foam really helps to absorb the energy of cone hit. We were lucky enough to get a local company with a CNC hot wire machine to cut our profiles for us. We wrapped the leading element of the front wings with two layers of fiberglass and one of Kevlar, and the rest of the element with just two of fiberglass. These not only stood up to cone impacts, but also survived being sucked under the wheels when a mount failed. It took a sticky throttle and a curb to actually destroy the elements (see pic), and they also saved the chassis and suspension from any damage.

[exFSAE]

You could just find some alternative materials and manufacturing methods, find the weight difference, and argue quantitatively that the very lightweight squeeky-squeeky design is better than the XXlb heavier non-squeeky-squeeky design. Point out that the loading of the wings on track does not include being leaned on by a fat Belgian man. Maybe point a camera at the wing during an acceleration run to show its stiffness in use.

Agreed on all points.

[RiNaZ]

Wesley, how much or how big is your Al ribs? You can try adding carbon tubes along those Al ribs. Or you can make a foam core with a carbon spar that goes along the wing. Check your library out, they should have some sort of video from burt rutan on how to do the wing w/out a mold. Here's some suggestion that you guys probably thought of. The red color represents carbon.

[kapps]

Interesting. I'll have to pass it on to our body guys. BTW, what's up with that tire. Positive camber?

[vreihen]

Originally posted by Bullitt:
We wrapped the leading element of the front wings with two layers of fiberglass and one of Kevlar, and the rest of the element with just two of fiberglass.

Was the Kevlar the outer skin, or under the fiberglass? Just curious.

FWIW, I noticed from pictures that I've seen around the web that at least one car running composite wings has them wrapped in clear chip/stone guard, I'm guessing due to "marbles" from the course getting picked up and chipping the composite skins. Did you observe this in any of your wings with two layers of fiberglass during your testing?

In terms of weight, it is simple to estimate the weight of a foam-cored wing. The typical Home Depot pink/blue foam is 2 pounds/cubic foot. (If you're using real composite-grade core foam, the density should be on the spec sheet.) The composite cloth is specified in ounces per square yard, and guestimating the fiber/resin ratio isn't too difficult. I'll leave the metric conversions as an exercise for the reader. Before you rule out this construction technique as being too heavy, I hope that you have at least crunched these numbers.

Oh yes, as an added plus, the foam inside will completely deaden the cracking sounds from the "Claude test" next year.....

[Bullitt]

Originally posted by vreihen:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bullitt:
We wrapped the leading element of the front wings with two layers of fiberglass and one of Kevlar, and the rest of the element with just two of fiberglass.

Was the Kevlar the outer skin, or under the fiberglass? Just curious.

FWIW, I noticed from pictures that I've seen around the web that at least one car running composite wings has them wrapped in clear chip/stone guard, I'm guessing due to "marbles" from the course getting picked up and chipping the composite skins. Did you observe this in any of your wings with two layers of fiberglass during your testing? </div></BLOCKQUOTE>

The first time around we had the Kevlar on the outside, just by coincidence. We found out really fast that it looks terrible if you have to do any sanding on it, so the next set had the fiberglass on the outside.

I didn't notice any chipping on the wings. I attribute this to the flexibility of the fiberglass and kevlar, the foam support underneath, and the room-temp cure we used for the resin.

[Wesley]

Originally posted by Superfast Matt McCoy:

He said it like it's a bad thing?

Point out that the loading of the wings on track does not include being leaned on by a fat Belgian man.

Well, one of the girlfriends was a trifle on the loose side. And it was because we're not running full inside endplates - it was the actual slat spacing, not the endplate gap.

Also, it was more that he almost broke our wing off, and we want to prevent that from happening, regardless of how we prove it doesn't need to be stiffer. On top of that, we're still having tire and endplate rubbing problems, indicating some transient stiffness issues.

I know they can be made stiffer without a weight penalty. I've got some ideas for a few methods I'm going to test out now, so if I come up with anything grand I'll definitely post it.

@RiNaZ: That's a good idea, I saw it implemented on an RC plane site, and I may give that a shot. Balsa, if not carbon, anyway.

[MalcolmG]

We ran wings in 2005 and 2006, they were fairly stiff, a sponsor of ours who is a composite part manufacturer has used our moulds and AFAIK a similar method to us to make wings for a numer of race cars that see speeds well in excess of FSAE, without any reported failures (yet).

The elements were made inside a female mould - challenging but not impossible. Material was 3K carbon pre-preg, with a small (probably around 5mm tall, 30mm wide) honeycomb strip on the lower face (with, obviously, a layer of carbon on top) to give it stiffness in bending. The only failures I ever saw were due to the bosses we post-bonded in for the end-plates pulling out.

There's a few pictures of the car on our website, under the 2006 galleries: http://www.fsae.co.nz/index.php?opti...ery2&Itemid=28 Nothing really showing wing construction though