DIY rear wing

[StuwieP]

I've been inspired by various people on this forum and elsewhere making their own aero, and thought that I'd give it a try.
It will be inelegant and probably heavy by comparison to pieces such as Dave (Lightyear)'s.
I was wondering if people would be interested in me posting the process by which I'm creating this wing (and be able to make their own by improving/refining my design), else I'll let this post slide into obscurity. There's no DIY guide for a wing on this forum that I can find.
The process I'm using isn't my own - found on a nissan forum.

Cheers
Stu

[Magpie]

Go for it, I would say that there would be a few people keeping an eye on this thread. Have you decided if it will be a 1D or 2D wing? Split wing? Profile?

[manga_blue]

Have you decided if it will be a 1D or 2D wing? Split wing? Profile?

Redneck?

[StuwieP]

Single element, single piece - I used some basic airfoil modelling software on the interwebs to 'design' the profile, starting with a basic NACA airfoil. I doubt that it is optimised but I think I found a good balance between (theoretical) lift and drag co-efficients.

For anyone else contemplating this sort of project - as with anything DIY, be careful! Any tools which make short work of metals will do the same to errant digits. Also, if you have access to a plasma cutter, use it! Cutting the sheet alloy around the delicate profile is a nightmare with a blunt hacksaw, an angle grinder and tinsnips.

I transfered my sketch to wooden proofs with small holes drilled to locate the profile pieces. The holes are also where the spanwise tubing will run.

rough.jpg

tinsnips bad.jpg

Dad came home later and showed me the drawer in which we had a good set of snips - would have saved about and hour and a half of work.

profile.jpg

pinned.jpg

filing.jpg

The wood rasps have very rough teeth but you can't use them if the alloy pieces are too different in size - the teeth catch an dwill bend a single piece very easily but if they are all in line, as in the above photo, they are very effective. I'm sure there are easier ways to do it, but this seemed to be safest (angle grinding soft metal like alu is out - apparently quite dangerous)

Shortly after this, the workbench on which the vice is mounted broke. By which I mean fell out of the brick wall and nearly onto me. Words will be had with dad about this rather unfortunate and delaying turn of events. Anyway, hopefully in the next day or two I'll get onto the next step.

Stu

[hks_kansei]

You should be able to angle grind alloy, I've done it plenty of time without noticing any dangers that aren't inherent to using a grinder.

I made my number plate mount from 3mm aluminium and pretty much excusively used the angle grinder and the bench grinder to finish the edges.


The usual wear glasses etc applies.

edit:
http://www.practicalmachinist.com/vb/ge ... num-73038/
Google suggests a danger.

[StuwieP]

that's talking about a stone grinder but yeah there's plenty more such warnings. given that I have other options I'll go with them - I did use the cutting blade on the grinder to score the sheet to get each piece. Again, the workbench pulled out of the wall today, and fell off it's legs- a 'pretty unlikely' event, so I'll stay away from anything that is 'unlikely' to cause a serious fire or shrapnel got dad's expired race-car extinguishers handy but still.... shrapnel...
Belt sander is useful but everything gets hot very fast.

edit: Manga - If I ever attach anything like that to my car, have me committed.

[NitroDann]

It would be horrible to do this with a plasma cutter.

An angle grinder and a jigsaw would be best Id say.

Dann

[StuwieP]

clearly I know little of metal cutting.
replace 'plasma cutter' with 'anything that cuts smoothly and accurately through aluminium alloy' - a jigsaw -maybe, with the right blades. The grinder worked well, I was just wary of overusing it on the soft metal, so i took the slow, imprecise but ultimately safe method of hawsawing and cutting through scores.
Anyway, I've finished cutting so this discussion really only aids anybody who thinks this looks like it could be a good plan :S

[NitroDann]

Question time.

Length of aerofoil and its Chord?

Where is it being mounted and how?

Dann

[StuwieP]

chord is 250mm - fairly short i think, haven't much to go by. looks like 30-40cm is about average.
span will be 180cm, which is pretty big for the mx. Have the option to go out to 2m. Hanging over the flanks for sure. Will look mean shame the driver is unlikely to live up to the looks
My belief is a high aspect ratio (relatively speaking) generates less induced drag (but less downforce) than a low aspect ratio. Stock engine so not looking for WTAC-levels of downforce - not that brave either

Mounted above the roofline, should be just about in line with the rear of the car, perhaps a little further aft. 80x3mm legs will go through a fibreglass-skin removable boot to a base on the floor, fairly widely spread, again, not sure just yet. Probably another brace just below the boot-lid level to be sure. I'll almost certainly need some wires to prevent lateral movement; I'll run them to the frankenstein bolts or just near the boot hinges (through the skin). I'll also need some removable bonnet pins to hold the boot down. Hopefully I can integrate the pin locations with the wing legs and the wire points.

I have no comp regs to build to (yet). Should all be fairly easily modifiable to suit any regs (to a point - I can always just remove it)

[StuwieP]

Bench fixed, so back to business.

Each profile piece was worked back nearly to shape. A slightly (1-2mm) thicker profile doesn't bother me and it gave me room for error while I was working on them. Cutting the 16mm rear and 20mm front holes for the tubing was nightmarish because I don't have a holesaw or 20mm drill bits. Instead, I broke out the files. So some of the holes are not "round" in a traditional sense, and I was surprised that the bars fit so regularly.

Set up.jpg

The leg attachments were doubled for peace of mind. The final profile pieces now have 3 holes drilled in each of them to fit bolts for endplates. Only two of the holes will be used (couldn't find enough similar bolts lying around!) on each side - plenty strong enough anyway (I hope). 10cm extra tubing on each side was cut off. Span is now 160cm, close to the width of the mx.

If I were confident enough in my fibreglassing skills I suspect that the structure above would be sufficient to support the forces this wing will (hopefully) generate. It looks like the superstructure of an aircraft wing, but I suspect without the foam I would end up with dips and troughs of fibreglass between the uprights.
I am using expanding foam to fill the voids and to give me a solid base onto whch I can lay up the fibreglass. If it can be done without the foam, you will save the majority of this wing's cost and substantially reduce the weight (2kgs - not sure of total weight yet).

Foamy goodness.jpg

2kg (1kg ea) was just enough to fill the void of the superstructure (about 0.07-0.08 cubic metres) but I mixed the solution to slightly incorrect ratios. I would guess that properly mixed you would make about 0.1 cubic metres, remembering that it is more than just the wing volume you are filling, unless you make a sleeve for the wing into which to pour the foam (and then, due to the uprights, the foam couldn't expand to fill the whole area). Due to this, we used a spatula to manipulate the foam until it became too tacky to work with, trying to ensure it spread around the entire area of the wing, rather than into wasted space where it would be sanded/cut away. At this point, I am not sure how successful we were.