JohnD

Dangerous Times Club?

Matt, No doubt your "fibreglass man" will have his own ideas, but may I offer a design I made and constructed, Gosh! Twenty years ago! Some of this account you will know already, but please forgive me for not rewriting it! And it may be useful to others. A Spitfire Air Dam/Splitter. Most cars, and a Spitfire is no exception, are wing shaped in outline, flat underneath and curved on top. As a result, airflow at speed tends to lift the car, just as the aircraft is lifted. Tyre grip is reduced, the car corners less well and it may begin to be unstable at speed. Much modern car design is directed at reducing lift, and for competition reversing it into actual downforce. While an F1 or NASCAR car has so much downforce it could be driven on the ceiling, this was not a concept when the Spitfire was designed. There are various lift reducing devices, but an airdam and splitter are easy to make, and can add to the car’s appearance. An air dam reduces airflow beneath the car, reducing turbulence and lift. A splitter is a horizontal forward extension of the bottom edge of the dam. Because the dam causes an increased pressure in front of it, a surface in front of the dam will have a high pressure on top, providing actual downforce at the front of the car! The design concept. This design is based on the spoiler that I made for my Vitesse. The Spitfire and Vitesse chassis are significantly different forward of the wheels, but the design method should serve for the Spitfire as well. The chassis rails under the engine are lower than the edge of the front valance. A flat sheet bolted to the underside of the rails will come forward several inches below the valance, and a dam between the two completes the spoiler. Diagram ‘A’ is a view of the front of a Mk3 Spitfire with a flat sheet bolted to the under side of the chassis rails. Between this splitter and the front valance is the gap filled by the airdam, and perforated by optional brake ducts and an oil cooler duct. A plan view of the splitter is shown in ‘B’, with the splitter in position under a rolling chassis in ‘C’. The actual dimensions will need to be found by fitting to the car. They will not be the same as for the Vitesse, and I don’t have a Spitfire any more, so I have not given any measurements. The general procedure will be the same. Making the splitter. I used a sheet of ¼”(6mm) marine (waterproof) plywood for the base sheet. A rough cutout for the wheel wells and for the part under the chassis rails will allow you to bolt or clamp the sheet in place and mark it out. Make sure that the wheels are clear of the base sheet, from lock to lock and when the car rolls. Decide where you will bolt the sheet to the rails. You may find some small holes in the flanges of the rails. If not, drill your own, as close to the edge of the rail flange as possible, without weakening it. The rearmost part of the base sheet needs to be wider than the width of the chassis rails (see below). The two suspension turrets are bolted to rectangular brackets that project downwards below the rails, so that two rectangular cutouts are needed on each side. You may also find that the antiroll bar (sway bar) mounts project downwards so that they need clearance holes to be made in the base sheet. These are not required on the Vitesse, but may be on a Spitfire. Mark the position of all the cutouts needed. Take a plumbline, and hang it from the bottom edge of the front valance. Move the line along the edge, marking the base sheet as you go. This will mark the foot of the air dam. Then take a length of stiff paper or thin card, a roll of spare wallpaper is good, and set this on edge along the line. Use short lengths of tape to fix it temporarily to the base sheet, and as the rear edge of the front valance is curved, it will stand up by itself. Trim the top edge of the paper so that it is just above the front valance edge. Mark the paper at the valance. When you remove this strip of paper, it is now a pattern from which you can make your mould. Now you must decide how far forward you want your splitter to project, in front of the airdam. On the Vitesse about 4”(100mm), takes it to vertically below the front bumper. The Spitfire front bumper is further forward, as much as12”(300mm) in front of the airdam, depending on model year and corresponding bumper. This is impractical, as it will scrape on bumps and run into kerbs. You must decide what looks best, and draw a smooth curve to form the front edge. If you wish to find out the best design in terms of lift/downforce, book a session in a wind tunnel! Making the mould. I made the mould in thin sheet steel, panel off cuts of 21g; about 1mm thick When cutting this out, I allowed a flange of about 1”(2.5mm) top and bottom. The bottom flange was bent to a right angle, and the top to a lesser angle, so that it would lie inside the front valance. Note that both flanges should be FORWARDS! I then curved the ends of the sheet to match the line on the base sheet. You cannot bend a sheet with a flange on it, unless you can stretch or shrink the flange. If you do not have one of those little ‘shrinker/stretcher’ gadgets, you will need to cut slots in the flanges. If this is difficult to imagine, look at diagrams ‘D’ and ‘E’, or else try making the paper model (See end of article). Even in thin printer paper, once the two parts are glued together, it becomes a fairly rigid structure. Place the finished mould on the base sheet, on the original line. Drill through the sheet and the bottom flange at several places and fix it temporarily to the base sheet with small bolts. Don’t use screws – they will be very difficult to get at when the dam is finished! Now offer up the base sheet and mould, and bolt it to the chassis rails temporarily. Adjust the shape of the mould so that the top flange fits just inside the valance. You are now ready to make the airdam/splitter! Working with GRP. There are many books that go into detail about how to use GRP, so I will only do so in general. Resin and hardener in the right proportions react chemically and become very hard, stiff and brittle. Glass fibre is very flexible, but has high tensile strength. Mix the two, and you have a hard, tough, flexible substance, Glass Reinforced Plastic, GRP, (called fibreglass in the US) that can be cast in a mould to any desired shape. The glass fibres come in a mat that looks unsightly in the final result, so the top layer of a GRP fabrication, the one next to the mould, is usually made of resin alone. This ‘gel coat’ will be as smooth as the mould it is laid up in. You can add pigment to the gel coat, or paint the GRP; it’s up to you, and some GRP ‘tissue’, rather like a paper tissue, will help hold the resin in the gel coat. Resin is also a good adhesive, so unless it is to be a permanent part of the construction, you will need to prepare the mould so that the resin will not stick to it. The traditional way to do this is to smooth the mould and then wax it with a non-silicone wax polish, or use a special “releasing agent”. Release agent can be difficult to get, unless you buy your resin and matting from a GRP specialist. Non-silicone wax polish is easier to find, but make sure that is non-silicone, or paint will never stick to the GRP! It is difficult to sand down a sheet of mild steel to a fine polish. Unless you want a really perfect finish, the easiest way is cover the steel with that thin, brown wrapping tape, sold as ‘Parcel tape’, to which resin does not stick. Check with a piece of tape and a blob of resin to make sure you have the right tape, and add a coat or two of wax to be sure. When you tape the upper flange, fill the slots or the resin will fall through! Use several layers of tape over the slots, as the tape is not strong or else use a stronger tape first, and cover that with ‘parcel tape’. This part will be invisible, so irregularities will not matter. At this stage, you should remove the mould from the base sheet again, so that you can apply a layer of GRP resin to both sides of the base plate first of all. Resin alone, well soaked into the plywood, will form a hard, smooth, damage resistant surface. Add glass fibre matting and the surface will be even stronger, but the matting will show through and leave a rough surface. Make sure that the line for the mould is well marked. To keep the holes open for later when you bolt the mould back on, leave a well waxed bolt, head underneath, in each bolt hole. When the resin has cured, remove the bolts. Sandpaper the surface on and behind the mould line to flatten any nibs and provide a key for the next layer. Then bolt the mould back onto the base sheet. Laying up in the mould. You are now ready to lay up the GRP. Follow the maker’s instructions to mix resin and hardener, and apply a thin coat of resin to the mould, as a gel coat. Let the resin go off (harden). Cut a piece, or more likely, pieces of glass fibre matt to cover the back of the mould and the strip of base sheet two to three inches behind it. Apply another coat of resin onto the mould and to the base sheet. Lay the glass matt on to the wet resin, folding it round onto the base, and apply more resin, stippling it in with a paint brush. Make sure that all the matt is wetted, especially where it overlaps itself, and that there are no air bubbles. Let this layer go off overnight. The next day, put on another one or two layers of resin and glass, allowing the first to go off, and you are finished! Leave the splitter for another day or two to really harden. Then remove the bolts securing the mould, and prise it loose. This may be harder to do than you expect, but persevere, levering from the edges and bending the mould rather than product. The curvature of the airdam makes the structure very rigid from side to side, but some front to back strengthening may be needed between the ‘dam and the rails. As you have cut the base sheet wider than the rails, you can add a ridge of GRP along the edge, from the rear corner straight forward to the ‘dam, outside the rails. See diagram ‘B’. Anything that will raise up a ridge of GRP will do, a wooden dowel, a piece of plastic tube or cardboard. Place this where you want the ridge, lay up another coat of GRP over it, and the sheet will gain enormous rigidity. Buy the cheapest possible brushes for laying up GRP, and throw them away; they are impossible to clean afterwards! Also buy yourself some disposable rubber gloves and throw them away frequently. Resin on the hands is very sticky and can cause dermatitis. Glass fibre can leave tiny irritant pieces in the skin for days afterwards. Mounting the splitter. The bolts into the chassis rails are into the flange on the inside edge of each rail, to give you access to the nut on top of the flange. I use cheap, dome headed roofing bolts, with little square nuts. The dome head minimises the possibility that it will catch on kerbs and bumps. The rail flange is quite narrow, and the nut will need to have a millimetre or two cut off one side, so that the bolt hole is not too close to the edge of the flange. If the nut edge is right up against the inside wall of the rail, it will be semi-captive, making fitting the splitter much easier. Once the base sheet is bolted to the rails, with the lip of the airdam inside the valance, it will be self supporting. The curvature of the dam, and its’ long base on the splitter, will make it very strong, like a wing. If the ‘wingtips seem to flap, add a piece of 6mm threaded rod behind the dam between ‘wingtip’ and a bracket inside the valance, or the internal bumper bar. Drill through the base sheet and use a washer each side to spread the load. Additional options. Because of the high pressure in the ‘stagnation zone’ above the splitter and in front of the dam, this is a very good place for cooling air intakes, for brakes or an oil cooler. You can make your own, or like me buy them ready made from a performance shop or by mail order. Demon Tweeks in the UK have a selection. If they are fixed in place on the mould before lay up, they become part of the dam, or you can cut holes and resin them in later. Some books on how to use GRP. - Books on GRP for boats; the techniques are the same – see Amazon. - Competition car composites by Simon McBeath, Pub.Haynes. - Ch.7, ‘Glass-fibre bodywork’, The Car Bodywork Repair Manual, by Lindsay Porter, Pub.Haynes. - The West System is a range of very high quality GRP products for boat building. Their “Technical Manual/Product Catalogue” is full of useful information and techniques for using GRP to build anything, and used to be FREE, from: Wessex Resins & Adhesives Ltd. 189/193 Spring Road, Sholing Southampton SO19 2NY Or: Gougeon Brothers Inc. Bay City Mitchigan, USA Acknowledgement. I am very grateful to Mike Nelson of Omaha for his help in translating my Vitesse experience into Spitfire possibilities. © John R.Davies, February 2001 PS Here's another pic of the airdam fitted and in action:

Wow! I had to look up an "MG42"! In my school's army cadets, I got to learn to strip and reassemble a Bren gun, and then to fire it. Three rounds, easily counted even on automatic, then re-aim. I doubt that was possible on the German gun! John PS should we rename this site "The Dangerous Sports Club"?

Sugar and weedkiller (NaClO3) anyone? Suitably confined it makes (made) a good bang. John

OoooooooooooooooH! Home explosives! Yummy. Anyone else remember the 'syrup tin' experiment in school? It works much better wit the can inverted! My school didn't run to a cylinder of hydrogen, but it works just as well with household gas. I was reminded of it at our recent visit to WonderLab at the Science Museum, where the same procedure was used to demonstrate 'Rockets' wioth a Pringles tube. John

Shyster? Or does the Type OO include a built in loo?

Maybe that's why the word "crucible" implies a ceramic container? Yes, molten aluminium + water = Aluminium oxide + Hydrogen. The hydrogen then burns/explodes. Exploding hydrogen balloons are dramatic but hydrogen in oxygen is a different matter! Hydrogen Balloon Explosion Analysis - 24-25 We saw this done at the WonderLab at the Science Museum last weekend - H2 +O2 is MUCH LOUDER than in the video! John

Hah! I follow that link to that website and am greeted with the demand that I accept 'cookies'. I can reject, but isn't it ironic that the, slightly paranoid on privacy, website wants to use my data? JOhn

I think this attitude stems from memories of the Holocaust. For generations, the Jewish diaspora tried to fit in, to conform to Gentile mores and the states they lived in. They dressed and behaved like their neighbours and largely were rewarded by acceptance. When the state(s) said, get on board these cattle trucks, they did as any obedient citizen would and got on the train. The Jewish state took the opposite attitude; never again will anyone/anystate tell us what to do unless we want to do that. When that attitude coincides with the Old Testament's "An eye for an eye", it describes Israel's post-war foreign policy. John

Not you, Paul! I saw the same distortion on Reddit and other "social" websites.

A "Corner weight guage" is more convenient if you are adjusting suspenson to achieve desired weighting. Rather than drivingjitbon and off the scales, you just insert it under a corner, lift and read.

"Raydon Glover" is Jaguar's CEO. I think the above is a deranged Internet distortion. But Jaguar have finally revealed the Type 00 ('Zero Zero') model, as above in "Miami Pink' or 'London Blue'. Available for sale in 2025, if you belive it, at more than £100K. Either way makes you wonder what they have been taking. John

Oh! You want corner weights?

Sigma, Have you considered a weighbridge? Commercial vehicles must be weighed and these are there to do that. To find one, ask your local council if they have one, or else look at: Find a weighbridge - GOV.UK John

I used to wonder about the support for Israel from America. It's not "the Jewish vote" - there aren't that many Jews in the US. Then I listened to, as I have to many episodes, Melvyn Bragg's "In Our Time" about 'The Rapture'. This is a religious legend that says that all true believers, living or dead, will be gathered up into heaven at the second coming of Jesus, while everyone and everything else will be destroyed. The usual narrative of this begins with the return of the Jews to Palestine and years of "troubled times", both of which we can all recognise. 10% of Americans, at least 40 million voters, believe that they will see the second coming in their lifetimes. That's the vote that supports Israel. John