Spaceframe Chassis Materials

[av8rirl]

Hi

This has probably been asked b4: What materials are used by chassis constructors (eg Van Diemen, Mygale, Vector, etc) in their Formula Ford Zetec chassis? I assume that it is a type of steel, but what is the exact spec??? Also, the welds? Bronze welded?? Anyone???

Much appreciated.

[KC]

If they are tubular space frames, then the best material to use is SAE 4340 steel. The shear stength of this material is up to 200,000 pounds per square inch depending on material specification and purity. A lot of people refer to this material as Chrome-Moly Steel. To create the strongest weld it must heli-arc welded (inert gas envelope) to reduce oxidation during welding. The welding rods are typically an allow of the same metal. If done properly the weld joint has a higher tensile strength than the two materials joined. NASCAR stock cars and sprint cars usually sport large diameter chrome-moly tubing frames.

If the chassis designs are more on a monocoque design then many lightweight non-ferrous alloys are available and the design of the structure becomes paramount as lower strength materials are used. Aluminum is prevalent in many lower cost monocoques and the typicval grade is T6 aircraft alloy. This material is heat treated and then annealed to increase its tensile strength. If cost is no object, then more exotic alloys, like Titanium or Carbon Fiber, are used instead. Colin Chapman popularized this design in many of his Lotus formula and sports car designs. The beautiful Jaguar D-type racer is an excellent example of an aircraft derived aluminum monocoque.

Hope this helps.

[ghinzani]

Originally posted by av8rirl
Hi

This has probably been asked b4: What materials are used by chassis constructors (eg Van Diemen, Mygale, Vector, etc) in their Formula Ford Zetec chassis? I assume that it is a type of steel, but what is the exact spec??? Also, the welds? Bronze welded?? Anyone???

Much appreciated.

I notice your racing FVee next year - planning to build your own chassis? there must be some plans out there on the web somewhere? Keep us informed if you do!

[av8rirl]

Thanks KC.

I'm just doing some homework before I go about building my first Formula Vee. I'd also like to use a roll hoop similar to the current day removeable Zetec ones. Any idea on the bolts used for attachment to the main chassis??

Maybe wondering if anyone knows of a good shareware version of a design package/finite element analysis/etc... as I'd like to create a model of the car first..

Grateful.

[av8rirl]

Yes Ghinzani

Hoping to build and race. The plans have been on the board for the past two season. Hoping to take the best bits from Vee's around the world and update them with some bits from todays Zetecs. Here are the priorities:

1. Driver cockpit safety
2. Structural rigidity
3. Aerodynamically (very) efficient
4. Cooling for that aircooled engine (VIP)
5. Easy to work on / adjust / set up
6. Look modern (too many old looking cars)
7. Go like the DB's
8. Not telling

If you see any plans around the net, post the url (please). Check out the Borland Racing site in Australia www.borlandracing.com

Nice formula fords...

[Ray Bell]

While some may well use chrome moly tube, most spaceframes have been from mild steel ERW tube, from F1 on through the classes.

I think ease of repair, reduced complications in welding etc have been cited as the reason.

Nickel-bronze welding has always been popular, with nice gusset filling, not a lightweight attachment. MIG is also used.

[KC]

The various sprint car guys like to use heavy Chrome-Moly tubing for the mai structure and then use mild steel tubing for nerf bars, push bars and other areas that may be struck during the race. Their idea is that bending it is better than breaking it and the mild steel tubes can be fixed at trackside much easier.

[bobdrummond]

I'm always a bit concerned that people's first idea when contemplating a design is "What do the others do?". You may be selling yourself short in that you could be capable of coming up with a better solution to your problem by approaching it in a different manner. My suggestions would be:

1)Study the Formula Vee rulebook. Is there a chassis material specified? Is the tubing/gauge specified, etc.

2)Don't look at competitor chassis until you've thought about it yourself first. Doing that could preclude you coming up with a good idea.

3) Don't underestimate the potential hassles in building a 'simple' spaceframe chassis. If you can, re-read the RaceTech articles on The Pashley Projects.

4) Bolts for the roll-hoop depend on the loading (shear/tension). If weight isn't a big concern, try using dowels, spigots or shoulder bolts to take the loads while using the bolts just to clamp the parts together. When you do use bolts, use the best quality you can afford and remember to use them correctly.

5) Remember that manufacturers like Van Diemen can afford to expend considerable resources on optimised welding.

6) If you can, go to Autosport International where you might be able to see chassis in an unclothed state. Ask the reps for information.

7) See what types of tubing are out there. Square or round. ERW or CDS. T45 or T6.

[av8rirl]

Thanks bobdrummond

All of your points are very good. Probably from years of practice in the business??

The rulebook is the first thing that I looked at. I am trying to build the car around both the rules and my priorities [of which there are now quite a few (driver safety being very high on the list)].

I am hoping to build a Vee that can be raced both in the UK and Ireland. The Irish rulebook is more strict than the UK. Basically, in Ireland, you must use a ferrous material for chassis construction. Composites are not allowed (whereas, in the UK, they are).

I do hope to use a mix of both square and round tubing. My only problem is that I don't know enough about specs. Are there any good sites that go into detail and specs about tubing? I have some ideas for suspension that I have not yet seen on a Vee, but we are pretty limited at the front as we need to retain the beam axle.

I buy RaceTech when it is in the local newsagent but I've not seen the articles on The Pashley Projects. Do you know what edition these might be in? A few years ago there was also a very good article on Borland Racing from Australia which provided me with the inspiration to design and build a Vee (and maybe more after that).

Many Thanks.

[enzo]

Small corrections from a chassis manufacturer:

To the best of my knowledge, 4340 does not exist in thin walled tubing form. 4130 is the most common of alloy structural tubing.

Stay away from ERW (Electric Resistance Welded) whenever possible - it has a greater chance of failing at the weld. CDS (Cold Drawn Seamless) is the best and preferred over all others.

Most likely the rules will require the main hoop and its braces to be of alloy tubing (as opposed to mild, or low-carbon). Most manufacturers use a combination of both, depending on the stress levels that that particular tube will see.

For welding, stick with TIG. It will give the strongest joint by far, and is more forgiving when it comes to mitering and coping the joint to a perfect fit. MIG should be avoided for high stressed applications like this. While it is by far the fastest method, it will create a brittle weld in thin walled tubes. Brazig with a nickle/bronze rod is also a good method, but will require much practice to do it well, and getting a PERFECT fit to the joint is an absolute must for maximum strength.

Welding 4130 tube to either itself or mild steel is best done using a mild steel rod. The rod will mix well with both alloys and give a weld almost as srtong as the parent 4130. If desired, or required by the rules, 4130 welds can be drawn back (annealed) using a rosebud tip.

When building the frame, you will need a heavy flat table to fixture to. Tack all tubes together before final welding all joints. If there are bungs or pickup points whose final location is critical, weld them in last, after the rest of the frame is welded. Welded structurs warp all over the place as the welds cool, so don't expect 2 decimel point accuracy after it it finished!

In a Vee, pay particular attention to how the engine is mounted - it really does not want to be a stressed member. If designed well, dismounting will mean undoing only 3 or 4 bolts - particularly important in Vee as you will find yourself changing engines a LOT. Be careful also that your design does not make transmission removal by itself tough either.

Stick to a Zero Roll with droop limiting rear suspension design, but make provisions for a very light anti-roll bar if you manage to get the front beam free enough when loaded ( they have a tendancy to bind up when heavily loaded). Stick to forward facing trailing links in the rear, and make them LONG for minimal toe change - the pickup point will be about halfway up the cockpit sides. Rear facing trailing links look cool, but produce a bunch of problems you don't want to deal with.

On the bodywork, pay particular attention to the reblending of airflow off of the front beam, and to head cooling. Airflow across your shoulders is also important, an how it reblends over the engine cover. If not done well, you can waste 3-4 HP or more very easily, and on a Vee, that's a lot!

Good luck with your project!

[ghinzani]

Enzo any examples of your handiwork on the web? You certainly know your Vee's, which ones in particular?

[Dereck Bennett]

Building your own car is an envigorating pursuit, but a frustrating one, also. As was suggested by another party: look at everything you can but make your own decisions. Keep in mind that if you really enjoy building your own, this first car will probably not be your last, so you don't necessarily have to attempt to build the ultimate vehicle. Use it as a learning experience. I would suggest consulting some of the popular books on welding- there are very good discussions on materials to use and weld methods. I personally wouldn't attempt to use 4130 for my first car. It's main advantages are: it's as strong as mild steel but in thinner, and therefore lighter, sections; it's easily welded using TIG or gas (for which it was developed in the early part of the 20th century before the TIG method was devised); and it doesn't corrode like lesser steels. Disadvantages are expense and sometimes availability and it should not be brazed or otherwise joined using the low temp. methods, due to it characteristic grain structure. The bronze, etc. flows into the weld area and upsets the grain, weakening the material. Read the Carrol Smith books on fabrication and materials- he cuts through a lot of the fog about what you should and shouldn't use and do. Good Luck!

[av8rirl]

Thanks for all the comments. All are really useful. I just have a few more questions (this could go on forever)

In a Vee, pay particular attention to how the engine is mounted - it really does not want to be a stressed member. If designed well, dismounting will mean undoing only 3 or 4 bolts - particularly important in Vee as you will find yourself changing engines a LOT. Be careful also that your design does not make transmission removal by itself tough either.

I am thinking of mounting the engine at an angle to lower center of gravity. Engine removal is also of high importance. I think over the last year we had the engine out approx 6 times over 14 races. I hadn't really factored in the gearbox being a high priority as you can do most of the work without taking out the full casing.

Stick to a Zero Roll with droop limiting rear suspension design, but make provisions for a very light anti-roll bar if you manage to get the front beam free enough when loaded ( they have a tendancy to bind up when heavily loaded).

Why is zero roll important for you? I like to know other people's opinions on these things. Also please explain the "tendancy to bind up when heavily loaded" (sorry for needing all this explanation)

Stick to forward facing trailing links in the rear, and make them LONG for minimal toe change - the pickup point will be about halfway up the cockpit sides. Rear facing trailing links look cool, but produce a bunch of problems you don't want to deal with.

I have thought about going forward with a long trailing arm so that toe doesn't change much. However, I still like the idea of going rearward with the trailing arms even though I have seen some problems. I am will try to work out how it is possible to minimise the toe problems (I am sure that this can/has be/been done successfully). I am looking to use pull rods and dampers with coilsprings (mounted under the gearbox) for the rear suspension. I am trying to get away from what appears to be the norm (ie Z-bar) with rear suspension in Ireland and the UK.

Read the Carrol Smith books on fabrication and materials- he cuts through a lot of the fog about what you should and shouldn't use and do.

Just started re-reading.

On the bodywork, pay particular attention to the reblending of airflow off of the front beam, and to head cooling. Airflow across your shoulders is also important, an how it reblends over the engine cover. If not done well, you can waste 3-4 HP or more very easily, and on a Vee, that's a lot!

Regarding the bodywork and aerodynamics, I would like to take everything inboard so that there is minimal drag being caused by shocks, etc... Any ideas for reblending the airflow off the front beam??? The head cooling is a very important one for me. I have some ideas. Any idea what the optimum head temp should be for running a 1300 (highly tuned) and a 1600 (moderately tuned)??

Lastly, I really do appreciate all the help and info from everyone. When this car starts to win races, and I form a team, and build more cars, and race in different classes, and get to be the next Eddie Jordan, you can tell everyone that you were involved in the luckiest project ever. Thats if the thing ever gets off the drawing board.

[enzo]

The airflow off of the front beam can be blended very well by utilizing a long, tapered "pontoon" trailing back from the beam (and its full width) alongside the cockpit. The top surface wants to be fairly flat - not downward sloping - and the bottomside wants to sweep up like the underside of a wing, and the side perfectly vertical. Depending on just how the British rules read, you can put a "sideplate" on it to make it more effective. Either way, they will generate downforce and minimise drag. We did some wind tunnel work about 15 years ago and found it to be a very good solution. They are also a handy place to put the battery and fire extinguisher.

Naturally, you will need to incorporate a well rounded nose in front of the beam to smooth the sirflow around it and onto the pontoons. Do yourself a big favor and make the nose into a good crash attenuater.

To help get airflow to the heads, try tapering in width the bottom of the chassis starting at the drivers butt. By using some small vortex generators along the side of the cockpit panels at the start of the taper, you can keep the sirflow attached and deliver a LOT of air to the shrouds around the heads.

The easy way to mount the engine is to build the frame to overhang the engine, with a detachable bulkhead that goes all the way around the gearbox at approximately the junction of the gearbox and engine, and a triangular subframe under the engine that attaches to the base of the main frame and to that rear bulkhead. The bulkhead attaches to the frame with 2 bolts, and to the subframe with 1 bolt. You will also want a rearward brace from the bulkhead to the hole in the top rib of the 'box to give vertical beam strength and stiffness. The front of the engine gets a mount to the subframe that has good lateral strenght, but little vertical. Making that mount too solid in all directions will stress the block enough for you to see a noticable power loss.

With this sort of layout, it then becomes fairly easy to lay out an exhaust system with the collector under the 'box ( sorry, I won't divulg the secret on how to make a flat 4-2-1 collector work!). Running the pipes down and out helps keep the engine cooler.

Sorry - I don't off hand know the best head temp for these cars. Each engine builder has different desires, so I leave it up to the customer to sort that out.

The reason behind not wanting rearward trailing arms is that under braking the axles will exert a huge amount of outward force on the sideplate flower, resulting in both a lot of wear and tear, and in a lot of fricton, nevermind the the toe out problems from all that flexing. You will also have the problem of tearing off the back of the box in a crash, and ......

A long forward trailing arm has the benefit of little toe change, and anti-lift characteristics can be easily tailored by allowing vertical mounting point adjustability. Braking stabiity is generally much better with a long arm.

Stick with the zero roll monoshock and pushrod setup. Ed Zink first came up with that design about 25 years ago, and nothing better has yet to be seen. The pushrods accept most of the conering loads, minimising the friction at the sideplate flower just when the suspension needs to be it's most free. Your pullrod design will aggravate that problem. Too much friction in the rear of these cars will cause an unsolvable loose condition. The anti-droop is needed to fine-tune corner entry characteristics.

The front beam arms undergo a lot of loading in corners. Have you ever noticed that both front wheels camber towards the OUTSIDE of the corner whn loaded? That's a lot of flex. The loads cause the barrel between the beam bearings to bend, in turn causing the barrel to try to cock sdeways within each bearing. Lots of friction. All that friction is why the front shocks are so soft. If that friction can be reduced, the front tires will develop more grip.

One way to combat the arm flex problem and reduce that friction is to use what we call a "Lilly Bar".It was first used about 25 years ago by a Kentuckian named Lilly, hence the name. It's nothing more than an external anti-roll bar that mounts in front of the beam, with lever arms that extend rearward between the beam tubes. The levers attach via short drop links to a triangular frame made up of small dia tubing. The frame itself attaches to either end of the kingpin. What happens is that the leverage exerted on the kingpin by the triangle counteracts the loads that the arms see during cornering, keeping the wheel more upright, and the tires grip better.

With more front grip available, you will then need to increase the front spring rate to the max possible to help control roll and ride heights better, and so then will need the small rear bar that I mentioned earlier.

If you really are ambitious, you can make the front bar a blade type, and that make it cockpit adjustable.

As well as the Lilly bar works, I'm amased that I haven't seen it on a car in 20 years, except one that we did for a customer a few years back, who promptly trashed it in the first race when he lost his brakes and stuffed it into a barrier!

Have fun!

[av8rirl]

Thanks enzo. Like ghinzani said earlier, you do know your Vee's. Please post a link to your site or to some of your handiwork. The cars that I've been racing over the past two seasons year are built in Ireland. Check them out at www.leastone-racing.com

They are run very stiff at the front (most of the adjustment is done at the rear). They are also very good handlers. This is my benchmark. I'd like to see if I can improve on this.