14 replies to this topic

[P 4 Staff]

Hi all.
I have a question for all you clever guys.
I´ve often wondered how those aluminum monocoques were constructed.
I can see that there are a lot of riveting.
My question is: are there a lot of bulkheads...How thick is the aluminum sheets e.t.c.
I took a picture of a Surtees at Östereichring in 1972...and there is clearly a bulkhead for the enginemounting.
Anybody can (maybe with some sketches) explain this to me.



Best: Staff.

[Antoine]

this kind of aluminium chassis are in alluminium panel riveted !
You can find some car like the LOLA B2K/40 which win the 24h of Le Mans in 2004 with that kind of chassis! And with the nowaday Epoxy glue the assembly is very stiff!
It's not carbon but....

[Greg Locock]

I'll finish your sentence


.... it is just as light, not as strong (but more crashworthy), almost as stiff, much easier to repair, and easier to make. It also costs a lot less.

There are some structures where carbon fibre's advantages are very useful. But in the context of 3 dimensional loads applied at discrete locations you have to put a lot of effort into a CF structure. The same effort applied to designing an aluminium structure would get you very close.

The killer problems for cf are designing the hardpoints, which tend to end up as big lumps of aluminium anyway, and getting the material so the fibres are correctly oriented to take the load. If you truly need to react 3D forces then only 1/3 of the fibre is going to be devoted to each load, so the apparently formidable advantage in permissible stress/density starts to crumble quite quickly. Then you add in typical attainable volume fractions, say 60-80% (the latter would be very good) and it takes another hit. Meanwhile your stiffness, which wasn't that hot to begin with, is also being discounted at the same rate.

If you are designing pure tension compression elements, sure, use CF. If you have a big budget, use CF.

[seymourglass]

I think the cost point is debatable. Sure, for large runs (many parts), composites represent an unacceptable cost, but for short ones, composites parts can have the advantage. I'll quote spacex here:

Mass Improvements
We have made significant mass savings in first stage, particularly in the inter-stage structure. By moving from an aluminum design to a carbon fiber composite design, we cut the weight of the inter-stage in half. Now, we started with a poorly optimized aluminum design and then moved to a really optimized carbon fiber/honeycomb design, so ordinarily you would not see that much of an improvement. The icing on the cake here is that it actually costs us less to build the carbon fiber inter-stage than the aluminum one! Long term, we will probably switch our aluminum fairing design to composite as wel

Your comments seems to suggest that cf should only be used when minimal performance gains are worth exorbitant costs, and while those qualities are certainly true of any space vehicle, the truth is that cf is not necessarily more expensive.

[P 4 Staff]

Guys My simple question is ...how is it constructed?
Some bulkheads...OK...Any sketches?
Staff.

[McGuire]

Originally posted by P 4 Staff
Guys My simple question is ...how is it constructed?
Some bulkheads...OK...Any sketches?
Staff.

Don't have any illustrations handy (I'm on the road at Daytona) but basically, a formula car aluminum monocoque is constructed by bending sheet aluminum (typically 18 or 20 gauge, .032" or .040", about one mm) and riveting to fabricated bulkheads or stations just as you observed. Aircraft purists will say this is really "semi-monocoque"...whatever.

The bulkheads can be milled aluminum or magnesium, castings or sometimes heavy-gauge sheet steel fabrications. Many cars such as Lotus used a mixture of different types of construction for the front, center(s) and rear bulkheads to meet varying needs in each location. On your Surtees pictured, the engine bulkhead looks like a milled aluminum piece.

There are literally hundreds of rivets in this type of construction. A crucial part of the maintenance involves carefully going over the tub with a rubber mallet or scewdriver handle searching for loose rivets. (A loose rivet may also have a black circle or stain around it, evidence of the rivet working and fretting the aluminum.) They must be drilled out and the holes carefully reamed and fitted with slightly oversize rivets for a good tight fit. A tub with loose rivets will lose a significant portion of its rigidity and the handling will go straight to hell.

[McGuire]

Originally posted by Greg Locock
I'll finish your sentence


.... it is just as light, not as strong (but more crashworthy), almost as stiff, much easier to repair, and easier to make. It also costs a lot less.

There are some structures where carbon fibre's advantages are very useful. But in the context of 3 dimensional loads applied at discrete locations you have to put a lot of effort into a CF structure. The same effort applied to designing an aluminium structure would get you very close.

The killer problems for cf are designing the hardpoints, which tend to end up as big lumps of aluminium anyway, and getting the material so the fibres are correctly oriented to take the load. If you truly need to react 3D forces then only 1/3 of the fibre is going to be devoted to each load, so the apparently formidable advantage in permissible stress/density starts to crumble quite quickly. Then you add in typical attainable volume fractions, say 60-80% (the latter would be very good) and it takes another hit. Meanwhile your stiffness, which wasn't that hot to begin with, is also being discounted at the same rate.

If you are designing pure tension compression elements, sure, use CF. If you have a big budget, use CF.

Good points. I am in Daytona this weekend for the Rolex 24, where the Grand American Daytona Prototypes are racing. These cars are very carefully spec'ed with two the major goals being safety and cost containment. Consequently their chassis are a mixture of steel tubing roll cage structure and riveted/bonded aluminum and CF semi-monocoque. If you can get past the awkward-looking body styling they are very clever and well-engineered...and look like they could withstand anything.

[dosco]

Originally posted by McGuire
Don't have any illustrations handy (I'm on the road at Daytona) but basically, a formula car aluminum monocoque is constructed by bending sheet aluminum (typically 18 or 20 gauge, .032" or .040", about one mm) and riveting to fabricated bulkheads or stations just as you observed. Aircraft purists will say this is really "semi-monocoque"...whatever.

Well, semi-monocoque indeed, but less so that the typical modern airliner....there are no "stringers" running fore and aft that connect the bulkheads prior to application of the skin. So you could argue the tub is "closer" to the ideal monocoque......anyway, splitting hairs.

As far as the Daytona Prototype category cars, I have a really hard time getting past the body styling. I'm more a fan of the IMSA/ILMS/ALMS/LMP body styling.....immature, yes, but the Daytona P cars are just to awkward and ugly for me to tolerate.

[McGuire]

Originally posted by dosco
As far as the Daytona Prototype category cars, I have a really hard time getting past the body styling. I'm more a fan of the IMSA/ILMS/ALMS/LMP body styling.....immature, yes, but the Daytona P cars are just to awkward and ugly for me to tolerate.

To me they came out homely and about 100 bhp short. I can understand how both came to be...the awkward proportions are caused by the big greenhouse to fit the NASCAR spec roll cage, while the 500 bhp level was set to allow the NA flat six Porsches in the game. Commercially the series hit the target dead center though....they now have a car the entrants can actually afford to run. 29 cars in the DP category for this race.

[P 4 Staff]

Thankyou Gentleman.
My plan is to construct an Aluminum Monocoque in Inventor (Cad)...with a Coswort DFV...bolted to it. A rather long-time project I guess.
But you guys + have helped me a bit on the way.

Thankyou: Staff.

[Ray Bell]

Another method of aluminium mono construction involved sheet steel fabricated bulkheads...

Typically there was a bulkhead at the front, on which the pedal assembly etc was located and from which most of the front suspension mounted.

Another bulkhead or partial bulkhead was at the dash panel, with the steering column mount and often including the mounts for the trailing arms of the front suspension... or is that leading arms?

The bulkhead behind the seat provided the engine mounting in later cars, but earlier monos extended right to the rear suspension bulkhead and saw the rear suspension mount to them and the gearbox and brackets built onto it.

There must be a cutaway drawing somewhere of a McLaren M10 to show you this?

[P 4 Staff]

Originally posted by Ray Bell
Another method of aluminium mono construction involved sheet steel fabricated bulkheads...

Typically there was a bulkhead at the front, on which the pedal assembly etc was located and from which most of the front suspension mounted.

Another bulkhead or partial bulkhead was at the dash panel, with the steering column mount and often including the mounts for the trailing arms of the front suspension... or is that leading arms?

The bulkhead behind the seat provided the engine mounting in later cars, but earlier monos extended right to the rear suspension bulkhead and saw the rear suspension mount to them and the gearbox and brackets built onto it.

There must be a cutaway drawing somewhere of a McLaren M10 to show you this?

Yes Ray.
I´ve got a lot of cutaway drawings of different cars...maybe I´m dumb or something...but these cutaways don´t give me the details of the construction.
Don´t get me wrong...maybe I just don´t understand how it´s done.
I´ll give it a try....thankyou for your input.
Best: Staff.

[Ray Bell]

In most cases, the main aim was to get the major torsional stiffness and beam strength out of 'D' sectioned sponsons (is that the word?) connected to each other by the floor, perhaps a fill-in panel over the driver's legs, and using the bulkheads.

Rivets and Araldite go back as team partners well into the mid sixties.

I don't know if this answers your exact question.

[Peter Morley]

The following simulation has some detail (I don't have the cutaway drawing handy) from the Lotus 49:

http://www.racing-legends.com/news.htm

Basically the 49 tub is made from 16 or 18 gauge aluminium sheet that is rolled (it is not just a straight cylinder, it is double curvature - e.g. wider in the middle than the ends).

The front bulkhead is a small steel frame in front of the drivers feet - which mounts the steering rack, pedals & has some suspension pickups.

The rear bulkhead is at the very end of the tub and consists of round 'top-hat' section aluminium hoops.

The rest of it is basically open (e.g. the 2 D-shape sections don't have any other bulkheads).

They did add some D-shaped bulkheads inside the front of the tub later, to re-inforce the top front wishbone mounting.
And the instrument panel mounting does provide some additional stiffening (as does the shape of the inner structure - like the seat back etc).

The whole structure is glued and rivetted together.

Later open top tubs are very similar:

e.g. March in 1974 the front bulkhead was an aluminium sheet, by 76 this was replaced by an aluminium casting.

Rear bulkhead in 1974 was a central casting (the outside parts of the tub were just to hold the fuel they weren't really structural) with the 2 outside pieces being aluminum sheet, by 76 this was all cast (by then they had removed the inner skin so the fuel tank was a structural part of the tub).

A couple of D shaped castings behind the front wheels provide the suspension mountings.
Then it is open all the way back to the rear bulkhead, with teh front roll hoop & instrument panel providing a bit of support.

Hope you can follow that!

[P 4 Staff]

Thankyou Peter.
All of you guys have helped me a lot.
My project includes drawing the DFV engine which I have some measured drawings of. (to speed things up i´m not going to draw every detail). (internals).
And then I will try to draw a two-seater monocoque sportscar.
Let´s say I use 1,2mm Aluminum sheets....what gague should the rivets be?
Best Regards: Staff.