chassis developments, or enquiry Mk 11

Okay okay, the last overwinded question went over like a lead balloon, so how about looking at specifically at how frames and chassis's developed thru the years.

Here are some quick thoughts and questions on my part:

When did the traditional chassis of two parallel frame beams supporting the engine and axle's begin to change? Along these lines, with the Maserati Birdcage, was the birdcage part of it supporting only the outer skin, or was it an integral part of the entire chassis's stiffness/structure? Wasn't Chapman the first to use an engine as the "rear part" of the chassis, with suspension bolted onto it, and speaking of suspension, when did traditional vertical suspension get moved to an inboard horizontal position with push arms doing the "pushing"?

Originally posted by djb
When did the traditional chassis of two parallel frame beams supporting the engine and axle's begin to change?

Begin to change, as in the first cars come along with spaceframe type construction? The W196 Mercedes-Benz of 1954 had a spaceframe, but Alec Issigonis had built a one-off monocoque car before the war, I think it was for hillclimbs. I think you would have to say that this was a long transition...

Along these lines, with the Maserati Birdcage, was the birdcage part of it supporting only the outer skin, or was it an integral part of the entire chassis's stiffness/structure?

It was a multi-tube spaceframe of such complexity that it was thus named, using many small diameter tubes for the chassis.

...Wasn't Chapman the first to use an engine as the "rear part" of the chassis, with suspension bolted onto it...

I would have to cite two examples of 1954/55 cars... the obvious one being the Lancia D50 which used its V8 engine as a stressed member, and the other one being less obvious... here it is:

http://members.atlasf1.com/raybell/pics/Zephyr.jpg

This car was built in Adelaide and had no chassis. The engine had the front suspension bolted directly to it, the rear suspension was bracketed off the Tempo Matador transaxle, which attached to the engine via a single piece of 7" diameter pipe. Quite a car, it was competitive with Coopers in 1960... the supercharged Mays-headed Zephyr engine running on alcohol fuels.

and speaking of suspension, when did traditional vertical suspension get moved to an inboard horizontal position with push arms doing the "pushing"?

Lotus in 1962 brought in the rocker-arm top wishbone that operated the spring/damper unit mounted inboard with the Lotus 24 and 25 models. Variations on this theme ultimately led to all sorts of different mounting systems and operating systems, particularly after rising-rate linkages started to be developed about 1969. The Lotus 72, though it had torsion bars, was one of the prime movers in the rising rate department...

hmmm... somehow I hit the wrong button here... Tim, could you please delete this, I tried and it wouldn't go away...

First of all, thanks Ray for the response. I've been busy as usual with work/home and haven't had time to answer.

I'm interested in this topic to better sort out in me noggin how chassis's work, and to visualize them better as well. Was the main advantage of a "spaceframe" chassis mostly weight, or stiffness, or both? The Birdcage was from later in the 50's no?, and was it's multi-tubing different from others only in the number of tubes-which I would assume would have been stiffer than fewer, longer ones?

It's interesting to note that with using an engine as a stressed member, that while the example of the Lancia was from '54/'55, I recall personally that production motorcycles didn't start using this until the late 70's or early 80's. There may have been some racing models before, but I'm pretty certain that I remember all the hoopala about the first bikes using their engine as a stressed part. I'm surprised the concept didn't transfer earlier.(could have been a vibration thing though)

About rising-rate shocks, just to make sure, is that where the initial travel is soft and with a corresponding shorter travel, the resistance increased? I'm the first to admit to not much detailed knowledge of suspension, but was part of the change to inboard stuff allowed by shock units that didn't require as much travel, and thus space to take up, to do their job?

until next time, djb

The spaceframe is economical of weight and inherently stiff... the birdcage was an extreme example using heaps of very small tubes, so many tubes it looked like a birdcage.

I think you'll find the Vincent HRD used the engine as part of the frame. Phil Irving told me there was a real shortage of steel after the way when he designed it, but no shortage of aluminium as they melted down the surplus bombers.

One of the main early reasons for Chapman going inboard was to reduce unsprung weight. The shaft weighs less than the whole of the rest of the damper, you see... and the rocker attaches to the shaft and the body of the damper remains attached to the chassis. There were probably benefits they didn't see, eliminating that silly half-laid over mounting method would have meant better wheel control I would say. In addition to this, he got them out of the airstream, so gained aerodynamically. A downside was a lack of cooling for the damper.

You've got the general idea with rising rate.

the great advantage of a space=frame is that all the chassis members are in tension or compression, that is all the forces act along the length of the tube. They can therefore be much lighter for a given stiffness than a traditional beam chassis, where the beams are subject to bending forces. The key to a successful spaceframe is triangulation, so that all forces can be designed in this way. Chapman was the master of the well-designed space-frame, as well as Lotus he acted as consultant for Vanwall and the later versions of the BRM P26. To the engineers, the frames of the coopers of the late 50s were horrible; they had bent tubes which went against all accepted theory. however, they got results.

As regards suspension, there are two seprate developments. The first is the use of a rocker arm to operate an inboard damper/spring unit. this was introduced by Chaspman on the 21 in 1961, not the 24/25 in 1962. It had previously been used by Maserati and LAgo-Talbot in the early post-war years. I thought that the advantage was improved aerodynamids, not reduced unsprung weight, but I may be wrong.

The push rod system was introduced by gordon Murray on the Brabham BT44 in the early 70's. It combined the advantage of inboard springs but was much lighter as it didn't require the heavy rocker arm of the Chapman system. It also meant that all suspension componenets were in compression or tension, giving greater rigidity and reduced weight, see above.

Lastly, although the Lotus 72 had rising-rate suspension when first introduced, it was soon abandoned. The drivers found it impossible to judge the limit point when breaking. The 72 appeared only in the spanish GP and the Intenational Trophy at Silverstone in its original form. By the time it started winning races it was known as the 72C, showing that while most of Chapman's concepts were right, others were not.

To my finite knowledge the features removed from the 72C were anti-dive and anti-squat, not rising rate suspension!!!? The 72, however, went along new avenues by introducing (?) torsion bar suspension, again to save weight.

Originally posted by fines
To my finite knowledge the features removed from the 72C were anti-dive and anti-squat, not rising rate suspension!!!? The 72, however, went along new avenues by introducing (?) torsion bar suspension, again to save weight.

Of course you're right!

Thanks all for the additions,
I could see that with tires getting wider and wider, more and more loads were being put into the chassis, so I imagine this whole development was part and parcel of the reality of dealing with these increases. Was the next step in monocoques the attaching of aluminum etc panels to the triangular bits of metal to further increase rigidity? After that, was the next step the use of carbon fibre?(I seem to remember that a Maclaren of John Watson's era was the first carbon fibred one, in perhaps 83 or 84?

Ray, the mention of the "birdcage" look of the spaceframe, makes me think of a WW1 era aircraft that had so many wires in the wing structure that it was said that one could check if any wires were missing by damage by putting a bird inbetween the wings and if it got out, you had to replace some.

It is interesting to see how part of the gain of the inboard suspension brought aero gains, leading into the whole increase of importance of the aero aspect into the 70's and onwards.Would any of you have any suggestions of websites that would have diagrams or close up photos of these parts of lets say, the Lotus 72, to give some visual examples?

djb

Originally posted by Roger Clark
As regards suspension, there are two separate developments. The first is the use of a rocker arm to operate an inboard damper/spring unit. this was introduced by Chapman on the 21 in 1961, not the 24/25 in 1962. It had previously been used by Maserati and Lago-Talbot in the early post-war years. I thought that the advantage was improved aerodynamics, not reduced unsprung weight, but I may be wrong.

I'm sure aerodynamics was important, Roger... but I don't think it was the prime motivator. Still important though. There's a lot to the angle of attack too, the conventional laid-over damper-spring units were in fact a falling-rate setup, something obviated by the inboard mounting.

I must admit that I'm very limited in knowledge of the 21... I wasn't following racing in 1961 and there has been very little printed information about that year cross my path.

After practice for the 1964 Belgian Grand Prix, when the Brabhams were first and third, Jack smiled and said "It must be our inboard suspension and monocoque chassis paying off on this fast circuit"

After the race, of course, Colin could smile smugly and recognise that if the chassis tubes hadn't got in the way of the fuel tanks Dan might have won...

Yes, I remember that comment, Roger, must have been in DSJ's Reflections or something... and he wouldn't half have savoured the comment too!