Torsional rigidity of the Elan Chassis

[Davidb]

I would think we could measure Your torsional rigidity by putting a bottle of wine in one extended hand and a wine glass in the other!

[Craven]

In general, torsional stiffness of the frame should be higher than roll stiffness.
Now you know why the Elan is so lightly sprung.

[The Veg]

So I just replaced the hinge in one of my Esprit doors and was not going to do the other one but wanted to be sure they both had about the same opening resistance. I took a fish scale and attached it to a built up piece from the two locating screws and found it to take about 23 pounds. So I’ve got my Elan S3 DHC body and chassis separated with the motor in the chassis, but I’ve got my PhD in psychology so is there any way to measure my torsional rigidity by hanging a rear wheel from the tree and hiking it up or something, we ought to figure out how to do it in 2020. Gordon Sauer

My dad had a PhD in psychology, and a JD too (he got into forensic psychology back before there were integrated degree-programs for it) and he was enough of an OCD-engineer-type* that he would have perfectly related to the story of your hinges' resistance. He once fretted about his digital clock that ran off the signals from the US atomic clock being inaccurate due to the delay of the radio signal reaching it! I countered that the amount of delay was inconsequential for any practical purpose that he could possibly have, and he smirked a little and said that while he agreed intellectually, his personal quirks still made him fret about it!

I'm neither a psychologist nor an engineer, but I did enjoy taking Psych 101 as an elective and I'd probably be an engineer if I was good-enough at mathematics to survive the schooling for it. I do have 'engineer' in my job-title, but it's just a fancy title for a glorified repairman.

My other vehicular perversion is BMW motorcycles, and I can recall one day when I was riding with three other BMW-pals and we stopped in a small town and parked outside the cafe and an older gent on a nearby bench said, "I'll bet you're all engineers, ridin' them Bee-Em-Dubyas!" None of us had a degree in engineering, but after we told him our four technical professions, he said, "See, I thought so!"

So Gordon, you have tested the resistance of the two doors, but did you make sure that the distinctive metallic CLICK of the Esprit hinges happened at the same number of degrees of door-opening, and the same pitch and volume?



*That said, Dad was into Sunbeams and Alfas rather than Lotuses, and he almost bought an XK120 for cheep in the '70s. I bought my first Lotus six months after he died and I wish he'd lived to see both of them- he would have loved them! And the conversations he would have enjoyed about my mechanical adventures with them...OH! He and I could prattle on for HOURS about technical things!

[Jentwistle3]

I’ve owned the Elite, Elan and two Europas both S1 and S6. Subjectively the Elite and the S1 Europa felt the stiffest to me while the Elan feels ok and the S6 Europa is a flexible flyer.

[Citromike]

Dear The Veg,

Your dad was right about the atomic clock delay but IF he had gotten a GPS satellite clock instead, at 10x the price, it would lock onto 8-12 satellites at once and calculate the time more accurately, within 500 nano-seconds. How do I know? I had to have one (4 actually)

[Andy8421]

Citromike, slightly off topic -

The good news is that any GPS device is able to give you 'GPS time' - it falls out of the GPS positional calculation, as long as the receiver can get a decent fix. No need to spend decent money on a fancy clock, there are apps for your phone that can access GPS time from the internal GPS receiver and set your phone clock to GPS time.

The bad news is that GPS spoofing is a thing, where bad actors either jam or broadcast hacked data to give position or time data that is in error. This can be a problem in securities trading where each trade is given a timestamp - it is possible to fool the system if you know where the GPS aerial is. One solution is to 'buy time' from one of the national standards authorities. You could run a fibre direct into your house if you are concerned -

https://www.npl.co.uk/npltime

[Andy8421]

Again, slightly off topic (it must be the lock down getting to me),

The Daimler Dart SP250 which was a contemporary of the Elan and as ugly as the Elan is good looking (apparently) had a chassis so poor that if you took a hump backed bridge too fast, both doors would fly open. Probably an apocryphal tale, but there were some dreadful designs around in those days.

A significant percentage of the vehicles being produced at that time were still using rear suspension designs that wouldn't look out of place on a horse drawn cart.

[Mazzini]

Andrew,

There was a great article on a talk given by a Kiwi Lotus engineer whom worked on the Elan chassis, it was here

http://www.ferraritestarossa.net/clublo ... x.html#top

but it’s been recently taken down. I think it was published by Club Lotus Avon. If I recall correctly the Kiwi said that the development Elan chassis had a much more substantial front crossmember, which gave a much greater torsional rigidity and rise to the number that we now have. The production crossmember they settled on was significantly cheaper and it's the one we have today.

Tim or Mike O might have saved the article.

Best,

Rob

[Frogelan]

Thanks Rob !

It is nice to get back onto the topic. I'll send a little note to Mike O as he is very much chief anorak on all these subjects !

Andrew

[Frogelan]

Quick note for Andy8421: leaf springs can be set up really quite well and can do the job quite effectively.

To give you an example, in 1996 my co-driver in my 1963 MGB in the Spa Francorchamps Six Hour historic race outqualified Marcus Pye (Autosport journalist) in his Lotus 23B...[3:02.99].

MGBs have humble leaf springs and Armstrong adjustable dampers and are 400kg heavier.

A

[nmauduit]

Your dad was right about the atomic clock delay but

I'm not so sure : a relatively stable delay (fixed emitter and receiver) can be measured and accounted for with precision.

My observation as a 40-year Lotus owner in the US and UK is that Lotus owners tend to be loners, consultants and engineers. That is, Nerds. Thus the Lotus social scene is a bit dull, compared to other brands. As demonstrated in this thread, conversations are technical not theatrical.

then was it the case before they acquired their first Lotus, or the result of maintaining it ...

[Foxie]

<Snip>
So I’ve got my Elan S3 DHC body and chassis separated with the motor in the chassis, but I’ve got my PhD in psychology so is there any way to measure my torsional rigidity by hanging a rear wheel from the tree and hiking it up or something, we ought to figure out how to do it in 2020. Gordon Sauer

Reading through this thread I was considering how the torsional rigidity might be measured, as I still have my original Plus 2 chassis hanging in the shed.

I imagine if the front was placed on two timber blocks at each side of the front cross member, and well loaded down with a plank stacked with concrete blocks, and a narrow support under the centre of the rear of the chassis at the wheel centre position, you could suspend a known weight (e.g. concrete blocks @ 45 lbs each ! ) from one of the rear suspension ears, measure the deflection, and calculate the answer.

I am in the middle of a couple of projects at the moment, but it's something I would like to do when I have more time, and of course, report back here !

[Matt Elan]

I was thinking along the same lines - clamp the front crossmember down, then support the middle of the tunnel but don't clamp it, then strap a long beam or scaffold pole across the tops of the rear turrets (where the lotocones fit).

Set up a spirit level on the pole and get it level. Best to have a few feet of overhang, especially if the value is 4000 ft lds - that 2 tons, then load it up with weights or pull with a spring balance and measure the change... Sounds simple but will probably go to rats when I try it!

[MarkDa]

I would very much doubt the bare Elan chassis was anything like 4500 lb/deg!

I have to agree - the chassis is only as stiff as the weakest section.
This must be the central box section which is, let's face it, not that large.
With the body attached we get a bigger section which is then stiffened by the dashboard.
If the Stag figures are correct for a much bigger car then there's now way the central 'tunnel' is c75% of that.
However I haven't sat down and done the calcs - maybe one of the other 'nerds' on here has the skills, inclination and time to analyse the bare chassis box section?

Or we can wait for the results of the practical experiments!

[Frogelan]

Mark

The central spine is the strongest part. As you know, it also has some very carefully designed flanges inside and is a torsion box (originally invented by Robert Stephenson).

The Elan interpretation was designed in one weekend by CC in 1960,and when the prototype was made, it showed enormous potential.

In November 1960, it was suggested to CC by John Standen that perhaps a chassis with twin torsion boxes might make a rather handy single seater.

I'm writing an article on this discovery at present and this is why I was fishing for information...

Andrew