Lancia Rally 037 successor

[rally037]

Long time no post - family, daytime job and home extension building work taking most of my time, but the Rally 037 project kept ticking over in my mind with time to consider project options. The house extension is now complete, with most of the building work done ourselves over the winter of 2021/2022 right when my work commitments were at their greatest - I work as a design engineer for one of the F1 teams and the winter of 2021/2022 was occupied by work on the now current generation of F1 cars which went off the chart in terms of work hours even compared to the traditionally busy winters in any F1 team. However, as the spring of 2022 dawned and there was the occasional hour to think about hobbies (and sneak in buying project stuff under the banner "extension building materials"), I managed to make some progress on the chassis/frame construction techniques. I am not an experienced/competent welder and although I don?t mind learning, I am a lot more confident at some other techniques, like bonding for example. So with that in mind and during the long winter months, I hatched up a plan in my head to experiment with alternatives to welding a tubular steel frame. Bonding opens up quite a bit of alternative options for the tube material, like aluminium, titanium and carbon fibre, while avoids heat distortion issues associated with welding, but it comes with the obvious question mark over strength and durability. So I decided to get four different material grades and experiment while I am not in a position to start the actual chassis frame. I went with a woven carbon fibre, Ti Grade 2, Al 6061 T6 and Stainless 316. The idea was to bond corner samples of each, leave them in the garden exposed to sun, rain, heat and cold for a year and see how much each joint has deteriorated. As can be seen, each of the materials I chose does not rust so it really was a question of pretty much what happened to the joints. The construction technique I went ahead with was 3D printed plastic corner tube fittings that join the tubes and then wrap each joint in a wet carbon fibre laminate. I guess it sounds more complex relative to welding, but when one is more familiar with this rather then welding, I can promise you it is a lot less daunting relative to ensuring welds are structurally sound and thermal distortion is minimised.

So, I modelled some split corner fittings and printed these in PETG - the job of the fittings is to mainly hold the joints together prior to laminating rather than to provide the structural integrity. I also went with split fittings as this would be worst case scenario versus a non split ones where the tubes can simply be inserted in each fitting - while most fittings in such space frame can be non split, inevitably there will be a point when a closing section of tubes will no longer be able to be inserted into a fitting and a split one will be required, which will represent the weakest link in a potential frame. Coincidentally, all that provided an opportunity to involve my kids in a sort of science project - while the elder one has now somewhat outgrown doing projects with dad, the younger one is very much in the midst of it, so I did not want to waste a great opportunity for spending meaningful time together. So in May 2022 we cut the tubes into smaller sections, prepared the ends of each section for bonding (preparation is pretty much the main contributor to structurally sound joint once adhesive has been chosen), bonded the tubes into the fittings, waited couple of days then laminated over the joints and after waiting two more days (no elevated heat cure as that would not be an option for me on the real frame) we placed them on a table in the garden and left for a year. Just to add, on each corner joint, we left one of each three arms unlaminated for one more data point.

Skip forward and it is May 2023, it was time to get the samples and see how they fared - considering the three arms on each joint, there were two sets of 90deg arms that we can test using our "calibrated" arms and body weight - in summary, we managed to break all junctions without a laminate over the plastic fittings but the ones with laminate over were solid enough to withstand the loads we can subject them to using various lever techniques. We called that as much success as we could have hoped for. The next question of course is, from the four material choices which is the right one - if it was to be based on cost, Al 6061 T6 and Stainless 316 win hands down being many times cheaper than carbon and Ti. If it was down to looks, at least to my eyes, the Ti one was by far the most aesthetically pleasing. Another bit to consider was that the Al 6061 T6 and carbon tubes can't be bent (the Al can be if it is annealed but that defeats the point), while Ti and stainless can. Then from the two cheapest options, the Al and the Stainless, on the strength and stiffness versus weight, the Al is the better choice. So overall, the Al 6061 T6 is the winner in my budget range. If spending (considerably) more is an option, then I would consider the Ti. By the way, in a potential Al boded frame, Stainless or Ti will still be required where bent tubes are necessary, as in a roll hoop for example. Bottom line for me is Al 6061 T6 with a bit of Ti Grade 2.

While all this was going on, thinking continued on the overall planning of the project and the more I looked into my resources the clearer it was that doing the full scale car at the quality level I will be happy with, is not an option currently, every time coming to the conclusion that another model stage (before the full scale car) would be required. And looking at what the most advantageous scale is, that came at 80 percent, ie 4/5^th scale. Comparing the budgets required for a full scale car and 80 percent model, the difference is nearly an order of magnitude at like for like on quality. That pretty much swayed my mind - 80 percent single central driving seat model with a bike engine - large enough at 3.3-3.4m length overall but small enough on features to make it doable on my budget. Ironically that made my frame experimentation techniques very academic for the time being as my choice for the 80 percent model frame is firmly set on bonded square aluminium profiles and aluminium sheets, ie not dissimilar in appearance to what a mid/late 1970's F1 car monocoques looked like (bar the rivets), so all bonded. More recent analogue (but not in appearance) are the Lotus chassis construction methods. I would say this is fairly straightforward, inexpensive and structurally very robust. Also no thermal distortion after welding and no rust.

And one more twist - my younger one just started secondary school, but after not being given the public school of our choice, which coincidentally is also the school closest to our home by a large margin (they are very happy to use our tax money by the way), we bit the bullet and went with a private school which means very slow project progress for the next five years, a question of priorities! Nevertheless this provides an opportunity to work on my "garage" facilities and be ready to push on with the project in five years time (if world still exists of course). I may also be able to sneak in a bike engine under some other budget banner in the meantime!


Printing the fittings










Tube preparation






Bonding the tubes in the fittings, very messy due to the split nature of these, one piece ones are infinitely easier to work with and cleaner looking. My daughter's work (the one on the foreground) is much neater than mine (the two other). Luckily easy to clean later.




Preparing to laminate the cloth




The wetted cloth




Laminated




Year later and "tested"

[Stratos Fear]

Very interesting development work Nik - its a shame we will have to wait 5 years to see if you get a chance to use it with the 80% car but I understand the reasons - family always comes first !

I suppose the challenge with this methodology is that it would be regarded as experimental and presumably could not be accepted in any competitive motorsport without some sort of technical approval process.

Keep up the good work - and occasional reporting on the forum - when time permits !

Peter

[rally037]

Thanks for the support Peter, it is genuinely appreciated.

You correctly suggest that a lot of what I do/will be doing can be considered experimental (I like experimenting) and unlikely to be eligible for motorsport competition other than exhibition events, but time will tell. Having said that, the bonded Al square profiles and sheets is perhaps not so much of an experiment being used in many other applications, but once again, let's see. One way or another it always comes down to the quality of any work done.

Thanks for reading,
Nik

[Longtimefan]

Nik, a fascinating read and insight into very very modern engineering techniques. I also think that in addition to obviously being a master of most trades (engineer, builder, probably joiner) you are very brave to be doing all that glueing and bonding on the laminate floor.

If I had tried anything like that when assembling my project, I would have been banished to the Shed forever.!!!!!!!!

Robin

[rally037]

Robin , I would have never gotten away with it if it wasn't for the fact it was the floor that was coming off in few weeks at the time to be replaced by a new one.

Massive thank you for the appreciation on the work front!

Nik