GT40 Aluminium Mononcoque Chassis

[Phil]

Mick:
Great job on your chassis, its a shame a lot of it will be covered at final assembly.
I totally agree with mounting the radius rods inboard at the front as it does make for better geometry at the wheel, also after doing many of these type suspensions I have found that keeping the radius rods as close to equal length as possible is essential.
This means staggering the fore and aft positions of the mounts, with the lower being slightly forward (to compensate for the difference at the top of the upright and lower wishbone).
I planned 5 deg. positive caster into my rear uprights and made the mounts accordingly which resulted in greatly reduced toe change through suspension movement.
Also, my lower radius rod has a 2 deg. rise from the lower wishbone to the forward mount to introduce a bit of anti-squat into the whole design.
I am running 14" wide wheels at the rear with 5" backspacing, and so far the setup looks to be as neutral as I can get it.

Nice build, keep the photos coming
Cheers
Phil

 

[Trevor]

Mick,
If you're using the usual GT40 rear layout then the front location of the radius rod is largely determined by the lower transverse control arm. You need to draw out the geometry of the rear upright and determine the arc that the rear pick-up point of the radius arm makes as the upright is moved about it's nominal ride height position (i.e. due to due to bump and droop). The resulting arc is usually but not quite circular. Now consider the front of the radius arm as the tip of a cone and the rear as the base of the cone as it moves. The closer you match the 2 two arcs the closer you come to the condition of minimum bump steer. Since the arc from the radius arm is perfectly circular, there will always be a small mismatch over some part of the 2 arcs. I have found that it is more important to match arcs over the portion from nominal to bump positions although small mismatches can provide useful (small) amounts of toe-in during cornering roll. The amount of toe can be altered by the vertical position of the front end of the radius arm. This can also affect the amount of rear end squat so in fact the location of that lower radius arm will effect handling a lot.
Hope this helps a bit.

 

[Mick Ridley]

Hi,

Thanks for taking the time to explain the rear suspension layout, much appreciated..... I will look into need to put the Radius Rod mounts further towards the centre of the chassis, but because the chassis was designed, to take the engine/gearbox and radius rod loadings directly into the side sponsons, rather than the cross member behind the seats, and then transfering the loading into the side sponsons, I may use a more up to-date suspension design, that doesnt use radius rods, but uses upper and lower wishbones

This will require a complete re-design of how I am going to mount the wishbones, and upper shock mounts to the engine/gearbox, but it wont make much difference to the weight

 

[gtpete]

I've been waiting a while for an ally chassis to come along. Mega work ( like your workshop too ) what engine/trans are you using ? If SBF you could defo use it semi stressed ( you have to carry a big chunk of iron around so might aswell put it to use ). Have you thought about pushrods and mounting the dampers to the box in some way. Also honeycombe is real cheap these days and so strong. Keep up the good work Mick. All the best Pete.

 

[David]

I believe Mick is using a Rover v8 with a UN1 gearbox.

 

[Mick Ridley]

Pete,

I had thought about mounting the shocks inboard, and making the suspension progresivly harder, but I didnt want to make it too complicated, and I will only be useing the car for the road and occasional track day.

As David says, Im useing a Rover 3.5 V8, with a Renault UN-IO3 gearbox. There are some large pieces of aluminium, where the bell housing bolts onto the engine, and at the top of the blocks, and these parts of the engine, used in conjuction with some Crome Moly 4130 tubing and some 6061 T6, and 7050 T7451 aliminium should give me sufficient strength and stiffness

As I said the engine and gearbox will be "Semi Stressed".....

 

[clive]

G'day Mick,

Only just found your log. Very impressive. As a fellow scratchbuilder, your build could well be a reference for my next. I'm far happier playing with alloy than steel.

An observation, based on a problem found with the original KVA kits (of many years ago). Do make sure your chassis allows a reasonable degree of front wheel lock. Gaining footroom is usually at the expense of lock, so a happy medium is always a compromise.

Clive

 

[gtpete]

Hi Mick. Cant wait to see your progress. Just as long as the loads go into the bulkheads it will be ok. Keep up the good work. Pete.

 

[Mick Ridley]

Hi,
Since my last post, Ive been busy working on my front suspension mounts. It has proved far more difficult, than I had imagined.

The first design I built started to get complicated, and wasnt easy to build, so that was scrapped.

The second design I built was relativly easy to build, but was far too strong, and heavy

The third design I built ticked all the boxes, simple, easy to build, strong, stiff, and light weight.....Im very happy with the deign....

I cant believe it has taken me 6 months to get it right....but thats the way it is with scratch builds, it can be very frustrating, but also very rewarding

The fisrt pic shows the bare chassis, with the coolant pipe in place



The second pic, shows the components ready for assembly



The third pic, shows it assembled on the chassis, with the anti roll bar, and shock in place. The basic layout, and geometry is similar to the MK IV

 

[Andrew Komosa]

Hi Mick. If you get over to my place, then I can show you a complete tenant monocoque, which you can measure and photograph at will. I live in Surrey. Just send me a message with phone number to [email protected] Regards... Andrew

 

[Jim Cowden]

Mike

I have read articals of chassis builders who have built space frames and mono tubs.
All have said that after building tubs they would never build another space frame.

Have you built a s/frame and would you agree so far.

I am toying with another build and am a little torn between the frame/originality and tub/strength practicality idea, the car I plan on is a frame originaly but I know the tub is more practical as I have cad skills and it will reduce the work load through laser or cnc router on the cut out stage and will become a fold /assemble job.

Your thoughts would be valued.

Love your work it looks magic

 

[Mick Ridley]

Jim,

Thanks for the comments, and intrest in my chassis.Ive worked with steel all my life, and decided to build an alloy mono chassis, as it would be a bit more of a challange than a space frame chassis, and it has proved to be quite a challange.....My chassis is very low Tech built. The side sponsons,floor pan and front part of the tub were were laser cut, and formed on a brake press, because my guiloteen and folder are only 4ft, and 3 ft, but they are the only High Tech bits on my chassis

I would imagine, that if you have good cad skills, and are able to design a chassis that is laser cut, including all the holes, and then formed up, on a brake press, so all you have to do is assemble it, then that would be easyer to build than a space frame chassis

Have you seen the F3L Piper chassis that Leopold is building..His was done in this way http://www.gt40s.com/forum/wings-wheels-keels/12585-ford-f3l-david-piper-6.html it is a truly amazing chassis......

When building a alloy mono chassis, getting the strength isnt difficult, but getting the stiffness is the hard bit, and a lot of research will be needed to get a chassis that is both lightweight, and stiff, Alluminium is only a third the weight of steel, but also only a third the stiffness of steel.Genrally people use 1.6 mm 16swg alloy sheet, but it how you join it that is the critical bit....If you use solid rivets, then you will have a stiff joint, but from the moment you start driving the car, the joint will start to loose siffness, The rivets dont fatiuge in the normal sence, but they or the holes will start to become oval and allow movement , which will reduce stiffness, to overcome this problem you will either need to reset the rivets, which means more work/ maintainance on the chassis, or you can use adhesive, and bond the chassis aswell as rivet it. the bonding wont make the chasssis any stiffer, but it will mean the chassis keeps its stiffness, if you have large lap joints, and a good adhesive.

Because im useing blind rivets, and there is no way I can reset them, Im useing mainly 50 mm lap joints, with a Single part Epoxy adhesive, that heat cures at 130 degrees Centigrade. the chassis will have to go in the oven at work for approx 2 hours to fully heat cure

I hope this answers some of your questions, but if you want to know more,just ask..... im more than happy to discuss chassis stiffness, etc on this thread

mick

 

[Jim Cowden]

Mick

I appreciate the info.
One of my concerns was the maintanance issues, I was thinking solid, and huck rivets in the non accessable areas.
Bonding is good insurance.

I think some of the issue is you know what you know and I dont mind venturing out ,but you are aware of the amount of time invested in a chassis.

I have seen the 3FL build and I think it is sensational.
The quality of the workmanship is second to non.

Jim

 

[Leon]

Hi Mick, Just came across you build and as one Alloy mono builder to another VERY nice work. A couple of questions 1) the rivets you are using (i may have it wrong) are blind rivets, do they have to be driven from both sides?? or have I got it mixed up, if they do?? how are you going to get to some of them ?? 2) the adhessive?? I just watched a program on contruction of the Lotus Evora and they use a heat cured addhesive, is it the same stuff?? As you know I used a steel bulk head in the rear of my tub (as per original) but I like the idea of completely alloy. The Blind rivet is much stronger than an ordinary Pop, this is why I used the SR Type on my tub as it leaves a full core in the rivet an is bacically as close the the strength as you can get to a driven blind rivet. I haven;t done much to my Chassis lately as I have been concentrating on wheels and Transmission casting moulds but hope to finish it soon. Keep up the great work and I will be keeping in touch, Cheers Leon.

 

[Mick Ridley]

Hi Leon,

I will be useing Avdel Avex rivets on my chassis.

Avdel Global :: Avex®

Although they may not have the same shear and tensile strength as a solid rivit, it just means you have to use more of them, They are used on Kit Aircrafts, They have a good clamp area on the blind side, and also they fill the hole complety when set, which is good for chassis stiffness

It doesnt matter what sort of rivits that are used on a chassis, because after time movement between the sheets will cause the rivets or the holes to become oval and the chassis will loose stiffness, that is why you need to use a adhesive to keep the chassis stiffness. If you didnt use an adhesive, the chassis would become baggy and fall apart

I was originally going to use Aralldite 420. A two part epoxy adhesive, it is used in the manufacture of Aircraft grade alluminium honeycomb. The problem with it, is that it only has a working time of 20 mins before it starts to cure

That is why I decided to use a single part epoxy adhesive. I can assemble the chassis over a period of time then put it in a oven to cure it

Im going to use Permabond ES 550 which has similar properties to Aralldite 420.

http://www.permabondllc.com/TDS/ES550_TDS.pdf

I was talking to one of the technical guys at Permabond, and he told me they were involved in the developement of the Lotus Elise chassis. I dont think im useing the same adhesive as is used in the Lotus Evora, but from my research these types of adhesive all have very similar properties

To give an indication of the strength of arraldite 420, John Edwads who lives 7 miles from me, who is building a alluminium honeycomb chassis, did a test. We joined two pieces of alluminuim with a cross sectional area of one inch. We lifted 100 lbs, and then added 100 lb weights, we got up to half a ton, and ran out of weights, we gave up after that. It didnt break.... it is incredibly strong.....

A pic of Johns chassis, and the test piece



I have followed your build with great intrest, My engine and gearbox will be mounted in a similar way to the Maclaren M20, and I must admit I copied the idea of the rear bulkhead from your chassis. The Maclaren M20 chassis is a very good design......I havnt done much to my chassis recently, but your post has given me the motivation to get started on it again

mick

 

[Dave P]

Micky:

Any updates?

 

[Mick Ridley]

Hi Dave.

Sorry I missed your post.

Ive been working on the engine /gearbox / suspension mounts. The first thing to do was invert the gearbox. I sent the gearbox to Chris Cole to have it rebuilt, and get the crownwheel swapped to the other side. Im useing Rover 3.5 V8, with a Renault UN103 gearbox. When I have seen this done before, the bellhousing has been cut in half, turned through 180 degrees, and welded up. But David Sharpe (fastdruid ) suggested turning the gearbox through 180 degrees, where it bolts onto the bellhousing, and this is what I have done, although it does present its own problems. It does make it easyer for me to do the suspension mounts

The pics show the first stage of flipping the gearbox, the gearbox, has been bolted and dowled to the bellhousing, that was the easy bit....I have now designed all the pieces needed and I am now Im ready to start building the rear uprights, next will come the wishbone mounts and shock mounts, then the wishbones.No doubt I will have to make changes as I go, so I will show it when I have completly finished that stage, rather than showing pics as I go. I hope it doesnt take too long, but I can see it will take a few months

 

[Dave P]

No worries.

I enjoy following your progress kind of wishing I had built a mono.

 

[Mick Ridley]

Not much to show on my car

But for my 51st Birthday, I did a Tandem Freefall Parachute Dive from 15.000 ft

[ame="http://www.youtube.com/watch?v=ZYtFIUqgPWE"]Mick Ridley Sky dive - YouTube[/ame]

 

[Ron Earp]

Cool! Not sure about jumping out of perfectly good airplanes but it looks like fun. That outfit has great video footage too.