Home     Updates     Hydros     Cars     Engines     Contacts     Links     ←Previous                    Contact On The Wire

Steve Betney's Work Bench

LOTUS 49: A Case of Creeping Elegance. 

I wanted to build a more modern F1 tethered car model than my usual favourite vintage front-engine types, and decided to make a quicker scratch build by using a 1/8 scale radio controlled car rolling chassis as a base. Following a recent trip to the Castle Donington museum, I was hooked on types with big butch rear tyres and 8 upright velocity carb trumpets sticking in the air. Review of modern scale r/c cars led to the conclusion that some vintage 1970s and 80s cars had the best, simple rolling chassis 2 wheel drive types for conversion to tethered car use, but that good examples of these have become hugely collectable, with corresponding high prices. I eventually bought a Mardave Marauder rolling chassis on eBay, which had good-looking tyres. So far, so good.

Research on suitable F1 cars resulted in the choice of Jim Clark’s 1967 Lotus Ford 49, the last good looking car of this type before fins, aerofoils and all of those sticking out bits spoiled the lines of F1 cars’ appearance, but not traction and performance of course. A small scale 3 view drawing was located from the web, and a scaling factor worked out from the known main dimensions of the full size car. 1/8 scale would give a 12" wheelbase, which suited the Mardave chassis and wheel sizes (rear 3.5" diameter by 1.75" wide, and front 3.0" by 1.25"). The track is somewhat over-scale, though still looks reasonable.

The wheels needed painting and the tyres required careful gluing to them with clear ZAP rubber toughened CA adhesive, then the tyres were sanded to run true in the lathe and their square edges rounded off for better appearance. So, we now have an outline plot for the project.

A new OS12LD car engine was to hand, which is a most interesting powerplant with a pull starter for flat mounting laid down on its side, and this is where the creeping elegance set in on the simple build. The quite nice OS black plastic engine cover was cast aside in the interests of cooling and appearance. The pull start was relatively simple to relocate by 90 degrees to a more suitable orientation, and it wasn’t an insuperable task to modify and fit a 28mm modern clutch plus flywheel assembly with a suitable spur drive gear, using a split taper collet to replace the OS prop driver. The carburettor was a more substantial issue, as the OS has a modern slide version rather than a rotary barrel type, and the orientation was 90 degrees from the desired position. Another rotary carb was found with the correct diameter stub and a vertical needle, and modified to fit by making a mounting flange, enlarging the air hole and making a knock-off arm to fit the barrel lever to use as a fuel cut out. The mounting holes for the original plastic body cover were used to affix a bracket with a power socket for a removable plug wired to a 2v starter battery to fire the glowplug. All in all, a good bit more work than hoped for.

Inspection of the Mardave rolling chassis led to the conclusion that it was quite well made and a simple, budget design for its day, but a number of modifications were needed to improve application as a tethered car (what’s that creeping in here?.....). This chassis plate of 2mm aluminium has folded up edges, but was considered a bit too flimsy and wide for this project, so a new flat plate of 1/8" hard alloy was sawn to size as a substitute.

This allows ˝" L section ali strips to be used fixed to the inside long edges of the body sides to enable eventual easy mounting with short M3 countersunk screws from the underside of the base into Hank nuts in the strips. The Mardave front and rear steel axle shafts run directly in the moulded black nylon suspension parts, and as there was insufficient space to fit ball or roller bearings, thin- walled, sintered bronze bearing sleeves were installed.

The original r/c push rods and fittings for the front steering were rather flimsy, so replacement 3mm steel rods were bent up and substantial ali fork and ball joint end fittings substituted, providing a still adjustable steering tracking arrangement to the locked centre arm. Again, all rather more additional work than originally envisaged, so the way of creeping forward was now well established.

How should the 8 dummy velocity trumpets be made for the carb? The idea of turning them up in the lathe from ali bar stock was shied away from as being over-kill, and I settled instead on using some dolls house lamp reflectors with ali tube extensions and a fillet of filler, re-shaped by sanding to final curved shape in the lathe. The air shield filters were made by stretching some soft fine ali mesh material over the suitably rounded end of piece of wooden dowel, then these parts snipped to shape and epoxy glued on to the trumpet parts. A shaped piece of hard balsa forms the base into which these are fixed and screwed to the top of the rear suspension plate, representing the top part of the Ford V8 engine.

By juggling and cutting some small sections of the rear LHS nylon suspension moulding and its ali top spring mounting plate, it was possible to route a piece of silver coloured 12mm internal diameter silicone tube from the OS engine’s exhaust manifold outlet through the suspension assembly to exit at the rear of the chassis. A suitable silencer was then welded up from rectangular ali box section material with a 12mm inlet tube to fit the silicone tubing, and two upswept 8mm outside diameter polished aluminium tubes for the outlets.

All of these parts were sprayed with flat black epoxy paint, and I think are quite a pleasing and plausible representation of the original car (stand off scale, as aeromodellers call it). Another quite substantial amount more of work than originally envisaged on this back end for the car, but it is creeping (even if not necessarily elegantly) towards being in sight of the finish.

The car body was constructed as simply as possible from two side cheek profiles of ˝" obechi sheet with a central block of rock hard balsa bandsawn to shape, assembled using Franklins Titebond wood glue and clamping the sandwiched parts until dry. It’s an easy enough and very satisfying task to carve, razor plane and sand this lump of wood to final external body shape, then saw out the cockpit area just a little over-scale to expose the engine compartment with access to the pull starter, needle valve, glow power socket and fuel tank filling cap. No space for a driver figure here though, unfortunately. Then a much more complex job to hollow out the body so that it fits over the rolling chassis and clears all of the suspension, power train and various internal parts and has a hollow nose part. The ˝" L shaped ali side strips mentioned earlier for affixing the body to the chassis plate are epoxy glued and screwed into place on the obechi sides, then the mounting holes drilled in the chassis plate through to these and the Hank nuts installed, a much better engineered approach than just holes tapped directly into the 1/16" material of the strips. The exterior and interior of the shaped and sanded body was then given a few coats of cellulose sanding sealer, rubbed down in between, then hard skins of 2 oz flexible weave glass cloth were applied with Z Poxy resin. After sanding the glass epoxy surfaces, more sanding sealer and final rubbing down gave a surface ready for painting.

Not so fast, time for more mission creep! The car top looked a bit unreal with no wrap-around windscreen, so the rather difficult job of shaping and fashioning one from 1mm clear plastic sheet was undertaken by making a cardboard template by trial and error until it fitted all round. A groove was then excavated in the body top around the cockpit in which to install this with RC canopy glue, and when dry, a large fillet of Humbrol filler was added and sanded to a smooth, faired shape, then more sanding sealer used over this to get back to the ready for painting stage.

Well, almost, as I then decided to add roll bars behind the cockpit, welding them up from 1/8" diameter hard ali rod.

The finish chosen was BRG cellulose with a yellow central stripe down to and around the nose area, as on the original Jim Clark car. I will not bore you with the challenges that this simple-sounding job involved in a long, cold & wet weather spell, but when the very expensive artists’ low tack masking film used for painting the yellow parts keyed into the (2 days hardened) BRG cellulose finish I was not pleased at all. This was only salvaged by a few hours’ very careful work using Servisol pectin-based label removing spray, as even though this does attack cellulose a little, it removed the tacky surface film glue then acted like T-Cut polishing compound to restore the BRG to a decent finish, good enough for fuel proofing. I’ll try to remember this tip for such problems in the future. The inside of the body was finished with flat black epoxy spray paint for motorcycle exhausts.

The car was beginning to look really nice, but naked, so I decided to add Shell and Firestone logo decals and racing numbers, made on an inkjet printer using white background decal material with images grabbed from the web. Another tip for future use: I have discovered by trial and error that importing grabbed image files into MS Word enables them to be edited and manipulated to final desired size and with any desired number of repetitions laid out on the page, which saves decal material. Does anyone know a good, fool proof, fuel proof product? I’ve tried them all, spray and brushed finish, and even when a reasonable finish is eventually achieved with multiple coats it is not resistant to even 10% or so nitro content glow fuel. Don’t tell me to use a diesel engine; I do out of choice whenever I can!

The model has taken about 3 times as much building time at around a couple of hundred hours than I had originally hoped due to the evolutionary design approach as it progressed (or "creeping elegance"), but I’m probably too old and inflexible to learn from this for the next project(s).........

©copyrightSteveBetney2018