Daylight on the Derby
Some notes by J Lowrey relating to the advanced fwd cars sponsored in this country by Douglas Hawkes.
After five long years with but one visit to Brooklands, and that made via a gaping hole through the Bylieet banking, it was very pleasant once again to drive round behind the Members’ Hill and drop down through the tunnel into the paddock. It is true, I was not bound for a race meeting, but at least I was visiting some real cars, in the form of the Derbys still cherished by Mr and Mrs WD Hawkes. .
Considering its advanced specification, including such items as front-wheel drive and all-round independent wheel springing, the Derby is surprisingly little known to British enthusiasts. Hence this effort to impart a little of the “gen” to the readers of Motor Sport.
Designed very definitely as a sports car, the Derby is of a delightfully simple layout. The chassis, which is substantially the same for all the models, has two perfectly straight channel-section sidemembers, low set and linked by an “X” bracing as well as by other cross-members.
Independent wheel springing is fitted at both ends, of the simple divided-axle type, using tubular members with transverse leaf springs below them. Such a layout is sometimes criticised on grounds of tyre scrub, but this is not apparently a serious factor with a firmly-sprung sports car. On the other hand, the divided axle layout introduces the minimum possible number of wearing parts, and, by giving a roll axis about 15 in above the road surface, eliminates all rolling tendencies on a reasonably low car. Each half-axle bears a superficial resemblance to one half of a normal banjo rear-axle casing. At the rear, this structure carries 18-in Magna wheels and the drums of Bendix brakes ; in front, the outer extremity of each swinging member carries, also, the enclosed universal joints mounted on the king-pin axis. The front spring is of seven-leaf construction, the Telecontrol adjustable shock-absorbers are fitted front and rear.
Steering is by means of a Derby-built worm-and-wheel box, the drop arm (if such it may be called) projecting vertically upwards from it. A normal drag link leads forward to the off-side front wheel, the two wheels being linked by a divided track rod pivoted centrally just ahead of the differential unit.
Several different types of engine can be fitted into this chassis such as the French Ruby, the British Meadows, or the unique Derby V8. The Meadows engines used are of the well-known “12/50” type, mounted with the flywheel at the front, and having two SU carburetters on a balance-pipe manifold, water pump, and coil ignition. Fuel feed to the carburetters is by an Autopulse electric pump.
The Derby V8 engine is both rarer and of greater interest. It has two banks of cylinders set at 90 deg, a three-bearing crankshaft, articulated connecting rods, and a single three-bearing camshaft driven by gears and running in an oil bath inside the V. This camshaft operates side inlet valves by normal tappets and overhead exhaust valves through tappets, push rods and rockers. On top of each cylinder head are four exhaust ports, an exhaust pipe leading down from the front of each bank of cylinders, while two Solex self-starting carburetters, mounted one on each side of the engine, feed to the inlet valves via passages bored through the cylinder blocks.
The cylinders are of 65 mm bore and 75 mm stroke, giving a swept volume of 1,991 cc, and a British rating of 21 hp. Using the normal 61-to-1 compression ratio, the French catalogue quotes a speed of from 75 to 80 mph, and a fuel consumption of rather more than 20 mpg.
With each type of engine, a single dryplate clutch is used, driving forward to a four-speed gearbox. This has helical gears with dog-clutch engagement for everything except bottom, the ratios used with the V8 engine being 4.5, 6.7, 9.0, and 13.4 to 1. Ahead of the gearbox is the spiral bevel gear and differential, driving the axle shafts via fabric type universal joints.
Various examples of the Derby still live at Brooklands, a Meadows-engined tourer, a similar four-door four-light saloon, a V8 Le Mans 2-seater and a remarkable forward-control van. The 4-seater tourer and saloon models were largely made in this country, using the minimum of components imported from France. Fittings include 5-in section tyres, “Umbrella-handle” gear and brake levers on the dashboard, and right-hand organ-pedal-type accelerator. Horizontal radiator louvres are fitted, and a rough measurement gave a scuttle height of only 38 in above the ground.
The Le Mans car, built with two others for the cancelled 1936 race, has a neat blue close-coupled 4-seater body, with the spare wheel enclosed in a rounded tail. The front wings have an unusual mounting by means of what are virtually leaf springs, the radiator has a wire Mesh stoneguard in place of louvres, and a central accelerator pedal is used. This car also has straight-cut gears in the gearbox and final drive, in the interests of efficiency and to reduce the cost of employing special ratios.
Finally, before departing into the dimout, I was able to have a look round one of the single-seater racing Derbys. This car is built on quite different lines from the road Models, and while it is of entirely Derby construction it owes more than a little of its inspiration to the Miller.
The engine is a twin overhead camshaft straight-eight of somewhat under 2 litres capacity, and a centrifugal supercharger, with its axis mounted horizontally fore and aft, is located at the front of the cylinder block. A single downdraught carburetter feeds the blower, which delivers to a manifold on the right-hand side of the engine.
Front-wheel drive is used, as on the sports Derbys, but not independent suspension. At the front there is a tubular axle beam, mounted on four 1/4 elliptic springs ahead of the differential assembly and with the ends swept back to the king-pins. The front-wheel brakes are mounted on the final-drive easing, and operate through the universal joints and axle shafts, giving a very low unsprung weight. The springs are damped by two large friction shock-absorbers.
At the rear, a tubular axle beam is used, a few inches below hub level, the springing being by underslung 1/2-elliptic leaf springs, damped by four duplex Hartford shock-absorbers. The steering box is located inside the cockpit, but the steering layout is orthodox, with an extremely long drag link on the left of the car and a normal track rod.
The body is a low-built single-seater, comprising little more than a bonnet, scuttle and rear fuel tank. The bonnet hinge is slightly offset to the right to give access to the central sparking plugs, and the cockpit has a surprisingly soft armchair seat, central throttle, huge treadle clutch and brake pedals, and a steering wheel with one sector of the rim cut away. The windmill in front of the radiator, conspicuous in so many photographs, drives an oil pump transferring lubricant from the sump to the scuttle tank. The bonnet is held by spring-tensioned straps.
Apparently about eight of these engines were built, some of 11/2-litres capacity, some of slightly more, and three or four complete cars. There is also in this country one racing Derby fitted with a Maserati engine, installed experimentally, since the characteristics of the centrifugally supercharged Derby engines are not altogether suited to road-racing conditions.