Test report for the Hotchkiss-Laffly 6-wheel vehicle (Super Contrôle, 6 June 1940)

In this document

The test report (p. 2-3)

This "Super Contrôle" report of 6 June 1940, addressed to Mr. Magès, provides an account of a test of the Hotchkiss-Laffly 6-wheel vehicle. In total, the vehicle covered 3,600 km, including 270 km of running-in and 450 km off-road p. 2.

The document lists the serious incidents encountered and the proposed solutions, in the form of a two-column table:

• Broken chassis at 3,460 km (including 400 off-road) and cracked front axle spacer: the original Citroën chassis had lasted 4,194 km (including 500 off-road) before breaking completely; a reinforced chassis then lasted 3,690 km (including 640 off-road) before cracking; re-welded with "C.2." wire, it was still holding after an additional 2,000 km (including 360 off-road) p. 2.

• Original steering: teeth broken at 1,780 km (including 130 off-road), deflection on the wheel shaft, battered splines. Tested variants (thicker sector wheel alone, then 2-bearing steering) gave differentiated results — the non-reinforced 2-bearing version, with 1,810 km (including 312 off-road), had "nothing to report" p. 2. A practical indication specifies that when the steering wheel play reaches 70 mm at the rim, the sector must be turned by 180° p. 2.

• Axle pivot: wobbling appeared at 1,400 km between 16-18 km/h and 30-35 km/h; proposed solution: ball joint grain with lower cup, Timken retained at the upper part p. 2-3. A comparison is made between 3,800 km on Citroën and 1,800 km on the Hotchkiss 6-wheel: the wobbling is eliminated, without seizing or deterioration p. 3.

• Needle bearing on the Tracta ball joint bowl: pulverized at 1,780 km; solution by maintaining the bowl with a centering flange, changing the bearing, modified bowl and oil seal — 4,000 km covered subsequently without breaking the needles p. 3.

Gear ratios (p. 4)

A separate handwritten sheet, titled "W-15-T", details the gear ratios of the gearbox (B.V.), the reduction gear and the wheel, with numbered gear diagrams.

Hourly speeds are also calculated: at 1,000 rpm in 4th (road), 13.95 km/h; at 3,600 rpm in 4th, approximately 48.7 km/h; in 1st reduced, 0.94 then 3.4 (development unit) p. 4.

Context

The Hotchkiss-Laffly mentioned is a six-wheeled all-terrain military vehicle, a category of vehicles developed around the Second World War for the needs of the French army. The comparison with a "Citroën" chassis suggests joint work or a reuse of Citroën elements on this prototype — a common practice at the time between manufacturers for military studies.

Paul Magès, then an engineer at Citroën, worked on suspension and mechanical handling issues; this type of intensive reliability test (running-in, off-road) is characteristic of the development of robust vehicles, foreshadowing certain concerns that would later lead to his work on hydropneumatic suspension.

Archivist's perspective

This document offers a concrete insight into the testing methods of the time: rigorous mileage tracking, comparative table of incidents and iterative solutions (reinforcement, re-welding, modification of parts). It seems that Magès was the recipient of this type of report to evaluate the mechanical endurance of military-oriented vehicles, in a context where the Citroën chassis served as a reference for comparison p. 2-3.

The date of 6 June 1940 — a few days before the entry of German troops into Paris — gives this document the value of testimony on the industrial activity underway until the final moments before the armistice. It is probable that this piece was filed with other technical documents from the same period, as suggested by the "Documentation" cover page dated 6 June 1940, which could be the folder that contained this archive.

The gear ratio sheet p. 4, although not explicitly signed or dated, usefully complements the report by providing the technical detail of the transmission of the tested vehicle — a rare example of Magès' raw calculations on this type of vehicle.