A photograph of the Daimler at, or passing, Coventry No 3 with certain details annotated. Some annotations are self-explanatory, others warrant further explanation. The radiators as seen here were a modification of the original layout; there were two underslung at each end and one of each pair was probably an oil cooler. On early internal combustion railcars it was normal to position radiators on or beneath the car ends or, in some cases, on the roof. The head and tail lights as seen here were apparently operational; many photographs of the railcar show them blanked off which suggests such photographs were taken during early trials. These lights notwithstanding, it remained a regulatory requirement to carry oil lamps although such is not visible here. It would have been on the other end. The power plant comprised two 105 hp Daimler engines, as described elsewhere, each coupled to a dynamotor (or 'dynastarter'). In this system a DC dynamotor would be connected across the batteries and thus operate as a motor to start the engine. Once the engine had started the dynamotor then acted as a dynamo supplying current to the traction motor, the Daimler car having two sets of this equipment.
Traction motors were also mounted on the raft, with transmission to the bogies being via carden shaft to the inner axle of each bogie. This arrangement can be seen clearer in other photographs and the carden shaft arrangement was similar to that used on the later GWR diesel railcars. The 6-cylinder engines were rated at 105 hp each and apparently this was 'Tax Horsepower', perhaps better known as 'RAC Rating'. As engines intended for road vehicles (to which Tax Horsepower applied) become more powerful and efficient this method of calculating horsepower became wholly inappropriate and was eventually abandoned in 1947 as it came to bear no relation to actual horsepower. However, at the time of the Daimler railcar, Tax Horsepower was a fairly accurate indication of actual horsepower so we can take it the actual horsepower of the Daimler engines was not far off 105 hp at the output shaft. Things are not, however, quite that simple as the power rating of internal combustion engines occurs at a certain RPM and it is unclear what the RPM of the Daimler/Knight engine at which 105 hp was developed actually was. A guess, which may or may not be accurate, might be in the region of 2000 RPM.
On the Daimler railcar there was a theoretical total power output of 210 hp but when taking transmission losses into account power at the rail, with both engines operating, would have been in the region of 170 hp at best. This was probably attained at a speed of somewhere around 30 - 35mph. Beyond that speed and when starting from rest, power at the rail would have been rather less and given this information we can deduce the Daimler railcar would have been incapable of towing a trailer, especially when fully loaded and tackling rising gradients. Therein probably lies the reason why the railcar was not fitted with full drawgear, just buffers and a coupling hook of which both were likely an LNWR requirement to ensure the railcar could be towed away in the event of a failure. Furthermore, the modified cooling radiators suggest even when running on its own the railcar suffered overheating problems and this was a frequent problem in the early days of internal combustion traction. The Daimler was nevertheless a brave attempt for its time but we should bear in mind that publicity of the time tended to trumpet achievements whilst brushing over, or ignoring altogether, the minus points and there would have been many of the latter.
Photograph courtesy of the LNWR Society. To order a copy please visit LNWR Society Photograph Orders and quote reference ' LNWRS 5078'.
Diagram of the Daimler & BSA experimental railcar
Extract from Commercial Motor