FROG 500 Glow (1949)

The FROG 500 glow plug engine was created by Bert Judge to take advantage of a gap in the British engine market a result of UK government import restrictions on luxury goods in cash starved post-war Britain this included restrictions on the import of American-made model engines which at this time were the most advanced glow plug engines produced in the world.

The sales success of the FROG 500 did not depend on it being the best in the world but rather on it being the only 5cc B class glow plug engine available to UK aero-modellers. Notably the FROG 500 bore a strong resemblance to the American K&B Torpedo 29 leading to speculation that Bert Judge may have had access to an example of the Torpedo 29.

While the FROG 500 may not have been a direct copy of the Torpedo it certainly appears to have served as inspiration to Bert Judge for its design. Production of the FROG 500 engine as depicted here began in late 1949 with the engine becoming widely available by early 1950.

The FROG 500 Glow engine pictured here notably bares the serial number 2904 and is fitted with a KLG Mini-glow plug which is correct for the FROG 500s production period which spanned from 1949 to 1963. It is of note that when FROG initially introduced the 500 engine they refried to it in their advertisements as a Hot Coil Ignition Motor rather than a Glow Plug Motor.

Capacity 4.92 cc (0.30 cu in) - Bore 19.05 mm (0.750 in) - Stroke 17.27 mm (0.680 in) - Power 0.38 BHP 13200 RPM (0.283 KW) - Weight 7.65 oz (217 g) - Ignition Standard glow plug - Induction Front rotary valve - Porting Cross-flow - Piston Liner Cast iron piston Hardened steel liner