There was no obstacle more frustrating to early Canadian bush pilots than the cold weather. Each night, the oil was drained and both the oil and the engine were preheated the following morning before re-installing the oil. This was a time-consuming, laborious and at times hazardous job involving a gasoline “blow pot”. Though highly effective, they were noisy, smelly and extremely dangerous, since the aircraft wings and fuselage were made of fabric. More than one aircraft was incinerated in blow pot misadventures.
Tommy Siers, the head maintenance manager for Canadian Airways at the time attended a Society of Automotive Engineers Conference in New York in the winter of 1937/38. One of the speakers was Weldon Worth, a mechanical engineer from the U.S. Air Force. He had suggested a method of allowing fighter aircraft to become airborne quickly without engine preheating. The idea basically involved diluting the oil with gasoline.
An Idea to Explore
Tommy immediately recognized the potential value of such a system since Canadian Airways – with a winter-operating fleet of roughly 40 aircraft – practically ‘lived by the blow pot’ during half of the year. When he returned to Winnipeg, Siers arranged a meeting with Canadian Airways President, James Richardson. He presented an outline of what he had learned and the safety improvements and cost savings that should result. Richardson immediately authorized the development and installation on one aircraft.
In January 1939, an oil dilution system was installed on Junkers CF-AQW by modifying the inside of the oil tank, creating two separate oil circulating systems.
A routine test flight was carried out and the machine was left standing overnight with oil in the tank. The next morning, it was -30°F with a stiff breeze blowing. AQW stood naked without her customary engine cover. To the spectator’s surprise , the prop turned quite freely, but optimism soon vanished as the starter, priming system and spark plugs were unhappy with the change in routine. It was early afternoon before the crew had the motor running. Finally, with the engine running and the oil pressures and temperatures approaching normal, the motor was shut down and inspected. The main body of oil in the tank was still stone-cold – even though the oil-in and the oil-out temperature readings had been normal.
In other words, Worth’s theories were practical. The transfer of heat from the diluted oil to the main oil in the tank was preventing the oil from over-heating and at the same time, it was warming the main body of oil.
Not Quite Ready For Prime Time
Crews still struggled with a series of problems and installed a larger primer, added additional primer jets (with an improved design), and installed a direct-cranking starter in place of the original electric one. These improvements led to consistent starts after overnight, sub-zero temperatures.
Although it worked, it was a long way from being reliable. The dilution valve was a manual affair and the crew noted recurrent leakage problems due to a lack of the proper type of seals. The booster mag was replaced by an ignition coil with a manual ‘on/off’ switch. The starter control was changed from a hand-controlled switch to a foot-operated switch because there weren’t enough hands to go around during the engine-starting attempts.
Another early problem was oil discharge from the crankcase vent. The overly thin oil was not able to withstand the combustion pressure in the cylinders. This ‘blow-by’ would increase the crankcase pressure and the resulting oil/ air mixture would discharge through the crankcase vent and splash onto the windshield, somewhat to the consternation of the pilot. In order to direct the oil to other – and less vital – locations, a vent tank was added.
Science Meets Art
The correct amount of dilution for an overnight stop was always a guessing game – more art than science. If the anticipated overnight low was -15º, a dilution period of perhaps three minutes might be used. It was also possible to end up with an over-diluted engine which required a prolonged warm-up period to burn off the dilution.
Engine covers and a blowpot were still carried as a precaution.
Canadian Airways Ltd. began to convert its fleet. The Norseman fleet was modified, as well as the Wasp-powered Junkers W-34s, and Beech 18s. (The system was incorporated into Junkers, CF-ARM that has been restored and is on display at the Royal Aviation Museum of Western Canada (shown here docked on the Red River).
Wartime Overtakes Experimentation
The American military had been paying close attention and an oil dilution system was included in the specifications for all of the military transport aircraft that were then in production – Lodestars, DC3s, C-46s and others. The cold-weather operating instructions published by the Canadian Department of National Defence and the FAA also included instructions on the use of oil dilution.