What have you been smoking? What’s the best smoke oil for aerobatics?

I recently received an email from Gordon Bowers concerning smoke oil for aerobatic aircraft. He was wondering what kind of oil to use and where to get it.

I recently received an email from Gordon Bowers concerning smoke oil for aerobatic aircraft. He was wondering what kind of oil to use and where to get it.

Smoke oil is another one of those lubricant recommendations that is more art than science. Most pilots have their own special blend. And oil companies are just a little nervous about the possible health and legal concerns when oil is partially oxidized and then blown into the air above a crowded airfield.

When selecting smoke oil, the number one concern should be safety ? for the audience and the pilot. For the audience, it is important to use oil that is a pure base stock with no additives. Never use an ATF or other additive-containing oil as the additives may be harmful to your health and the health of the spectators.

Choosing an additive-free oil sounds simple, but it is not. Most oil companies sell industrial oils that are additive free. But there are products out there that are called non-treated or other such nomenclature that are blended with line flush from the lube plant. They may be sold for uses such as form release oils or chain oils and are labeled as not having additives, but may contain some additives from the line flush. Always ask for a product that is additive free or zero ash.

The other safety concern is the flash point of the product. If the flash point is too low, you can have a real problem, especially if you have any leaks, your system is not installed properly, or your engine is not operating correctly. In the past, the primary recommendation was for oil with a minimum of 300?-350?F flash point. Now a lot of people are using oils with a flash of only 250?F. I cannot find any data to base a recommendation on, so will just say the higher the better. Do not dilute with diesel or Jet A. If you dilute your smoke oil with over 10% fuel to get the oil to flow, you can reduce the flash to an unsafe point.

The other two important requirements for smoke oil are the amount of smoke that it produces and the amount of deposits it leaves on the belly of your airplane. A general rule of thumb is the lighter the weight or viscosity the better. Usually an additive-free oil with a viscosity of about 10 centistokes at 40?C should work well. A thinner oil would probably be better. The problem is that additive-free oils with a viscosity less than 10 are not readily available.

Also, you should try to find a paraffinic type I base oil as type II and non-paraffinic base oils do not produce as much smoke.

So where are you going to find a non-additive oil with a high flash and low viscosity, blended with type I paraffinic base stocks? Your local lubricant supplier probably doesn’t have a clue. I would suggest you call the oil companies’ lubricant information centers for the name of a product that will meet these specifications. Good luck.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at [email protected].