How aircraft make smoke

PISTON ENGINE AIRCRAFT

Smoke oil tanks come in a variety of sizes and are installed and mounted differently based on the aircraft type. The tank connects to a pump that continuously operates, even when empty, without reducing the effectiveness or causing damage to the pump or the aircraft.

An oil mixture valve attaches to the outlet of the pump to optimize the flow of oil. A pressure hose runs from the oil mixture valve to the aircraft firewall where it connects to a bulkhead fitting. Teflon-lined stainless steel braided hoses deliver the flow to the injector or multiple injectors. This flow is controlled by the pilot by means of an electrical switch.

After the biodegradable paraffin based oil passes through the injector, it is immediately vaporized by direct injection onto/into the exhaust system, depending on system used.

Because the systems are mostly used on aerobatic aircraft, they are usually tested up to 10+ “G”.

What is Smoke Oil?

Smoke oil is a blend of mineral oil with a paraffin base that produces a brilliant white smoke trail. For those green people among you; it is non-toxic and environmentally friendly, and is free from additives like zinc, phosphorus, sulphur and metals. It’s highly refined base oil that has been properly atomized and the low viscosity produces good results while leaving fewer residues on the aircraft itself. Remember those days of cleaning your glow plug balsa and plastic models after a day of flying. Not nice.

TURBINE AIRCRAFT

When it comes to turbine engines, the process is a little different. This type of smoke oil system injects the smoke oil through a nozzle several inches ‘away’ from the turbine exhaust. The exhaust and shear forces create a fine mist into the exhaust, producing airshow quality smoke.

JET ENGINE AIRCRAFT

The biggest difference here is that the biodegradable paraffin based oil is injected direct into the exhaust system.

OTHER

Smoke may also be produced by special generators with an external power supply system.

Coloured smoke is just a colouring agent added to the smoke oil.

Uses of Smoke Systems

• Visibility

Smoke systems function as visual collision avoidance system. A large plume of white smoke makes it easier for other pilots to see your path. Especially helpful in many rural areas with limited or inactive air traffic control.

• Airshows & Exhibition Flights

Smoke systems highlight aerial performances. Smoking systems even work while the aircraft is inverted.

• Fire Control

Forestry services and fire departments have use smoke systems to mark the optimal areas for helicopters and larger aircraft to drop their payload of water and fire retardants during wildfires.

This is usually red or orange in colour, depending on the operators.

CONTRAILS EXPLAINED

Aircraft, especially high flying airliners also make trails. This is usually from condensation in the exhaust gases.

As the airplane’s engines release exhaust gases, moisture vapour is released as well. The cold temperature and low air pressure at high altitudes forces this moisture to condense, which creates the characteristic white smoke trail for which airliners have become widely known.

Do all aircraft leave contrails?

Aircraft with hotter engines are less likely to form contrails, as the heat of the exhaust prevents ice from forming. Modern aircraft with more efficient engines burn hotter, but use bypass air to cool the exhaust, making them more likely to leave contrails in a wider range of situations.

At what altitude do contrails form?

Generally above 26,000 feet.

Contrails form when an airplane is at cruising altitude. The air at this altitude is usually around minus-40 degrees Celsius. Contrails form in the same layer of the atmosphere that cirrus clouds form in.

Why do some contrails not dissipate?

If the humidity is low and the temperature is not cold enough (above -40 degrees Fahrenheit, -40 degrees Celsius) contrails will dissipate quickly. However, if the air is moist and the temperature is -40ºF or below, then a contrail will “persist” for as long as 30 minutes to an hour.

Are contrails pollution?

While it is easy to imagine that contrails are just dirty streams of pollutants billowing out of aircraft as they cross the sky, in reality they are mostly ice crystals with a small amount of soot particles.

Like other clouds, long-lasting contrails can trap heat in the atmosphere.

Contrails, can heighten the effect of global warming and account for more than half (57%) of the entire climate impact of aviation. Not good, and as a result manufacturers are looking at new fuels and engines to help combat this negative effect.