Question: What gives with Model Airplanes Engines? What's a 2 stroke? What's a 4 Stroke? What do you mean by Glow as compared to Gas? Now there are electric motors being adapted to replace engines... how the heck do I choose what is right for my model?

Answer: Well, answers to this can take a bit of explaining. Here is an overview.

2 Stroke (sometimes called 2 cycle)

• Is what the majority of current modelers mean when they say "Model Airplane" or "Glow" Engine
• Noisy screaming type of sound that must be carefully muffled and never sounds like the real thing.
• Uses Model Airplane Fuel (alcohol, oil, nitromethane and additives)
• Uses a Glow Plug hence the term "Glow" Engine.
• Generally the cheapest, lightest, most powerful engine for the money.
• Referred to by displacment in hundreds of cubic inches (or in cubic centimeters = cc)
• Imperial measure is cubic inches and a slang has developed
  • .40 cubic inches is referred to as "a 40"
  • .90 cubic inches is referred to as "a 90"
  • 1.20 cubic inches is referred to as "a 120"
• Generally range in size from .049 to 1.80 although some smaller and bigger engines exist.

4 Stroke (sometimes called 4 cycle)

• Has become more popular since the 90's with those wanting quieter more realistic engine sound for use in semi-scale or scale models.
• Quieter more familiar engine sound when in the air. Much more realistic for scale flying models. Sounds much more like the real thing.
• Uses Model Airplane Fuel (alcohol, oil, nitromethane and additives) although special blends with more or less oil and more or less nitro may be required for some engines.
• Uses a Glow Plug hence the term "Glow" Engine can be used for either 2 stroke or 4 stroke engines
• Generally costs more, weighs more and gives less power for more money than a 2 stroke engine of similar size.
• Referred to by displacment in hundreds of cubic inches (or in cubic centimeters = cc)
• Imperial measure is cubic inches and a slang has developed
  • .52 cubic inches is referred to as "a 52"
  • .91 cubic inches is referred to as "a 91"
• Generally range in size from .25 to 2.50 although some smaller and bigger engines exist.
• To get the same power as a 2 stroke, add on about 30-50% in size. This is a very rough rule and does not consider weight and torque issues but it is a good guide.
  • A model calling for a 2 stroke .46 would require roughly a 4 stroke of size .60-.70
  • A model calling for a 2 stroke .61 would require roughly a 4 stroke of size .80-.90

Gas (sometimes called Ignition Engine)

• Has become more popular for use with big models.
• Quieter more familiar engine sound when in the air. Much more realistic for scale flying models. Sounds like the real thing  because it pretty well is the real thing!
• Uses Gasoline. Special oil or additives may be added to the gas in some cases. Gas is 25-50% cheaper than Model Airplane Fuel.
• Uses a Spark Plug hence the term "Ignition".
• Often adapted by the manufacturer from some other purpose such as a weed eater, leave blower etc. Although the engines end up quite different with regards to fuel supply, ignition, prop adapter and flywheel etc, they usually started with an existing product and adapted from there.
• Seldom used on smaller models and nearly always used on big models due to the higher weight of the engine and ignition system.
• Generally costs more, weighs more and gives less power for more money that a 2 stroke engine of similar size. May cost and weigh more than a 4 cycle Glow engine.
• Referred to by displacement in cubic centimeters (cc) (or in cubic inches but almost universally now in cc)
• Metric measure is cubic centimeters (cc) and the cc is nearly always noted in referring to these engines
  • for example "30 cc"
• Generally range in size from 20cc to about 65cc although some smaller and considerable numbers of bigger engines exist.

Electric Motors (both brush type and brushless type)

• Have become more popular since 2000. Increasing in popularity
• Just as a combustion  Engine needs and is succesful depending on the type of fuel it burns, an electric Motor needs batteries.
• As battery technology put more and more power (run time) into batteries of a certain weight (we call this energy density) electric powered flight is starting to take off (literally)
• Generally brushless motors are taking over. They can be very expensive when coupled to a suitable electronic speed control and a good set of NiMh or LiPo batteries.
• Main advantage is quieter and no mess. No fuel to buy.
• Main disadvantage is price and flight time per charge.
• They will continue to improve and be more popular in time.
• The rating system is not yet standardized so it is hard to compare apples with applies. Generally if a model calls for a .40 two stroke engine, modelers need to select an electric motor that can provide similar power in order to have similar flight characteristics. This can vary widely by motor type (brushless is better), battery type, speed control and wiring.

Please note that to this point this article makes no attempt to advise on if a particular model can be adapted to accomodate a different type of power system. For some considerations related to fitting 4 stroke engines into a model please search on "Four Stroke" for further assistance.