Major differences between gas and glow is in the fuel metering and the activation energy.
Glow engines are initiated by a catalytic reaction of the methanol to a hot platinum coil
Gas engines are initated by a timed spark createed by the gap in a copper electrode. What is key is the "timed" bit.

glow engines ignition timing is dependant on the heat of the platinum coil, the concentration of methanol to oxygen in the combustion chamber.
Gas engines ignition timint is dependant on the timing of the spark initiated by the ignition coil. Air fuel mixture does not affect the timing of the spark but does influence the speed of combustion.

GAsoline has a higher heating value than methanol fuel, so for every firing of the air fuel mix more heat is generated and hence more power can be released. in theory gasoline engines can be more poweful than glow engines. the reason they are often not is due to design. Most Glow engines are relatively higher compression ration engines. Methanol has a high Octane and hence it will not detonate uncontrollably. Gasoline typically has a lower octane value set by the specification for gasoline in various countries. Gasoline is rated according to the Research Octane Number or RON and this the resistance to knock at part load. the RONfor Methanol is around109RON(average).

Cmpresion ratio is the biggest determinant in the efficiency of an engine ans since Hobby glow engines are designed for max performance they do perform well thanks to the compression ratio's being higher than Gas engines.

Most gas engines sed in RC currently however have their origins in industrial equipment such as chain saws, weedwhackers, small generators etc. All these applications calls for engines operating at mostly constant speed but at high torque and they have t be durable so their specific power output per cubic inch is low. Engine designers call this under stressed. Glow engines by comparison would be close to over stressed.

So currently when we compare glow engines and gas engines we are comparing an engines that is purpose built for RC against an engines that was built with power to weight ratio NOT being a concern. And therefore gasoline engine are slated for anot having sufficient power.

That is changing however. Th new engines coming out of China have been placed on stringent diet and exercise programme and hence their power to weight ratios ar improving.

A year ago the cut off point at which gas became too heavy was around 30cc or 1.6 class airframes. Now with an engine like the DLE20, the cut off has been moved to the 90/1.20 size plane.Perhaps if the Magnum XLS 52G actually makes an appearance it will move the cut off even further down to .46 size birds. the naysayers will disagree of course.

the big change with the newer gasoline engines is the improvement in ignition timing and compression ration coupled to engine blocks that are a lot lighter.
There will always be a lower limit of mass for a gasoline engine of given capacity simply due to the fact that the hrat energy in the fuel has to be absorbed by mass and that means more metal. Methanol fuel takes more heat away form the engine on its journey to oxidation an that means that the engine can be a little lighter.


GASoline as a fuel will require different types of additives an oil. Mostly 2 stroke motorcycle oil or chain saw oils are suitable. Synthetics are highly recommended due to higher film strength and also for cooling since the synthetics designed for this market have lower heat of vapourisation and take more heat out the exhaust.


My personal preference is for gasoline engines and I ould probably stick to the DLE engines at this point in time since they do appear to be the most competeive on power (and thrust) to weight ratio