When are four stroke glow engines preferred over two stroke engines ? 

What are typical usage scenarios where 4 strokes have a significant advantage over two strokes, and why ?

Is there a preference for 4 strokes when used for hovering and torque rolls ? 

A four stroke on a scale bird sounds much more realastic and is able to spin scale sized props. Also since these scale birds tend to be heavy (what with all the bells and whistles) the four bangers with thier higher tourque are able to spin larger props with finer pitch giving the required urge.

So 4 strokes have higher torque, but 2 strokes have better rpm...   So the slower high alpha 3D moves which demand significant power to weight ratio are better on a 4 stroke ?

Also, how do they compare from a fuel consumption perspective ?

I'm not sure but 4T engines are more fuel efficient then 2T engine of same size !

QuoteI'm not sure but 4T engines are more fuel efficient then 2T engine of same size !

Most certainly, yes!

QuoteSo 4 strokes have higher torque, but 2 strokes have better rpm...

I am unable to comment on 3D flying but am pretty sure of the fact that 2 stroke engines have higher RPM and therefore more speed. But 4 strokers have a more consistent "pull" due to their higher torque. I have only 4 C/T engines and find that I can fly wide loops at a little above mid throttle without "sagging". The speed is also more constant throughout.

Slightly at a tangent, but relevant here.
Last sunday, flew a very heavy SPAD BUHOR (WEIGHS AROUND 5 KG) with a 40 ringed supretigre with a Davis Diesel  Conversion head.
It flew reasonably well with a 12X5  APC prop. (around 11,000 rpm) in pretty windy conditions. Flew for around 12-14 min on a 250 ml tank at full throttle. Good transition with the throttle.
A diesel would also give much higher torque with a lower rpm- something like a 4 stroker. But hardly anyone flies diesels nowadays- i want to use it on a 40 size camel WWI model
Avijit

I do not know how things are today, but have used diesels in the 50s when they were the only type of engines available. An absolute pain to get started!

Quote from: avijit17basu on October 08, 2009, 02:31:00 PM
Slightly at a tangent, but relevant here.
Last sunday, flew a very heavy SPAD BUHOR (WEIGHS AROUND 5 KG) with a 40 ringed supretigre with a Davis Diesel  Conversion head.
It flew reasonably well with a 12X5  APC prop. (around 11,000 rpm) in pretty windy conditions. Flew for around 12-14 min on a 250 ml tank at full throttle. Good transition with the throttle.
A diesel would also give much higher torque with a lower rpm- something like a 4 stroker. But hardly anyone flies diesels nowadays- i want to use it on a 40 size camel WWI model
Avijit

Ahh!!.. I remember that engine... Never thought it could haul a 5 kg plane.