2 Stroke reliability

[crash-proof]

Is that why it quit?
And all my engine failures (3) HAVE been in four strokes so I guess I'm talking out my a$$. Cool video anyway.

I thought he had a 2-stroke "seizure", not run out of gas. I'd think it be hard to run out of gas, simply look in back and see if there's gas sloshin in that 5 gal semi-transparent tank

 

[Grey Ghost]

As the issue is a small engine in an ultralight aircraft, all the numbers don't really mean squat...the point is mute. Efficiency is being able to power an aircraft in this case with a very light engine. You could probably make it happen with a really big engine, heavier structure, carry more fuel, blah, blah, blah...but that would make it...less efficient. Get it?



I made no such claim...I did however correctly assert that efficiency may be defined in many ways.

If a finely designed four stroke engine with the inner workings of a swiss watch is too heavy for the structure in which it is targeted, then it just ain't that efficient. Period. Efficient is what is light enough to fit in that aircraft and deliver the power required.

As for your comments regarding engine RPM and torque, they do not apply, except in a fixed pitch installation for comparitive purposes. Torque becomes an issue in a constant speed, or variable pitch application, which is inclusive of some ultralightor light airplanes utilizing two stroke engines with flexible propellers, or adjustable propellers. As pitch is increased on a propeller (as it is moved toward coarse), more torque is required to generate the same RPM for any given airspeed...torque is more than merely propeller RPM. It must consider propeller loading, which includes other factors such as blade angle and angle of attack, which in flight may be considered a function of pitch and airspeed, among other things.

Clearly there's more to the topic. Fact is that for the same size (eg mass, or weight), a two stroke can put out more power, particularly with regard to small light aircooled airplane engines. A heavier four stroke engine will be required to put out more power to sustain the same flight condition, because the aircraft is heavier. In so doing, any comparitive difference in fuel efficiency is lost...the point of diminishing returns has been reached, and one may well find that one burns less fuel with the two stroke as less fuel is required to accomplish the same thing for a given parameter...time, speed, distance, etc.

Exactly what the numbers are will of course, vary with the aircraft and flight conditions (eg, density altitude, operating weight, etc).

Two strokes are cheaper to operate, cheaper to overhaul, cheaper to purchase, lighter, put out more power per pound than compartive four stroke engines of the same mass, are much more simple in construction, more tolerant of change in operation, and in many cases, ideally suited for the light aircraft they power. Getting into the lighter aircraft, a 1/2 vw still can't compete with a typical Hirth or Rotax...and even if you could wrap it up enough to produce the same power, it would be burning considerably more fuel and would have become...you guessed it...less efficient. Including fuel efficient.

As an AP, I would go with the 4 stroke, thrust to weight ratio, 4 strokes do the job. The fuel second to overhaul cost, and the fact they can run long between overhauls.