2 Stroke reliability

[avbug]

Re-read my post, and you'll learn that the most efficient engine in the world, as cited, is...a two stroke. Go figure.

Pound for pound, the two stroke has the potential to put out twice the power that the four stroke does. Which puts out more power (forget bales of cotton or tons of lead); a one ton two stroke, or a one ton four stroke...and you'll find it's the two stroke engine. Once you get away from very small two strokes, the fuel efficiency on the four stroke is still superior, particularly for the power produced. Fuel effiency was never part of my discussion; this was introduced by others and attributed to me.

I did say that pound for pound the two stroke is more efficient, and it IS.

When considering the power it can produce, it's utility makes it far more advantageous in many installations from light aircraft to heavy cruise ships, and owing to the ability to do what it can do vs. a four stroke that would have to be built to compete, it's still more fuel efficient.

You may have noticed some of the comparitive links regarding fuel burn vs. work performed..and you'll find that there's little disparity on the count of fuel burn. Read again, a little more closely.

 

[VNugget]

To avoid this kind of confusion, just always specify the type of efficiency you're talking about when you use the word... i.e., alway say fuel efficiency, or weight efficiency, or whatever the case may be. Presto, everybody's talking about the same thing.

 

[avbug]

Sometimes I find that not doing so tends to promote discussion, where those involved are able to remain civil.

 

[ackattacker]

Re-read my post, and you'll learn that the most efficient engine in the world, as cited, is...a two stroke. Go figure.

Not a fair comparison. We're talking about aircraft engines. That engine is a *diesel* and weighs over 2000 tons. It has almost no common features with a gasoline 2-stroke. For example, it has a 4-stroke style crankcase filled with engine oil. It uses a turbocharger and high-pressure common rail fuel injection directly into the cylinder, and seperate blower for exhaust scavanging. As for weight efficiency, it produces only .025 hp per pound. That means that if you scaled it to aircraft size, a 60 hp engine would weigh 2400 pounds.

It is possible to bring the fuel efficiencies and emmisions of 2-strokes up to near 4-stroke levels using technologies such as direct injection. The Evinrude E-tec outboards are a good example. However the complexity increases and so does the cost and weight. So far we have not seen any of these "advanced" 2-strokes for aviation use.

You keep claiming that you were never talking about fuel efficiency, or being deliberatly vague to promote discussion.... but I just don't see it. You repeatedly brought up fuel efficiency, and made the specific claim that a 2-stroke engine produced more power for the fuel burned.

and as far as fuel efficiency, far more efficient than a four stroke engine

 

[avbug]

The horse is beat dead, answering your post would only rehash what I have stated before, which is true and correct, and by which I continue to stand.

I'm done with this thread.

 

[DieselDriver]

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[Lead Sled]

Discussions on efficiency aside, there is another aspect to the reliability issue that needs to be mentioned - these engines are used on amateur-designed, experimental aircraft. I've got a good friend who has been involved in the ultralight movement since day one. (There are two or three aircraft that he's been involved with at hanging at the Air & Space Museum in Washington D.C.) I've flown my share of ultralights and I've never really had an engine failure in one, but I have had a propeller and an airframe failure. The engine is probably the least of my worries - I wouldn't touch one unless it came with a ballastic parachute system.

LS

 

[icefr8dawg]

Why I would buy a four stroke...

http://www.youtube.com/watch?v=dxj1sbPi9dk

 

[ultrarunner]

Why I would buy a four stroke...

http://www.youtube.com/watch?v=dxj1sbPi9dk

Oh, don't get your panties in a wad ice, that four-stroke of yours would do the same thing with no gas!

 

[icefr8dawg]

Oh, don't get your panties in a wad ice, that four-stroke of yours would do the same thing with no gas!

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.

 

[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.