I guys, I am new in this hobby.... what is the difference between a 2c and a 4c engine????? why models .40 for example ask for a 2c of .40 OR 4c of .60???????? what is the main difference???? power?????

A 4 stroke goes around twice for every power stroke, a 2 stroke produces power with each revolution so it makes less power. They also (in general) run lower rpm and more torque which makes them better swinging larger propellers slowly where 2 strokes come on in the higher rpm bands swinging smaller props.

4 strokes also sound better.

Here's an article http://www.masportaviator.com/ah.asp?CatID=8&ID=95

Ok, I think I got it, I read the article which explains clearly how it works..... so, what I understand is that the 2 strokes should be use for basic flying and the 4 strokes for sport flying?????? because it has better performance?????

I have a question, I think I am gonna get a cessna... it says it requires either an engine 2c .40-.45 or a 4c .60 Can I use a 2c .46 engine to fly it?????? or it's too big?????? I would prefer this because I want to train with this basic plane, just basic flying...... and then... when I feel ready or more skilled... I think I can get another plane and set up a 4c which will have better performance...... am I thinking right??????

There are NO reason to avoid 2 strokers for "sports flying".

There is a tendancy to put certain engines on certain planes.

My rough rule of thumb, e.g. what I usually do.

.32 sized and smaller - Electric
.40 through .60 - 2 strokers
.60 through .90 - Toss up. Depends upon what you want to spend and your target. 2 or 4 strokers work equally well in this range.
.90 through 1.60+ - Four strokers
1.80 and larger - Gas

2 strokers have a better cost per performance ratio up to a point. Beyond that four stroke engines give you power and MUCH better fuel consumption figures which ultimately result in a lower operating cost to you... again this is up to a point.

Once you get into larger planes, even a four stroker will seem to be ingesting relatively expensive glow fuel at a high rate. One of the reasons that gas is preferred.


You will get the "four strokers can swing a bigger prop" arguement, which is valid, but at the same time you can usually afford a much more powerful 2 stroke engine for the same amount of money in the smaller sized planes...

It's up to you to decide how to power the plane.

4strokes:
are appreciably heavier for the same displacement,
are significantly more complex so they also
cost more,
require more maintenance,
and produce less power

2strokes:
are lighter
simpler
less expensive
require little maintenance
and produce more power

4strokes swing a larger diameter prop at slower rpms and sound different than 2strokes. These are two reasons often given by some modelers who prefer them.

Either can be used for basic or sport flying. Performance is measured by power-to-weight and by power-to-displacement and 2cycles win both those comparisons. It is usually more difficult for a beginner to handle a 4cycle. It is harder to hear the change in speeds when setting the highspeed needle. For that reason, many engine experts recommend that a tachometer be used to set the carburetor needle. It's good advice.

You can often use larger engines than recommended. A 46 is basically in the 40-45 range in weight and power.
Forget the idea that a 4c gives better performance. They don't. A heavier, larger 4c can give equal aerodynamic performance however the extra weight will make that more of a challenge.

In aerodynamics, weight is a penalty.

When choosing an engine for a specific airplane, you need to consider what the engine weighs. That affects both the final weight of the airplane, which affects the climb performance. And it could cause you to need even more weight to balance the airplane. In a few cases, the extra weight is a benefit, such as for airplanes like the Sopwith Camel which will need quite a bit of weight up front.

Noone today chooses a 4C to race or fly combat who wishes to win. Precision aerobatics can be flown with either, but the airplanes have to be balanced to the engine's weight and some years only 2C was the 1st choice. But they both work in that event because the modelers tailor the airplanes to the engines. Basically there are no events where 4C engines are 1st choice for anything other than for their sound.

4C's however are fun just for themselves. Lots of the 4C bigots love them for what they are and what they do. Whatever that is.

Good answers guys, I appreciate that..... I got it. Thanks again! You are really helpful.

When considering the weight of engines, remember that because of noise, it is impractical to operate engines without mufflers.
As an example, a typical two-stroke engine such as the OS46AX weighs 17.2 oz WITH standard muffler whereas a four-stroke engine such as the Saito 82a weighs 17.6 oz WITH the standard muffler. You get 78% more displacement at a 2% weight penalty by choosing a four-stroke engine. In most applications a Saito 82 will significantly outperform the OS46AX simply because it provides more power at the RPMs we are typically operating our engines at.

/Red B.

Do you have the numbers for that? What is the difference in power?

This comparison is exactly what should always be done when shopping for engines. The Saito's are known for their power/weight performance. And some sizes of engines are perfect for the type engine in question. For example, the 1/2A engines are so small that they are hard to keep hot enough to run with power unless significantly high nitro fuel is used. And for years, 40-45 size engines were considered the perfect balance for 2C model engines' for power output and weight of the engine. But keep in mind that the weight of an engine also does good and bad not only for it's use to balance your airframe, but also for the power output and longevity of the engine.

Whenever you search for the right engine, there are more details to consider than just one or two.

As we shop we often focus on specific details, such as power to weight. And we might lose sight of other details.

For example, the Saitos are known for their power/weight. And how do they do it? Engineering and possibly extra steps in manufacturing. Which would explain why the FA82 sells for $255 and the simpler 2C OS46AX sells for $105.

When comparing different engines, all the generally known differences are not always present. Model design and execution are almost always a balance of choices. So shop wisely, and look at all the things that matter to you.

Personally, I'd like to see what Saito would do if they produced a 2C line of engines. They could be awesome. Actually, they SHOULD be awesome.

I just hate that "4-strokes require more maintanance" arguement. I don't do anymore to my 4-strokes than I do to my 2-strokes.

In general, I prefer 4-strokes, but that is mainly because of the types of planes I fly.

There are some planes that I think a 2-stroke is much better suited for.

To give you a good analogy, If I were building a Dirt Bike, I would use a 2-stroke. If I were building a Harley, I'd use a 4-stroke.

It's the same with airplanes.

Can you put a 2-stroke on an Ultimate Bipe? Sure you can. Would I? I'd rather gouge my eyes out with knitting needles! [X(]

After Googling for some performance figures :-) I found the following figures to be rather representative of what one may expect from these engines using 15% nitro and rather typical propeller sizes:

OS46AX, APC 11x6, 11.7 krpm
Saito 82a, APC 14x6, 9.2 krpm

According to the manufacturers the OS has the edge with 1.65 bhp at 16000 rpm vs. 1.5 bhp at some unspecified RPM for the Saito.

Because we often use propellers that give RPMs below peak power RPM only some fraction of the peak power is available.
Using Pe Reivers [link=http://home.wanadoo.nl/pereivers/prop-power.xls]prop-power spreadsheet[/link] I found that my RPM measurements are equivalent to power otuputs of 0.9 bhp and 1.1 bhp for the OS and Saito respectively. The static thrust would be 6 lbs for the OS and 8.5 lbs for the Saito.

My interpretation is that the Saito develops its peak horsepower at RPMs that are much closer to the RPMs listed above than is the case for the OS, thus a larger fraction of the peak bhp is available from the Saito compared to the OS.

In my experience the figures above seems reasonable and when comparing my own OS46SF and Saito 72 engines that weigh about the same I have observed that the Saito provides more static thrust, shorter take offs and faster climbs compared to the OS even though the OS have a higher peak BHP.

For high speed aircraft, where high rpm and high peak bhp are both of importance I would choose to use the OS.

/Red B.

and you don't balance propellers either

It's really not an argument. It's a simple fact that there is no maintenance required for the valves on our 2-cycle model airplane motors. None. Ever.

The valves on a 4-cycle can require adjusting. Some will do it. Some won't. It's not exactly a winning argument that it doesn't ever need to be done because some people don't or haven't ever. My nextdoor neighbor doesn't paint his house.

We should add to the list of differences between a 2c and 4c engine is that there is PASSIONATE, sometimes blind bias for each type.

Excellent.
That illustrates both our posts very well.

It's to everyone's advantage to take a sensible look at all the details. Since you've provided a comparison between two specific individual of the two general types, let's go a step further.
Which is heavier?
Which is more complex and might require more maintenance.
Which has more power for it's displacement.
Which has more power for it's size/weight.
Which is more expensive.

Heavier? They're about the same. Since the original basis for comparison used equal displacement, what does either a Saito 46 weigh or an OS100? The smallest Saito is almost a 60size. Comparing 45s to 60s is a stretch. The closest OS to a 100 is the 91FX and it's about 24oz.
More complex? The 4C
More power for it's displacement? The 2C
More power for it's weight? About the same? Is this true of all 4C's?
Expensive? The Saito is over twice the price of the compared 2C.

If the original topic was "what is the difference between an OS46AX and a Saito82, we'd have that topic covered.
But truth is, I hope everyone sees the general differences as well as getting an extensive discussion that illustrates the detail needed to compare two very specific engines. You'll very often benefit from shopping around. And looking very closely at every detail of the choices.

Ouch, I put in Tower .46's on my Ultimate 40s'. They overpower this plane and the purple anodized heads match the Ultimate colorschemes too.

I better get my eyes checked!

You're right on point "B", but there is always room for argument...

It is a simple fact that I burn a heluva lot less fuel, and I rarely ever need to spend 10 minutes at the end of each day wiping slime off my planes.

So let's see, spend 10 minutes checking the valve clearance once or twice in the life of the engine vs. spending 10 minutes after each flying session cleaning slimey 2-stroke residue.

Sounds to me like there's more work involved in using 2-strokes.

Well, I agree with you opjose on your size theory - for 40-size planes, it's not that big of a deal.

I also think that a 2-stroke is perfect for the Ultra Sport - which is one of my all-time favorite planes.

So I don't have a BLIND bias for 4-strokes.

To me, they just work best in the type of airplanes I fly the most.

I run my Saito with a Keleo header on my Mustang, I have to clean slime off BOTH sides!

Yea, I had one of those mufflers.

They ARE messy.

Look pretty cool though

Chuckle chuckle.........

Always room for sure.

I usually take a minute or two sometime before each airplane's maiden and stick a 3" length of silicone hose on my muffler pipe to route the "slimey residue" away from the airplane. What don't hit the airplane ain't gotta be cleaned off. And darned if my 4stroker doesn't mess up whatever it's exhaust hits. However, to the 4stroke's credit, there is a lot less and the muffler is very directional.

And since I got a $105.00 OS46AX on my model instead of a $255.00 Saito, I took the $155 left over and hired a guy to wipe down my airplanes when they need it. Since that takes him less than a minute per model, I have him take them apart and put 'em in the car with his free time. (always time for a bit'o humor too, eh)

I gotta get me one of those guys

Actually, I used to have a girl that did that stuff for free.

Then I made the mistake of marrying her [&o]