jigeye

New to airplane r/c. considering putting a four stroke in my next bird.
1. What are the advantages of 4 over 2?
2. How reliable are these engines?
I know they cost more and sound cooler, what else?

carrellh

1. They tend to spin bigger props at lower RPM which often means they are quieter than 2 strokes.
2. They are typically very reliable. They need a valve adjustment once in a while.
I have two strokes and four strokes. I like both.

STG

My Feedback: (26)

If you want a fast transition they are not so sensitive to the correct needle settings ( easier to tune than 2 strokes ).

What plane and what kind of flying do you want to do? As with 2 strokes, not all 4 strokes are created equal.

touch and go

My Feedback: (11)

Very reliable if operated properly. Not only do they sound great, but most people perceive that they are quieter than 2 stokes. They generally operate a lower RPM and swing bigger props.

STG

My Feedback: (26)

True when comparing a 2 stroke 46 to a 4 stroke 70 ( different displacements ), but not true when comparing a 2 stroke .91 to a 4 stroke .91 (same displacements ).

William Robison

My Feedback: (3)

A four stroke engine is heavier, and generally less powerful than a two stroke of the same displacement. A four stroke engine is more complicated mechanically than a two stroke, and has more parts to fail.

More parts means more inspections, more adjustments, and more expense to purchase and maintain.

With all this in mind, why indeed buy a four stroke engine?

If you have to ask, stay with the two stroke engines. There's no logical explanation for liking the four strike engines.

Bill.

djlyon

Bills right. It's just pure sex appeal. I like my 4 strokes. But then read my signature. My like for 4 strokes is purely on the sensual level. If all I wanted to do was tow an airplane around reliably I would have stuck with 2 strokes only.

Denis

STG

My Feedback: (26)

[X(] [sm=lol.gif]

Rcpilot

My Feedback: (78)

Thats total BS.

A 2-stroke engine of the same displacement will outswing a 4-stroke. Any day of the week.

This is a MYTH. Plain and simple.

What size prop do you run on a 91 4-stroke? 14-6 typically.

What size prop do you run on a 2-stroke 91? 14-6 typically.

But the 2-stroke will turn that same prop a few thousand RPM faster than the 4-stroke.

Yes, you CAN put a 15-6 or a 16-6 prop on a 91 4-stroke and turn it at 7000RPM.

You think a 2-stroke engine won't do the same thing?

You can put a larger prop on a 4-stroke if you want. Doesn't make it more powerfull than a 2-stroke.

XJet

Is that always true Bill? I know that (for example) a .45-ish Saito probably weighs *less* than the same sized two-stroke with muffler -- after all, the Saito 82 is little more than the weight of a good .45 and has about the same HP.

Then there's the YS63, every bit as powerful (if not more so) than your average 60-sized 2-stroke.

JPMacG

My Feedback: (2)

I think Bill said it pretty well. I love four-strokes but cannot really tell you why.

I will make the comment that, while four-strokes have a more pleasant sound than two-strokes, their sound seems to carry farther than the sound of two-strokes. I say this based on personal observation. At the entrance to our field, about 2000 feet away from the flight line, I cannot hear the two-strokes but I can hear the four-strokes. I think the higher pitched two-stroke sound is more rapidly attenuated as it travels through the air.

Motorboy

4 stroke engines drinking less fuel than 2 stroke engines, good trottling control in rpm range to example use in scale airplane model who need realistic speed. 4 stroke engines cost more than 2 stroke engines cause more parts inside. Need more nitro for reliable idling and improved power, but not all to example Laser 4 stroke engine do not need nitro in fuel.

Jens Eirik

William Robison

My Feedback: (3)

[b]XJet:

There are some heavy and weak two sgroke engines, and some light and powerful four stroke engines. Always exceptions, that's why I said "Generally" heavier and less powerful.

Bill.

flipstart

Bill could not have said it better. I have both 2S and 4S, OS and Saito. 2 strokes are just easier to maintain, less finicky, and for same displacement provide more power. The large displacement 2 Stroke engines do not have that loud high pitched scream that their smaller cousins exhibit, and with the proper muffler actually sound more realistic than a 4 stroke. It boils down to what you like the best.

B.L.E.

This is a HOBBY so we don't need no steeenkin' reasons to use four stroke engines. The fact that we think they are cool is reason enough.

STG

My Feedback: (26)

Another myth. Yes, in theory they are more efficient, but in practice in a lot of applications you can find the 2 stroke more economical. You really need to do a motor to motor comparison when comparing 2 strokes to 4 strokes.

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The last 10 years there has been relatively little in the way of 2 stroke development for this hobby. On the other hand, the 4 stokes have been getting all the R&D money and now there are some real good power plants with very good power to weight.

SA82, SA100, SA125, SA180, SA220, YS63, YS110, YS140,YS160 will all offer top of the line 4 stroke performance on higher nitro(power to weight) in competition to the better 2 stokes that are out there without a tuned muffler.

rclement

My Feedback: (1)

I put up with the 2 strokes that I have....... I love the 4 strokes that I have...... Other than that, there is no difference at all...... LOL

NM2K

My Feedback: (14)

The idea of having control over an airplane that is not physically connected to us via control lines is one of the great appeals of R/C control. We like to control things from a distance, but truthfully, we just like to control things - period.

I think that the idea of having tiny camshafts, tappets, pushrods, rocker arms and valves moving at our command is part of the attraction. Again, we like to control things.

I like the four-strokes ability to tolerate idling longer without protest and with immediate response to throttle.

I like the more civilized tone of the exhaust note.

I like the miserly way in which the four-strokes sips its fuel allotment.

I like the idea that it relies upon me for more maintenance than just glow plug replacement, needle tweaking and fueling. Granted, there isn't much extra work in adjusting the valves, but it needs me more than the two-stroke.

I like the way that the four-stroke handles larger props for a given size model (built-in increase in four-stroke displacement accounted for).

Somewhere inside, I know that, at least to me, the four-stroke engine helps move my model away from the "toy" classification by being more sophisticated. Others may not perceive it this way, but I do.

With all of that said, I still love my two-stroke engines too. <G>

blw

My Feedback: (3)

Kinda funny how everybody ignored RCPILET's ranting. What a hoot.

I would have argued about the comment that some 2 strokes are economical with fuel, but I have a .46NT that sips fuel.

I like the instant response with 4 strokes where you have to wait on 2 strokes to spool up. I don't miss crankcases loading up with fuel either.

STG

My Feedback: (26)

My OS 2 strokes have very good spool. They are, however, sensitive to the correct needle setting and tuning. My OS108 and 160FX needed a pump (I like to run my fuel tank back a CG so no prob). I do admit that most 2 strokes that I see are not tuned for good spool and I cannot speak for any motors other than the OS25fx, OS46FX, OS91FX, OS108 or OS160FX.

My OS 1.6FX and OS108 are very good on fuel. My YS110 is not. My SA100 is. My OS25fx is not.

I like good 2 and 4 strokes.

RVman

http://www.rcuniverse.com/forum/m_3832210/tm.htm
heres a comparison between two specific engines. I find there is a huge difference between cheap chinese twostrokes and the good ones like Jett, Webra, MVVS, Irvine etc especially in the quality of the carb and midrange behaviour. Why not compare the $250 fourstroke to a $250 twostroke instead of the $70 chinese engine?

DarZeelon

Barry,


Remove the hot glow-plug that is in your Evo and replace it with a colder one. Also, change to fuel that contains only 5% nitro.
Your engine does not need any more than that, but you will have to readjust both needles, to get the transition optimized.

Your engine will 'sip' about 30-40% less fuel than it did before.

NM2K

My Feedback: (14)

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Because I won't pay $250 for a two-stroke when I can buy something that does the job for much less. If I could buy a four-stroke at much lower prices, I would. I used to buy Magnum four-strokes, when their prices were more in line with their actual value. HINT - HINT! <G>

Back when I was competing a bit in pattern (at least in my own mind), I would pay premium prices for a two-stroke. Now that I sport fly, no way am I going to spend that much money on an engine just to fly around. The el cheapos are capable of doing that just fine with identical results.

This is not to say that I don't buy an expensive engine occasionally, but it is just a kind of on the lark kind of thing. I don't actually "need" an expensive two-stroke.

I do, however, agree with your basic premise.

B.L.E.

True, but 2-strokes were already highly developed when 4-stroke engines were introduced. The first four stroke engines were kind of novelty engines that no one expected to be powerful, there was a lot of room for improvement. Then pattern rules were changed to allow 1.2 cubic inch 4-strokes to compete against .61 2-strokes and the 4-stroke horsepower race was on. Then they undid that rule and now there is a lot of attention being paid to 1.2-1.6 two strokes as well as LiPo/brushless motor power systems.

I think that if the pylon racing rule makers has opened a 4-stroke only racing class for .40 size engines, we would today have a line of 25,000+ rpm 4-stroke screamers that can only be used with 7 or 8 inch racing props. Did anyone hear that Ferrari doing the burnout during the Winter Olympics opening ceremony? That thing had a 4-stroke engine in it!!

britbrat

I'm a 2-stroke guy. When necessary, I use 2-strokes to swing huge props -- every bit as big as a 4-stroke of the same, or even larger displacement. They don't make their peak power that way, but they certainly match, or better the 4-stroke with the same prop, & they do the job very well for a lot less $.

The 2-stroke engine is also lighter than a 4-stroke of the same displacement & prop-swinging ability -- it's just that nasty big 2-stroke muffler that adds extra weight. That little problem can be addressed through light-weight after-market mufflers & still be a lot cheaper than the 4-stroke. Additionally, a 2-stroke swinging a big prop doesn't burn significantly more fuel than a 4-stroke swinging the same prop.

Finally -- sound. I admit that a small 2-stroke doesn't sound right in a Cub or something similar, although when it is "over-propped" it isn't too bad in that regard. I have an OS 46 LA with a pitts muffler, swinging a 12-4 on a 6' Unionville Beaver. It doesn't sound bad at all. Similarly, a TT 42 GP on a 1/7 scale Bucker Jungmeister, with a modified stock muffler & swinging a 12-4, also sounds pretty good. When it comes to a V-12 fighter, a big 2-stroke with an appropriate muffler sounds a lot closer to reality than the put-put-put of a single-cyl 4-stroke.