STG

My Feedback: (26)

I think the best prop for the .91FX is a 15x6 apc. Mine was on a 10 pound Spacewalker. Although I did not time my flights I noticed a big difference in fuel economy and thrust when I went from the 13x8apc to the 15x6apc. I plan to transer the motor to a 6.5 pound Ucan-do type plane next and will most likely run a 13x6 apc and just let it rev up. I like smaller dia props on lighter planes, but that is another story.

Another consideration when choosing between 2 and 4 stroke is the survivability of a crash. I had a 1.08 on a plane that I recently put in. The motor was fine. In this case I think the YS110 would have been going back for service.

drumbum

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my O.S. 91FS im running a 15x4W.. i have used 15x6 in a pinch but it greatly increases the speed of my model.

drumbum

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As far as cheaper fuel. I always run YS 20/20 in anything and Me and my friend split cases. he runs it in his 2 strokes too so for me it would be cheaper that way too instead of having to buy double the fuel..

I think all of this just boils down to personal prreference and The size of your wallet at the time of purchase..

Both will fly a plane great. and have their ups and downs..

drumbum

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Not24

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My F90 has the OS 1.08, and I don't think it's the ideal engine for this plane if you are trying to 3D it like Kyle does. It'll swing the 16-4 at about 10k, but it is slow to spool up in the midrange, making power adjustments sluggish and sloppy. For constant power settings or gradual changes in power, a 2 stroke is fine. If you need to make quick changes, such as during rolling harriers, you will be sorely disappointed with the 2 stroke's power curve and sluggishness. Keep in mind, I'm not talking about stumbling accelleration, just plain slow to adjust to the new rpm. Mine is obvious enough that I'm going to play with lighter props to try and reduce some of the flywheel effect.

By the way, i can fly for a full 20 minutes on a 14 oz tank and still taxi to the pit after landing. And that's flying hard, not just putting around.

STG

My Feedback: (26)

Are you using a pump or cline regulator? Where do you have the gas tank? I think you will like a lighter prop better on the motor. Do you still have the restrictor sleeve in your carb?

drumbum

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keep the thoughts coming guys ...

this is the most interesting thread ive seen in a while..

thedak

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4 strokes r 4 pimps. It's that simple.

drumbum

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no speaka

Barry Cazier

My Feedback: (17)

Having riden dirt bike motorcycles for many years, I've recently seen 4 strokes take over in almost every area. I'm certain they don't make more peak horsepower but they certainly ride differently. The four stroke has more horsepower over a broarder RPM range. It probably doesn't make more peak horsepower but certainly makes more over a longer curve. The same is true with model airplane engines. You are seeing a 4 stroke revolution. Eventually they will take over every part of the market because they are easier to prop, tranistion, do stunts with etc. To visualize the difference picture in your mind to identical airplanes, one with a 4 stroke and one with a 2 stroke, flying vertical at slow RPM, as if in a drag race. Somebody yells GO and both planes take off. The 4 stroke, based on lighter weight, quicker throttle reaction, and broader HP curve would immediately streak into the lead. It would stay ahead for a certain distance and then the 2 stroke would eventually start to overtake the 4 stroke. Who would win the race. Depends: on the length of the race. If given enough time the 2 stroke will make more peak horsepower and take over the 4 stroke. But it will take quite a while. But, if you race to a certain area, slow down for a curve, stunt, or something else, and then speed up again and then do it again, and again, the 2 stroke will never catch up. That's why the 4 strokes are so good at 3D. Up, down, down, up. And there nothing like broad horsepower. It's the feel, not peak horsepower. That said, I still have 2 stroke motorcycles and 4 stroke motorcycles, and 2 stroke airplane engines and 4 stroke airplane engines. But 4 strokes are here to stay and they WILL eventually be proven better in all but a very limited applications. They just simply have to broad of a base to be kept down.
Thanks,
Barry

Barry Cazier

My Feedback: (17)

Sorry about a second post but I wanted to say more. It is a common misconception that a 4 stroke engine will always spin less RPM than a 2 stroke. In airplanes, for the time being that is probably true. The same was true just 5 years ago in motorcycles. Now days a CR250 Honda 2 stroke engine will have a peak RPM at about 9700. It has a powerband that is useable only from about 7000 to 9000. A CR450, (the 250 main competetor) has a peak RPM of 11900. And a usable powerband from about 4500 to 11000. They both make approximately the same horsepower, 53. With the difference in breath of powerband it becomes easy to see why the 4 stroke is much perferred. The same technology is happening in airplane engines. So they will turn more RPM than 2 strokes and have a much more greater usable powerband. That will be the kiss of death to the 2 stroke engine. But that's ok. It has had a long and great life.
Thanks,
Barry

STG

My Feedback: (26)

Barry Cazier,

What if they let the 2 strokes run 450's against the 4 stroke 450's? Looks like you are comparing dissimilar displacements?

oldbloke

Well said Spacewalker

My original question which seems to have sparked off a heated debate was to compare 2 strokes with 4 strokes of the same capacity/displacement, we know you can't beat cubes.

Therefore would a 2 stroke of a larger displacement than a 4 stroke trounce all over it then in terms of hp AND torque, and if so why bother with the 4 stroke ?

Over to you guys.

Sprink

When comparing equal displacement, you are right, the 2 stoke is more powerful (though not much in it with YS engines), but for what we need, that is not really the issue. All our 3D machines are powered so that they can hover/torque roll at around half power or less, so we want contol at that half throttle, which we get far better with 4strokes compared to two stokes.

With, for example, people here putting Saito 100s on their Funtana 40's, the fact that the saito is less power than say the OS 91FX is not really important.

Ultimately throttle is a fourth control surface, and as with the other three, is very important for 3D flying.

EXTRA ADDICT

My Feedback: (2)

In reply to Sprink!! Now that is about the best explanation I have read so far!! Is it just me do 2 Strokes seem to leave much more slime on the plane than 4 strokes?

drumbum

My Feedback: (1)

Correct Due to TORQUE.... 3d is flown with torque..

Spoiler

This has been about the best thread I've ever seen on the 2v4s debate. I am sorry I didnt fork out some extra money and buy a saito 180 for my Funtana 90, instead of the 2s 120 it now has. I have also recently seen a 4s powered Funtana 40 being pulled around by a Saito 91 and the throttle response and 3d capability was clearly far superior to a Fx 61 powered model flown on the same day.

However, it seems that 4s hasnt taken over in the larger gas powered model arena. Chip H's double vision for instance, 3d's very well with a 2s 50cc (judging by the promo video) and al the TOC style planes use big gassers. Does the gasoline guarantee better toque and throttle response. Isnt it possible to tune a 2s to respond more like an electric/4s motor?

Barry Cazier

My Feedback: (17)

GPSpacewalker, you are right, in motorcycles 4 strokes are allowed to race an engine almost twice the size of the 2 stroke. 450cc vs. 250cc. This rule was allowed by the rulemakers because just five years ago there were no 4 stroke motorcycles that were competetive. Now the 4 strokes have almost taken over. So, for now at least the 4 stroke seems to need a displacement advantage to make similar peak horsepower. However that is changing very quickly. Even with similar displacement, the 4 stroke favors a wide, wide powerband. Much wider, perhaps 2 times as wide as the 2 stroke. In many applications the powerband width is more favorable that overall peak horsepower. This seems to be the case in airplane engines. The 4 stroke will spin that bigger prop quicker and gives that instant power and over a mid RPM to peak RPM that the 3D pilot seems to like. And some manufacturers (YS) don't seem to have a power disadvantage at all. YS 160 DZ engine seems to put out just as much as the OS 160, and still has that great 4 stroke feel. Also, it was mentioned that the larger airplanes seem to favor gas 2 strokes. That is true but I read about a manufacturer that is making a 4 stroke gas engine for planes. It was a small one. But it is just the start and we can look forward to 4 stroke domination in that area as well in a few years.
Thanks,
Barry

Barry Cazier

My Feedback: (17)

I hate to keep making extra posts, sorry, but this is interesting stuff. Also don't mean to keep comparing motorcycles to airplanes but they have many similarites at least in 2 stroke vs. 4 stroke. In the 1950s and early 1960s the same rules applied to 2 stroke engines that apply to 4 stroke engines today. The rules makers wanted to see more competetion from the 2 strokes so they allowed them to be twice the displacement. In those days the 2 stroke need more displacement to make equal power. So we've seen it go full circle. At least for the time being 4 stroke engines are receiving all the research and development. They are the engines that will get better. The 2 strokes are remaining the same until something changes I still see the 4 strokes getting better and better. Look at how many more 4 strokes are introduced to the marketplace than 2 strokes. The only new 2 stroke I've seen in a while is the Evo 100 and the 46AX. But YS has introduced a 63, 110, 140, and 160. Saito has a 82, 100 and 180. OS has introduced a low cost 70, a high cost 70 and I'm not too sure about Magnum, but I think they introduced a couple of new 4 strokers. Anyways, the market seems to be driven to 4 strokes.
Thanks,
Barry

STG

My Feedback: (26)

Barry Cazier,

In Cycles the 4 stroke would not have a chance with the similar 450cc 2 stroke.

I think to be fair in comparing the airplane motor you have to look at the weight of the motor not the displacement. Of course when you do that you need to include the muffler. This is where some of the new 4strokes really shine--saito 82,100,180, all YS's.

Fuji is making some larger gas 4 strokes- BF25 & 34. You can see them at Tower Hobbies.

I would not be too sure that in a matter of a few years you will see 4 stroke gas motors take over in the 50cc+ area. I not saying that it could not happen, I am saying that I doubt it.

Right now there is not a 4 stroke motor that I know of that I would put on a plane weighing 14+ pounds for 3D.

Another factor that has not been discussed yet is adding a properly tuned(power pipe for 3D) exhaust system on a 2 stroke. This can increase the response and power of a 2 stroke significantly.

Sprink

Dont know much about Gas engines (yet ), but I suspect that it is only really a time issue. Gas powered large planes have only really taken off in the last five years or so, with mass production of both large kits, artfs and dedicated engines for them. Prior to that gas engines were converted from existing engines (strimmers, lawn mowers etc) and the planes were mostly special builds.

2 stroke is simpler technology, but given another 5 years I'm sure that you will start to see 4stroke gas engines built light for model aircraft, and we will be discussing why no one buys DA50s any more, but gets XYZ 75cc 4stroke instead.

Barry Cazier

My Feedback: (17)

GPSpacewalker, CR500 Honda 2 stroke rated horsepower = 55. CR450F 4 stroke rated horsepower = 53. Both motorcycles are from same manufacturer and are intended for Motocross racing. They would compete in different classes though. The 450 in the 250 class and the 500 in the open class. So in many ways we are already at the break even point in displacement. Also the YS 160FZ claims to have the most horsepower of any engine in it's class, 2 stroke or 4 stroke. I'm assumeing that would mean the OS160FX which seems to have been the class leader. I think we are really starting to see a trend to 4 strokes.
Thanks,
Barry

Cobra1

My Feedback: (42)

This debate is also happening in the marine industry. Mercury, and others, are developing 4 stroke outboards that are quiet and powerful but they have a big weight disadvantage. It is going to be hard to get the weight down on a 50-75cc 4stroke until a replacement for the heavy parts (steel) is used.

STG

My Feedback: (26)

We can also look at the 2stroke domination in outboard motors and snowmobiles. If you look at power to weight it is hard to compete with the 2 stroke. There has been a push for 4 stroke technology here though as they have the capacity to "run cleaner".

Really though, for all practical purposes, it might be best to limit our comparisons to the available motors that we can use on our planes? To me it is not just as simple as 2 or 4 stroke, but what 2 or 4 stroke do you like and why.

I like my 1.08 O.S. 2 stroke enough to put it on a new Funtana F90 even after I have a YS110 on my Yak.

Sprink

FIve years ago, when I goined this hobby, hardly no one at my club had a 4 stroke. 4 strokes were only for the dedicated scale builder only.

Now, five years on, the reverse is becoming true.