les40

My Feedback: (1)

THe OS 91 FX turns a 14X8 prop at usable 9500 rpm and the engine only weighs something like 19.6 oz. My Saito 100 4 strk turns the same prop at a usable rpm of 9000 (using 30% nitro) and weighs 20.9 oz. I guess 2 strks still have the edge when it comes to performance.

If I'm wrong let me know. I'm a 4 strk fan but have been wondering which technology has the best usable power to weight ratio. To me it still looks like the 2 strks take the lead.

w8ye

My Feedback: (16)

You are comparing an apple and a orange. They are both from the fruit group...

There are many different factors to keep in mind besides all out power such as torque at the different usable rpms and throttle ability of each engine.

donkey doctor

Hello; Depends on the criteria; if you only measure one prop at top revs, you've only found out one thing. That might be useful if that's the only way you use those engines.

NM2K

My Feedback: (14)

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When it comes to all out power, the two-stroke is still king.

However, in flying model airplanes in a sport manner and several other manners, peak horsepower per displacement unit isn't the only criteria by which to judge an engine. As others have stated most eloquently.

broke_n_bummin

try the same test with a 17x6 prop and let us know what you find out.

Flyer95

My Feedback: (1)

Are you sure the 91fx is lighter than saito100? According to Tower the 91FX has a total weight of 24,3oz and according to Horizon the saito100 weights 20,9 muffler included.
But the quiet mufflers on the twostrokes are heavy and they also rob some power. If you install a quiet tuned pipe on your 91fx I am pretty sure it will become stronger than most 120-sized fourstrokes.

les40

My Feedback: (1)

Thanks for all of your replies. In general those arguing against me are arguing with subjective points such as throttle ability. Both engines throttle up well enough if tuned properly. The power I'm talking about is what you need when you're flying a horizontal line and need to pull vertical for awhile to do a humpty bump. That power is directly measured (objectively) by measuring how many rpm you can get out of a particular prop with a tachometer. I am definitely NOT comparing apples and oranges. I'm taking measurements of prop rpm which is directly related to thrust. Am I wrong?

I'm so tired of people clouding this issue with irrelavent, subjective data.



The weight I got for the OS engine came from the OS website. It doesn't specify whether it is engine alone or with muffler. Maybe it is engine alone. I will do a little research and repost.

les40

My Feedback: (1)

I stand corrected. The weight I specified for the OS .91 is WITHOUT muffler. I cannot find the spec. for the muffler weight. but I would imagine that it would put the engine a few ounces heavier than the Saito 100. Not sure though. At any rate I would estimate that the power to weight ratio of each engine is about the same.

Another thing I would like to point out. My Saito 100 is rated at 1.8 hp. I can get about 1.7 hp out of it. My 2 stroke .46 is rated at 1.7 hp but I can only get about 1 hp out of it running a prop that will give enough thrust such as an 11X6. I could put a 10X5 on it and get more rpm and more calculated hp output but the smaller diameter would produce less thrust and wouldn't be practical. So the lesson learned is that you can get about 94% of the rated hp out of a 4 stroke but only about 60% of a 2 stroke's rated hp.

blueline

My Feedback: (6)

YES,YES,YYEEEESS, way to go Les! Finally someone has put this arguement to rest for a ,week. I agree with your earlier statement
regarding people clouding the issue with "in my opinion as well" irelovent issues. Good job with putting it in plain text, be well.

B.L.E.

Most people really chose 4-strokes simply because they like 4-strokes, though they will cite a whole bunch of "advantages", many of them illusionary or mythical, to defend their choice of engines. It is amazing how good the torque curve, throttle linearity, and low rpm torque of a 2-stoke can be when we stop trying to milk every last ounce of horsepower out of them. Some of them have even turned the tables on 4-strokes when it comes to noise....one of the reasons that the pattern rules were changed to undo the earlier .61 two stroke/1.20 four stroke displacement limits.
If cold reason and logic dictated what type of power plant we used in our planes, a lot more of us would be flying electric....no goo to clean off our planes, no fiddleing with needle valves, no servo killing vibration, unmatched throttle linearity, no deadsticks unless on purpose.

les40

My Feedback: (1)

Electrics? Have you priced a battery pack that could power a 25% aerobatic airplane? There was a guy at the last IMAC with an electric 25% Extra. I was awesome and had as much vertical as the gas powered ones but his battery pack cost him $1,300...just the pack. You can buy a lot of gasoline for that.

blw

My Feedback: (3)

I fly both for sport and pattern. This 2 stroke is better thing makes absolutely no sense. I know that if I want smooth power to pull a vertical the 4 stroke delivers without waiting like a 2 stroke to reach speeds and the power band. Also, a lot of things are better if you have torque available immediately and without the high RPMs all the time. You can fly smoother with a 4 stroke unless you have a really overpowered engine that will pull a plane around *smoothly* at 7000-8000 RPM.

One thing nobody has mentioned is that you can have a lighter plane if you have a 4 stroke since you don't need to carry around a lot of fuel. How many 2 stroke planes can fly around for 12 minutes on a 5 oz tank? Not many.

If you are hyped up about wiping a plane down at the end of a day, 2 and 4 strokes alike, just use some polymer based wax on the covering and it comes off in one swipe. And, the plane looks better too.

Who cares about noise? I like loud planes! Too many people whine about noise.

edited for spelling

joesabido

Holy cow! What kind of pack was it? Plutonium? [X(]

I assume it had like TEN $130 packs in paralell/series? [&:]

sigrun

Absolutely. Right on the money. It's what the 4 stroke versus 2 stroke 'argument', as perennial as it is pointless, is really all about.

NM2K

My Feedback: (14)

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I'm not argueing against you, nor for you, for that matter.

You can't make a fair comparison without taking weight into consideration. Also, one thing we may have missed is the extra fuel load that is required by the two-stroke engine versus that of the four-stroke engine.

A purpose designed two-stroke can share many of the good qualities of a four-stroke engine. Reduced fuel consumption, better ability to swing a large prop, good tractability with great fuel draw without using a pump, etc. To say that it is strictly a matter of which engine turns a given prop at whatever rpm is missing the boat, as far as I'm concerned.

Personally, I enjoy both types of engines. For Humpty-Bump maneuver flying, I think that you can find good engines in either two or four-stroke types.

skiman762

by towerhobby the os 91fx is 24.3 with muffler
by Horizon saito 100 20.9 with muffler.


Another thing to keep in mind HP is worthless without max torque being in the same rpm range for all but flat out speed.
I'm pretty sure with the above 2 engines turning 14x8 props on two identical planes of the same weight vertical at full throttle that the 4 stroke will be pulling after the 2 stroke stalls maybe not but I think it will
but I'm also sure that the 2 stroke will out run the 4 stroke in a flat out speed race with the same two planes the 4 stroke will get the lead from off idle but will give it back once the planes are at max rpm
there are just too many variables to make a comparision between the two

B.L.E.

This is what I have been saying all along. The inverse is also true, a purpose built four stroke can share many of the qualities of two strokes. Designed with big carburetors and ports with radical cam timing for ultra high rpm use and four-stroke engines can also be thirsty, peaky, and not able to tolerate large props. Oh yea, I forgot to mention noisy. Listen to the four-stroke engines used in Indy cars and you'll see what I mean.

MinnFlyer

My Feedback: (4)

Why not compare full size airplanes that use 2-strokes Vs 4-Strokes?

If 2-Strokes were so good, wouldn't more full-scale planes use them?

Dirt Bikes use 2-strokes, why don't Harleys?

BTW, sometime when you have notrhing better to do, compare fuel consumption of an OS 91 Surpass to any 2-stroke .60

alan0899

Me thinks that was a typo, Harleys do use 4 strokes, I have just been for ride on mine & it sure sounded like a 4 stroke to me.

B.L.E.

Mostly because this is the glow engine forum and the moderators delete posts if they get that far off topic, if you haven't noticed.
Glow engines don't have oil sumps and glow plugs don't carbon foul like spark plugs so a lot of the arguments for and against four strokes are moot when you deal with glow engines.

Hobbsy

My Feedback: (102)

The only factor that even matters is "which one do you prefer".

NM2K

My Feedback: (14)

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To me, this is the essence of it all. I like all of them. <G>

However, every day there are new folks coming into our hobby that are just getting their feet wet. So, we end up repeating the same old stuff over and over and over. But that is okay. That is how new folks learn. It also keeps some of the veterans on their toes too.

I like all model engines. I think that deep down, most modelers do too. Or at least they will if they fly long enough. I even like electric motors, these days. I never thought that that would happen.

Hobbsy

My Feedback: (102)

My very first RC engine is an Enya .46 MKII which I still have, I bought it at half price in Manassas, Va. in 1992 when it was discontinued. I haven't been tempted by them "lectrics" yet, an engine has to suck, squeeze, bang and blow for me to use it.

Sport_Pilot

A two stroke built for torque will out do an equivalent displacement four stroke in torque and power. I think the 91 FX would turn that prop faster but I am not sure, although the Saito has the advantage of extra displacement. Pattern aircraft are now unlimited in displacement and engine type and two strokes have or have started to take over. The only four strokes that can keep up are the supercharged YS. Because of a 93 Db noise limit the prop speeds are kept low and many are turning in the 8,000 RPM range. IMO I would consider buying the FX without muffler and add a light weight pipe or mousse can muffler to it, or a light weight pitts muffler if scale. The OS mufflers are way too heavy.

sigrun

Amen. [sm=idea.gif]