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OS 120AX, 21 ounces with or W/O muffler???

Old 02-23-2006, 03:41 AM
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bodywerks
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Default OS 120AX, 21 ounces with or W/O muffler???

Just wondering what the actual weight was of this engine. It says 21 ounces on their site, but doesn't say whether that's with or without the muffler...If it's without, then may need to choose a different option.
Old 02-23-2006, 03:45 AM
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flyinGraham
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

Don't know the actual weight of the engine but its very powerful!
Old 02-23-2006, 06:45 AM
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Don M.
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

Displacement: 1.218 cu in (19.96cc)
Bore: 1.197" (30.4mm)
Stroke: 1.083" (27.5mm)
Practical RPM: 1,800 - 9,500
Power Output: 3.1ps/9000 RPM
Weight of engine:22.82oz (647g) without muffler,extension or adaptor
Weight of muffler:7.074oz (219.2g) with 90° adapter installed
Weight of muffler:7.907oz (245g) with extension installed




This is from Tower Hobbies web site, it looks worse than you thought. [][][]
Old 02-23-2006, 06:54 AM
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gunfighterII
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

The weights are as follows,

Engine w/o muffler 20.88
Use the 90 degree adaptor for pitts, add 7.074oz
Use the long extension, add 7.907oz.
You can't use both, so with the 90 degree & muffler is 27.95oz.
With the muffler and long adaptor it is 28.78oz.

Very nice motor I took these numbers out of my manual.
Old 02-23-2006, 07:18 AM
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gunfighterII
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

Hi Don M,
I'm going to take issue with Tower's numbers as they are different in the listing for the engine without muffler as they are with the engine with muffler. they are showing 22.82 for the muffler version and 20.88 for the non muffler version. I just did some checking and your right the 20.88 is without muffler, so all the other weights are muffler and adaptor together.
Old 02-23-2006, 07:58 AM
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Don M.
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Default RE: OS 120AX, 21 ounces with or W/O muffler???


ORIGINAL: gunfighterII

Hi Don M,
I'm going to take issue with Tower's numbers as they are different in the listing for the engine without muffler as they are with the engine with muffler. they are showing 22.82 for the muffler version and 20.88 for the non muffler version. I just did some checking and your right the 20.88 is without muffler, so all the other weights are muffler and adaptor together.

I didn't write them just copied and pasted them. [sm=confused.gif]
Old 02-23-2006, 09:26 AM
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bodywerks
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

That's all I needed to know - looks like I will be going with the Saito 125 to save nearly a half-pound and to swing a bigger prop!
I was only concerned because I may be using it to rediculously overpower an Aeroworks Edge 540T, and too much nose weight, not to mention extra weight is no good...
Old 02-23-2006, 11:03 AM
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STG
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

ORIGINAL: bodywerks

That's all I needed to know - looks like I will be going with the Saito 125 to save nearly a half-pound and to swing a bigger prop!
I was only concerned because I may be using it to rediculously overpower an Aeroworks Edge 540T, and too much nose weight, not to mention extra weight is no good...
1) If you use a 4.5oz bisson pitts muffler you will be closer to 26oz and the SA125 is 24.5 with muffler so that is 1.5 oz not 8oz.
2) Swinging a larger prop? I think not. In fact, I bet the 120AX does better on a 17x6 than the SA125 on 5% to 15% nitro

Am I saying to go with the AX over the SA125? No. My choice in the edge would be a .91 two stoke with light muffler or the SA100. [8D]

Old 02-23-2006, 11:41 AM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???


ORIGINAL: gunfighterII

The weights are as follows,

Engine w/o muffler 20.88
Use the 90 degree adaptor for pitts, add 7.074oz
Use the long extension, add 7.907oz.
You can't use both, so with the 90 degree & muffler is 27.95oz.
With the muffler and long adaptor it is 28.78oz.

Very nice motor I took these numbers out of my manual.
Not sure whether these numbers are correct either. Take a look at the review for the 120AX at rcpowermag.com. About half way through the review there is a table of advertised versus actual weights listed. Actual is 22.6 for the engine alone.

I've always been puzzled as to why 2 stroke RC engines tend to weight more than 4 stroke RC engines. In motorcycles the reverse is usually true.

Malcolm
Old 02-23-2006, 04:45 PM
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STG
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

ORIGINAL: malcolmm
I've always been puzzled as to why 2 stroke RC engines tend to weight more than 4 stroke RC engines. In motorcycles the reverse is usually true.
Malcolm
1)A bigger silencer is needed.
2) 4 stokes have been getting all the R & D $ -- not a lot of newly developed 2 stokes out there.

Look to Jet for light 2 stokes.

This new 120AX with a light free flowing muffler or a semi-tuned exhaust system will hold its own in power to weight against ANY 4 stroke -- Especially if you run similar low cost fuels.




Old 02-23-2006, 05:11 PM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

Yeah, I forgot that Saito had redesigned their mufflers. The last time I had one they still only came with straight pipes - that was well over 15 years ago!
As for ability to swing similar size props, with the standard muffler, I find that hard to believe. The 125 spins a 16X6 without breaking a sweat, at over the 9000 mark, according to reports. While the 120 may be able to swing a 16X6 at nearly the same RPM, it will likely be way below it's ideal torque range, no?
I guess flight reports would help there...
As for the Bisson, no thanks, they are power robbers - even worse than standard mufflers.
Old 02-23-2006, 09:43 PM
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STG
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Default RE: OS 120AX, 21 ounces with or W/O muffler???


ORIGINAL: bodywerks

Yeah, I forgot that Saito had redesigned their mufflers. The last time I had one they still only came with straight pipes - that was well over 15 years ago!
As for ability to swing similar size props, with the standard muffler, I find that hard to believe. The 125 spins a 16X6 without breaking a sweat, at over the 9000 mark, according to reports. While the 120 may be able to swing a 16X6 at nearly the same RPM, it will likely be way below it's ideal torque range, no?
I guess flight reports would help there...
As for the Bisson, no thanks, they are power robbers - even worse than standard mufflers.
I have had very good luck on the Bisson for the .46, .91 and 160. Better than standard mufflers with baffel on the .46 and .91. The criped ends need to be cut for the 160FX. What motors have you found them to be worse than stock mufflers?

According to recent reports the 120AX is swinging a 17x6apc 9,200 on 5%. That is easy for me believe as my 108 does the same and the 120 should do a little better.

As for the torque thing........

4 strokes typically do have a flatter torque curve than 2 stokes. That means that, although peak torque is similar between 2 and 4 stokes the 4 stoke will typically produce more at lower RPM. How does that translate to model airplane motors? Well if both my 2 stokes (OS108) and 4 strokes (YS110) can transition from (almost no load or thrust) about 1800RPM to full load & thrust (~9000 rpm) in a fraction of a second then where is the torque difference? How can this torque difference be a factor?

It is not a factor because the props we use impose very little load on the motors at low rpm. As the rpm increases the load on the motor is exponential.

For instance with a 16 x6apc prop:

4000rpm----.2hp
5000-------- .35
6000-------- .6
7000-------- .9hp
7500-------- 1 hp
8000--------1.3
9000--------1.9hp
9500--------2.3hp!


As you can see the prop does not load the motor much from down low--2000 to 6000 rpm-- That is why I say these motors do not need much torque.

The down low power that people I think are attributing to 4 strokes has more to do with how fast they experience them to spool up (go from idle to full throttle). This has more to do with how well the carb meters fuel at lower and mid settings than the actual torque curve of the motor. A 4 stroke is less sensitive to the correct needle settings when it comes to spool & transition.

That is why the YS motors have an edge over the other 4 strokes on spool up. Not because they have more torque, but because the pressurized and regulated fuel system lets them meter fuel needs more accurate at lower and mid power settings.

That is also why 2 strokes get a bum rap--because it is harder to get them to meter fuel accurately from idle all the way thru to full(and some 2 stokes may not have a good enough carb to get it right). My experience has been if they are just a little bit lean or rich at idle or on the high end the transition and mid range running suffers a lot. That is why a pump has often been the answer for me as it allows for a leaner setting at idle and at full as the fuel supply does not change when you put the plane in the air.

Now I am not speaking for all 2 strokes only OS.25fx, OS46FX, OS.91FX, OS108, OS1.60fx.
Old 02-23-2006, 09:56 PM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

I just got an OS 120 AX in the mail today. It looks awesome! i'll start with an APC 17-6
Old 02-23-2006, 10:14 PM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

ORIGINAL: AeroDave

I just got an OS 120 AX in the mail today. It looks awesome! i'll start with an APC 17-6
I think a good wood 17x6 will be the best prop for this motor. I like the Skorepa 17x6 wood.


Had a chance to try out the 17x6 wood Skorepa this weekend. It was on a OS108 with Jtec pitts on some ~15% nitro concoction.

16x6apc 9650 @ 15 pounds of thrust
16x6Sk 9600 @ 14.7 pounds of thrust
17 x6aapc 9250 @15.5 pounds of thrust
17x6 Skorepa 9100 @16.1 pounds of thrust
Of course the Skorepa wood is about 1/2 the weight of the APC and spools instantly.

I have it on a 10 pound F90 and after 3 flights, without a doubt, the 17 x6 Skorepa is the best prop for this combo. I am looking forward to trying the 18x6 on a bigger motor.
With a free flowing or slightly tuned exhaust system I would not be surprised to see the AX turn a good 17x6 into the mid 9's


Old 02-24-2006, 12:45 AM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

I don't own them, but have flown both motors on similar planes. The OS 120 is considerably more powerful than the Saito and is much smoother and quiter. The Saito is a mini paint shaker compared to the OS. Both motors do run well, and are wonders considering the weights.
Old 02-24-2006, 03:19 AM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

Well, when I go to pick up my Aeroworks 260, I will know if my wife ordered the Edge 540T. I told her that if she bought it to just have them hold it for Nick when he picks up his 260...
STG, the poorer performance I was talking about was with many of the 50cc class gassers.
Anyway, if I do get the plane, I'll start eying both engines more closely.
Old 02-24-2006, 04:40 AM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

Just ran my 120 AX . APC 14-14N 8700 RPM on YS 20-20 fuel and mufler with no extention. APC 15-10@ 9200 RPM ,and very smooth.
Old 02-24-2006, 09:37 AM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

ORIGINAL: bodywerks
STG, the poorer performance I was talking about was with many of the 50cc class gassers.
That makes sense as the stock mufflers that come with the 50cc class gas motors are more like free flowing exhaust deverters (no real baffling) than mufflers--not that there is anything wrong with that. I like the Slimline or turbo-jett better than the bisson(on glow motors).
-----------------------

Just ran my 120 AX . APC 14-14N 8700 RPM on YS 20-20 fuel and mufler with no extention. APC 15-10@ 9200 RPM ,and very smooth.
What glow plug are you using? If you are not at high elevation you might consider a cooler glow plug with 20% nitro in this motor. It could help you lean out your needles for better performance and economy--might be worth a try. I know this motor is happy on low nitro at lower elevations.
Old 02-24-2006, 11:41 AM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

Those weight numbers are pretty much what they should be for this type and size engine.....

The Jett BSE-120 is just under 28 oz with the muffler as well (including the spinner nut, glow plug, and muffler hardware- ready to run)......... same size and type of engine --- so it tends to reason they would be about the same weight.

The reason the Saito tends to weigh less, is because they pay a great deal of attention to the engine design - taking out a gram or two of aluminum casting here or there.... in the right place ..... can add up fairly quickly. The crankcase on a 4c (in that case) basically just holds the cylinder, crankshaft and bearings - there are no ports or anything significant internally that may need more metal, or take up space - all of the porting is in the cylinder head. Plus the crankshaft itself can be smaller/lighter - has no hole in the middle for fuel intake. Of siginificant weight savings - the exhaust system is not massive - just a small muffler and exhaust tube. That makes a big difference.

Bob
Old 02-24-2006, 12:38 PM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

The engine weight is a funny topic for the 120 AX. I had to verify it myself today. So I weighed the engine just by itself, and it came out 22 oz. Then I removed the prop nuts and washer, only after doing so did the weight go below 21 oz.

Also, the muffler weight depends on if you include the muffler bolts or not. The really long muffler bolts for the extension, they themselves weigh close to 1 oz.

So, with everything including plug, washer, nuts, and muffler bolts, total weights are:

Extensnion configuration: 31 oz
Pitts configuration: 30 oz
Simple muffler configuration: 28 oz.

I would like to comment that the washer is not very light. You can save another 1/2 oz by going to a lighter washer. If you use lighter muffler bolts, you can shave another 1/2 oz too.
Old 02-25-2006, 12:23 AM
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Default RE: OS 120AX, 21 ounces with or W/O muffler???

These are the same weights I came up with. By the way the strait extension is worth 300 RPM with the 15-10. The pitts extension is the same as the muffler only unless you use it with the strait extension too.Glow plug is OS #8 and I ran it on 20%, because I left my 10% at home. Still it ran very good with no detonation, and no over heating,but I will run it on 10%.

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