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OS 1.20 Go Boom....!!!

Old 06-23-2013, 08:21 AM
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Giant_Scale_Gasser
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Default OS 1.20 Go Boom....!!!

Just another day at the field. But a first for me did occur. OS FS 1.20 in my Ultimate Bipe let go at about 40 feet up just after a nice knife edge climb out. Rolled her wings level powered up and just as I was pulling into the vertical, a loud sharp crack, like a home run ball being hit, and the prop went flying off! I ruddered her over and tried my best to gain as much energy going straight down and then tried to time my pull.... and missed by about a foot. Ripped the gear out of the plane, but no other damage that I can see.

Pulled the OS apart and it was literally in parts! I have never blown an engine in flight. Toasted a couple on the test stand trying to wring every ounce out of those plylon engines, but never in the air.

Boom.... Here's Your Parts!



Old 06-23-2013, 08:30 AM
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Kmot
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Default RE: OS 1.20 Go Boom....!!!

Well, at least you did a good job of it!
Old 06-23-2013, 09:38 AM
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pe reivers
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Default RE: OS 1.20 Go Boom....!!!

probable sequence:
Lost prop, over-revved for a few revolutions, and exploded before anyone knew about it.
Nice show.
Old 06-23-2013, 09:46 AM
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Default RE: OS 1.20 Go Boom....!!!

It is almost a sick perversion that I do take some pleasure in viewing the chaos that is distruction. I do not understand why. We almost all do it. Thanks for sharing. Ya dun blowed that thar engine up good!
Old 06-23-2013, 10:34 AM
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Default RE: OS 1.20 Go Boom....!!!

pe reivers -

Prop did not depart first, that I am 100% certain of. Huge metallic "CLANK", then the prop departed. That engine never over revved. It was under load at about 3/4 throttle and the exhaust note never changed. She was starting to chug uphill and "BANG", prop departed.

Mr67Stang -

I agree 100%! I couldn't wait to get the cover off!


Old 06-23-2013, 12:49 PM
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pe reivers
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Default RE: OS 1.20 Go Boom....!!!

The loose bearing does not look like it suffered. The conrod split because of too high loads.
Just my idea from the pictures. A closer investigation might be needed though. However, it does not look like a bearing seisure.
Old 06-23-2013, 01:08 PM
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Default RE: OS 1.20 Go Boom....!!!

IMO the piston lost parts of it's skirt...which locked it up....connecting rod didn't like that and couldn't decide which way it wanted to go...developed a split personality...

Seen another O.S. 1.20 with the bottom of the piston skirt missing...tore the innards up good, but not as extensively (throughly ) as yours![X(]

It makes me wonder sometimes, when I look at how much material they (O.S. ) have removed to lighten the piston....there isn't a whole lot left down there and it must flex somewhat because of piston rocking / side loads...
Old 06-23-2013, 01:17 PM
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Default RE: OS 1.20 Go Boom....!!!

Also a possibility.
Old 06-23-2013, 01:25 PM
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Default RE: OS 1.20 Go Boom....!!!

Wow, totally impressive too. Sort of a which came first the chicken or the egg in that situation. Either the piston skirt came off or the rod let go or both maybe at the same time. I would probably bet on the piston skirt coming off first though.

Is it repairable if you replaced the rod and piston?

Thanks for sharing the pics of the failure. It is something worth thinking about.

What size prop were you using and what fuel were you using too? Just curious.

Old 06-23-2013, 01:57 PM
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Default RE: OS 1.20 Go Boom....!!!

This is how I got a "Free" O.S. 1.20 Surpass...

Friend handed it to me one day at the field...told me to have a look inside and see what was wrong...then tell him how much $$ to fix it...and when I told him of the cost of the parts (he wanted only O.S. parts ) he told me to just keep it.

The major thrust side of the piston skirt had dropped off, and the bottom of the rod, and inside the case had been nicked / gouged by the bits and pieces...

I polished out most of the roughness in the case, and replaced the piston, ring, rod and bearings with Magnum parts and it runs just fine again...or about as well as an O.S. 1.20 usually does...no "Powerhouse" but decent...steady, etc.
Old 06-23-2013, 02:32 PM
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Default RE: OS 1.20 Go Boom....!!!


ORIGINAL: earlwb

Wow, totally impressive too. Sort of a which came first the chicken or the egg in that situation. Either the piston skirt came off or the rod let go or both maybe at the same time. I would probably bet on the piston skirt coming off first though.

Is it repairable if you replaced the rod and piston?

Thanks for sharing the pics of the failure. It is something worth thinking about.

What size prop were you using and what fuel were you using too? Just curious.

Yes it's repairable. Nothing else is damaged. It needs piston, liner, wrist pin, clips & con rod. Not sure if I'll rebuild it or not. I ordered a new 1.20AX to stick in there in the meantime once I repair the airplane. I have several other "donor" 1.20 OS FSEngines on the shelf so I'll have to see what is what eventually.

I was running a 16x6 APC on 15% Morgan Fuel. And I do not run my stuff very hard. I am all about throttle control. I am not that guy who is wide open from take off to landing. I don't high G load my airplanes either. I am pretty easy on my stuff overall.

Old 06-23-2013, 02:43 PM
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Default RE: OS 1.20 Go Boom....!!!


ORIGINAL: proptop

IMO the piston lost parts of it's skirt...which locked it up....connecting rod didn't like that and couldn't decide which way it wanted to go...developed a split personality...

Seen another O.S. 1.20 with the bottom of the piston skirt missing...tore the innards up good, but not as extensively (throughly ) as yours![X(]

It makes me wonder sometimes, when I look at how much material they (O.S. ) have removed to lighten the piston....there isn't a whole lot left down there and it must flex somewhat because of piston rocking / side loads...
I agree with your theory, however, none of the piston skirt parts are damaged. They are all clean breaks, no gouging or smashing that would be consistent with trying to lock anything else up.
I think, and who really knows, that the cleanly broken big end piece (2nd from left, top of pic next to the big bushing) actually fractured first, thr crank with it's interia and prop rotating came around hit the opposite side of the rod (You can see a good sized dimple in the left side of the rod beam just down from the big end) snapping the top and spitting the prop off.

From what I heard and saw when it happened, I am willing to bet that was the sequence. The engine stopped "NOW". When the crack sound was heard, the engine was already stopped dead and the prop was on it's way forward and off the right of the airplane. If I had to bet, that engine didn't make 1 or 2 revolutions once the rod fractured. And I'd say it was nothing more than fatigue from what I can see under a magnfying glass looking at the material. It's not a sheared or torn. It's like someone simply lifted off that piece. It fits back on that big end perfectly, placed together you cannot tell it's broken.

Just my post rod kicking guess...


Old 06-23-2013, 05:52 PM
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Default RE: OS 1.20 Go Boom....!!!

I think I would agree that the rod went first. The rod looks like it was cast and then machined. I remember cast rods letting go before in the past. The rods probably has some sort of a casting flaw in the metal from when they were made. I have a couple of engines I need to make new rods for myself where the rod had broken.

You don't think that the engine exceeded its max RPM rating in the air with the 16x6 prop do you?


Old 06-23-2013, 06:55 PM
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Default RE: OS 1.20 Go Boom....!!!

How many gallons has that engine gone through?

Speaking of over-reving:

I wonder how the NEW YS115FS pro warbird Pylon engine will fair...

It has a usable rpm of 2,000-18,000 RPM's WOW....

A typical 4-stroke will run up to 9,000-10,000 RPMs.

The last theory of what happened seemed to match what could have
Old 06-23-2013, 07:47 PM
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Default RE: OS 1.20 Go Boom....!!!

Green fuel?
Old 06-23-2013, 10:02 PM
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Default RE: OS 1.20 Go Boom....!!!


ORIGINAL: earlwb

I think I would agree that the rod went first. The rod looks like it was cast and then machined. I remember cast rods letting go before in the past. The rods probably has some sort of a casting flaw in the metal from when they were made. I have a couple of engines I need to make new rods for myself where the rod had broken.

You don't think that the engine exceeded its max RPM rating in the air with the 16x6 prop do you?
With the 16x6 (which is a recommended prop size by OS) it was turning 9000-ish on the ground. The engine RPM range is 2000 - 11000 and it makes peak HP at 11000. Under load in the air it never exceeded 10000 I am quite sure and like I said, I do not abuse my stuff and run it wide open all the time. I come downhill idling 90% of the time so it's not over revving on the downlines.

When the engine popped, I had just left a knife edge climb out configuration where it climbed out at about 2/3 throttle and I started to power up to 3/4 - full. If I had to guess, it was turning maybe 8000 when it let go. It certainly was not at full song.

Old 06-23-2013, 10:04 PM
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Default RE: OS 1.20 Go Boom....!!!


ORIGINAL: Javier-RCU

Green fuel?
Yes, Cool Power 15% synthetic. 17% oil content and while OS does reccomend 18% oil, I have used Cool Power for a long, long, long time with no issues.

Old 06-24-2013, 12:28 AM
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Default RE: OS 1.20 Go Boom....!!!

Hi mate hey don't waste the parts eh?? do you know someone who will set them in a clear resin block like that pix and you can stand it up on the bar top at home(mines in the shed) evem kmot would be jealousalthough i wish he'd done that to one of his jett engines..just said that cause i know popeys reading this thread.
Old 06-24-2013, 02:35 AM
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Default RE: OS 1.20 Go Boom....!!!

I read somewhere the new O.S. AX  1.20's are   Made in China now, might wanna check that out
Old 06-24-2013, 03:35 AM
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Default RE: OS 1.20 Go Boom....!!!

Yep, but what can you do about it? If I want one and that's where they are made... I am not sure what else there is to do.
Old 06-24-2013, 03:57 AM
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Default RE: OS 1.20 Go Boom....!!!

Buy one..the chinese or whoever make them better maybe??
Old 06-24-2013, 04:57 AM
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Default RE: OS 1.20 Go Boom....!!!

Is that burned on oil on the rod? It looks like the con rod got hot.
Old 06-24-2013, 05:41 AM
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Default RE: OS 1.20 Go Boom....!!!

Hey Giant Scale,   Did you already order a 120?   if not I have a couple and would be glad to sell you one real reasonable.
Old 06-24-2013, 06:49 AM
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Default RE: OS 1.20 Go Boom....!!!


ORIGINAL: controlliner

Is that burned on oil on the rod? It looks like the con rod got hot.
Nope, it's the golden brown of rust. The crank counterweights were rusty. Clearly not enough after run was used at one point in it's life. It never overheated while I was running it. I always run em rich to keep them cool. I rather have a little burble every now and again. I am not the lean it our and let it eat guy.

modracer07 - PM me and let me know what you have, I am always buying & building. I have a brand new 1.60FX and a DLE20 on the shelf for the next projects and the new 1.20AX on the way, but I can always use another couple of engines for the right price.

Old 06-24-2013, 08:24 AM
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Default RE: OS 1.20 Go Boom....!!!


ORIGINAL: Giant_Scale_Gasser


ORIGINAL: controlliner

Is that burned on oil on the rod? It looks like the con rod got hot.
Nope, it's the golden brown of rust. The crank counterweights were rusty. Clearly not enough after run was used at one point in it's life. It never overheated while I was running it. I always run em rich to keep them cool. I rather have a little burble every now and again. I am not the lean it our and let it eat guy.

modracer07 - PM me and let me know what you have, I am always buying & building. I have a brand new 1.60FX and a DLE20 on the shelf for the next projects and the new 1.20AX on the way, but I can always use another couple of engines for the right price.

Rust is ruddy red not golden brown. Looks like castor oil stain to me. But not enough to say it got too hot.

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