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OS 120 AX ON PIPE

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Old 05-28-2010, 06:36 AM
  #1
nitrometan
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Default OS 120 AX ON PIPE

Dear gentlemen,I want to share you my results in trying to get the most useful thrust from OS 120 AX.
After many many many experiments and lost money for recomanded propellers and exhaust systems ,I finally found out the winning formula.(in my case)
So,the results are the following:
Engine:OS 120 AX
Exhaust:Tuned pipe Krumscheid for 15-20cc engines.Nr:1010-5
Pipe length:520mm from engine exhaust flange to reflecting cone.
Fuel: 10% nitro,15%Aerosynth 3
Glow plug:Rossi 4
Temperature outside 20 Celsius,80% humidity
Propeller:18X6 Graupner G-Sonic.
RPM:9500 rpm(short peak to 9800)
Thrust:7.5kg measured very"scientific" several times with a fish scale.(9500 RPM)
Disadvantages:
Quite noisy
Very fuel-hungry(500 cc in less than 10 min,50%WOT,50% with carb barrel half open,in which case I had 7000 rpm,alternating 30s WOT,30s at 7000 rpm.
Heat build up,without cowl WOT in 30 sec head temperature over 120 Celsius degrees(did not use any deflectors or so for cooling)
If anybody has another PRACTICAL DATA(not theory,i am sick and tired of various stories) PLEASE POST HERE.
I will appreciate any experiment done.
My opinion is that the cooling fins simply can not cool down the engine at this power level.

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Old 05-28-2010, 09:51 AM
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Default RE: OS 120 AX ON PIPE

that's insane power
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Old 05-28-2010, 11:02 AM
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Default RE: OS 120 AX ON PIPE

I know,I was surprised myself,and I wish I had the next big pipe from Krumscheid,which is for 25-35cc.It has more volume(50mm diameter) and bigger exhaust diameter(14mm instead of 12),but I am sure that this combination will kill the engine.It can not disipate so much heat.Actually the pipe is 10 mm longer(that means on the safe side),because the absolute maximum I obtained was 10000 rpm 3 times,but in 10 seconds the engine is already hot.I did not measured any thrust at this rpm,but I suppose it can be around 8 kg.
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Old 05-28-2010, 01:33 PM
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Default RE: OS 120 AX ON PIPE

Subscribed.....
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Old 05-28-2010, 05:27 PM
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Default RE: OS 120 AX ON PIPE


Yes, you maybe making more power than the cooling fins can shed while on the ground. In flight the engine will have a better supply of cooling air but may still overheat if you run it at full throttle all the time. Maybe a colder plug or lower nitro will help to contain the thermal runaway you have here.
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Old 05-29-2010, 01:27 AM
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Default RE: OS 120 AX ON PIPE

You will just need to make sure the needle is rich enough, right at the edge of fourcycle with a full tank. I ran a piped 108 at 12,000 rpm for a long time without problems. Your 120 should handle 10,000.
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Old 05-29-2010, 09:08 AM
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Default RE: OS 120 AX ON PIPE

OS 108 is a legendary engine and a very solid one with more than enough cooling fins.The problem is not the rpm,the problem is the heat generated,because the power is almost 4hp.Even without pipe,the 120 AX has cooling problems at 9500 rpm...As I wrote before,it sips fuel so fast...
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Old 05-29-2010, 05:42 PM
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Default RE: OS 120 AX ON PIPE

so how does that copare to the standard prop and pipe. muffler?
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Old 05-29-2010, 08:58 PM
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Default RE: OS 120 AX ON PIPE

You could try different fuel blends to get the high cylinder head temperatures under control, a little more lube to start, and maybe trying a predominately castor based blend. Higher nitro content can also reduce cylinder and EG temps too, but the trade off is higher fuel consumption.

Mike.
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Old 05-30-2010, 01:14 AM
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Default RE: OS 120 AX ON PIPE

The heat can be turned down by opening the needle. A pump and inflight mixture control may be required to prevent engine damage. My 108 survived many lean runs, some careful mixture control should keep your 120 in good shape.
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Old 05-30-2010, 05:49 AM
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Default RE: OS 120 AX ON PIPE

I tried to make a rich mixture as much as possible,because if i tune everything on top performance i can obtain a little over 10000 rpm,so i rotate the HS needle 45 degrees counter-clockweise to keep a rich mixture,and the pipe is tuned 1 cm longer as it should be and the engine still runs extremely hot.Aerosinth 3 is a VERY good oil,and a lot of oil can be observed at exhaust outlet of the pipe.It has also a clean slightly yellowish colour and does not smell burnt like in some heli engines running at 17-18000 rpm.
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Old 06-02-2010, 01:11 PM
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Default RE: OS 120 AX ON PIPE

Hi everybody!

Today I made another test with another propeller,Graupner G-Sonic 18X8.Pipe length 540mm same fuel.8500 rpm steady 8,1-8,2kg pull.20 ounces of fuel in 7 minutes.Engine about 120-130 Celsius.I think that this is the absolute maximum power it can be obtained from the engine.I hope that this informations can be useful to another members .
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Old 06-12-2010, 01:43 PM
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Default RE: OS 120 AX ON PIPE

Greetings, nice performance you pumped out of the 1.20AX.

Was just wondering what a normal temperature would be like for the 1.20AX when not trying to push every rev out of the little bugger.
Currently running it with a mejzlik 16*8 and the stock powerbox on 5% nitro fuel.
Would switching to a 18*6 heat it up more (considering this because the field officials are complaining about noise)?
Kind of conserned here with the temperature, I can't tune it on the ground with the cowl on because I would hear the oil sizzling after I cut the engine (might be an airflow problem though).

Regards,
-Bed.


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Old 07-16-2011, 09:31 AM
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Default RE: OS 120 AX ON PIPE

This may be too late, being this talk started a year ago.....
I have not ran my OS1.20ax piped in that long....
I had it on a QQ 69" yak54 with mac header and mac muffled pipe.

I must have had heat problems in the past, and didn't realize it, as my 1st 120AX had it's head shim melt into the head
and couldn't be removed....

My new engine, has always been run rich...
It also made very good power....11,00RPM's on a 17x6 APC.... not sure on exact numbers...as I discused this in some of the other posts...

This was my issue with the engine.
Made awsome power, but didn't hover. It would loose power and fall over....
1. backed needle off from full RPM (2. Placed lengths back into header (thinking I cut too much off) but didn't effect this issue at all....

after adding the length, it began falling off the pipe when level, and go back on when verticle. I suppose it would lean abit, and cause it to go back on...
I believe at this point, the header was TOO long....so it didn't have the effect I was looking for....

I then chased a blubbery rich, to lean engine that had great power for F3A but nothing for 3d....
I wish I had video, as it was amazingly powerfull but nothing on the bottom...
Yes this sounds like the header was too short but it wasn't....

I then took just the fuse, ran the os120ax, and pointed the nose up...
I then ran it like I was trying to hover the plane.....And it happened...
Bamm....The prop flew off (landed 40yards away) and I said enough....

Placed a saito 125 on it, and while running it in, the wing pulled off in a flat spin ( the small wing bolts, didn't have a washer on it)
and went in....

THis was last year, and have not ran it since....

I was thinking about a gasoline/ignition conversion....

Perfect candidate if you ask me....

TIG weld on it's way....
Tip a pipe to a flat alum piece, and I am going to have a gas engine....

Or abandon that idea and run the engine in a GP Cosmic Minnow, and reinforce the wings....as I know it would fold them up
w/o one hard verticle pull....

Could my tank clunk was hitting bottom of tank, and causing the leaning??
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Old 07-16-2011, 09:39 AM
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Default RE: OS 120 AX ON PIPE

Header length before adding lengths....
Deff not too short...
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Old 07-17-2011, 01:39 AM
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Default RE: OS 120 AX ON PIPE

I always had to richen up the low speed needle in order to hover my piped OS engines. OS are the worst in this regard since the mid range runs so lean to begin with. Its great for cruising around with a muffler but too lean as the pipe starts working. Way too lean in a hover.
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Old 07-17-2011, 05:26 PM
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Default RE: OS 120 AX ON PIPE

I get 9,800 on full macs pipe, and 9,600 with Jett muffler on a APC 16x8.
9,400 on APC 14.5x14.5.

Hovering this engine on a big prop will have zero to no air flow around engine cause it to heat up and loose power. After it heats up the rear head bolts start to come loose.......
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Old 07-17-2011, 11:38 PM
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Default RE: OS 120 AX ON PIPE

Although OS 120 AX has amazing power for its size,it can be used only for light frames for 3D.the total weight must not exceed 10 LBS wet.My AX on pipe pulled vertically an EXTRA 330 from CMP 12LBS weight endless,but for hoovering the engine has not the necessary cooling area,even with baffled air ducts.Also at high levels of power the fuel consumption is very high.
@kochj
The conversion to ignition will not improve the cooling area...
My opinion is that this engine is in fact a 91 FX with a little more umph...I think it is very useful in frames where in fact a 91FX with pipe find its place.You have 20cc and no pipe at almost same weight.That is the only advantage.
If you want really power from a 20cc engine(120) use a Thunder Tiger 120 PRO.Just 200 grams more than 120 AX but way more powerful for the same fuel consumption and no overheating issues.
On pipe I got 8900 RPM on ground using Graupner Gsonic 18X8 prop and 9 kg pull from TT 120 Pro,and after 2 minutes WOT it has only 115 Celsius degrees of temperature,and no rpm drop at all.
I think a better one is the TT 120 Pro RE but did not tested one.
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Old 07-18-2011, 12:22 PM
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Default RE: OS 120 AX ON PIPE

you can get the OS to stay cool just need a little work. its needs tight ducting with great flow. most of the air needs to go to the rear of the engine. If you have a large prop then the hub area doesnt have much flow even at full power. A Stock tru turn spinner can be modded to help puch air thru the cowling. cut slots on a 25-30 degree angle just liek a small DF fan blade. then some 1/4 holes in the spinner angled to draw air into the spinner. greatly helps cools the engine. like i said though alot of work to make and balance the spinner.
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Old 07-25-2011, 08:03 PM
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Default RE: OS 120 AX ON PIPE

Perhaps it is best, if I place the engine in a speed machine, and leave the hovering to other types of engines...

Have you guys found, that the motor runs Hotter, when piped??
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Old 07-26-2011, 09:34 AM
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Default RE: OS 120 AX ON PIPE

It runs anyway hot at WOT if more than 1 minute.Piped it runs hotter because it burns extra mixture otherweise should be lost(that is why we use pipe ).I think a speed maschine can be an option for the engine piped.
I respect OS engines for their work,but definetly the 120AX was made only to be a power pack in the lightest possible case,not an engine for high output for a long time.A TT 120 Pro which is almost 200g heavier will stay at 110 Celsius maximum at WOT on pipe and will not quit.With 120 AX I wont do it!
The problem is well known from OS 91 FX which runs hot no matter what when you need high power.From an engine which is 5cc more anh has only 100g more than the 91,what would anyone expect?
I said and I sustain my opinion:OS 120 AX is just an engine wich works VERY GOOD where an OS 91 FX piped must do the job.
Better weight and no pipe.
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Old 08-02-2011, 08:12 PM
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Default RE: OS 120 AX ON PIPE

So is the answer to the overheating better ducting or add some wraped pipe to add to the heat reduction?

http://www.youtube.com/watch?v=BVH_Yi377eY

I think this one was less than 10lbs.. around 8-9lbs

This one had a ys110
no overheating issues...
http://www.youtube.com/watch?v=7H0Nx...eature=related
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Old 02-04-2013, 02:52 PM
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Default RE: OS 120 AX ON PIPE

I will be running a 1.20ax on a Midwest Super Hots shortly. I will however use the Krumscheid 25cc pipe instead of the 15cc pipe.
The way I see it, the 1.20 on the stock muffler has barely more power as an old ST S90K on the stock muffler. I've read all the rpm numbers. It's a dog on 15cc size props, and only works on huge 17" - 18" props. Rpm's below 9000... it will not rev higher due to limited transfer passages probably.

I think the problem with the small pipe and 10% nitro is probably too much back pressure, and resulting soaring head temps. This thing should have more than enough cooling area than any .90 IMO.

Will report back.
I'm aiming at 10,000rpm with at least a 15x10 prop. My old S90K ran over 10,000 on the stock muffler, without nitro on a 15x6. So a full piped 1.20 should pull a 15x10 without problems!

Piped engines do not need 20% nitro to make power...I really think this is key here. Either run a lot of nitro, and the stock box, or pipe it and lower the nitro and/or compression.
From what I've read, this thing begs to be run piped....properly...
Airraptor runs his piped, and appears to get amazing power from his.

I will not be hovering a lot however....that could be a problem if you're running close to WOT during the hover. That's a hard place to be for any engine. If it hovers at 50-70% throttle, it'll be much easier on the engine. Depends on the AUW of the plane.
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