OS 46 LA inverted problem
 

Engine gurus!

I just finished a SIG Rascal 40 and used an OS 46 LA engine. The problem I seem to be having is when I point the nose up to test the air bleed, the RPM always increases. If I point the nose down, the engine will stop. Doing this at full throttle, up is fine, down shuts down the motor. I have opened up the air bleed to a whopping 7 turns out from closed and it still acts the same. It seems unaffected by any change in the air bleed.

Throttle response is fine from idle to WOT. If I leave it idle for long the engine will quit as well. I dont have it to low, its a mix issue for sure. I have about 3 tanks of gas through it so far and it keep acting the same. I would like ot fly but as-is I am worried if I dive or loop under power I will dead stick. I am not new at this and have 4 other planes that work just fine. I am just missing something here. Are there any known issued with a LA engine and running inverted?h

Any ideas? The only different thing is that I have the needle valve off the motor and screwed to the firewall so the needle can be turned from the bottom of the plane. I dont see how that could so it but you never know.

Any help would be great. I want to get this bird in the sky!

Ryan

RE: OS 46 LA inverted problem
 

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What you are describing is completely normal for a new engine with only three tanks of fuel through it.

Also, it is normal for the engine to speed up when the nose is raised while being held on the ground. Most engines will remain running if held nose low, but this is something that gets better and better with more running time on the engine. The carb on the OS.46LA is a good carb. Not to worry.

When the model is descending, the fuel inlet is seeing less than 1 gravity's (G) worth of pressure from the fuel tank, so when flying, the engine should not quit from being flooded.

We hold the nose upwards and adjust the high speed needle for a slightly rich mixture with the engine pointed vertically upwards. This ensures that we have enough fuel at the end of the tank to run the engine safely without going to lean. The variations you are seeing in mixture are perfectly normal for a suction fed glow engine and should not be considered a defect. The engine's running will improve considerably as you accumulate more running time.

Good luck with your Rascal 40. I have the ARF Rascal 40 NIB here and am about to get started assembling it. Sure is a pretty model.


Ed Cregger

RE: OS 46 LA inverted problem
 

Engines with "Air-bleed" type carbs like the OS LA series give more trouble inverted than do the ball bearing engines with the twin needle carbs.

RE: OS 46 LA inverted problem
 

What does that tell you? Think about it.

No surprise then, it's stopping (nose down) at idle as well.

Reset the bleed air idle screw at half-way open across the small hole you can see in the front of the engine AND LEAVE IT ALONE That will be very close too the ideal setting in our climate. Temp. Av. east coast Oz MSL temp pressure and humiidity. If you must fiddle, it'll only need a minute adjustment, probably towards leaner (screw out = anti-clockwise) but no more than 1/8th of a turn at a time. If it needs more than a 1/4 of a turn either way, your problem almost certainly lies elsewhere. Ergo....

Refer back to my opening sentence.

It's a normal characteristic of all today's Schnuerled engines with the huge ports and high timing that if you leave the engine idling for a prolonged period, especially on the ground, and then open the throttle too rapidly, the crankcase will be filled with such a gutful of fuel such that even with the optimum low speed needle or bleed air crew setting, they will stop. The LA is more prone to this than the AX. Partially it's a characteristic of O.S. air bleed carb. They should have asked Enya to design and make it.

With the engine inverted, this problem will be exacerbated because of where the gutful of fuel in the crankcase pools and the plug being drowned. An detrimental fuel tank to carb height relationship will exaggerate this. You can try using a hotter plug with a superior heat sink and more robust element such as an Enya #3, but that's just a kludge to address the fundamental underlying problem.

The height of the N/V mounting is important, as is vibration isolation from the airframe. Use good quality thick walled fuel tubing of the recommended ID & OD O.S. advise throughout the contiguous feed system. The quality and dimensions of the tubing between the needle outlet and carb inlet are particularly important to a consistant engine run in O.S. RNV type engines.

The 46LA is often beaten up on because it doesn't wear a shiny new glamour suit and afford boasting rights. In it's role, it's a superbly reliable enigne which can be flown straight out of the box. Fit a known good condition plug preferably either Enya #4 or O.S. # 8, an A3 will do if you must and an Enya #3 is fine if you're on low/no nitro , an 11x 5 APC or 10.5 x 6 Bolly Clubman prop, use fresh quality fuel preferably containing some (20% by volume of the total oil content minimum) castor (plain bearings love it as do any engine for their first hor of running), fire her up, set her so she's in a rich two stroke at the bottom of her peak band just before she starts to significantly drop RPM and go fly. Just don't keep her at full hammer continuously during that first hour. ie: CWOT aka "Remember, you've got a throttle servo and it's not there just for ballast".

She'll run like a Swiss watch. After about 3 to 5 flights, you can start to progressivley lean her out until by about 10 (2 hrs running) you can run switch to your preferred brew, tune normal peak and go ballistic. GL.

(Edited to remove questionable language)

RE: OS 46 LA inverted problem
 

For some reason, I forgot that his LA was inverted. A good point.


Ed Cregger

RE: OS 46 LA inverted problem
 

Thanks for the info guys, good stuff as always.. I'll give it some time and see how it goes.

RE: OS 46 LA inverted problem
 

I own an fl 70 4c, the one with the airbleed carb. Ran horible inverted, as you described. Mounted sideways, problem partially solved. Low end always acts rich but i was able to at least keep it from quiting when pointing the nose down at idle.

RE: OS 46 LA inverted problem
 

O.K. now for the other side...:D There has been debate about the need for this, but...
There are several of us here on RCU that have actually made an LA .46 run inverted...by (OMG ;)) drilling out the air bleed hole.

I have a Cermark Bobcat (low wing sport ship ) w/ an inverted engine. I couldn't keep it running long enough to shoot touch-and-go(s) because it would load up and quit.(extremely aggravating ...and the engine was / is broken in BTW )
I had the air bleed screw so far out that it actually fell out...and that's when I discovered that it needed more air than possable in the stock configuration, because it actually began to run better that way! (just a bit too much air though )

I can hear the others now..."change the tank location"...:)
I did that...I lowered the tank so it would run well while flying up-right, but when I rolled inverted, the engine would go too rich.

If you drill out the air bleed hole to 1/16 or 5/64 you will get your adjustability back.
Just make sure you don't get any alum. chips down in the engine of course...
I did mine w/ a pin vise, a little vaseline in the venturi to prevent chips from going down in the engine, and some Q-tips for clean-up.

RE: OS 46 LA inverted problem
 

So there are known problems with the 46LA running inverted.

When you say drill it out, are you putting the same screw back in? As you said in yor post, I have backed the screw out as far as I can and it still acts the same.. To me it seems that the engine just does not like being inverted. However, as others have said, I have not put enough time on it either. I typically use the FX engines and have good luck with them. I just didnt want to try and shove a 46ABL in the front of the plane. Seemed a bit much. The LA engines I have ran upright have been just fine and very reliable. This inverted one seems to be a real pain.

Ryan

RE: OS 46 LA inverted problem
 

hmm my la 46 will also die if it goes nose down for too long due to an airlock being sucked up wen there is no fuel near the intake, is this normal??? just made me deadstick today and have to do a dangerous landing lol. no damage tho

RE: OS 46 LA inverted problem
 

Ryan...yes, you use the same screw (I had to use a replacment, because mine fell out, :eek: but...)
The hole you drill out is the small one right in the front of the carb body, that the air gets sucked through...just make it a little bit bigger.
(also, just to be sure you don't get chips in the engine, you could take the carb off...that choice is up to you )

There have been several threads on the LA series...
More than a few of us have drilled the air bleed holes out...and more than a few have said that it's unnecessary...
I tried everything including 4-5 different glow plugs, different props, leaning the high speed out as far as possable, etc. etc.

Funny thing was...it actually continued to run until landing one time...and I said "hmmm?"
I looked at it and noticed that the air bleed screw was gone!:)

Jarrah...I'd say it's normal...because if the clunk doesn't slip toward the front of the tank, the engine's gonna suck air.
Quite often, if you do something like a 5-6-7-or more turn spin, the clunk will get un-covered, and the engine will pull an air bubble and quit.
You could use a more flexable clunk (fuel ) line that allows the clunk to go foreward when you're in a prolonged nose down attitude.

RE: OS 46 LA inverted problem
 

Hi!
OK Here we go!
There is nothing wrong with the OS LA series of engines and has never been. There carbs are simple airbleed carbs and are so good that nothing else is needed.
There is absolutely no need for drilling the airbleed hole larger! At least if you live/fly at sea level and fly under normal air temperatures from -20 to +40 degress centigrade.

For good engine behaviour it's vital that you follow some simple rules. Which are...

Always use good fuel. This in the OS LA case means using fuel that contains 5-15% nitro.When it comes to oil percentages it's good to use at least 20% if you are using commercial fuels. Castor oil or syntetic oil or a mix doesn't matter. Personally I use 15% all syntetic oil (Motul "Micro" or Aerosynt 2 or Aerosave) but Klotz oils will also be fine, but use 20%.
I mix my own fuel as most people do over here, but as long as you use commercial fuel, everything will be just fine. But see to that you run at least 5% nitro and that the fuel is fresh. Do not use more than 15% nitro!I personaly use 5% nitro in all my engines.

The airbleed carb idle needle should be set half open. That is the standard setting. Open it slightly if the engine doesn't have instant throttle respons.
Al OS engines can sustain long periods of idle running and still bark to life instanly if just set correctly.

The way you adjust the high speed needle is vital.
Not to rich and not too lean.
By holding the nose of the plane straight up for a few seconds you can check if the engine is set correctly. Always set the needle a little rich from full rpm. Do not shake the plane when doing this , just hold it straight up!

Correct glow plugs are also vital.
For your engine and 5-15% nitro an Enya 3 or OS 8 is what I personally would use.There are of course other plugs that will work too.

When it comes to props a 10x7, 11x6 or 12x4 is what I would recommend if you have a low winged sport model or slow high winged trainer type model.

Tank position and size is also very,very important.
For a .46 engine a 240-300cc (8-10oz) tank is what should be used. Anything bigger and you risk having engine setting problems due to engine could not cope with such large pressure variations inside the tank.
It's also very important that you follow the simple rules that says: "Always place the tank so that the center of the tank is inline with the carb intake orifice when plane sits horizontal". If you follow these simple rules any engine will run well, throttle perfectly and have instant throttle respons even after several minutes ideling, upright or inverted doesn't matter.

RE: OS 46 LA inverted problem
 

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I believe you proptop.

My wife's first trainer (Andrews A-Ray) was powered by an OS Max .35S R/C (1970). The engine was mounted upright, but we could not lean out the low speed mixture enough and eventually ended up running the engine without the airbleed screw in the carb too. It ran fine that way.


Ed Cregger

RE: OS 46 LA inverted problem
 

Jan,

In this case I believe there is more to it than just fuel quality and nitro. I run Wildcat 15% in all of my models as well as Cool Power from time to time. I have been through many gallons of that fuel and its served me well. I use all OS number 8 plugs. What I am seeing is that engine just does not work like the other LA of FX engines I have. Nose up, RPM up. Nose down, shuts down. Throttle response fine. The engine will bark just fine. I am swinging an 11X5 currently and have an 11X6 as well. I believe there very well may be something to the air bleed not being big enough for the application. There has to be more to it than Fuel vs. Glow.

Ryan

RE: OS 46 LA inverted problem
 

Hi!
Before you do anything to the idle hole in the carb ...check out the piston if it is damaged in any way ...might be worn out (bad piston to cylinder fit).

RE: OS 46 LA inverted problem
 

I can do that..

Wouldnt I have crummy compression if that were the case? It would have to be pretty messed up to be worn out on tank 3 but I'll lay an eye on it when I get home today. I'll try anything. I want the bird to fly!