OS 46 LA : Information/Advice Please.

[Robin_Holden]

Greetings all from the Southern Charente in France. Just got my hands on my first OS46LA.

May I ask a few questions please regarding this engine , and apologies if it's been covered before.

1. What is the set-up of this engine ..... ? ABC , ABN etc.
2. What is the suggested running -in regime please ? The OS booklet suggests the odd tank of fuel before flying !
3. What fuel 'brew' would you suggest ?
4. What prop would be best for stunt please ? Looks like an 11x6 to me pehaps.
5. Last but not least , is it worth having my engine ' modified ' by one of the experts ? Hemi head etc maybe ?

Very much obliged for any comments fellas and thanks ,

Robin [ ex-pat Brit in the Charente full of ex-pat Brits ] 

[Brett Buck]

4. What prop would be best for stunt please ? Looks like an 11x6 to me pehaps.
5. Last but not least , is it worth having my engine ' modified ' by one of the experts ? Hemi head etc maybe ?
Robin [ ex-pat Brit in the Charente full of ex-pat Brits ] 

     I think the definitive prop is the 12.25-3.75 APC. It has been my experience that many of the aftermarket conversions have the effect of making the engine very smooth, but very very weak - so you end up needing an 11-6 or 11-7 and can't spin a 12.25-3.75 fast enough to fly the airplane.  It's an excellent engine straight out of the box, I would suggest at least trying it stock before going down the rework path.

    Brett

[GEOFFREY]

we  are using 10/18 fuel with a add of 4 ounces of Castor.. doesn't require.much for break=in. 1 or 2 soft flights. Brett is useing what you need for  a strong stunt plane ,, some of us.. play with 11-5/ 4 apc -would not work on this best out of the box motor.i did replace the screws with hex bolts.have fun Geoffrey

[Mark Scarborough]

The setup that Pat and I ended up with is the .275 venturi, a ST sized needle valve assembly, Powermaster 10 x 22 fuel ( 50 castor 50% synthetic) The APC 12.25 x 3.75 prop. On my profiles I typically launch around 9600 to 9700. On full fuse ships, around 9800. My profiles lean slightly due to the tank location relative to the needle hence the lower launch rpm.
I run several tanks, a few short runs at a time per tank, smaller prop say a 9 x4 or 10 x 4 right on the rich two stroke range. Fly it slightly rich and the more time you get the sweeter it will come on.
great engine for intermidiate sized airplanes. I have flown one over 600 inchs and it was a tank,, almost emberassed to say it was 54 or 55 oz and it flew effortlessly.
have fun,,

[Dennis Moritz]

Versatile, can be run fat rich or lean enough to break fairly hard. I've run with an extra head gasket, .283 venturi, OS FP needlevalve, powemaster 5% 22% (50/50), 11.5x4 apc. 12.25x3.75apc also works. One club member suggests clipping a 1/4" off each tip when using the 12.25 apc. Thunderbolt RC plug. The extra head gasket softens the break a bit. It's been fun pulling Vectors around at a dead rich setting. Slows everything down (including my life).

[rustler]

Are all these using the stock silencer?

[GEOFFREY]

stock muffler at delta park with tank presure

[RandySmith]

""It has been my experience that many of the aftermarket conversions have the effect of making the engine very smooth, but very very weak - so you end up needing an 11-6 or 11-7 and can't spin a 12.25-3.75 fast enough to fly the airplane."'"

Some of the reworks..NOT all.
If I were to recommend it runs stock I would at least put the NVA in the front, and seal or replace the backplate, plus it does benefit many times by adding 1 head shim. The ProZ 12 x 4 and 12 x 5 are also good props to use on the 46 LA.

Regards
Randy

[Gary Anderson]

""It has been my experience that many of the aftermarket conversions have the effect of making the engine very smooth, but very very weak - so you end up needing an 11-6 or 11-7 and can't spin a 12.25-3.75 fast enough to fly the airplane."'"

Some of the reworks..NOT all.
If I were to recommend it runs stock I would at least put the NVA in the front, and seal or replace the backplate, plus it does benefit many times by adding 1 head shim. The ProZ 12 x 4 and 12 x 5 are also good props to use on the 46 LA.

Regards
Randy

Hi Randy,
what rpm would you run with the 12 x 4 or 5 would work the best?  Would you run it around 10,000 or less?  I tried the 12.25x3.75 and set the rpm's around 10,000 using gma 10/22 and it seemed to run to lean (it was starting to turn the head a different color.) Just not sure what to try, appreciate your help, Gary

[Geoff Goodworth]

There are a couple of LA 46s at our club running the following with no internal mods.

Std FP 20–40 NVA through the venturi, metal backplate and the small venturi that used to come in the box with the FP 35/40.

I think this venturi is .265" dia. but no longer available. The FP 20/25 venturi available from Tower is .258" dia. 17/64" is 0.265625" so I would try the FP 20/25 venturi and push a 17/64" drill through it if needed.

If our friend on the forums—is it Curtis Schipp?—cannot supply an aluminium backplate, Thunder Tiger 4 U lists the GP 40 backplate as available, $6.29.

Cheers, Geoff

[Robin_Holden]

Geoff , very much obliged for your comments , in particular the availability of a suitable backplate.

Many thanks ,

Robin.

[Dwayne]

When sealing the back plate should you remove the gasket or leave it on?
Thank you

[Greg L Bahrman]

leave it on

[Phil Coopy]

Lowering the compression helps but if you choose to lower the compression it is much better to do it by enlarging the combustion chamber than by adding  head gaskets. Adding head gaskets effectively moves the squish band away from the piston top which kills this very important function which in turn will cause your power to fall off too much between 2/4 and also narrow your needle setting especially on hot days.  And you'll find that with the lower compression the 12.25 X 3.75 prop still works well. I have only experimented with the LA46 so I can't say that this stuff applies to all engines.

I modify the head as suggested by Carl Shoup. Pics show stock and modified heads.

[RandySmith]

Hi Randy,
what rpm would you run with the 12 x 4 or 5 would work the best?  Would you run it around 10,000 or less?  I tried the 12.25x3.75 and set the rpm's around 10,000 using gma 10/22 and it seemed to run to lean (it was starting to turn the head a different color.) Just not sure what to try, appreciate your help, Gary

HI Gary

There is not one RPM, that will vary from point to point , and with the drag, weight, size, type plane it is pulling, You can look at 10,500 being close, I setup mine with the motor running just between a 4-2 on the ground, they go up and within 1\2 lap, drop to a fast 4 cycle, then they just beep hi RPM 2 in the very tops of manouvers, The setup with the Bolly 12 x 4 is at 11,000 RPMs on the ground and run a perfect 2\4, and sounds like it is a typical ST 46 type run. If you use the PRO Z  props expect closer ro 11,000 with a 4 pitch and 10,000 with a 5, The RPMs will vary.

Randy

[Mark Scarborough]

Randy, good specific info!

On my LA .46, when using the 12.25 x 3.75, I have found my profiles like to launch at 9600 ( this is on a 580 sq inch profile weight about 54 oz) as it takes of and unloads, the engine leans slightly from the outboard tank position hitting the correct setting for ME/
On my Oriental that weighed 43 oz with an LA .46, using the 12.25 x 3.75 APC I would launch about 9850, on take of it would be a bit lean for the first lap and as it cooled with the airflow, it would settle into the perfect run for ME.
I used GMA Powermaster 10x22 fuel( 50 castor 50 synthetic) the venturi I use is .275 with a ST needle, actually is a ST sized needle from some dude in Georgia that makes the best assembly available!