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Author Topic: OS 40FP  (Read 3162 times)

Offline Richard Logston

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OS 40FP
« on: June 21, 2014, 04:10:33 PM »
This is an engine that has been very reliable easy starting and good runner in an RC plane over the years. I now have it in a 1952 plans built Smoothie. I removed the RC carb and installed a ST needle valve and tongue muffler. I decided to run the engine in the back yard and it ran started ok by hand propping but had to turn needle almost all the way out to get it to slow down to a four cycle, even then it did not slow to a steady speed. Maybe I need an extra head gasket or a different NV assy. Is this a flaw in trying to run this engine in a CL configuration? Richard
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Online Tim Wescott

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Re: OS 40FP
« Reply #1 on: June 21, 2014, 04:54:57 PM »
What size venturi are you using?  I'm not sure what the exact "right number" is, but for stunt flying I think it's around 1/4" (0.28 is, I believe, too big).
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Offline Richard Logston

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Re: OS 40FP
« Reply #2 on: June 21, 2014, 07:36:49 PM »
Not sure the size as it was ordered over a year ago for this engine. Same with the ST needle assy.  Might mention I'm using 80/20 all castor plus I tossed in an 8oz bottle of Hobbico 1/2 A fuel that has 25% nitro. The prop is a wood 11/4. Same glow plug that I used for RC. Richard
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Online Tim Wescott

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Re: OS 40FP
« Reply #3 on: June 21, 2014, 09:29:20 PM »
Whoops -- I missed something.

The 40 FP does not like being run in a 4-cycle.  That is not the right way to run a 40 FP.

You want it to run in a fast, wet 2-stroke, with a flat prop.  The 11-4 is probably good.  Most people feel that the APC 11-4 or the Thunder Tiger 11-4.5 are better than wood props.

Try a launch RPM between 9500 and 9800.  Experiment around with it.  If it runs away in the air, you'll know it by the fact that your right arm will be longer than your left.  If you can't find a happy needle setting that will let it run at a consistent & decent speed, then your venturi is too big.  You can effectively cut down the venturi size by putting pantyhose over the venturi: just keep piling on layers until you get the run you want.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online kenneth cook

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Re: OS 40FP
« Reply #4 on: June 22, 2014, 04:19:16 AM »
             Richard, how's the o-ring under the venturi? Suggesting that you had to unscrew the needle almost all the way out indicates to me that you have an air leak. I've had to double the o-ring under many OS venturi's and use a padded Quick Grip clamp to compress it down to install the spraybar. In addition, you do have the spraybar hole orientated down at approx the same angle as the stack? If that's not resolving issues, I would check the tank and all fuel lines for leaks. I've seen hair line splits that don't reveal themselves until you flex the tubing and discover that there's a nick or a complete split in the tubing. These kind of splits don't generally leak fuel as a indicator as to where they are. If running a Dubro inline filter, make sure it's secure as they can be subject to leaking. Ken
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Offline Richard Logston

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Re: OS 40FP
« Reply #5 on: June 22, 2014, 03:20:46 PM »
Thanks everyone for your input. I think the problem is my trying too run it like a Fox or McCoy C/L engine. Will run it in a wet 2 cycle. I'm trying to relive my old U/C days again, so getting used to converting RC engines back to U/C is a learning experience for me. Richard.
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Offline Bill Little

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Re: OS 40FP
« Reply #6 on: June 22, 2014, 03:30:33 PM »
Hi Richard,

You are correct.  A stock FP .40 will not run like a Fox .35 or McCoy Red Head.  The timing just doesn't allow a 4-2 run.  *Some* R/C engines will do a decent 4-2 but most modern engines will have to run a high rpm/flat pitch prop.

You can have the FP .40 reworked to run a 4-2 but most of the time it kills the power of the engine so there is really no need to do it.

Just set the FP in a "wet 2" and let it do its thing.

BIG Bear
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Offline Richard Logston

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Re: OS 40FP
« Reply #7 on: June 22, 2014, 05:33:06 PM »
OK, The thought just came to me, why not re-install the RC carb and muffler and run the engine in it's original design mode. This engine has been flown a lot in RC airplanes and I was able to richen it up with no problem. Just a thought.
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Offline David Felinczak

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OS 40FP
« Reply #8 on: July 02, 2014, 06:43:45 AM »
Richard,

I am flying a Gieseke Nobler with a stock OS FP40 Stunt Motor. Original motor came with 2 venturies, L and S. The large increases power and the small decreases power and increases fuel suction.

Fuel should be 5-10% nitro/23%castor.
Prop= 11x5
Glow plug= Sig RC long
Spray bar- ensure spray bar port is centered in Venturi opening oriented approx. to the 7:00 position.

The problem converting a RC to CL motor is engine "runaway" caused by motor porting in the cylinder wall and crankshaft. Try adding a head shim to decrease compression.


Sent from my iPhone using Tapatalk.
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Offline Dennis Moritz

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Re: OS 40FP
« Reply #9 on: July 05, 2014, 12:59:39 AM »
10.5x4.5apc. Powermaster 5%or 10%, 22%oil(50/50 castor/synthetic). I like .272 venturis for most models these days. Small venturi is .256 (I think) large is .283. Venturi's are available from Jim Lee. Tongue muffler with a lot of holes. Run healthy 2-stroke. Usually they have a mean crackling sound when all is well. Will break into a harder 2-stroke. Ken is right. I've doubled the 0-rings at times when encountering an erratic engine. There needs to be no air leaks anywhere. Even a tiny leak can create havoc. Pressure test tank. Check all tubing. Engine screws. Head gaskets regulate break.
« Last Edit: July 07, 2014, 01:46:44 PM by Dennis Moritz »
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Offline rich gorrill

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Re: OS 40FP
« Reply #10 on: July 06, 2014, 08:04:14 PM »
Hi Richard, having recently returned to the hobby I am no expert but all the tips you have been getting are spot on. I'm running an fp35 in a Twister and ran into some of the same problems you are having. Thanks to Dennis M and Steve D. in the Philly Fliers I've cured most of the problems. I had to go to a 10-4 APC to cure the runaway. I'm using a uni-flow tank with muffler preasure and a stock os 3030 muffler. Tried a tongue muffler but got better results with the stock one. I also added one extra head gasket and that helped a lot. Biggest problem now is the engine goes rich in outside loops or inverted flight. I moved the tank higher but haven't had a chance to test yet. I also use the os needle valve but am going to try the one from Randy Smith, sometimes one click is too much or too little. If all else fails I'm going to try an LA40. Good luck.

Rich
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