I was wondering if it's possible to convert an OS 40 fp rc engine to control line by removing the existing carb and replacing it with a venturi and needle valve assembly. The engine is new in the box, and I was hoping it could be done without altering it in any way just in case I wanted to use it for rc again.


Thanks for any input,

Maurice

If OS makes a venturi and spraybar, it'll certainly be possible. If not, then finding a venturi that fits and a spraybar that works will require some serious looking. Unless someone around here has already done the deed and knows what parts to get.

Lots of people just lock the throttle wide open and go from there. That works great.

Maurice,

Should work without problem. You may still be able to find the venturii and needle valve assembly at Tower. If not there are some 3rd party "cottage" guys who can supply the pieces.

Depending on what type of CL flying you'd like to do, the FP has served well. For some, box-stock (other than the venturii/NVA change) worked well. For more serious "stunt" CLPA fliers, there were various mods. There are many good CL fliers in Eastern NJ, btw.

If a manufacturer produces the same engine in CL/FF and RC versions, often, the CL/FF versions are identical to the RC version, except for a venturii/NVA in place of a throttle. For CL Stunt, engines like the 40-FP have done well with mods as simple as one or two added head gaskets.

The "Classic" 4 cycle/ 2 cycle "stunt" run mode always sounds good, but so many "modern" (i.e., ABC or equivalent, Schenurle-ported) engines are primarily designed for the higher RPM RC use. You would lose too much power running them around 9,500-10,000 RPM to get that sound. The answer has often come down to running a slightly larger, flatter pitch prop to get nearer the engine's best power range and still keep airspeed (thus laptime) manageable.

Recommended prop for RC with a 40-FP RC version is something like a 10-6; for comfortable CL use an 11-4 or 11-5 lets it rev to its comfort zone, and doesn't spin you dizzy on 60+foot lines.

Another few things have worked reliably: a fairly hot plug, 10% nitro, 11% each castor and synthetic oil fuel, and muffler pressure to the tank. BTW, the huge stock muffler can be replaced by a much smaller, lighter "chip" or "tongue" type. These look like the extension neck on the stock mufflers, capped at the outer end and drilled with many small holes to let the hot gases out. They reduced sound well, if not as well as the big trashcans, and can provide muffler pressure for the tank.

The run setting should be a "wet 2-cycle" - smooth, steady 2-cycling, but not peaked out. Definitely visible exhaust "vapors." In stunt, maneuver airloads caused the firing mode shift from 4- to 2-cycle in the older iron piston/steel sleeve, baffle piston engines. If things went right, you heard a 4 cycle purr and a 2 cycle shriek as maneuvers loaded the engine. With a "wet 2-cycle" run, there's little audible change in engine sound.

You start to think there's no RPM change. (I still think there is, but we can't discern it as easily. It isn't the sound of firing every other revolution then shifting to firing every time as in the traditional 4/2 style run.)

If you can find the Joisey control-line guys, they can help you a lot...

Luck!

Hi Maurice

I recently bought a 2nd-hand 35 FP which had been modified exactly as you describe. The RC carb came with it and can be easily retrofitted if I want. I haven't flown it in a model yet, but it runs well on the bench.

I can't imagine that the 40 FP would be much different.

Steve

The FP-40, unlike the LA .40 has a boost port. Blocking the boost port will help the engine run better with large props in the RPM range that CL stunt uses. If you intend to fly CL stunt, contact Leonard Neumann on Stuka Stunt Works. He has prepared many, many FP .40's and is always willing to share the information he has gained. He can also recommend the best venturi size and needle assembly to use. He will even sell them to you if you decide to remove the carb.

Here is a link that explains how they rework the FP .40: http://www.clstunt.com/engines.htm

George

Lou,

Thanks for all the valuable info. You answered all the questions I was going to ask next.
Yes I believe I can get the needle valve assembly and the venturii from Tower Hobbies.
I have a Brodak Cardinal that I plan to put the engine in.
Up to this point I've only done a little bit of U-control flying but I'm defenitely hooked. It's a lot of fun.
I'm going to take your advice and seek out some of those Jersey fliers and see if I can learn how to do this right. I have a couple of old Fox 35s but I would like to see if the OS is much different as far as power. Hopefully it will fly well.

Maurice

Hi George,

Thanks for the link. I will contact leonard Mon. and see what he suggests.


Maurice

Steve,

Do you know if any modifications were done to your 35 or did they simply put on a venturii and needle valve?


Maurice

Hi Maurice, as far as I know it's standard, but I haven't pulled it apart yet. The previous owner mentioned using it for mainly CL stunt and a bit of RC, but made no mention of mods.

Steve

I am going to go against convention wisdom.

I have a lot of fp 40 time. 3 of them. There are a lot of people telling you you must block the boost port or get expensive rework done to use it for control line. None of mine are. You don't need it, unless want to fly contests and are real picky. I think many people that suggest rework never owned one. And yes some have had issues with it.

People block the boost port to detune the engine and make it happier running slower. They also sometimes change the head shape or change the timing by gringing on the sleeve.

I have been successful by going to a real flat prop(11x3), fuel with a little more oil, and an extra head gasket. If you run a 5 or 6 in pitch prop, the plane will fly quite fast. And yes I still have a a few run aways on hot days. Not very often anymore. Unless I have driven 200mi to a contest I don't care.

Again, don't send your motor out to get reworked until you know you like flying stunt. It might cost you $50-$75 and be gone for a month to get this done. Is that motor worth a $50 rework? Probally not. Save your money and go out and fly, then the use rework money to get a Brodak 40, the new evo 36 or an OS LA 46, if you feel the need.


There are fliers in NJ than can help you. They use this motor without rework and are happy with it.

http://www3.towerhobbies.com/cgi-bin...&I=LXCX05&P=ML

I think this will fit.
http://www3.towerhobbies.com/cgi-bin...&I=LXCR49&P=ML

get a couple of head gaskets too.
http://www3.towerhobbies.com/cgi-bin...&I=LXCM64&P=ML

Marurice,

If you don't want the Carb that you are removing I'll buy from you, I use these engines all the time for CL scale and like to have spare carbs on hand for my CL models that use throttle.

Thanks
Fred

Hi maurice. The FP is a very nice engine. You also could use it in UC just screwing on all the rotor stop screw until the carb rotor stay all opened. This way it will run like a UC engine and also, you could retrofit it to RC use anytime you want. The Venturi from the OS 40/46 LA-s is exactly the same if you intend to use it on your FP.
The RC and UC version from this engines are absolutely identical, just the carb is different, and in some later motors, OS made a smaller muffler for their 35 and 40 FP, to satisfy the stunt community (OS 762 "S")..

Hey Guys,

First of all I would like to thank everyone for all the suggestions and info.

The route I plan on taking is purchasing a venturii, needle valve assembly, a few head shims from Stuka Stunt Works and converting the engine myself without any machine work and seeing how that runs. I'm sure that at this stage of the game it will meet my expectations since I'm fairly new at this control line stuff. If I discover that I'm unsatisfied with it I'll just purchase a Brodak 40 or similar since in the long run that would be cheaper; considering in the cost of the engine plus the additional $65 for machine work and additional cost for the parts plus shipping. If anyone has a source besides Tower Hobbies where I can purchase the needed parts, please let me know. It would be greatly appreciated.

Thanks again,
Maurice

Maurice,

You will probably be satisfied with it as-is. If later you feel the need to alter the engine, consider installing a LA .40 piston/cylinder. On the LA, they eliminated the baffle port, probably as a cost reduction. I believe it is a drop-in fit.

Good luck.

George

Hi again. my advice is, go with the engine absolutely stock. Is a great engine as it is, for sport and training duties it will give you years of very nice flying...
Remember thats is much better to have a very nice stock engine than a ruined by a bad reworking.
If you need a more powerful engine, i suggest you to buy another engine with a bigger displacement (OS 46 LA, ST 51, OS 40/46 SF-S among many others...)
good luck Maurice

I've been running an OS.40 FP in my ARTF Nobler for a couple of years now. Like yours, mine was an r/c engine, I bought the NVA and venturi ( same as the LA part ) from my LHS. I'm a big fan of the FP series engines for C/L, also got some .15's and a .25, all converted from r/c to C/L. They're good engines, you'll be happy with your FP.40.

Maurice,

I read all the mail on the conversion I am now going to call Stuka to convert the 40 FP I have so I could put it on my Douggie Cardinal and get rid of the Johnson .35.

Ed Pasick
Brick NJ

Hey guys! I contacted Leonard at Stuka Stunt Works as some of you suggested. I ordered the following parts; a venturii, needle valve assembly, head shims, tongue muffler and a thunderbolt glow plug. I ordered the parts on Saturday and they arrived on Monday! It was a pleasure doing business with him. He was very helpful. Here are some pics of my converted engine. I am sure it will perform just a good as it looks. I plan on running the 11-5 prop on it. Now all I have to do is put my ARF Cardinal together and see how it performs. Thanks again for your suggestions.

(Assuming my photos upload), here are some shots of a very slight improvement on simply locking the throttle open (which works just fine of course). I build a throttle control assembly from common RC hardware. then rubber band the pilots throttle control wire to a bolt so that it will remain in whatever position it's set in.

The only real difference is that I can start the motor at idle (throttle control wire in the "up" position), stroll out to the center, then have my trusty ground crew push the throttle control wire full down, which opens the carb (and engine) wide.

I don't know about you guys, but I've always felt a bit bad about leaving some poor slob hanging onto the end of a SCREAMING machine while I run out to the center and give the controls one last check before signaling for a release. This is all cool if your ground crew is a fellow brain damaged Modeler, but if your wife, girlfriend, child, or just some dummy strolling by has been pressed into service, the time from engine start to release seems TOO LONG.

WORSE if this is an air launch...

I apologize if my photos or verbage do not fully explain what I intend. I can pull it apart a bit and try new photos if anyone is interested.

Keep 'em turning!

Matagordababy (Steve) / [email protected] / 1-979-335-4552

Maurice,

You will probably be satisfied with it as-is. If later you feel the need to alter the engine, consider installing a LA .40 piston/cylinder. On the LA, they eliminated the baffle port, probably as a cost reduction. I believe it is a drop-in fit.

Good luck.

George

[/quote]


Unfortunately, the LA .40 sleeve/piston are different than the FP .40 and cannot be used as a drop in replacement.
DennisV

Please excuse my ignorance, but where are the exit holes in that tongue muffler? None seem to show in the pictures.

On the underside opposite the pressure fitting.