Author Topic: OS FP Runaway Solutions (Read 2551 times)

Phil Spillman · « **on:** February 01, 2022, 09:05:25 AM »

Most recently a dear friend gave my a beautiful original Magician Profile plane. I mounted an OS .35 FP engine on the plane a went flying! It has flown great up to the horizontal 8"s at which time it went balistic in a run-a-way status! I spoke with Bob Zambelli about this and he suggested that I send it to him to have the head hemied out! I sent it off and it is on its way back to me in less than one week! I haven't received it as yet but I am confident it will run much better when I do! Many thanks to Bob for his diagnosis and fix on this engine! I sure hope it works!

Phil Spillman

Bootlegger · « **Reply #1 on:** February 01, 2022, 09:15:52 AM »

Phil, something else that you might try is adding head shims instead of reducing the "squish band of the head"... Food for thought

Brad LaPointe · « **Reply #2 on:** February 01, 2022, 10:02:32 AM »

Leave it stock . Use the .25 sized intake (.256”) and a 11x4 prop . The stock muffler with this setup runs almost like .

Brad

Tim Wescott · « **Reply #3 on:** February 01, 2022, 10:12:34 AM »

Were you running a 10-6 prop in a 2-4 break? Are you bound and determined to continue doing so? In that case then spending $$$ de-tuning the engine so that it runs like it's 1948, instead of putting the correct prop on it and running the thing the way it was designed, may be the best bet.

If you hadn't already sent the head off to be cut up, I'd suggest an APC 11-4 prop, running the thing in a wet 2-stroke (absolutely not a 2-4 break -- that will make an FP run away every single time), and adjusting the venturi size until you get the right balance of speed in the levels and power up high. Then if you like the results, experiment with similar props to find the best one for your airframe/powerplant combination.

David Hoover · « **Reply #4 on:** February 01, 2022, 02:21:00 PM »

Fill the boost port! You'll be amazed at the difference it makes and the grunt it has.

Brett Buck · « **Reply #5 on:** February 01, 2022, 02:29:20 PM »

It never ends.

Brett

Robert Zambelli · « **Reply #6 on:** February 01, 2022, 03:26:23 PM »

GREAT responses, Guys.
All make good points.

Gil - I did indeed try your suggestion on an FP 40 with a .265 venturi. I tried 2, 3 and 4 head shims, same plane (profile), same day, same fuel. They all showed varying degrees of improvement but the modified head was by far the best. I was looking to eliminate runaway and get a decent 2-4 run.

Tim/Brad - I don't know what prop/fuel/venturi setup Phil was using. He just asked me what setup I was using on my FP 35 (.255 venturi). Mine ran perfectly.

Brad - does the stock muffler have a baffle? If so, should it be removed?

Dave - you suggested filling the boost port. How is that accomplished?

I've been told that the RC and CL FP engines are identical except for the carb/venturi. Is this true?

Brett - You are CORRECT!!!

You fellows have good information - keep it coming.

This is the head mod that has worked best for me on the FP 35 and 40. I've also used the mod on some LA and K&B engines.

Bob Z.

Brad LaPointe · « **Reply #7 on:** February 01, 2022, 04:35:22 PM »

The muffler seems to give a more “pipe “ style run when left stock .

Brad

Air Ministry . · « **Reply #8 on:** February 01, 2022, 05:12:25 PM »

seeing someone mentioned bunged boost ports !

https://stunthanger.com/smf/engine-set-up-tips/os-40-fp-set-up-q's/msg569552/#msg569552

Pictures of the Adamisin set up . Basically J B Weld as the filler . Incidently the 40 P/L & Head fit in the .35 & V.c.V . And the FSR 40 . So you can build a FSR twin ball race heavy .35 . o.k. for RAT maybe .

wwwarbird · « **Reply #9 on:** February 01, 2022, 05:43:19 PM »

Quote from: Brett Buck on February 01, 2022, 02:29:20 PM

It never ends.

Brett

No kidding.

I've ran a ton of FP .25's, .35's and .40's, without question my favorite engines. Most are bone stock except for some with the Jim Lee venturis. Break in is during the initial flights, meaning none. I've had the same experience with the LA's. They're dead reliable out of the box and left alone. If you're having run issues it's NOT the engines fault.

Dave_Trible · « **Reply #10 on:** February 01, 2022, 07:38:47 PM »

Quote from: wwwarbird on February 01, 2022, 05:43:19 PM

No kidding.

I've ran a ton of FP .25's, .35's and .40's, without question my favorite engines. Most are bone stock except for some with the Jim Lee venturis. Break in is during the initial flights, meaning none. I've had the same experience with the LA's. They're dead reliable out of the box and left alone. If you're having run issues it's NOT the engines fault.

X3.....These are great engines-left alone and allowed to run in it's own 'happy zone' which is fast on a pretty flat pitch prop. I always used the APC 11-4 with good results. The LA simply isn't as strong and usually took an 11-5 to get similar thrust. I've been converting a handful of Thunder Tiger .42 to CL. These have characteristics quite a bit like the FP .40 except I think even a bit more powerful, and are a drop in fit to the OS engines. Again they have one happy speed-nearly flat out. However some have made these engines a hobby of it's own-just like the old Fox.....

Dave

Lyle Spiegel · « **Reply #11 on:** February 01, 2022, 08:37:45 PM »

Does anyone know details of the mods done by Byron Baker to the OS 46LA? I have three engines he did for me and they run superb. Thunder Tigre 11x4 1/2, 10-22 powermaster fuel , uniflow, Thunderbolt RC idle bar , one muffler by Scott Dinger, One muffler from Randy, one is OS OEM. One setup with sock OS NVA. Two have ST style from Randy.

Dan McEntee · « **Reply #12 on:** February 01, 2022, 10:48:28 PM »

Quote from: Lyle Spiegel on February 01, 2022, 08:37:45 PM

Does anyone know details of the mods done by Byron Baker to the OS 46LA? I have three engines he did for me and they run superb. Thunder Tigre 11x4 1/2, 10-22 powermaster fuel , uniflow, Thunderbolt RC idle bar , one muffler by Scott Dinger, One muffler from Randy, one is OS OEM. One setup with sock OS NVA. Two have ST style from Randy.

I think Byron was one of the first to advocate the hemi head. You should try the same parameters you spell out here on a stock, unmodified FP-40 and see what your results are.
Type at you later,
Dan McEntee

kevin king · « **Reply #13 on:** February 02, 2022, 12:14:58 AM »

Quote from: Brett Buck on February 01, 2022, 02:29:20 PM

It never ends.

Brett

Brett! What exactly would you recommend for a stock OS La 46 on a 45oz Vector? Props, head gaskets & venturi? The La 46 I have is stock, but i dont know if the venturi or the # of head gaskets is still the same.
Kevin

Perry Rose · « **Reply #14 on:** February 02, 2022, 05:43:14 AM »

Sea level to 1000' msl I run stock .46 LA engines, stock .282 venturi or similiar replacement, .156 diameter needle valve asm, APC 11.5 x 4, stock glow plug, stock w/baffle removed or tongue or Fox ,35 muffler, 4 ounce metal uniflow tank or Du-Bro 4 ounce plastic tank(holds 4.5 ounces) on uni flow both on muffler pressure and 5% 22% fuel max or mix your own 2% 22% fuel. I have run full castor, full synthetic and 50/50. Same set up year round from Connecticut to Louisiana.

Paul Van Dort · « **Reply #15 on:** February 02, 2022, 07:27:22 AM »

Quote from: Bootlegger on February 01, 2022, 09:15:52 AM

Phil, something else that you might try is adding head shims instead of reducing the "squish band of the head"... Food for thought

Adding head shims is increasing the squish distance, also making the squishband less effective. Same issue with the ST51. Making the dome deeper while keeping the squishband size, together with increasing the squish by omitting shims would be best. But difficult to achieve without eating up the thread of the glowplug....

Tom McClain · « **Reply #16 on:** February 02, 2022, 07:44:18 AM »

I have bought over 6 OS 40 FPs from Ebay. All were RC engines and full of carbon and congealed castor. I dissembled them, baked them in AntiFreeze in a crockpot for 24 hours and then cleaned them with a brass brush and tooth brush and finally fine steel wool. Reassembled them with an OS NVA and .280 venturi with one head shim. All ran fine on GMA VP Racing 10/22. I have no problems with them and fly them without modifications here in Phoenix.

Cleaning them, GMA 10/22, .280 venturi, XOAR 11x5 propeller, 8900 rpm and OS NVA for a 40. That's seems to be the ticket.

Gary Dowler · « **Reply #17 on:** February 02, 2022, 09:13:56 AM »

Quote from: Lauri Malila on February 01, 2022, 09:23:02 AM

I'd go the other way; increase compression, preferably to factory setting, and use the engine at the rpm & setting where it's been designed to run. L

EXACTLY. Run it two cycle as it’s made to do and there’s no where for it to run away to.

Tim Wescott · « **Reply #18 on:** February 02, 2022, 12:10:31 PM »

Quote from: Air Master on February 02, 2022, 11:38:46 AM

Thats what I do with mine. It runs the same speed and I can change that speed by adjusting the needle valve. Maybe that works for me because I'm not a expert. If I wanted an expert level stunt engine I would call Randy and get one already set up.

I have found that tinkering with the venturi size (either by literally having a collection of venturis or by stacking nylon mesh on a slightly oversized one) can do a lot to tune the run.

Running richer for a given venturi size makes the plane slower in the levels, but also gives you more boost up high. In the extreme case, it'll 4-stroke in the level, get "on the step" in the eights, and then you'll spend six minutes going very fast and wondering if your arm will fall off.

Running leaner for a given venturi size makes the plane faster in the levels (up to a point), but gives you less boost up high, or, if you go too far, it sags lean up high.

If the plane is over-boosting, or running a 4-stroke in the levels, then you pile on some nylon mesh and try again.

If the plane needs to be leaned out to go at all, then after making sure it's not in need of de-varnishing you go to a bigger venturi, and try again.

Dennis Toth · « **Reply #19 on:** February 02, 2022, 01:33:43 PM »

Phil,
You're getting lots of options on how to get it to run a 4-2-4 but the FP's don't like that run mode (same for most current RC converts). They can be forced to do it but it is under protest and if they get any reason to flex their muscles and go, they will!!

I know we like the sound of a good 4-2-4 especially in Classic and 70's but to take advantage of these current designs motors you need to run them more like a combat engine. Let the rpm get up there and use pitch (4" or less) to control lap time and diameter (10" - 12" with various blade widths) to adjust the pull though of the model in maneuvers.

One thing, no matter what run style you work with, make sure the uniflow tank vent is up out in the free air stream and not below the side of the fuse on a profile (funny swirl turbulence cause pressure fluctuations). Either run a tube through the fuse to the inboard side (above the top of the tank edge) and point it directly into the airstream about 3/16" off the side or make a tube clip the mounts off the rear bolt on the engine and sits about 3/16" above the fuse again pointing into the free airstream. This tip was presented many years ago at a GSCB winter stunt forum. I had a couple profiles that I tried to use the uniflow vent off the top of the tank on the outside edge, that would not hold a run. I remembered this tip and changed the vent, instant solid run. I posted a picture of the vent on my old Ringmaster, this works.

Let us know what you do to get the run you want.

Best, DennisT

wwwarbird · « **Reply #20 on:** February 03, 2022, 06:34:59 PM »

Quote from: Brett Buck on February 01, 2022, 02:29:20 PM

It never ends.

Brett

Air Ministry . · « **Reply #21 on:** February 03, 2022, 09:50:11 PM »

A surface of revolution obtained by rotating a closed plane curve about an axis parallel to the plane which does not intersect the curve. The simplest toroid is the torus. The word is also used to refer to a toroidal polyhedron (Gardner 1975).

Perpetual Motion . or Treadmill .

Phil Spillman · « **Reply #22 on:** February 04, 2022, 03:39:53 PM »

Wow!!! This response was terrific! I do appreciate and thank all of you for your many kind responses! Bob Z-man did indeed modify my FP's head and I am looking forward to trying it out! I will in fact try the high rpm props and mentioned my many above. I have been flying with another friend who has one of the most beautiful running Brodak .40s ever! He's been running it on some off brand fuel but it still purrs on! The FP .35 has always been a better Stunt performer right out of the box and mine has not been any exception except to when it has reached the horizontal 8's when it turns ballistic! If the new head mod doesn't fix the problem I'll simply install 11 X 4 APC or some other prop in my box and go on from there! For the past 24 years I have been flying mostly LA .46's with 11 X 5 Pro Zinger props running either 10N 11/11 castor and synthetic oil. Most of these have run like clock work for me in profile, N/30, and OTS.

Again, Many Thanks to all who have responded to my post!

Phil Spillman

Allen Eshleman · « **Reply #23 on:** February 05, 2022, 05:51:32 PM »

Just notice the pinned thread above on inside diameter venturis! Here on Engine Setup Tips!

RandySmith · « **Reply #24 on:** February 07, 2022, 02:59:42 PM »

The best way to get a better run from the FP 35 and 40
Get RID of the STOCK C/L version muffler, it is too small and causes too much heat, or modify the opening, The stock OS RC muffler would be far better
Get RID of the tiny OS spraybar for one that is .157 diameter, or replace the stock venturi with one that is .255 to .250
Do NOT try to use a 10 x 6 prop, use a 4 to 5 pitch instead
Use a fuel with at least 20% oil and at least 1/2 synthetic

I modified around 300 of the FP series for pilots all over the country as well as many clones GPs Tower etc, the above works

Randy

Robert Zambelli · « **Reply #25 on:** February 07, 2022, 03:55:21 PM »

I’ll admit that this topic has drawn quite a bit of interesting replies, many quite useful and a few just totally off the wall.
Around twenty years ago, my good friend Steve Dinnerman asked me to modify two OS FP 40s for him. He liked the way they ran for the first few maneuvers but then went into what he called a “runaway” – very lean, very fast. He asked me what could be done about it. I had heard and read quite a bit about changing the blowdown by raising the sleeve intake ports. Although I did not feel comfortable cutting through a plating interface, Steve wanted me to try it anyhow – so I did it on one engine.
I then modified the second engine by modifying the squish band, effectively lowering the compression ratio. This may have been done before but I was not aware of it.
I should mention at this point that both Steve and I were looking for more of a “classic” run, as exhibited by a properly set up Fox 35s. In other words, a two-four break. Without running either of them, I gave them back to Steve, to let him decide. I suggested three or four flights with each engine on the same day/same plane/same fuel. He promised not to disassemble them until I gave the word. For identification, I stamped each engine lug with an “X” and “Y”. He preferred “Y” which turned out to have the modified head.
After picking up some used FP 35 and 40 heads, I began experimenting with slightly different combustion chamber configurations. The one shown in the earlier photo suited my needs the best so I used it whenever I modified a head.
I put the 35 and 40 in two different planes. Yes, I was pleased with the way they behaved but what really got me was how many people commented on my engine runs. This happened at a number of contests and I revealed my setup. After that, I did around 30 modifications for friends. Mostly FPs but a few LAs and Super Tigers also. The Tigers had baffle pistons.
The best part was the feedback – EVERY ONE POSITIVE. Not one person was displeased with my work. I almost broke my arm patting myself on the back.
I read that a number of you don’t care for mods – I have no problem with that. The best thing to do is what works best for YOU.

Bob Z.

Phil Spillman · « **Reply #26 on:** February 08, 2022, 08:31:03 PM »

OK Guys, Here's the rest or at least the start of the rest of the Story! When I got home from a Swap Meet on Saturday my hemied head was waiting in the mail box. OH Joy! I went for the rest of my .35 FP and reinstalled my Hemied head! Sunday afternoon several of us WAMS went to the field so that i could try my modified head. The first flight was superb! On and off at just the right places! Second flight ok but not as great as the first. Third flight nothing was going right but over all all flights were much better than any prior flight had been! I believe that the plug is going bad and that I should experiment with different props. These changes will be tried this Thursday morning so I am most anxious to try again!

In my opinion much of the real fun and growth we all experience in this hobby sport comes from experimentation and that's what I am enjoying in this effort!

My fuel is at least trippel filtered. I am running 7:11/11 fuel which is more than adequate for most of the year here in Virginia. The tank is clean and solid without any leaks and the tubing is all new!

My friends with me during the Sunday flying session all remarked how well the engine ran! So I am getting close!

Bob Zambelli did a marvelous job in modifying this engine's head! Many Thanks to You ZMan!

Phil Spillman

Dan McEntee · « **Reply #27 on:** February 09, 2022, 08:01:59 AM »

All the other suggestions regarding plug, props, fuel, tank and such will still have an effect. The engine will still make it's best power near it's designed RPM range peak and prop will affect that. Change one thing at a time and then fly, or you will not know what fixed it!
Type at you later,
Dan McEntee

Phil Spillman · « **Reply #28 on:** February 12, 2022, 03:52:43 PM »

Hi All, Here's the rest of the next cog in this climb! Thursday came and the weather was delightful! Flew this outfit three time which actually could be counted as flights! There were 3 other flights wherreein the plane flew through the three inside loops well but almost immediately on exiting to inverted the engine quit! This happened twice and I lowered the tank from the upright position. That worked but not completely to my satisfaction. Next I installed an 11X 5 Pro Zinger and tuned the needle to its wet 2 setting. Bingo! It was a happy bird! However the wind came up hard and we left.

Today, 2-12-22, the early time were great low wind and warmer temps about 55 degrees F. I set the needle at it's wet 2 position and flew three reasonable patterns. Then I tried to get the really sweet "Stunt" run and it all went away! Lesson learned and I'll stick with the wet 2 setting until I don't like it any more! From the comments I got from the viewers, the plane never flew any better and I just have to be happy with what I got!

Thanks again for all of the input!

Phil Spillman