Author Topic: os fp 35 engines (Read 7313 times)

Bootlegger · « **on:** April 18, 2016, 12:23:45 PM »

Guy's I have an os fp 35 with a .277 venture, long reach idle bar, and plan to run 10% P/Master fuel, on a model with about 550 sq in weighing about 48 oz, what prop would you suggest and why?

Thanks

Dane Martin · « **Reply #1 on:** April 18, 2016, 12:37:57 PM »

Something with some low pitch, cuz those things are too much power! Lol
I ran a 10x3 on a magician. I didn't like it because my plane only weighed like 29 oz. I should have had a .20 on it

Geoff Goodworth · « **Reply #2 on:** April 18, 2016, 07:00:12 PM »

Gil, what NVA are you using? If you are using an ST NVA—4.0 mm OD—your venturi is probably fine. If you are using the OS NVA—3.5 mm OD—it's almost certainly too big. The stock venturi for the FP 20/25—6.55 mm ID—is probably more appropriate—if you are using the OS NVA.

I would try the APC 10.5 x 4.5 for starters. You may have to go flatter.

Tim Wescott · « **Reply #3 on:** April 18, 2016, 07:34:08 PM »

What Geoff said, but -- you can pile on layers of pantyhose material over the venturi (hold 'em on with an O-ring; a rubber band works for about a month before it turns to goo). This works like a restricted venturi, but you can fine-tune the amount of restriction.

I do it on all my engines; works a charm.

Geoff Goodworth · « **Reply #4 on:** April 18, 2016, 11:25:37 PM »

But Tim, my wife hasn't worn pantyhose for a decade or more.

And I do not dare ask the 19 year old next door.

Tim Wescott · « **Reply #5 on:** April 18, 2016, 11:51:46 PM »

Quote from: Geoff Goodworth on April 18, 2016, 11:25:37 PM

But Tim, my wife hasn't worn pantyhose for a decade or more. And I do not dare ask the 19 year old next door.

Just go to the store, find the prettiest salesgirl you can, and ask her which color goes best with your skin tone.

Bootlegger · « **Reply #6 on:** April 19, 2016, 08:28:30 AM »

I am running an .077 venture, with a R Smith N V A ...As for as I can tell the engine is stock, with a stock cyl head..

Dennis Moritz · « **Reply #7 on:** April 19, 2016, 11:58:47 AM »

No. OS offers (still offers) two venturis for 35/40/46 FP/LA. S and L. 6mm 7mm. Large works out to .283. With a plane of that weight you'll need the L. Large. Free flowing muffler. 10.5x4.5 apc sport prop. Good place to start. I like the fuel. Venturi matches to the OS clicker needle. I've run many stunters in this weight range with this combination.

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RandySmith · « **Reply #8 on:** April 19, 2016, 12:19:47 PM »

Quote from: Bootlegger on April 18, 2016, 12:23:45 PM

Guy's I have an os fp 35 with a .277 venture, long reach idle bar, and plan to run 10% P/Master fuel, on a model with about 550 sq in weighing about 48 oz, what prop would you suggest and why?

Thanks

Many people use the PA NVAs or ST NVAs, these are a standard size of .157, and use the nominal 280 size, if you use the tiny OS 20 spray bar that is 130 or 135 us the .256 OS venturie or similar, Do not use the larger bar with the small venturie, or the large venturie with the small spraybar, Yes you can maybe make it work running a 2 cycle, but it is easier the above described way, The 46 will pull that setup loafing

The OS stock S venturie is 6.5mm .256 inch ID
The L OS stock venturie comes in .277-.283 size?? I have checked many and don't know why the 2 sizes

Randy

Bootlegger · « **Reply #9 on:** April 19, 2016, 01:45:10 PM »

The damn thing is running "goofy" run away lean then too rich. I changed to a .257 venture with all other things the same, no different in the runs.
I am thinking about adding some oil, both syn and castor, maybe 1.5 oz of each in what seems to be about 1/2 half gallon of fuel.
What is the thinking on this? Is the venture too small? Boy, this is aggravating to no end...

Tim Wescott · « **Reply #10 on:** April 19, 2016, 01:54:53 PM »

Quote from: Bootlegger on April 19, 2016, 01:45:10 PM

The damn thing is running "goofy" run away lean then too rich. I changed to a .257 venture with all other things the same, no different in the runs.
I am thinking about adding some oil, both syn and castor, maybe 1.5 oz of each in what seems to be about 1/2 half gallon of fuel.
What is the thinking on this? Is the venture too small? Boy, this is aggravating to no end...

If you mean that from flight to flight it's either too rich throughout the flight or it leans out and runs away, then that's usually a sign that the venturi is too large, or that there's some problem with the fuel system.

In my (OK, somewhat limited) experience, necking the venturi down will give you more consistency but less power -- until, eventually, you have a 100% reliable engine that won't pull you through a pattern.

Try it with and without muffler pressure, see if one or the other makes it happy.

Double-check the fuel system, make sure you don't have any tank problems, pinholes, dirt, etc.

Dunno what to suggest beyond that.

RandySmith · « **Reply #11 on:** April 19, 2016, 01:56:56 PM »

if your using my NVA then use the L venturie , around 280, use 24% oil part castor is OK. check for any binds, and it maybe good to remove the head and inspect the sleeve inside, how much time does it have on it? do you know if you have a steel/iron FP or a ABN FP ?
use open uniflow, no pressure, check the tank, make it close to the engine

Randy

Dennis Moritz · « **Reply #12 on:** April 19, 2016, 04:11:08 PM »

Fp stunt engines 40s and 35s were shipped with small and large intakes. Obviously those engines were using OS needles. I always run muffler pressure to unifo unless there's vibration issues. Then I run muffler pressure to overflow and cap unifo. Fp stunt 40s and 35s were also shipped with extra head gaskets. These engines are meant to be tuned to the aircraft. Weight drag will determine engine set up.

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Dennis Moritz · « **Reply #13 on:** April 19, 2016, 04:22:24 PM »

Sounds like this fp 35 is set too rich on ground. There's a false sweet setting sounds great on ground engine heats up in flight run run runaway. What fuel consumption? I suspect you're using 3 ounces or so for hyper pattern. Not enough fuel going through engine to cool it down. A well set up Fp or Tower will use 4.5 ounces maybe a tad more for a pattern. This cools and stabilizes run.

For a plane of the weight you describe you need a big Venturi and free flowing muffler. Usually a tongue with a lot of holes. Both contribute to cooling. Set the engine at a 2 stroke with a slight miss. Try the 10.5x4.5 prop.

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Steve Helmick · « **Reply #14 on:** April 19, 2016, 06:34:38 PM »

Nothing specific has been said about the muffler, but I know that the "stunt" muffler that came with genuine .35/.40 FP-S engines was very restrictive. That creates heat, and contributes to the "runaway" problem, as does too much prop load.

Steve

Brett Buck · « **Reply #15 on:** April 19, 2016, 08:50:22 PM »

Quote from: Dennis Moritz on April 19, 2016, 04:22:24 PM

For a plane of the weight you describe you need a big Venturi and free flowing muffler.

You *do not* need a big venturi for this model. The engine, with the stock parts and stock small venturi, is a very good runner and will easily fly a Nobler-sized 48-ounce airplane with no special effort. I flew my ST46 airplane (630 square inches and about 48 ounces) with an iron-liner 35FP and it flew about as well as it did with the ST. A much smaller airplane will fly much better than that.

Brett

RandySmith · « **Reply #16 on:** April 19, 2016, 09:52:44 PM »

You do not need the "big" venturie if your using the stock OS NVA, if, as you stated your using mine, then YES you need the "big" venturie, it is really not big with a .157 diameter bar across it, it is big with a .135 diameter across it,
and if your using the tiny tiny hole stock 742 muffler, that can be a problem, as it is very very restrictive and causes lots of heat in the engine,
Stay away from muffler pressure until you get things sorted, that engine Will, as I said earlier fly that plane with ease, and it will pull a wide range of stuntships.

Randy

Dennis Moritz · « **Reply #17 on:** April 20, 2016, 05:18:48 AM »

Stock FP Stunt engines came with 2 venturis. S and L. L is stock. Tower still lists them. Currently I'm using FP35s,40s,Tower 40s, in: Oriental, 2 Vectors, Tanager, Galaxy, RD1. I have run them in dearly departed Vectors, a Prowler, a fab cheater Magician weighing 32 ounces, a Buster, Twisters and stuff I am not remembering. Club members are running them. If the tank is good, if the filter and needle-valve are clear, if the muffler is free flowing, if the fuel is right, if the prop is right, if vibration issues are handled, engines run well set up the way I described. Often we go to the Large venturi to pull draggy models weighting over 40 ounces. We use the OS clicker needle. The Supertigre style needle has its advantages. A finer adjustment. We find the OS needle good enough for our applications.

I often cringe when I see questions about FPs on these forums. Without the model present at the flying field, where it can be flown and directly trouble shot, answers are at best hit or miss. Tank issues, vibration, engine mounting, something in the filter, a barely visible spec in the needle, a needle out of alignment, a venturi gasket not sealing, and so on, can all defeat an excellently setup FP or any other engine.

The FP35 sounds like its muffler needs to be opened way up. I would also go to a .283 (L) venturi even tho the .277 is nearly there. It fits a classic runaway scenario. I suspect insufficient fuel is going through the engine. Any of the other issues I mentioned could also be the problem.

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Geoff Goodworth · « **Reply #18 on:** April 20, 2016, 06:41:56 AM »

I sense a bit of confusion re the factory venturis.

When they were first introduced, OS supplied two venturis with the FP 35 and FP 40. They were 6.75 mm ID and 7.1 mm ID.

The 6.75 mm venturi is no longer available but the 7.1 mm part was the stock venturi in the LA 46 S. It may have been supplied with the LA 40, but I don't know—I've never had one.

There is a smaller factory venturi available—the one for the FP 20/25 which is 6.55 mm ID. I use this venturi and run a 6.75 mm reamer through it to produce the intermediate size. While this is not best practice, when taking out ~0.008", I don't think it matters.

There was an article in Stunt News some years ago where the author said that the 6.55 mm venturi, with the OS NVA, was successful in preventing run away in a stock FP 40.

We have a multiple Australian champ at our club who had good results with a stock LA 46 fitted with the 6.75 mm venturi. His muffler has been opened up to about 9.5 mm diameter.

I tried an FP 40 fitted with the 6.55 mm venturi and the 6.75 mm venturi in a 565 sq in model weighing 58 oz and it ran away with either venturi. I tried a hemi head scooped out to Bob Zambelli's spec and still it ran away. I fitted an LA 46 with the 6.75 mm venturi—success. Today, the FP 40 with the hemi head, 6.75 mm venturi and stock Randy Smith lightweight tube muffler is drawing positive comment for the engine run in an ARF Cardinal weighing about 51 oz.

In all cases, these engines that I have observed or used have run the factory 3.5 mm OD OS factory NVA.

We have an interesting mix of NVA preferences at our club in Sydney. Some prefer the positive click-lock action of the Factory NVA, while some prefer the infinite adjustment of the ST-type NVA from Randy and others. Plus we have the luxury of a Steve Rothwell collet-lock NVA—like the ST—with a 3.5 mm OD like the OS factory parts. Then, for those engines that need a 4 mm OD NVA, we have the choice of the infinitely adjustabl NVA from Randy, Steve Rothwell. et al, and the click-lock adjustment with the Enya NVA. So many choices!

Dennis Moritz · « **Reply #19 on:** April 20, 2016, 06:56:58 AM »

Fps will run with the smaller venturi. If the muffler is opened way up so that enough fuel can move through the engine to cool it. In larger models over 40 ounces or so, or so, (depending on drag, even the specific engine) will need the larger venturi for increased power. That's my experience.

Another factor. FPs, Tower 40s, and similar bushed engines vary in factory tolerances. Fit between crankcase and crankshaft is critical. Recently I have been running a Tower 40 on an Oriental. It was down on power compared to other Towers I use. The piston/cylinder fit is excellent. Almost no observed bleed down. A combat flier clued me into what was happening. He noticed a significant amount of black exhaust residue. He concluded that the crankshaft/crankcase fit was lapping in. In other words, engine was breaking in. As I continued to fly the plane the black residue diminished. Power came up. Engine run, always good, appeared even more consistent.

Bootlegger · « **Reply #20 on:** April 21, 2016, 10:11:33 AM »

I haven't installed it on a model yet, just trying to get stable runs on the bench. Is the 10.5x4.5 too much prop? As for the muffler I am running an after market tube muffler with about a 3/8" outlet, so I don't think that restrictive .
I have some 10x4 props that I can try, but I don't think this is the problem, I still wonder if there is enough oil in the fuel? Again thanks for the advice...

Tim Wescott · « **Reply #21 on:** April 21, 2016, 10:22:20 AM »

Quote from: Bootlegger on April 21, 2016, 10:11:33 AM

I haven't installed it on a model yet, just trying to get stable runs on the bench. Is the 10.5x4.5 too much prop? As for the muffler I am running an after market tube muffler with about a 3/8" outlet, so I don't think that restrictive .
I have some 10x4 props that I can try, but I don't think this is the problem, I still wonder if there is enough oil in the fuel? Again thanks for the advice...

That changes things. Whatever you'd run in the air, you need to go down in size for bench running. More prop than you need (because no airspeed) and low airflow (because no airspeed) will work together to overheat the engine. I'd try the 10x4, and if you get it so it's almost right figure that you're probably close enough to warrant slapping it on a plane and trying it out.

Was it new in box when you started with it, or did you receive a big ball of varnish with an engine somewhere inside? My flying buddy will give me hell about my own engines when he sees me say this -- but if it's really gummed up inside and out it may be getting hot from that. A good cleaning, even on the outside (yes, Tom, I hear you) may work wonders.

Bootlegger · « **Reply #22 on:** April 21, 2016, 11:41:27 AM »

I got it new..

Tim Wescott · « **Reply #23 on:** April 21, 2016, 11:43:04 AM »

Quote from: Bootlegger on April 21, 2016, 11:41:27 AM

I got it new..

Still, if you're bench-running it you have to take into account the fact that it's going to tend to get hotter than in a real plane -- I'd try with a 10x4 prop (assuming you'll run a 10.5 x 4.5 in the air). Or just bolt it onto the plane and go fly.

Dennis Moritz · « **Reply #24 on:** April 21, 2016, 11:52:10 AM »

Uhh. An uneven run on bench. Check the needle valve. Reverse flush. Check fuel tubing for pinholes. Check tank. Make sure no leaks. Check Venturi is it firmly seating on gasket. Is the needle valve hole pointing down parallel to Venturi sides. Is needle valve tightly cinched with nut so it doesn't move. Are you getting leaks from backplate. Check gasket check tightness of backplate bolts. Check headbolts. Sounds like a leak somewhere or weird tank if run is erratic. Lean rich lean rich. Prop is fine. If an abn do not run real rich. Run fat 2 stroke. Later gotta go.

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Gerald Arana · « **Reply #25 on:** April 21, 2016, 12:59:52 PM »

Quote from: Dennis Moritz on April 21, 2016, 11:52:10 AM

Is the needle valve hole pointing down parallel to Venturi sides.
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Wrong position for the NV hole. It should be just out of sight, front or back (Your choice) NOT straight down!

The most suction (vacuum) is at the smallest point of air/fuel flow. Does that make sense to you?

Hope I explained that right, but if I didn't I'm sure someone will correct me......

Jerry

Dennis Moritz · « **Reply #26 on:** April 21, 2016, 02:20:42 PM »

You might be right. But I set the hole like I stated. Lotsa of engines I've set up run just fine.

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Bootlegger · « **Reply #27 on:** April 21, 2016, 02:37:28 PM »

The needle valve hole is in the apprixmate 7 clock position from one side and 5 o'clock from the other side. I have all my engines set up this way.
Next visit to the shop will have to try magnet and see if the piston is steel or alum.

Bill Adair · « **Reply #28 on:** April 21, 2016, 03:58:40 PM »

Those refrigerator magnetic signs are good for only two things that I know of. I use them to hold photos or notes to the fridge, and to slice a quarter inch strip off one end, and lay it on top of the FP piston to see if it sticks.

Some of the FP engines have a different size bypass bulge, but I don't know about the 35's?

Bill

PS got your check for the tank. Thanks!

Geoff Goodworth · « **Reply #29 on:** April 21, 2016, 08:46:47 PM »

Guys, this has been discussed before but the late model FP 20, 25, 35 and 40 look like this—with the soft curve—around the transfer port on the exhaust side and the boost port on the other side.

Unless somebody has messed with it, an engine with this crancase style should have the ABN piston and liner.

Geoff Goodworth · « **Reply #30 on:** April 21, 2016, 08:50:59 PM »

Although this is a Magnum 40, the crankcase shape is the same as the early—iron piston—FP 20 25, 35 and 40.

The only caveat that I will put on this is that I bought a new FP 20 from a hobby shop that had this crankcase style and an ABN piston and liner.

Geoff Goodworth · « **Reply #31 on:** April 21, 2016, 09:07:17 PM »

I agree with Dennis Moritz on the positioning of the spraybar hole. There is a great deal of turbulence in the wake at the back of a cylindrical body and it can fluctuate. See https://www.eng.fsu.edu/~shih/succeed/cylinder/cylinder.htm

Maximum flow and vacuum are on the sides so placing the hole just out of sight puts it in the region of maximum vacuum—and smooth airflow.

Spraybars with two holes usually have them approx 170° apart so they are placed in the area of maximum vacuum.

If you put such spraybars in the wrong way, you get a lot of fuel spraying out of the venturi—and don't ask.

Dennis Moritz · « **Reply #32 on:** April 21, 2016, 09:50:24 PM »

Fp35s same as FP40s came in ABN or steel cylinders. Steel Cylinder engines have the bulge longwise on the exhaust side. For one reason or another I have run mostly ABN and Tower 40s a near FP clone with a true chrome ABC cylinder. Towers are probably better machined as well. Are the variations in run happening on the bench? Apparently so. If the run is erratic. Won't keep a needle setting, goes lean to rich, back and forth, sounds like one of the basic issues I itemized above. The list can be longer no doubt. It the run is erratic, shifting back and forth, running fast then slow, issue is not typical FP runaway. Something is wrong with engine or there's an issue with the fuel system. If the crankshaft bushing is worn out, that can also cause erratic running. Lots of fuel would be coming out the front end. Check for crankshaft play. FPs, when operated correctly, do not typically wear out the front bushing. Unlike Fox35s. But it can happen after long hard use. If the front bushing has noticeable vertical and horizontal play as you look at the engine from the side, could be trouble. Crank movement back and forth, does not usually effect the engine's run. Ahh. See. The list goes on and on. Part of why diagnosing without engine in front of us, hit or miss.

Bootlegger · « **Reply #33 on:** April 24, 2016, 03:52:05 PM »

Today I got another tank and put it on the bench with the engine, same fuel, plug and a 10x4 prop, the engine ran great for both tanks (3oz) of fuel, BUT yesterday I ran a Fox 201 on that earlier tank and it ran just fine.

Still don't unnerstan the problem??
Any got a guess???

Dennis Moritz · « **Reply #34 on:** April 25, 2016, 03:32:10 AM »

Bad vibes. Harmonics. Or. Which is why it's hit or miss trouble shooting when engine and accessories are not here and now. Look at this long thread. Look at all the blah blah about FP engines.

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Bootlegger · « **Reply #35 on:** April 25, 2016, 07:39:56 AM »

It didn't have bad harmonics with a different tank though, and as I said the Fox engine ran well with the old tank on the same bench set up.

I changed tanks and the 35 ran very well, just changed tanks only...

Thanks for your input...

Dennis Moritz · « **Reply #36 on:** April 25, 2016, 03:29:54 PM »

That happens. Different engines have different vibes. Even same models. Fox 35 FP35 very different. Will the Fp hold a close to max rpm setting. Don't run it screaming lean. If so. Fly it.

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