Hi all, the weather in Belgium is not allowing a lot of flying, so I am now starting to experiment statically with an OS 40FP.
I am not using this engine in any model, but some club mates are using them on many models with variable success and a lot of frustration.

So I purchased on Ebay a second hand RC version, put on a 7mm venturi, a 4mm Enya spray bar and an OS standard OS40 muffler.

Perfect compression and not too much signes of extensive running.

10x4 prop to start with

On the testbank with 78% methanol, 15% Klotz and 7% castor.
Static uniflow tank, No muffler pressure

Findings:

A good starter (even at 0 degrees Celcius).

After 5 minutes running in a decent 4 stroke, i pinched the fuel line and hopla, 2 stroke mode and very reluctant to return to the  4 stroke.
An attempt to run it in a rich 2 stroke was not possible. full 2 stroke or full 4 stroke. Nothing in between.
Not an engine I would put on my model with this behaviour.

It is my purpose to make this engine behave properly for my club mates. It is meant to be a "learning experience" track to pass this winter.

So what is the plan (any extra suggestions are more than welcome):

1. Perhaps the engine needs more break in. So I will let it run for an extra 30 minutes
2. I will try a 30% (20 Klotz 10 Castor)oil fuel. Just to see the effect of more oil .
3. Muffler pressure. I am not really in favour to mask a bad engine behavior with muffler pressure. But who knows...
4. A smaller venturi (from an OS25)
5. colder glow plugs
6. Less compression
7. Other head shape(s) (smaller squishband and deeper dome)
8. Blocked boost port

I will keep you informed. I don't have the tools to make changes to the port timing. so this is something I will not touch.

Any feedback from FP40 experiences/ experiments are welcome. Fun!
Paul

I'm no expert but I think that a smaller venturi with the enya NVA will throttle the engine too much.

Steve

Apart from first stages of running-in, it's usually very difficult, or impossible, to draw any useful conclusions from bench running. Waste of time and fuel.
But if you insist, how about less load to better simulate the level flying load? 9x4 or so.
Also, I think in this case the *7* will be counter-productive, or at least prepare to use more nitro. With small engines it's quite crucial to have an efficient and clean burning process, and probably the head shape that OS ended up with is about as good as it gets.
The best running LA's I've seen are straight out of box, apart from Venturi & muffler maybe. L

Think I got fleeced on a NEW one of these . Was not exactly tight . Running 9 C / 9 S / 5 Nitro , to try'n tighten it . Playing musical pistons with other ( used ) for decent fit . So BEWARE . Europe should be o.k. ?



A LOT STRONGER . 12 x 4 props good . So if your spending loot , look out for them . Head patterns 45 FSR . Rods al the same . As is GP intakes - cinch bolt type . FSR 45 gives better 4-2 than 40 , too .

44 GP with the thre ports is probly stronger than a LA 46 , which has two .( NOT the Magnm 42 ! )



Oily recomended , for a FP 40 FIT .

Top Ends Interchange .



and the 40 FSR for the 40 FP .almost . C clips - Pads . must have clips in FSR .

I hate to be a Johnny one note, but, it seems very clear that your venturi is too large, not even being able to needle it on the ground is the absolutely classic problem. I do note you aren't wasting your time with a 10-6 or something like that, you will get best performance with a 10-4, 11-4, or something even lower.

So what is the plan (any extra suggestions are more than welcome):

1. Perhaps the engine needs more break in. So I will let it run for an extra 30 minutes

Almost certainly not, but benign

2. I will try a 30% (20 Klotz 10 Castor)oil fuel. Just to see the effect of more oil .

   That will almost certainly make it worse, particularly at 32F. It's not overheating, and 30% is going to turn the oil to Jello at those temperatures - making it harder to pull it through the fuel line, which is already a problem.

     A more interesting experiment would be to use something like 18% all synthetic - again, it's not going to wear out or overheat when it is freezing outside. That gives you an outside chance with the existing venturi.

3. Muffler pressure. I am not really in favour to mask a bad engine behavior with muffler pressure. But who knows...

    You are not "masking bad behavior, you are overcoming the problem it probably has, which is more directly solved by:

4. A smaller venturi (from an OS25)

The .276 ("7 mm") venturi with the stock spraybar is marginally too large, it is particularly worse with no nitro and 22% oil at freezing temperatures. Normally you would need less nitro with temperature, but you need more nitro to handle the larger venturi (to make it less touchy to needle). The cold fuel is much thicker than it would be in the summer, it might work OK if it gets up to 85 degrees or higher, but at freezing, it just aggravates the fuel draw issue. The .257 ("6.5 mm") is huge change and will greatly improve the fuel draw, which is the right direction to solve your problem, but may be overdoing it. It might be apprpropriate way to deal with the low temperatures - which will give you more oxygen per unit volume.

5. colder glow plugs

   No, that probably make it worse.

6. Less compression

   Maybe, but if a .005 shim does not fix it, that is not the problem. Lauri is also right, you can't determine this by a ground test - it won't even needle on the ground, there is not point to trying to fly it, and flying is the only way to determine the right compression.

7. Other head shape(s) (smaller squishband and deeper dome)[/quote]   Nothing about this suggests anything wrong with the head.

8. Blocked boost port

Reducing the power with no other changes just makes the problem worse, not better 

I will keep you informed. I don't have the tools to make changes to the port timing. so this is something I will not touch.

   Nor should you, all this "raise the head/carve the head/grind the ports" nonsense is classic stunt BS. Other people have made it work with a stock head, stock compression, and stock ports, therefore, those are not the problem. The only thing you are doing different is the FAI fuel, that makes it more touchy, but you certainly aren't going to need less compression going from standard fuel to FAI, if anything that would suggest adding compression, not reducing it.

   It won't needle, that means the venturi is too big for the power level, fuel viscosity (very high because it's cold outside and you have a good bit of castor oil), and nitro. Fix that problem, fly it (keeping it out of a 4-stroke in level flight), adjust the speed with the pitch.

    Brett

I have a question.  Is the 6 mm venturi too small?  This is what I have been buying with the OS size NVA for conversion of LA 25, 40, 46 and FP 25,40. Should it be bored out just a little?

Hi Brett, thanks for the  great feedback. So if I understand it correctly, you state that not being able to maintain a stable rich burpy  2 stroke is due to the insufficient fuel draw. It holds a full 2 stroke and it holds a full 4 stroke easily. But in between is impossible. I was rather suspecting a heath problem, creating an advanced ignition timing, making the engine not wanting to return to the (colder) 4 stroke. I will take your advise and go further with muffler pressure and the smaller NVA, although the Enya 4mm spraybar is already reducing the venturi opening, compared to stock. Testing with a 9-4 for less load is also a good hint. Thanks Lauri. ( I will not be able to make to Turino in June :-( ) ...

  You probably should have mentioned you were using an off-brand spraybar and drilled a hole in your engine. But don't disregard the outside temperature increasing the fuel line drag, that is a potentially critical issue here, particular with lots of castor oil.

      Brett

p.s. I note that you don't really need it to needle all the way from blubbery rich to peaked out lean, and that is not important. You want to run it in a 2-stroke because that is where it is stable, you need just enough needling  be able to adjust it in a 2-stroke, and the correct venturi and prop to achieve the desired power in-flight. Depending on what airplane and what prop you are using, that could be really small (small airplane and higher pitch) or relatively big (big/draggy airplane and low pitch).

    Over the decades, most of the problems I have see have been trying to use too much pitch on too small an airplane. These engines are *much power powerful* that ancient 4-2 break baffle-piston engines, and you generally can't use them (unmodified) on traditional "35-sized" airplanes. They meant a 35 from 1955, not 1990. Trying to do that start the spiral of "runaways" (which means the engine working the way it was always intended), leading to "modifications", which are the bane of modern stunt.

Another ' thing ' from the early schneurle era , was ' engine bay venting ' Ducts OUT , Hole up through the top block , canopy , or a bore Ea Side through or above bearers .

General opinion was it was neccesary with the H P 40 & FSR , to have CRANK CASE Cooling . The FP runaway is generally atributed to overheating . As its the SAME TOP END ,
if fully cowled !!  some consideration to airflow through over the cranckcase mightnt be a bad idea .

Maybe the stock big FP venturie , with the 4 mm Spray Bar , gets it into workable areas . Or the Lighter Fluid added to avoid flame out , if things are all wintery .

They all mutter about MUFFLERS being intregal to the FP 40 Behaving , Gotta be the ' correct ' one , which isnt the ' other ' one .  Perhaps someone'll enlighten us there . Or try Search .

I'm not at all familiar with trying to run this engine without nitro,  but we (myself and several family members ) have run these for years and even now have a couple airplanes so equipped.  The first "problem" is I think HOW you are trying to run it or what you are trying to achieve.  These engines are not set and timed-designed to run a 'stunt run'.  Never will cycle as you seem to be asking for.  People have been bashing these for years trying to get a 'Fox .35' type run-ain't happening,  at least without remaking the engine into something other than an FP .40.  These were designed to run mostly flat out as a sport RC engine.  We have good luck running them box stock with an 11-4 APC or similar and in a solid two cycle-forget 4 cycling.  They do pretty well in this mode.  I do the same with the Thunder Tiger .42 which is yet considerably more powerful than the FP.  The frustrating (to Me) downside is that this pretty monotonous run yields a decent level lap speed but slows down considerably in maneuvers. There is really no reserve power to reach for.  Once back to level flight the airplane is back to normal level lap speed.  It can be hard to notice until you go to an airplane that doesn't do that and realize your timing is all messed up.  For me and this type use, like on a profile, I've gone back to the Enya .45 or ST. 46.  These more properly cycle up and down and maintain a more constant airspeed between maneuvers and level laps.  The FP is hard to beat for general flying if not overly nitpicky like I am AND if you use it's strengths by letting it run in a style it prefers.....Dave

Hurumph ,

WEIGHT , Id think say 50 ounces is a ' good ' weight , for a FP 40 ? ( Others chime in , Its just a guess . ) My Caudrons picked up some , changing it from clockwise to anti clock . 60 + struggles a bit with the FP 40
or at least isnt authoritive power . BUT it De Tooned with the HEMI Head . The prop I think was right for the barometer . The MUFFLER was the long Adamisin ribbed tube muffler - sounded brilliant if noisy . But the
cows didnt seem bothered out there .

Mr Urtnowski , in parts , goes on ABOUT PROPS considerably ( You can see the reasearch Dept. has the research , So comments are not neccesarilly MY observations , but the general aerobatic communities ! . 

TEMPERATURE / BAROMETER . quotes :

Cold Weather theres more bite , a fine pitch prop is required , 4 or 5 on ST 60 . High Temperature and altitude , ( the Reno Nats ) High Pitch Required . 6 or 7 on ST 60 .

SO if its snowing and youve got a FP 40 , you might need to go to three inch pitch , or down to 10 in so as not to overload the motor .

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I don't want to hear an engine to go overlean at the top of the vertical 8 :-

The Oh Fudge bit , is if it STAYS LEAN , If youve not got it doing that , thats one less problem .
Usually regarded as THE problem with the F P's .

In Kiwiland in the 70s NITRO hadnt yet been imported by the Drag Racers ( about 75 it was - then AFFORDABLE )

O S engines had the reputation of being fine , with No Nitro .
If theyre starting o.k. , and theres no rpm drop pulling the electrickery off the plug , that should be o.k.

But theyre NOT going to needle as well or give the tourque of running NITRO . 5 % is to even it out / needle better . 10 % is to get some more Boogie . Turn More Prop .

SO , youre gunna wanta bit less prop than a Nitro Man .
It should have a 1/2 turn range minimum on the needle . Preferably a 1/2 turn ' in the zone / from min workable to max . Better 3/4 but thats probly nitro territory .
Think the old OS max 20s from the 70s were 1/3 turn , stop to start .
A GOOD set up was the COMBAT Nose Up , turn in till it goes dry - then out 2 to 3 clicks . Then shake the snot out of it to see it stays running , sometimes takes a click or two more juice .
Ive tried this for a laugh on F2B stuff , in generall it gives a excellent needle setting .


=====================================================

Have you tried multitudinous glow plugs on the same device , to find THE GOOD ONE , for that set up .

The Stuka Stunt FP's , tickuly the 35 ( the Liners Interchange ) was blocked boost & Hemi Head ( they say ) to swing some lumber . 12 inch & suchlike with a bit of pitch .
SO it may be worth doing ONE engine as a test set up - for your semi arctic set up .
If you had a dozen lawn mowers you could try souping one up , tune pipe'n all .

I think its the 7030 muffler thats required , or the TOWER one . ( Not the Small control line 40 S one ! )

ALSO , blowing a long fuel line through all the fuel tank pipes , and putting the tank to your ear , will tell you if theyre all ' FREE FLOWING ' If its straggled & whimpy , THATS the problem .
Fuel Line Runs were semi critical , no nitro seems to suck less , the olde neoprene clear plastic days , it needed tucking up adjacent the bearer ( Side Mounted ) to avoid drying off on inside loops .
Also the fuel had to be up near to the intake , a empty line , the prime'd be gone before i'd dragged the fuel up . So maybe the tank wants to be imediately aft of the engine , not set back more than 1/2 inch .

 

Paul,

Since you are doing extensive ground testing for these experiments, and since you are convinced that the lack of thermal stability is a major factor in unstable ignition timing, why not run a test where you set the engine close, then spray a continuous stream of water on the head? You could use something like a fuel bulb to do this. Then you can consider the results.

On the other side of this, as a practical consideration, would a larger heatsink head really be worth the weight to help stabilize the setpoint? And why exactly do other engines perform the cycling run with little difficulty without a large heatsink head? The Fox .35 which seemingly defined the 4-2-4 run has minimal fins on the head and cylinder. Just a few thoughts....

Good luck with your project. It is interesting....

Dave

I am convinced that the slow retun to a rich lean run has to do with heath. The combustion chamber apparently remains too hot , advancing the ingnition, creating even more heath.

Ere's an EATH .



Whereas , EAT .



We wont get onto Solder !  Just taking the micky . Now SERIOUSLY .

1. See the Adamisin's recomendations 18% oil " Oil reduces the OCTANE RATING ."

Therefore 23 % oil fuel will have lower octasne than 18% oil fuel .

2. Heat Dam . Generally , Aero Products / Mr Smith - cuts a groove about the plug ( in the head ) to RETAIN Heat in the Plug .

3. The Super Tigres are offten ' De Head Finned ' to reduce heat loss . Said to get the stable rich burbly run Thus .
   
    As a Aside , the Big Jim recomendation of 6 Oz   fuel Consumption for the 60 - to cool  - Is comparable to your LARGER INTAKES BETTER .
    More Fuel Reqd. for same mixture ratio , with the more air . So in a sense you could say its richer . In the matter of it getting MORE FUEL .

4. The ' wont switch back ' , is generally state to be CRANKCASE COOLING related . As In , if theres NO AIRFLOW across the crancase , it wont ' switch ' back rich .
    probably fuel vapouriseation , in the case - creating a gas . rather than the atomised vapour ! . Which shows how misused werds are .
http://aeromodelbasic.blogspot.com/2012/02/fuel-spray-nozzles.html

As in the mixture becomes vapour - gas - in a uncooled crancase . Whereas it should be vapour , like mist is . Upper cowl cooling vents on inverted FSR's were said to be mandatory . , Mc Donalds , Cassel , Baron etc .
AND the motor ( FP ) is a plain bearing FSR .

Tecnicly you have 5 % over 18 % ( oil ) . 1.277 less octane ? . or 0.78 octane of 18 % fuel , perhaps . STRANGE thing was pre ign. sound - rattly hammery ish of GP40 ( FP ) on the Hemi Head - out west . Not in Town .

AND FURTHER . the ball race FP - FSR -> the Fuel tank hight REQUIRED is 1/8 low - on a inverted arangement . Suggesting FPs also might like the tank in the right place .
If on a Test Bench , the Tank is NOT centered on the spray bar , as in if its miles of , THAT could cause all sorts of bother .
Thus , if your ' test bed ' isnt an aircraft - Trying getting the TANK HIGHT right for same speed run upright & inverted might be required . Id go forther to the same angle , 20 or 30 degrees , for the SWITCH to 2 stroke .
as in same of horizontal upright & inverted . But first get 1/2 hight at the spraybar , if its a ' test plank ' and have 1.2 inch clearance aft of the backplate so its not in stagnant airflow . 

AND check the fuel , some of mines OF , with the big Covid Winter . Antique even . Older than a year methanol is suss . Unless in a brimmed sealed container , even plastic can breath a bit , so sealed plastic containered fuel can be hygroscopic .

Yea , go at it all ways .

I had ( have ) a FSR 25 that it was very difficult to get a bad run with .

Side Mounted . 7.5 intake, 3.5 taipan spray bar, rattly needle. Seal it and it was usless .
See : ' atomiser tube ' = Weber ' Emulsification Tube " . 
Cowled bottom end , unvented .

Not my idea , but the speedups generally atributed to oveheated C'case . ?

You could use a leaf blower to unload the prop.

More nitro! Seriously.

I'd also try less cooling, as well as more cooling. Wrap 1/64" plywood around the engine's cylinder fins and secure with a rubber band. It will be interesting to bench run it with and without, I promise. Mine was slip on and off, so I could take it off or put it on while running the engine. The NV will need to be opened a lot with the cooling blocked.

Most of my speed models had no cooling through the cowl, but the head was exposed. If I knew I'd have fuel consumption issues (i.e., not enough space for fuel), then I'd build the cooling duct through the cowling and expose the head. Less cooling increased fuel consumption by a significant amount. Exactly opposite of what the Physics books predicted, of course.
  Steve

We run these stock. Vary venturi some. I like a .273, halfway between the large and small OS venturis. 10.5x4.5 apc prop. Run them 2cycle. If it runs a slow two stroke then runs away, lean up on ground before you fly. You're trying to run the engine too slow. Powermaster 10% 22% oil (50/50) is easier to set than 5%. %5 can work. If your model is light, 28 ounces or so, you can add a few head gaskets to soften break. You do get a slight break when needle is adjusted to optimum setting. The stock OS needle works, but is pretty crude. Optimum setting is often one click is right, one click off either way, not so good. Supertigre style needles are way more precise and easier to adjust.  Aim for a steady two stroke setting on the fast side. Stock muffler is too restrictive. Use a tongue muffler with a lot of holes. Basically we run these stock with a free flowing exhaust, prop as described. Tower 40s are true chrome engines. They run real well initially, if tuned in optimum range. I've a few run for years. They break in slowly, run better and better.