OS 15 LA- free flight/throttle

I also meant to mention to train the bladder. With a new non inflated bladder and a syringe, inflate the bladder slowly while cupping your hand around the front of the bladder. Don't allow the front to blow up PERIOD. Whatever portion blows up first is now the weakest portion of the bladder which will continuously blow up in this area. It's also the first area which develops a embolism in short time and burst. So, keep the bladder inflating to the rear and if it does semi expand in the middle, with a little air in it , work it back to the tail end and keep it inflated for a minute or two. Deflate and proceed to fill with fuel and use the bladder.

              If you don't currently own one, use a 2 oz. syringe because it's easier to inflate a bladder with a smaller syringe then using a large one. You can obtain a Luer Lock syringe which you can utilize the removable tip fittings. I make small tubing tips from 1/8" copper necked down to 3/32". This allows the tip to tightly fit into your bladder supply tubing.

Very good instructions Ken, I really appreciate it, best Ive read (and I have read everything I can find), the two videos here are also very helpful as well as the follow up posts. Appears the process is going to take some practice.
Yes, it is an RC engine, thus my question with stabilizing the throttle at wide open, guess Ill just tie it open with wire at the fuse. I dont have experience with the engine mods you mentioned so right now Im stuck with what I have.
My fuel didnt show up, not sure whats going on at Sig. All I have is Sig35, not sure I want to run that in the new OS but may try it anyway, what do you think?
Again, thanks for taking the time to post the detailed information, I have the highest regard for your knowledge.

As I mentioned, I have no idea in regards to the r/c carb. I know this is becoming a expensive project but the OS LA-S stock spraybar is excellent to use with a remote style needle valve. My concerns would be, will the stock rc carb needle valve offer a fine enough adjustment for bladder?  Will it withstand the pressure of the bladder without leaking?  You will know better than I will.

         I use the LA.15 for clown racing, I use 60% nitro when I run that engine. My experience with using it is superb. I remove the stock head gasket and use no head gasket when doing so. In stock configuration, I use Sig 35% fuel for .15 combat. There's a huge fallacy that goes through peoples mind when one suggests high nitro. First reaction is that your going to burn up the engine or it's going to run too hot. I found it too run cooler. I own 4 LA .15's. All but one has been running on fuel in excess of 25% nitro since their introduction in the 90's. I run them at high rpm's on APC 6.3x4 pylon props. I just recently had to take one apart last season when the control horn pulled through my elevator and caused the engine to go worm hunting and it ate a lot of dirt. Upon taking it apart, the engine looked very new.

        Depending on how you want the engine to run is how I would select my fuel. For sport freeflight, I probably would keep things on the timid side as you don't need a Atlas missile, you just want to get some altitude. Therefore depending on your altitude, 10-15% nitro should suffice just fine. Obviously the higher you are and the hotter it is, the engine is going to want a bit more go go juice. The big thing to remember though, when using bladder, your needle adjustments work light years better when you run higher nitro. Your Sig 35% is expensive but it would be very effective to work but it will be harder on your stock plug and especially on your paint finish. Sig 35% is like paint remover if spilled on the finish

Good info, thanks.
After your posts, now I want to convert this engine to C/L from R/C. Im assuming parts for 15 la-s fit the RC version.
I found this guys store on ebay below.
Would this venturi and NVA work? Am I missing anything?
https://www.ebay.com/itm/223517272428?hash=item340aaae96c:g:edQAAOSwEnpc3Ltn

Yes, those parts fit. OS discontinued many parts . The stock C/L OS was the FP-S .15, it didn't come with a through the venturi needle valve assembly like Shtterman depicts. it came with a remote needle valve on the rear of the engine and just a spraybar /no needle assembly . Many of us purchased the FP.15 assembly which was still available as it's a similar crankcase and used that particular assembly. What Shtterman has done using available needle valve assemblies from Enya was to insure the needle valve body diameter is the same.

Great, thanks.

Ken Cook wrote:The stock C/L OS was the FP-S .15, it didn't come with a through the venturi needle valve assembly like Shtterman depicts. it came with a remote needle valve on the rear of the engine and just a spraybar /no needle assembly.

Ken, that may have been true with the later .15FP-S, but the one I bought back in the 1990's (or late 1980's, before the remote needle craze for finger protection) did come with with the standard NVA through the venturi.

This is the one I have mounted on my now venerable Sterling Ringmaster Jr. (original version). For the lack of a better picture, what I have cached on my computer (will have to later pull off the wall in the garage):





Mind you, I only bought one, and I am not intimate with the model's total history, but at least my example came with the through the venturi needle.

Sceptre Flight Engine Tests has an article dating back to the mid 1985's with an OS Max .40FP-S with the through the venturi needle like my .15:

Sceptre Flight Engine Tests - OS .40FP-S

If needle valve goes through the venturi in shtterman product it appears that I would also need a different backplate to convert the rc version to cl, correct? Guess Ill check his store for this too.
Today didnt go so well, couldnt even get the motor fired up, all these roadblocks are very frustrating.
May be the old ignitor I have, plug may not be burning hot enough because I kept flooding it (red glow). Ken, I am using a tank on bench right now, I just really wanted to figure out the tune before going to bladder.
Im also finger flipping, wish I could afford a starter!!

I don't know if the .15FP-S venturi would fit the .15LA carb mount area or not.

You could probably just carefully remove the needle and spring from the back plate. I don't know if the needle valve seat area is screwed in. If pressed in, you probably don't want to try remove that or you compromise the fit and could crack the plastic. Another option is buy another LA plastic backplate and carefully trim off the remote needle section.

Other option is simply wire the RC carb wide open. I did that with my Enya .15-III TV when I used it on my Ringmaster Jr. Flew fine, had adequate suction. The purist may poo-poo the idea as not looking "CL", but at least you're flying.

firstwordisee wrote:
Now my stupid question, is there anyway to modify the engine's throttle control to stay WOT without wiring it to the fuse?

I am not sure if your original question has been answered, but try driving the adjusting screw on the RC carb fully in. That will interlock the throttle barrel in fully open position.

The LA should literally start in one to two flips. I personally never go straight to the running. Clear any residual factory oil from the engine by burning off a prime prior to hooking up the fuel line. Does the engine run on prime? Did you hook up a syringe and blow through the needle valve assembly to insure it's not blocked?  I burn a prime off  with a engine that sits for some time, clear it out by burning off a prime which not only clears it, it gets some heat into it. The LA series has plastic backplates which break very easy. The screws require special screwdrivers which are JIP phillips. If you use a conventional phillips, you run the risk of screwing up the head. Insure the backplate is snug not overbearingly tight as it will break. A loose backplate can and will prevent proper fuel draw. This is a non issue when running bladder pressure as the bladder feeds the fuel not the suction of the engine.

There could be a few issues working against you here. First, not to sound condescending, the plug is lighting? If the temps are down, 50 and under, the engine is going to require a bit more prime. I personally wouldn't prime through the carb. Break in with no muffler if possible. Prime through the cylinder, connect battery, rotate slowly through the compression stroke while holding the prop and the prop should try and kick back in your hand which is known as a bump. Don't continue flipping if no bump, restarts the process. Another issue could be  the r/c carb. Sometimes, some r/c engines don't like to start with the throttle wide open which may require you to close it halfway. Many many times, the reason for not starting initially is too much prime and the smaller the engine, the easier it is to flood it.

          I personally like fuel tubing I can see through, not that colored stuff because I can see the fuel come up the fuel line. Insure that your tank is not too low and when you place your finger over the carb and rotate the prop that fuel draw is taking place. Regardless of plane, test stand etc., keep your fuel line as short as possible.

        I'm assuming your starter battery is correct and properly charged? A flooded engine and a low battery is a recipe for your hand to fall off. On new engines, I should've stated this first. WEAR A GLOVE, SAND YOUR PROPS AND REMOVE ALL FLASH AND MOLD LINES. This is especially with Master Airscrews.  Fast flipping isn't always the answer, generally, I've found new engines to become very easy to get flooded. Therefore, I don't flip my props in a counterclockwise rotation like most do. I prime, I then pull it through the engine with one rotation. I hook battery to plug. I rotate the prop clockwise until it comes up on compression, I don't go through the compression stroke. I raise the blade counterclockwise a 1"-2" and smack the prop backwards. The prop hits the compression stroke and flips back counterclockwise and generally starts. This is a excellent way to clear a flooded engine and it also prevents your fingers from being hit.

            If I get a engine that's really flooded, let's just say your tank for instance is too high and it gravity fed into the case. Obviously, pulling the plug and turning upside down while rocking the prop will rid the engine of the majority of fuel. Place your lips on the carb and blow back through it with the exhaust facing away from you rotating the crank until the shaft window lines up with the opening in the case and blow it clear. Also, blowing into the exhaust port can rid a flooded cylinder in which you now start the entire process over again.


     I've never EVER had the need to use a electric starter, I feel they do more damage than good and the r/c guys laugh at me. However, I've seen them screw more @#$$ up then anyone using the starter. I also watched them break noses off of airplanes. Total idiots and I just laugh. The rod on a LA is fairly beefy, however, the bottom of the rod on the big end can be subject to breaking if a starter is used on a flooded engine. In addition, the wrist pin can also bend in this engine so therefore, not telling you what to do, I just wouldn't use one  as these parts aren't exactly inexpensive, a rod is probably $20.

Ken Cook wrote:I've never EVER had the need to use a electric starter, I feel they do more damage than good and the r/c guys laugh at me. However, I've seen them screw more @#$$ up then anyone using the starter. I also watched them break noses off of airplanes. Total idiots and I just laugh. The rod on a LA is fairly beefy, however, the bottom of the rod on the big end can be subject to breaking if a starter is used on a flooded engine. In addition, the wrist pin can also bend in this engine so therefore, not telling you what to do, I just wouldn't use one  as these parts aren't exactly inexpensive, a rod is probably $20.

Agreed on the electric starter. I've seen others use them, and one can probably get away with it on the larger R/C engines, since the manufacturers have taken this into consideration in their design since the 1980's on.

The earlier engines like the Testor McCoy Red Heads, K&B .35 Stallions, and I think the K&B Torpedoes use a nylon crank spacer in the end of the hollow crank pin to prevent the hard crank steel from gouging the aluminum back plate during hand starting. Use of an electric starter pressing on the front end can quickly erode this spacer. In a pinch where the spacer was missing or shot, I have used a 1/8" aluminum pop rivet with end gently filed smooth, which fits perfectly. It is a harder aluminum than the back plate, and as such I consider this only as temporary until I can fit a suitable replacement.

However, it is considerably better than the harder cold steel of the crank pin gouging the back plate. (Once started, the prop pulls the crank pin away from the back plate.)

Properly set up and with a good ignition battery, the smaller engines will start easily with a couple flips. The legacy .35's start easy with a couple flips. I also learned early on, that the smaller engines do not seem to tolerate idle bar plugs as well as standard ones. (Hence why I gather, Cox and other small engines don't use idle bars on their glow heads.) My 1965 OS Max .10R/C is a good example.

Interestingly enough, I found out that my Enya .09-III TV (actually .099 in displacement) would start with a couple flips on lighter inertia wood props, but struggled with the heavier plastic fiber/glass reinforced props.

Backed up, slowed down and followed your instructions Ken, it fired right up, ran for about 30 seconds, then my homemade fuel tank got a leak. But confident now! Going to fix the tank, run it a few more minutes rich, find optimum NV setting, then move on to bladder.
Thanks guys for all the info on this thread, invaluable to me, this site is my only support. Local free flight flying group I joined hasnt helped me at all but I havent gotten too involved yet so dont blame them. From what I can gather most of these guys dont even fly power free flight anymore, especially large planes.
Galloping, If I can get this to start on WOT with bladder then for now Im going to wire the throttle until I can mod engine, nice to know others have done this.

You don't want to run your engine rich . The LA is a modern engine and you want it hot but not overheated which it won't overheat anyway. Running it rich can actually harm it. The LA uses a nickle plate cylinder and these can peel up neat top dead center. Running the engine rich is not good for the cylinder or the conrod. The cylinder walls are not parallel until they heat up. You want to repeatedly heat cycle it by getting it hot and letting it cool down. Running it in a wet 2 cycle not a 4. After about 30 seconds pinch the fuel line and let it really lean and release the tubing doing this every now and then.

180 degrees open from optimum (what I meant by "rich") is what I had planned to do, maybe that is in the 2 stroke area. What you say makes a lot of sense.