Barron
Heliman
Location: Honolulu
| Squirrel,
I have had my 3D since December of last year. I run mine on cool power 5% and it runs smooth and never skips a beat. The only negative tendency I have noticed is that it "hangs on the pipe" a little which is not uncommon with tuned pipes. The way I have eliminated much of this is by running a colder plug like the Enya #4 and richening the bottom end needle up a little to keep it "wet."
As far as running a stock OS carb etc. It is not optimum for zero or low nitro fuel because the adjustments cannot be as finite as required because of the taper of the needle, as a result you will be chasing the needle constantly from day to day. Incendentally, this is one of the only drawbacks of low nitro fuel, the needle is always sensitve and almost always needs to be adjusted on each flying session.
This is one of the reasons the Japanese engine manufactures started using high nitro in the early 80's, as it allowed for most of us normal folk to get reasonably good results and high power from engines without burning them up and alllowing them to run cool (overheating used to be a big problem for helicopters). As you know we tend to run the engines rich as compared to the airplane guys and we use the hot plugs to compensate for the "wet" mixture.
I have my needles set to 2 turns open for the main and have the bottom set at 1/2 turn open from the point that the screw sits flush with the body.
FYI, I have tried coolpower 10% in my model and it flew terrible which leads me to want to try zero nitro rather than going higher. I agree that it is definitely possible to run the 3D on 30% with more shims but it kind of defeats itself because you have to lower the compression so much to get it from detonating, you can only hope to get the power back through the use of 30%
I think the reason most people run into problems with the 3D is because they don't have the throttle curve optimised for the characteristics of the 3D (high power, lightweight and low drag drivetrain). The "unconventional" set-up of the throttle linkage is the culprit to this problem. It is important to have a little load on the engine at all times.
If the barrel opening is larger than the fuel/ air requirement of the load on the engine, the engine can exhibit lean tendencies because the velocity through the port is less than optimum or there can be some 'turbulence' in the throttle body and as a result the fuelmetering is not optimum as well, leading to detonation or kicking.
Please pardon my less than articulate explanation on this, basically you need load on the engine so the vacuum is doing it's thing!
All in all I am a big fan of the Lotterle carb. It is one of the simplest most efficient carbs I have ever used. If you dont agree.....OS will be introducing a slide carb on its new heli engine in the future, as it provides better throttle response. This is due to the concept behind the slide carb as you allow air to pass by the "gate" rather than opening a butterfly and the air has to "route" itself around a few obstacles before entering the crank.
I hope all of this makes sense and helps.
Barron |
Just the Yanks have to be converted 
