Yeah I’m not necessarily committed to 6500 RPM as a fixed number. I was only under the impression that I was supposed to set C/L engines at 4-cycle prior to launch, then letting the plane 2-cycle in maneuvers,
That's probably not a realistic approach, and in any case, if you managed it, it would be going *much faster* than 6500 in the air even in a 4-stroke. If your airplane it going too fast when you launch it at 6500 RPM, it's far too small. Typically for these sort of very small engines, you end up more-or-less running a conventional setting and need all the power you can get.
Some CL stunt engines will work the way you are describing, but not likely this one, and in any case, 4-2 breaks as you are attempting have not been a mainstream approach for over 30 years now - and have been causing people to get frustrated when they couldn't manage it for a lot longer than that. It's almost certainly not going to work well on a Gilbert 11.
BASIC ENGINE OPERATIONS: But since there is so much "stunt lore" AKA bullshit floating around about "stunt runs", the standard way that virtually all production 2-stroke engines are intended to be set and run is:
Start the engine
lean the engine out into a 2-stroke
slowly lean it out until the engine reaches maximum RPM and a even a little more lean causes the RPM to drop audibly
Richen the engine back to peak RPM - this process finds the "ideal" mixture
richen the engine very slightly to the richest setting that keeps the rpm audibly the same or *very slightly* drops
This will put the engine in a 2-stroke at near the ideal mixture. *This is the way the engines are designed to run* and probably exactly what the instructions that came with the engine say to do, and provides the maximum power - *which is what is is designed to do*. Not just a Glibert 11 - virtually all of them.
If it won't hold a setting on the ground using the *manufacturer* recommended prop, it probably has not been broken in enough and may start to "sag", which can be recovered by opening the needle slightly. That means it needs to run more.
It may not ever be able to hold its setting with not-recommended (larger) props, which means that you have to run it richer than intended on purpose. This means you are generating much less power than designed, and very likely that the choke area of the venturi supplied with the engine will need to be somehow reduced in order to support running at much less than the designed power levels.
BASIC ENGINE THEORY (functional): Power, when swinging a propellor and to first approximation, goes with the cube (3rd power) of the RPM, so the power difference between your examples is a factor of 4.84 - 1/5th the power. Since the engine is effectively a self-powered air pump, that means that about 1/5th the amount of fuel/air is being burned for power. Running rich makes it ineffective but figure you are running maybe 1/2 the air through it at 6500 rather than 11000. That means the fuel draw pressure is also around half, you have the same thick fuel, so it's straining to get the fuel out. That's why it doesn't like running that slow and doesn't run smoothly. Not to mention that it was never intended to run in a 4-stroke in the first place and is running vastly cooler than intended.
You can probably get it running much more smoothly at low rpm by reducing the venturi choke area drastically (maybe 4.84 times smaller) which will vastly increase the fuel draw, however, then it will want to be running an ideal mixture, just much less of it. RC engines do this, it's called a throttle, and its contained in a carburetor, they have no problem running smoothly at 2000 rpm.
This suggests an approach for CL - change the venturi diameter when you want to change the power level, and then adjust *slightly* around there with the needle. NOT - run the same venturi that was intended for 5x the power and try to tweak the needle. The needle is not a throttle.
Brett
Topic: Holding a needle-valve setting (Read 1827 times)