Started with the 11/7 because I had no experience with engines bigger than a 35 and that's what I was recommended to get. Now I'm told that's too much prop for this 1.6hp schedule ported engine. Hence my recent test wit the 11/4, and then I got the 10/8 and 10/7 to try. I run a 10/5 on my 35 powered bird, and it has half the power of this 46.
Just trying to learn. Problem is that so many have conflicting advice, it's hard to discern what I really need to do. Next flight will be with the 11/4.
I am not sure who you are hearing this sort of stuff from, but you should stop listening post-haste. A stunt engine in the year 2017 runs 3.5-4" of pitch. In the air, the 8"(!) pitch prop will want to run about 7500 RPM which turns your 1.6 hp engine into a .25 hp engine - which means it is LESS load than a 4" pitch prop of the same general diameter. It's more drag on the ground but you don't care about what it does on the ground. It also almost guarantees that you will have either a "runaway" problem (where the engine doesn't really want to run at 7500 rpm because that is close to idle, so it speeds up wildly as soon as you take off) and certainly guarantees that if you close the throttle enough for it to suck fuel at that RPM, you will get dismal performance in the maneuvers.
Running engines at low revs with 6"+ pitch props went out the window more than 30 years ago and the vast, vast majority of contest wins since about 1988 have been with engines running about 11,000 rpm in flight with ~4" pitch propellors. Many, many people who are not familiar with the event still think we chug around at low revs and attempt to modify/butcher engines to make that possible and that 2-stroking burns up engines (because that's sort of true for a 1958 mode McCoy 35 you got for $3.95 on a bubble pack). That gives up most of the horsepower possible.
Leave the carb on the engine, and make it ground-adjustable, get some APC 12.25-3.75s, some APC 11-4.25s. Start with the 11-4.25. Set up the carb as per RC, i.e. set it for high speed, idle, and smooth transitions, all in a slightly richer than peak 2-stroke. Start with a ground RPM of about 10,500 by setting the throttle to a fixed position. You can short-tank it to get a short level flight. Have someone time your laps. If it's slower than 5.2 seconds a lap, speed it up 200-300 rpm, try again, until it is less than 5.2. If it's faster than 5.0, slow it down 200-300 at a time until you get it up to about 5.0. That should get you in the ballpark of a flyable speed.
Based on the advice you might have gotten to date your advisors might be screaming at you about "burning up the engine". If it's leaving a reasonable smoke trail, you aren't going to burn it up. Once you have a good basic speed, leave the throttle alone, and then adjust the high-speed needle by peaking the engine out on the ground, then backing off until you get a *distinct* drop in speed, but still 2-stroking. Then fly a full flight.
What you want is for the engine to run along in a rich 2-stroke in level flight, and then pick up to a medium 2 in the maneuvers. This helps control the speed, so the drag of maneuvering is compensated for by the engine running a little stronger. It's entirely possible to get too much speed-up in the maneuvers. In that case, close the throttle a tiny bit, then lean the engine out a bit, so you are not running quite as rich in level flight. If it goes too lean or "sags" lean in the maneuvers, open the throttle a little and richen up the engine to get the same level flight speed.
That should get you very close to right. Note that for most CL airplanes, the throttle is not used, but you adjust the "throttle" and the variation using a very similar technique, just by changing the entire (fixed) venturi smaller or larger, playing off the speed VS the needle setting. I can tell you from painful experience that ~50% of the people reading this have never even heard of this in concept, much less used it in practice.
The only advantage you have with a CL venturi is that it tends to be a bit steadier in holding a setting. Every once in a while the carb will just shift a bit and the speed will change slightly, sometimes multiple times per flight. On 2-stroke engines it's pretty livable, but it makes a lot of difference in 4-stroke engines. The people in France who best managed 4-strokes (the Berringers, Gilbert and Remi) came up with what amount to a very-finely adjusted throttle to do the same adjusting as described above on a flight-to-flight basis since the mixture adjustment is very insensitive on 4-strokes but the fuel consumption is very touchy.
The "good" CL engines like the 20FP, 25LA, 46LA, happen to come with venturis that are about the right size as long as you use about 4" of pitch, more-or-less. The venturis tend to be much too large if you wanted to run 6-7" of pitch. This is not an accident and it leads people down some unfortunate paths trying to get it to work with inappropriate props.
If you let us know where you are, we might be able to find someone close by who can help. The internet is a great resource but having someone actually watch can find a whole bunch more things that might help but you wouldn't think to ask about.
Brett
Topic: Fuel consumption (Read 2984 times)
