AS I had written in my email to you, This is the setup you should start with for the plane. Use the 2 blade bolly 11 3/4 x 4 1/4 cut down to 11.5 inches, The stock pitch the way it comes is about 3.8 at the 10 inch station, USE the prop as is... first, adjust later if need be
I use a #14 venturie with this prop a 16 7/8 inch pipe lenght, You should be on the ground at about 11,000 RPMs, launch with the motor just into a 2 cycle, after launch it should drop into a strong 4 cycle within 1 lap...mine drops at 1/2 lap.
Matt,
To expand a bit on what Randy says, 17.5" of pipe is appropriate for about 9200-9500 (ground) rpm for this particular engine. I am running 17.5, but I launch at 10000 and have more exhaust duration (which also makes it want to be longer). Where you are headed with pitch is certainly consistent with pretty low in-flight RPM of around 9500-9600. It will run that way, but you are giving up tremendous power by running too slowly.
If, at that length you try to crank it up all the way to 11,000 on the ground (maybe 11,700 in the air), it will have to be over the top lean because the pipe is set to try to *fight against* going that fast. In fact, I predict that as you were trying to get up to 10,600, the needle stopped having much effect, and you had to turn it a lot to get the last few hundred RPM. The pipe is there to regulate the speed, and you have it set to prevent going that fast. A shorter pipe regulates at a higher RPM, so you need to set the pipe length to correspond to the desired RPM. For 3 3/4" of pitch on this type of prop you will need about 11,500 in the air/11,000 or so on the ground, so the pipe need to be set accordingly. You *want* less pitch, that's why piped systems work better than 70's- style 4-2 break systems. Once you get it set, there's hardly any need to fiddle with it any more, only slight tweaks maiy ever be required once you really know what you are doing. The pipe part of it is a known quantity, you set it and forget it.
Note also that cutting down the prop from 11 3/4 to 11 1/2 as recommended has a huge effect on the load on the engine, and require significantly less torque to spin at a particular RPM. Once you get the pipe right for the rpm, then you set the rest based on prop load. For the stock venturi, to get a reasonable setting you need to get a light enough load that it will 4-stroke in level flight. You *might* be able to run more load (either more diameter or a 3-blade) with a bigger venturi or more nitro, but until you have a baseline system working there's no way you should start futzing with it in that way. IF you have too much diameter, you will be too lean in flight and it will either shift your "operating point" so that it breaks when you don't want it to, or it will be too soft.
For the advanced user, there are other things you can fiddle with, but you would probably be surprised at how little people mess with it. For the most part, even at the highest levels, you get a working baseline system, and then forget about it. I literally haven't touched any of my piped engine setups for 7-8 years now - and I know what to do. The engines are so consistent and repeatable from day to day and from engine to engine that it's trivial for Randy to tell you exactly how to set it and have virtually complete confidence that it will work the way it's supposed to.
None of this is intended to dampen your enthusiasm or interest in experimenting, but you *must* get a working baseline system before you can go off into the world of experiments. So I very strongly urge you to put the pitch back to normal, set the engine up the way Randy says, and get it working. After you get some time, then you can experiment.
Brett
p.s. BTW, I went back and looked at my notes, and as a point of interest, my last PA40 setup, after years of fiddling, is essentially identical to what Randy recommends, and recommended at the time. Now, that was before the UL version but as near as I can tell they run about the same. The pipe length and pitch were certainly not in debate! This was about 15 years ago, but the laws of physics haven't changed much since 1995. I also think my little buddy/WC Team Member Derek ran essentially the same on the engine I sold his dad, when he gave me a run for my money at the 2006 NATs.
There is one thing I did slightly differently but I think it's a complication you don't need at this point.
Topic: She's ready to fly! (and now I need to repair her)(pics of repair) (Read 16871 times)