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General control line discussion => Open Forum => Topic started by: Kafin Noe’man on June 03, 2024, 09:19:28 PM
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I’m currently trimming my P40 with LA-46.
Weight is 50-51 oz
Prop is ThunderTiger 11x4.5 and fuel is 5% Nitro, 20% oil 50:50.
I have flown several times and tried to fly at various RPM:
- At 9,600 — it had a very noticeable 4-2 break (sometimes it happened at weird times) ; very significant power gain when climbing which made it hard for me to maintain the shape of the loop ; lap times 5.5 - 5.6 sec/lap ;
- At 9,800 — it still had a very noticeable 4-2 break (sometimes it happened at weird times) ; very significant power gain when climbing which made it hard for me to maintain the shape of the loop ; lap times 5.3 - 5.4 sec/lap
- At 10,000 — the 4-2 break was much less noticeable but still there ; better control for me as it was more ‘predictable’ ; lap times 5.1 - 5.2 sec/lap (I guess this needle position was on the verge of getting too lean)
- At 10,250 — it sounded very solid 2 throughout the flight (which I really like due to its predictability) ; but it sagged when I was doing the second inside loop ; lap times 4.8 - 4.9 sec/lap
So, my question are:
1. Is ThunderTiger 11x4.5 prop a ‘4-2 kinda’ prop?
2. Since my engine seems to be running well at 10,000ish but the needle position was on the verge of getting too lean, is it safe to say that I should try 11x4 prop? On paper, the 11x4 will give more power without having to close the needle further (so it still will be in its happy range), as well as slower lap times?
Looking forward to hearing more from you guys.
Best,
Kafin
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LA46 isn’t a 4-2 engine.
59 ft lines and 9600 rpm.
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I added more nitro to get a steadier run from the same set up and weight, 15% seemed to make it settle down. I also eventually went to a wood prop. Cut down Rev Up 12x5, cut to 11.
Chris…
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APC 11.5 x 4 for the LA .46.
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LA46 isn’t a 4-2 engine.
59 ft lines and 9600 rpm.
+1 on Dan's comment. I don't try to run any of my LA's in a 4-2-4. My experience is that the LA's run their best at a fast 2-cycle. Maybe open between 1/8 to 1/4 turn on the needle rich from peak rpm just when you notice the rpm drop a little from peak.
A few things to also try.
- Try reduced prop pitch to control to the lap time you want. So, try an 11-4. And not all 11-4's perform the same. Try APC, MAS, BYO, XOAR, etc.
- You can also try longer 62' or even 64' lines
- Open up the OS muffler and ensure the internal cone is installed. The engine runs better with it installed.
- If your 46LA is stock, it should have a 7.2mm venturi. You can also try a 6.5mm venturi. If you have a stock OS 25 LA, it is the 6.5mm one that will fit on a 46LA. (I run the smaller 6.5mm venturi on a 40LA on my Nobler)
- The sag you noticed on your loops 'might' be due to fuel draw causing it to go lean. Try using muffler pressure. I run all of my LA's on muffler pressure.
Continue to experiment.
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It’s not the prop that gives a 4-2 break.
I have had several LA 46 motors give a 4-2 break. It has to do with engine setup.
The TT prop is a good prop for that motor, it might not be the right combo for the plane.
As others said, try a few different props till you get the one that the plane is happiest with. Some props will load up the motor more and some will allow it to unload. Better overheads or better corners. Fly several flights the swap.
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Thank you all for your responses.
I noticed that there are various prop sizes that I can try on my LA46.
However, the question is, how do I know if I need to try some new prop sizes?
How can you tell if it’s the ‘wrong’ prop size instead of ‘wrong/not optimum’ engine setup (for example: RPM not high enough, too much nitro/too low nitro, etc.)?
Best,
Kafin
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Thank you all for your responses.
I noticed that there are various prop sizes that I can try on my LA46.
However, the question is, how do I know if I need to try some new prop sizes?
How can you tell if it’s the ‘wrong’ prop size instead of ‘wrong/not optimum’ engine setup (for example: RPM not high enough, too much nitro/too low nitro, etc.)?
Best,
Kafin
Basically, the bigger and heavier an airplane is, it will require more prop for best performance. It's mainly about experience. If you have an LA.46 on a Twister like a lot of guys seem to do at 40 ounces, it will take an entirely different set up to get a Legacy.40 or any other full fuselage model to perform like it should at a weight in the 50 to 60 ounce range. In this size range, an APC 12.25 by 3,75 will haul the freight. Nitro ranges can stay the same in my experience.
Type at you later,
Dan McEntee
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If you need to do a 4-2 run to get down to 9600 RPM, then your venturi is too big.
If you can get a few venturis in steps of half a mm or .025 inches smaller, try that. If you can find some nylon mesh, with a grid of 1mm or 1/2mm, try layers of that.
I had a heavy 54 oz twister that launched between 9600 and 9800 RPM on that prop, in a wet 2, and it flew great.
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Thank you all for your responses.
I noticed that there are various prop sizes that I can try on my LA46.
However, the question is, how do I know if I need to try some new prop sizes?
How can you tell if it’s the ‘wrong’ prop size instead of ‘wrong/not optimum’ engine setup (for example: RPM not high enough, too much nitro/too low nitro, etc.)?
That's very difficult and takes a lot of knowledge and experience. This is where having someone with experience can greatly speed up the process. That is also why you see me and others give people give these extraordinarily detailed setup instructions - it's trying to remove the need to evaluate and diagnose problems to the extent possible.
Unfortunately, there are also plenty of people who - with no malice and with the best of intentions - will give you such wildly variable advice. People have been flying stunt in more-or-less the modern form for around *75 years*, over that time, many ideas have come and gone, most of them were not right in the first place. So you might hear any of those, parts of one idea and parts of another, or almost anything. For most of the 75 years, it was utterly impossible to come up with system that would work for everyone - because the engines were so poor and so variable from day to day or individual engine to individual engine that what worked on one of them may not work for any other.
More modern engines are far more repeatable, for the most part, which is why almost everyone recommends OS LA series - they are *dead nuts* repeatable, so you really can come up with a "working" system and have some chance that it will work for someone else, too. Semi-custom engines like those used in competition (Jett 61, PA series, etc) are even more like that, if you have the same engine configuration, *they will run the same way*.
I don't have a set up for an 46LA, lots of other people do and there is a pinned post about it. Avoid any advice that talks about running more than about 5" of pitch and for sure any advice that tells you to open up the engine and grind/drill/file on it, because that is patently not necessary. Also avoid anyone who wants to grind/drill/file it for you, they are wrong and do not know what they are doing.
Obviously a big airplane requires more performance from the engine than a little one. But how you harness it with something like a 46LA is generally nothing like it was for most of the history of stunt - you can run more diameter, less pitch (and whatever reduced diameter is required to get the necessary RPM in a favorable setting). etc. The most dominant engine/prop system we have ever had used a tiny prop on a huge airplane (40VF with a little Bolly 11.3-4.25 two-blade). I have someone in mind to give you a setup for a conventional-sized airplane but I want to ask him first before putting him into the firing line.
Brett