One of the things about 1/2A's that I am curious about are the line length used and the lap times that work for stunt? I know back in the day we used 35' - 42', 0.008 lines and just set the engine to a clean 2 cycle run and flew. We use 5x3 props and never knew about lap times. Now being older spinning really fast is a challenge so that's why the question.

Thanks,   DennisT

That recipe still works. Trying to reduce the rotation rate takes a lot more effort. Probably not going to happen in even a small breeze unless you start messing with canting the engine thrust-line out bigtime--maybe even 20-30 degrees and all the bad dynamics that come along with manufacturing line tension that way. But there are designs that do that. If you want to do some research on high performance 1/2A, go look for the published AMA articles from 1985 on the "Ridiculous" by R. Porter. That is a good starting point. Note that he was limited to a TeeDee .049. If you are willing to consider the more modern 1cc engines that opens things up further. There are a bunch of competitive 1/2A stunters--but very, very few have slow rotation rates.

From a head in the clouds theoretical standpoint, if all you're trying to do is maintain the same g-force on the lines, here's your lap time vs. length:

line length = 35, lap time = 3.9
line length = 40, lap time = 4.2
line length = 45, lap time = 4.4
line length = 50, lap time = 4.6
line length = 55, lap time = 4.9
line length = 60, lap time = 5.1
line length = 65, lap time = 5.3
line length = 70, lap time = 5.5

That's ignoring wind, the fact that everything on the plane has to be twice as accurate if it's 1/2-A sized, and just general size-induced squireliness.  I'm guessing that unless you're a master builder and trimmer, on 45' lines you'd need to be closer to 4 seconds/lap than 4.4.

Or do one of those Igor-style indoor ships, but that's just a different kettle of fish.

I flew my Pathfinder/.061 on 42' radius. It flew good but, it seemed to be a minimum line length. I have a set for 52' radius but haven't tried them.

Back in the day 35' was for Baby Bee and 42' was for TD .049.

MM

Quote from: Dennis Toth on December 24, 2025, 11:45:07 AM
One of the things about 1/2A's that I am curious about are the line length used and the lap times that work for stunt? I know back in the day we used 35' - 42', 0.008 lines and just set the engine to a clean 2 cycle run and flew. We use 5x3 props and never knew about lap times. Now being older spinning really fast is a challenge so that's why the question.

Thanks,   DennisT

    You can search on here and look for the threads regarding my experiences with some 1/2A stunt in recent times and at both ends of the spectrum engine wise. What you spell out would be for Cox reedies, Medallions and TDs. The other end of the spectrum would be the Norvel and similar type .049 and .061 (1cc) . On the Cox end of things, I have been flying a Brodak Baby Clown ARF powered with a Medallion .049 at first, and after that seemed to be over powered, I then switched to a product engine from the last batch of engines that Cox sold off, the ones with the gray backplate and choke tube. That engine produces some good power also, and it was eating reed valves, only getting a few flights before the reed got so distorted the engine wouldn't run. The reed would be deformed when it was bent around the seat it seals against on the backplate. They came with stainless reeds stock, and I tried everything that I had accumulated over the years. Then a tried making some from different plastic materials, and have settled on some .005" plastic shim stock that we used for leveling machinery and printing press print units. Super tuff stuff, and has lasted dozens of flights with consistent runs. I have found out along the way that different vintages of the the Cox back plates require different thickness reeds and retaining springs differ. On the Baby clown, I started out at 40 feet, and I think I got out to 44 feet on 10lb Spectra lines I would have to check the limes and handle for that model. Lap times were in the 4 second range, maybe a bit slower, i haven't kept accurate records and haven't been able to keep at the test flying. The model only weighs about 7 1/2 ounces, and can hardly feel the model out on the end of the lines, but it is trimmed fairly well, stays out there solidly and with a custom tank I can do a pretty decent complete AMA pattern with it. I would have to check the airplane to see what prop I have on there but have been trying a variety pf props that I have, 5 and 6 inch diameter and 2 to 4 inch pitch, left hand and right hand props also. My goal with this airplane , along with the other one, was to try and get to a 4.5 or slower lap time, and I'm not quite there yet. I don't think I can go longer on the lines to slow it down, as oddly enough, I don't think the airplane is heavy enough. I think models of this size have a pretty narrow range of weights and to fly longer lines, the "rock" on the end of the string needs to be heavier!! Ever try to swing a string or rope around your head with next to nothing tied to it?? That's what I'm taking about. The engine can only do so much.

  The Norvel side of the spectrum is a Netzeband Doodlebug, the middle on of the three "Doodlebug Brothers" that he presented in Flying Models Magazine, one for Cox engines, then the middle one for the ,061 crowd, and the larger one for the .074 engines. It weighs between 11 and 12 ounces, and was originally built by a local friend, the late James Wilson, who I learned had several models designed and published in the magazines, with most of the plans on Outerzone. I had to really work to learn the Norvel engine in this environment. I have hundred of hours running them on trainers at KidVenture in Oshkosh, but that isn't as demanding as flying stunt. With the help of several members here, I began to work my way through understanding how to run the and what to use for props. They do NOT like the props that Cox engines like. I think Cox engines make more torque and can pull more prop than the Norvel but not at as many RPM. They are just different. Tank location is critical and than means solidly anchored and still adjustable. I had many flame outs trying to get consistent runs upright and inverted. I made a custom tank that I can run on uniflow or on standard venting, pressure or to atmosphere and I think it likes muffler pressure best, but can run both. I think it's about 1 3/4 ounces. The muffler mounting needs some work and the vibration really eats away at the muffler seat. Prop selection narrowed down to an APC 5.5 by 2.5 I think it is, the one that a lot of people recommended. RPM is in the 20,000 range on 10% SIG Champion type fuel. I don't really think the higher nitro fuel is necessary, and I find it attractive that I can run this engine on the same fuel I feed my OS engines. I have a custom handle and lines for this airplane and have gotten out t 45 feet I think, and have been in the 4.5 second range for the most part on lap times. That doesn't feel too bad to me, but getting closer to 5 seconds would be better, but I just don't know if that will be possible with this airplane. It flies a pretty respectable full pattern also. I just think that it is at it's limit. If I try any longer lines, I think flight performance will degrade. When weather gets back to the area, I may try some higher nitro to get the RPN up to maybe go to longer lined, in the 46 to 48 foot range. This model is heavy enough I think for a better "rock on a string" feel. I just need to see what higher nitro will do for engine speed, and also play with glow head configurations also. I'm back to using the stock glow plug, and have tried several other after market ones, and even tried Cox glow heads. Yes, they will fit.

      I'm headed in the right direction with both, just need more time at the game. Life kept getting in the way this last year, and we'll see what this year brings. So basically we are looking for the same thing I think, a slower, more comfortable 1/2A model to fly, that can fly and handle as much like a bigger model as possible without a lot of fussing and finagling, just take it out, fuel it up, flip it and fly. If using electric, I think weight will be your biggest issue if looking for weight below 8 ounces, and figuring out all the other parameters of motor, battery, timer, etc. will be a chore. Again for a trainer it's pretty easy but for a full patter capable model, that's different. I have several kits of full bodied 1/2A models that will come along as I get stuff figured out and make them worth the effort. I think what I want is something as big as I can build it and still weigh about 12 ounces or a bit less will get me out as far as I need to  go  to get to 4.5 plus second lap times.

  Type at you later and MERRY CHRISTMAS!!
     Dan McEntee