xiangyu wrote: ↑
March 13th, 2020, 2:00 pm
coachchuckaahs wrote: ↑
March 13th, 2020, 1:45 pm
Sequestered at home with nothing to do? Tired of rules that change every year? Tired of planes that are designed to minimize flight time?
Build a P18 or an LPP over the next 2-3 weeks. Then use late May to go to the AMA Nationals instead of SO Nationals, and compete in a 95' ceiling dome! Youth entry, if I recall correctly, is only $10. Gliders welcome too. Hotels are not plentiful, but they are cheap.
Hey Coach Chuck,
I am looking into building and flying a LPP just for fun (probably not going to go to competition). In terms of materials, what should I start with? I'm used to building with carbon fiber and to the 8 gram minimum so I'm wondering what kind of materials you recommend to build to 3.1 g instead for LPP.
Also, is it a good ideas to build my own propeller or use Ikara? If you recommend making my own propeller, do you have some tips to get me started?
I would love to hear any other tips as well.
Thanks in advance
All good advice from the others above.
Bill's Carbon Penny builds very much like the FFM SO model. This is because we took ideas form Bill into our SO model, and Dave likes what he saw when looking at the planes at CSU Nationals.
Bill's carbon penny uses 0.039" x 0.016" rectangle carbon for the wing, and 0.020 carbon for the tail. That is simple but makes a tank.
You will need an LPP prop hanger, I would get Ray Harlans. Plenty of videos of how to wind one form wire, but Ray's work nice.
On the prop, you will need a prop form. We built ours from balsa scrap. We used two radial rectangles, standing on edge, probably 30 degrees apart. One was 1/2" high, the other I cannot recall, maybe 1.5-2". Run through the math and you can figure the angle you want at a certain radius. Then you plank between these two with 3/16" square pieces. But, now I 3-D print them. There is a printable prop block on GitHub (an older version by same guy on Thingyverse, but you want the newer version).
I would probably use 1/16" square basswood for the prop spar, that is what all my kids did (as did I). I have built Gowen hubs before, but the basswood is simple.
The prop blades are put on using a pitch gauge. Build one like the FFM one, but with 4" radius.
The prop blades are out of fairly run-of-the-mill light C-grain balsa. 6# wood is fine, even approaching 7#. Get 1/32" and sand it to 0.025" thick. We use a sanding block, wrap with 5 layers of blue tape (0.005" per layer) at two places, about 4" apart. Then sand carefully on a sheet of glass, it will stop sanding at 0.025".
You can get really good wood at Specialized Balsa, but you will pay $10-12 per sheet for weight and grain selection. Sig can get you close for about a third the price, and they are back cutting. Or take your gram scale down to the local hobby shop, you can find some gems in the pile of random wood.
All of our wood was Sig, generally about 6-7#, so nothing super exotic. All four kids, and me, built within 10mg of minimum weight first try.
I think the Carbon Penny will build a bit heavier, but even with "normal" light wood you can make weight. An all balsa plane may be more forgiving of wood weight, but more impacted by humidity. Either way works.
The motor stick is the critical item. You have to select a stick that has good bending stiffness but still light. You can get heavy in a hurry here. I used to not only weigh the hobby shop wood, but also set up a simple bending system with one end of the sheet on the scale, the other on a block, then press the middle down an inch onto another block, recording the force it took. This may not be accurate for every cut, but will give an idea if the sheet is stiff or not.
Good luck, and keep in touch if you have questions! More than willing to help.