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Author Topic: Novice Build - Livingroom Flyer  (Read 251 times)
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Hermie
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« on: December 22, 2021, 03:16:58 AM »

I haven't touched balsa since being a pre-teen, but I've jumped back in with a living room flyer. COVID gave me the nudge to start, and now I'm really enjoying it.

I started with the "Three Dollar Penny" plan from the gallery, and scaled it to 55% (about 10" span). I'm in Hong Kong, and sourced my balsa from a hobby store. I'm covering with produce bag plastic. Nothing fancy here!

Build #1 was grossly overweight and hopelessly nose heavy. At the time the finest wire I had found was almost 1mm diameter. Weight was 2.14g! There was no information on the plan about CG or prop design, so I kept to the plan and built a roughly 1.8 P/D prop 180mm diameter.

Build #2 improved. I learnt about using guitar strings, so the metal weight is more appropriate. I decided I need more wing area, so I increased the span to 300mm (12"), but kept the same chord and tail surfaces. I was frustrated with CA glue, and switched to Titebond for the wood-wood joints. It seems much stronger. Still the final weight was 1.8g.

Build #3 is pictured. I made an effort to keep the weight down, and it comes in at 1.45g. I haven't found a source for proper rubber, so I'm just powering it with thin rubber bands from the stationery store. The bands are about 120mm (4.5") loops, and I usually join two. It flies - in a gradual descent, and the turn radius isn't quite tight enough for my living room at the moment.

I'm already thinking about building again. I think I need more lifting area, and I really need to reduce weight. But maybe first I should try to improve my prop and get more power from a better motor.

Some questions:
 - is a 1.8 180mm (7") prop reasonable for this size?
 - this plan uses a "conventional" aerofoil shape, and the ribs I made are actually more curved than the plan. I notice that other plans have maximum thickness further back, with ribs that are more arc shaped. Is this the way to go?
 - other plans seem to have a larger tail area. Should I try that as well? At the moment CG is 76% chord. Would it move back with a larger horizontal stabilizer?

Thank you for any suggestions.
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Novice Build - Livingroom Flyer
Novice Build - Livingroom Flyer
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lincoln
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« Reply #1 on: December 22, 2021, 04:18:46 AM »

You could use a lower aspect ratio to get more wing area. Suggest you look at some Ministick plans and scale them up, or scale down pennyplane plans. I suggest you keep the prop diameter to less than 3/4 of the wing span. You can find a bunch of useful information, including plans, at indoornewsandviews.com , mostly in the download section.

It looks to me like the wood sizes you used are too large, except for the motor stick.  If you get stubborn enough, I'd guess you can get the design you show down to 2/3 of a gram or so. You can probably do better, for now, with a thin balsa sheet prop than a built up one. A 14 inch EZB prop can be between one and two tenths of a gram, and you won't be making one nearly as large.

Are you lubing your rubber motors and then testing to destruction to find out how many turns you can put in? That might help with the climb. You can probably put in at least 3/4 of the turns required to break the motor. Other things the might help the climb:
-less pitch in the prop or a different prop, or a smaller one
-shorter motor to save weight
-wider motor

If it climbs too much, you can try the reverse of the above. Additionally, you can wind up all the way, and then back off some turns.

A couple of rules of thumb, which will get you in the right neighborhood:
-If you wind to maximum turns, and then back off half of them, the model should fly lavelbat first, neither climbing or descending. If so, it means the model, prop, and motor are matched up reasonably well.
-If the model lands with the same number of turns left that you backed off at the start, that's another sign of a good matchup. Obviously this doesn't apply if you hit something.

You should see if you can get some FAI rubber. It's much better, though I suppose if your model has already hit the wall, the extra time good rubber gets you is useless. Usingbthecright width is important, but rubber strippers are expensive. Some suppliers used to provide packets of rubber sliced to thinner sizes.
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Hermie
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« Reply #2 on: December 22, 2021, 04:42:25 AM »

Thank you for the quick reply.

I haven't lubed the rubber yet, and I haven't pushed the winding as I'm still trimming. I plan to pick up some proper rubber when I visit the US next year. I'll order from Josh Finn - it was his youtube channel that inspired me to try.

I've been cutting wood from a 1mm thick sheet of balsa, so yes its probably too thick. I've been aiming for 1g; I know I can do better.

I've already reduced prop pitch "a bit" from design. I agree, a bit more will help use the power I have more efficiently. Or maybe build a smaller, narrower prop...

I'll still leaning to a rebuild to get weight down first. Is Titebond ok, or is it adding weight?
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lincoln
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« Reply #3 on: December 22, 2021, 05:04:22 AM »

I doubt if Titebond is adding much, if any more weight than some other glue. Just apply it sparingly. I use a toothpick. Solvent based glues like Duco, Sigment or Beacon 527 (have I got that number right?) can be loosened up or thinned with acetone.

Are you double gluing end grain? Just put a little glue, maybe even thinned glue on the end grain. Wipe off after a couple of minutes and then immediately glue as normal. At least that's how I do it. I've seen a 36 inch rchlg with solid wood wing halves double glued together with Titebond. It was a simple butt joint, end grain to end grain. Eventually, they broke apart, but next to, rather than on, the glue line. It probably helps that Mark Drela built it. He's a real craftsman and I'm sure the fit was nearly perfect.

I hope that I've caught all the mistakes the so-called spell checker has tried to insert in this note. For example, it changed Drela  to Feel a. Duck became Duck. Oops, I mean Duco became Duck. And so on.
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Hermie
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« Reply #4 on: December 22, 2021, 06:45:22 AM »

No, I haven’t been double glueing endgrain. And I have been rather generous at times when I try to make up for a lack of craftsmanship.

I haven’t found a solvent glue here. I’ll keep asking around. At the moment I have CA (liquid and gel), white glue and Titebond. And I do have 3M 77 for the film.

Thanks for the suggestions, it helps a lot.
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TimWescott
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« Reply #5 on: December 22, 2021, 04:06:46 PM »

I'm surprised you haven't found solvent glue there -- but I don't know Hong Kong.  I'm sure the brand names are different.

Lincoln said about everything that I was planning on saying.  The only thing I can add is that you really want to shop for wood.  In fact, you want to obsess over wood.  If it doesn't get you kicked out of the hobby shop, pull out every sheet of the thickness you want and assess it.  You want the strongest lightest stuff you can find.  If your hobby shop caters to RC folks, you'll actually be taking what they think of as undesirably weak wood, so it's kind of win-win.  While you're looking at wood, keep an eye out for wood that's straight grained but doesn't have grain parallel to the sheet -- you can cut along the grain.  Also look for wood that's "patchy" -- sometimes you'll find a piece that has some hard spots mixed in with light spots.  For indoor, you can just use the light stuff, and save the hard stuff for motor sticks or as gifts for RC builders.
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bentodd
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« Reply #6 on: December 22, 2021, 05:56:26 PM »

I have been thinking about having another go at a living room flyer or parlor mite.  For rubber I was going to try cutting up a laytex glove.
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Hermie
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« Reply #7 on: December 22, 2021, 11:57:10 PM »

I’m sure that there is solvent glue here, it’s just that it will be a different brand. There are lots of hardware stores, and only a few hobby stores. The hobby stores are heavily skewed to plastic display models. The best balsa is actually at an architectural supply store near the university.

I’m still learning, and enjoying the challenge.
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