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Re: Wright Stuff C

Posted: March 13th, 2020, 2:00 pm
by xiangyu
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.

Coach Chuck
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 :)
Xiangyu

Re: Wright Stuff C

Posted: March 13th, 2020, 2:35 pm
by calgoddard
Xiangyu -

It is much easier to build an LPP near the 3.1 gram minimum weight than you might think. The 12-inch diameter prop is made of balsa wood and typically weighs only about 0.70 to 0.80 grams. A plastic prop would be way too heavy for an LPP.

See this link for instructions on how to build an LPP prop.

https://indoornewsandviews.files.wordpr ... v-134a.pdf

The instructions for building the LPP prop start on page 6.

The same John Barker who authored the article about the LPP prop also published complete instructions on building the air frame of an LPP. I could not find them on line for free. Some service wants to sign up in order to get them.

See https://www.scribd.com/document/3630318 ... ohn-Barker

Maybe Chuck or Brian have a link to a full set of LPP instructions by John Barker.

You can make the wing spars of your LPP with .030-inch carbon fiber rod and the stab spars with .020-inch carbon fiber rod, but this is not necessary. My best LPP is all balsa wood. Use Ultrafilm for the wing covering. You can buy it here: https://www.indoorspecialties.com/

Grocery bag or tissue are too heavy in terms of covering material for an LPP.

There are two John Barkers of some note in free flight. John Barker of the UK was a legend. He just passed away. He was a brilliant designer and builder and very helpful to anyone who asked for help.

John Barker of Georgia wrote the instructions for building an LPP. I have never communicated with him.

Or you could just buy one of the LPP kits from J & H Aerospace. They are very high quality.

Good luck.

Re: Wright Stuff C

Posted: March 13th, 2020, 2:52 pm
by calgoddard
The system won't allow me to add to my last post.

Unless you are trying for an AMA record, the particular design of the LPP is not critical. I know that Chuck likes Bill Gowen's Carbon Penny.

For many years the Limited Penny Plane by Cezar Banks, another legend in indoor free flight, was a very popular design. You should be able to find the plan for that LPP on line.

In my experience, the keys to success in the LPP event in terms of the longest flight duration are matching rubber to prop and winding. Does that sound familiar? In my opinion, the LPP is the easiest of all indoor models to trim.

Have fun.

I am sure that Brian and Chuck will weigh in on this topic.

Re: Wright Stuff C

Posted: March 13th, 2020, 3:31 pm
by bjt4888
Xiangyu,

As usual, Calgoddard’s info is very good. I agree with him in that you can build a fun and competitive Limited Penny Plane entirely out of balsa and Cezar Banks’ design is a good one and accessible on the internet. Pay close attention to wood densities and keep part weights to plan specs (wing, stab, etc). Wood densities needed are probably available at a good local craft store if you select carefully.

I also like Bill’s Carbon Penny and its not much more difficult to build than a balsa PP. Ordering the carbon stock does add to the cost, but makes for a very strong set of flying surfaces. There is very good tutorial-like info on Hip Pocket Aero for building Bill’s design.

Yes, they are very easy to trim and satisfying to fly.

Next step after Penny Plane? I would recommend F1L, a “heavy” 1.2 gram version of EZB. Also not hard to build (a little more challenging propeller) and very easy to trim.

Brian T

Re: Wright Stuff C

Posted: March 13th, 2020, 4:24 pm
by klastyioer
Xiangyu,

https://www.rcgroups.com/forums/showthr ... tion/page5 click the third bullet point link to download a pdf of the scribd document so that you don't have to put in credit card information for a free trial

Re: Wright Stuff C

Posted: March 13th, 2020, 9:41 pm
by coachchuckaahs
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.

Coach Chuck
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 :)
Xiangyu
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.

Coach Chuck

Re: Wright Stuff C

Posted: March 14th, 2020, 7:43 am
by bjt4888
Good advice from Coach Chuck on the Carbon Penny. His comment about the quality of the motor stick wood being important made me think of one more thing.

If you find a reasonable sheet of 1/4" sheet wood at the craft store and it seems a little heavy (Maybe 7 lb cu ft), don't despair. Most sheets of wood will vary in density quite a bit, so you can cut several motor sticks from a slightly heavy sheet and probably find some sticks are 8 lb cu ft (too heavy) and some are 5 to 5.5 lb cu ft (just right).

If the best sticks cut from this sheet are still a little heavy, you can taper slightly in height from the middle to the two ends (maybe 1/16" taper) and/or sand in thickness a couple hundredths of an inch. Of course, the stick needs to be adequately stiff. And, actually, stiffness is not super critical if you are flying low-ceiling as you will be backing off torque quite a bit to keep the plane from climbing too high. Stick stiffness is very important when flying in a high ceiling site as you need higher launch torque.

Have fun.

Brian T

Re: Wright Stuff C

Posted: March 14th, 2020, 7:57 am
by bjt4888
Sorry, reasonable 3/16" thick sheet is good for motor stick wood, not 1/4" sheet unless pretty light.

Re: Wright Stuff C

Posted: March 14th, 2020, 8:04 am
by xiangyu
Thank you all for your advice! I am planning to start ordering materials today, looking forward to this project!

Also, I have a kit of FF left, would the motor sticks from that kit work? I was also thinking about using some of the carbon from the kit as well.

Xiangyu

Re: Wright Stuff C

Posted: March 14th, 2020, 8:33 am
by bjt4888
Xiangyu,

Sorry, here's a better analysis of the wood used for Bill's Carbon Penny based upon calculated wood volume for each part.

If you use 3/16" thick wood for the motor stick and follow the plan specs for .25" stick height dimension, tapered to .16" at both tips, 8.7 lb cu ft wood would give you a 0.7 g motor stick. Using 8 lb cu ft 3/32" thick wood for the tailboom, if tapered from 3/16" height to 1/8" at tip would give you a .25g tailboom. Adding the rear hook and front bearing would bring you close to the 1.17 g shown on the plan.

However, I'm thinking that the 1.17 g shown on the plan includes the wing posts and the stab posts as these are glued to the motor stick and tailboom. So, if using 1/16" square basswood (or 16 lb cu ft balsa) for wingposts and lighter (maybe 12-14 lb cu ft) for stab posts, the weight of these components would need to be subtracted from the 1.17 gram target weight and the motor stick and tailboom wood reduced a little in density to compensate and give you the target weight of 1.17g.

I'll let you weigh sample wingposts and stab posts, recalculate weight allowance and density for the motorstick and tailboom. After all, this is part of the fun of the design.

Coach Chuck can give you better guidance on specific part weights as he and his students have actually built the Carbon Penny.

Brian T