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Author Topic: "Novice" Penny Plane by Cezar Banks attempted by a novice... maybe  (Read 7274 times)
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dslusarc
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« Reply #25 on: March 30, 2014, 06:25:16 PM »

Density = 3.81 * weight in grams / (length x width x thickness)

So a 3" wide x 36" long sheet of 3/16" wood that weighs 32 grams would be

Density =  (3.81*32)/(3*36*3/16)= 6.02 lbs per cubic foot

Sometimes a sheet when you look at it you can tell one side is heavier wood and the other is lighter, that is when you can find the "hidden" wood. Just because a sheet calculates 6# does not mean all of it is 6#. Also shining a light on the back side will show hard streaks but that really only works for thinner wood like 1/8" or thinner. Also most 1/32" wood is typically closer to .040" thick not .032" so the actual density is less as it is thicker. I actually have a chart I made in excel that I take to the hobbyshop and I bulk sort their wood and then when I get home with what I bought I use my calipers and due a more accurate measurement for the density. Sometimes I cut sections out and then reweigh. I bought some SIG contest grade wood in 1/16" C grain and the average weight on the sheet was ~5 pound but when I held it up to the light I saw a light streak in the middle and cut a 18" long 1" wide sheet from that area, it was 3.7# density!
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dslusarc
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« Reply #26 on: March 30, 2014, 06:38:14 PM »

Here is the table I use. Across the top is 4,5,6 and 7 that is density in pounds per cubic foot, below that, 1,2,3 is sheet width. Off to the left is sheet thickness and the top table is for 36" length sheets and the bottom is for 48" sheets. The populated table values are the weight in grams that the sheet for that thickness and width should weight for that density. So using the same example from my previous post, a 3" x 36" x 3/16" sheet that is 6# density should be around 31.89 grams per the chart.  If the sheet weighed 26.57 grams it would be 5#, in reality you will typically always be in between values on this table, say 28 grams for a sheet, so you know it is about halfway between 5# and 6#. So I go through all the wood racks and check all the sizes as you never know what you may find. Most will be over the 7 pound density but I always seems to find a few light sheets.
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Jimmy JFlyer
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« Reply #27 on: March 30, 2014, 06:54:12 PM »

Don that is awesome! Thanks for the formula. I went through the Hobby Shopper article some too. Now I can't wait to get back to the hobby store and look through the wood again. That table of yours is great.

So if I can ask... is it generally better to find the lightest possible density?
and...does the density directly affect how flexible a given sheet is? Did I see somewhere A & B as being more flexible with C being stiff? So is it grain that ends up being used to judge how flexible a given strip is... I know deflection is a test as well. Probably going a bit too deep for my newb brain before starting a beginner LPP.

Looking at Cezar's "Novice" plan it mentions ribs & blades as "soft" balsa and everything else "medium." This is about the last dots I need to connect in understanding the wood enough to feel comfortable in getting to cutting wood & getting started on this build.

Thanks again for all your time & advice Don.
Jimmy
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cglynn
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« Reply #28 on: April 02, 2014, 10:32:14 AM »

Jimmy,

For LPP spars I usually look for wood around 6-7lbs/cuft.  If you have 5lb wood that is stiffer than the 6 or 7lb wood, use it.  For props and ribs I use 4-5lb wood.  Penny Planes are nice in that the minimum weight is large enough that you don't have to be super discriminate when it comes to wood.  One of the students I work with built a Penny Plane with 8lb wood for the spars, and it came in at weight.  Now, if you can use lighter wood for the spars and prop, you get more weight to put in the motor stick, which usually makes the stick stronger.  This leads to more consistent flights and better performance.

Find yourself some wood and get building.  The Banks' design is the one I started with and it is a great flyer.  Just be careful, this indoor stuff is addictive.

Chris
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Jimmy JFlyer
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« Reply #29 on: April 02, 2014, 09:08:35 PM »

Hey Chris, thanks for the advice. I have 6#, some 5# and my 1/32 C prop wood is 7#. They were all sold out of anything lighter. But that will do. I forgot to get more 1/32 for the ribs so I will be using 1/20. The only 1/32 I got was one sheet for prop blades. No clue why I didn't get more than one sheet. Brain farted there. I goofed because I ended up with a bunch of 1/20 & 1/16. But it'll work.

Jimmy
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cglynn
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« Reply #30 on: April 07, 2014, 08:42:54 AM »

That should do nicely Jim.  While I would try to build as close to weight for all parts of the model, if your materials prevent that and you are a few mg heavy on your final model, I wouldn't stress about it too much.  It will still fly great.  For your first LPP, I would make sure that everything is built straight and true.  That will make trimming the model much easier.  Also, there is so much to learn about indoor flying.  Rubber selection, prop selection/pitch, trim, etc that will all contribute to the overall performance of the model far more than a few mg's.  Granted, those few extra mg's here and there do add up, but if you are careful, even with the materials you have, a 3.2-3.5g LPP is very, very doable.  FWIW, my first LPP weighed 3.5g and flew great.  It wouldn't set records, but neither will my 3.2g model.

Chris
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Jimmy JFlyer
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« Reply #31 on: April 07, 2014, 09:16:50 AM »

Finally tried my hand at cutting indoor balsa. WOW! What a different world! Blades were pretty easy. I found the perfect metal 5"dia container too for when it is time to shape em. No protractor so I used Sketchup to make a template for the blade offset on the cylinder.

Then finally tried my hand at stripping balsa for spars. Again I repeat... WOW. After the first 2 tries doing the 1/20 stab spars I almost started to think this wasn't going to happen without a stripper. Then just got careful with the double edged blade, studied how it separated the wood and how easy it is to loose your line and the 3rd piece was nice and even. just eyeballed the .040 width and it turned out quite nice. I took a small piece of .050 and laid it on the balsa and just went a bit smaller. Seemed to work OK.

I used Mike Kirdas rib arc templates and cut them out of USPS shipping boxes. Then CA'd the cutting edge and gave it a smoothing with sand paper. Left the very edges slightly rough to make it bite and hold well when laying down on the sheet. Ribs cut real nice.
Thanks for posting the templates in the plans gallery Mike!

Cutting out the bigger spars for the wing was a lot easier doing the 1/16 sq.

This was a fun learning experience. I got a good feel using that super skinny blade and learning what it does to soft balsa.
Can't wait for the next free build time to start gluing things together.

W/O mics & a scale this won't be the lightest and most correct build regarding measurements but it will be a good experience and I think it'll fly well enough. The budget is used up for now so maybe I'll find the cheaper equipment & get the birthday wish list ready. Though I think I won't wait for getting a scale. Gotta find a cheap thousandths gram scale. But can one find a good digital scale of that caliber on the cheaper side?

Figured I would share some pics too.

Regards,
Jimmy
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Re: "Novice" Penny Plane by Cezar Banks attempted by a novice... maybe
Re: "Novice" Penny Plane by Cezar Banks attempted by a novice... maybe
Re: "Novice" Penny Plane by Cezar Banks attempted by a novice... maybe
Re: "Novice" Penny Plane by Cezar Banks attempted by a novice... maybe
Re: "Novice" Penny Plane by Cezar Banks attempted by a novice... maybe
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cglynn
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« Reply #32 on: April 07, 2014, 11:44:39 AM »

Jim, you are on the right track.  Everything is looking good.  Look on amazon for a scale.  The one a bunch of us use is called "Mini Digital Scale."  It goes for around $20 (I think) and does the trick.  It may be off by a few mg from time to time, but will get you really, really close.  Being as you are building from weighed indoor wood, and following an established design, you would have to work pretty hard to build something that is too heavy, or at least too heavy to fly well. 

Keep at it.  When it comes time to glue everything together, take your time, make sure your joints are tight, and spars straight.  Judging by your drawings and CAD work, I doubt any of that will be problematic for you. 

When it is all said and done, I think you will be pleasantly surprised at the performance you get from your model, especially if this is the first indoor plane you have built/flown.

Chris
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ram
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« Reply #33 on: April 07, 2014, 12:03:08 PM »

I am in 100% agreement with Chris on how to proceed.  Build as straight and flat as you can.  Don't be afraid of discarding any spars that aren't straight.  Your weight will be within the ballpark.  My first indoor plane was the IMS Novice PP.  Very similar to the Banks.  I used the Banks prop on it.  It flew for over 13 minutes at the USIC (80' ceiling) this past summer in its 2nd time out.  I didn't have a practice place at the time.  You will be very surprised on how well these LPP's fly. 

When you do get ready to fly it, start slow and conservative and make one change at a time.  You will learn a lot that can be applied to future planes.

Rey
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Jimmy JFlyer
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« Reply #34 on: April 07, 2014, 01:50:03 PM »

Thx for the advice guys. I looked at scales on Ebay... wow there are a lot of them on ebay, so many that they are going for dirt cheap. Mostly the same kind at different ranges. But they only go down to .01. Should I look deeper for down to .001? I can't believe how cheap they are going for. Here is a link... does this look like a good scale?

http://www.ebay.com/itm/300g-x-0-01g-Portable-Small-Mini-Digital-Jewelry-Pocket-Gram-Scale-LCD-Brand-New-/251492964830?pt=US_Pocket_Digital_Scales&hash=item3a8e2619de
Current bid a whopping $1.50 and only 10 hours left.

This brand/kind seems to be the most common. Now it doesn't have a tray like some others do but wow it is going to go for cheap.

I like the tray on this one, though more expensive. Of course I am just talking dollars here though.
http://www.ebay.com/itm/LCD-Jeweler-Digital-Pocket-Mini-Scale-Weigh-For-Jewelry-Lab-100g-x-0-01g-Gram-/390810699870?pt=LH_DefaultDomain_0&hash=item5afe22085e

Chris... I actually don't have any CAD software, never used it. That is actually from an older version of Sketchup, free software for drawing & measuring found on the internet. A lot of foamy scratch builders use it who don't have CAD. I used it for the degrees scale I made which took all of about 50 seconds to draw out. It is a really nice program. I just measured & drew out the wing & stab and eyeballed the prop blade. Close enough...

Rey... I was just looking at your thread last night and noticed the prop and thought it looked familiar. What size rubber did you use?

I need to get my hand on wire that I can use to seal off/plug up my needle caps. I only have .015 right now, too big for my smaller gauge needle and too small for the bigger one. I need .020 anyway for the shaft & hook anyways. Will start gluing once I get that. I don't want the needles clogging, want to take care of them.

Thx again for the help guys!
Jimmy
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cglynn
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« Reply #35 on: April 07, 2014, 03:04:51 PM »

Jim, thanks for the tip on sketch up.  I need to start using it.  As for .020 wire, head on over to your local music shop and get a .020" guitar string.  Should be about 85 cents or so.  Great source for cheap wire. 

I checked out the scales you linked and may see an issue.  They only measure to .01g.  If you are going to be serious about indoor, consider getting one that measures to .001g.  For penny plane, the nearest .01g may be okay, but it really is nice to measure to the milligram.  Perhaps more expensive for the .001 scale, but it will be worth it if you start building the lighter classes.

Chris
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Dave Andreski
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« Reply #36 on: April 07, 2014, 03:19:31 PM »

Jimmy,
This one is highly recommended by many-
http://www.amazon.com/American-Weigh-GEMINI-20-Portable-MilliGram/dp/B0012TDNAM

Dave
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Jimmy JFlyer
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« Reply #37 on: April 07, 2014, 09:50:37 PM »

Thx for that link Dave. Yeah now that I look at scales that go down to .001 the price definitely goes up. That is what I will go for as I do see myself doing the lighter classes when the skill gets there.

Chris, I took your advice & hit the local music score. Jackpot! Yup, they had .020 but even better, they have down to .008 in stock. Too bad it was cash only so I didn't get it but will tomorrow. The first thing the counter guy who is obviously a music teacher asked was what was it for when I asked for .020. I told him planes and he loved it! Then we started talking about it. He was quite curious. As soon as I get Larry's Micro-stick done I am taking it there & letting it go in the store to show him. Maybe pass the balsa bug along!  Wink

ps... the plans show the "tips" of the wing & stab are tapered. I gave it a shot tonight and only ended up with just shortened sticks. I kept tapering them too thin. I think for my first build I am going to forego the tapering part and keep them the same thickness end to end. I don't want to keep having to cut more spars and I don't want to do the tips separate as I want to build solid flat wing & stab for ease of covering, then do the dihedral after.

Anyone think that is a bad idea?

Regards,
Jimmy
« Last Edit: April 07, 2014, 10:57:50 PM by Jimmy JFlyer » Logged
Olbill
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« Reply #38 on: April 07, 2014, 10:54:54 PM »

Re: scales

I have owned and bought for resale many milligram scales. I don't recommend the Gemini 20. The one I've had success with is this one:

http://www.amazon.com/NEEWER%C2%AE-Digital-Milligram-Weighing-Precious/dp/B00GWG15FU/ref=sr_1_16?s=home-garden&ie=UTF8&qid=1396922962&sr=1-16&keywords=milligram+scale+.001

It has written on the front of the lid "Mini Digital Scale". Although it looks a lot like the Gemini 20 (and probably shares some parts) there are some important differences. The LCD  on this one has larger, more readable numbers. The buttons are raised higher above the case and have a more positive feel.

The Gemini 20 comes with a guarantee and that may be important to you but at this price I would just consider the scale to be disposable. If you can, buy two of them and have one as a spare.

For this type of scale to be usable you can make a very simple modification. Find a piece of aluminum or brass tubing around 1/8" and another piece of tubing or dowel that will be a snug fit inside it. Glue a short  length of the larger tubing to the weighing pan with epoxy. Then you can make a removable weighing platform with the smaller tubing. I make a hole in the lid so the scale can be used without opening the lid but this is optional. Here are a few pictures of modified scales.

There are people who disagree with most everything I write about so as they say "you pays your money and you takes your choice".
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Re: "Novice" Penny Plane by Cezar Banks attempted by a novice... maybe
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leop
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« Reply #39 on: April 07, 2014, 11:30:40 PM »

Same scale as Bill recommended.  Better price and the price includes shipping.

http://www.ebay.com/itm/PRO-20A-0-001g-20g-Digital-Milligram-Gram-Electronic-Scale-Balance-Weight-Dk-/271328658366?pt=Cake_Decorating_Supplies&hash=item3f2c72c3be

LP


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Jimmy JFlyer
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« Reply #40 on: April 08, 2014, 07:46:22 AM »

Thanks so much for the links guy. Bill great scale, and LP great find!
Bill I love your scale mod!

Gotta wait for another paycheck, but then I'll grab one. Totally worth it.

Thx again guys!
Jimmy
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« Reply #41 on: April 08, 2014, 08:08:42 AM »

It's beautiful, George. Best of luck with it. I love the transparency of the finish.

john ernst
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« Reply #42 on: April 08, 2014, 08:14:38 AM »

It's beautiful, George. Best of luck with it. I love the transparency of the finish.

john ernst

oops...wrong thread. Sorry.
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leop
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« Reply #43 on: April 08, 2014, 09:42:58 AM »

Here are some pictures of my hanging sale setup.  I bring this to contests.  Bill Gowen and others have made similar setups.

LP
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« Reply #44 on: April 08, 2014, 10:08:54 AM »



Rey... I was just looking at your thread last night and noticed the prop and thought it looked familiar. What size rubber did you use?


My Lpp seems to perform best with a 17.00" loop weighing 1.555g.  This works out to .046g".  Remember this is for a cat3 ceiling height.  I haven't flown it in any other heights.  My 12" banks style prop is set at 22" pitch at 4" radius. It's as close to helical as I could get it at the time.  Wound and backed off to .402"oz it gets right to the roof (about 80') in Champaign armory where USIC was held (13:13).  I still had about 4 minutes of turns left, so shortening it a little more should bump up the time (but I ran out of flights to try this).  My average RPM is 140.

Rey
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Dave Andreski
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« Reply #45 on: April 08, 2014, 10:28:24 AM »

Re: scales

I have owned and bought for resale many milligram scales. I don't recommend the Gemini 20. The one I've had success with is this one:

http://www.amazon.com/NEEWER%C2%AE-Digital-Milligram-Weighing-Precious/dp/B00GWG15FU/ref=sr_1_16?s=home-garden&ie=UTF8&qid=1396922962&sr=1-16&keywords=milligram+scale+.001


Sorry for the bad info guys.
I was told that Olbill used the one I posted a link to.
Thanks for posting the 'correct one'.
Dave
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« Reply #46 on: April 08, 2014, 10:43:43 AM »


Thanks for the link. I just ordered one.
Dave
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« Reply #47 on: April 08, 2014, 11:25:57 AM »



Rey... I was just looking at your thread last night and noticed the prop and thought it looked familiar. What size rubber did you use?


My Lpp seems to perform best with a 17.00" loop weighing 1.555g.  This works out to .046g".  Remember this is for a cat3 ceiling height.  I haven't flown it in any other heights.  My 12" banks style prop is set at 22" pitch at 4" radius. It's as close to helical as I could get it at the time.  Wound and backed off to .402"oz it gets right to the roof (about 80') in Champaign armory where USIC was held (13:13).  I still had about 4 minutes of turns left, so shortening it a little more should bump up the time (but I ran out of flights to try this).  My average RPM is 140.

Rey

This is a good case in point for how different techniques can produce similar results. For my winning flight at USIC I used a 23" loop that weighed 2.71 grams with sleeves and o-rings. My launch torque was .35 in-oz, prop pitch 25 and average RPM was 156. There were 640 turns remaining. The model had one gentle bump on one of the main girders but the flight was no-touch otherwise.

Rey was only 12 seconds behind Brett Sanborn who was putting up a pretty good fight for first until tangling with one of the obstacles on his last flight.
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« Reply #48 on: April 08, 2014, 05:04:56 PM »

Rey & Bill, thx for the rubber info. I am still too new to translate using just measurements and weight and am only understanding thickness and length at the moment. No torque set up so I will be just winding hundreds at a time & testing at church when the opportunity arises. I have 1/8 and 3/32 SS from Peck that I figured on using in my embryos. Though I have seen that thickness rubber mentioned in LPP posts before. I also have indoor cut .065 from A2Z as well. This is all I have for now and no more purchasing atm so we'll see how I do. I will do some more research on what is being used in comparable planes and just use what I have that is the closest in size to what is successfully being used.

The family and I (3 days off this week) went down to Toledo for the Zoo (better than Detroit) and on the way back home I stopped at the local music store and got that .020. Turns out if the LHS has it, it is cheaper there. But the really small sizes are available at the music store where as not so at the LHS. This will last me forever anyways.
So now I can start gluing now that I have the .020 to use for plugging up the 20g needle cap properly to keep it from clogging.

As mentioned in my last post, I decided not to taper the wing & stab tips as it was hard to do and I don't want to have to keep cutting spars after my goofs so I am just going to leave the size constant. Does anyone think that will make much of a difference in weight? I can't see it being much and for my purposes not really a concern. I just want to get through this build and start using this plane to learn trimming & power differences with rubber motors.

Might start gluing tonight now that I can use my needle cap bottle. Can't weight!  Grin

Regards,
Jimmy
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« Reply #49 on: April 08, 2014, 07:17:37 PM »

3/32 will work. Constant chord wing will be fine. Some vertical tip plates on the end ribs would be even better but would require some additional fiddling.
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