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  #111  
Old 07-28-2020, 10:36 PM
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mbauer mbauer is offline
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Using Triangle to Fix Part Fit Issue

Okay, drew up a small drawing to show how I finally used a Right Angle Triangle to make the nosecone top skin (and bottom skin for that matter).

Problem: How to correctly size the top skin to bend around the Side Fuselage Shape in 2D, and place the bends at the correct location.

Up till now I've been able to do this on most models so far as I just kept a straight side profile shape for the fuselage, leading up to the firewall for the rubber band mount.

For the Bomber models I've decided to make, this would look really weird, so decided one way or the other I would figure out how to do the bends and part fit, without printing several test pieces and then adjust until the parts fit. Not the most accurate part fit doing it this way.

I like accurate part fit, that is why I draw my models out to six decimal places: 0.000000 using AutoCAD (possible to go all the way to sixteen decimal places with AutoCAD).

Here is an example of the P38 Nacelle before I corrected an issue with it. This was an easy fix, just narrowed the bottom skin where it bends to the balsa mount/firewall for the prop bearing location. This photo is before building the corrected nacelle: Notice how wide the bottom is, and the sunken in sides of the upper nacelle sides? Ugly looking and not very good for flight!
Rubber Band Power-pict0916.jpg

Rubber Band Power-pict0917.jpg

Rubber Band Power-pict0918.jpg

Did not want the bomber to look like this so, worked and worked on ideas until realizing it was a triangle issue with all of the bends on the side of the fuselage.

Here is a screen shot of a drawing trying to explain how I finally figured it was a triangle problem. Used an on-line triangle calculator to find the value for side B:Forgot to mention, I drew a line exactly the length the calculator said Side B would be, then I started a new line at the top of side A, this line was angled down to the far end of Side B, Side C was now in place. Then I measured it, and it was the exact value of side C as shown. That's when I knew it would work.
Rubber Band Power-screen-shot2-triangle-corrected-part.jpg

And the very first part fit test after printing everything out for the top and bottom skins as shown on the post above:
Rubber Band Power-pict0914.jpg

Whew, back to designing the rest of the model.

Thanks to aansorge, bought some 1/32" wire rope to test as a flexible drive-line. $22 on eBay for a 100ft coil.

Should work by creating a loop on the ends, super gluing and then wrapping with thread before supergluing again.

Contacted a company that makes micro wire rope as small as 0.010 diameter to see what a minimum order will be for a spool of even smaller diameter cable...Should simplify power system and minimize power loss of a U-joint, or wire to wire system.

This triangle method will be used on some models I've started, but never finished because could not figure a way to get the skins to match, the bends.

Mike
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Last edited by mbauer; 07-28-2020 at 11:08 PM. Reason: Explain how side C was drawn to test
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  #112  
Old 07-31-2020, 06:25 PM
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maurice maurice is offline
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To fix a nose

Previously when commenting on design threads I've only ever mentioned in passing my preference for using geometrical methods, thereby avoiding the need for labourious trigonometric & arithmetical calculations in the design process. ( pi being a bit of an exception - sometimes.)

But I've never actually given an example of what I mean.

Seeing the fourth image in the above post (post 111) presented an opportunity to correct my omission, hence the attached .pdf .

Mike assures me this is useful and that he welcomes it being posted in this thread.
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File Type: pdf Design by Drawing.pdf (34.2 KB, 27 views)
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  #113  
Old 07-31-2020, 06:54 PM
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mbauer mbauer is offline
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Quote:
Originally Posted by maurice View Post
Previously when commenting on design threads I've only ever mentioned in passing my preference for using geometrical methods, thereby avoiding the need for labourious trigonometric & arithmetical calculations in the design process. ( pi being a bit of an exception - sometimes.)

But I've never actually given an example of what I mean.

Seeing the fourth image in the above post (post 111) presented an opportunity to correct my omission, hence the attached .pdf .

Mike assures me this is useful and that he welcomes it being posted in this thread.
Hi Maurice,

Yes, Everyone I invited him to post this after a couple of emails. His method works for several shapes. Just did the tail fuselage using his method.

If you design in 2D you'll appreciate what Maurice is making available as a great resource.

With two methods to check the part, hopefully will help verify part fit even more accurately. I've made plenty of mistakes, finding out when building is the norm.

Thank you Maurice!

@aansorge; Bought some 1/64" [.39mm] cable today. Cost for 3 each 24" long SS wire rope fishing leaders: $1.80. Was ready to buy a spool, all could find, won't have to now. Will test the cable idea as these are incredibly lite! Just twisting them they rotate well.

Going to use a R/C control wire sleeve to make sure they don't twist up like the band, balsa supports at both ends. Might be why they use wire. One way to find out! If the cable doesn't work, maybe the control wire will, already have the housing mounted where it goes.

Mike
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Last edited by mbauer; 07-31-2020 at 07:12 PM. Reason: wire instead of cable fix
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  #114  
Old 07-31-2020, 07:22 PM
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maurice maurice is offline
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Thanks Mike

.... and mentioning mistakes ... there's a windscreen panel in there I forgot about
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File Type: pdf Design by Drawing amend.pdf (34.7 KB, 17 views)
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  #115  
Old 08-06-2020, 08:25 PM
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mbauer mbauer is offline
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Moore Drive

Okay, going to use the Moore Drive.
C. Rupert Moore A.R.C.A. 1944 Patent#514974
A professional artist who liked to design Free-flight model airplanes for a hobby.

There is a book about his paintings. He painted aircraft, book is 15-pages, price on-line is $50.

The screen shots of the Short Scion show the drive in detail.
Rubber Band Power-short-scion2.jpg
Rubber Band Power-short-scion3.jpg
Rubber Band Power-short-scion4.jpg
Rubber Band Power-short-scion6.jpg
Rubber Band Power-short-scion7.jpg
Rubber Band Power-short-scion8.jpg
Rubber Band Power-short-scion9.jpg

Wondering why the "cogs" are open from the prop to the triangle loop on the drive shaft?

Looks rather difficult to make, wondering why he didn't use the looped ends that are used on his center bearing blocks?

My propeller shafts end in a triangle, thinking they should work to transfer the rotation from the rubber bands to the prop.

Bought some boxes of mixed gears, hoping to get something working in the front of the B25B.

Waiting on the plastic gears, 1/4" Rubber band. The B25B will get built in stages, waiting on parts etc.. Printed two models that are both ready for the build stages. Decided to build both at same time.

Re-drew major issues with the P38 Lightning. Moved the landing gear back, shortened the nosegear.

Streamlined the nacelles, using methods just learned.

Going to use it for an experiment I thought up. Big surprise, when you see it. P38 has the perfect tail shape for what I plan to do.

B25 will also work for this idea. B25 will have a 42" wingspan, same as the Short Scion that the Moore Drive was designed for. He used real hardwoods in his model designs. They were known to be heavy, but some have lasted till present, restored back to flying condition. If his drive designed worked on his heavier than normal aircraft, thinking his drive will work on my paper airplane models.

Start cutting when I finish typing. Both models over the weekend....

Mike
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  #116  
Old 08-12-2020, 09:46 PM
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mbauer mbauer is offline
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Wing Mounted Rubber Bands

While cutting out the P38 and B25 got to thinking about the drive system again.

Thinking about using a modified Moore Drive. Instead of running to a gear setup to utililize a longer rubber band length inside the fuselage. Why not mount the rubber band in the wing. The spar can be the anchor for the far end. As shown in the screen shot below, it has a 20" long length vs., 12" for the angled direct mount to fuselage as shown.

This screen shot is a quick draw to show method. Rubber band will probably pass thru the spar for clearance and decrease the angle needed of the Moore Drive.

Rubber Band Power-b25-screen-shot3-rubber-bands.jpg

Mike
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  #117  
Old 08-16-2020, 06:25 PM
USSMissouri USSMissouri is offline
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Cool

A rubber powered cardstock airplane. Cool.
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  #118  
Old 08-30-2020, 10:27 PM
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mbauer mbauer is offline
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B25B & P38 Wing Spars

Both models have the wing spars done. Added a tube to the fuselage of the B25 to make sure the tail doesn't wobble. Photos show both side by side.
Rubber Band Power-pict0940.jpg

Notice how the mount for the paper tube ties into the wing supports?
Rubber Band Power-pict0925.jpg

Rubber Band Power-pict0928.jpg

Getting ready to add the wings/nacelles, then cut our large section of the body and wing to create/install Moore Drive parts and the rubber bands.

The P38 is painted to match a Double Ace in the Pacific.

Slow progress, re-drew the B25 3-times, been looking at drive ideas and how to hook up rubber bands.

Mike
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  #119  
Old 11-21-2020, 10:08 AM
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New Project: B25 & P38 on Hold-Propeller Design 101

The Mitchell B25 and the P-38 Lightning projects are both on hold.

Envisioned a different type of rubber model while searching for ways to power the B25. Pulleys, gears, you name it. Once it is figured out, will resume project. Bought a bunch of plastic gears to test ideas with.

One problem with the P-38 is want to do this biggest model with counter rotating props. Found some that were three bladed blanks, still needing carved. I chose to skip the price, then due to Covid they went away.

What to do?

Why not design my own to scale prop, but use the most efficient design possible.

After several searches, found a gold mine of info, for the last several weeks been reading and designing a prop per what I learned about rubber band power.

Now that I know more, decided to do a 2-bladed project first. Not the B25-still too much designing needing done.

Then it hit me, a long thought of project. Something that has history back to when I was a young lad and both my grandpas gave me some control line models. One of them gave me a scar to this day, clearly visible.

Anyway this is about the prop design:

Searched and found some PDF about a Professor Larrabe and his ideas for a prop design. Basically change the whole look of a rubber band propeller to be more efficient.

Wider blade by the shaft that has an elliptical shape to lower drag losses.

The I found a table and instructions on how to multiply your prop needs into a plottable design, just like how I do my aurfoils. Hey I can do this!!

My new project is huge! Needs a 17.3" diameter two bladed propeller. Why not build my own prop for this project and move it to the front of the line?

I've been designing this complicated project for three months part time-weekends, evenings after work. Never had a project last more than two weekends! As close to scale as I can make it and get it in the air. Special 260gsm paper in use.

The prop material will be 300gsm MOAB, thinking to get the curve need to double glue blades back to back and then using a steam iron and piece of PVC pipe to "iron" a shape to permanently form the proper curve needed.

Here is the 17.3 inch diameter propeller and carbon fiber hub drawing. Plan is to make the hub out of the available carbon fiber tubes I have, and the propeller blade material out of MOAB Slickrock Metallic Silver paper to mimic the shiny aluminum version of the real one.

Prop is proper scale diameter, it is not scale shape or pitch; it has a P/D of 1.00 meaning the pitch is 17.3 the same as the diameter of the prop 17.3:
Rubber Band Power-17.3inch-larrabe2.jpg

The airplane part of this project is still being designed, a few things left on the fuselage then the printing starts. Going to do the propeller first and test with planned 6-strands of 1/4" Super Tan rubber band. Bought a ten pound box. Plenty to build models for!

Mike
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  #120  
Old 11-28-2020, 02:36 PM
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Boeing P26 Peashooter: Printing Started!

Well after several weeks of part time drawing, printed page 3 of the new P26 Peashooter project. Still need to do the wing-spar.

Tried to make it as close to 1/6 scale as I could, needed to make some changes here and there to keep it to actual scale size, not identical to scale for some of the parts.

Parts have been modified for flight and ease of construction.

Going way over board on the printing for this model!

Photo paper used is called Simply Elegant Silver Metallic. I bought a 24 inch x 100feet long roll back in 2014. Just checked, it is no longer available.

Cost per 2ft x 3ft print sheet is around $15 for the photo paper and $3 for ink coverage. 7-sheets + 1 sheet of 125lb Tag will be needed. The Tag Cardstock will be for patterns that need made out of balsa wood. No sense in printing on expensive stuff.

Since it is a silver based photo paper with underlying glitter, it turns ink into 3D paint!!!!! It requires a clear coat to seal it. You have about 10-days before it starts to smudge! This is the reason foe one sheet at a time. Get the sheets printed for specific parts, make the parts then seal with Clear Gloss Acrylic UV spray. Print next set and so forth till done.

At issue is the color White. My inkjet printer doesn't have white as an option. Found some really cool looking White Glitter 104LB cardstock as shown in the photo for doing the white areas as "decals".

As you can see, Yellow Looks like gold and Gold looks like darker gold! Yes, it really is that shiny, photo does not show true look: Rubber Band Power-pict1003.jpg

Rubber Band Power-pict0999.jpg

Rubber Band Power-pict1002.jpg

Rubber Band Power-pict1005.jpg

Here is the pack of white glitter from Wal Mart. 10-sheets cost around 50-cents each. $5+ for the ten pack. Colors Really Jump Out and Look Alive!!!!:

Rubber Band Power-pict1001.jpg

Mike
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Last edited by mbauer; 11-28-2020 at 03:04 PM. Reason: Forgot Clear Coat
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