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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, 9 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, 4 views)
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  #115  
Old Yesterday, 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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