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› Soild Main Shaft vs Hollow Main Shaft, New Info ! Soild is Stronger ??? i wish i knew ???
02-05-2012 05:51 PM  6 years agoPost 21
GetToDaChopper

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Las Vegas , NV

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thats a great point as i have never had a crash that didn't bend the main shaft !

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02-05-2012 10:49 PM  6 years agoPost 22
yannick

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South Korea

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The answer is that the resistance to bending moment is directly linked to the outer diameter of the shaft. However for flying stuff you also want a light shaft...
So lets say that a 10 mm plain shaft is X gramm.
For the same weight you can maybe make a 12 mm hollow shaft. This 12mm hollow shaft will be stronger than the 10 mm plain shaft for the same weight. It will anyway be weaker than the 12 mm plain shaft, but it will be lighter.

Conclusion:
1: for the same material, and for the same final weight, a hollow shaft is stronger than a plain shaft as it has a larger outer diameter.
2: for he same material, and the same outer diameter, a holow shaft will be lighter but always weaker than a plain shaft.

Hope this makes sens...

Cheers!

Is it me or this time the ground was higher than last time??

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02-06-2012 01:42 AM  6 years agoPost 23
GetToDaChopper

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ya thats kind of what i was thinking.....

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02-18-2012 01:53 AM  6 years agoPost 24
joesimmers

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Mansfield, Ohio usa

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I am a toolmaker/precision machinist and I completely agree with yannick above!

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03-17-2012 10:06 AM  6 years agoPost 25
karakoram

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Reno, NV

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The difference between a solid shaft and the hollow shaft is the total surface area. The more surface area the stronger the shaft.

A solid shaft only has an outer surface, with one circumference. It takes longer to heat treat a solid shaft and is subject to warping / twisting. As the holes are pre-drilled before the heat treating process.

A hollow shaft has two outer surfaces, two circumference areas. This adds more rigidity to the shaft. The hollow core acts as a support for the length of the shaft. Which makes it harder to bend, plus the fact that during the heat treating process…the hollow shaft is easier to penetrate and doesn’t need as much time in the oven. Resulting in a more accurate product (the pre-drilled holes won’t move during the heat treating process).

Here is an easy test to try to see (feel) the difference. Find a coat hanger (the original wire coat hanger) and a piece of fuel tubing (1/8" or larger). Bend the coat hanger first, then bend the brass tubing. You will notice the wire hanger bends very easy and the brass tubing is much harder to bend.

The wire coat hanger does get harder to bend as the bend goes past the 90 degree mark, and even harder past the 180 degree mark.
Nope!!

Completely wrong, Sorry!

Bending strength has to do with the "moment of inertia" of the object in question, the direction of the load relative to the moment of inertia, and the strength of the material in question.

Has NOTHING to do with surface area. A tube with more diameter, even if it has less material overall--less weight, will have a greater resistance to bending (that is before buckling) than a solid rod that has less diameter, even if the rod has more material (more weight), assuming they are both made of the same material.

If you have a tube and rod (shaft) of the same material, with the same diameters, the rod will be a tiny bit stiffer in bending or torsion (twisting), but will be a lot heavier (less efficient use of materials). One other advantage of a solid rod: it won't buckle as easily as a tube. Buckling is a different failure mode than bending.

This is known as stiffness (not the same thing as strength). If you make the wall too thin, even if the tube is large in diameter, it will buckle easily. Round tubes increase in stiffness by the square of their radius. http://en.wikipedia.org/wiki/List_of_moments_of_inertia thus a tube with 2x the diameter is 4x stiffer.

As an aside note, tubes are a more efficient use of material to resist torsion (twisting loads) as well. This is why vehicles with drive "shafts" actually have hollow drive tubes (think of trucks, and such). In ye olden times, cars had actual drive shafts, but it was a inefficient use of materials.

As for bending past 90 degrees, that's a completely different phenomenon known as "work hardening".

The above are not a complete descriptions of either case. You really need to take a Strength of Materials engineering class to understand everything. I could not explain it very well in a single post.

Here is some further reading: http://www.eng-tips.com/viewthread.cfm?qid=36587

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03-27-2012 12:45 AM  6 years agoPost 26
GetToDaChopper

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karakoram what you just said does sound very familiar it's just that it's been a long time since i heard it in the first place...... lol

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03-27-2012 02:45 AM  6 years agoPost 27
karakoram

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Reno, NV

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Its basic mechanical engineering. Any 200 level mechanical engineering student learns this. Strengths of Materials was the course.

When loads are in tension, only cross-sectional area, and type of material matter. When things are in bending or compression, that's when it gets interesting. Direction of loads, shape of the material (cross-section shape), cross sectional area, and type of material are what matter.
The answer is that the resistance to bending moment is directly linked to the outer diameter of the shaft. However for flying stuff you also want a light shaft...
So lets say that a 10 mm plain shaft is X gramm.
For the same weight you can maybe make a 12 mm hollow shaft. This 12mm hollow shaft will be stronger than the 10 mm plain shaft for the same weight. It will anyway be weaker than the 12 mm plain shaft, but it will be lighter.

Conclusion:
1: for the same material, and for the same final weight, a hollow shaft is stronger than a plain shaft as it has a larger outer diameter.
2: for he same material, and the same outer diameter, a holow shaft will be lighter but always weaker than a plain shaft.

Hope this makes sens...

Cheers!
This is correct. Larger diameter has more stiffness given the same amount of material (same weight), that is until wall thickness becomes so thin, you get localized buckling failure. Think of an aluminium can vs. an aluminum heli shaft. The can has greater stiffness until it buckles, but it has lower overall strength. Folks, remember that strength is NOT the same as stiffness.

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03-27-2012 05:02 AM  6 years agoPost 28
GetToDaChopper

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Las Vegas , NV

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that kind of reminds me of the time i tried to make a main shaft for a 450 size heli out of CF like the blade msr has, lol, it had tons of strength but not much stiffness LOL needless to say it didn't work to well.

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09-17-2012 11:35 PM  5 years agoPost 29
Herky

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Dallas, TX

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know this is a little bit of an old post, but I vaguely recall my engineering friend point out the main struts on a B-1 at an airshow and how it was likely hollow inside, which, being an engineering dropout (Business major...More chicks! lol) I had the same questions as we're discussing about the hollow vs solid mainshaft on a mini-protos.

So I understand this, FOR R/C HELI APPLICATIONS of a main rotor shaft, if they are the same circumference, a solid shaft is a more durable (for our typical useage) choice, at the expense of weight, than a hollow, correct??

thanks smart guys

TREX 700N, V-Bar, OS 105HZ-R, MP-7, Mini-Protos 4s, JR 9303

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02-11-2013 06:47 PM  5 years agoPost 30
AV8TRX

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USA

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Might anyone be able to send me the over all length of the mini protos shaft and the distance between the "jesus holes" please. I am trying to research this as a means to lathe a new one.

Thank you

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02-12-2013 01:29 PM  5 years agoPost 31
AV8TRX

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USA

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Got the answer thank you!

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06-15-2013 12:51 AM  5 years agoPost 32
GetToDaChopper

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And the answer is ?????

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