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Moment of inertia of Carlson spars

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PTAirco

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Carlson supplies extruded 6061 spars used on many different aircraft and they might just be suitable for something I'm doodling on. I asked if they publish data on these such as Ix, Iy etc but had no response. I know I can sit down and dig out my old books and try to calculate it by hand but I haven't done that for 30 years and what do we have the internet for anyway? Has anyone come across these and found the appropriate numbers for them? They are so widely used, I suspect somebody must have. I also noticed at least one discrepancy in the table below, there might be more. They also talk about the "ultimate yield strength" (some terms on the site get used indiscriminately) of the material, so I'm dubious if they have any actual engineering knowledge or just re-sellers of this product.


Carlson Spars.PNG
 

PTAirco

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I know about skyciv. I can do the math if I sit down and give myself a refresher, but somebody out there must have done it for me.
 

TFF

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My question about the Carlson spars is, at the same size, are they the same as Citabria spars, just not certified. From what I can tell they look the same. Just blanks.
 

Pops

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I was told that Ernie had the dies made and extruded.
 

BoKu

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I once looked for this data myself and didn't find it. I suspect you'll have to fire up Excel and use the method of composite sections.
 

proppastie

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you can draw the cross section in 2D autocad turn into a "region" and ask for mass properties.....it will give you the "I" of the section just like the solid works post above leastwise my autocad 14 does it...I draw a line from the centroid and make the centroid 0,0,0 to get the results that make sense
Here us a sample of my stiffener fix for on the Aluminum Dragon
xsection mass properties.JPG
 
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mcrae0104

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Bite the bullet and break out the books. bh^3/12+ad^2 isn't that bad. Each instance takes about 5-10 min to calculate by hand, but if you invest 10 min in a simple spreadsheet, you can crank out any one you want in 10 seconds.
Capture3.JPG
 

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kubark42

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I really enjoyed speaking with Carlson Aircraft. They were very nice to me so I thought I would do them a favor back:

Screen Shot 2020-12-01 at 21.04.18.png



The interactive file is online at OnShape. You can change the section of interest by using the dropdown box in the top left corner.

The values you're after are in the bottom right, with arrows pointing to them.

NB: Please note that I believe there is a discrepancy between the reported masses and the reported volume. In other words, when I make the section according to their data and then calculate the volume for the length they sell, I get numbers off by 20%. I trust that my numbers are very accurate for my input data, so either I entered data wrong (I triple checked), or the webpage data is off.

P.S. I believe they have engineering knowledge. Based on my conversation, the gent on the phone tried to write his website so that non-engineers could have some chance of understanding. That might be why it's written "ultimate yield strength" instead of "ultimate yield stress".
 
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TFF

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Carlson probably did have their own dies made, but they are darn close to what the Citabria Decathlon ones look like; which is good in my book.
 

Victor Bravo

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But find out whether Citabria / Decathlon spars 6061 or 2024? There are plenty of extrusions made in both materials, and the 2024 gives you more "strength" at almost the same weight for only a little bit more money per pound.
 

plncraze

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Some of the old books will have design values for various section shapes. You might check that out too.
 

David L. Downey

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2024 is much harder on the dies and harder to extrude than 6061! and usually more costly...with better performance and less corrosion resistance!
 

Pops

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Carlson probably did have their own dies made, but they are darn close to what the Citabria Decathlon ones look like; which is good in my book.
Bob Barrows had his dies made for the struts on 4 seat Bearhawk and used the same struts on the Patrol. On the LSA Bob bought the Carlson struts because of the high cost of having dies made. After Ernie died and Mary had the business for sale, I tried talking Bob into buying all the dies for the spars and struts for his business and have the supply of the Bearhawk LSA struts but he never decided to do it.
From what I was told, Ernie Carlson had the dies made for the spars and struts. ( I can't remember if it was Ernie or his wife Mary).
I was visiting Ernie a couple months before he was killed in the accident. Ernie and I started flying model airplanes together when we were 15 years old at his parents farm that was about a mile down the road from his factory.
Ernie and myself and 5 others started the local RC club in the mid 1960's. Ernie's first RC model is still hanging up in the company office. ( Free Flight Buzzard Bombshell with rudder only ). RC club is still active.
 

PTAirco

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The interactive file is online at OnShape. You can change the section of interest by using the dropdown box in the top left corner.

The values you're after are in the bottom right, with arrows pointing to them.

NB: Please note that I believe there is a discrepancy between the reported masses and the reported volume. In other words, when I make the section according to their data and then calculate the volume for the length they sell, I get numbers off by 20%. I trust that my numbers are very accurate for my input data, so either I entered data wrong (I triple checked), or the webpage data is off.

P.S. I believe they have engineering knowledge. Based on my conversation, the gent on the phone tried to write his website so that non-engineers could have some chance of understanding. That might be why it's written "ultimate yield strength" instead of "ultimate yield stress".
Thanks for that. I was going to point out some discrepancies on their site to Carlsombut didn't want to come across as critical, I know what their numbers meant. (There are also some values listed in PSI when it should be actual lbs.) I think one of the section should be listed as having a 0.049" web thickness, not 0.060", that would make the numbers work.

I'll try out the spreadsheet later, thanks for the responses.
 
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Mary Carlson is an engineer and likely has the numbers. They have the dies and have the spars extruded at a mill. 2 of the soars are the same as piper spars. She is 93 years old I believe, She may be hesitant to give out such numbers maybe due to liability. All you can do is call and ask. She’s a great lady and good friend - glad I saw this post. Need to call and say hi.
 

PTAirco

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The On-shape file had all the numbers I needed, thanks a lot. Found a couple of sizes that work perfectly for my purpose.
 

PTAirco

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Mary Carlson is an engineer and likely has the numbers. They have the dies and have the spars extruded at a mill. 2 of the soars are the same as piper spars. She is 93 years old I believe, She may be hesitant to give out such numbers maybe due to liability.

Wouldn't there be greater liability on not publishing the numbers?
Regardless, I have them now. Thanks everybody.
 

Pops

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Don't believe Mary is that old, maybe 83 years old. Ernie was the same age as me. I'm 80 years old and Ernie was the same age as me when we were growing up ,if I remember correctly. I remember when they got married.
 
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