Steel Tube Fuselage

[redtail58554]

Hey guys,
Not sure if this is the right place to put this but here it goes. I am thinking about designing an aircraft with a steel tube fuselage. My problem is determining which size tube I should use. Is there a source that would have this info. I did look at a few sets of plans and everything is a little different. I realize different loads require different size tubes, I am just not sure of what I should use and where. Any help would be great.
Matt

[WLIU]

It sounds like you need to start with a textbook on what mechanical engineers call "statics". R.C. Hibbeler is the text most commonly used in university classrooms. Covers calculating the strength of different shaped elements like tubes and I beams. Then 14 CFR Part 23 and the advisory circular that expands on those strength performance requirements will give you the input loads you need to design for.

You can also purchase plans for an existing homebuilt aircraft similar to what you want to build and look at how that aircraft design uses fuselage trusses.

Best of luck,

Wes

[martymayes]

A good beginner level book for analyzing a steel tube truss without a lot of analytical skills is called "Stress Without Tears" by Tom Rhodes.

No pecuniary interest, I just enjoyed reading parts of it.

[Bill Berson]

Usually tubes fail in compression by buckling long before tension. So get some data charts for tube buckling length from old NACA reports. Another source is Evans Lightplane Designers Handbook.
I would look at similar frames. Then build it and load test it with sand bags on the tail. The amount of sand load required is in a chart in the appendix of FAR23.
Practicle Airplane Design by W. Fike (from EAA) might help.

[conodeuce]

You might also send a query to a well-experienced expert in tube fuselages, like Earl Luce (Buttercup fame) or Bob Barrows (Bearhawk designer). Contact information for both gentlemen is available via a quick google.

Best of luck!

[Mike Switzer]

It sounds like you need to start with a textbook on what mechanical engineers call "statics". R.C. Hibbeler is the text most commonly used in university classrooms. Covers calculating the strength of different shaped elements like tubes and I beams. Then 14 CFR Part 23 and the advisory circular that expands on those strength performance requirements will give you the input loads you need to design for.

You can also purchase plans for an existing homebuilt aircraft similar to what you want to build and look at how that aircraft design uses fuselage trusses.

Best of luck,

Wes

If I remember correctly, Hibbeler only covers calculating the loads transmitted along the members, to calculate the tube size required he would also need a book in Mechanical Engineering Design, mine is "Mechanical Engineering Design" by Shigley & Mitchell. The calculations require a good understanding of algebra & trig.

[lathropdad]

I may be mistaken but SolidWorks Student version (the version that a EAA member can down load) will do static simulation. This is FEA modeling. I am not a trained engineer but I have made very good use of FEA modeling as I developed tube frame chassis for race cars. I have also modeled the 4 place Bearhawk that I am building.

My problem with modeling the Bearhawk is that I do not have a good understanding of the forces that the fuselage will encounter. But if I were going to design a fuselage for an airplane, this is where I would start.

My experience with race cars is that this has been invaluable tool in developing my designs. I started with cars that were less than 2000 foot pounds per degree when twisted front axle to rear axle. My car are now over 7000 foot pounds per degree and that is both a number calculated in simulation and actually measured in testing. And the frames are lighter that the 2000 ft pound versions.