Which Type of Stringers cross section is most preferred in aircraft wing and fuselage 2

[MCA1983]

Based on bending + compression + buckling which type of stringer cross section is most preferred for aircraft wing and fuselage ? C or T or L or J or I or hat or inverted hat section..

 

[SWComposites]

Question is too generic.
Shape depends on loading - tension or compression, manufacturing considerations, attachment considerations, fuel tank requirements for wing, etc, etc.

Please stop with the overly vague questions. And answer or reply to the comments in your other posts.

 

[SWComposites]

Suggest you obtain and study these texts:

https://www.amazon.com/Airframe-Structural-Design-Information-Structures/dp/962712804X

https://www.amazon.com/Aircraft-Structures-Dover-Aeronautical-Engineering/dp/0486485803/

 

[rb1957]

yes !? ... different shapes used all the time, though hats are less frequent these days.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[MCA1983]

Sorry if my questions was too generic. I was reading about these topics in book not getting proper reasons.. thought of using eng tips.com to get some proper reasons.. thanks for feedback I will ask proper queries.. for my previous posts I'm yet to study on those.. I'm writing it down in book so that I will check on does comments.. yes it does help a lot to me.. thanks

 

[SWComposites]

Another thing that drives stiffener shapes is inspection requirements for damage tolerance. I.e., accessibility for inspecting for fatigue cracks.

And re attachments, stiffener shape depends on whether the adjacent ribs or frames must be shear clipped to the stiffeners or not.

On a given commercial transport aircraft a number of stiffener shapes are used, in different locations.

 

[rb1957]

re DTA ... also load redistribution (as skin cracks) and crack arrest loads (as crack grows)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[sdm919]

Of course it depends on many factors, but for high aspect ratio wings, as used on commercial transports for example, the most commonly used shape is probably the Z section, at least for metallic structures. It is good because it has good bending stiffness (moment of inertia) and also has good access for attaching it to the skin.

A "C" and a "Z" with the same dimensions would have the same moment of inertia, but the C would be harder to attach because the outstanding flange would get in the way of the tool, whereas the flange on a Z is turned in the opposite direction giving better access for the tool.

A simple angle could be used, but is inefficient due to having a lower moment of inertia. Therefore, when angles are used, they are usually in the form of an extrusion with a "bulb" at the free edge to stabilize it as well to add some moment of inertia.

A "hat" often shows up as best when analytical trade studies are performed. The have good moment of inertia and they reduce the space between stiffeners, giving more support to the skin. But for metals, a big disadvantage is that there is a hidden area within the hat where corrosion and cracks could occur and be hard to find during inspections. But hat stiffeners seem to be popular on modern composite wings.

The book "Aircraft Loading and Structural Layout" by Denis Howe (published by AIAA 2004) contains data for preliminary sizing of aircraft structures. Table 13.4 on page 385 gives values of "buckling efficiency" for different shaped stiffeners. The higher the number, the better (at least from a theoretical weight point of view).

Z stiffener (built-up) 0.96
Z stiffener (machined) 1.02
Blade stringer 0.81
Hat stringer 0.96
etc.

The old NACA reports contain many studies of stiffened skins with different stiffener shapes.

I have attached a few picture I took at an air museum where they had a C-135 (military version of Boeing 707) with the outer wing cut off so you could see the inside. As you can see, they mostly used Z shaped stiffeners.

 

[sdm919]

here is the second picture I intended to send in the previous post

 

[WKTaylor]

NOTE RE photos of C-135 wing-cut...

Amongst all the 'Z' stiffeners, there are [2] sealed 'hat' channel stiffeners shown... essentially [2] mirror-image z-stiffeners fused together on the free-flange... located @ ~mid-chord attached to the upper skin... which illustrates the complexity of the issue of wing stiffener design. In addition to being structural stiffeners, they are also intended for what other purpose...???? [hint: sealed]...

OH yeah... and there should be an effort to ensure stiffener secondary bending effects are minimal or are stabilized. "I" and "Z" stiffeners can be very stable under compression or tension.

Also... pop-quiz... what are the differences between a 'stringer', a 'stiffener' and a 'longeron'???

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[MCA1983]

Thanks everybody for your knowledge sharing..

 

[WKTaylor]

M CA...

Hmmmmm Not curious enough to discuss my 'challenge questions' RE the KC-135 'hat channel stiffeners'???

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[MCA1983]

Sorry I'm beginner in aerospace domain.. don't have much knowledge to debate.. found eng tips useful to learn and gain knowledge..

 

[WKTaylor]

No debating... just learning-in-motion... do You have any ideas/guesses regarding my questions?

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[ArunKumar Bala]

As for my knowledge, Stringer profiles are selected based on the failure mode and stress to be withstood when it is attached to the skin. And in more the cross-section area of the stringer plays a major role in the design stage. Based on FEA extracted stress acting on the particular area, and material of the stringer and profile is selected based on Ftu and Fcy required in that region.