×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Bending moment acting on an aircraft rib
2

Bending moment acting on an aircraft rib

Bending moment acting on an aircraft rib

(OP)
Hello friends, I am having trouble with the estimation of the bending moment acting on an aircraft rib. The method shown in the images attached was given by a teacher at the university. I know how to do all the calculations up until the bending moment diagram, there I am struggling, since that was I've drawn bending moment diagrams was to use the areas under the curve of the shear diagram, but for this case that doesn't seem to work, or maybe I am doing something wrong ( most likely).

I really don't understand where the bending values are coming from.

Thanks in advance my friends



RE: Bending moment acting on an aircraft rib

Look at the rib freebidy - The skin shears contribute to bending moments, not just the vertical shear.
Once you account for the skin shears your BM plots should make sense.

RE: Bending moment acting on an aircraft rib

rather than a rib in bending, think of the rib as three torsion cells. The shear flows in the skins balance the shear in the spar webs.

This problem looks suspiciously looks a student problem ?

another day in paradise, or is paradise one day closer ?

RE: Bending moment acting on an aircraft rib

RB... This IS a university student...

"...The method shown in the images attached was given by a teacher at the university. …"

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
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", Homebuiltairplanes.com forum]

RE: Bending moment acting on an aircraft rib

(OP)
It is kinda like a student problem to shows how to initially dimension a light rib, taking the shear force to size the web of the rib and bending for the flange. Just i cannot find the correct bending, the shear diagram is easy, I took the component of the vertical shear in the a-d and b-c sections, but when i try to get the bending i just cannot find the correct one, between a-d and b-c, and thus my diagram doesn't end in 0dazed.

RE: Bending moment acting on an aircraft rib

the rib doesn't work like a beam in bending, but like three torsion cells.

please note, student posting is not permitted.

another day in paradise, or is paradise one day closer ?

RE: Bending moment acting on an aircraft rib

I glassed over problems like this in school cause I knew I'd never be the one doing that... I just figure out how to make stuff. I have Bruhn sitting on my shelf with crisp pages still.
I enjoy seeing this stuff/been afraid to ask sometimes.

RE: Bending moment acting on an aircraft rib

I wonder how many Bruhns went to their graves with crisp pages ?

another day in paradise, or is paradise one day closer ?

RE: Bending moment acting on an aircraft rib

I fear mine will. Was never my world. But my 43.13 and machinery handbook have taped spines and coffee stains. If I'm missing my starrett scale its in the thread charts.

RE: Bending moment acting on an aircraft rib

When we were introducing FEA at LandRover/Jaguar 4 decades ago lucky greg was the one who got to build FEA models of the worked examples in Bruhn and than try and puzzle out what was wrong, ably assisted by my manager, who knew Bruhn backwards.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Bending moment acting on an aircraft rib

I imagine that Bruhn is close to a ROD and shear web model ?

another day in paradise, or is paradise one day closer ?

RE: Bending moment acting on an aircraft rib

You can get remarkably good correlation between dummy loads method in bruhn article A.?? and cshears and crods.

One takes about an hour to set up and seconds to run. The other takes about a month, but brings far greater satisfaction.

RE: Bending moment acting on an aircraft rib

I also think something doesn't add up in the bending moment diagram.

The F/S reaction is approx 1878N and the R/S is ~250N. The remaining ~255N comes out as the vertical component of the shear flow in the inclines.

At the front spar, it's just 3.56*260*260/2=120,328N/mm. (Matches)

At 332.5mm, the bending moment is 3.56*332.5*332.5/2-1878*(332.5-260)-4.06*sin(6.2)*(332.5-260)*(332.5-260)=58,310N/mm. (value quoted is 82,468N/mm)

RE: Bending moment acting on an aircraft rib

Try accounting for the horizontal component of shear flow in the skins, not just the vertical component. I haven't run the numbers on this one, but that is usually where people slip up with these problems.

RE: Bending moment acting on an aircraft rib

While I get that the reaction system with 4.09N/mm shear flow reacts the torsion, I do not understand what it does to the rib. For example, what if there was no rib in this system (when looking at torsion alone)?

RE: Bending moment acting on an aircraft rib

Neat topic... wouldn't the bending moment occur because of the lift and the cantilever from the fusilage? or is that the obvious part? ponder

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

RE: Bending moment acting on an aircraft rib

Dik: this topic pertains to bending in the plane of the rib web, (not wing bending).

Jp: for a wing in pure torsion, if there were no rib at this station, the macroscopic effect would be greater warping of the wing cross section (wing becomes more torsionally flexible), at a detail part level the onset of panel buckling would occur at a lower load.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close