×
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

Tension Fitting (Angle and Channel) understrength mitigation

Tension Fitting (Angle and Channel) understrength mitigation

Tension Fitting (Angle and Channel) understrength mitigation

(OP)
This is a question for aero stress engineers.

We have a few locations showing negative MS where an external load (modification) is attached to a fuselage through the skin into a new reinforced channel or angle type fitting. The stack-up of parts on the fuselage side consists of skin double (0.10in), original aircraft skin (varies but 0.085in typ), intercostal (0.063in) and the new reinforcement channel or angle (tension fitting).

The fastener tension analysis is conducted using 100% of the tension load on the end pad of the channel of angle fitting. BA methods (BM7024.01.03.03 Rev B) is conducted and the fitting fails in end pad bending. Typical margin is MS= -0.06.

Given the significant stack of material/parts which is there to assist in reacting the tension load l believe a valid mitigation is to show a load path for the excess tension loads. This can be done via an increase in the effective end pad thickness (lets call it tb(eff)) much in the same way a stress pad (contour pad or throat pad, depending on which version of English you speak) provides additional support.

I need some input into the viability of this mitigation approach and, if possible, a reference to quote to support its use.

Many thanks,

RE: Tension Fitting (Angle and Channel) understrength mitigation

Sure, a thicker pad gets a higher MS. But that's obvious in the BA methodology. Somehow I suspect this isn't the direction you want to go.

Showing the positive MS on paper is one thing. Being certain that all variables have been well bounded and assumptions are valid is another. Beefing up a low-MS intercostal flange to secure an external mod's load seems to be tempting fate. Why aren't you proposing to make more substantial fittings mounted to this intercostal? Fittings like the ones shown in the first 3 figures of the BA reference you cite are suitable in some cases - have they been ruled out?

External mods have a lot of load cases. Which load case is driving the low MS?
Have you accounted for high angles of attack? icing? bird strikes? handling and abuse?

STF

RE: Tension Fitting (Angle and Channel) understrength mitigation

Are you using Fitting Factor ?

Certainly you can increase your tension fitting flange (or endpad) thickness. Personally I wouldn't count on the skin and doubler to carry out-of-plane load. How are you managing the torsion that I assume appears in the member supporting the tension fitting (frame) ?

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

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