Fuselage Cutout
Fuselage Cutout
I need some assistance on where I could find an analysis method for cutouts in a fuselage. I need to add a small opening in the side of an Aluminum semi-monocoque fuselage. I'm not cutting any frames or stringers, just the fuselage skin boxed within the frames and stringers. I don't have any loads data for the airplane. I was thinking about using shear-flow to compare the loss in skin structure to the added doubler and or internal frame. I've looked over the internet and in some of the classics (Bruhn, Niu, etc.), but I haven't been able to find a method that would work in my application. Does anyone have any directions or pointers? Thank you.





RE: Fuselage Cutout
Hi Gutboy,
Niu's two books (airframe design and airframe strsss analysis) deal with such cut-outs, as does Bruhn. Peery (1950) also has some material on cut-outs.
Andries
RE: Fuselage Cutout
a part 25 a/c ?
usually you'll need a dblr to reinforce the skin. can be external or internal. same thk as skin, riveted to the skin (two rows better than one) this is like a repair patch, research that for some further clues.
if you're mounting a "large" blade antenna (like a VHF), then you'll need to add a U-channel, attached to the adjacent frames, to make a stiff installation.
be aware, the FAA is taking a lot of interest in buffet/flutter, and may require flight test to Vd. we usually argue them back to Vmo.
RE: Fuselage Cutout
No antenna.
It is Part 25
It is a small opening for a sensor that will not be extending into the airstream. No loads are transmitted from the sensor to the opening. I "just" need to show that my opening and the external doubler I'm putting around the opening returns the local strength back to original or greater.
I started down the path of of shear flow, q=VQ/I, and tried to set the q(no cutout)=q(with cutout). Then I started getting a little lost after that.
I'll do some further research on the repair patch.
Thanks.
RE: Fuselage Cutout
the easiest approach is to show you've added area at least equal to the area removed ... a ring doubler, width = the hole radius or wide enough for two rows of rivets. same thickness as the skin. i think Bruhn has an analysis for a ring doubler (maybe Niu as well), but it's not Vq/It.
as FAR25, you'll need to consider the damage tolerance impact ... if you have an external dblr it's more involved (new inspection technique ?) an internal doubler could have no impact on the plane's ICAs.
RE: Fuselage Cutout
Mass of the sensor, if it's significant, cannot be ignored. Aerodynamic loads due to its shape and size, (again, assuming it's fairly large) are a factor, too.
STF
RE: Fuselage Cutout
RE: Fuselage Cutout
as part 25 you'll need to think about DTA, but unpressurised the loads'll be very low (i'd think).
RE: Fuselage Cutout
RE: Fuselage Cutout
RE: Fuselage Cutout
RE: Fuselage Cutout
Info on RapidC can be found here:
http://www.eng-tips.com/viewthread.cfm?qid=284439