Interal Pressurization Loading

[724napier]

Hello All,

I am analyzing a small exterior mounted GPS antenna being installed with an external doubler. I can calculate the shear loading on the rivets due to hoop and longitudinal loading from internal pressurization. My question is, how do you determine what portion of that load acts in tension on the fasteners due to curvature of the fuselage. Essentially, the problem is a cylindrical pressure vessel with a rectangular doubler installed exteriorly with 4 rows of rivets. I can calculate the shear acting on the rivets, but how do you correctly determine any tensile loading on them?

 

[rb1957]

I think conventional analysis says that the doubler works like the rest of the fuselage, and reacts pressure with hoop stress.

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

 

[rb1957]

of course, how much of the external dblr is exposed to cabin pressure ?

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

 

[Sparweb]

Since aerodynamic forces on a "small exterior mounted GPS antenna" should be quite small, even at VD, I do not believe the tensile forces you are considering are due to the antenna itself. So you must mean the internal air pressure, pushing "out" on the doubler. In fact, a correctly installed doubler will convert all internal pressure loads into surface stresses in hoop/long directions.
However, if the size of the GPS antenna was understated (some of them have blades), and you actually do have loads at the antenna base, then reinforcement is necessary where the antenna is attached by screws. This reinforcement should resemble a "beam" that traverses from frame to frame (ideally), or stringer to stringer (if necessary).


STF