## Fuselage Hoop Stress Calculation

## Fuselage Hoop Stress Calculation

(OP)

We had a discussion in our group on how do the hoop stresses are calculated in a fuselage section composed of different radii (non circular shape).

Do you use the biggest radius (being conservative)?

Do you use the local radius for a given panel?

Do you use the opposite radius of the panel you are calculating?

Do you use an average of radii?

Which method is the most broad and complete one that we could rely on and give away the conservatism when needed.

Do you know any methodology or a paper with a methodology?

Thanks in advance for any feedback.

Do you use the biggest radius (being conservative)?

Do you use the local radius for a given panel?

Do you use the opposite radius of the panel you are calculating?

Do you use an average of radii?

Which method is the most broad and complete one that we could rely on and give away the conservatism when needed.

Do you know any methodology or a paper with a methodology?

Thanks in advance for any feedback.

## RE: Fuselage Hoop Stress Calculation

Becarefull about assuming there is an obviously conservative approach. Non circular fuselages have significant secondary effects (in the frames). The floor support beam is also a source of stress trouble.

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

## RE: Fuselage Hoop Stress Calculation

Yes, indeed non circular fuselages cross sections promotes secondary effects, but the uncertainty itself is specifically about the theoretical hoop stress (P * r / t). In a circular fuselage there is no issues...r is the radius...case closed. But in a non circular fuselage cross section with 3, 4 different radii along its perimeter. What should be done? Taking the biggest radius will cover for everybody, but sometimes it is too conservative. From there the discussion was generated...what should we use to avoid being too conservative? Is there a methodology to calculate theoretical hoop stress for non circular fuselages?

## RE: Fuselage Hoop Stress Calculation

One thing you'll see is the pressure vessel skins will try to conform to some common radius (like the height of the fuselage/2). The skin panels will deflect out-of-plane (slightly) and the frames will have "funky" bending.

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

## RE: Fuselage Hoop Stress Calculation

## RE: Fuselage Hoop Stress Calculation

If you remember your calculus, and have a copy of Roark for the joints, you'll be done in an hour or two (all too quickly, I'm sorry).

If you want the fun to last, you can do as SWComposites suggests. You will still be fussing with the model days from now. Enjoy!

www.sparweb.ca

## RE: Fuselage Hoop Stress Calculation

## RE: Fuselage Hoop Stress Calculation

I Know that this is done (by OEM) for a bi-lobe fuselage. Where this works for an oval fuselage was a guess. Ultimately the oval fuselage will deflect to a circular shape (if there's not preventing it from doing this, like frames and tie-beams) with, I expect, and equal circumference.

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

## RE: Fuselage Hoop Stress Calculation

http://www.structuralfea.com

Brian

www.structuralfea.com