longtimelurker
Member
I would like to raise a somewhat philosophical question.
I have been working on a aluminum stressed skin tailcone, constructing C-Frames of a roughly rectangular shape with curved corners. The top corners approx 5 inches radius, the bottom corners roughly 8 inch radius. The frames themselves are 2 inches deep, with 1/2 inch flanges, that I bend and hammer over a form. The material I'm working with is 6061-T4, .025. I am trying to stay within the range of technique of the hand-builder, no big machines or CNC anything.
I have done two sets of frames to date;
The first set was with fluting on the outside corners, and a full 1/2 inch all the way round the inside. The inability of the inside to stretch significantly limited the inside angle to 45 degrees.
The second set was with tabs on the outside corners, and the inside flange was reduced to 1/4 inch around the inside corners, allowing me to bring the inside flanges to 90 degrees.
However, in both cases, the inside flange can best be described as visibly wavy, not a very smooth surface, unless I over-beat the inside flange against the form resulting in a smoother flange surface, but a frame that doesn't lie flat unless I flute the inside (re-introducing the waviness).
The lumps and bumps will certainly result in an earlier buckling of the flange under load.
My question is: How good (smooth) does the inside flange need to be? And how can I reliably test my work other than at full scale?
An alternative is to go to a built-up inner flange by riveting stringer material to the frame - would anyone consider that a reasonable approach?
All inputs gratefully received at this point....
I have been working on a aluminum stressed skin tailcone, constructing C-Frames of a roughly rectangular shape with curved corners. The top corners approx 5 inches radius, the bottom corners roughly 8 inch radius. The frames themselves are 2 inches deep, with 1/2 inch flanges, that I bend and hammer over a form. The material I'm working with is 6061-T4, .025. I am trying to stay within the range of technique of the hand-builder, no big machines or CNC anything.
I have done two sets of frames to date;
The first set was with fluting on the outside corners, and a full 1/2 inch all the way round the inside. The inability of the inside to stretch significantly limited the inside angle to 45 degrees.
The second set was with tabs on the outside corners, and the inside flange was reduced to 1/4 inch around the inside corners, allowing me to bring the inside flanges to 90 degrees.
However, in both cases, the inside flange can best be described as visibly wavy, not a very smooth surface, unless I over-beat the inside flange against the form resulting in a smoother flange surface, but a frame that doesn't lie flat unless I flute the inside (re-introducing the waviness).
The lumps and bumps will certainly result in an earlier buckling of the flange under load.
My question is: How good (smooth) does the inside flange need to be? And how can I reliably test my work other than at full scale?
An alternative is to go to a built-up inner flange by riveting stringer material to the frame - would anyone consider that a reasonable approach?
All inputs gratefully received at this point....
