Stop Rumbling Sounds

[ILikePike]

DonFromTX, I did notice that your external stiffeners were riveted to the formers. This may help keep any cracks from forming???

Jon, I don't think my roar is from the cowl. I built up the edge with micro to make a 3/4 strip for the felt to sit flat on the top skin. It adds stiffness and seals very well.

[BillL]

Originally Posted by sf3543

To keep it from causing cracks at the ends of the added angles, the angles should be attached to the two bulkheads at each end. A joggle to lap over the flange at an existing rivet or a 90 bend and riveted to the bulkhead if the flange is on the other side of your stiffener.

Originally Posted by ILikePike

DonFromTX, I did notice that your external stiffeners were riveted to the formers. This may help keep any cracks from forming???

There are a couple of loadings that cause cracks. One is the pressure loads from the skin which loads the stiffener, well, like a beam. That loading will concentrate on the skin with no stiffening at the end if not attached to the bulkhead. However on that part of the fuse, there are longitudinal forces stretching the skin between the bulkheads, and attaching to the bulkhead will do nothing for that. There is a lot of skin there, and if the "stiffener" is the same thickness then is is likely of little consequence but would concentrate that stiffer effect at the last rivet.

I avoided (-7) the lengthwise stiffening all together by forming a couple of .025 bulkhead-like lateral stiffeners and did not rivet them into the J channel they do attache to the skin overlap rivet line. They were formed over a buck made to the floor contour, standard flange and just under an inch tall. Three rivets with 3M weather weld - bonding to the floor. Prior to stiffeners, a feather light touch was all that was needed to initiate the oil can and with some down force on the tail it self initiated easily.

YMMV