Here is an interesting composites problem for the brain trust...
I have a rectangular "shop made" large overhead console/air duct about 10-12" wide and ~3" deep running down the length of the ceiling of my plane (~6' long). The duct walls are 2-3 plies of 8oz E-glass with spanwise balsa/glass stiffeners at ~24" intervals. The stiffness is enough to support the air vents and the air pressure just fine, but it turns out the areas between the stiffeners resonate noticeably when the engine is running at cruise RPM.
The challenge: I'd like to add some additional spanwise/transverse stiffeners to increase the resonance frequency of the unsupported areas. Unfortunately, the duct is permanently bonded to the ceiling and all painted/nice looking so this will have to be an "inside job". The only real access is through the existing ~3.5" vent holes which are just large enough to get my wrist and a bit of my forearm through.
I've been thinking about how to create the necessary ~12" long stiffeners that could be inserted through the vent holes and then bonded into place with really only one hand's worth of access. My best thought so far is to create a "fruit roll up" of 6? pre-wetted plies of glass with a plastic backing. This roll could be slid in through the vent hole and then maneuvered into position before being unrolled and rubbed down into the bonding area.
Do you guys have any better or more creative ideas? I'd love to hear them.
David
I have a rectangular "shop made" large overhead console/air duct about 10-12" wide and ~3" deep running down the length of the ceiling of my plane (~6' long). The duct walls are 2-3 plies of 8oz E-glass with spanwise balsa/glass stiffeners at ~24" intervals. The stiffness is enough to support the air vents and the air pressure just fine, but it turns out the areas between the stiffeners resonate noticeably when the engine is running at cruise RPM.
The challenge: I'd like to add some additional spanwise/transverse stiffeners to increase the resonance frequency of the unsupported areas. Unfortunately, the duct is permanently bonded to the ceiling and all painted/nice looking so this will have to be an "inside job". The only real access is through the existing ~3.5" vent holes which are just large enough to get my wrist and a bit of my forearm through.
I've been thinking about how to create the necessary ~12" long stiffeners that could be inserted through the vent holes and then bonded into place with really only one hand's worth of access. My best thought so far is to create a "fruit roll up" of 6? pre-wetted plies of glass with a plastic backing. This roll could be slid in through the vent hole and then maneuvered into position before being unrolled and rubbed down into the bonding area.
Do you guys have any better or more creative ideas? I'd love to hear them.
David
