Easy to Remove Inspection Panels

General Composites Discussions Composites Talk
#1

Hello,

I’m looking to build a fiberglass aero shell for a recumbent bicycle, using an existing female mold. The only detail I have not been able to work out are easily removable inspection panels. The panels themselves will be several square feet, and cut directly from the finished shell layup, flanged, and reinstalled. In the past, I’ve used about two dozen screws to attach the panels, which is a pain in the butt.

I’ve struggled to find any existing documentation on techniques for very easy access panels and covers. The general aviation industry makes use of quarter turn Dzus fasteners for things like oil stick hatches, which is an improvement, but not the simplicity I’m imagining. Ideally the removal of a 2’x3’ panel would take several seconds at most.

Based on previous experience with this shell design, it would be advantageous to have the connecting interface of the panel and shell to be as continuous (eg piano hinge) and strong/light as possible, yet also allow for the complete removal of the hatch (eg not piano hinge :p), to be stowed away from the vehicle temporarily.

I would greatly appreciate any insight into this problem, it’s a VERY interesting engineering challenge!

#2

Commercial hook and loop. And not the sewing store Velcro either. 3M makes some great hook-n-loop that will be perfect for what you’re doing if you use small washers and dots at the corners. You can even relieve the mold flanges to make them flush.

Check McMaster, etc.

http://www.mcmaster.com/#hook-and-loop-fasteners/=hifqvw

#3

I like the ALCOA fastener.

#4

For my streamlined recumbent I’m using magnets and som velcro straps to make sure the panels stay in place when I ride over bumpy roads.

#5

If you have a female mold. Draw panels in the mold with sharpie. Use 3m white mask as a template and trace. Trim template to trace line. Lay template onto 1/8 sheet wax and cut wax. Place sheet wax in the mold. Layup shell per norm. Remove shell and allow 1" joggle and cut out holes. Lay up .100 thick laminate access door per norm. Trim.

Trick fastening flush option. Layup some thin steel sheet metal inside the fiberglass door layups. Then click bond some high quality magnets on the backside of the joggle flange.

The thicknesses are for made up but… Having a thinner door compared to sheet wax thickness will allow you to roll a thin layer or rtv on the joggle. This will stop chafing on the door and maintain a flush panel. Just an idea.

Cam loc fasteners and dzus are the bomb. You could rob some gas tank pops and latches from the junk yard remote no tool required door access.

The possibilities are endless. Good luck

#6

Yes they are, here is one place I get mine. 1/4 turns work but are not as nice a Cam loc.

http://www.milspecproducts.com/26002700C-Spec.htm
http://www.milspecproducts.com/4000C-Spec.htm

#7

If he goes with an aircraft fastener the grip length of the stud is 1/16 increments. so if you have .250 thick material you’d want a -4 stud or a #4 stud. Cam locs require special pliers to pop the stud through the washer and hole… FYI. The receptacle can be bonded or riveted in. Hole diameter is measured in 1/32" so a 3/16" hole would be a -6 or #6 fastener… Although most cam and dzus are 1/4… 5/16 and larger…

This is standard for aircraft stuff…

Hole diameter for rivets

3/32 (#40) rivet = -3
1/8 (#30) rivet = -4
5/32 (#20) rivet = -5
3/16 (#10) rivet = -6

The numbers on turn loc fastener pin heads usually indicate length not to be confused with hole diameter. They are also identified with - 3 -4 -5 and so on. Or the last number of the fastener part number usually.

Just FYI if you do choose aircraft hardware. I get my stuff from the yard store. They are pretty good at helping you out over the phone if you have questions.

#8

Be aware that with quarter turn fasteners the material on the backside needs to be stiff enough to prevent inward deflection or you’ll push in on the fasteners and they won’t engage.

Typically this is done by riveting or bonding an angle alongside the receptacles.