Bonding aluminum to fiberglass
Bonding aluminum to fiberglass
(OP)
I am building aluminum fuel tanks for my KR2 and was thinking about adding a layer of fiberglass over the outside of the alum. Would the difference in the expansion rates cause any problems. The tanks are about 5 ft. long and the epoxy is vinyl ester if that has any bearing.





RE: Bonding aluminum to fiberglass
I am not sure what the reasoning is for laminating the tanks with fiberglass, I guess for protection or maybe some abrasion prevention? I don’t know, haven’t built any planes lately, I do have an instrument rating however.
Anyway, lets see if this help you out. My thought on the matter is that one would need to know the thermal coefficient of expansion for all of the materials to be used.
Alum: 2.5 x 10^-6 in/in -F°
Fiberglass: 11.1 x 10^-6 in/in -F°
Epoxy: unknown variable
Then determine a realistic temp variation and calculate the two material expansion.
For this example I will assume the outside temp is 40°F and the raised temp is 80°F giving us a temp range of 40°F. Additionally I will use your 5 ft. tanks.
Aluminum tank length in inches at 40°F = 60.000 inches
Aluminum tank length in inches at 80°F = 60.00003 inches
Fiberglass sheet length in inches at 40°F = 60.000 inches
Fiberglass sheet length in inches at 40°F = 60.00011 inches
The thermal expansion for the two materials is not much (difference of 8/one hundred-thousands of an inch). The epoxy thermal expansion rate should be available from the supplier. If the coefficient is between 2.5 x 10^-6 in/in -F° and 11.1 x 10^-6 in/in -F° than I would not be too concerned. However, I have not built a plane am not exactly sure what the normal process is.
If you get a chance, check out this website
www.navpen.com
best regards,
Jay
RE: Bonding aluminum to fiberglass
RE: Bonding aluminum to fiberglass
no thermal expansion specs there, but shrinkage on the order of 7% appears fairly typical. I wonder if the residual strain from that much shrinkage might be more important.
RE: Bonding aluminum to fiberglass
see = www.rapidcoating.com
RE: Bonding aluminum to fiberglass
Jay:
I think your numbers are wrong - using your data the 60 inch aluminium structure would expand to 60.006 not 60.00003.
Don't think it matters anyway in this case - I'm just picking nits!