Oil Base polyurethane WILL yellow in about 6 - 7 months. Waterbase polyurethane does not yellow, HOWEVER it is only fuel RESISTANT WITH THE FOLLOWING CAVEATS:

1. Let the clearcoat dry for a MINIMUM of 7 days before exposing to glow fuel.

2. Do not let the residue remain on the surface for longer than 4 hours. After 4 hours the surface begins to soften.

MOST ACRYLIC clears are fuel proof. I suggest doing the following: 1. Use an ACRYLIC clear ENAMEL for a clearcoat. Enamel can safely be used over lacquer, but not the other way around. 2. Before commiting your plane, do a test panel and perform AT LEAST these tests - raw fuel test and exhaust residue test. Raw fuel - exactly what it says. Pour some raw fuel on the clear coat and come back in several hours. Exhaust residue - put the test panel in the exhaust stream of a running engine for about 5 - 10 minutes. Come back in a couple of hours. You will know if the clearcoat is good or not.

I would also add a 3rd test - leave your test panel out side for about 3 weeks to find out if it is going to yellow.