Jet engines use synthetic oils - why? Also you never need to do an oil change on a jet engine because it works via a replace via replenishment.
Another topic for study could be CRP (Carbon Reiforced Plastics) although not strictly chemical you could look at the types of CRP use in aerospace applications as opposed to other industries. Look at what polymers are used to bond the material. Look at Pre impregnated materials and study why these are so succcessful.
Another area is hydraulics. You could do an assignment bassed on pneumatic vrs a sealed synthetic system. What are benefits and disadvantages of both and relate each of these back to a chemical stand point.
Combustion seems like an easy concept, you put fuelin and you burn it - ta da. I think though if you went to some detail it might be a bit heavy and messy.
However saying that, if you can get your hands on some applicable data, you could do a comparison of NOx omissions from the early 70's to current data. ICAO might be a good place to start with that also EPA organisations that monitor levels could be interesting.
Hey another topic could be crazing of aircraft windows, thats where due to sunlight the plastic window starts to delaminate internally and its transparency is reduced.
Also do some basic analysis on the hygroscopic paste that is used for detection of water in JETA1 or the addetive that is used to prevent fungus growing in fuel tanks of a large transport aircraft.
You could also do a project on paints used by the industry and the removal and disposal of such, which as mentioned on this site is a bit of a problem. Getting back to basics you could do something on plating. Most metallic a/c components are cad plated to provide a protective corrosion layer, you could extend this out to include anodizing, and chrome plating of oleo struts.
I could probably go on but I wont. Feel free to drop me aline WRT to any of these ideas. My only advice is go with the option that has the most data that you can get your hands on, it make less work for you in the long run.
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Its life Jim, but not as we know it!!