i wanna ask few things!!!

Ghetto2k4

600 grit should work fine for sanding primer as long as you are not trying to remove any runs. If you have any runs I would reccommend using 400 grit.

Check your local auto supply store for finer grits of sandpaper (If you have an autmotive paint supply store, that's even better). My local NAPA has been able to get me 800, 1000, 1200, 1500, 1800 and 2000 grit sandpaper for me.

what is best girt to sand primer? b/c i just primer a model car and now i dont know what grit to use to sand with lol

What kind of aircraft? Most (but not all) military aircraft have flat or semi-gloss finishes. Commercial aircraft (and a few military) aircraft have gloss finishes. Also, some military aircraft have "Natural Metal" finishes which were not painted at all and were just the color of the skin (of course for a model you will need to paint it). If you are building something with a flat finish don't worry about sanding the primer. It will probably be smooth enough.

In my opinion the best way to paint an aircraft is to assemble as much of the fuselage as you can. Fill and sand any seams that need to be fixed. Mask off the cockpit, mask off the wheel wells, mask off anything else that needs to be masked, and paint it all at once. That way you don't get differences in tones that might occur if you paint it in pieces and you have eliminated the seams from the construction.

i got something esle to ask after u put on primer what grit do u use to sand it? i only have 220,320,400,600 & 1500 grits b/c i cant find no 2000 grit sand paper no where so..i wanna know if 600 will work to sand the primer

i use a airbrush to paint with

i gather that you dont have an airbrush. so basically the best way to lay on paint would be with a large soft brush, and thin your paint a little so that you dont get brushmarks. for detail painting use a small brush.

as for putty, if walmart has any hobby putty, just get that, failing which, there is this stuff called porc-a-filler i heard of, available at home depot and the like. i havent used it or seen it, but give it a try. perhaps other people can tell you more about porc-a-filler. its actually for filling gaps in pottery.