Orange peel effect when airbrushing model

Ya the bigger areas are broader, takes a little different technique. What brand paint and thinners are you using.

And with acrylic in particular you really should prime.

Mant Things can cause orange pee- distance from airbrush to surface, thinning ratio, air pressure.  You need to vary these till you get the right combination.  And for larger surfaces, be sure you move airbrush parallel to surface, not in an arc (ends of stroke will be further from surface than center). Keep that distance constant.  More thinner, less pressure, closer distance, or some combination usually solves orange peel.  Practice on scrap plastic until you get the right mix.

Thanks for the replies.  The paint that I am using is Mr. Color acrylic.

So I've since pulled back the paint coat and have noticed that the plastic itself is grainy.   I've also looked at unused parts still on sprues and have observed that they have a grainy texture too.  I assume this finish was done to aid with paint adhesion.  Being that acrylic applies so thinly,  it's apparent that that the grainy effect is what's causing the Orange peel.  

Is there a way to get rid of the grain without sanding the parts completely smooth?  The model is a little small to perform detail work with 2000 grit and there are also some winglets in the way to boot.  If not, then I will either have to paint very thinly or switch to a matte finish.

Depending on the grain in the plastic, once scuffed and a couple coats of primer might cover it. But if you want a smooth surface finish you need a smooth surface for it to go down on. I use 000 steel wool quite a bit for prep if needed and also to smooth the primer coat. It offers a different action from sand paper. Just sayin.

From what I understand about Mr Color acrylic paint it seems that Mr Leveling thinner works well in it. I haven't used that one yet but it seems as with Tamiya acrylic it can be thinned with lacquer thinner which should offer good leveling if so.

I use Mr Color which is similar to Tamiya paint and both thin VERY well with Mr Color Leveling Thinner. It enhances the Tamiya paints and the best gloss I've seen is Tamiya gloss thinned with Mr. Color LT.

Here's a kicker, shoot Mr. LT by itself over the fresh sprayed gloss and it blends and smooths out the finish even more.