How to improve?

How can I imporve on these shots? What should I look for when shooting this type and what should I have done in PS?

1.

I would try for a less fussy background also on propellor shots it nice to get the blades blured not easy to do as it means a slowish shutter speed but nice shots well worth keeping at it.
Rob.

Great models.....I agree with Rob. Perhaps less depth of field or changing you position to place the models against the sky would work.

Obviously, auto focus is going to see the background, not the model. I would try manual focus, taking the shots from a known, set distance, and then adjusting the aperture to throw the background out of focus. I suppose setting it so that the model's position would be in center depth of field would be where to start. Obviously, that will mean a wider aperture and faster shutter speed. If keeping the propeller blur is important, you may want to use a neutral density filter to cut out some of the light, thereby allowing for a slower shutter speed.

I would try shooting from further away using the Sigma at 300mm. This will keep the background nicely OOF. You could also drop the ISO down to 200 and drop the shutter speed to around 1/400s to help get some more blur in the props/blades.

Yes! Get down on your belly (or back) and get them with the blue sky as a background (but try to keep the horizon in the shot- maybe at the bottom third of the frame)

I do some aviation photgraphy (You can see some of my photos at www.usefilm.com/photog​rapher/10851.html) and I would definately say the best thing to do is use shutter priority and set your shutter speed to get a nice burn on the prop. For most of the aircraft I shoot, I use 1/90th of a sec for a twin prop, and 1/125 for a three blade prop. I dont know the rpm of one of those remote control planes, or helicopters for that matter, but you can experiment with it to determine your shutter speed.

So yes, you will probably have a large DoF, but if you want to lose background detail, stand to the side of the flightpath and pan with the plane. You will get some nice streaks, just remember to stand far back and zoom in with a 200mm lens or so.

I don't see anything wrong with having the background as it is, personally....however I think they're slightly overexposed, and the first one shows considerable highlight clipping.

Everything else has already been said by other people.