I shoot a lot of air shows. I remember my first air show shoot, I was so excited. The images were so sharp and crisp, I had a great shot of a P-51 flying by -- shot at 1/750.
I posted the image and the first reply was "no prop blur".
I never even thought of it until someone with more experience pointed it out, and then it was -- well of course it looks better with prop blur. I never made that mistake again.
This is what these forums are for -- we learn from each other.
Now, as posted earlier... I think shooting at 1/250 is still way too fast to get good blur. The term is often called "full prop blur" when you see a full circle of color. The tips are usually yellow or red, and it will draw a full circle at the correct speed.
Planes standing with props on - 1/30s
Plane taxing slow on runway - 1/60s
Plane taking off or landing - 1/100s
Slow bomber fly-by - 125s
Fast fighter fly-by - 1/60 to 1/80s
Getting a fast fighter fly-by will "full prop blur" is really hard and requires panning.
I will post some of my "full prop blur" photos later, I am not at my home computer. But I did a quick Google and found an good example to look and compare:
http://classicwarbirds.net/tag/nazzi-harani/
Notice there are two shots (#1 & #5) with full prop blur. Notice the #2 shot does not have full prop blur, you can see 4 distinct areas of blur on the blades. That "4 blade blur" look is very popular.
The numbers I provided above are just a guide. If the pilot revs the engine, the prop speed changes, so there are no exact numbers. Just a starting guide. But next time you shoot an airshow with prop planes, do a test -- shoot at different speeds of a plane just sitting static warming up the engine. Go from 1/250 s all the way down to 1/10s and see what you get.
I will try to dig some images up of mine where I did that exact same thing. And you can see each one has a different prop blur look.