I googled this and found this site with half the answer I was looking for, and that was this:

It is quite simple. (Number of Blades) * (Prop RPM / 60) will give you the denominator of the shutter speed.

For example, 2 blades, 2500RPM - The above equation gives 2 * (2500/60) = 83.33. This means that your shutter speed would have to be 1/83.33 sec or slower to get a full circle.

Another example, 3 blades, 2500RPM, requires 1/125th sec.

Dean

I was wondering if someone could help me further. We're looking for a half circle blur instead of a full circle. If someone could help me out in the format that Dean had posted this I would appreciate it

For a half-circle, double the shutter speed. What was 1/80 and 1/125 in the example above becomes 1/160 and 1/250.

7 months later

Remember this all depends on the setting of the throttle and the type of plane.

For example, a P-51 taking off has full RPM. You can shoot this at 1/60 or 1/125. On the other hand, a taxi shot you have to go lower, but it is still possible to get full circle.

On helicopters, most likely 1/60 or lower because the rotor action is slower than a prop even at high throttle. It is good practice. Try different levels with different planes and take notes for the future.

2 months later

Basically if the plane is at full RPM such as takeoff or air to air, 1/30 to 1/60 will get you full blur. If on the ground in idle, you may need to go to 1/15 to 1/30 and that can be a problem for sharpness. It also depends on the plane. For example - P-51 props are very fast at high RPM but C-130 or Huey helicopters etc are much slower. I just basically use that rule. This was done with a Sigma 150-500 hand held about 1/30 no vibration control and manual focusing and the results came out fine...

http://joefernandezimaging.smugmug.com/Other/Airshows/18197445_zTGMPc#!i=1768075803&k=5jcGwVP&lb=1&s=XL

a month later

I googled this and found this site with half the answer I was looking for, and that was this:

It is quite simple. (Number of Blades) * (Prop RPM / 60) will give you the denominator of the shutter speed.

For example, 2 blades, 2500RPM - The above equation gives 2 * (2500/60) = 83.33. This means that your shutter speed would have to be 1/83.33 sec or slower to get a full circle.

Another example, 3 blades, 2500RPM, requires 1/125th sec.

Dean

I was wondering if someone could help me further. We're looking for a half circle blur instead of a full circle. If someone could help me out in the format that Dean had posted this I would appreciate it

My teacher says set your speed at 250 and you will get prop blur, not full circle but 3-4 blades blurring nicely. Used this technique when shooting warbirds air to air and found it acceptable.