A New Speed prop?

RV7AV8R · #1 08-04-2009, 11:34 PM

Jeff Lavelle already has the fastest Glassair at Reno Air Races. Is this a new speed prop he is testing on his RV4?

Photo taken by Larry James out of an RV8.

N713R · #2 08-05-2009, 06:30 AM

Looks like his cowl cheeks will be short lived.

I have never understood why that does that, I have a picture of a Dehavilland Chipmunk taxiing by, and the prop appears to be bent far forward. Looks weird, but its pretty neat. Anyone know the actual science behind the effect? Doug? Other Photographers?

Ben

the_other_dougreeves · #3 08-05-2009, 07:43 AM

I believe it's from a digicam / cell phone camera that uses a CCD without a shutter. The CCD is getting scanned from top to bottom (or reverse). The prop is moving fast enough that you're seeing it rotate 180 deg as the frame is scanned off the CCD into memory.

TODR

RV7AV8R · #4 08-05-2009, 12:22 PM

This photo was taken with a cell phone camera (blackberry I think). I didn't know they don't have shutters, but that explains a lot. When on the ground sitting still the blades tend to 'melt', this is the first I have seen in flight.
John

BruceS · #5 08-05-2009, 01:30 PM

I think it's because the camera is using a CMOS chip instead of a CCD. In reading my Nikon(D90) manual some time back (I admit it) it mentioned that the newer models changed from the CCD sensor to the CMOS sensor and it records from top to bottom, (unlike the CCD) giving you these issues. I can't remember seeing this type of issue before CMOS sensors entered the market.

I'll go back and reread that portion so I can be sure this is a correct statement. Just going on memory at the moment.

Veetail88 · #6 08-05-2009, 03:40 PM

with focal plane shutters.

Focal plane shutters are in 2 parts. At faster shutter speeds, as the first half moves, opening the shutter, the second half starts closing right behind it so that a slit of light moves across the film. The shutter is never fully opened.

So we get the same result because the prop is spinning so fast, it's position changes as the shutter moves across the film.

All kinds of weird things happened with those cameras at fast shutter speeds. Bent dragonfly wings, you name it.