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So any guesses as to what caused this?

Pay close attention at about 9 seconds into the video, just after the second stage ignites.

I know, just want to find out what the experts think...

Hence USS Bakula....I'm digesting this....I suspect it has to do with shear stress from a high rate of rotation.

Does this class of rocket pop the sound barrier?

After conducting a careful frame-by-frame analysis of the video, I think I have found the answer. There is in particular one very revealing frame that I think you will find very illuminating.

I wish to warn you that what you see you might find quite alarming:

miftah wrote:

Hehe... that's the ticket!

Miftah, that was great! Glad I wasn't drinking something...it would have come out my nose.

You too Bio, although you were just building on what others had done...

You two need to get together and add those things to the video, rather than stills...then I can repost to the rocket community...they would get a laugh out of it...

Yes, this rocket (and others) broke mach, only just though...but that isn't what specifically caused it, and the rotation may have contributed, but isn't root cause. Good guess though Bugs.

OK...hmmm...what happens in a stage change...rocket is probably decelerating slightly before...aha, note that the vanes change position relative to the camera after the distortion is resolved.

Well my guess is that this would probably not have happened if the rocket were fused together, so my guess is that spin/torque and inertia caused the illusion of flapping fins as the halves rotated at different rates during the spin as the rocket hit maximum velocity - the camera was most likely fooled.

HOWEVER:

This of course assumes that the fins are made of metal. If they are some form of plastic, then the drag of the fins and the low pressure aft helped to distort the fins and the resulting torque rotated the boost stage independent of the nosecone/camera. I bet the camera blisters out on one side of the rocket as well.

Ok bugs, you are on the right track, so I'll just give up the goods.

The first problem is known as Fin flutter in the rocketry community. Basically it is movement of the fins in a periodic (harmonic) fashion. The harmonic vibration can be disasterous, think Tacoma Narrows Bridge.

The second is a issue with the camera. The frame rate of the camera is 12fps. If the vibration is greater than that you can get Aliasing, which is another word for weird artifacts. The cause of this is undersampling. Another thing that would cause it is the way a CCD works. They scan from top to bottom in the same fashion your TV would.

SO you combine that the fins are moving at a high rate of speed, on the order of 1000hz, with the undersampling, scanning, and MPEG-4 compression and you get this weird effect. If you imagine that when the scan of the CCD begins the fin is in one position and when if finishes its in another, so that would make the fin appear curved, this is happening frame by frame, and the MPEG compression is trying to make sense of the whole thing, so it builds what it thinks its seeing.

In short, the fins were moving a lot, but the weird bending and flexing is just camera tricks!

Yes, the fins are plastic...fiberglass FR4 G10 fiberglass to be exact. The same stuff circuit boards are made out of...very, very strong material. Metal isn't generally allowed.

I don't know the configuration of the camera, but generally there is a bubble of some sort with a mirror in it on the side of the airframe.

More on rockets that take movies during flight can be found here.

Thanks for the educational exercise, Rocketdork!

Bugs