Two for the Darwin awards...?
 

Was Artie Johnson flying the Yellow One?

Epic fail on the second one but the first looks distinctly dodgy - the blades aren't going round quick enough to get a heli airborne.

Crab,

It's just an unusually smooth example of frame rate synch - their other vids (of aircraft that are clearly in flight) have a similar effect.

Anyway, just sit back and enjoy their factory tour guide. I mean, their factory tour. :E



I/C

Certainly looks better than what one is used to see from Robinson. And their helicopter looks better of course, too. :)

not convinced by that - although she could guide me anywhere, anytime, the end of that vid when she starts the rotors has a much faster blade passing rate than the alleged airborne with guys on the skids video.

I think we have all seen lots of video footage of helos with varying effects on the rotors but that first one is unlike any others I have seen. Usually the frame rate can make it look like the rotors are turning the wrong way or standing still but moving that slowly?????? Maybe a video guru can confirm or deny.

It's definitely a frame rate issue. Look at the tail rotor blades - they look like they are curved like a banana. That's another tell-tale of a frame rate/shutter speed issue. There are several examples of the same 'phenomenon' in the Helicopters around the World thread.

Look at the Revs of the Swash-plate, not the blades !

(nice tour of the factory also):ok:

OK I give in, having looked at the end of the video when they shut down, I can see the blades change their relationship to the shutter speed/frame rate and appear to reverse direction.:ok:

How much do Konner charge for an hour's rental? For the helicopter?

Dunno what they'd charge, I've watched that video numerous times and can't figure out what it is they're selling.....:ooh:


I'm going to watch it a few more times, just to see if I can work it out....

Well, for €300, you get a night in a hotel, fed for the day and an hour's flight!

Try Konner K1

The orange coloured one looked stable but the one in black has a twitchy tail.


Variable frame rate is used as a means of controlling exposure.

Pro cameras have a manual frame rate adjustment where the frequency can be dialled in to match the frequency of the movement of the subject. On Sony cameras its called "clear scan" and is adjustable in 0.2Hz steps.


Mickjoebill

Not often I get to explain something to Crab. Plenty of the other way around. All assuming of course that this isn't a massive waaaaaa.

Someone much cleverer will give you a better explanation, but this is how my understanding of the frame rate works...

The video is made of a series of stills (30/s is typical). If the 'shutter' time of each of those stills is quick enough, the blades will not be blurred in each of those frames.

Take the example of a 3-bladed rotor doing 600rpm. That means 10 Rev per second or 0.1 seconds per revolution. With 3 blades, that means the time between blades going through any particular point on the disk's path is a third of that, or 0.033 seconds. If the video was at 30 frames per second (call it one frame every 0.033 seconds), the disc would appear stationary. This is because each of the stills of the disc would show the blades in the same place.

Now increase the Nr by a little and the video would show the blades turning slightly in the correct sense, because each blade is able to get a little bit past its predecessor in 1/30 of a second. Slightly below 600rpm and the blade will appear to be going backwards because each blade has not quite got to the position of its predecessor in 1/30 of a second.

This is also true for multiples of 600rpm. At twice the rpm, the blades appear stationary, but this time because in each frame, the position of a blade matches that of the one 2 ahead.

Simples. Also called Strobe Effect.

Good explanation. The multiples will hold as fractions too remember - for your 3 bladed rotor one third, two thirds, 1 times, 4/3 times, 2 times etc. hold.

Pleased about the fractions because I have been imagining a 3 blade MR system at 600 RPM and feeling a bit queasy .... :8

That video had the production quality of a porno! Shame the outcome wasn't the same...

The fractions don't work. I chose a worryingly high 600 rpm as the slowest that works with a 3 bladed rotor and 30 frames per second. An Nr any lower and 1/30 second isn't long enough for a blade to take its predecessor's place. :8

I'm no videographer, but I'll bet that these crappy videos where the blades appear to stop are from mobiles with slow frame rates.

With fractions in the next frame the preceding (etc) blade takes the place of the current blade. As the two blades look alike (at this resolution) the blade appears to be static.

ADDED BY EDIT

Say disc running at 480 rpm - so that's 8 RPS
3 blades - 24 blade passes per second
One of the standard for FPS is indeed 24 (actually often run as 23.976 FPS).

So, using a Nikon D7000 DSLR at 24fps to shoot a video clip would make a disc running at 480 rpm appear to have stopped still. It would make my 120 disc at 415 rpm (top of the green) look like it's turning backwards. Slowing the FPS to 20.75 would make the 120 disc at 415 rpm appear to have stopped

iPhone 5 video capture runs at 30 FPS.
For a 3-blade machine that's going to need 10 rps to have a blade always at the same point of shot
Hence the 600 rpm calculation above would apply to the crappy iPhone.

.

That white helicopter hardly has anyone riding on the skids ..... here is how it should be done ...


.
http://www.bell47.net/Family/Ship3wBell.gif

That SAR Chap - nice one, consider yourself CR(A) on videography:ok: