The story behind the build

The starting point of this build was a repetitive situation that I assume most of you know:
Angry people coming towards you and yelling at you to get out of here with that bothersome "thing"...
I don't like this experience - and that's the reason, why I wanted to build a quad that's as silent as possible, but without limiting flight performance.

Choice of components

It was clear to me, that a 5- or 6-blade prop should be quieter, so I searched for a suitable prop.
The only one I found was the HQProp 4x4x6, what defined the build to be 4".
Furthermore I want as high PWM as possible, why I chose the FETtec ESC with 128 kHz.
After that I had to look for suitable motors. And on my search I found this Quadmovr video.
So the choice for the motors was clear an I changed my mind, to make it 6S instead of 4S :)
Of course the weight got a big influence on the noise level. So I watched out for a lightweight but durable frame.
I found the Ultralight 4 frame which seemed to be a good choice.

Building

The build was pretty straightforward without bigger problems.
I really like the look of the motors, so I tried to match the color scheme of the raw aluminum for the entire build.
But the stack and Vista didn't fit in the frame, so I put the ESC under the base plate, as I did with my toothpick build.
I had to make my own mount for the video antenna, where I chose aluminum of course.
This is the first time I have mounted the Immortal T on the front. The reason is that I can (mis)use it here as a bumper for the ESC deck.
But since it's easy and cheap to replace, that seems like a good idea.
The video system is detachable, for easy access to the FC.

Flight quality

This thing is really silent - completely comparable to the video above.
And it's damn fast... Not as fast as in the video (because of the higher weight), but it's really amazing!
The tuning was pretty difficult - on stock PIDs it's more or less unflyable.
I found a good tuning, but here I have to spend more work to get the last 10 %.

Update

I didn't manage to get this build fly properly on KISS (vibration issues), so I gave up my tuning efforts and changed to Betaflight. I want to keep the Fettec ESC, because it works great, but unfortunately this means no RPM-filters. On 4.2.11 I had to do a lot of work to find the right filter settings, but I found a good tune and everything was fine. Now I tried 4.3 RC2 and it is a really big improvement for this build. It works almost perfect on stock settings - good work BF devs!
The fine tuning is still in progress but I'm confident to make it fly like I visualize...

Data

Weight with props: 199 g
AUW with 6S 650 mAh: 312 g
Flight time (650 mAh): approx. 3:30 to 5:30