I recently modified my Protos500 FPV trainer, installing a 4 blade main rotor head, featuring lead lag and flap hinges.

The video is related to the third flight, and still need to fine tune PID's and phase:

https://www.youtube.com/watch?v=K_zL4B7Axt0&feature=youtu.be

First impressions are positive, collective response is WAY more precise and "powerful", especially during sudden stop maneuvres (exiting the TEL aerodynamic condition, which in FPV I think it's one of the most tricky things to get used to...), you simply add a "touch" (even less...) of collective to stop the sudden loss of lift.

In fast forward flight the collective was very "low" about 1-1,5°, I was impressed how much I had to lower the collective, compared to the 2 bladed head.

Still need to fine track& balance the main rotor, but here attached is the vibration chart:

 while the 2 blade chart was:

I made a total of 4 flights, the longest been around 10 mins, in which the battery dropped 2456 mah, out of 4200 mah @6s (mostly flying around, two minutes of loiter and couple of RTLs).

Here attached my mechanical setup:

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Hi Ferruccio,

looks nice !

What kind and size of blades do you use - symmetrical 430 or 470 ?

Did you make a comparison regarding efficiency 2 vs. 4 blades at the same headspeed ?

In fast forward flight the collective was very "low" about 1-1,5°, I was impressed how much I had to lower the collective, compared to the 2 bladed head.

IMHO you have a good chance for longer flight times by reducing the head speed with the right choice of pinion, motor and/or battery (even ESC with active freewheeling must be wide open for efficiency).

I use this simple formula to set the headspeed on my helis: 1800 / disc diameter in meters = HS for 2-blades. The 1800 is not cast in stone, it depends mainly on the loading, the altitude above sea level, the wind and turbulence and the pilot :-))).

To get the HS for my 3-blade head I calculate HS for 2-blades * sqrt( 2 / 3 ) to get the same amount of climb rate - would be sqrt( 2 / 4 ) = 0.7 for 4-blades. This results in 1096 rpm for a TT E550 3-blades stretched to 600 (1.34m disc diameter) - actually I am flying with 1020rpm, still very agile. To get this HS I had to modify the motor from 1150 in delta configuration to 665 in star - easy on the OBL44/11-30H that comes with the E550, the motor needs quality bearings anyhow.

For 'low rpm' + 3D you might need a bigger tail rotor.

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