N5cTT Tail Rotation

[Carzan]

Now I know its been a while for me but it seems I remember tails rotating in a counter clockwise direction as observed from the starboard side of the heli. I was looking through the manual for the N5cTT and it shows a CLOCKWISE rotation. So I pulled up a few pics and low and behold based on the orientation of the tail blades it does indeed rotate "backwards" to what I understood a tail rotor should.

Can anybody enlighten me as to why this might be?

Jay

[Chris Sexton]

The reason is simple, the transmission is mounted upside-down relative to other Synergy models on the Nitros to make room for the motor.  There are no performance issues. To make the tail spin in a more "traditional" direction would require specialized tail parts that would be cost prohibitive for a smaller company.

[Carzan]

I thought about this more last night after posting and have come to the conclusion it really should not matter. Model helix spend a large amount of time inverted. Therefore due to the fact that the tail is dealing with draft from the main rotor moving in both positive and negative directions it simply becomes a wash no matter what direction the tail turns. Thanks for the comment and answer! 

[Rodney Kirstine]

The tails on my N5C and my N7s (N7 also turns clockwise) have all been rock solid even at some ridiculous tail-first speeds.  I've done some tail slides from what looked like a mile high clear to the deck and the tail is so solid it doesn't even make me pucker at all doing it.   

[Mike King]

Yep, those Synergy tails hold like vices.........

[Mike Dipalo]

As you noted, the biggest point in a 3D heli is not the rotation (as it becomes moot with the main rotor flow reversing all the time), but whether the tail is designed as tractor or pusher along with speed and disc solidity.

There's quite a bit written and researched on the subject of tail rotor design. A really good chapter (and book overall) is 6:Tail Rotor Design from The Princ. Of Helicopter Dynamics by J. Gordon Leishman. The chapter on tail rotors boils it down in the end that pusher rotors are more efficient per input power. The low energy intake zone being disturbed by the presence of the fin(s) and case is less of an issue than the high energy (and more narrow) flow of the tail rotor having a chunk of metal and carbon in front of it. Having a tail fin with holes in it helps alleviate this which is why the MA helis could get away with it (although you'll find anecdotal stories of pro pilots bemoaning an occasional lack of tail authority in high power maneuvers). The tractor tails actually produce a higher percentage of thrust due to the more isolated rotor and intake air, but this generally ends up with a net loss due to the tail being in the way.

As for rotation, you'll find most full scale helis rotate the tail blades into the oncoming rotor wash for an efficiency gain. You'll also notice tail rotors deviating from "pusher is best" when design considerations pop up. Eg, the "hawk" series of helis have tractor tail rotors canted upwards for additional lift and stability. This allows the nose to be relatively short (tail rotor deals with a rearward CG) and for a lower tail profile.

Hope you enjoyed the WallOfText

PS someone worth talking to about rotorcraft mechanics is Extrapilot from HF. I'm fairly certain the guy's a aero eng. Really knows his stuff on the subject. If you want to set him off just mention how ~90* link phasing is due to procession.