Blade Nano CPS Non-level Hover - RC Groups
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Nov 01, 2017, 08:40 PM
Registered User
Help!

Blade Nano CPS Non-level Hover


Hi everyone,

I'm am decently new to Helis and just received my first CP as a gift a couple weeks ago. Still flying it in the safe mode but have noticed something strange about the way it hovers. When i hover it there is a noticeable angle to its hover meaning the blades are not parallel to the ground. Have a look at the pictures i posted. I started looking at the swash plate when i had throttle hold on and noticed in the safe mode it is not level but as soon as i go into full CP 3D mode it levels out. Any idea whats going on here? If this were a plane id have it figured out but the heli is leaving me stumped.

(Yes i know the pictures are a little blurry )
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Nov 01, 2017, 08:50 PM
Registered User
not sure if you get a response in here... should have put it in the Nano CPS threat that is out there... wish I could help you all the same... good luck
Nov 01, 2017, 10:09 PM
Registered Mike Visitor
rotorist's Avatar
Normal behaviour, a hovering helicopter with a single main rotor and tail rotor will always hover one skid low.

Check any YouTube video of full size helis, they will lift and hover one skid low.

I think the only copters that does not do this is the twin rotor Chinooks.They have counter rotating rotors.Also the Kaman K Max and Kamov.
Nov 02, 2017, 01:58 PM
Registered User
The tail rotor is not level with the main rotor center (white line is the distance )
That creates a torque that is IMHO the main cause of the tilt.
Regards
Nov 02, 2017, 03:16 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
This is 100% normal behaviour for any single rotor heli. It's nothing to do with torque as suggested in the last reply, but it is related to the thrust from the tail rotor.

The tail rotor produces a 'side thrust' that (on a clockwise main rotor) pushed the heli to the left. So if the heli hovered level it would 'drift' to the left pushed along by the thrust from the tail rotor. The only way to stop this drift is by tilting the main rotor slightly to the right, the thrust off the main rotor then tends to push right and so balances out the thrust from the tail rotor and the heli hovers stationary.

There is a special term for this phenomena, it's called 'translating tenancy':
Translating Tendency (1 min 29 sec)
Nov 02, 2017, 03:32 PM
Registered User
@JetPlane: You are saying what I said but in different terms

The "hinge"point is the center of the main rotor. Look carefully at my sketch
Nov 02, 2017, 04:22 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
No, not the same thing. The tilt isn't due to to any torque from the tail rotor. You would have the same effect even if the tail rotor was level with the main rotor. The tilt is entirely pilot induced and is simply to prevent the heli drifting sideways due to the sideways 'push' from the tail. A heli can in fact hover with the rotor level but if it does it drifts sideways, as illustrated in the video I posted.

A heli is not a pendulum, so the thrust from the tail does not cause the heli to rotate around the centre of the rotor head. The rotor head is not fixed a fixed pivot around which the heli rotates, it's free to move in any direction.

Quote:
Translating tendency is defined by the textbooks as: The tendency for a single rotor helicopter to drift laterally, due to tail rotor thrust.
http://www.helicopterpage.com/html/forces.html
Nov 02, 2017, 04:43 PM
Registered User
@Jet Plane: thanks a lot for the extra explanation and link, "got it "

Cheers
Nov 02, 2017, 05:13 PM
Registered User
Hope the forces at play are correctly depicted now

The tail rotor forces are "scaled up" to better view the detail as both the main motor and tail rotor horizontal components must be the same and opposite.
Last edited by joao; Nov 02, 2017 at 05:54 PM.
Nov 02, 2017, 09:35 PM
Registered User
Wow you guys are awesome! Thanks for all the replies this makes total sense now that i think about it. Just kinda surprising that it is so pronounced for such a small heli.

Cheers
Nov 03, 2017, 04:59 AM
Registered User
Here I go again…hope this makes sense:

Smaller wings usually have a lower lift/drag relation than larger wings (larger models fly “better”)

The drag in a rotary wing produces torque that needs to be compensated by the tail rotor
So a sub micro heli tends to have a proportionally higher drag than a larger heli-->larger torque induced in the heli body-->larger counter torque action needed in the tail--> larger drift “force”--> larger tilt of the main rotor needed to compensate for the drift.


Cheers
Nov 03, 2017, 05:21 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Quote:
Originally Posted by joao
Hope the forces at play are correctly depicted now

The tail rotor forces are "scaled up" to better view the detail as both the main motor and tail rotor horizontal components must be the same and opposite.
Spot on!
Nov 03, 2017, 09:29 AM
Destroyer of Threads
Steve_'s Avatar
Back when I first got into helicopters I can remember arguing about the same topic, thinking
that if the tail rotor shaft was on the same plane as the main rotor that it should hover level.

What I was forgetting about was explained above.

An easy way to make it clear is that if you want a level hover, you would need two opposing
tail rotors (another tail boom sticking out from the front of the canopy) to equal the
forces.


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