Translating tendency

StanFoster

Active Member
Joined
Nov 16, 2003
Messages
17,139
Location
Paxton, Il
Aircraft
Helicycle N360SF
Total Flight Time
1250
Yet another helicopter phenomena is translating tendency. This is rather simple as it basically is the result of the thrust of the tail rotor causing the helicopter to translate to the right with ccw blades. This force is compounded with also the torque of the fuselage causing the nose to also tend to go to the right.

Often the main mast is rigged to the left slightly to counter most of the cylcic inputs to correct this.

Once again...more detailed explanations are welcome. This is good review for me typing this stuff out as it makes my verbal explanation more consise.

Stan
 
Translating tendency or Tail Rotor Drift in the Hover

The Tail Rotor creates a force to overcome the torque and stop the helicopter fuselage from rotating in the opposite direction to the rotor system. the tail rotor is mounted out on an arm ( The Tail!) and by generating thrust it generates a moment through this arm that cancels out the torque.

so looking at the helicopter from above we see the blades moving anti-clockwise, this will cause the fuselage to want to go clockwise.

We stop this by getting the tail rotor to apply thrust to the right.

This is achieved by getting the tail rotor to act on air and blow it from the right of the helicopter, to the left.

So Newtons third law states For every action there Must be an equal and opposite reaction:

Getting air through the tail rotor and accelerating it to the left will cause the helicopter to drift to the right

to overcome the Translating tendency designers use three methods

1. Rig the controls so that with the cyclic in the neutral position the disc is tilted to the left (R22)

2. Tilt the mast to the left (Enstrom, Have a look at one head on the next time you are down at an airport the mast tilt is real noticeable)

3. Rig the collective controls so that when collective is raised that it also applies a cyclic input that tilts the disc to the left, the Idea being the more pitch pulled, the more torque, the more tail rotor thrust, the more tail rotor drift.
( Some large helicopters, The Aerospatial Super Frelon being one)
 
And some designers don't do anything to compensate & the pilot just has to deal with it :)
 
Some helis are in track and balance if you can sit in the seat without being thrown out, Your good to go!
 
I've flown in a few where the owners thought that!

That sort of thing always bites you down the road though, everything wears out faster.
 
Stan,

In your Helicycle, I believe the turbine exhaust stack is directed down and to the right to help cancel translational lift.

Just an added benefit as you are burning 12+gph!

-Mike
 
StanFoster

StanFoster

Mike- You are correct on the turbine exhaust exiting to the right, and reducing the translating tendency. If that exhaust is directed up, it burns the frame, if its directed to the left, this tends to mess up the airflow around the tail rotor. If the exhaust is directed down, fields could catch on fire! So, to the right is the best option, with translating tendency being reduced as a bonus. True also on the fuel consumption at 12 gph. However, if I compared my SparrowHawk that would burn 9 gph on a cross country at 80 mph to the Helicycle burning 12 gph at 105 mph, its almost the same mpg. Of course the Helicycle will still burn 12 gph while hovering , something that I always wanted to do anyway but couldnt! Stan
 
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