Push me pull you?!

[Pumaguy]

For the experienced guys out there... How would you explain to a novice about push and pull tail rotors and how to spot which one you have?!

[paco]

here's one attempt:

The tail rotor makes the body spin in the same direction as the main rotor. If it's on the retreating side it is a pusher.

Phil

[serf]

What if it's in the middle?

[paco]

Just think of what it has to do to make the body spin the way it needs to and which side you stand so your hat doesn't blow off :)

Yeah, a problem for those types unless you know which way it spins I suppose.

phil

[[email protected]]

What if it's in the middle? I guess you have to look at which side the hub of the fenestron is on (as opposed to the actuator and gearbox), that will be the 'IN' side for the air in normal conditions and therefore the way the force will act.

[Gemini Twin]

T/R push and pull, a bit odd describing a T/R as either a pusher or a puller.
They just counter torque with the thrust being adjusted as required with the thrust direction dependent on which direction the M/R turns.


If you want to see a T/R that pushes, take a look at the Lockheed Cheyenne!


I suppose though if you wanted describe them that way, when the trust produced is directed toward the t/r gearbox it's acting as a "puller" and when the thrust produced is directed away from the T/R gearbox it's acting as a "pusher". Similar is to a prop on a fixed wing, in a conventional installation during take off, it's acting as a "puller" and upon landing when thrust reverse is selected the prop is acting as a "pusher".

[[email protected]]

The terminology is just a way of highlighting what the TR does to the tail boom which is determined on which side of it the TR is mounted.

if the air (in normal powered flight in order to counter Tq) comes round the tail (b oom or pylon)and exits the 'free' side of the TR then it would be a pusher. If the air enters the 'free' side of the TR and exits towards the tail boom (or pylon, or whatever structure it is mounted on) then it is a puller or tractor TR.

[ShyTorque]

The tail rotor is fitted to prevent the airframe from rotating in the opposite direction to the main rotors, due to torque reaction. A pusher tail rotor would stay on its shaft if the nut on the end fell off. A puller would be on the opposite side of the tail and if the nut on the shaft wasn't there it would pull itself off, so to speak.

[GipsyMagpie]

As the air coming out of a rotor is of higher pressure than that going in, you would therefore get more drag on the airframe for a puller. Hence a lot of tail rotors are pushers. And most will also having forward blade going up. One big exception is blackhawk which has a puller that's tilted.

Simple rule of thumb for american helicopters is on the left is a pusher. Opposite for European and Russian.

[John Eacott]

The thread Tail rotor position (http://www.pprune.org/rotorheads/296643-tail-rotor-position.html) has a lot more informative discussion from some years ago, with some learned inputs from Nick Lappos :ok:

[cattletruck]

I want a tail rotor that does both in the hover - push against the opposing moment of torque and pulls along the favourable moment of torque.

Of course this means the tail rotor would be facing bacwards and the tail rotor blade pitch would be 180 degrees out of sync with each revolution.

And in forward flight the tail rotor reverts to being a pusher.

[[email protected]]

As the air coming out of a rotor is of higher pressure than that going in Oooohh are you sure about that statement??? It may be going faster but higher pressure??? I'm sure Mr Lappos will have something to say about theories of lift production on that one:ok:

The converse of having the puller TR 'downwash' impinge on the tail pylon is that with a pusher, the air has to come around the pylon which can lead to blanking and require a bigger TR to give the same thrust.

The direction of rotation can be changed as it was on the Lynx from Mk1 to Mk 7 - the Mk1 had the forward blade moving down through the MR downwash and had poor TR control as a result. The Mk 7/8/9 has the forward blade coming up and is very effective.

[The Night Owl]

Excuse my ignorance, can someone name some pullers?

I know the difference each side of the pond but assumed they were all pushers

[Evil Twin]

Good example to look at is the Mil 8/Mil 17. Mil 17 has the TR on the left Mil 8 on the right both clockwise rotating MR.

[SuperF]

Bell Mediums are another example. 204/205/UH1 started with a left hand Tailrotor. Later in their construction they moved to right hand side.