Why ?

[The Nr Fairy]

Why, when in a balanced turn in a helicopter, is a bit of back pressure on the cyclic required t prevent the nose from dropping ?

One suggestion I've heard ( admittedly I've only asked one person ) is the result of gyroscopic precession, although this would only work for ccw helicopters a la Americain.

Any ideas ?

[sprocket]

Nr: Are you talking about a heli with hyd power controls or without?

[Arm out the window]

Here's a couple of things I can think of:

a. If you're turning in the direction that tilts the tail rotor thrust downwards, the nose should drop.

b. Tilting the lift vector with no compensating increase in collective pitch should cause a sideslipping descent, and if you have a decent fin surface, the aircraft should weathercock downwards, so to speak.

Caution: that's just off the top of my head, so could be all crap!

[S76Heavy]

You tilt your Lift vector towrds the centre of the turn. Therefore, thepart of the Lift opposing the Weight becomes smaller. One way of increasing lift would be to pull collectiove, upsetting the balance of the helicopter by requiring more pedal, adjusting the ANU to remain level, etc, the quick way is to pull the nose up a fraction, so the Lift vector is less tilted in a FWD direction and more upright, resulting in an equilibrium with gravity. If you keep it ther too long, thought, you will lose speed because of less Thrust due to the tilt of the lift vector.

Something like that anyway..:D

[Bertie Thruster]

There is something very retentive about all this! Why don't you just look out of the window and fly the thing?

[tigerpic]

i didn't know that the helicopter nose would drop when in a turn, unless you physically moved the cyclic forward?? is there something i have missed since flight school? they did teach me that you lose altitude unless compensating with aft cyclic (or lift collective). s76heavy explained this.

what i found out when teaching, was that students during the first couple of hours would enter a right turn with a nose drop, and a left turn with a nose up attitude. the reason was that the right arm is located in an angle in reference to the direction of flight, and not like an f-16 jetfighter (or airbus a320/330/340) where the steering stick is placed on the pilots right (or left) side and not in the middle.

tigerpic

[rightpedalRIGHTPEDAL]

C'mon guys let's go back to the basics.
The horizontal component of lift, which is the centripetal forces acting on the airframe in a turn, causes a loss of lift for a given angle of attack and airspeed.
This is why either back cyclic, or increased collective will be required to maintain constant altitude. (The two dynamic components in the lift equation, angle of attack, and velocity).

And for Bertie, I personally believe its better to at least have an idea of WHY you're doing WHAT you're doing, rather than work it out as you go.

[Shawn Coyle]

There is another big part of the picture you're missing. Turns are not just about angle of bank, but about pitch rate - the nose has to track across the horizon.
The only way to do this is to pull back on the stick.
For those who are more techically oriented - pitch rate in a turn is like G. You need to pull back on the stick to generate G, and the same happens in a turn.

[S76Heavy]

As far as I know, if I move the cyclic to either side and keep the ball centered, my machine will start a turn in that direction. If I don't pull the cyclic it will turn with the nose below the horizon, but it will turn and not traverse sideways.
So you've lost me here, I'm afraid.

[BlenderPilot]

Just look out the window and fly the thing, I remember I used to worry about all these things, I had sooo much weird information in my head it always made flying more difficult for me. I was always thinking of werid effects and aerodynamics.

Then I stopped worrying about all this stuff, went out and strapped a helicopter onto my back, and starting that moment I felt more comfortable than ever flying a helicopter.

There are some helicopters with nasty habits that require some thinking on the pilots part to find out what's causing this erratic behavior and try to deal with this as you are flying, but if it doesn't well thats less thing to worry about.

[Nick Lappos]

Read Shawn Coyle's response carefully, he said it all.

The banked turn involves a constant pull-up, as the nose sweeps through the horizon. Imagine the turn as a 90 degree banked turn, and you can see that the maneuver is virtually a pure pitch maneuver.

Since the turn requires a continuous pitch rate, a continuous back stick is required. The horizontal tail is being swept down, so it makes an up force (actually, it makes a lesser down force) and this is countered by the aft cyclic.

[helmet fire]

BP,
If you dont like reading about it or thinking it through, you dont have to. Great Pics by the way - very jealous of your flying!!

NR Fairey,

Your Q has been well and truly answered here, but I like the response of the first person you asked who attributed the nose drop to gyroscopic precession. Does that mean a nose up when you roll the other way, or does it mean nose up on all French/Russian helicopters when they are turning?

Log that puppy on to Pprune for a good spanking will you?

:D :D

[Bertie Thruster]

Thanks for agreeing BlenderPilot. Too much PoF gets in the way(and in mho can be a flight safety hazard) Understanding the potential for any Vortex Ring state is essential but as for the rest........

thats after 7k hrs on piston, turbine, cw, ccw, fenestron, tandem and notar.