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Howto talk:Fly a helicopter

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Revision as of 00:52, 9 April 2013 by Flughund (Talk | contribs)

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Subsequent a draft of an update to this article which I wrote while I was excluded from the wiki because of the mail server incident. Since I did not see a chance to get back rights to edit articles soon, I stopped working on it. Now I don't have the time anymore to complete and revise it. Feel free to continue that work:

I have no idea about learning to fly helis IRL. I am just looking at the general physics of helicopters, which basically applies to most types. With that knowledge one is able to learn to control many helis relatively easy. 

Some basics on helicopter physics
=================================
Compared to planes, rotorcrafts need much more effort on the controls to keep it straight all the time. A change on any one of the physical parameters requires one or more control input to compensate. And because air is a inconstant medium, parameters practically change continually.

The way I drive any apparatus, such as bicycles or cars, is to feel its movements and then act accordingly to make it doing my will. The most important instrument is the "Popometer", Niki Lauda once said. So, if one does not have a motion platform attached to FG, first thing to do is to compensate the missing Popometer with some display settings. The most important 'instrument' here is the real horizon. It is not delayed and seeing its motion compared to an object in the cockpit, or some other part of the heli, helps seeing forces applied to the heli. Such as a change in wind speed or direction and in which direction the fuselage urges if a control input by the pilot takes place. Finding a setting to have a good view on the horizon is a good preparation to learn on any rotorcraft you never have flown before.
Option might be zooming out in Cockpit View (drawback: instruments are getting unreadable), using a multi screen setup (if one has the descent hardware), in Helicopter View (but that is not "like real") or any setting that suits you well.

Most important things to know to fly a helicopter are its controls and what they are doing 'exactly' and to understand the whole concept. To illustrate that, I'll use a plum. Imagine it is lying in front of you on the table. To make it move upwards and hold altitude, we need to imaginary attach a rotor to its top. To make our rotor spin we need an engine which we carve out of the plum's stone. But because the air is a drag to the spinning rotor blades, the engine needs something to hold on to or it will rotate to the opposite direction as the blades do. Therefore we stick a toothpick into the plum, pointing horizontally away, and mount a small rotor at its other end and calling it a tail. The tail rotor is pointing to the opposite direction as the fuselage, along with the engine, does yaw because of the main rotor's air drag. (Since the plum does not have much friction on the table it does yaw very easily on ground, just like some FG models but unlike real helis (except they're floating on water or such).)

To be able to slowly lift the plum off the ground we need to be able to adjust the rotor blades to have more or less angel of attack (AoA); so they press more air from above the plum to below the plum, in order to make it move upwards. To do so the pilot has a collective pitch control, which in FG is the axis used as throttle on airplanes.
As we pull the pitch lever we stumble upon a by-effect of increasing AoA. The main rotor's drag increases as well and therefore we have to adjust the tail rotor, because now the engine needs more counterforce to compensate the 'change of yaw rate' caused by the 'change of AoA'. Helicopters have pedals to control the tail rotor the same way planes use them for the rudder. Incidentally FG's helicopters make use of the rudder axis for this as well.

Slowly we further pull the collective pitch to increase the upward force of the main rotor. For several reasons this force will not point straight upwards if the plum is on the ground and the cyclic pitch control (cyclic stick) is centered. So, as we are getting closer to the point where the rotor's upward force beats the gravitational force the plum will more like tip over than hover. During this phase we have to watch the plum's roll and pitch axis very carefully to see how much we have to correct the direction of the main rotor's force with the stick.
This control is equivalent to airplane's elevator and aileron axis' controls. Moving the stick forward increases the blades' pitch while they are moving through the back half of the imaginary circle they are drawing and decreases it on the blades in the front half. So the blades in back half produce more lift than the ones in the front, which means the force of the main rotor slightly rotates along the plums pitch axis to the front. This will end up in a 'nose down', just as if you'd move an airplane's yoke forward. The same applies to moving the stick left and right to adjust direction along the roll axis.
So, if the plum is going to pitch forward, pull the stick slightly back and if it is going to roll to the left, move the stick right hand and vice versa.
Finding this virtual neutral point where the main rotor's force nearly equals gravitational force and points directly upwards is an advanced task because it changes according to the wind's direction and speed and the atmospheric pressure and therefore it is not the same each time even for the same plum. However, it is not witchcraft and with some training it gets better and better.

Now that we have a basic understanding on the forces involved at take off and on how to adjust them, it is time for our first field trial. I suggest to paint the plum yellow, if it isn't already, and name it bo105. This helicopter has a pure feeling of the controls, it reacts very fast, so the student feels/sees their effect instantly, and it is also relatively forgiving, compared to other non-aided helis at least.
To make it more easy for beginners, especially the ones who do not have pedals, I suggest to set up a weather scenario with wind blowing consistently along the runway with about 15 kn. This way one sees the direction of the wind and the wind's velocity helps to stabilize the heli along the yaw axis; and therefore, if the heli heads into the wind, the student mostly can avoid bothering with the tail rotor on take off and touchdown and can focus on collective and cyclic pitch controls first.

Take off (or 'quick start' for the eager)
=========================================
After starting the engine "}" and waiting for the rotor reaching it's rotational speed we start the procedure to find the neutral point. On the bo105 you may start with pulling the stick about 1/3 way and moving it slightly right hand. Now start pulling the collective pitch slowly until the fuselage starts tipping noseward. Release collective a bit, so the bo105 is back again on the skids completely, and pull the stick a bit further. Start pulling collective again and redo this procedure until the bo105 does neither pitch forward nor backward but moves upward. Of course, parallel to the pitch axis the roll axis (stick left/right) has to be compensated as well. If you prefer to have the stick centered for this point, hold "]" while moving the stick back to center position.
If you did not set up the suggested weather scenario, you have to compensate any yaw movement during this procedure at any time with the tail rotor. If you did set it up, you still see the bo105 yawing a bit left hand and right hand, giving an impression of the forces involved.
Now pulling the collective any further should move the bo105 more or less straight upwards into a hover.

To get it moving forward we now have to point the main rotor's force slightly to this direction to virtually add a second force pointing forward. Since this force took its power away from the upward pointing one, we have to apply a bit more collective to compensate this. Otherwise the heli will be back on the ground quickly, though in a forward motion. So it is wise to increase collective pitch immediately before pushing the stick forward.
Additionally to speeding up we probably want to gain altitude, so we add even a bit more collective.


To remind you
=============
As we discovered with our plum model any control input causes one or more additional inputs for compensation. So especially beginners should be gentle on the input controls to be get used to the compensation inputs and to not suddenly loose control. For a hovering/slow flying heli following applies:
* Input on the collective pitch needs compensation by tail rotor.
* Input on the cyclic pitch needs compensation by collective pitch and therefore tail rotor, too.
* Input on the tail rotor needs compensation by the cyclic pitch and collective pitch.

Transition
==========
...from hovering/slow flying to cruise causes to change some behaviours. 

Flughund 04:52, 9 April 2013 (UTC)



Here's a collection of various related links containing further references, tutorials or educational material. Some users may find these interesting, or may even want to incorporate some of these links or info into the original FlightGear-related article.

General Info

Helicopter Flying

Helicopter Aerodynamics

Helicopter Flight Instruction

Web based

Youtube Videos

Non-English

This is a talk page, not a link grave. A nitwit who put them in here instead of into the article itself.
Flughund 04:52, 9 April 2013 (UTC)