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Helicopter Air Files and Configuration - Part 1

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There are many things you can adjust within the default Bell 206 flight model for Microsoft Flight Simulator in order to achieve a unique and more accurate flight simulation experience for any helicopter you might be considering.

There are many important parameters that must work in harmony in order to achieve a fluid and enjoyable flight model that others will deem realistic.

Without judging what is realistic or enjoyable, I am going to try and share what information I can in order to empower you to make the changes you desire to create the flight dynamics you are striving for.

The default Bell 206 flight model within Microsoft Flight Simulator is spread out across two important sources. The first being the aircraft.cfg file and the second being the .air binary file associated with each aircraft.

The aircraft.cfg file is a plain text file in the main directory of every helicopter within the aircraft folder of Microsoft Flight Simulator. You can edit this file easily using a plain text editor such as Notepad, the default text editor that comes with Microsoft Windows.

In this article, I will be focusing on important helicopter flight dynamics related parameters contained within the aircraft.cfg file. The good news is that there are very few parameters to understand within the aircraft.cfg file. However you will need to know them well.

empty_weight
This is the parameter that Microsoft Flight Simulator will use to calculate the basic empty weight of the aircraft you are adjusting. This is a very important variable, as it will affect the feel of so many other adjustments you could make.

For the default Jet Ranger this parameter is set to a fairly realistic value of 1760 Lbs. This is made possible by the fact that other parameters within the .air file give the engine and rotor blades the power and lift properties they need to handle this weight realistically. Simply stated, if you were wanting to adjust this empty weight to be much heavier in order to represent a much larger helicopter, there will be considerable work needed within the the aircraft.cfg file, as well as the .air file in order to realistically move that weight around.

For the sake of this article I will assume that we will be adjusting that weight around a light single turbine helicopter in the same weight category as the Jet Ranger. Otherwise, it will become to difficult to succinctly explain how to achieve harmony amongst all of the required parameters.

empty_weight_CG_position

This can be an important parameter because it effectively tells the helicopter simulation engine where the center of gravity for your aircraft will be. By default this is set at the true center of the model (0,0,0) but in some cases this can be adjusted to achieve more interesting and realistic effects. For example, most skid equipped helicopters are capable of run-on landings during autorotations. The default values of 0,0,0 will not always produce this desired effect. Lowering the CG by even a tiny amount (such as -0.3) upon the vertical access can sometimes give you the stability you are looking for during run-on landings in skidded helicopters.

This CG parameter can also help produce a helicopter that doesn't unaturally drop or raise the nose during flight. By default, many helicopters within Microsoft Flight Simulator do not respond well to aft cyclic when the collective is reduced. In most cases this can be attributed in part to a CG that is slightly forward of neutral. Amongst other things.


;Moments of Inertia
empty_weight_pitch_MOI = 6000
empty_weight_roll_MOI = 4000
empty_weight_yaw_MOI = 10000
empty_weight_coupled_MOI = 0


This is one of the most important sections in the default helicopter aircraft.cfg file for Microsoft Flight Simulator. These numbers determine how much mass the simulation engine will attribute to each of the axiis. Imagine two large bicycle wheels, one made of light aluminum and the other made of solid lead. The aluminum wheel could be spun by hand quickly, and be brought up to a high speed of revolution with little effort, but it can also be stopped in a an instance. The lead wheel on the other hand, would required more effort to get spinning, and be more difficult to stop quickly. That is moment of inertia. The higher the number, the more the axis will be attributed mass that is harder to move, and more difficult to stop. This is extremely important for realistic helicopter flight dynamics modeling.

There is a temptation to lower these MOI numbers in order to achieve a more responsive reaction upon a particular axis. However, this is a bit of a trap. Because by lowering the number, you will get a faster reaction to a control input that affects a particular axis, the intertia and momentum attributed to that axis will not be realistic. It will be shallow and twitchy. It will lack the momentum that a heavy object should normally have.

It is desirable to keep the MOIs as high as you desire them to be, and find additional control repsonsiveness through other means. The net result will be a responsive helicopter, with a nice solid momentum on each of the axiis of rotation (roll, pitch, yaw). In short, these MOIs should be tailored more toward the size and weight of the aircraft you are attempting to configure, and should not necessarily be used to tune the responsive of the cyclic control inputs. There will be other, more effective ways of achieving that , which we'll get into later on.


low_realism_stability_scale

This is an extremely important parameter, and is typically set to a default of 1.0,1.0,1.0 for each axis respectively. This parameter is basically a stability multiplyer on each rotation axis of the helicopter. The values of this parameter are attributed to the lowest level wet on the general realsim slider of the helicopter within the Aircraft->Realism Settings menu within Microsoft Flight Simulator. So by default, you are getting a 1.0 worth of stability augmentation, when the general realism slider is set at its lowest position. In this case, stability means an artificial sense of control. Rotations upon any of the axiis of the helicopter will be artificially stabilized, to the point of feeling steril.

By decreasing these values, you can cause the helicopter flight model to become much more fluid and reactive to gravity and momentum. In most cases, this is much truer to real life helicopter dynamics. The default Jet Ranger values of 1.0,1.0,1.0 are highly stabilized. Most likely this was a choice made by the Flight Simulator team to try an increase the chances that a new user would have a positive experience with the helicopter simulation flight model. However, for realism sake, these values are typically too high. Try lowering them all to .5 to get a feel for what effect this has on the aircraft if Flight Simulator.

This appears to be connected to the problem of 100% on the general realism slider for helicopters in Micrsoft Flight Simulator. This 100% setting probably removes or unrealistically reduces the stability factor for the helicopter in Flight Simulator, and usually leads to results that are a simply unrealistically unstable. This is why Hovercontrol recommends that new pilots set their general realism slider to 99%. In order to avoid that problem. Simply stated, there seems to be a great difference between 99% and 100%.

An important consideration to these stability numbers comes into effect when dealing with helicopters that will have high cruising speeds. The Yaw axis stability factor will sometimes need a factor much higher than the other axiis in order to avoid "wagging" upon the yaw axis in high speed cruise flight in Microsoft Flight Simulator Helicopters.

However, as this yaw stability is increased, it will have a deadening effect upon the yaw response in the hover. So finding the right balance between cruise stability, and responsiveness in the hover can become a challenge.

If you really want to experiment with these easy-to-change settings in the aircraft.cfg file, simply make a backup copy of your default Jet Ranger's aircraft.cfg file, then make whatever changes you wish to experiment with. If you get frustrated, or confused, simply revert back to the original copy and try something new.

Most of these aircraft.cfg file parameters that are closely related to the helicopters need to be tuned in conjuction with other more complicated parameters witin the binary .air file for the aircraft. However, I'll be addressing more of that information in the next installment of this article.

I hope this encourages you to play around with some of the aircraft.cfg file settings for yourself. Perhaps you will come up with an approach that is all your own, and will produce a very unique flight dynamic experience for helicopters in Microsoft Flight Simulator.

Until next time, have fun, and don't be afraid to experiment.













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