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Old 11-02-2011, 07:57 PM
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Tuning Vehicles to Work in RealFlight 6

For RealFlight 6 we have improved many areas of the flight physics implementation. The aim was to significantly improve accuracy in Realistic difficulty mode. As a consequence, this will affect some of the characteristics of Swap Page vehicles that were set up for earlier versions of RealFlight. They may not fly like they did in G5.5, or how you might prefer them to fly.

In some cases, nothing, or very little, will need to be adjusted to make them fly realistically.

As a general rule, in RealFlight 6 you should expect to be able to reset some of the “cheats” like boosting propwash or fuselage scaling, lift factors, etc. that may have been needed in earlier versions. (For example, most of the stock FlatOut type planes simply had to have all the settings restored to defaults in order to fly realistically.) Some of those artificial compensations, if kept, may result in unrealistic handling now. Of course, if your aim is to make a more-mild or more-wild aircraft than is realistic, that's fine.

(Please note that there are many approaches to setting up vehicles. It is also very difficult to get an accurate impression of the flying characteristics in the sim, to compare to real life, because of the limitations of the screen, sounds, ambient conditions etc. This is only a bit of a guide as to what you can expect to need to look at.)


Airplanes

Before adjusting the model for trim, make sure all digital trim controls are set to neutral on the Interlink.


Pitch Trim and CG location

A lot of airplanes in the standard monoplane configuration will need a bit of elevator down trim compared to earlier versions. It is also possible that if previously, the CG was set farther toward the rear than the plane would have it set in real life, it might need to be moved forward.

In general you should expect it to now fall within actual recommended placement ranges, whereas in previous versions sometimes it had to be set more rearward than would be allowed in real life.

Some planes may need to have the down thrust and main wing incidence checked or adjusted as well, because the propwash may affect the wing differently, and as well the airfoil lift curve and moment coefficient curves may have changed.

Airplanes with reflexed airfoils can expect more of a change in the pitch trim, due to significantly more accurate Moment Coefficient curves, especially at low Reynolds numbers.

Planes using the Balsa Flat Stab for the horizontal stabilizer can expect an extra tendency to climb compared to the previous version, because that airfoil previously had a small error in its profile that gave it non-zero lift at zero angle of attack. (This also affects rudder trim for the same reason.)

For some vehicles all of this may add up to a significant need to re-trim the aircraft. We would have liked to avoid this, but since the effects are distributed across different aspects of the physics and since each vehicle will be affected differently, we did not see any clean way of automatically adjusting vehicles for the new physics.


Yaw Trim and Stability

Vehicles with substantial fuselage area may be less stable in yaw than before. The airfoils that are typically used to represent the fuselage aerodynamically now tend to have a somewhat farther-forward center of pressure.

Compounding this will be any fuselage Wetted Scale Factor above 100% on the Z axis. This increases any effect of the center of pressure location of the fuselage, relative to the vertical stabilizer. In some cases this fudge can be removed since it is usually only used to give better knife-edge flight performance, and there are now other ways to achieve that.

Note that if the C.G. is moved forward due to the updated airfoil pitching moment curves, then the yaw stability will also be improved.

Dihedral effects will seem stronger if there is less yaw stability, as well.


Roll Trim

The propeller counter-torque has been eliminated at high speeds, because in real life the model would be set up to fly hands-off under those conditions.

You may find that if you previously had set up something like rudder incidence, or had shifted the CG laterally, or tuned the right thrust, or added a small trim tab, or turned down the back torque factor on the engine to eliminate a slow hands-off roll, that you do not need those tweaks any more.


Knife-Edge Flight

The changes to the fuselage and propwash aerodynamics should make most planes a little better at knife-edge flight.

There are several settings that in the past were used to add some extra knife-edge capability to airplanes, when the earlier versions of the sim did not give them enough.
  • Fuselage Wetted Scale Factor – this was often increased to give more side force.
  • Fuselage Aerodynamics percent – often increased to make it generally more effective (at the cost of increased drag)
  • Engine Prop Wash Factor – typically increased to give more rudder effectiveness (but can result in unrealistically easy hovering)
It was found that the fuselage aerodynamics were the greatest factor in the lack of knife-edge flight realism.

There are new properties that can be adjusted to help achieve realism without as many unrealistic side-effects as the settings listed above.
  • Aspect Ratio Factor - Side – this can make the fuselage give more side force at typical knife-edge flow angles, without adding frontal drag or affecting the center of pressure. At the default of 100% it already has some effect, so it may not need to be changed.
  • Center Of Pressure Modification - Side – lets you have a very large amount of control over the yaw torque generated from side forces. Even small changes to this can be noticeable. In general, if everything else is set to the defaults, and this one setting is changed, you can likely tune the knife-edge behavior. Moving it too far forward (positive values) can result in yaw instability and laughable behavior, so adjust it in 10% steps, for example. Read the help text.

Propellers

The propeller calculations were very substantially revised to more closely match measured data. Some props will have more “bite” than before, and some will have less. In general they will have more drag torque.

There may be a noticeable difference in top speed due to these changes.


Hovering

Since the prop drag torque is likely higher, and now the counter-torque is also higher, planes will tend to have much stronger torque roll behavior.

In addition, improvements in the accuracy of control surface edge handling, and in the propwash shape and velocity, will likely reduce the aileron control authority in hover. Together this should produce a relatively more realistic level of difficulty than earlier versions.

Changes in prop inertia and engine acceleration/deceleration may also be visible as an increased responsiveness to the throttle.


Helicopters

The changes to the physics touched virtually all aspects of the heli physics. In general, helis set up with older versions of RealFlight will still fly, unchanged. However, they will likely seem under-powered.

In general, the physics is best able to give a realistic simulation when given accurate physical dimensions, weights, ratios, airfoils and other parameters. In previous versions it was more necessary to work around some inaccuracies by “fudging” some of the properties. In RF6 some of these old workarounds result in inaccurate behavior. When tuning for RF6, it is best to check all basic properties for accuracy, and only after these are known to be correct should you “tweak” the settings for final behavior tuning.


Blade Aerodynamic Drag

The lift and drag calculations, changes in the friction calculations, and the new airfoil curves have the net effect of demanding more torque. This makes the energy losses in autorotations, especially blade-stop autos, much more accurate. (No, it doesn't make it any easier to recover from a blade-stop auto!)

However, since the airfoil curves have been generated based on typical model airplane construction, they do normally have a bit higher zero-lift drag coefficient than a typical high-quality finely-finished fiberglass or carbon-fiber helicopter blade. Therefore, if you have set up a custom blade for your heli, you may wish to adjust the blade drag coefficient slightly.

The property belongs to the blade resource. (Main Rotor, Blade Type, […] ). It is called “Drag Coefficient Adder” and now it allows negative values.

A value of zero should be used for a small-scale blade, wooden blade, plastic, molded etc.

Medium size blades that are well-constructed, polished finish, smoothly rounded nose, thin trailing edge, and have a consistent and accurate airfoil shape may also use a reduction e.g. -.0010 to -.0020 but the effect may not be very noticeable.

The larger scale, more accurate blades can go down to -.0025 with -.0035 being the largest change we would expect a blade to need.

You may be able to detect a difference in autorotations, and hover power.


Blade Balance Point

There is a new read-only property that tells you where along the blade span the blade in the sim balances. It is given as the distance from the lead-lag pivot to the balance point. If you have set up a custom blade that is supposed to match one that you own, you should check to see if the “Weight of Lead” and “Distance from Tip To Lead” are set up in a way that makes the balance point correct in the sim. This affects autorotations and general handling. See “Blade Balance Point Radius” in the Main Rotor properties. If there is no lead weight specified, it should be half of the blade length.


Engine Power Curves

We at Knife Edge had found that some of the engine power curves were unrealistically weak below the power peak. Since accurate numbers, let alone curves, are very difficult to come by, you may want to adjust any custom engines that you have created to fatten up the torque curve below the peak horsepower point, if you know that the peak power is relatively accurate. In general, the torque at peak torque can be considerably higher than the torque at peak power. There should be at least some region of the torque curve, toward RPMs lower than the peak power point, that rises (going leftward), curves over, and creates a peak torque point. The slope must be kept reasonable, or else you'll create a new, different power peak (power is proportional to torque x RPM, so the torque x RPM at any point on the curve should never exceed torque x peak-power-RPM). But that means that, for example, if the torque peak is at half the peak-power-RPM, then it could be almost twice the torque at the peak-power-RPM, without exceeding the original peak power (it would normally be somewhat lower than that).


Flybarred Roll Rates

The inertia of the flybar rod is handled differently now. The diameter of this rod makes a big difference in the inertia of the whole flybar system, and therefore affects the roll rate. (Advanced properties, Flybar Diameter.) Make sure that it is accurate. Of course it is important for the paddle weight, chord, length and overall diameter to be accurate, as well.

In general you may find that if the mixing ratio was set artificially low in G5.5, you can now set it to what it actually is in real life.


Collective Throws

You may find that you need a bit less collective in the sim than before for accurate thrust generation. In previous versions, many helis were set up with artificially high throws.


Fast Forward Flight

Previous versions of RealFlight tended to give unrealistically high top speeds. You will probably notice a reduction in FFF top speed. This is due to a number of factors including blade aerodynamics, drag calculations, flapping physics, etc.

In addition, there is now a Heli Fuselage airfoil that you can select for the Canopy component. It, like most canopies that are simple shells open to the rear, has much higher drag than a NACA airfoil, and that will result in lower top speed.

(Check to make sure that the heli does not have Fuselage Aerodynamics Percent set to non-zero values on both “Fuselage” and “Canopy”.)

One result of a reduced top speed is that there will be noticeably less sensitivity to pitch inputs than before. (There are other physics changes that have also affected this.) Make note of the top speed in level flight in the sim and compare it to real life top speeds before drawing conclusions about the pitch sensitivity. The collective pitch throw and the flybar setup have a large influence on this, as well.


Gyro Setup

The new gyro is a complete rewrite. Most of the settings will carry over and allow general functioning in a similar manner to G5.5 but a few will need to be adjusted.

In general, Control Override should first be tried at 0%. There is usually no need to override it. If the heli isn't responding to commanded yaw correctly, look at other settings first.

If the tail is oscillating, turn the Heading Hold gain to zero, and if it still oscillates, turn down the Rate Gain to find a point where it is as high as it can be without oscillations (flick the rudder stick to try to induce oscillation). Then add some Heading Hold gain back in. If you can't add enough HH gain back in without oscillations occurring, then reduce the Rate Gain a bit and see if that helps. In general, HH gain does the most work for you, so you really want that gain to be strong. Too much HH gain will generally cause very low frequency swings of large amplitude.

You may find that if you had to turn down the Rate gain a lot, then raising the Relative Damping Gain a bit to e.g. 150% may help stabilize the tail. Too much will cause high-frequency oscillation. Too little will generally cause low-frequency oscillation.

The Heading Hold Range should be kept relatively small – no larger than necessary to make the tail hold firm in all the desired maneuvers. Large settings here will likely cause correspondingly large tail “bounce” when running large tail loads, high collective, or low head RPMs i.e. when the tail can't really keep up with the Deg./Sec. that you are commanding.

Be careful when setting up a Rotation Rate that you do not set it higher than the heli can actually yaw, under the conditions you expect to see. You should experiment briefly with higher numbers, and ensure that you see quicker rotation, just to be sure you are below the maximum it can do. This will reduce the likelihood of tail bounce.

Feed-Forward gain is not normally needed. It is there to accommodate unusual situations.


CG Location

Use the new Fuel Tank Empty/Full toggle (“F” key in Vehicle Editor when the viewport has focus) to ensure that the CG is accurately placed when the tank is full. You may be surprised to see where the CG is with a full tank. The CG with the tank empty should be in the same place it was displayed in G5.5.
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Old 11-03-2011, 01:05 PM
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WONDERFUL POST!

Quite often we have to find these things through trial and error.

I would say I had already found about 95% of this stuff pertaining to airplanes
thanks to testing and comparison. So I can confirm everything you've posted I've seen.

I was missing most of the heli settings,

The above guide really helps.
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Last edited by opjose; 11-03-2011 at 06:51 PM.
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Old 11-11-2011, 02:42 PM
flip3d flip3d is offline
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Thumbs up G6

It appears that the Lift, Drag, and Moment figures in the Airfoil Selection have been revised. Long overdue, as well as the engine torque curves in the Engine Selection list.

My first impression of flight physics is positive. Very well done and a tremedous improvement over G5.5.
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Old 01-02-2012, 11:20 PM
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Aircraft Editor - RealFlight Airliner - Brakes

I hope this is the right place to ask - searched the RF6 Forum- did not find any threads on how to specifically tailor models.

RF Airliner - Aircraft Editor

How do I enable brakes on the mains and how do I assign a switch on the interlink to activate the brakes?

Open Aircraft Editor:
- AirFrame > Main Wing > Main Gear > Wheel

Brake Servo = Brake Servo (Default Value) Choices available are not logical for brakes .... with one possible exception - Throttle Servo. Could i use the lower half of the throttle travel to be the brakes? Further back the more that brakes are applied? further forward (adding power) less brakes. There will have to be a real happy balance here to keep from skidding the tires under power.

Suggestions?
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Old 01-02-2012, 11:25 PM
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Quote:
Originally Posted by Fun2av8RC
Throttle Servo. Could i use the lower half of the throttle travel to be the brakes? Further back the more that brakes are applied? further forward (adding power) less brakes. There will have to be a real happy balance here to keep from skidding the tires under power.

Suggestions?
Thats exactly how many have done it

Under Electronics you can add a new physical servo
And assign it an input
assign the brake the new servo a
If you add channel don't forget to assign an output feed
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Last edited by Maj. Numbskully; 01-02-2012 at 11:43 PM.
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Old 01-04-2012, 11:55 AM
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Adding Brakes to the Airliner (1 of 3)

I guess I missed a step as it did not work. Assuming that the three position switch positions are numbered 0, 1, and 2 - What I would like to do is add brakes to the #2 postion. Attached are the steps I went through - clearly I missed somehting as the brakes still don't work.

Please let me know where I went wrong - I will update the screen shots and repost for others to use.
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Old 01-04-2012, 11:57 AM
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Adding Brakes to the Airliner (2 of 3)

Steps 6 - 10
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Old 01-04-2012, 11:58 AM
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Adding Brakes to the Airliner (3 of 3)

Steps 11 - 14.

Thanks for looking - hopefully you will quickly spot the error and I can use brakes on my Airliner.
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Old 07-21-2013, 09:34 AM
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Stringfellow Stringfellow is offline
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In the g5.5 gyro, there used to be a setting called Acceleration rate. It controlled how fast the heli would reverse from full rudder one direction to full rudder opposite direction. Smaller helis usually are slower reversing than larger ones. Now that setting is missing and all helis reverse instantly.
Is there some way I can adjust this to have just a little delay for my smaller helis?

Last edited by Stringfellow; 07-21-2013 at 10:09 AM.
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