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GrimPhoenix9349 avatar image
GrimPhoenix9349 asked SWS-AlexVletsas commented

Flaps 'add incidence' setting

I am struggling to use the 'add incidence' setting in the flaps section to create the correct pitching motion required. Only extreme inputs give any recognisable response and it always appears to give a strong nose-up pitch on initial flap deployment followed by a strong nose down pitch on later flap positions. Positive and negative make no difference to the behaviours.

The SDK suggests very little, but does mention that it is in degrees. Unfortunately, the correct amount of degrees required (6) entered into the field for full flap gives no visible change in pitch. It is only when much higher figures are used that anything noticeable occurs and then it goes suddenly to extreme and uncontrollable behaviour.

I've now tried this with several aircraft and have found the same results each time.

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Simbol avatar image Simbol commented ·

Dear Asobo,

I remember this was very easy to do in P3D and FSX days. This was effectively archivable by using the Pitch moment flaps:

Given Alex results and his extensive experience with realistic flight models, it looks like we are now unable to achieve similar results?. Unless there is a way to achieve this that we don't understand?

There are lots of aircraft that behave this way in real world, so it would be good if we can get some ways to control this, specially because as Microsoft Flight Simulator becomes more and more popular (thanks to all your efforts), Aircraft manufactures are becoming more aware of the potential to use MSFS to show case their airplanes and their real world capabilities, and as a result they are imposing to 3rd party developers very tight restrictions in order to grant licensing, some of these aircraft manufactures are now even performing inspections of the flight models we are creating for MSFS and if their required expectations are not achievable we incur into a high the risk to lose the right to even sell these airplanes for MSFS.

I have suffered this myself with TL-Ultralight for the Sting S4 when they were very blunt and told me, no parachute, no release! and I am currently working with other aircraft manufactures who are imposing similar red lines on their contracts with me regarding particular characteristics of their airplanes.

Sensing Alex tone, I am guessing this could potentially become an issue for SWS and they are walking a similar path, specially knowing how proud Pilatus is about their aircraft.

Where I am going with all this? Microsoft and Asobo has done such a great work for this simulator that now Aircraft manufacturers are seeing this as a serious business. This is a compliment to both Asobo and Microsoft, simply put you guys have done just an excellent Job to promote flying simulation to a new level.

Now although this is amazing on one hand, at the same time this means the pressure for 3rd party developers has increased considerably, to a point where we can just lose rights to sell airplanes if we are unable to reproduce certain real flying performance or characteristics of a product.

I am just passing honest feedback on this matter so you guys understand our position a bit better, pretty much sometimes when we post asking for help on these kind of airplane behaviours that we are unable to replicate is a pretty much cry for help since it could mean very bad news for our business.

Thanks one more time to Asobo and the entire team for all the efforts you guys do, we do appreciate everything you guys do.

Kind Regards,

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GrimPhoenix9349 avatar image GrimPhoenix9349 Simbol commented ·

I totally agree with Raul, and as I have been saying for a long time we, the 3rd party devs, need ultimate control of all aspects of how an aircraft flies. Simple, effective control on top of the core flight model.

I spent close to 30 hours in the Pilatus-approved simulator to gain a feel for the aircraft, and to be unable to reproduce such a basic behaviour which would previously have been simple is massively frustrating from a personal / professional viewpoint but as alluded to, concerning from a business stance.

So many of those 'legacy' coefficients and tables gave precise control.

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SWS-AlexVletsas avatar image SWS-AlexVletsas commented ·

It is really pulling the nose down hard and gets the plane out of control. If a copy of the flight model file is needed, we'll be happy to provide it.

Edit: the behaviour is reproducable in both SU11 and SU12 beta. Here we have exaggerated parameters to get the plane to respond somehow and -of course- it will spiral out of control.

flaps-position.0 = 0,-1,1,1,1,0,0,0
flaps-position.1 = 15,163,1,1.6,1.07,0,0,7
flaps-position.2 = 30,130,1,3,1.2,0,0,20
flaps-position.3 = 40,130,1,3.25,1.27,0,0,25

The aircraft we are working on will nose down when you apply flaps. During final approach and flaps at 40 degrees, we were approaching to land at a negative AoA to stay on the glide path.

If we try shifting the CG aft, then the actual shift needed is huge and then we have to increase lift a lot to be able to maintain level flight. This causes a lot of other problems and leads the plane far away from its real behaviour. Also, using flaps 40 will cause the plane to go into an uncontrollable nose-dive.

On the other hand, using the "add incidence" parametre doesn't seem to produce any effect until you reach about 3 degrees. At that point, the plane will uncontrollably nose down.

Therefore, the questions are:

1) Do the parametres to shift the CL and incidence with flaps work correctly?

2) If yes, how can we achieve the nose-down attitude that the real aircraft exhibits when extending the flaps?

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SWS-AlexVletsas avatar image SWS-AlexVletsas commented ·

To add further information to this topic, I think we have hit a weird bug within the core flight model again.

I have modified the flaps to the following configuration, which gives us close to correct approach AoA at flaps 30, but flaps 40 is unusable and the plane nose-dives uncontrollably.

flaps-position.0 = 0,-1,1,1,1,0,0,0
flaps-position.1 = 15,163,1,1.6,1.07,0,1,0
flaps-position.2 = 30,130,1,3,1.2,0,7,0
flaps-position.3 = 40,130,1,3.25,1.27,0,7,0

So at flaps 30 the plane flies close to what it does in reality and the resulting flight behaviour is correct, but having the wing forces applied that far back is a bit... unnatural. As incidence doesn't seem to work, is there another way to make the aircraft fly nose-down with the flaps, other than moving the wing all the way back to the tail?

This is what the sim forces look like with the only known working configuration so far:

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SWS-AlexVletsas avatar image SWS-AlexVletsas commented ·

Another update to this issue: shifting the CL aft using the offset will still not give us the right result. IRL the plane with full flaps will fly at 5 degrees negative AoA but we cannot get this result without a working pitch moment parameter.

So we come back to the original question: the incidence angle does not seem to work at all. Is it broken or are we doing something wrong? What is interesting is that it worked well in FSX but no longer does.

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FlyingRaccoon avatar image
FlyingRaccoon answered SWS-AlexVletsas commented

Hello @GrimPhoenix9349 @SWS-AlexVletsas @Simbol

The description of this parameter is incorrect.
The "add incidence" parameter is a scalar that lets you define how much of the additional lift is applied at 0° AOA.
So, when set to 1 (100%), the additional lift is added constantly on the whole AOA range.
When set to 0.5 (default value), only 50% of the additional lift will be added at 0° of AOA and 100% at the stall AOA. The values in between depend on the normalization process.
0.5 (50%) is the minimal value and you can go beyond 1.0

Our recommendation to tweak the flaps are the following:
Set the stall AOA in the lift table to the highest stall AOA across all flap settings.
Set the stall lift in the lift table to get the stall speed and recommended speed AOA with clean flap setting right.
Set the flap lift coefficient to get the correct AOA at full flap stall speed.
Set the flap incidence coefficient to fine tune the AOA at recommended speed at flap levels.

@Nocturne for documentation update

I hope this helps.


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SWS-AlexVletsas avatar image SWS-AlexVletsas commented ·
I am adding this video for reference on this problem, at 18:14:

As you can see, the Cirrus SR22 also exhibits this behaviour and unlike the real plane, the default SR22 lacks this. One of our devs that flew an SR22 mentioned this to me and I found some evidence.

Also, @FlyingRaccoon the problem seems to have been the lack of pitch moment with flaps all along. Do you think it would be more helpful to report into a new, clean topic, or leave it here?

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GrimPhoenix9349 avatar image GrimPhoenix9349 commented ·
@FlyingRaccoon Thank you for the response. Unfortunately, that is basically what I tried first and to get the correct pitch angle alteration using the flap lift coefficient required a setting which gave a roughly 4000fpm increase in the vertical speed at max extension ias. Not at all realistic.

What we need to create is a pitch alteration across the operating speed range of the flaps, not tied to stall speed. The pitch alteration to the aircraft in flight (not the stall AoA) per flap setting is constant from the max speed for that setting down to the stall speed. Effectively, pitch from flaps needs to be dealt with separately from lift, and currently the core flight model is not giving the correct result.



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SWS-AlexVletsas avatar image SWS-AlexVletsas commented ·

@FlyingRaccoon Unfortunately that isn't what is needed. If I understand what you wrote correctly, by setting the "incidence" to 0.5 we would get considerably more lift at low AoA and the pilot would have to trim down in order to maintain level flight. This could result in negative AoA and potentially give us the correct flight attitude for various stages of flight.

However, that solves only half the problem. What we experienced in the plane was not just a negative AoA after the plane had settled, but a nose-down pitching motion as the flaps were extended. We didn't have to trim down, the aircraft pitched down by itself as flaps were extended and that is missing.

In the past we were able to vary the aircraft's pitch by using pitch_moment_flaps but this has been deprecated. Is there a way that we can get that result in the modern FM or can this be added back in?

A simple explanation of what happened in the real aircraft

Flaps 0: plane flies normally, for example 2 degrees AoA so level flight is 2 degrees nose up.

Flaps 40: as the flaps extend, the plane noses down at the same time without pilot input. In the end the plane will end up flying at about 5 degrees nose down at the same speed. Some trimming may be required to level the plane, but the pitch-down movement is not due to pilot input but due to forces exerted on the flaps during the extension.

Edit: Check this video at 29:44 where he goes to flaps 30 and flaps 40.

You will notice that his Vertical Speed indicator hardly moves. At flaps 30 his attitude goes from 1 degree to about 2.5 degrees nose down. When he says "Flaps 40 selected" his nose moves down another 2.5 degrees and the VSI stays fixed. This is the pitching moment effect that we are missing. In both instances, his hands are off the trim switch on the yoke and he isn't pulling back on it.

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SWS-AlexVletsas avatar image SWS-AlexVletsas commented ·

As we haven't been able to get the pitching moment to work, we decided to return the flaps to a configuration that gives correct lift & drag, even though the pitch will be wrong.

I should also note that the TBM has the same attitude in reality, so it could go into the default 930 just as well as our own TBMs. Here is a video showing the approach attitude and a screenshot of the real vs ingame TBM. Note the flight path vector and AoA.


It is unfortunate as the landing gear seems to generate a pitch down moment just fine.

@FlyingRaccoon is there any consideration to add back the pitching moment parametre or refine the flap dynamics to produce that effect?

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GrimPhoenix9349 avatar image GrimPhoenix9349 SWS-AlexVletsas commented ·

It is yet another example of:

When the core flight model does not get it right, we must have a clear and straightforward way of making these individual adjustments without affecting any other part of the flight model. Not having that ability reflects badly on all, and as mentioned upthread could potentially have a significant impact on individual businesses and their agreements with aircraft manufacturers.

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mattnischan avatar image
mattnischan answered SWS-AlexVletsas commented

@SWS-AlexVletsas @Simbol @GrimPhoenix9349

If you are looking for flaps to generate pitching moments, you can use the `add aft feet` parameter in the flaps position config, which has been present in the sim since I think SU4, if I'm not mistaken. This parameter changes the lift center of the wing for the given flaps level by adding an offset. A negative offset will add a pitch down moment, and a positive offset will add a pitch up moment.

I generally start with just a few feet, maybe 1-3. Something important to note is that unlike the `incidence` parameter, this does not change the AOA at which the plane will fly for a given airspeed, this only changes the moment (the force) experienced when in that flaps position. So, for example, if you're flying at 0 degrees AOA and the increased flaps lift now makes that level flight CL for the current speed occur at -4 degrees AOA, the plane will tend to balloon as you're still flying at 0 degrees for a bit until you trim out to -4 degrees of pitch. However, by using this `add aft feet` parameter, you can change the lift center to add a pitch down moment to balance these effects.1679588111485.png

Hope this helps,


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GrimPhoenix9349 avatar image GrimPhoenix9349 commented ·
Hi Matt,

Thanks for the suggestion, but we tried that - to get anywhere near the correct pitching motion we had to shift quite a way aft. The result was awful, and having the lift that far aft did not actually change the AoA of the aircraft in level flight, just gave a need for a stronger pull on the stick. You could still maintain level flight at the original AoA.


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mattnischan avatar image mattnischan GrimPhoenix9349 commented ·

Yes, that is correct. A change in level flight AOA for a given speed requires (even in the real world) a change in CL. An increase in CL will result in a decrease in the AOA, and likewise a decrease in CL will result in an increase in AOA. This is the primary mechanism by which flaps alter the AOA for a given speed (all geometry changes boil down to that, really). If you don't change the CL, then the AOA will remain the same.

To modify the flaps CL for a given AOA in the sim there are two options: the flaps setting lift scalar and the incidence scalar. These achieve the following effects (stall AOA in the example is 10 degrees, x is AOA, y is lift with an arbitrary scale, red is clean, green is flaps, black is some constant speed):

Incidence at default (0.5), some additional lift scalar:


Incidence at default (0.5), even more lift scalar:


Incidence at 1.0, first lift scalar:


Incidence at 1.5, first lift scalar:


In other words, the lift scalar moves the curve up, and the incidence parameter changes the slope. You can see how the resultant AOA/pitch for the given speed is altered via the changing of these parameters.

Hope that helps,


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GrimPhoenix9349 avatar image GrimPhoenix9349 mattnischan commented ·
I'm not sure if we haven't been clear in the detail we provided further up this thread, Matt, but the behaviour in game when trying this is not anywhere near realistic for this particular aircraft. It has a fairly excessive pitch change on flap extension whilst maintaining speed and level flight. From experience with both the real aircraft and the manufacturer-approved simulator, there is no ballooning and yet to get the required pitching in this game we ended up with a stupidly high (4000fpm+) sudden climb rate even with the flap lift shifted almost back to the tailplane!
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