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.
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.
1. flaps-position.0 = 0,-1,1,1,1,0,0,0
2. flaps-position.1 = 15,163,1,1.6,1.07,0,0,7
3. flaps-position.2 = 30,130,1,3,1.2,0,0,20
4. 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?
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.
1. flaps-position.0 = 0,-1,1,1,1,0,0,0
2. flaps-position.1 = 15,163,1,1.6,1.07,0,1,0
3. flaps-position.2 = 30,130,1,3,1.2,0,7,0
4. 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:
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.
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:
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, Raul
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.
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. Regards, Sylvain
@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. Thanks,
Paul.
@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 p itch_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.
https://youtu.be/Ri5af7YXVy4?t=1784 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.
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.
https://youtu.be/wfolBgMhU0U
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?
It is yet another example of: https://devsupport.flightsimulator.com/t/4529
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.
I am adding this video for reference on this problem, at 18:14:
https://youtu.be/1TFx9BnB49Q 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?
@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.
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. Paul.
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:
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, Matt
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!
I read all the responses provided, yes, but it seems like folks are confused
about causes and effects and what does what, so that’s why I provided that
comment, so it would be easier to visualize how the parameters move the AOA
for a given speed. Right now I don’t believe it’s possible (nor was it in FSX,
pitch_moment_flaps was just a force and not a change in AOA for a given speed)
to affect the AOA for a given speed except by a change in lift amount. Either
the flaps lift scalar or flaps incidence scalar (which is really just lift
slope) will add or subtract lift. There isn’t any parameter for just moving
the lift curve only to the left at this time (keeping total lift the same);
you can only change AOA left by adding lift in some way via those two params
(which will result in the ballooning you see). Previously, developers worked
around these limitations with custom systems in code that would use virtual
surfaces, like dynamic flaps/slats based on AOA, dynamic spoilers, systems
that would alter the center point of the elevators, etc. In the CJ4 for AAU1
we ran into the same issue: at VRef with correct flaps stall speeds the
approach angle was 4.5 degrees, when it should be 0 degrees. We adjusted the
incidence parameter to bring the nose to 0 degrees, but upon release we
received a large number of community complaints regarding the ballooning with
this configuration. As a result, in SU12 we split the difference: we reduced
the incidence parameter, giving us a natural 1-1.5 degrees or so at VRef, and
added some negative lift center to counteract the (much lessened) ballooning.
The result is not perfect but it is probably 85% there. If you want to get
closer than that you’ll need to go the custom coding route at present.
I think it will have to be custom, then, because we are looking at 6+ degrees
of pitch change, - 8 on the approach (likely hence the excessive ballooning).
It could be faked pretty convincingly in FSX, I actually worked with a VC10
instructor to get as close as we could with the varying pitch changes for slat
and flap extension on that aircraft (some nose-up, some nose-down) using a
combination of lift and pitch forces. It’s a shame that we can’t have the same
control here because external coding really should not be the aim. I don’t
think the problem is ‘cause and effect’, as you suggest. I think more the
amount of the effect required and the fact that we cannot ‘massage it’ to get
the correct effect. It’s another instance of the correct geometry and core
flight model not producing the correct result, so the third party dev needs a
way to manipulate it.
Like Paul said, we are looking for a pitching effect with flap extension. If
you observe the PC-12 video above (29:44 mark) you will see that the VSI
remains still and the nose comes down, while the pilot doesn’t touch the
controls. Link: https://youtu.be/Ri5af7YXVy4?t=1784 That is what we
experienced in the real plane and replicated multiple times in the training
simulator, a pure pitch change with no change in vertical speed.