[REQUEST] Add Flaps CL vertical offset or re-introduce the pitching scalars

We are trying to create a pitching motion upon extension of flaps for our
PC-12, Zenith 701 and upcoming TBMs to be able to simulate the negative AoA
approach that these planes do as well as the pitching moment. What happens in
real life on the PC-12 when trimmed for level flight and speed is constant, is
that upon deploying flaps the nose will start pitching down but the vertical
speed will remain at or close to zero (no more than 50fpm change). If you were
flying at 0 degrees AoA and pitch before flaps you will end up at 8 degrees
nose down. As indicated
incidence-setting.html), using the current tools (incidence and CL offset) we
are not able to get the required behaviour and I will give an example of why.
Let’s say that with a clean aircraft, lift is 1 and the CL is 1ft forward.
This creates a pitching up moment of 1x1=1 which is what the plane experiences
when clean. If we go to full flaps, that lift scalar becomes 3 and let’s
assume that the CL moves back 0.5ft. Our new pitching moment is now 3x0.5=1.5
nose up which is still up and even stronger. That is opposite to what is
needed and also more problematic as we get more pitching up. So what I would
like to ask is that the flap pitching scalars are re-activated or that we get
a vertical offset parameter for the CL so we can move the applied force down
in order to get the pitch moment.

I think you could achieve this with the Flaps Section, editing per each flap
position by adjusting the 2 highlighted parameters for the attitude you
require ?

Aft CL and/or incidence do not produce the desired effect as I said in the
second to last paragraph. What is needed is a pitching down moment caused by
the surface of the flaps that is exposed to the airflow, which will create a
nose-down pitching moment. This seems to be ignored in the flight model but
was present in FSX as its own flap pitching moment coefficient that could be

Works fine here I just re tested … I use it to reduce the amount of nose up
trim required at low speeds by pitching the aircraft forward when flaps
deployed (same thing your trying to do I think ) ? dont know what you tried
but mine uses POSITIVE Numbers to force a nose down pitch

What we are finding is that it will create a nose-down movement but that can
then be trimmed out to fly level on the vsi at the original AoA, it
effectively only moves the required trim position. The aircraft we are dealing
with adopts a strong nose-down pitch which is a significantly different AoA in
level flight when the flaps are extended. This was noted in the company-
approved sim and also commented on by type-rated pilots and instructors. Hence
the request to re-enable the ‘pitch on flaps’ coefficient.

Add camber to pitch nose down

Check the posts above - we have tried adjusting all of the flap settings and
none give the required change in AoA in level flight. All changes can be
trimmed out so that level flight is at the original AoA.

The above posts don’t mention anything about trying camber, only incidence and
cl offset.

Yeah, okay - this is the second thread on this topic unfortunately because it
is quite important to us. We’ve tried all available flap adjustments and
according to the SDK, the camber raises the max lift coefficient or the upper
limit to lift a wing can generate. This ties in with what we are seeing,
further confirmed by the entry for pitch scalar stating that it is no longer
available as flap pitch depends on lift added and longitudinal position of the
wing. All of that is trimmable, as stated above, to the same AoA when flying
level. Once again, we have type-rated instructors and pilots, along with time
specifically checking this out in the Pilatus-approved sim, all of which
informs us that the aircraft has a pitching moment from the flaps of
approximately six degrees nose-down which cannot be trimmed to zero AoA for a
constant airspeed.

I understand the effect you are going for. You are saying that after trimming,
there is no difference in AoA between flaps up and down? That would seem to
indicate that no lift is being added by the flaps. Looking at the stall speed
chart for a PC12 at 10450 lbs, I get the following lift coefficients. Clmax (
flaps 0 ) = 1.23 Clmax ( flaps 40 ) = 2.47 Therefore, lift_coef_flaps = 1.24
Also, check the lift vs AoA table for the correct lift slope. For a PC12, with
aspect ratio of 10+, the slope should be 5.25 or so, per radian. Also check
the lift scalar in the flap section. In order to realize the max lift
coefficient, the scalar should be, lift_scalar = 57.3 / 40 (max flap angle) =

I have a plane that is using a value of 23 for added flap camber to prevent
the nose rising with flaps. I didn’t expect I would have to use such a high
value, but it works. The only other thing I can think of is CG position. If
it’s too far aft, the nose is going up, no matter what, I suppose.

Thanks for the comments, but I have to counter with ‘been there, tried that’!
We have actually spent about three months on this (amongst other work),
apologies if my notes aren’t clear or specific enough but we have tried so
many permutations of the flap settings it’s getting to the point where
presumably we are repeating tests but I’m actually losing track. The only
setting I have which does not correspond with your figures is the flap lift
coefficient, I did start around that point though. Everything else is, if not
identical, very very close. The reason the lift coefficient does not
correspond is that by having it set at that level the aircraft instantly
increases its vertical speed by over 1000fpm. There is no gradual movement
while the flaps travel, but even with varying lift offsets aft and camber
settings, it does not behave as it should. Dropping the lift coefficient
(0.549 was the figure I ended up with to stop the ballooning, it actually gave
the correct stall speeds per flap setting at various weights) stops the
upwards elevator effect but as mentioned (and as you surmised), there isn’t
enough lift to create a pitching effect. Moving the centre of lift further aft
whilst maintaining the lift at 1.24 still gives a massive lift increase which
lifts the whole aircraft and the nose rises because of this. We were testing
at one point with the centre of lift behind the tailplane just to try and get
the nose dropping. In all instances, we could only get a partial result -
either a pitch down but it could be trimmed (lower lift) or a movement which
should give the required AoA change but because of the effect of the lift it
simply doesn’t. I accept that the PC12 has a strong pitching moment, more than
most GA aircraft. However, we cannot achieve the correct movement and as
mattnischan noted in the thread on the ‘add
incidence’ setting, others have had a similar problem. We appear to have yet
another example, then, for the unanswered thread from almost a year ago - If
the correct geometry does not give the required effect, what are we as
developers supposed to do?

CG position is measured precisely from the datum provided by Pilatus in their
maintenance manual, the sim datum point is positioned to that so that all
measurements correspond exactly to the manufacturer’s spec. We’ve ranged from
0.5 to 40 on the camber. No joy.