Are air and ground spoiler aerodynamics implemented in SU10?

[MSFS 2020] Questions & Community Discussions Aircraft
1

The preliminary SDK associated with the SU10 beta flighting includes new
parameters for the flight model for spoiler lift and drag while in the air,
while the existing spoiler lift and drag variables now pertain to ground
operations (unless the in air spoiler lift and drag parameters are not used).
I’ve been testing how these parameters work using the default A320 and have
had some curious results. I only investigated the drag effect, and to make
sure the lift effect did not interfere in some way, I set the lift affect for
both air and ground spoilers to -0.001. First, I looked at the spoiler drag on
the ground. I set the ground spoiler delta cd to 0.001 and the in air spoiler
delta cd to 0.1. I was surprised to see a Cd spoiler of 0.06109.

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I then set the air spoiler
delta cd to 0.001 and the ground spoiler delta cd to 0.1. Again, on the
ground, I was surprised to see spoiler cd of 0.00006.
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In the air, with the air
spoiler delta cd set to 0.001 and the ground spoiler delta cd set to 0.1, the
spoiler cd was given as 0.00006.
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Swapping the delta cd values in
the flight_model.cfg file resulted in a spoiler cd of 0.06109.
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With the air spoiler delta cd
set to 0.14 and the ground spoiler delta cd set to 0.15, the spoiler cd was
given as 0.08552. From these results, it looks like the air spoiler drag is
being used both in the air and on the ground, and that the ground spoiler
delta cd is not being used at all. (Note: I did go back and double-check that
the gear is on ground simvar returned a “true” value for these cases.) It also
appears that the spoiler drag value shown in the drag debug window is always
61% of the delta cd value in the flight_model.cfg file. Why is this? As I
said, I did not check the effects of the ground and air spoiler lift
parameters, but I am concerned that they may also exhibit these issues.
Regards, Don

2

Hello @donstim The doc is misleading here. The coefficient is not used based
on whether the aircraft is in the air or not but rather on whether it has its
spoilers in ground or air configuration. It’s using the spoiler_limit and
air_spoiler_limit parameters for this. The air coefficients will be used
when spoiler angle is inferior to the air limit and will be interpolated when
that angle is in between the two. @Nocturne will review the description.
Regards, Sylvain

3

I still find this confusing. Is use of the spoiler_limit and air_spoiler_limit
parameters based on whether or not the airplane is on the ground? For example,
at maximum spoiler handle position, will I get the spoiler_limit deflection
and therefore full spoiler lift and drag on the ground and the
air_spoiler_limit deflection and corresponding full air spoiler lift and drag
while in the air? (This assumes the spoiler_limit and air_spoiler_limit
parameters are different, and the spoiler_limit is larger than the
air_spoiler_limit.) As an example, if I set the air_spoiler_limit to say 10
and the spoiler limit to 35, and the drag_coef_air_spoilers to 0.02 and the
drag_coef_spoilers to 0.15, should I not get a spoiler cd of 0.15 when on the
ground with the spoiler handle and spoiler positions at 100%? Instead, I get
0.09164, which is the 61% of the .cfg delta cd value as I noted before. EDIT:
I should also note that this does not fully address the differences between
air and ground spoilers deployment on most airliners although it is a helpful
addition. The difference between air and ground spoiler deployment may not
even involve different maximum deflection angles, but rather a different
number of spoiler panels being deployed. Or, it could be a combination of
both, with some panels being deployed to a lesser angle in the air than on the
ground in addition to having more panels deployed on the ground. For example,
for the A320neo, which has 5 spoiler panels on each wing, only panels 2,3, and
4 extend in flight. In flight, the maximum deflection of panels 3 and 4 is 40
degrees, while panel 2 is limited to 20 degrees. On the ground, all panels
fully extend to 50 degrees.

4

Hello @donstim Your first assumption is right. The spoiler limit angle that
will be considered will depend on whether the aircraft is on the ground or
not. As for the reason why you don’t reach the drag coefficient you specified
in your cfg, we forgot to mention it in these parameters descriptions but they
work on the same principle as the flaps lift/drag evaluation.

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Following the FSX design, the
computed lift/drag coefficient is multiplied by the surface deflection in
radians. So you need to compensate for this deflection if it’s inferior to 1
radian to reach 100% of your lift/drag coefficient. We don’t have any scalars
for spoilers so you want to compensate directly in the coefficient parameters.
We will make sure this is mentioned in their description. Thank you for
bringing our attention on this. Regards, Sylvain

5

Wow, that’s a major difference. Thanks for clearing that up.