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donstim avatar image
donstim asked donstim edited

Are air and ground spoiler aerodynamics implemented in SU10?

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.

1657761142024.png

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.

1657761282066.png

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.

1657761527175.png

Swapping the delta cd values in the flight_model.cfg file resulted in a spoiler cd of 0.06109.

1657761616581.png

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

flightmodeldocumentation
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FlyingRaccoon avatar image
FlyingRaccoon answered donstim commented

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.

1658223260646.png

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


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donstim avatar image donstim commented ·
Wow, that's a major difference. Thanks for clearing that up.
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FlyingRaccoon avatar image
FlyingRaccoon answered donstim edited

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

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donstim avatar image donstim commented ·

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.

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