Realistic gear compression at spoiler extension

[Finn-D-AEWG]

Aircraft Version

Development

Description

It would be cool to have a realistic simulation of the gear compression when the spoilers are extended after touch down or even on rejected take offs. Right now the spoilers have nearly no effect on the landing gear compression. At touchdown the landing gear, iirc compresses realistically in the A32NX but when I deploy the spoilers nothing really happens. IRL the gear compresses at that point and the aircraft kind of bounces and "sits down"...

References (optional)

From the outside: https://youtu.be/WA5UGY4uPO8?si=HLNj8DmVw8vKEzl1&t=20 https://youtu.be/SkNizDt2pl8?si=rg-LTuSjeCuzHlz6&t=9 https://youtu.be/Y7ltaDKpq4I?si=wdaFK-2cVXNImYzl&t=499

From the cockpit: https://youtu.be/_zixZ-zxEEQ?si=LKTgblQCjQDOI1f_&t=535 https://youtu.be/S9f9y_gANl8?si=RIxRDMzGggEzGTTP&t=232

There are probably thousands of better reference videos but in these the gear compression is quite noticeable.

Additional info (optional)

No response

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Finn_D-AILY

[donstim]

The gear compression in the A32NX is affected by ground spoiler deployment. There are also other factors affecting gear compression during landing, and these factors are hard to separate out in the videos of real airplanes landing. Gear compression is a function of the force on the gear, which is affected by the weight of the airplane, the airplane configuration (flaps and spoilers), the speed, the angle of attack of the wings, and the quality of the landing. The higher the weight, the more force that is put onto the gear, all other things being equal. The higher the flap setting, the more lift is produced, which reduces the force put onto the gear. Before the airplane's nose touches down, the wing is at a higher angle of attack, which produces more lift and reduces the force on the gear. Deploying spoilers reduces the lift, increasing the force put on the gear. As for the quality of the landing, I'm referring to the touchdown loading on the gear -- too high a touchdown rate of descent and the airplane may bounce, too low a touchdown rate of descent and the load on the gear is reduced.

To show that the effect of spoiler deployment on gear compression does exist in the A32NX, I've recorded a video of an autoland at KSEA 16L with delayed spoiler deployment. Included in the video are open developer debug windows showing the effect of spoiler deployment on lift, force (weight) on the gear, and gear compression. From that video, I made 3 screenshots, one just after touchdown, one just before spoiler deployment, and one after spoiler deployment.

Just after touchdown (observe the white puffs of smoke behind the airplane), the lift coefficient (circled in red) is about 1.79, and the left and right main gear compression levels are 27% and 25%, respectively.

Just before spoiler deployment, the lift coefficient is about 0.89 (reduced due to lower angle-of-attack of the wing). The lift force is reduced even further, increasing the load on the gear due to the lower speed. The gear compression is now 48%/47%.

Lastly, just after full spoiler deployment, the lift coefficient is reduced even further due to the spoilers to about 0.36, increasing the load on the gear. The main gear compression is now 60%/59%.

So, and effect is clearly there. Is this exactly the right magnitude? Perhaps not, though the effect of gear load changes on gear compression is based on IRL data. Another item that enters into visual perceptions of gear compression in MSFS is the animation sequence. For reasons I don't know the answer to, the animation of the gear compression is a much smaller percentage change than the actual gear compression is. This is why I don't think you are noticing the gear compression due to spoiler deployment. Hopefully, when we can put together our own custom model, this can be addressed further.

[Finn-D-AEWG]

The gear compression in the A32NX is affected by ground spoiler deployment. There are also other factors affecting gear compression during landing, and these factors are hard to separate out in the videos of real airplanes landing. Gear compression is a function of the force on the gear, which is affected by the weight of the airplane, the airplane configuration (flaps and spoilers), the speed, the angle of attack of the wings, and the quality of the landing. The higher the weight, the more force that is put onto the gear, all other things being equal. The higher the flap setting, the more lift is produced, which reduces the force put onto the gear. Before the airplane's nose touches down, the wing is at a higher angle of attack, which produces more lift and reduces the force on the gear. Deploying spoilers reduces the lift, increasing the force put on the gear. As for the quality of the landing, I'm referring to the touchdown loading on the gear -- too high a touchdown rate of descent and the airplane may bounce, too low a touchdown rate of descent and the load on the gear is reduced.

To show that the effect of spoiler deployment on gear compression does exist in the A32NX, I've recorded a video of an autoland at KSEA 16L with delayed spoiler deployment. Included in the video are open developer debug windows showing the effect of spoiler deployment on lift, force (weight) on the gear, and gear compression. From that video, I made 3 screenshots, one just after touchdown, one just before spoiler deployment, and one after spoiler deployment.

Just after touchdown (observe the white puffs of smoke behind the airplane), the lift coefficient (circled in red) is about 1.79, and the left and right main gear compression levels are 27% and 25%, respectively.

Just before spoiler deployment, the lift coefficient is about 0.89 (reduced due to lower angle-of-attack of the wing). The lift force is reduced even further, increasing the load on the gear due to the lower speed. The gear compression is now 48%/47%.

Lastly, just after full spoiler deployment, the lift coefficient is reduced even further due to the spoilers to about 0.36, increasing the load on the gear. The main gear compression is now 60%/59%.

So, and effect is clearly there. Is this exactly the right magnitude? Perhaps not, though the effect of gear load changes on gear compression is based on IRL data. Another item that enters into visual perceptions of gear compression in MSFS is the animation sequence. For reasons I don't know the answer to, the animation of the gear compression is a much smaller percentage change than the actual gear compression is. This is why I don't think you are noticing the gear compression due to spoiler deployment. Hopefully, when we can put together our own custom model, this can be addressed further.

First of all, thank you very much for this detailed explanation:) And yes, I didn’t meant that the gear compression after spoiler deployment isn’t there at all, it is just visually not that obvious to spot. And of course many factors play a role there but I can nearly take every IRL video in any condition I want (FLAPS 3/4, hard/smooth landing, high/low pitch on touch down, lower/higher speed, lighter/heavier weight) and this effect is still a lot more visible than current in the A32NX. Since I don’t know exactly how the MSFS flightmodel works and what data you‘ve based on irl numbers, but for me it feels like even the percentage change you mentioned is not enough. I certainly hope that with a new model this will improve further but I assume that can take a while because of the 380‘s priority. But still, keep up the incredible work so far!

[donstim]

I noticed that there are a couple of new parameters available in the MSFS SDK that may be related to this issue. I will investigate and see if any improvements can be made.

[Finn-D-AEWG]

I noticed that there are a couple of new parameters available in the MSFS SDK that may be related to this issue. I will investigate and see if any improvements can be made.

That would be great! Really looking forward to an improvement