MiG-29 Landing Bounce and Gear Struts Overstressed

[Tin_Rat]

When landing in the MiG-29, even gentle landings see the landing gear struts compress greatly, and the wheels bounce off the runway. Based on videos of real landings, they shouldn't be so extreme. The bounce and strut behaviour can be seen in the linked video below and images.

The track file is also attached. Landing is done with ~1500kg fuel, 4 R-77 and 2 R-73s on a MiG-29S.

 

@IronhandThanks for the help, the time looking into it, and video link.

Issue MiG-29 Land - Light - Bounce Flare 2.trk

[Ironhand]

I’ll add this track as well. From the cockpit I had no sense that I’d bounced. 

MiG-29A Landing Bounce.trk

[draconus]

13 hours ago, Бойовий Сокіл said:

Can you upload a video of your landing from the cockpit?

You can play the track.

[Rifter]

The wording 'gear struts overstressed' might be misleading for the ED team.

Hard to tell wether the compression damping on touchdown is too soft compared to reality.
But from the video the rebound damping seems to be too big, since the wheels lose contact to the ground although the maximum downward travel of the gear would allow to stay on the ground.

[draconus]

17 minutes ago, Бойовий Сокіл said:

Tracks don't replay like they should (not 1:1)

Yeah, it depends, but this one does. I understand being afc but it is good smooth landing if it was what you're interested in.

[Ironhand]

Well… it’s not guaranteed that you’ll bounce. I was both lighter (40% vs 70% fuel) and careful to do this landing pretty much by the numbers (height and speeds over outer/inner markers, threshold etc). TRK attached. If time allows, I’ll try again this weekend with the heavier version.

MiG-29A Senaki-No Landing Bounce.trk

Edited March 3, 2023 by Ironhand

[Tin_Rat]

On 3/2/2023 at 3:55 PM, Бойовий Сокіл said:

Can you upload a video of your landing from the cockpit? Also 1500kg of fuel is on the heavy side with that loadout.

Should be attached. 

 

12 hours ago, Rifter said:

Hard to tell wether the compression damping on touchdown is too soft compared to reality.

True, though there are some videos for comparison. My impression of the Indian one is the first landing seems kind of high speed of descent compared to the 3rd (2:14). Compression and rebound work together, and fixing rebound would make it look/feel better in my mind.

3 hours ago, Ironhand said:

Well… it’s not guaranteed that you’ll bounce. I was both lighter (40% vs 70% fuel) and careful to do this landing pretty much by the numbers (height and speeds over outer/inner markers, threshold etc).

Nice landing. To me it looked like the right wheel left the runway. (Images below from your landing). Though actually, that does make it look like the above Ukranian MiG landing. Attached a track similar to that with my heavier weight (4 R-77s). What also struck me is that in my track, though the left wheel leaves the runway, it smokes as if it hasn't and both wheels stop smoking at the same time (5th image). Both of your wheels also seem to smoke the same way.

Issue MiG-29 Land - Light - Bounce Flare.trk 2023-03-03 16-22-53 - Copy.mkv

Edited March 3, 2023 by Tin_Rat
mention 5th image when talking about wheel smoke

[Ironhand]

Looks like you’re right about that right tire. I didn’t check from that side. From the left side it looked like both stuck.

At first I was going to protest that those images weren’t from my track but then I realized that I was using a custom Ukrainian skin. So, of course, you’d see the default Russian skin.

Watched your video. From the cockpit, you’d never know that the tires left the ground. 

[Ironhand]

Had time this weekend for 3 quick landings at a gross weight of 13652 kg which is fairly close to @Tin_Rat’s landing weight in his original post. The first 2 were similar to the one I posted above with one wheel coming off the runway. The third resulted in both wheels sticking. Interestingly enough, there wasn’t any wheel smoke either. This was probably the smoothest  landing I’ve ever made in this aircraft. TRK attached. (I porpoise in the first minute of the flight. It’s not the TRK misplaying.)

Here’s a quick video at 1/8th speed of the few seconds before and after the landing:

 

MiG-29A Senaki--GW-13652kg.trk

[Tin_Rat]

That's a really smooth landing. Very impressive. One thing that jumps out is that landing gear doesn't seem to rebound at all in that video. 

8 hours ago, Ironhand said:

gross weight of 13652 kg which is fairly close to @Tin_Rat’s landing weight in his original post.

Probably within 150kg, so negligible difference. 

 

9 hours ago, Ironhand said:

Interestingly enough, there wasn’t any wheel smoke either.

From what I could tell in my tracks, I only got that (no wheel smoke) in one (sketchy flare), and it seems to have been the one where my rate of descent was super low. 

 

This proves it's possible to avoid the bounce. But still seems to be more difficult than it ought to? Seems to be between 0.5 and 1.5 m/s descent on the dial. Unless there were some bounces I missed in my tracks. 

Issue MiG-29 Land - Light No Bounce - Flakey Flare.trk Issue MiG-29 Land - Light No Bounce 2.trk Issue MiG-29 Land - Light No Bounce 1.trk

[draconus]

Any micro bounce in normal landing is nothing unusual. RL runways are not perfect either.

No smoke otoh is not realistic. The tire needs friction to accelerate to 250-270kmph in a very short time no matter how smooth or hard the landing. That means there should always be smoke.

[Ironhand]

8 hours ago, Tin_Rat said:

...This proves it's possible to avoid the bounce. But still seems to be more difficult than it ought to? Seems to be between 0.5 and 1.5 m/s descent on the dial...

A small bounce, as draconus notes, isn't really an issue. In fact, you won't even notice them sitting in the cockpit. You'll only notice them in the external view. So I don't know how much of an issue it is. If you're landing properly, you'll only get a small bounce, at most, from one or both wheels. If you lightly kiss the runway in landing, there won't be any bounce at all because of the slow rebound. The absence of smoke in a very gentle landing is puzzling. The only scenario I can imagine is one in which you are skimming the wheels so lightly over the runway that there isn't enough friction to spin them up quickly. And, then, you finally settle down.

[Ironhand]

16 hours ago, Бойовий Сокіл said:

You were dangerously close to 15 AOA there, normal approach and landing should be made with 11 deg. AOA. 15 is high risk of nozzle strike.

That’s a valid criticism. In my defense, I know that a pitch of 14° at my height above the runway brought the nozzles no closer to the runway than the recommended 10° pitch up recommended for takeoff. And doing so allowed me to land as gently as possible.

While I agree that the landing should be made with an 11° AoA (mine was 11.5° and the source I have says “about 11°”), I’m wondering why you state that the approach should be made at 11° as well. Is that your opinion or do you have a source? I ask because nothing I have states anything like that.

[Ironhand]

4 hours ago, Бойовий Сокіл said:

No, bad wording on my part. It should be less than 11° obviously - you aim for around 340 on approach, about 300-290 over the treshhold and respective parameters on touchdown. In that video you had almost 15° over the runway, which you then corrected to close to 11 on touchdown. Especially in the 29 getting too slow isn't a good thing as drag increases with AOA fairly rapidly. The bounce issue may be apparent in external view but from the cockpit I generally dont even notice the touchdown all that much when I manage a smooth landing. While the suspension physics are likely not true to life they are good enough and them being the way they are in the game has basically no impact on your landings.

Then we mostly agree. Like you, I never notice a bounce in a good landing even though the tires leave the ground in the external view. In fact, it was Tin_Rat’s post that alerted me that it was happening at all. Definitely a fun aircraft to fly.

 

[Tin_Rat]

On 3/7/2023 at 2:07 AM, draconus said:

Any micro bounce in normal landing is nothing unusual. RL runways are not perfect either.

No smoke otoh is not realistic. The tire needs friction to accelerate to 250-270kmph in a very short time no matter how smooth or hard the landing. That means there should always be smoke.

That's a fair point. I think there's already some wheel wobble and bounce at high speed. It can be seen in the above videos too after the struts extend. But on the Su-27 for example, the touch down doesn't look like this from my experience. The landing gear rebounds so that it still touches the runway (actually, I think it looks pretty great). Well, unless you bounce so high you actually leave the runway. I've really only noticed the sort of thing shown in the original video (top of this thread) on the MiG-29. But yeah, minor thing overall.

On 3/7/2023 at 8:56 AM, Ironhand said:

A small bounce, as draconus notes, isn't really an issue. In fact, you won't even notice them sitting in the cockpit. You'll only notice them in the external view. So I don't know how much of an issue it is. If you're landing properly, you'll only get a small bounce, at most, from one or both wheels. If you lightly kiss the runway in landing, there won't be any bounce at all because of the slow rebound. The absence of smoke in a very gentle landing is puzzling.

On the wheel smoke question, I realized that initial video had wheel smoke when the wheels weren't touching the runway too. So I'd guess that there's a good chance it's merely a visual thing. Would explain why it doesn't feel like a bounce from the cockpit view too. It's probably minor. Maybe the landing gear should be stiffer too which might slightly change the feel of landing. It's not the most important issue. We can still land after all. 

[draconus]

6 hours ago, Tin_Rat said:

Maybe the landing gear should be stiffer too which might slightly change the feel of landing. It's not the most important issue. We can still land after all.

Don't belittle your own bug report. In conclusion it's mostly the strut force that should be looked at, right?

[Ironhand]

18 hours ago, Tin_Rat said:

…

On the wheel smoke question, I realized that initial video had wheel smoke when the wheels weren't touching the runway too. So I'd guess that there's a good chance it's merely a visual thing. Would explain why it doesn't feel like a bounce from the cockpit view too. It's probably minor. Maybe the landing gear should be stiffer too which might slightly change the feel of landing. It's not the most important issue. We can still land after all. 

Might be minor but still worth the report. Something is not right about the struts.

Edited March 10, 2023 by Ironhand

[Tin_Rat]

19 hours ago, draconus said:

Don't belittle your own bug report. In conclusion it's mostly the strut force that should be looked at, right?

Think so. Specifically, how they contract and rebound during landing. Videos of real MiG-29s seem to have them more stiff, and the way they rebound in game is weird. I wouldn't expect them to be that far off the ground as in the top most video and still smoking. Or put another way, wheels should smoke when they are touching the ground. Seems they should maintain contact with the ground as they extend back. 

7 hours ago, Ironhand said:

Might be minor but still worth the report. Something is not right about the struts.

Agreed. It's a sim after all. Details matter, and landing is a fun part of flying.