X-Plane "Inverse" Ground Effect?

Flight Sims
#1

My recent experiences in the FlyJSim 737-200 have raised an issue and I’d like some help to verify before filing a bug report to the dev and potentially embarrassing myself or wasting his time. The issue is this: At about 100 feet before touchdown the nose lowers on its own and the sink rate increases. This also seemed to happen on @BeachAV8R’s posted video of his landing with the same company’s 727. Just to rule out my own input I set up an approach fully configured and trimmed for Ref + 5. With power stable the plane tracks nicely on glidepath at 800fpm. I did not touch the stick other than to poke it gently left or right to stay on track. At 100 AGL the sink rate increased and accelerated to a VS of about 1300 fpm at touchdown. I have read elsewhere that LR are making changes to ground effect. So this most likely is an LR issue and not specific to the 737-200. I don’t own anything else big so I was hoping someone could try the same experiment on a largish, but different plane than I am using. Thanks!

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#2

I’ll give it a whirl…be right back… :slight_smile:

#3

I think I read a while ago that due to the changes in ground effect, 3rd party devs had to change their models to adapt to X-Plane 11.10 or something like that.

Maybe FlyJSims has not done that, or LR has gone wild on the flight model code again.

EDIT: this was being said in connection to the Carenado Do228, and other Carenado models if you want to verify or look it up

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#4

Thanks!

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#5

This has existed since one of the early builds of xp11

#6

…and yes, I just tried a similar setup with the default 737-800 and I was showing a 700 FPM sink rate on short, stabilized final at a Vref of around 135 (not sure if that is a close Vref for the -800, but that felt right). As I got over the threshold, nosed pitched down a few degrees and sink shot up to 1,200’ FPM with no input from me.

#7

Also tried the same setup in the CRJ-200 and got the same behavior…around 75’ or so, nose wants to pitch down and vertical speed increases.

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#8

Good! Really appreciate the check. Hopefully the oracle will get his update out soon!

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#9

11.30 will see a major overhaul to a lot of things having to do with flight modelling. Could be this is adressed in this update…?

#10

So, is this the cause of the excessive amount of yoke pressure needed on landing that you mentioned previously? I’m guessing so.

#11

Also…does it counter the takeoff pitch input too… :thinking:

#12

I don’t believe so. I’m surprised this hasn’t been fixed. It’s been like a year.

#13

Inverse ground effect and broken ground handling are present in a lot of third party aircraft, especially Carenado/Alebeo/Thranda. Beginning about the Do228 release, they began to fix it, but aren’t in a big hurry. Of note are some of the aircraft designed and sold as XP11 aircraft like the the B1900D, which they continue to sell. The only fix is to open the .acf file in a text editor and add some authority to the horizontal stab’s trim function.

Strangely, most designed for XP10 a/c do not have this issue.

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