[REPORTED] Error in Ground Effect?

[oldcrusty]

I've noticed the opposite. When landing in an airfield, just below 30/20 ft, a second or so before touchdown, there is a sharp pull down that I try to resist with almost full back stick which seems to be completely ineffective. Feels like there's a magnet that pulls the nose down to the runway...

 

I probably played with power too much and missed it somehow... Anyways, you guys ID'd this issue (more or less)

[Svend_Dellepude]

Here is a track that shows the effect when crossing ridges at very low alt.

In another flight the pilot blacked out because of negative G's. Not in this one though.

Ground effect.trk

[Nealius]

Does this happen over the deck of the Stennis as well? I'm noticing that I can have a perfect ball all the way down to the deck, then all of a sudden the ball drops as I cross the deck despite me not changing any power settings and while remaining on-speed.

[SCU]

Does this happen over the deck of the Stennis as well? I'm noticing that I can have a perfect ball all the way down to the deck, then all of a sudden the ball drops as I cross the deck despite me not changing any power settings and while remaining on-speed.

There are two different things here: the VV dropping, and the nose dropping. What you are describing sounds more like the 'burble' effect, where disturbed air coming from the island's (tower) wake causes turbulence on your jet which in turn can drop you (the VV) below glideslope. I think the burble is semi modeled in DCS.

[SCU]

PS: Real life Hornet pilots have to take into account the effect of the burble.

[Nealius]

My nose does not drop, and the burble does not occur over the deck itself.

[Svend_Dellepude]

Try just flying over the carrierdeck at 10-20ft. If you get sucked down, then it's probably the same thing.

Have not tried at low speed and haven't noticed anything when landing on the carrier.

[Nealius]

I just reviewed a bunch of my carrier touch and go's to check. Every single time I will be on speed all the way down until the radar alt reads 10 feet, at which point my VV suddenly drops in the E-bracket and the AoA indexer flashes "fast."

 

In the attached pictures, 1 is on-speed. 2 is the moment where my VV suddenly falls. You can see from the controls screen that there was no pitch input from me to cause an AoA change.

 

I'm not sure if this is an error in ground effect over the carrier, or something else I may be doing wrong.

[Druid_]

@Nealius

 

Looking at both those pictures and comparing your VVI to the horizon/waterline I would say your VVI has risen and not fallen. Since ground effect reduces your Rate of Descent by producing a cushioning effect I would expect therefore your AoA to rise as shown in your 2nd picture. Your rate of descent in the 2nd pic has also fallen.

 

 

Admittedly there have been a few issues that required tweaking regarding ground effect and it is something we will continue to monitor. The high speed sucking effect at around 10ft is reported.

[SCU]

[..]

Admittedly there have been a few issues that required tweaking regarding ground effect and it is something we will continue to monitor. The high speed sucking effect at around 10ft is reported.

How about the slow speed effect? You know, the nose sucking effect right before touching down on an airfield?

[Druid_]

How about the slow speed effect? You know, the nose sucking effect right before touching down on an airfield?

 

I just tried 2 airfield landings, both times I tried to put the wheels on the very edge of the tarmac and both times it landed exactly where I expected it to. That said, I need to review the trk files in slo mo just to make sure what I saw in pit is represented outside.

 

That's always a good thing to do, save trk file and replay in slo mo.

 

If it was bad, I'd find doing this impossible to do :smilewink:

 

edit: further testing does seem to indicate something strange happening over carrier decks. Reported !

Edited July 8, 2018 by Druid_

[SCU]

I just tried 2 airfield landings, both times I tried to put the wheels on the very edge of the tarmac and both times it landed exactly where I expected it to. That said, I need to review the trk files in slo mo just to make sure what I saw in pit is represented outside.

 

That's always a good thing to do, save trk file and replay in slo mo.

 

If it was bad, I'd find doing this impossible to do :smilewink:

 

edit: further testing does seem to indicate something strange happening over carrier decks. Reported !

 

I haven't had the chance to fly for the last few days, but today I took the F-18 for a ride in the same mission I had the 'negative' ground effect behaviour, and it's just not there any more! It seems that it was fixed in the last update, and get this: I can actually aerobrake now, just like some (few) real Hornets do.

[Druid_]

I haven't had the chance to fly for the last few days, but today I took the F-18 for a ride in the same mission I had the 'negative' ground effect behaviour, and it's just not there any more! It seems that it was fixed in the last update, and get this: I can actually aerobrake now, just like some (few) real Hornets do.

 

:thumbup: although I think there is still a problem over the carrier deck.

[SCU]

Haven't tried carriers yet since last update unfortunately.. RL not giving me too many chances to sim at all currently, but I'll try to do some tests when I have time and report back here on any issues I believe are present.

[Weta43]

WRT to the Ground Effect:

 

If you set yourself up over the flat land outside the map on the Caucasus map - or over the ocean gear up, flaps up or down, establish about 8 to 10 degrees nose up then engage the attitude pitch AP and use the throttle to control your altitude. Establish a descent rate of somewhere around (-) 50 fpm (I tried successfully with sink rates up to 150 fpm then stopped testing).

 

At about 50 feet your descent rate will start to decrease as you meet the GE and somewhere between 10 and 20 feet the GE will stop the aircraft's descent and the plane will do a little damped phugoid, then just stably fly along at that height.

 

There may be a separate question regarding the amount of pitch down that accompanies the extra lift & how that interacts with the FCS gear down - but it is WIP Beta :).

[Thomas27]

Flying over the carrier is just a way to demonstrate it. Flying over terrain like peaks or hills causes the plane to nose down as well. Its not entirely consistent with Caucasus being spotty and PG being reliable at demonstrating the behavior and other possibly unknown variables.

[Weta43]

Flying over the carrier is just a way to demonstrate it.

 

Yes, but what IT is, is the question. :)

 

The contention is that:

It's like the ground effect is actually inverse of what it should be.

 

or that:

There's no increase in lift.

 

The test above shows that there is ground effect modelled, and that it does increase lift, and that it does work in the right direction (up :-)

 

What's left is that the nose tends to pitch down as that lift is applied (as it used to for flap extension), and that the pitch down is particularly noticeable:

 

1/ when the gear is down & the FCS is in PA mode.

2/ when the ground effect is modelled over the carrier.

 

(edit: The pitch down, and those last two things are entered as bugs)

Edited July 11, 2018 by Weta43

[FZG_Immel]

just tested it on the AC... I have it as well. Absolutely aweful

 

huge Pitch down moment as soon as I pass the deck

[JaBoG32_Dirty]

Hey there :-)

 

@Weta43: Thank you for being rational, precise and right to the point here. Shows a good (and much appreciated!) amount of professionalism when you said: "Yes, but what IT is, is the question" Thumbs up!

 

I’d like to add a point to the discussion that I don’t see considered in this thread so far:

 

Ground effect is NOT a „cushion of air“! That term is just an image/metapher given to novice pilots to describe what it feels like when entering ground effect.

 

Ground effect IS the reduction of induced drag / increase of lift coefficient close to the ground. Nothing more.

 

I find this distinction to be especially important in this case, because many of you observed this effect when flying close to the ground (or the carrier deck) at rather high speeds. Speeds at which induced drag is an almost negligible factor anyways.

 

Just so that we are all talking about the same thing here:

-Wing generates pressure difference —> Lift

-Air wants to equalize pressure and thus forms vortices around the wingtips

-Vortices are already forming ahead (upstream) of the wing (subsonic flow)

-Wing continuously flies in its own downwash —> Kinda like having to fly „uphill“ all the time

 

…when the aircraft is slow, these vortices have plenty of time to form ahead of the wing.

…when the aircraft is fast, these vortices have no time to form ahead of the wing and thus the wing will „feel“ the air coming at it at almost the same angle as the free air stream.

…when the aircraft is flying supersonic (M>1.5), there should be no more ground effect noticeable. The wing wouldn’t even „know“ that there is a ground present.

 

When the aircraft flies close to the ground, the ground presents an obstruction to the downwash of the wing - greatly reducing induced drag. At landing (slow/dirty/high alpha) that effect is easily noticeable and definitely present in DCS. At high speeds (fast/clean/low alpha) this effect is quasi negligible. In real life as in DCS.

 

While I DO notice this effect and highly encourage the developers to look into this,… I wouldn’t necessarily attribute it to ground effect, because I was only able to reproduce it in fast, clean, low alpha configurations.

 

My guess would be that this effect is neither a feature, nor a bug! I suspect that it is an artefact from some „quick and dirty“ fix they may have applied (I’m speculating here!) to correct something else a while ago. If I were on the team, I’d try to remember (or ask my co-workers) the last time I heard someone say: “We don’t need to fully model this…. Let’s just create this plausible illusion by…“ :-)

 

A broader „crowd-sourced-approach“ to this problem would be to check where else we can or cannot observe this effect:

- Is it present in other jets?

- Is it present in other props?

- Is it present in helos?

- Is it present in the AI flight model?

- Is it present in other maps?

- Is it present during night?

- Is it present over water/grass/treetops/buildings/in tunnels?

- Is it present when flying close over other aircraft?

- Is it present with collisions on/off?

- Is it present when flying inverted under a bridge?

- Is it present in knife edge flight along the side of a tall building?

- Is it present in arcade mode?

- Hell,… we could even check if this effect could be reproduced in LOMAC or Flanker 2.0 if someone still has these installed.

 

What I’m trying to say here: Let’s not only focus on ground effect, but let’s gather some data and maybe we can point the developers in the right direction. Doesn’t Wags occasionally mention how often he gets requests from people to be invited into the testers team? Well, THIS is a chance for us as community to be productive and learn something in the process.

 

Wether on the team or not.

 

Have fun!!!

 

Dirty

[BlueAngel]

I would say the data is just inverted. Remember the exaggerated negative angle of attack when deploying flaps on approach? Also looked like inverted data, as the expected result should be exactly the opposite. Maybe all it takes is turning negative numbers to positive or vice-versa.

[Thomas27]

Any news on this? Issue still persists with anything under the plane not just over the carrier.

Edited August 24, 2018 by Thomas27

[oldcrusty]

Any news on this? Issue still persists with anything under the plane not just over the carrier.

 

Yes, it does. The "event horizon" is still there.

[Eldur]

Just had this while doing an 82X run.... I even reacted to the massive pull down by applying full back stick, but that was not enough.

[Ala12Rv-watermanpc]

+1 on this...tried a extremely low pass over the runway and suddenly a strong downwards force appeared making me crash ...I applied full back stick and even that wasnt enough to scape from it.

[razo+r]

Flying close to the ground still ends up getting sucked into the mud.