Excessive ground effect on landing

[ArturWashton 3]

HI Bob and all,I´m a former ATP and my experience is on 737-700 (no wl) and I can tell that she's a floatty girl, and as in every aircraft it's a matter of a combo of tech-feel. Even in the same airplane, it behaves differently when light or heavy when landing, and of course the rule is Vref + 5 when crossing the threshold at 50 ft. What I've developped that I recall was when light go idle at the threshold, no flare till 10 feet or so; when heavy what I did was to idle just at 10 feet and a VERY little back pressure if none till touchdown. I personally tried landings with flaps 25 when heavy front wind and it works at least in real life.Is fs I applied this personal tech on the beloved TinMouse and it behaves quite real, now on the NGX I think it has to be retouched a bit since I also noticed that overfloating effect a bit. I agree with Paul Deemer in the tech he depicts above but as an old instructor told us once..."Landings are as brushing your teeth" a personal taste within the limits of a good tech.Have a good day my friends.Art Washton

[MrKen 3]

Maybe someone can answer this for me, why would headwind matter on approach? Who cares if we're going 20kts faster or slower relative to the ground? Compensating for gusty conditions I understand, but why add any of the steady head/tailwind?I'm not trying to be a smartass, it's a serious question.

[kevinh 409]

Maybe someone can answer this for me, why would headwind matter on approach? Who cares if we're going 20kts faster or slower relative to the ground? Compensating for gusty conditions I understand, but why add any of the steady head/tailwind?I'm not trying to be a smartass, it's a serious question.

In the real world, as you get close to the ground the wind will decrease due to the boundary layer close to the surface. It's like a mini windshear. So you need additional airspeed to compensate. Whether FSX reduces wind close to the ground I don't know, but it's something we always model in full flight simulators.Kevin Hall

[MrKen 3]

In the real world, as you get close to the ground the wind will decrease due to the boundary layer close to the surface. It's like a mini windshear. So you need additional airspeed to compensate. Whether FSX reduces wind close to the ground I don't know, but it's something we always model in full flight simulators.Kevin Hall

Thanks for the info. It didn't even occur to me to consider wind diminishing near the ground.

[ArturWashton 3]

That's a fact, wind dynamics generates a sort of turbulence when reaches the ground, as Ken says, a kind of mini ws, thence reducing momentum and speed, beside the density altitude and local temp that counts a lot, wing makes it's ground effect also. The other main reason is the posibility to go around and keep momentum in case you can't land for any reason. As I get it, all that arose when those early days of the golden age when a lot of accidents occured due to wind shear, if you were with less momentum when getting into it you hit the ground, till they learned how to trade speed for altitude or at least keep'er leveled and steady, there's in fact not too much room left for manouver in those cases, remember aviation has beed defined as hours of boreing by seconds of real terror... to be in the mood these days.Art Washton

[veldthui 0]

I had a session with a RW pilot on a proper simulator and when I went to land he told me to make sure that I flew it into the ground otherwise I would float down the runway. Ever since then that is what I do with the NGX and never float down the runway unless I forget to.

[Tabs 2,790]

I've been told the airfile line 400 isn't for aerodynamic ground effect, it's the effectiveness of the thrust while on the ground - lowering that value's going to make breakaway for taxiing require a lot more power, that's it. FSX doesn't actually simulate aerodynamic ground effect.Regardless, I did ask one of our test team pilots and he said what others have said here - it's very difficult to land the NG well, it does want to float.

[martin-w 3,234]

What I can't understand is why I personally haven't had any issues with floating. Perhaps some hidden variable at work.As for Paul's suggestion that VREF was 10 knots too high, I checked the manuals, and according to the charts, the computed VREF is spot on.I tend to think people flare too much, rather than the mere two degrees required. I use the HUD, which makes landing a piece of cake.Autothrust on or off Bob? Always off for the approach for me. Autothrust on, may not be automatically disingaging and throttling back soon enough.I wouldn't want to argue with Bob Scott though, most of us long time simmers will be well aware of Bob's experience, and contribution to our hobby.

[Spin737 102]

HI Bob and all,I personally tried landings with flaps 25 when heavy front wind and it works at least in real life. Have a good day my friends.Art Washton

I've never heard of a F25 landing that wasn't caused by some QRH. It's not even certified for a F25 landing. Huh.

[Bob Scott 7,719]

I've been told the airfile line 400 isn't for aerodynamic ground effect, it's the effectiveness of the thrust while on the ground - lowering that value's going to make breakaway for taxiing require a lot more power, that's it. FSX doesn't actually simulate aerodynamic ground effect.Regardless, I did ask one of our test team pilots and he said what others have said here - it's very difficult to land the NG well, it does want to float.

Not sure who's telling you that Ryan, but table 400 in FSX is the lift augmentation due to ground effect...one axis (the input) is height above ground expressed as a fraction of wingspan, the other axis (output) is a multiplier applied to the coefficient of lift. Experimentation with this table demonstrates that FSX does indeed simulate at least this aspect of ground effect, and indirectly there is also some impact to induced drag as the relative AOA (and consequently induced drag) for a given CL is lowered as the ground effect's impact to CL increases.I'm not trying to split hairs here, or argue that landing distance is 3800 ft when it should be 3600 ft. There are (so far) only two characteristics of the NGX that raise a red flag for me...one is the excessive amount of ground effect and resultant float, the other is a rash of brake malfunction episodes, which I seem to be able to avoid pre-SP1 by leaving the autobrake off through the whole flight.

[syn 0]

For me hf4 is generally giving a realistic feel. I'm getting a similar reaction with ngx and in the real plane. Not spot on but close enough (you know, no pitch down moment due to thrust reduction and all those things fsx doesn't simulate).Haven't tried the strong hw scenario though.

[opherben 0]

FSX doesn't actually simulate aerodynamic ground effect.

AIRCRAFT SIMULATION TECHNIQUES USED IN LOW-COST, COMMERCIAL SOFTWARE

Michael K. Zyskowski*

Microsoft Corporation

Redmond, WA

*AIAA Member, Aerospace and Software Design Engineer

AIAA Modeling and Simulation Technologies Conference and Exhibit

11-14 August 2003, Austin, Texas

AIAA 2003-5818Quoting from page 7:

Mach and Ground Effects

The effect of Mach number on the aircraft coefficients,

drag, power and stability and control are handled

through a similar table look-up interpolation routine to

the one used for high alpha/beta corrections:

(21)

Ground effect is handled the same way. However, we

utilize the ratio of height AGL to aircraft wing span to

simulate the additional lift experienced in ground effect.

[Bob Scott 7,719]

FWIW, I went into the .air file and scaled down the ground effect in table 400 by 40% (max of 15% lift augmentation) and it looks much more reasonable to me. It still floats, but no longer like a DG-808 competition sailplane.What I was looking for is something like in this video of a landing at TNCM:

http://www.youtube.com/watch?v=vBZ4yvrDc44

Or this one at RJNG:

Note the deck angle change in the flare is considerably more than 2 deg (more like 4-5), and the jet doesn't float for more than 500-1000 ft in the flare.

[martin-w 3,234]

IIRC Boeing do state 2 degrees for the flare, it's in the manual. After Hotfix 4, I see 2 degrees deck angle on the approach, and a two degree flare resulting in 4 degrees pitch or there abouts..The NG has an artificially high VREF to help avoid a tail strike, thus lower deck angle.With the short field package it has a lower VREF and higher deck angle.Referring to Youtube videos isn't very helpful, as you can't see the instrumentation and have no idea if the aircraft is fast or slow.

[as-lu 0]

StrangeMine (HF4) flares just fine. Flaps 30, 2 deg deck angle on app, Vref + 5, idle at 20-30 ft, adding about 2 deg (about 4 deg deck angle on touchdown). I tried up to 20 kts headwind, and with Vref + 10 same result: a flare somewhere between 600-800 ft.