teopereira

Too much ground effect?

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A question for real pilots: isn't the NGX "ground effect" exaggerated? The "landing technique" you use in the real world is the same you use for the NGX?

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In general, FSX has too much ground effect. The flare procedure for aircraft is a 2 to 3 degree pitch change. So a good approach aiming 1000ft down(captain bars), on speed/on glide path, with a flare starting at about 20ft AGL with a 2 to 3 degree pitch change, with throttles reaching idle by touch down will have your mains touch right near your 1000ft aimpoint. If you find that the NGX is floating past this point with the text book flare, then the ground effect is on the strong side. Shoot me a PM if you want more info. 

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The ground effect isn’t fixed in FSX. The airfile designer can increase or decrease it quite easily. I guess ground effect feels too much in FSX because too many sim designers leave it as default.

I have no experience flying a real 737NG but I’ve found using flare techniques described by RW 737 pilots in this forum gives good results. So it seems PMDG did a good job.

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It is perhaps in general a bit over the top in all ESP-based sims, along with some other notable issues, such as iffy ground friction etc. Decent add-ons can do a bit to alleviate that, but it is still an issue. Having said that, the 737 is famous for floating a bit and there is perhaps no better demonstration of that than the crash of Turkish Airlines Flight 1951 at Schiphol in 2009, where the 737-800 involved kept on flying, albeit at a quite fast descent rate, when well below 100 knots.

As I'm sure you are aware, a typical Vref speed for a 737 NG is around the 130 knot mark, maybe a little more depending on weight, winds etc. Flight 1951's stick shaker activated when it was doing just 83 knots and its Vref was set at 125 knots, so it didn't actually threaten to stall and drop out of the sky until it was a full 40 knots below Vref. The stall warning stick shaker prompted the crew to shove the throttles forward, and it was accelerating to around about 95 knots and recovering from its fast descent, but it ran out of room before the recovery was complete, struck the ground tail low and broke into three segments finishing up some way short of the actual runway.

Despite the damage, it is indicative of how much ground effect cushioned the impact in that although there were a number of fatalities (nine in total) and critical injuries (eleven of them serious) among the passengers, the overwhelming majority of people on board escaped with only very minor injuries and some with no injuries at all; this was an aeroplane which had 135 people on board so whilst not full and as heavy as it could have been, it certainly only had a few empty seats, so it was by no means lightly loaded. You'd tend to think a 737 would stop flying altogether at below 100 knots, but when right in ground effect, it clearly can float a long way if Flight 1951 is any indicator of the actual speed where the wings and ground effect will completely give up providing lift.

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From what I have heard from real NG drivers (I am not one) the NGX is a little floaty; for instance, in the sim you can get away with closing the thrust levers at about 50R, something which I am assured in the real world would likely loosen some fillings on arrival at the very least, if not bend the airframe! However, within the confines of a desktop sim it's probably pretty close overall.

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56 minutes ago, Chock said:

It is perhaps in general a bit over the top in all ESP-based sims, along with some other notable issues, such as iffy ground friction etc. Decent add-ons can do a bit to alleviate that, but it is still an issue. 

Since you can make ground effect zero if you wish, the addon developer can completely overcome the problem of too much float. What you can't do is get around the lack of pitch or drag effects in GE. In FSX/ESP GE only affects lift. However the trim change and drag reduction are less important than the lift change.

As for ground friction FSX/ESP has a screwed up table of friction values, but it's possible to update this with more reasonable numbers. Some addons do this (FSL A320 for example). PMDG and others try to compensate in other ways, but that's a compromise. Utilities such as frictionality are available to modify and improve the friction model and FSUIPC has a free fix for it too. But of course if an addon has adjustments to thrust and braking to overcome incorrect friction effects then using such modified values with it will cause problems.

In both cases it only remains an issue because some developers either assume nothing can be done, or choose to do nothing.

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