Ground Effect and the 777
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Ground Effect and the 777
Has anyone done any detailed study of or have knowledge of the impact of ground effect on the last say 100 ft AGL downwards on the B777 and B744. Just trying to filter out the impact of ground effect from pilot induced changes in that last 100 ft using our FOQA data.I know there's some logic built into the control laws on the 777 FBW system to give a pitch down at 30 ft so as to prompt a positive flare but other than that there's not a lot of detailed info around on what will happen as a stabilized in trim heavy approaches the ground.
Thanks
Thanks
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Not a problem really....simply that it looks like on normal (say <1.4 G landings) below about 50ft RA there's a gradual pitch up leading into the flare which seems on average (777-300) to lead into a defined 2 degree flare starting at 30 ftRA or so. I was wondering what role ground effect has in that. It's not a problem so much as a query. The Boeing FCTM says to flare at 20 ft wheel height which (depending on actual pitch etc) is only about 15 ft RA and yet it seems that FOQA shows that most pilots are beginning a gradual flare sometime well before that. Personally I'm looking well outside then and until this airline had never spent much time wondering about it all.
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019360,
Regarding flare heights, pitch rates and techniques; have you compared manual landings with George's technique during an autoland? Without looking at FOQA, the autopilot appears to start it's flare later than most pilots (ie. closer to the ground) and yet it does consistently good landings.
Regarding flare heights, pitch rates and techniques; have you compared manual landings with George's technique during an autoland? Without looking at FOQA, the autopilot appears to start it's flare later than most pilots (ie. closer to the ground) and yet it does consistently good landings.
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Yes, the A/P does flare noticeably later. It seems that the average autoland drifts a shade above the G/S below 70 ft. This is followed by a slight reduction in pitch immdeiately prior to the beginning of the flare. This is what made me wonder about the impact of ground effect. I presume the A/P would be trying to not be affected by ground effect until it was ready to flare, hence the effort to remain on G/S until the inertial reference takes over and the flare begins. Interesting.
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The 742 and 744 start flare as early as 50' if done on AP or by the FHB, but technique from 8 years flying them says starting the flare in the 744 at 30' or so gives a much better landing. The 742 lands well with the "gradual" flare starting at closer to 50'.
I suspect ground effect and wing differences play a lot into it.
I suspect ground effect and wing differences play a lot into it.
The only problem with the 777 is the flunky in the R.H.S. being afraid of the ground and flaring about 10 feet too early, with the resulting float and hard landing, generally exaccerbated by the continuing pitch inputs the longer the flare continues. My gentle elevator forward push usually puts it on the RWY within the prescribed touch down zone and the guy in the R.H.S. generally is not aware of it. Will they ever learn how to fly?
P.S.: Have 777 pilots noticed that during autolands the flare point seems a lot later than what we "mere mortals" would normally dare! Could any Boeing engineers comment on the reason(s) for this. The actual flare rate during autolands is very abrupt compared to "mere mortal" landings. Most autolands that I have observed seem to result in reasonable landings however.
As mentioned above, the slight push forward at about ten feet works on all 777 models in most instances. However it is a must on the 300ER with the longer wing.
Watching collegues use the regular flare technique on the ER isn't pretty.
halas
Watching collegues use the regular flare technique on the ER isn't pretty.
halas
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Hi, the 74 classic and the 744 both have pronounced ground effect below 50 feet. In the 744 it is much more obvious such that a more gentle pilot input is required during the flare when compared to the 74 classic. This effect can be experienced from 100 ft on the 744. There are no funny electronic inputs in either aircraft with the possible exception of the fail passive (two autopilots only) autoland system when a slight nose up trim input is sent during the flare to cater for the possible loss of the penultimate autopilot. This feature is not evident on a fail active (three autopilot) autoland. Can't speak for the 777.
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BTW, if that "slight nose-up trim input" in the 742 is sent early (say, starting at 200' or so) and goes all the way to 12 deg nose up, expect the airplane to NOT flare at all, even if "Flare Armed" is green! Been there; done that -- just this morning! The trim does keep the nose from falling through, though... 
