ground effect

[serviceceiling 135]

Well, a lot depends on the wind and your speed - just read the "landing" chapter in the FCTM. The procedure that has always worked for me goes as follows: Pass the treshold at 50ft and vref, close the throtle somewhere between the 30 and 20 callout and initiate the flare at about 20 feet, very gently. Pitch up about 2 degrees - not more otherwise you will float. After all you have to develop a feel for the aircraft and a lot also depends on the precision of your hardware controls. The NG somewhat likes to be flown onto the runway untill around 20-10 feet. The flare itself is very minor in most cases. 

[WingsofMontana 0]

 

 

They do, but they behave differently according to those laws.  As an example, a high wing aircraft behaves differently from a low wing aircraft in ground effect.  Comparing to similar aircraft - a Cessna 172 and a Piper 180 - you'll find that they behave rather differently, given otherwise very similar characteristics (pertaining to ground effect).  Both have very similarly-sized and shaped wings (not exact, but similar enough), and ground effect is generally seen somewhere near the wingspan of the aircraft.  So, despite beginning to feel the effects at about the same time (similar wingspans), and having similarly shaped wings, the Cessna is less affected because the wing stays higher in the descent to the runway.
 
Additionally, there are other factors that can affect how the aircraft behaves while still in ground effect.  While engines don't play a role in ground effect characteristics, their placement, thrust output, and so on can all have exaggerated effects on aircraft performance while it is still in ground effect.

Yes and also the planes have different descents in ground effect. Low wings will have a very shallow flight while the high wings are steeper. Also the weight of the plane greatly effects its characteristics while in ground effect. For example in a PA28-235 will flare better when it has passengers in the back then when it is just a pilot.

[Matt2218 4]

Well, a lot depends on the wind and your speed - just read the "landing" chapter in the FCTM. The procedure that has always worked for me goes as follows: Pass the treshold at 50ft and vref, close the throtle somewhere between the 30 and 20 callout and initiate the flare at about 20 feet, very gently. Pitch up about 2 degrees - not more otherwise you will float. After all you have to develop a feel for the aircraft and a lot also depends on the precision of your hardware controls. The NG somewhat likes to be flown onto the runway untill around 20-10 feet. The flare itself is very minor in most cases.

Thanks Bogdan...I did read the FCTM...or more accurately MISread it. I've been flaring a little too late and too aggressively.

 

It also said that the flare should last 4-8 seconds, which is what I've been getting on my non-balloon flares. Feels like an eternity!

[kevinh 409]

So you are saying the values in the .cfg are related or are they not related in some way to calculation of ground affect?  :blink:

What I'm saying is that if you wish to increase or decrease ground effect in FSX, changing wing area is not much use. It changes lift/drag/sideforce and pitch/roll/yawing moments overall. That includes ground effect of course, but you can't increase or decrease ground effect independently in FSX using wing area. If you increase wing area you increase all the aerodynamic forces and moments in direct proportion.

 

The only place you can independently modify ground effect in FSX is table 400 in the air file. So yes, I am saying there is no parameter in aircraft.cfg which independently affects ground effect. It is true that an aircraft of the same mass but with a larger wing area (and so a lower wing loading) will usually have an increased ground effect. But you can't simulate that in FSX simply by increasing wing area. FSX doesn't "know" that wing area affects ground effect. You would have to modify table 400 to do that. Table 400 defines how C_L due to ground effect changes with relative proximity to ground and what the maximum percentage increase in C_L is.

 

The .cfg contains values for aircraft geometry, the.air file includes lookup tables, one with a dozen or so values for ground proximity - doesn't mean that ground effect is worked out there. However these are values the calculation uses with airspeed and aircraft geometry to work on ground effects. I thought maybe what you were saying Kev, is to exclude the usefulness of the .cfg and the aircraft geometry in those calculations. :smile:

That table is the only source of ground effects data in FSX. It defines the increase in lift coefficient due to ground proximity. If all the values were 1.0 then there would be no ground effect, no matter what you did with wing area. If the value is 1.1 that means ground effect is increasing lift by 10%. Wing area is of course part of the computation of lift from lift coefficient, but changing wing area does not change ground effect in FSX.

 

I'm certainly not excluding the usefulness of aircraft.cfg and I don't see where you can have got the impression that I was. Aircraft.cfg contains important aircraft parameters and tuning scalars. It defines ground contact points. It also controls drag and lift effects of flaps, so of course it's very important. All I said was it has nothing in it which simulates or controls ground effect.

[JoeDiamond 67]

It wouldn't make the plane pitch up, but it would shallow the descent (there's a difference between pitch angle and flight path angle - you can hold your nose on zero degrees and still get a descent simply by reducing power).  Since the descent is shallowed by the ground effect, you would touch down with a lesser vertical speed, in theory.

 

In theory.  In reality if you don't flare the plane is going to burn through the last 30 feet so fast you won't even notice any ground effect.  The 30-20-10 RA calls merge into one long call followed by what would best be described as an "arrival".

 

At least that's what I have heard anyway, I wouldn't know from personal experience. 

 

I've never noticed the jumping off the ground behavior during rotation.  I'll watch for it next trip but it's been my experience that the plane comes off the ground smoothly.  I only fly the -800, perhaps the shorter models handle differently.

[serviceceiling 135]

Thanks Bogdan...I did read the FCTM...or more accurately MISread it. I've been flaring a little too late and too aggressively.

 

It also said that the flare should last 4-8 seconds, which is what I've been getting on my non-balloon flares. Feels like an eternity!

 

I'm glad you learned something! Your flare also depends on various factors such as weather, wind, runway-lenght, contamination etc. You'll get it down after some time flying the NGX only. I remember my first landing with the Q400 after having flown the NG almost exclusively for about a year...crash-8 describes it quite well, haha. 

[Matt2218 4]

I'm glad you learned something! Your flare also depends on various factors such as weather, wind, runway-lenght, contamination etc. You'll get it down after some time flying the NGX only. I remember my first landing with the Q400 after having flown the NG almost exclusively for about a year...crash-8 describes it quite well, haha.

I can definitely see why there have been so many runway overruns In the 737!

[SteveW 1,792]

Another thing (was it mentioned?), is that we're most often landing into the wind, and I've been caught in gusting winds causing quite a bit of extra lift.

[syn 0]

Well, I have to say it is still too floaty compared to the real thing. Definitely the SP improved it a lot compared to the first release version, but whenever I try to land the NGX I notice that too much ground effect kicks in just in the last couple of feet compared to the real -800. -900 is even less floaty and more thrust dependent than -800 but I haven't tried the -900 in sim.

 

About the rotation effect that somebody mentioned in the post, I think he refers to the "deadband" that you have when rotating through 8-9 degrees due to aerodynamic interaction with the tailplane. It is a little bit difficult to explain, but the aircraft will want to stop the rotation at around that attitude if you don't anticipate it. Personally I haven't noticed this effect in FSX, but maybe it is just my old crappy logitech joystick. 

 

There is another handling characteristic very typical of the 737 that is the thrust-pitch coupling. Changes in thrust require a pitch input or trim due to the momentum generated by the underwing mounted engines. This doesn't happen in FBW aircraft as it is automatically compensated, or on rear-mounted engines, but I really miss it in the NGX. We will see it in the P3D version maybe? 

 

And yes SteveW, a gust can definitely mess up your whole landing, but then you just blame the FO  :wink: 

[dave_paige 11]

syn;

 

Do you fly the real thing, in real life?

 

Dave