ground effect

[kevinh 409]

Ok then when the Boeing 737 gets into ground effect it wants to float.There is no need to be rude. If I feel in that I disagree with a post that is my right to disagree with it. It is not up to you. When the Boeing 737 gets into ground effect if wants to float. And as for the PMDG, it is not modeled in the aircraft.cfg but that is not to say that is in another place.

You are both talking about the same thing. You about ground effect in general, Kyle about a specific dynamic effect PMDG modelled for the NGX. As the aircraft rotates it starts to generate lift, and being in ground effect means that lift is greater than it normally would be for that AOA. That might be described as a lurch upwards I suppose. and if the ground effect was too much it might need to be toned down, as Kyle described.

 

aircraft.cfg is not the place to look for ground effect modelling in FSX. Most of the aerodynamic model is in the .air file, including the ground effect function.

[SteveW 1,792]

...although the aircraft.cfg contains wing area geometry which are factors in the ground effect.

[kevinh 409]

...although the aircraft.cfg contains wing area geometry which are factors in the ground effect.

Wing area affects everything, not just ground effect.

[SteveW 1,792]

Wing area affects everything, not just ground effect.

 

Yep, let's hope no-one tries to argue against that kev.

[cmbaviator 5]

thanks for the explanation.

 

I also notice that after rotation, i had to release the stick, because the plane keeps pitching ups quickly, i guess that is due to the ground effect and seems to be realistic as on all the video i've watched, the PF quicly release the back pressure on the yoke after rotation.

 

I ahve an other question :

 

during the flare, if the pilot doesn't flare, ie maintains the pitch attitude that was at 50'RA so a vertical speed of -750 fts/min ( standard -3° slope app), will the ground effect make the plane pitch up and the Vertical Speed at Touch Down will be like -500 / - 400 instead of -700 ?

 

Camille MOUCHEL-BLAIST

France

[scandinavian13 5,192]

 

 

will the ground effect make the plane pitch up and the Vertical Speed at Touch Down will be like -500 / - 400 instead of -700 ?

 

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.

[kevinh 409]

Yep, let's hope no-one tries to argue against that kev.

Steve, it's not about arguing about things. It's about explaining things and not confusing the issue.

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.

If anything, ground effect will make the aircraft pitch nose down.

[SteveW 1,792]

I thought to point out the .cfg might play a part in the calculation of ground effect, would help lessen the confusion. :biggrin:

[PhantomTweak 3]

It sounds to my tired lil ol pea-brain as though we are all having a lively discussion (nice euphamism, no?)  all on the same side of the issue, just using different words.

I do, however, agree with Kyle that posting a disagreement or dislike of a post that is correct and accurate as to the facts can have a detrimental effect on subsequent reader's conceptions. I am trying to tread as delicately as possible on this issue so as to not offend...

Anyway, I just wanted to toss in my 2 cents worth. And you want a great example of how ground effect really works, get into a glider, and land on a long, hard-surface runway someplace. It will float along on that cushion of compressed air for an awful long way! When I was flying out of Calistoga, Ca., I was able to get a glider almost to it's parking space from the far end of the runway, just floating along in ground effect, then using the spoilers to set it down where I wanted. Saved me a LOT of pushing gliders around the airport, which was my job as a line-boy anyway Used to hit rocks that were out on the runway on occaision, they would fool me into starting to brake early and getting a lot harder touchdown than I wanted! Embarrassing

I know all this may seem like it's totally unrelated, but think about it, a 737, Piper Cub, Glider, or C-17 all obey the exact same laws of aerodynamics, so what one does can be related to how any of the others function.

Just my way of trying to explain ground effect in different way...

Pat☺

[SteveW 1,792]

Saved me a LOT of pushing gliders around

 

  :Big Grin:   Nice story and very amusing, cheers Pat.

[scandinavian13 5,192]

 

 

And you want a great example of how ground effect really works, get into a glider, and land on a long, hard-surface runway someplace. It will float along on that cushion of compressed air for an awful long way!

 

Thanks for sharing that.  Makes me want to go add some glider flights to the logbook!

 

 

 

I know all this may seem like it's totally unrelated, but think about it, a 737, Piper Cub, Glider, or C-17 all obey the exact same laws of aerodynamics, so what one does can be related to how any of the others function.

 

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.

[kevinh 409]

I thought to point out the .cfg might play a part in the calculation of ground effect, would help lessen the confusion. :biggrin:

Except that it doesn't. You're just adding to confusion by saying it's part of the ground effect simulation when it isn't. If you change wing area in aircraft.cfg you change lift (and all other aero forces and moments) in all flight regimes (including in ground effect). There is no way to only affect ground effect by using wing area.

[SteveW 1,792]

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:

[SteveW 1,792]

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:

[Matt2218 4]

You can fly the NGX pretty much by the book - the flare works just as described in the FCTM.  

 

I always seem to balloon and/or float a little bit...even when I cross the threshold at Vref.

 

I start my flare at the 10ft callout, pitch up a couple of degrees (result being generally less than 5 degrees total) and gradually close the throttle but it still seems to take awhile to get her down. Maybe I'm not doing it smoothly enough?

 

Does anyone have a ballpark estimate of how far the aircraft should travel from the start of the flare to touchdown?