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cmbaviator

ground effect

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Hi all

 

I was wondering if PMDG has tweaked the ground effect of FSX, because it seems to be very realistic, during the flare, you just need to pitch up + 2° and maintained it and you'l get a nice kiss landing

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I was wondering if PMDG has tweaked the ground effect of FSX, because it seems to be very realistic, during the flare, you just need to pitch up + 2° and maintained it and you'l get a nice kiss landing

 

It's not really tweaking the ground effect of FSX.  It's just modeling the 737 to behave as it does in the real world.  There's also some kind of quirk on takeoff while still in ground effect, too.  That is modeled as well.

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

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There's also some kind of quirk on takeoff while still in ground effect, too.

 

Teach us, master!

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Teach us, master!

 

I guess what Kyle is referring to is the ground effect during takeoff, which I personaly only really notice with the NGX and maybe Q400 - rotate by raising the nose to about 5-7 degrees (do not exceed 7° with the 737-800 and -900 to prevent a tailstrike), gain some altitude, get out of the "ground-effect" and then continue to raise the nose to around 15° or higher, depending on the payload or departure procedure. (This is an airline SOP, which works for me) 

 

However, if you have decent and precise hardware controls you should get used to a constant and smooth pulling back on the joke/joystick which ensures a safe takeoff with any type. (-600 to -900)

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I'm actually referring to a quirk of the real aircraft, on departure, while still in ground effect.  PMDG actually made a few last minute changes just before the NGX release (or maybe the SP?) to include it based on feedback from the tech team.  I won't go into what it is because I don't have the slightest clue how to explain it, but it might still be around the forums if someone searches it.

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I'm actually referring to a quirk of the real aircraft, on departure, while still in ground effect.  PMDG actually made a few last minute changes just before the NGX release (or maybe the SP?) to include it based on feedback from the tech team.  I won't go into what it is because I don't have the slightest clue how to explain it, but it might still be around the forums if someone searches it.

If I remember correctly, it's the behavior where the plane "jumps" or lurch upward quickly for an instant during rotation. It was present in RTM and then slightly toned down in the SP, I think. 

 

As for the origin of the behavior itself, I'm not sure. The NG's engines are mounted low to the ground, so during rotation, when the engine's thrusts are pointed slightly toward the pavement, maybe this gives the plane an extra boost effect? 

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If I remember correctly, it's the behavior where the plane "jumps" or lurch upward quickly for an instant during rotation. It was present in RTM and then slightly toned down in the SP, I think. 

 

That's the one.

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Ground effect is when the airfoil of the wings drag is reduced because it flows away from the wing a long the ground. This intern makes the aircraft want to fly before it truly can. Also the plane will float in ground effect when landing as well. Also, it is only between the ground and ruffle the wing span length of the plane. The higher off the ground you go the faster the ground effect lift is diminished. Ground effect can be a great think especially when you have a muddy field. For example in a C172 you can perform a soft field take off by adding power and holding the yoke back to keep the nose from digging in the ground. At around 50 to 55kt the plane will want to lift of the ground due to ground effect. Once this accrues the plane is rotated off the ground and then level off just a few feet of the ground until airspeed has built up to Vx so that the plane can successfully climb out of any objects. If the plane is climbed out of the ground effect before sufficient airspeed and lift is created the plane will start to sink and could even stall. Many accidents have been caused because the pilot believes the plane is "ready" fly but in fact it is not.

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Ground effect is when the airfoil of the wings drag is reduced because it flows away from the wing a long the ground. This intern makes the aircraft want to fly before it truly can. Also the plane will float in ground effect when landing as well. Also, it is only between the ground and ruffle the wing span length of the plane. The higher off the ground you go the faster the ground effect lift is diminished. Ground effect can be a great think especially when you have a muddy field. For example in a C172 you can perform a soft field take off by adding power and holding the yoke back to keep the nose from digging in the ground. At around 50 to 55kt the plane will want to lift of the ground due to ground effect. Once this accrues the plane is rotated off the ground and then level off just a few feet of the ground until airspeed has built up to Vx so that the plane can successfully climb out of any objects. If the plane is climbed out of the ground effect before sufficient airspeed and lift is created the plane will start to sink and could even stall. Many accidents have been caused because the pilot believes the plane is "ready" fly but in fact it is not.

 

Thanks for the ground school lesson?

 

Not sure why you marked Preston's post with "disagree," as he was actually describing a realistic behavior of the 737, not the generic PPL definition of ground effect...

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Thanks for the ground school lesson?

 

Not sure why you marked Preston's post with "disagree," as he was actually describing a realistic behavior of the 737, not the generic PPL definition of ground effect...

Am sorry but lurking up is not ground effect and the original poster was asking about ground effect. This is not just a private pilot definition, but a general principle of the airfoils effect near ground. Yes I used a Cessna 172 as an example but could have used any plane. I just wanted the original poster to have some knowledge as to what ground effect is. Is that a crime?

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Am sorry but lurking up is not ground effect and the original poster was asking about ground effect. This is not just a private pilot definition, but a general principle of the airfoils effect near ground. Yes I used a Cessna 172 as an example but could have used any plane. I just wanted the original poster to have some knowledge as to what ground effect is. Is that a crime?

 

It's certainly not a crime, but if you took the time to read the thread progression, his description would make more sense.

 

The OP asked if PMDG had tweaked the ground effect of FSX to make it seem more realistic (as such, one could assume that the OP knows full well what ground effect is).  I then stated that, not only is the aircraft specially coded to augment FSX's flight model to make it more realistic, it exhibits a unique quirk while still in ground effect.  Preston then hypothesized why the aircraft might lurch (again, realistic behavior) ahead while still in ground effect.  It's not a misunderstanding at all, despite how it might have seemed without first reading the preceding posts.

 

We all know what ground effect is.  The question was "was it tweaked from FS defaults to make it better," which then became a general discussion of ground effect quirks of the 737.

 

What I meant by the "private pilot definition" wasn't that it suddenly changes when you get your IR, Comm, Multi, or ATP.  I was simply making the point that the discussion is a little higher than the elementary ground effect discussion you'd otherwise get in PPL ground.  My point was that we weren't discussing the generic definition of ground effect, as we were discussing a specific aircraft's behavior while in ground effect.  Moreover, to come in and mark a post with disagree just didn't sit well with me, because the post is quite literally explaining a realistic behavior of said specific aircraft while in ground effect.  It's one thing to come into a thread and add knowledge or correct something that's wrong, but if you're going to do it, it's best to ensure it's necessary, and that you're correct.

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Ok then when the Boeing 737 gets into ground effect it wants to float.

It's certainly not a crime, but if you took the time to read the thread progression, his description would make more sense.

 

The OP asked if PMDG had tweaked the ground effect of FSX to make it seem more realistic (as such, one could assume that the OP knows full well what ground effect is). I then stated that, not only is the aircraft specially coded to augment FSX's flight model to make it more realistic, it exhibits a unique quirk while still in ground effect. Preston then hypothesized why the aircraft might lurch (again, realistic behavior) ahead while still in ground effect. It's not a misunderstanding at all, despite how it might have seemed without first reading the preceding posts.

 

We all know what ground effect is. The question was "was it tweaked from FS defaults to make it better," which then became a general discussion of ground effect quirks of the 737.

 

What I meant by the "private pilot definition" wasn't that it suddenly changes when you get your IR, Comm, Multi, or ATP. I was simply making the point that the discussion is a little higher than the elementary ground effect discussion you'd otherwise get in PPL ground. My point was that we weren't discussing the generic definition of ground effect, as we were discussing a specific aircraft's behavior while in ground effect. Moreover, to come in and mark a post with disagree just didn't sit well with me, because the post is quite literally explaining a realistic behavior of said specific aircraft while in ground effect. It's one thing to come into a thread and add knowledge or correct something that's wrong, but if you're going to do it, it's best to ensure it's necessary, and that you're correct.

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.

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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.

 

I wasn't aware that I was being rude at all.  I was simply explaining what was going on in the thread.

 

You are correct.  It is absolutely your right to disagree with the post, but it's also my right to disagree with the notion that the sky is blue, and instead believe it is neon green.  That doesn't mean I'm right.  Similarly, you disagreed with a post that was factual.  It's certainly your right to disagree, but your disagreement with it isn't in line with the facts of the situation.  Those aren't up to me, either.  I don't dictate how air behaves, or how aircraft behave in it, or what opinions you're allowed to have.  Like I said, I'm not telling you not to have an opinion.  I'm simply telling you that your disagreement with the above post isn't in line with the facts.

 

It's also correct that this isn't modeled in the aircraft.cfg.  Most payware aircraft that behave realistically don't rely on the aircraft.cfg alone to modify flight dynamics.

 

 

 

You seem to be a smart guy.  You also seem to have a passion for the details of the industry/hobby.  I can tell that from the post you made earlier about ground effect.  Based on your posts, though, it might be worth doing a little observing before going diving into posting.  Wanting to share knowledge is great, and I don't want to stifle that.  As someone who shares the same passion of sharing information, I totally get it, and I absolutely encourage it, but at the same time, the information should be relevant to the discussion at hand, and it should be correct.  I know that sounds harsh, but when people don't fact check and throw around information, it just propagates bad information.  As an example, there's a huge misconception about the 250/10,000 rule because people heard an oversimplification of the rule, and kept repeating it.  While none of the information you've posted is false (it's actually rather accurate), you marked a post that contains correct information with "disagree," which could undermine someone's perception of those facts when they read this later.  Your right to an opinion is not something I want to take away.  I'm just trying to point out that your opinion - whether it's right or wrong - has an effect on other people.

 

I could write a 100% factual post about how wings create lift, but if three or four people marked it with "disagree," people might ignore the post and dismiss it as non-factual simply because people chose to exercise their right to their opinion that they disagree.  Those people who ignored it because others incorrectly disagreed with the post might now have an improper idea of how wings work.

 

If I came across as harsh, I apologize.  It's absolutely not my intention to be mean or rude.

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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.

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

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

Wing area affects everything, not just ground effect.

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Wing area affects everything, not just ground effect.

 

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

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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

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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.

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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.

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

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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 :D 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☺

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Saved me a LOT of pushing gliders around

 

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

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