Weird flare behaviour

[K4bel123]

I´m not sure if anybody else has noted/posted this but I think I´m experiencing a weird flare behaviour. I mean by this that when I flare to about 5° nose up, I feel how the nose pulls back down a bit. This always makes the landings a bit hard. Is this a noted bug or some aerodynamic behaviour I don´t know of?

[Hotdawg]

Is it after touchdown and are you using autobrakes?

[Nils]

It is normal for the nose to come back down after the initial pull up on flare. Part because the stabilizer comes into ground effect, part because speed is decaying.

 

[Morrigan]

Ergo - a mystical force called gravity. 

[Morten]

Actually, it's a bit more complicated than that

When the wing enters span-dominated groundeffect - at about 1 span altitude - or about 100 feet agl on the 737CL, several things start to happen.  One of them is that the downwash from the wings starts to hit the ground and it can no longer move downwards as at does in free air.  Also, the wing tip vortex has less room to rotate and will slow down so you will see a drag reduction. 

This creates a "nose-down" already long before the flare.  You will also see a speed increase because of this and the reduced drag.  Then, when you enter chord-dominated ground effect, at about one chord altitude (20' agl or so on the 737), you will get a lift increase.  The SUM of all this means that if you flare a tad early, you will "float" quite a bit.  As Nils says when you raise the nose in the flare, this again will increase drag so while trying to keep the nose up, speed will decrease rapidly and you'll sink pretty fast and have a "hard" landing eventually and nosegear slamming into the ground.

All this is modelled and our 737 and X-Plane and we have a "tuned" custom ground effect.

So it's all about the timing of the flare (or "break" as Jan calls it) AND timing of retard of the throttles. If you watch some of the "amateur" videos of the 737 up on youtube you'll see they tend to flare a bit early and float in most of them.  If you then watch Jan's "pro" landings in our videos, you'll see that they are much more "firm" and no float - for a reason!

So, there is nothing weird going on here, it's all aerodynamics that we in X-Plane are very fortunate to have and that IXEG has refined.  I could tell you about stuff like this the rest of the evening that e.g. FSX and other xp aircraft do not have modeled accurate, but I'll wait until the subjects arises

M

Edited April 30, 2016 by Morten

[cmbaviator]

@OP,

 

you need to flare à 5° pitch but then you need to hold that pitch by applying/keeping some back pressure until touchdown.

from the tip given by a B737Cl/NG pilot and my experience with the IXEG:

 

if at 30fts yourV/S is <-700fts/min, start slowly to flare,then at 20 feets, flare +2/+2.5° and maintain that pitch until touch down. At 10fts, reatrd slowly the throttle to idle.

 

If at 30 fts, your V/S is approx at -700fts, you just need to flare +2/+2.5° at 20fts and retard at 10 fts.

 

start to look @8:05, and watch the yoke input at 30 Fts until touch down.

[cmbaviator]

23 minutes ago, Morten said:

Actually, it's a bit more complicated than that

When the wing enters span-dominated groundeffect - at about 1 span altitude - or about 100 feet agl on the 737CL, several things start to happen.  One of them is that the downwash from the wings starts to hit the ground and it can no longer move downwards as at does in free air.  Also, the wing tip vortex has less room to rotate so you will see a drag reduction. 

This creates a "nose-down" already long before the flare.  You will also see a speed increase because of this and the reduced drag.  Then, when you enter chord-dominated ground effect, at about one chord altitude (20' agl or so on the 737), you will get a lift increase.  The SUM of all this means that if you flare a tad early, you will "float" quite a bit.  As Nils says when you raise the nose in the flare, this again will increase drag so while trying to keep the nose up, speed will decrease rapidly and you'll sink pretty fast and have a "hard" landing eventually and nosegear slamming into the ground.

All this is modelled and our 737 and X-Plane has a "tuned" custom ground effect.

So it's all about the timing of the flare (or "break" as Jan calls it) AND timing of retard of the throttles. If you watch some of the "amateur" videos of the 737 up on youtube you'll see they tend to flare a bit early and float in most of them.  If you then watch Jan's "pro" landings in our videos, you'll see that they are much more "firm" and no float - for a reason!

So, there is nothing weird going on here, it's all aerodynamics that we in X-Plane are very fortunate to have and that IXEG has refined.  I could tell you about stuff like this the rest of the evening that e.g. FSX and other xp aircraft do not have modeled accurate, but I'll wait until the subjects arises

M

 

Morten, does wind comes into account regarding ground effect.

 

the greater is the headwind component, the later i have to flare.

with no HD component i start to flare gently at 30fts but with a HD like 15kts, I have to start near 15-20Fts, otherwise i will float too much

[Morten]

1 minute ago, cmbaviator said:

Morten, does wind comes into account regarding ground effect. the greater is the headwind component, the later i have to flare.

No, not in theory, but the stronger wind, the higher your landingspeed will be (Vref+5+wind component) so it will float more if you flare to early.

Also if there is a crosswind it requires a slightly different technique since you come in with a crab or in a slip, but I'm sure there are more qualified people here than me explaining those techniques.

M

[K4bel123]

31 minutes ago, Morten said:

Actually, it's a bit more complicated than that

When the wing enters span-dominated groundeffect - at about 1 span altitude - or about 100 feet agl on the 737CL, several things start to happen.  One of them is that the downwash from the wings starts to hit the ground and it can no longer move downwards as at does in free air.  Also, the wing tip vortex has less room to rotate and will slow down so you will see a drag reduction. 

This creates a "nose-down" already long before the flare.  You will also see a speed increase because of this and the reduced drag.  Then, when you enter chord-dominated ground effect, at about one chord altitude (20' agl or so on the 737), you will get a lift increase.  The SUM of all this means that if you flare a tad early, you will "float" quite a bit.  As Nils says when you raise the nose in the flare, this again will increase drag so while trying to keep the nose up, speed will decrease rapidly and you'll sink pretty fast and have a "hard" landing eventually and nosegear slamming into the ground.

All this is modelled and our 737 and X-Plane and we have a "tuned" custom ground effect.

So it's all about the timing of the flare (or "break" as Jan calls it) AND timing of retard of the throttles. If you watch some of the "amateur" videos of the 737 up on youtube you'll see they tend to flare a bit early and float in most of them.  If you then watch Jan's "pro" landings in our videos, you'll see that they are much more "firm" and no float - for a reason!

So, there is nothing weird going on here, it's all aerodynamics that we in X-Plane are very fortunate to have and that IXEG has refined.  I could tell you about stuff like this the rest of the evening that e.g. FSX and other xp aircraft do not have modeled accurate, but I'll wait until the subjects arises

M

Well, I was almost certain that this wasn´t a bug but superior IXEG/X-Plane physics that I wasn´t quite familiar with (I´ve flown other XP payware aircraft before ). So thanks for taking your time and explaining this. Sounds very convincing and therefore - as soon as you know what to expect upon flaring - I think landing the IXEG 733 will be way easier .

But - because I see that you take these physics extremely serious - I really hope that we will be able to have these ground physics from v1.0.0 as an option in the future (I use a separate joystick as a tiller). The new physics seem to be less realistic - still way better than others in XP . It´s just that now upon landing you also slide a bit on the runway when applying rudder (you know what I mean?).

[Morten]

Sliding on the rwy is nomal in xwind, however, we had a problem with the ground spoilers not deploying on touchdown which makes xwind landings really hard, but it will get fixed soon!

M

[Tchou]

On 30 avril 2016 at 0:37 AM, K4bel123 said:

But - because I see that you take these physics extremely serious - I really hope that we will be able to have these ground physics from v1.0.0 as an option in the future (I use a separate joystick as a tiller). The new physics seem to be less realistic - still way better than others in XP . It´s just that now upon landing you also slide a bit on the runway when applying rudder (you know what I mean?).

I don't get what you mean, 

It Seems that you'd like the plane/sim to adapt to you whereas it should be to you to learn how to fly it, real pilots tell us that the real 737 does hover a lot if the flare is not done correctly, it's up to you to learn how to do it, not to the sim/developer to change the physics. 

If you try to lose weight, the correct way is to start adapting your food behavior and also to have a more fat burning activity,

not changing the Newton gravitational constant of the Earth…

[Litjan]

44 minutes ago, Tchou said:

If you try to lose weight, the correct way is to start adapting your food behavior and also to have a more fat burning activity,

I will try to keep that in mind, thanks!

Jan

 

[ayarov]

Reading about the art of t/d with the 737 might I suggest something:

It would be great if Jan could produce a couple of landings where he also records his joystick(throttle and stick/yoke) movements. that would be really awsome and might  help newbies and veterans get better at landing this beauty  

[Litjan]

1 hour ago, ayarov said:

Reading about the art of t/d with the 737 might I suggest something:

It would be great if Jan could produce a couple of landings where he also records his joystick(throttle and stick/yoke) movements. that would be really awsome and might  help newbies and veterans get better at landing this beauty  

What, and pass on my secret tricks??

[Tom Stian]

While Jan keeping his secrets.. 

Here is a great video from a 737-400. Pretty "rough" handling just before landing ^^

 

[mgeiss]

1 hour ago, ayarov said:

It would be great if Jan could produce a couple of landings where he also records his joystick(throttle and stick/yoke) movements. that would be really awsome and might  help newbies and veterans get better at landing this beauty  

Or I can do a video of a crappy landing, and you just do everything completely different.

[K4bel123]

4 hours ago, Tchou said:

I don't get what you mean, 

It Seems that you'd like the plane/sim to adapt to you whereas it should be to you to learn how to fly it, real pilots tell us that the real 737 does hover a lot if the flare is not done correctly, it's up to you to learn how to do it, not to the sim/developer to change the physics. 

If you try to lose weight, the correct way is to start adapting your food behavior and also to have a more fat burning activity,

not changing the Newton gravitational constant of the Earth…

Well you didn't get what I meant. I was talking about the ground handling of the IXEG 733 and not anymore about the flare. I absolutely believe that the physics of the flightmodel are spot on and really don't want them to be changed. It's just that IXEG featured a more direct ground handling in the release version and told us that this would be as realistic as possible. Then people were complaining and so they changed it a bit "to adapt it to the people whereas it should be to them to learn how to handle it on the ground" (in your words). And therefore I asked kindly to get the more realistic ground handling back. Do you understand now what I mean?

[Tchou]

@K4bel123

Yep, thanks for the clarification.

 

[aculver]

On 2016-05-02 at 1:24 PM, Tom Stian said:

While Jan keeping his secrets.. 

Here is a great video from a 737-400. Pretty "rough" handling just before landing ^^

 

On 2016-05-02 at 1:24 PM, Tom Stian said:

 

Very instructive. Thank you.