XP 11 flight model [status]

[737NUT]

On 4/5/2018 at 10:11 AM, Morten said:

Also note that if you have XP's pitch control sensitivity setting set to a HIGH % (more non-linear), you will need to input MORE elevator to counter the pitch down tendency in ground effect!

Our recommended setting is 25%.

I have mine at 5%

[Andrey Novikov]

Litjan, in your video you start rotating significantly before 50 ft AGL, is it normal? Do you use joystick or yoke, btw? You definitely have to test Boeing with yoke.

Morten, I fly Zibo 738 in parallel and there is no such significant nose down effect. (IXEG, Zibo ans X-Plane are all the latest public versions).

 

[Morten]

3 hours ago, Andrey Novikov said:

Morten, I fly Zibo 738 in parallel and there is no such significant nose down effect. (IXEG, Zibo ans X-Plane are all the latest public versions).

Aircraft that do not have a nose down effect, are most likely still using the OLD flight model of X-Plane!  To know you need to have a look inside the airfoils and aircraft files. I suspect IXEG to be one of the few that are using the new flight model atm (which overall is much more realistic).  It does not matter if it's the "latest" version of XP or the aircraft, it is up to the designer to implement it or not!

ALSO, everyone needs to understand that how much nose down effect WILL VARY with aircraft type/geometry/wings

• High tail/low tail: An aircraft with a high T-tail (type MD80) will have less or no pitch down at all.
• High wing/low wing: An aircraft with a high wing low tail (type C172) will have a lot of pitch down
• A wing with a high L/D ratio or high incidence is likely to have more pitch down
• A long fuselage aircraft is likely to have less pitch down than a short of the same type (Type 737-800 vs 737-700)
• A low AR (long chord) aircraft is likely to have more pitch down than a low AR
• When the effect starts depends on span, so a B738 and a B733 decending at the same speed (700 fpm) will enter the effect at different altitudes, the B733 at a much lower altitude so it will "seem" a lot more dramatic to the pilot as you are closer to the ground.
• An aircraft with more swept wings will be likely to have more pitch down as the wing tip will create more lift as it enters and center of lift moves back
• An aircraft with winglets is likely to have less pitch down than one without.
• etc.

So Rob and Andrey, even a real B738 pilot cannot predict the nose down effect of a B733 unless he has actually flown it! So the one to listen to with regard to the IXEG 737 is Jan - as always

As you can see, comparing aircraft in ground effect is pointless, and this goes for the other types of ground effect as well.  This is what makes this area really-really complicated.  What you can be sure of though is that XP does this really well.

M

Edited April 7, 2018 by Morten

[Litjan]

1 hour ago, Andrey Novikov said:

Litjan, in your video you start rotating significantly before 50 ft AGL, is it normal? Do you use joystick or yoke, btw? You definitely have to test Boeing with yoke.

Morten, I fly Zibo 738 in parallel and there is no such significant nose down effect. (IXEG, Zibo ans X-Plane are all the latest public versions).

 

I go from about 3 degrees pitch to 6 degrees pitch. This is a change of 3 degrees. If you are coming down on a -3 degree glideslope and want to go to a 0 degree flightpath, this is the minimum amount of degrees that you need to change your pitch to enter level flight. Plus you need to another degree or two for a short time to "decelerate" your sinkrate. This is called the "break". It is not a "significant" rotation, it is the minimum needed on any aircraft to change the flightpath by the corresponding number of degrees.

Just like Morten said above: It could be that the Zibo is an .acf file that was never saved on the newer XP-version, so the new pitch-down does not take effect (Laminar has implemented an opt-in model, you need to resave your aircraft for the new aerodynamics to take effect). Otherwise I do not see how the zibo mod would not be affected.

Last but not least - if we had a chance to "deselect" this nose-down effect, we still could not do it - without it the plane would lift off by itself during the takeoff run. In fact we had an artificial "nose down" effect before XP11.10 to avoid the plane rotating early - its effect was limited to "on ground", only, though.

If you want to go and harass Austin to "soften" the effect, please be my guest - I would not mind a small reduction, but overall the effect is realistic and needed for the airplane to perform correctly during takeoff.

Jan

 

Edited April 7, 2018 by Litjan

[Morten]

.... and should you contact Austin, I recommend you first read up on this document as this is what he uses as a reference.

Ground effect downwash.pdf

[Hullu-poika]

On 02.04.2018 at 11:55 PM, Morten said:

. The pitching moment is a tad on the high side, but austin disagreed.

M

and

4 hours ago, Morten said:

 What you can be sure of though is that XP does this really well.

M

May be I do not understand it correct. But I see different meaning in these sentences.

[Morten]

No, as Jan just stated as a pilot, and I as an engineer, overall the effect is really good as we see it, but might need a *slight* adjustment.

 

[Hullu-poika]

Thanks for your answers!

[737NUT]

On 4/7/2018 at 5:21 AM, Morten said:

So Rob and Andrey, even a real B738 pilot cannot predict the nose down effect of a B733 unless he has actually flown it! So the one to listen to with regard to the IXEG 737 is Jan - as always

Morten,

Just for clarification, the pilot that flew my sim currently flies the exact aircraft as the ixeg 733   Jet2Go still has the classic series in use.    Also he gave the ixeg very high praise for authenticity other than the flare issue and made it clear to him that was an xplane issue and not the ixeg.  As we all know, x-plane is a moving target.  

 

Rob