Flap deflection on speed and pitch...

[Yo-Yo]

You mixed PITCH DOWN tendency, that means that the new trim AoA with flaps is less than trim AoA w/o them, and flightpath changing. The fact is that CL with flaps can be even greater at the decreased AoA than the CL in clean condition at its AoA. Thus, the plane balloons even at lower AoA, and the flightpath angle changes overcomes AoA changes.

In both cases I presume stick fixed.

 

Trim of the P-51 was tuned using real test curves.

 

One can check this pitch tendency looking to the AoA of the level flight at the same stick position with and w/o flaps.

[Anatoli-Kagari9]

You mixed PITCH DOWN tendency, that means that the new trim AoA with flaps is less than trim AoA w/o them, and flightpath changing. The fact is that CL with flaps can be even greater at the decreased AoA than the CL in clean condition at its AoA. Thus, the plane balloons even at lower AoA, and the flightpath angle changes overcomes AoA changes.

In both cases I presume stick fixed.

 

Trim of the P-51 was tuned using real test curves.

 

One can check this pitch tendency looking to the AoA of the level flight at the same stick position with and w/o flaps.

 

Yo-Yo,

 

in the real p51d, from many sources, including Dudley Henriques, as you deploy flaps, say from a trimmed level flight situation, at any speed ( and associated AoA ), the aircraft pitches down, and I believe it immediately does so. That's what the pilot sees, the nose dropping... not rising... ( ask your sources if you still can... )

 

In the DCS P51d the nose, always, pitches up.... Yes, after a good while, but really a gooooood while depending on the start speed, the nose starts dropping.... but the stability is also playing it's role here, and depends on the power settings how fast this drop takes place, of course...

 

The math behind it, the physics model, can be doing superb calculations, but the end result does not agree with the real behavior, unless the sources are missing that transition phase, but even so, it is soooo prolonged in DCS 's p51d, that I doubt it is matching the real thing ?

Edited November 3, 2015 by jcomm

[Crumpp]

The math behind it, the physics model, can be doing superb calculations, but the end result does not agree with the real behavior, unless the sources are missing that transition phase, but even so, it is soooo prolonged in DCS 's p51d, that I doubt it is matching the real thing ?

 

It does agree with the real behavior.

[Anatoli-Kagari9]

It does agree with the real behavior.

 

I would be very glad if this proves to be the case - after all I have DCS, and the p51d in particular, in my highest rating among any similar sim...

 

Still trying to gather more info from RW p51d pilots.

 

Will update my "findings", hopefully confirming that indeed an initial pitch up is expected during the transition phase...

[Crumpp]

Anything I can do to help, just let me know, jcomm!

[Yo-Yo]

Yo-Yo,

 

in the real p51d, from many sources, including Dudley Henriques, as you deploy flaps, say from a trimmed level flight situation, at any speed ( and associated AoA ), the aircraft pitches down, and I believe it immediately does so. That's what the pilot sees, the nose dropping... not rising... ( ask your sources if you still can... )

 

In the DCS P51d the nose, always, pitches up.... Yes, after a good while, but really a gooooood while depending on the start speed, the nose starts dropping.... but the stability is also playing it's role here, and depends on the power settings how fast this drop takes place, of course...

 

The math behind it, the physics model, can be doing superb calculations, but the end result does not agree with the real behavior, unless the sources are missing that transition phase, but even so, it is soooo prolonged in DCS 's p51d, that I doubt it is matching the real thing ?

 

If you grab the trim curves for the Mustang (elevator deflection vs IAS) convert it to elevator deflection vs CL and repeat this math for the same curve for the landing configuration you will get the answer... NACA report gives all material for the work. :)

[Anatoli-Kagari9]

Yo-Yo,

 

understood, and I stand corrected ! Also my thanks you to Crumpp...

 

It's valid when deployment occurs within flap deployment speeds, which is after all the only case it should be used, unless under combat for the first two notches of flaps...

 

Will test again ASAP, but I think I now understand why I was sometimes getting a pitch up... :thumbup:

Edited November 3, 2015 by jcomm

[Crumpp]

You are most welcome. Anytime I can help, jcomm!

[Anatoli-Kagari9]

I did try starting from 150 KIAS. Trimmed for level flight, deploying the first and 2nd notches of flaps still creates a nose up tendency.

 

As further flap detents are used it the starts to pitch down, and will eventually settle in a descent, full flaps, around 145 KIAS.

[Crumpp]

deploying the first and 2nd notches of flaps still creates a nose up tendency.

 

Yo-Yo explained:

 

The fact is that CL with flaps can be even greater at the decreased AoA than the CL in clean condition at its AoA. Thus, the plane balloons even at lower AoA, and the flightpath angle changes overcomes AoA changes.

 

Understand the first few degrees of flaps represents ~75% of the flap design lift gains for only 25% of the flaps design drag losses.

 

That is why combat flaps are on only ~10 degrees or so.

[Anatoli-Kagari9]

Ok guys,

 

here's an important, for me at least, follow-up on this subject which pretty much confirms that indeed the DCS P51d is doing it just right !

 

I asked many sources, but would like to post the response from a pilot from "MustangsMustangs" who cared to answer:

 

"Hello Jose,

 

When deflecting the flaps, the initial response of the aircraft is to pitch up because of an increase in lift with shallow flap deflection. This turns into drag as the flap deflection increases and then the nose lowers.

 

Hope this helps."

 

It certainly did help a lot :-)

Edited November 6, 2015 by jcomm