Gear Down, Pitch Up

[jaylw314]

Any flap should cause a pitch down moment when lowered due to increase lift.  The ones that don't (like most high-wing Cessna's) are only because the flaps direct airflow towards the horizontal stabilizer and have the opposite to expected effect.  A high-wing T-tail aircraft should behave conventionally.

[peevee]

7 hours ago, jaylw314 said:

 due to increase lift. 

due to change of angle of attack is how I'd put it. same thing, different words.

[peevee]

On 2/28/2017 at 6:20 PM, Hank said:

Yeah, you confused me, too . . . Now it all makes sense! 

I'm good at that. It's why I don't teach much. That and a burning disdain for most people

[Mooney in Oz]

My J also slightly pitches up then returns to normal with gear extension. If I apply the speed brakes in level flight, my J will pitch up to a greater extent than gear extension.

[Shadrach]

On 3/2/2017 at 8:55 AM, peevee said:

due to change of angle of attack is how I'd put it. same thing, different words.

Angle of attack does change.  But I think a more important factor in terms of the visual perception of pitch change is due to the effective wing chord change when the flaps are lowered. This effectively increases angle of incidence which is to say that for a given AOA, the nose will be lower with the flaps deployed.

[Shadrach]

13 minutes ago, peevee said:

The change in wing chord is what causes change in angle of attack as by definition angle of attack is the difference between the chord and the relative wind. I would not apply angle of incidence to this as that is generally considered a design feature. Sure it changes with the change in chord but...

AOA is as you've defined above, thanks for the definition. It's worth mentioning that the same AOA can be maintained with flaps up or flaps down, though other factors would necessarily change .

The AOI is angle of the wing chord (line drawn from leading edge to trailing edge) and the longitudinal axis of the fuselage.  It is certainly a design aspect when designing a plane, but when the wing chord is changed, the AOI necessarily changes even though its function of deploying flaps. You can't have it both ways (Though the FAA does on the PPL written test).

When the flaps are deployed the lead of the wing does not move (unless it's equipped with leading edge slats).

The trailing edge rotates down and depending on the type of flap, shifts aft increasing wing area.  So new trailing edge position equals new wing-chord, new wing-chord equals new AOI. In this case new AOI is greater.  This means the longitudinal axis of the fuselage will be more negative for a given AOA.

Additionally, when flaps are deployed the center of pressure moves aft. This is basically like moving the fulcrum on a balanced seesaw.  In this case the fulcrum is moved toward the tail causing the nose to drop.

[Andy95W]

14 hours ago, Mooney in Oz said:

My J also slightly pitches up then returns to normal with gear extension. If I apply the speed brakes in level flight, my J will pitch up to a greater extent than gear extension.

My C sometimes pitches up with gear extension.

I've noticed it only does it when I unintentionally pull the yoke when I swing the Johnson bar!

[jonhop]

On 3/1/2017 at 11:44 PM, Hyett6420 said:

Gear up = no attitude change

gear down = pitch up, then pitch down.  Only slightly as gear moves through its transit.

 

Flaps up = point nose at the moon

Flaps down = point nose at ground.

 

the gear one i never have to do any trim for.  The Flaps i have got used to raising the flaps while having my finger on the trim switch adding in nose down trim and the opposite for when i lower them.  

This is in a 1986 J

Andrew

+ 1 exactly...

[carusoam]

There are so many things going on at the time...

1) The aircraft is slowing to below 140kias (LB numbers) to operate the gear.

2) The aircraft is slowing more with the gear and doors out in the wind. All things being equal,  the airspeed continues to slow towards white zone for flap deployment.  (Another design feature)

3) the CG moves slightly forwards as the nose gear rotates forwards into the down position.

4) Center of lift moves backwards as the flaps are deployed.  Nicely described by Ross above.

5) with so many things going on at the same time, I don't recall any upward nose motion when the gear is lowered.

6) I immediately went to fly the MSFS simulator of the Bravo.  Set it to fly level at 140kias. Lowered the gear.  The nose immediately dropped and began a descent of about 500fpm.  Some oscillations occurred. And it settled on a descent of 300rpm...

7) one thing the MSFS doesn't get right... flaps down in real life readily pulls the nose down.  The flight sim, the nose oscillates up and down while finding equilibrium.  (The LB flap system is designed to operate at the same speed as the trim to balance the attitude changes.  Start them both at the same time)

8) continue to make observations while lowering the gear. Try to determine if there is something else going on at the same time.

 

PP ideas only, not a CFI...

Best regards,

-a-

Edited March 4, 2017 by carusoam

[cleatus99]

I'll add that yes when I lower the gear in my J the nose pitches up... if trimmed level in the pattern, no input it will climb a hundred feet or so till it slows down..