Flap deployment and pitching moment... and gear drag...

[jcomm]

In the P51d Civil, as I deploy the first notch of flaps, and all of the subsequent settings, a pitching down moment is quite evident, at any speed, requiring a combined use of the pitch trim wheel to compensate.

This is, apparently, in agreement with some movies I am able to watch in youtube, of rw footage from p51 flights, but I wonder if it that's really the immediate reaction of the aircraft to the deployment, or if there should be an initial pitching up moment due to ballooning, although I can perfectly understand that both ballooning and the pitch down are possible at the same time...

The other question I have regards the drag from the landing gear. Sometimes I forget to raise it right after takeoff, and the aircraft refuses to accelerate past, say, 130-140 knot. As I remember to retract the gear, the gain in speed is notorious. Is gear drag really this big in the real thing ?

[Tug002]

Hey there Jcomm, as far as I know everything is made to reflect flying the actual aircraft. Hopefully DHenriquesA2A will see this post and shed some light on the subject for us as I know that he has flown actual P-51's and will know the answers for the questions that you ask.

Keep smiling
Tug

[jcomm]

Yes Tug,

that's what I really would like to get - Henrique's comments on his real experience with pitching moments at flap deployment, as well as the drag from landing gear ...

[DHenriques_]

In the P51d Civil, as I deploy the first notch of flaps, and all of the subsequent settings, a pitching down moment is quite evident, at any speed, requiring a combined use of the pitch trim wheel to compensate.

This is, apparently, in agreement with some movies I am able to watch in youtube, of rw footage from p51 flights, but I wonder if it that's really the immediate reaction of the aircraft to the deployment, or if there should be an initial pitching up moment due to ballooning, although I can perfectly understand that both ballooning and the pitch down are possible at the same time...

The other question I have regards the drag from the landing gear. Sometimes I forget to raise it right after takeoff, and the aircraft refuses to accelerate past, say, 130-140 knot. As I remember to retract the gear, the gain in speed is notorious. Is gear drag really this big in the real thing ?

Hi;

The 51 does have a tendency toward a nose down pitch when flaps are lowered. Same thing with the gear.
The gear does have a lot of drag. An added note is that the gear has a LOT of drag in transit up or down. On go-arounds many Mustang operators leave the gear down both for safety reasons (forgetting to lower it again) and to eliminate the extra drag from retraction as power is added for the go around. It's the fairing doors that cause all this trouble. They are like two barn doors hanging out there in the breeze.
Dudley Henriques

[Tug002]

Thank you very much for the response Dudley

Keep smiling
Tug

[DHenriques_]

Thank you very much for the response Dudley

Keep smiling
Tug

My pleasure.

[jcomm]

Thank you very much Dudley!

[L.A.]

My Van's RV6 (low wing) always pitched down with flap deployment. Never balloons up like a Cessna. In fact, one RV owner who had engine problems, picked out a landing site on a road, while he applied flaps to land. He then realized he was going to come in short, and raised the flaps. When he did, the nose pitched back up, and he lost sight of the road. Ended up tearing down some fence posts with the wing.

But then............my RV was painted like a P-51 Must had something to do with it...

[DHenriques_]

My Van's RV6 (low wing) always pitched down with flap deployment. Never balloons up like a Cessna. In fact, one RV owner who had engine problems, picked out a landing site on a road, while he applied flaps to land. He then realized he was going to come in short, and raised the flaps. When he did, the nose pitched back up, and he lost sight of the road. Ended up tearing down some fence posts with the wing.

But then............my RV was painted like a P-51 Must had something to do with it...

Center of pressure moving back on your airplane with flap deployment with the cg a constant creates a nose down pitch moment. Same on the Mustang.
On the Cessna you get a lot of downwash off the high wing onto the horizontal stabilizer that helps with a positive pitch moment.
A lot depends on the exact design of the plane of course. Some aircraft develop some "weird" moment arms with flap deployment due to where the cg is as relates to expendables moved or dropped in the case of military aircraft.
Dudley Henriques

[jcomm]

Dudley,

just one more question - out of your memory, can you recall if, although the aircraft ends up pitching down when flaps are deployed, during transit there could be an initial nose up tendency, or is the pitch down immediate with the flap deployment ?

Thx again !

[DHenriques_]

Dudley,

just one more question - out of your memory, can you recall if, although the aircraft ends up pitching down when flaps are deployed, during transit there could be an initial nose up tendency, or is the pitch down immediate with the flap deployment ?

Thx again !

It's fairly immediate. It happens as the physical changes occur on the wing.
DH

[jcomm]

Thx Dudley!

[L.A.]

Dudley,

just one more question - out of your memory, can you recall if, although the aircraft ends up pitching down when flaps are deployed, during transit there could be an initial nose up tendency, or is the pitch down immediate with the flap deployment ?

Thx again !

Is there a model, that might be wrong? My airplane felt as if the nose was connected to the flap lever. It just nosed down. At the same time, it's not as if the pitch down, requires some heavy trimming (or pulling back on the stick), so it won't dive. The upwards ballooning of a Cessna, and the need to push against the yoke, was always much more noticeable, than the pitch down, of a Piper Cherokee model, or my RV.

[DHenriques_]

Dudley,

just one more question - out of your memory, can you recall if, although the aircraft ends up pitching down when flaps are deployed, during transit there could be an initial nose up tendency, or is the pitch down immediate with the flap deployment ?

Thx again !

Is there a model, that might be wrong? My airplane felt as if the nose was connected to the flap lever. It just nosed down. At the same time, it's not as if the pitch down, requires some heavy trimming (or pulling back on the stick), so it won't dive. The upwards ballooning of a Cessna, and the need to push against the yoke, was always much more noticeable, than the pitch down, of a Piper Cherokee model, or my RV.

Not sure I understand the question? What model? Which model? Real airplane? Sim airplane? )
DH

[L.A.]

Dudley,

just one more question - out of your memory, can you recall if, although the aircraft ends up pitching down when flaps are deployed, during transit there could be an initial nose up tendency, or is the pitch down immediate with the flap deployment ?

Thx again !

Is there a model, that might be wrong? My airplane felt as if the nose was connected to the flap lever. It just nosed down. At the same time, it's not as if the pitch down, requires some heavy trimming (or pulling back on the stick), so it won't dive. The upwards ballooning of a Cessna, and the need to push against the yoke, was always much more noticeable, than the pitch down, of a Piper Cherokee model, or my RV.

Not sure I understand the question? What model? Which model? Real airplane? Sim airplane? )
DH

I was just wondering why jcomm was asking. Figured it's some sim model, or a question in a different forum, perhaps. Not too long ago, a question was raised about a Carenado Piper Warrior (could have been the Archer) on the X-Plane org. forum. A student pilot thought that the Piper should pitch up with flaps. My recollection was..............that it was almost neutral or pitch down. The Piper definitely didn't pitch up like a Cessna high wing. Never the less, my reply's over there are moderated, and in this case, the student pilot's opinion was the last one, as mine never got posted. Of course, the A2A Cherokee doesn't pitch up. Now that I got that off my chest, it has nothing to due with this thread....