PA28 Flaps/Pitch

[engineno9]

Hi folks,

Out of curiosity, I just wanted to canvass the experience of you guys who may have flown PA28's more than me in the past regarding the pitch changes when adding flap on approach.

On all aircraft I've flown, including the 4 or 5 PA28's in my logbook, there's a discernible tendency for the plane to try and pitch nose-up as you apply each notch of flaps, which you generally learn to counteract with some forward pressure on the yoke (and some nose down trim) to keep it going in the right direction. This is in keeping with my expectations based on the theory I've learned.

However, I flew one last night for the first time where each click of the flaps lever actually caused the nose to drop, and in fact required a bit of back pressure/trim to correct - I found it a bit odd.

Any ideas why this might be the case and why this might differ between one aircraft and the next? This was one of the older PA28s with the shorter wing.

[3wheels]

Were you flying slower than normal when you lowered the flap?


My PA 28 161 would require forward trim if you were flying at normal speeds, say 90- 100.
If however you allowed the speed to automatically drop, after lowering flap, to about 70, and held the load while this happened, then re-trimming was not required.

[engineno9]

No not at all, I would've been at around 90/85/80 kts respectively for each stage of flap, it was a fairly instantaneous drop of the nose. Actually a bit like you'd get as you retract flaps on climbout after a short field take off. All very strange!

[piperboy84]

No not at all, I would've been at around 90/85/80 kts

Seems awful fast for a warrior fixing to land, I owned a PA 28-151 many years ago, if I recall correctly my speeds in the pattern were at least 15kts slower than that

[3wheels]

On all aircraft I've flown, including the 4 or 5 PA28's in my logbook, there's a discernible tendency for the plane to try and pitch nose-up as you apply each notch of flaps

My recollection is that the nose up pitch change is only on the first two notches. Full flap lowers the nose.

[engineno9]

Originally Posted by piperboy84

Seems awful fast for a warrior fixing to land, I owned a PA 28-151 many years ago, if I recall correctly my speeds in the pattern were at least 15kts slower than that

I was more making the point that I wasn't going particularly slow - these wouldn't be exact.

At the risk of diverting my own thread I'd generally shoot for around 85/80/75>70 on downwind, base and final. So extending the flaps at speeds probably a bit higher than that (as estimated in my other post) and allowing drag to take effect before adjusting power.

[BEagle]

The Cherokee exhibits a nose-down trim change when flap is extended, whereas the Warrior exhibits a nose-up trim change.

The difference should have been covered during your variant familiarisation, which is now a mandatory requirement under the Aircrew Regulation.

[Genghis the Engineer]

What model PA28 are you flying final at 70kts?, or is that mph?

G

[ChickenHouse]

What kind of PA28? Know your plane and make yourself acquainted with the particular aircraft before take-off ... Is it in the POH and did you really read that carefully before? While quite some usual trainer-like aircraft have a tendency to balloon and stick nose up on setting flaps, the opposite is not less uncommon.

The biggest rodeo ride in a small SEP may be a typical Mooney, which will really dramatically lower the nose on setting flaps. On the opposite, when getting flaps in from take-off setting a Mooney will shoot straight up like holy toledo.

[TheOddOne]

We have 2 PA28s in the hangar, both with 180hp O360. One is a 1974 Archer, which exhibits nose-up pitch when flaps are lowered, the other is a slightly older Cherokee 1970 vintage, which pitches nose-down. Both appear have the older plank wing, so the difference must be quite subtle.

Know thine aeroplane...

TOO

[Haraka]

The Cherokee exhibits a nose-down trim change when flap is extendedThanks for that Beags. Certainly my memory on flying "140's" at O.A.T.S, in '68 (and subsequently on being re-acquanted with one of the very same ex O.A.T.S stable at Swanton Morley in '83).
All a prelude to flying Wallis Autogiros.

[A and C]

Too fast !

Don't lower the flaps untill 70kts, then the pitch change and re-trimming will be minimal.

[eckhard]

I think that the answer may be to do with the different span of the stabilator.

As I recall, the original PA-28s had quite a short span stabilator. This was increased on later models. The down wash from the flaps acting on the larger stabilator results in a net pitch up moment.

On the earlier, shorter stabilator, the pitch up effect of the down wash is overcome by the rearwards movement of the centre of pressure and the lowering of the drag line.

[9 lives]

The biggest rodeo ride in a small SEP may be a typical Mooney, which will really dramatically lower the nose on setting flaps. On the opposite, when getting flaps in from take-off setting a Mooney will shoot straight up like holy toledo.

Well, maybe not straight up.....

Let's remind ourselves that the certification requirements for which the Cherokee series, and all Mooneys would have been found to be compliant would read:

(b) During each of the controllability demonstrations outlined below it shall not require a change in the trim control or the exertion of more control force than can be readily applied with one hand for a short period. Each maneuver shall be performed with the landing gear extended.

(1) With power off, flaps retracted, and the airplane trimmed as prescribed in paragraph (a)(2) of this section, the flaps shall be extended as rapidly as possible while maintaining the air speed at approximately 40 percent above the instantaneous value of the stalling speed.

(2) Same as subparagraph (1) of this paragraph, except the flaps shall be initially extended and the airplane trimmed as prescribed in paragraph (a)(2) of this section, then the flaps shall be retracted as rapidly as possible.

(3) Same as subparagraph (2) of this paragraph, except maximum continuous power shall be used.

(4) With power off, the flaps retracted, and the airplane trimmed as prescribed in paragraph (a)(2) of this section, take-off power shall be applied quickly while the same air speed is maintained.

(5) Same as subparagraph (4) of this paragraph, except with the flaps extended.

(6) With power off, flaps extended, and the airplane trimmed as prescribed in paragraph (a)(2) of this section, air speeds within the range of 1.1 Vs1 to 1.7 Vs1 or Vf whichever is the lesser, shall be obtained and maintained.

(c) It shall be possible without the use of exceptional piloting skill to maintain essentially level flight when flap retraction from any position is initiated during steady horizontal flight at 1.1 Vs1 with simultaneous application of not more than maximum continuous power.

So there can be pitch force changes, but none such that an attentive pilot would have difficulty controlling.

the opposite is not less uncommon

Which is something like: "it's getting less worse more slowly."

[tmmorris]

It may just be our (A and C's) PA28, but Piper seem to have set it up so that it naturally settles without retrimming from cruise:

No flaps, 110kts
One stage: 90kts
Two stages: 75kts

I've always assumed this was a design feature.

After that the third stage is mostly drag so you do have to be more careful of speed.

[Flyingmac]

I've never extended flaps in a PA28 when downwind, and I've never used 1st stage for anything except take-off. I'm genuinely interested to know why it's done.

[engineno9]

Originally Posted by eckhard

I think that the answer may be to do with the different span of the stabilator.

As I recall, the original PA-28s had quite a short span stabilator. This was increased on later models. The down wash from the flaps acting on the larger stabilator results in a net pitch up moment.

On the earlier, shorter stabilator, the pitch up effect of the down wash is overcome by the rearwards movement of the centre of pressure and the lowering of the drag line.

Thankyou Eckhard, this is exactly the type of insightful answer I was looking for. Interesting that there should be such a notable difference. Thankyou BEagle also.

And maybe I should have known better than to mention final approach speeds on here having read these forums for long enough...! Suffice to say I'm happy that my approaches are in the right ballpark for the a/c and aerodrome in question.

[3wheels]

I've never extended flaps in a PA28 when downwind, and I've never used 1st stage for anything except take-off. I'm genuinely interested to know why it's done

To increase separation in the circuit if required;
Bad weather circuit;
In order to apply carb heat without increasing speed;
Better view ahead and below;
On a PFL if too high;
etc.....

[Flyingmac]

Nah. Still waiting.

[tmmorris]

Because the station flying order book makes it compulsory to fly downwind at 80kts when Tutors are in the visual circuit and the aircraft is nicer to fly at that speed with flaps?