Pitch Change with Flaps

HF17

HF17

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Why does the nose rise when flaps are deployed on a piper warrior? I understand that for a high wing airplane, more air is being deflected onto the horizontal stabilizer. Is it the same for a low wing airplane?


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I think ANY pitch change is due to a change in the position of the center of lift.

Note: center of lift is apparently a very complicated thing, so this isn’t technically accurate, but I think essentially the case for all practical purposes.

That being said, everything I’ve flown with regular or Fowler flaps has a more nose down attitude with flaps, one of the reasons to use them, better vis over the nose. Split flaps don’t seem to change attitude much if at all.
 
Every low wing single I have flown, flap deployment results in a nose-down moment, whereas every Cessna I've flown results in a nose-up moment. I haven't flown a Warrior, but I have flown a few Cherokees.
 
Cirrus gives you a strong pitch up when deploying flaps
 
I thought that for both Cessnas and Pipers (and even Cirrus), deploying the flaps increased the camber of the wing, resulting in a lower AOA required to maintain a given airspeed. So, if you're trimmed for 70 with 0 flaps, and you extend to flaps, you'll have to reduce the AOA to maintain 70. That seems to me to be the way it works anyway.
 
If you reduce speed in anticipation of flaps you may not need to re-trim.
 
When you lower the flaps, that squeezes the streamlines under the wing causing a venturi effect (just like the curve on the top of the wing) that reduces lift and can cause you to get sucked into the ground. That's why you never increase flaps once you get close to the runway.[/SARCASM]

Other than that, how much the pitching moment of the wing changes depends on the basic airfoil, and the flap configuration. Add the interaction with the airflow over the tail, then one would want to get into some detailed computer fluid dynamics to do an accurate prediction. Or, just learn how the airplane you are flying behaves and don't worry about why. It's not like pilots have to understand how lift is generated by a wing given that many don't have a clue.
 
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........causing a venturi effect (just like the curve on the top of the wing) that reduces lift........
Yep, the same Venturi that sucks the aircraft skywards (the curve on top of the wing is now facing the earth) when flying upside down. :)
 
Tools said:
That being said, everything I’ve flown with regular or Fowler flaps has a more nose down attitude with flaps, one of the reasons to use them, better vis over the nose.
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The confusion:

1. Flaps increase the angle of incidence which increases the AoA, they increase lift and drag, all requiring a nose-down attitude to maintain the speed.

2. Downwash off the flaps cause a pitch-up in some airplanes as the horizontal stabilizer is affected. This is entirely a different affair from the attitude change needed with flaps extended, and is the one the OP is asking about.

My old Auster AOP6 had two trim tabs, one on each elevator. One was connected to the trim crank. The other was connected to the flap system, and applied nose-down trim as the flaps were extended, eliminating the pitch-up often noted in high-wing airplanes.
 
Dan Thomas said:
The confusion:

1. Flaps increase the angle of incidence which increases the AoA, they increase lift and drag, all requiring a nose-down attitude to maintain the speed.

2. Downwash off the flaps cause a pitch-up in some airplanes as the horizontal stabilizer is affected. This is entirely a different affair from the attitude change needed with flaps extended, and is the one the OP is asking about.

My old Auster AOP6 had two trim tabs, one on each elevator. One was connected to the trim crank. The other was connected to the flap system, and applied nose-down trim as the flaps were extended, eliminating the pitch-up often noted in high-wing airplanes.
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Good summary, thanks. This is one of those things where worrying about why it happens academically can confuse what your reaction should be. This is covered in every checkout (light airplanes only for me) I've done. For the Cirrus, if you don't pay attention, going from no flaps to the first setting can pop you up a few hundred feet really quickly, plus the corresponding speed bleed off. It's just another one of those things flying you need to deal with, hopefully as it happens not after the fact.
 
wilkersk said:
I thought that for both Cessnas and Pipers (and even Cirrus), deploying the flaps increased the camber of the wing, resulting in a lower AOA required to maintain a given airspeed. So, if you're trimmed for 70 with 0 flaps, and you extend to flaps, you'll have to reduce the AOA to maintain 70. That seems to me to be the way it works anyway.
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How did it take until post #6 to get the right answer?

Deploying flaps changes the camber of the wing, which increases the angle of attack. Same indicated airspeed as before, but higher AOA means a pitch up.

If you decrease the power before flaps, you can minimize the pitch up. If you decrease the power a whole lot or have a really draggy airplane, you might even pitch down.
 
bflynn said:
How did it take until post #6 to get the right answer?

Deploying flaps changes the camber of the wing, which increases the angle of attack. Same indicated airspeed as before, but higher AOA means a pitch up.

If you decrease the power before flaps, you can minimize the pitch up. If you decrease the power a whole lot or have a really draggy airplane, you might even pitch down.
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Because that's not the right answer.
 
bflynn said:
I can quote many sources that say it is. Here's one https://www.boldmethod.com/blog/2013/10/how-does-lowering-flaps-affect-angle-of-attack/
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No, your source does not say that lowering the flaps causes a pitching moment, let alone have an explanation why. It has nothing to do with OP's question.

bflynn said:
If this is wrong, how about explaining what is right and giving a link so we can all get smarter?
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It's already been explained, by two different posters in this very thread, but, here's an excerpt from the PHAK, page 6-9.

Screen Shot 2022-01-04 at 2.04.37 PM.png
 
Flaps add drag. Drag causes the nose to drop. If the CP moves aft with flap extension, and it often does, the nose will want to drop more. Now, with the stab in some airplanes being close to the wing's downwash, the nose will rise because that factor is stronger than the nose-dropping factors. And I don't believe that the downwash actually has to strike the stab. Just the downwash angle steepening under the stab would do it. It will affect the airflow all around the stab.

If you just extended the flaps and held the same pitch attitude, the speed will fall off not only because of drag but because the AOA, caused by the change in effective incidence of the flapped section of wing, has increased.
 
bflynn said:
I can quote many sources that say it is. Here's one https://www.boldmethod.com/blog/2013/10/how-does-lowering-flaps-affect-angle-of-attack/

If this is wrong, how about explaining what is right and giving a link so we can all get smarter?
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Confusion over words. Yes, lowering the flaps increases the AoA because the angle of incidence changes, and if the nose doesn't drop, or if it rises and you don't get it down, that higher AoA is going to slow you way down. You still have to fly the airplane.

But none of that has much to do with the pitch-change tendencies when flaps are extended. Those are caused by CP movement, drag, and stabilizer airflow changes.
 
Flaps cause drag. In a high wing that drag will contribute to nose up, low wing, nose down, but I think there’s more things that can alter that. I think it depends on a lot of things and each aircraft will be different.
 
Tapered wing archer - nose goes up
 
What really blew my mind was when a friend let me take the controls of his mooney (201) and in steep turns, you had to apply down pressure. First plane I've flown like that.
 
Hang 4 said:
In my Hershey bar wing Archer (73)
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Was there such an airplane? I thought all the Hershey-bar wings were on Cherokees of various HPs. IIRC the Archer and Warrior were the first tapered-wing airplanes.
 
Dan Thomas said:
Was there such an airplane? I thought all the Hershey-bar wings were on Cherokees of various HPs. IIRC the Archer and Warrior were the first tapered-wing airplanes.
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The early Archers had a straight wing that was a little longer than the typical "hershey bar" airplanes, if I'm remembering right. I think it only lasted a couple of years.
 
Dan Thomas said:
Was there such an airplane? I thought all the Hershey-bar wings were on Cherokees of various HPs. IIRC the Archer and Warrior were the first tapered-wing airplanes.
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There are. In 1973 the Challenger was introduced. It was a Hershey Bar wing with the extended fuselage of the Archer. They dropped the Challenger name and it became the Archer. It was out for about three years until the Archer 2 came out. The Archer 2 was the first PA-28 181. The Taper wing model numbers have a 1 added, so 161 (Warrior), 181 (Archer II and III) and the Dakota went from 235 to 236.
 
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