Pitch when at cruising altitude

[Marenostrum 4]

I am flying at FL340....no alarm...all seems to be right...but why have I the ange of attak gauge at 2.2 (I see I am not leveled also in the PFD)?

Flaps are retract...spoilers off. 

Is it due to my unbalance load? (144 pax and 10 + 100 cargo load aft and fwd)

Edited May 25, 2018 by Marenostrum

[scandinavian13 5,192]

36 minutes ago, Marenostrum said:

I am flying at FL340....no alarm...all seems to be right...but why have I the ange of attak gauge at 2.2 (I see I am not leveled also in the PFD)?

It's natural to have a slight pitch up when at cruise. It's just how aircraft are, across the board. In fact, there was a 727 out there in private service with a 3 degree tilt on the bed to counter the natural nose up pitch at cruise.

37 minutes ago, Marenostrum said:

Is it due to my unbalance load? (144 pax and 10 + 100 cargo load aft and fwd)

Nope. Just how planes work.

 

 

You've been posting a lot of questions lately. While that's certainly helping you learn, I would suggest taking some time to do a bit of reading and learning on your own as well. Seems like you're operating on an understanding of aviation that doesn't have a solid base. That's okay, but at the same time, you'll find it incredibly difficult to understand the complexities of our products, when some of the basic points of flight aren't fully understood.

[Ephedrin 418]

Most if not almost all airplanes have their step pitch at around 2 degrees nose up which is the most economic attitude, lowest drag. That‘s fine.

[Marenostrum 4]

51 minutes ago, scandinavian13 said:

 

You've been posting a lot of questions lately. While that's certainly helping you learn, I would suggest taking some time to do a bit of reading and learning on your own as well. Seems like you're operating on an understanding of aviation that doesn't have a solid base. That's okay, but at the same time, you'll find it incredibly difficult to understand the complexities of our products, when some of the basic points of flight aren't fully understood.

Thank you,

I am in the initial learning curve of this aircraft...I am learning by reading a lot, looking a lot of tutorials on youtube, flying, and finally asking....I come from about 1000hrs flown over the Q400 by Majestic, another complex aicraft, and to "switch" into this one is more complicated than I expected (many many things are different in behaviour and setting).

During the flight, in the cruising phase,  I usually have some time to better explore instruments, panels, etc etc.

When I do not find an answer in the books (I have to say that the manuals are not so easy to explore) I ask here...continuing my a mix of reading, viewing, flying...and asking.

And I have to say that all of you are very helpful...so I will continue this way...but please Kyle feel free to not answer if you find it excessive!! 😉

btw you are one authors of the tutorials I see

[downscc 1,327]

57 minutes ago, Marenostrum said:

When I do not find an answer in the books (I have to say that the manuals are not so easy to explore) I ask here...continuing my a mix of reading, viewing, flying...and asking

Ask away my friend, I think Kyle was simply trying to encourage you to explore wider.  My bible when I was a student pilot many decades ago, and is still a good source is the Airman's Information Manual (I think they changed Airman to something PC like Aeronautical but it is still the AIM): https://www.faa.gov/air_traffic/publications/

Your question was not answered above.  You asked about angle of attack and the answers were to attitude pitch.  While it is true that both AOA and pitch are usually positive during level flight, the reasons for each are different.  It's possible to have a nose low pitch and a positive AOA, this is like a B-52 climbing with nose down attitude.  Back to question:  Angle of attack directly influences lift and in level unaccelerated flight there is a need for lift to balance weight therefore the positive AOA.  As the air gets thinner (less dense) the AOA required will increase given the same true airspeed, because as lift is a function of airspeed, air density and angle of attack (plus other stuff like coefficient of lift yada yada).  Less dense air means either higher speeds or AOA.  This continues upward until you get to a point where you can't go faster due to Vmmo (maximum mach operating speed) and you can't go slower or you stall.  AOA is one of those parameters that is very important to understand to be a pilot... I encourage you to dig deeper on this subject.

[Marenostrum 4]

11 minutes ago, downscc said:

Ask away my friend, I think Kyle was simply trying to encourage you to explore wider.  My bible when I was a student pilot many decades ago, and is still a good source is the Airman's Information Manual (I think they changed Airman to something PC like Aeronautical but it is still the AIM): https://www.faa.gov/air_traffic/publications/

Your question was not answered above.  You asked about angle of attack and the answers were to attitude pitch.  While it is true that both AOA and pitch are usually positive during level flight, the reasons for each are different.  It's possible to have a nose low pitch and a positive AOA, this is like a B-52 climbing with nose down attitude.  Back to question:  Angle of attack directly influences lift and in level unaccelerated flight there is a need for lift to balance weight therefore the positive AOA.  As the air gets thinner (less dense) the AOA required will increase given the same true airspeed, because as lift is a function of airspeed, air density and angle of attack (plus other stuff like coefficient of lift yada yada).  Less dense air means either higher speeds or AOA.  This continues upward until you get to a point where you can't go faster due to Vmmo (maximum mach operating speed) and you can't go slower or you stall.  AOA is one of those parameters that is very important to understand to be a pilot... I encourage you to dig deeper on this subject.

Thank you downscc....very interesting and technical  explanation ...as engineer always curious  I will read more about it. It reminds me some  curiosities I read about the famous Blackbird. 

I downloaded the 744 pages bible....it will be my slow reading book... really thank you for the link.

about the wider exploration....I am simulating flights on the 737-800 after only 24 hours of reading, asking, viewing...so I am aware I need nothing  less than a very deep/wider exploration.....and  this "training  on the job" way to explore while I fly makes it easyer and I think more practical.

So really thank you Dan and Kyle

 

 

[downscc 1,327]

15 minutes ago, Marenostrum said:

It reminds me some  curiosities I read about the famous Blackbird. 

Exactly, the SR71 operated in the corner of the flight envelope they call "coffin corner."  Up around 70,000 ft it had about a 10 kt window to operate within.... and the excitement began when an engine stalled.  Those guys earned their flight pay.

[Andrea1 6]

Ciao Stefano,

(sorry for the underline but I can't find how to delete that selection, I've tried by pressing the U button but w/o success).

As you  know in an airplane (pitch) attitude, power (N1%) and speed are linked togheter so is paramount thatYou've to study and memorize ("by heart") the attitude and power needed for the various phases of flight by looking at the "performance inflight/flight with unreliable airspeed/turbulent air penetration speed" section of the FCOM1 (I can't remember exactly the page but "performance chart should be around page "700") or by looking at the same section in your QRH"Chapter PI-QRH General Section 10) now I've looking at a QRH of an airline an there is at page 279.

Looking at those figure you'd learn that i.e. at 60 tons ISA 35000 ft if you aim for a level flight at 0,76 Mach in i.e. manual flight you should set at 2 degrees pitch nose up and 86% (about) N1%.

But these figures are mandatory to learn about APPROACH settings: there are published for Vref+10 flaps 30 and 40  but also for Vref+5 flaps 30-40 are similar. By heart: when I'm in the "big" sim (I go often in a fixed base B738 sim near Bergamo) flaps 30 Vref+5 60-62 ton I know I've to fly with pitch 2-2,5 degrees nose up engine 50-55% N1 with flaps 40 pitch 0-0,5 nose up engine 60-65% n1, you should try w/o FD and memorize those settings because this can be very useful the day that you've to disengage your A/P early i.e. for a failure (happened in the big sim) and execute all the approach and landing "by hand".

Ciao, a presto

Andrea Buono

[Ephedrin 418]

Dan,

Assuming that the wing‘s profile is parallel to the fuselage isn‘t the AoA the same as the pitch in level flight? 

Or in other words, the difference between angle of attack and nose up attitude is always the same in level flight. 

Of course, when climbing the pitch is higher than the AOA as the pitch relies to the horizon and the AoA to the airstream. But assuming an economically ideal climb the difference between pitch and AOA is around the same 2-2,5 degrees for „typical“ aircraft.

Isn‘t that correct? Or am I off the track?

[Marenostrum 4]

51 minutes ago, Andrea1 said:

C

But these figures are mandatory to learn about APPROACH settings: there are published for Vref+10 flaps 30 and 40  but also for Vref+5 flaps 30-40 are similar. By heart: when I'm in the "big" sim (I go often in a fixed base B738 sim near Bergamo) flaps 30 Vref+5 60-62 ton I know I've to fly with pitch 2-2,5 degrees nose up engine 50-55% N1 with flaps 40 pitch 0-0,5 nose up engine 60-65% n1, you should try w/o FD and memorize those settings because this can be very useful the day that you've to disengage your A/P early i.e. for a failure (happened in the big sim) and execute all the approach and landing "by hand".

Ciao, a presto

Andrea Buono

Ciao Andrea,

Among the thousands pages this is for sure something I have to know as a feeling....I found the page, but (it is the only one I found...but possibly it is written in another page) it refers only to VREF+10 and it is in the section "30.43 Flight With Unreliable Airspeed TurbulentAirPenetration)...

Am I reading the correct section?

[Marenostrum 4]

45 minutes ago, Ephedrin said:

Dan,

Assuming that the wing‘s profile is parallel to the fuselage isn‘t the AoA the same as the pitch in level flight? 

Or in other words, the difference between angle of attack and nose up attitude is always the same in level flight. 

Of course, when climbing the pitch is higher than the AOA as the pitch relies to the horizon and the AoA to the airstream. But assuming an economically ideal climb the difference between pitch and AOA is around the same 2-2,5 degrees for „typical“ aircraft.

Isn‘t that correct? Or am I off the track?

After that Kyle and Dan pushed me to study it...my understanding is that, by definition they are two different angles.

Pitch  is the angle between the front/back axis of the wing and the horizontal "ground"

AOA  is the angle between the front/back axis of the wing and the direction of the aircraft motion

Yes they should be similar in many flight situation but I think they could be really different depending the aircraft design and scope (think the military aircraft)

Did I correctly understand?

[downscc 1,327]

1 hour ago, Ephedrin said:

Or in other words, the difference between angle of attack and nose up attitude is always the same in level flight

 

13 minutes ago, Marenostrum said:

AOA  is the angle between the front/back axis of the wing and the direction of the aircraft motion

Good topic.... common misunderstanding played out here.  The AOA and pitch will differ significantly if the aircraft encounters rising or falling air.  The significance of AOA becomes paramount during approach, in fact many unstable early fighters flew their approach using AOA as primary and IAS secondary.  At a given air density, the wing will stall at the same AOA regardless of speed or pitch.  The direction of aircraft motion would be better replaced with the angle between chord and air motion in front of the leading edge.  Ever notice the GA stall sensor is simply a little tongue depressor sticking out in front of the leading edge?

[skelsey 765]

2 hours ago, Ephedrin said:

Of course, when climbing the pitch is higher than the AOA as the pitch relies to the horizon and the AoA to the airstream. But assuming an economically ideal climb the difference between pitch and AOA is around the same 2-2,5 degrees for „typical“ aircraft.

Pop quiz:

In a steady climb, angle of attack is:

a) Less than the AoA in level flight

b) The same as the AoA in level flight

c) Greater than the AoA in level flight

(Assume airspeed is unchanged).

What about for a steady descent?

[Ephedrin 418]

5 minutes ago, skelsey said:

Pop quiz:

In a steady climb, angle of attack is:

a) Less than the AoA in level flight

b) The same as the AoA in level flight

c) Greater than the AoA in level flight

(Assume airspeed is unchanged).

What about for a steady descent?

The AoA is always the same as long as you fly with the same IAS. A variing pitch for climb or descent simply changes the vertical speed. 

As your pitch increases, the lifting force increases too and so Fres (vector) points upwards. Pitching down Fres (vector) points downwards. 

If you now decrease your airspeed either you have to increase your AoA or you have a lower lifting force and so your Fres (vector) points down again.

 

[skelsey 765]

2 hours ago, Ephedrin said:

The AoA is always the same as long as you fly with the same IAS.

Not quite. 

Anyone else? Think about:

- The lines along which each of the four forces act and how they change in a climb or descent

- Which force controls the climb? (Hint: it's not lift).

I'll draw a diagram in the morning ☺️