Pitch stays too high in the big jets

Hi everyone,

 

I have noticed that, in some of the big jets I fly, the pitch remains too high. I am expressing this correctly, right -- the nose is pointed up.

 

So, for example, let's say that I am flying the FSX SE default Boeing 737. I use autopilot on a straight course, normal cruise speed, and flaps and landing gear retracted. But the nose stays pitched up a few degrees.

 

Incidentally, this helps my landings because I don't have to worry about executing the flare procedure now that the aircraft's attitude is already correct for the landing. Still, this is not a normal cruising attitude.

 

This does not happen with the default Learjet 45. But it does happen with some of the large jets. Does anyone know why?

 

Thank you.

 

Stanley

Being pitched up a few degrees during cruise is normal for jets.

 

You still should flare during landing. A few degrees nose up during landing will not provide the correct attitude.

But the nose stays pitched up a few degrees.

As bkmetz says, this is normal. Due to the higher altitude, thus thinner air, an aircraft (not just jets) must keep the nose higher (I'll leave angle of attack out of this, for now) -- this is related to the fact that the indicated airspeed is less at those altitudes than for the same TAS at lower altitudes. That thinner air has lots of effects.

As bkmetz says, this is normal. Due to the higher altitude, thus thinner air, an aircraft (not just jets) must keep the nose higher (I'll leave angle of attack out of this, for now) -- this is related to the fact that the indicated airspeed is less at those altitudes than for the same TAS at lower altitudes. That thinner air has lots of effects.

 

But this is happening even at lower altitudes -- even at 1500 feet.

reduce total fuel to approx 20%

For the jets, that's still normal, especially during approach. My previous post was about cruise, since that's mostly what your post concentrated on, so you might note that you are still at the same, or lower, indicated airspeeds when on approach as you were at cruise, and all aircraft, when slow, will have their nose up a bit (try flying the C-172 in level flight at 65 kts with no flaps). This is so they can generate enough lift for the flight regime they're in.

 

Since this bugs you so much, I'll suggest that you look up "angle of attack" on Wikipedia, and perhaps also look through some of the related articles. You might also read the Wikipedia article Flight Dynamics.

 

It also might be good if you go to the Real Aviation Tutorials and FAQs section of this forum (in the Real World Aviation section) and read things there in the stickies, including airspeeds and altitudes, maneuvers, basic aircraft control and more.

The real 737 pitches up too, about 3-4 degrees, that is how it was built. Actually, most airliners do, AFAIK it helps with fuel efficiency. I am not aware that this attitude is limited to high altitudes, but if it is, it could well be that the default aircraft in FSX just don't take the altitude into account at all and simply pitch up all the time.

As almost everyone has already pointed out, often a specific model of plane will fly at a different pitch per IAS than others. The best example I can provide is the B-52 flies during cruise with a nose down attitude pretty much regardless of altitude.

It's all down to how accurate the .air file graph for Cl vs AoA - table 404 - is drawn & how close it is to reality. One can change the aircraft attitude by moving the slope left or right of its current position, as well as changing the pitch moment coefficient at AoA = 0 - Cmo- in table 1101. There is also a pitch moment coefficient for flaps Cm-df. Also don't forget that the actual indicated airspeed for most airliners is within a very small speed band dictated by critical Mach Number & Stall speed, which gets to a point at maximum altitude where only one speed is possible - i.e. where Critical Mach = Stall speed.

If the designers have got it right then the fuselage datum should be zero degrees & the angle of incidence should be at the cruise ideal - but it will have a tolerance depending on passenger & fuel load.

In the real word straight and level MEANS what it says

 

If a wing is 'level' at 4 or 5 degrees pitch UP

 

It is 4 or 5 degrees closer to stall

 

Not a good thing in the REAL WORLD

 

I reduce fuel and payload so they fly LIKE THE REAL WORLD

In the real word straight and level MEANS what it says

 

If a wing is 'level' at 4 or 5 degrees pitch UP

 

It is 4 or 5 degrees closer to stall

 

Not a good thing in the REAL WORLD

 

I reduce fuel and payload so they fly LIKE THE REAL WORLD

 

Sorry, but that is not correct. Airliners do not cruise at "wings level". Look up the specifics of the aircraft before you tweak it. The 737 REALLY flies 3-4 deg. nose up. A 767 about 1-1.5 degrees. It is different for each type and load - it all comes down to the aerodynamic profile of the wings and the position of the CG - these determine the ideal angle of attack for cruising.

Some terms being used wrong here I think.

"Straight and level" means:

flying in a straight line, not making a turn. and also

not climbing. Staying at the same altitude (level).

 

"Wings level" maens:

No bank angle, not one wing down and the other up. Wings level.

 

There is also:

"Pitch n degrees" or "n degrees nose up"

for example "4 degrees nose up".

 

"Level" in "straight and level"

has nothing to do with pitch.

 

And, almost all aircraft fly several degrees nose up in cuise. This is perfectly normal.

in the b737 it's around 5 degrees.

In the A321 it's less if I remember correctly.

 

fly a slower IAS, and the nose will pitch up more.

(when you extend flaps the nose comes down again.)

 

By the way, all if on Autopilot of course. Otherwise you will have to use the trim yourself to get the nose in that attitude.

 

Make sure you set "Indicated airspeed" in "realism settings" -menu.

Not "true airspeed".

and in cruise, use Mach speed in the autopilot. But take a look at IAS as well. You'll be surprised how low it is.

In the real word straight and level MEANS what it says

 

If a wing is 'level' at 4 or 5 degrees pitch UP

 

It is 4 or 5 degrees closer to stall

 

Not a good thing in the REAL WORLD

 

I reduce fuel and payload so they fly LIKE THE REAL WORLD

 

Actually, in the real world, straight and level means that you are not turning and you are not climbing or descending. It has nothing to do with aircraft attitude. Heavy and/or slow aircraft WILL fly nose up in the real world, whether jet or prop. At designed cruise speed (IAS, not TAS) at sea level under standard conditions, most aircraft will have an angle of attack near zero. Any slower and the angle of attack will increase. In slow flight (which at very high altitudes may be near cruise speed in TAS), there will be a fairly large angle of attack. A typical light aircraft might stall somewhere around 17º-18º angle of attack.

 

The aircraft's pitch attitude is only one factor in affecting angle of attack, since if you're in a thermal or a downdraft the pitch attitude will be different from the still air pitch attitude for the same angle of attack. The same is true if you are pulling G's. Angle of attack is the angle of the wing's chord line to the relative wind, and that relative wind under the above conditions is NOT parallel to the longitudinal axis of the aircraft.

 

I'd hoped to avoid getting into angle of attack, but...

And, almost all aircraft fly several degrees nose up in cuise.

 

In high altitude cruise that will be true, at least in still air. Near sea level a typical light aircraft will (still air) have a pitch attitude near level. Many jets that low may not be able to reach a normal (TAS) cruise airspeed, due to air load limitations, but would be decidedly lower in pitch than in cruise at altitude.

 

Otherwise you're spot on.

Hi everyone,

 

I thank all of you for your interesting and instructive replies.

 

Just to experiment, I am trying to reduce the fuel supply in my 737. I am surprised that I cannot figure out how to do this.

 

Could someone please give me guidance.

 

I appreciate everyone's contribution. It helps me learn a lot.

 

Stanley

bbrz -- isn't that what I said?

@Inuss

An airplane basically stalls due to a too high AoA which is related to IAS not TAS.

Although the attitude at high speed cruise is higher at high altitude the reason is a completely different one.

The IAS limit decreases with altitude so while at low altitude you can cruise at e.g. 320kias, at FL 400 the max IAS and hence cruising speed might be only 240kts.

 

Your statement has a fundamental error in it. The AOA is the critical element, and it has no relation to speed. Exceed the AOA and you will stall at any given speed.

No point in going any further here. You have no idea what you are talking about.

Just a quick side note to all this...

His screen name is actually (lower-case) L-NUSS, not (upper-case) I-NUSS. I made the same mistake, but was put straight :) It's a problem with the way computer fonts in general display characters. I thought it was the fault of a failing eyeball, but thankfully, no.

Common error, apparently :D

Pat☺

The angle of attack is the primary factor when it comes to stalling, however, in most aircraft the airspeed is all the pilot has to avoid a stall. Unfortunately, airspeed alone won't always tell you if you are nearing a stall, especially at the edges of the flight envelope. AoA indicators really should have been in all aircraft years ago, and this may finally be changing. The Icon A5, for example, comes with an AoA indicator.

 

https://iconaircraft.com/a5/safety/

 

http://www.flyingmag.com/technique/tip-week/flying-angle-attack

 

After the Air France AF447 crash, the BESA recommended the FAA and EASA mandate AoA indicators be installed on airliners.

Stanley777 - In windowed mode there should be at the top of the screen various tabs - click on 'Aircraft', from the drop down menu choose 'Fuel & Payload'; then click on 'Change Fuel', which will give you another panel where you can change your fuel load. Same for payload.

Hope that helps you - happy landings.

Could I suggest a pragmatic compromise?

 

It is true that a wing stalls when it exceeds a critical angle of attack regardless of airspeed.

 

It is true that most aircraft do not have AOA indicators/gauges.

 

For the sake of the original poster of this thread, and others who do not have an understanding of this, could we just advise them of the importance of maintaining the proper airspeed during flight- particularly during the approach to landing.

 

We use indicated airspeed as a surrogate for angle of attack. As long as you are flying the proper airspeed and do not suddenly or abruptly change the aircraft attitude, you won't stall.

 

This is a fundamental teaching for pilots. It is easy to remember, and it works. People stall in the pattern when they get too slow, or bank too steeply (which increases the stall speed), or when they get into a cross controlled situation. Teach the new guys and gals to avoid these things.

Erm, no as you are adding TAS to this equation which doesn't apply in this case.

 

Granted that you are correct about IAS (actually CAS) being the determining factor (along with G-loading), but perhaps you should reread my post carefully. I mentioned TAS as a sidenote, and was attempting to make it clear that at high altitudes an IAS that is in slow flight may also be yielding a TAS near cruise. For instance I said, "In slow flight (which at very high altitudes may be near cruise speed in TAS)" and obviously TAS at high altitudes won't be a useful figure to know about slow flight.

 

Perhaps I was clumsy in the description, but so many simmers are hyped on the "published" cruise speed (which is TAS) that I was attempting to give them a point of reference. Sorry if it was confusing

Your statement has a fundamental error in it. The AOA is the critical element, and it has no relation to speed. Exceed the AOA and you will stall at any given speed.

 

Actually, Robert, AoA does have a relation to speed in unaccelerated flight, which was what we were discussing. In accelerated flight, though you are absolutely correct. I once stalled a Stearman coming out the back side of a loop at roughly a 60º nose down attitude -- relaxing the back pressure (lowering the AoA) broke the stall and allowed me to finish the loop.

For the sake of the original poster of this thread, and others who do not have an understanding of this, could we just advise them of the importance of maintaining the proper airspeed during flight- particularly during the approach to landing.

 

I think that 's a great idea, and is why I tried to keep AoA out of the discussion -- didn't work.