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Pitch up during cruise?
Posted:
Sun Feb 05, 2006 1:59 pmby fm3
Some aircraft simply refuse to fly , during cruise, at a level pitch; the nose is always pitched up. How can this be fixed? Especially some Kittyhawk and FFX boeings. Very annoying! Happens on auto pilot too. I thought perhaps I was doing something wrong, or it was due to proper trim falling between two trim settings (not uncommon; I often find this situation). But even with some planes that exhibit this, on auto pilot the cruise seems pretty level.
Any help would be appreciated! Thanks!
Re: Pitch up during cruise?
Posted:
Sun Feb 05, 2006 2:18 pmby Nexus
Why do you want to fix something that is completely normal and realistic?
Every airliner pitches up a few degrees during cruise.
Primary reason is that the wings wont generate enough lift at level pitch, so by increasing the pitch angle you effectively increases the AoA = more lift is generated.
An extraxt from a post made by me regarding nose up pitch during cuize
"...actually, anything higher than that (5 degrees pitch up) will cause the stabilizer NOT to be streamlined with the airflow, thus creating unnecessary drag.
Re: Pitch up during cruise?
Posted:
Sun Feb 05, 2006 3:12 pmby Lazerbeak
I noticed that too. At first, I thought it was odd (being unfamiliar with how airliners work), but after a while I just figured it was supposed to be like that. I guess this confirms that it is.
Re: Pitch up during cruise?
Posted:
Sun Feb 05, 2006 3:47 pmby microlight
Hey Lazerbeak,
Is that Janet airlines 732 one of yours? Nice!
It and its destination do not exist....
Re: Pitch up during cruise?
Posted:
Sun Feb 05, 2006 4:06 pmby Lazerbeak
Hey Lazerbeak,
Is that Janet airlines 732 one of yours? Nice!
It and its destination do not exist....
Indeed, painted her meself! She's one of my favourite heavies, in the livery of my favourite nonexistant airline.
Dunno why I haven't uploader her yet, though...
Re: Pitch up during cruise?
Posted:
Sun Feb 05, 2006 4:33 pmby fm3
"...actually, anything higher than that (5 degrees pitch up) will cause the stabilizer NOT to be streamlined with the airflow, thus creating unnecessary drag.
It's preferable to cruise below 5 degrees upward pitch. This in turn allows the aircraft to be operated at its optimal thrust setting to obtain the maximum range, without having to waste engine thrust to compensate for drag.
An aft CG position (which causes the nose-up attitude) results in:
Makes the aircraft less stable
less stick force
Increased stall speed
Plus, will also give you less drag. compared to a FORWARD CG.
the 737 in general, has a 3degree pitch in level flight, and most other commercial jets (767, 747 etc) flies similar to that, but they don't go as high as 5 degrees, that is not desirable"
there are some performance gains by flying nose-up (and have an aft loaded aircraft): Better climb rate and faster cruise...
Hmmmm......just seems like the pitch up is excess of 5 degrees, really noticeable...so much so that it makes me think the thing is on the verge of a stall! I know that they should pitch up a bit at high altitude but this looks wrong to me. Guess I'm wrong, but it seems to exceed normal parameters.
Re: Pitch up during cruise?
Posted:
Sun Feb 05, 2006 4:45 pmby Nexus
Then I guess you're too heavy for the altitude you're flying at. THat's usually the case if your aircraft is pitching upp too much...that or a slower than normal mach speed. :)
Re: Pitch up during cruise?
Posted:
Sun Feb 05, 2006 8:58 pmby Nav
Height and speed are highly relevant - if you're trying to fly flat-out with a full fuel load at 40,000 feet the engines may simply not have the power to cope.
The pitch angle will reduce as the fuel load lightens, anyway. Unless you're flying maximum-range trips all the time, try going to the fuel page and reducing the load to suit the length of the trip before you set out.
Re: Pitch up during cruise?
Posted:
Mon Feb 06, 2006 2:44 pmby TheBod1357
I probably am doing something wrong as well, but I also became annoyed, especially with the 747 of the awkward pitch angle, but through a stroke of luck (hitting the wrong key) I found out that deploying a slight amount of flaps will effectively lower the nose of the plane.
However, I have not tried this with the difficulty settings (plane stress and such) at full, so this may cause a minor catastrophe. But good luck anyways.
Re: Pitch up during cruise?
Posted:
Mon Feb 06, 2006 3:12 pmby elite marksman
Firstly, DO NOT deploy the flaps during cruise if you have any intention of using them during landing. At max weight, a 747 *should* be able to keep FL340-350 at cruise speed. If for some reason you cant hold alt. without excessive pitch, request a decent of 2000' until you can. Likewise, as you burn gas, probably about every hour of so, ask for a 1000' increase to keep you at an optimum alt. I dont remember the speed for a 747, but it should be between M.80 and M.85. I reglarily fly heavies and do not have this problem, its just a matter of accurate planning.
Re: Pitch up during cruise?
Posted:
Mon Feb 06, 2006 5:43 pmby beaky
At lower power settings and/or higher density altitudes, any airplane will settle into a "mushing" gait- that is, nose-high- to some extent, trying to compensate with more A of A.
And of course improper loading, or even normal changes in CG due to fuel burn (although less likely in modern ships) will be a factor.
Re: Pitch up during cruise?
Posted:
Mon Feb 06, 2006 6:17 pmby Nexus
[quote]At lower power settings and/or
Re: Pitch up during cruise?
Posted:
Mon Feb 06, 2006 7:35 pmby TheBod1357
lol, I thought I must be wrong
Re: Pitch up during cruise?
Posted:
Mon Feb 06, 2006 8:59 pmby Chris_F
I don't get how CG effects AOA at cruise. At cruise the aircraft has to generate enough lift to keep the weight aloft, so given a constant airspeed and altitude more weight means more AOA and more pitch up. I get that part.
But what I don't get is how CG factors in. If you need 5 deg nose up to maintain altitude you should need that regardless of CG, right? Sure moving the weight around should effect how much trim you need to keep that 5 deg, but regardless of where the weight is you still need 5 deg. (granted more trim means more drag and more fuel burn, so I can see how it's a factor in effitientcy.)
Or am I missing something?
Re: Pitch up during cruise?
Posted:
Mon Feb 06, 2006 11:35 pmby Nav
The proper way to trim any aeroplane is by reference to the 'Rate of Climb and Descent' gauge, not the nose position. You're aiming to achieve level flight, regardless of the aeroplane's attitude.
Chris_F, you're largely right. In smaller aircraft, just someone walking aft will alter the trim, the nose will pitch up, the aeroplane will begin to climb, and the pilot will have to re-trim. If the change of seat is 'permanent' he will probably have to add a touch of power too, to maintain speed against the fractional extra drag caused by the trim-tabs being at a greater angle to the airstream.
What happens to the attitude I don't know off-hand - I've never looked :) - but I would expect that the aeroplane would finish up with the nose pitched a trifle higher as well. With the CG that much further back from the ideal point, more power will be going into maintaining altitude and less into forward speed.