big AOA when cruising

[xinmayu]

hi, all guys,

My aircraft always 5 to 10 degrees nose up when cruising at high attitude, such as FL350. The higher I go, the larger AOA is. But i am not climbing, I am cruising at normal speed.

Anybody knows why? How to solve it?

THanks for help.

Andy

[Staiduk]

Don't worry about an AoA of 5-10deg. at 35,000ft. xinmayu - that's exactly what the aircraft's supposed to be doing.

Straight and level flight is a balancing act between the Four Forces. Thrust equals drag; lift equals gravity. At low altitudes; the air's thick and thus the wings produce plenty of lift to support the plane. At altitude though; the air's less dense and the aircraft has to increase its AoA in order to produce the same amount of lift - it has to take a bigger bite out of the air; you might say, in order to keep the forces in balance and the aircraft in level flight.
Thus; the aircraft flies at a higher angle of attack.

Don't worry about it - what you describe is perfectly normal.

[IanK]

Andy

hi, all guys,

My aircraft always 5 to 10 degrees nose up when cruising at high attitude, such as FL350. The higher I go, the larger AOA is. But i am not climbing, I am cruising at normal speed.

Anybody knows why? How to solve it?

That is a bit excessive. In Fs2004 you need to move the lift slope in T404 .air to the left by 5 to 10 degrees to get a level fuselage. In FS2002 and previous change the Wing Incidence parameter but this makes it incompatible with upgrading to newer sims.

Thanks for help.

Andy

Ian

[xinmayu]

Thanks, Staiduk.

I UNDERSTAND THE THEORY ALREADY.

However, I feel strange about it in the real world. When I flew with Cathay pacific at FL380, I didn't feel that the plane is nose up. When I walked arround in the aircraft, I felt it is leveled.

How to explain this? I mean I never feel the slope, so I thought a plane should be leveled when cruising.

Is it possible that real poilot will apply flap to level it? But I think apply flap effect the speed, right?????

[xinmayu]

Sorry, David. I don't really get what you mean, can you explain more to me. You mean I need to edit the .air file of the aircraft?

[IanK]

Hello Andy,
I am Ian not David, yes edit the .air file with ACM or AirEd:

get those from Herve etc:

Air File Editors
http://perso.wanadoo.fr/hsors/FS_Soft/fsairfile.html

and have a goodlook at:

Air File Board, post March 2003
http://www.avhistory.org/scripts/MegaBBS/logon.asp

for more tips.

Ian

[xinmayu]

ok, Ian. Thanks. I will try it out.

[Nexus]

It's not normal to have an AOA above 5 degrees during cruise. You're either too heavy for the altitude or cruising too slow, my guess is the you're too high and heavy

[Moach]

the fuselage has to be pointing a wee bit UPWARDS to minimize the drag.

wouldn't that be the other way around?

i mean, to compensate the (positive) angle of attack of the wings, the fuselage would point a few degrees down in relation to the wings, wouldn't it?

c ya

Moach

[Nexus]

No, the wings accelerate airflow downwards, for the fuselage to be somewhat aligned with the airflow, it has to be parallell with the airflow obviously, thus the nose points upwards.  :)

[IanK]

Well the fuselage is orientated to minimise drag and assuming it does not produce lift then it must reduce the cross-sectional area to the flow and should be aligned with the flow assuming a pure cylinder.

The wings have an angle of incidence of the mean chord line to the fuselage axis (water line) to generate the required lift when the fuse is horizontal.

Downwash and upwash will effect the effective angle of attack so the zero lift line of a cambered wing will not correspond to the mean chord.

By changing the AoI of the wing on the fuse you can change the slope of the floor on the passenger cabin.

Many a/c seem to be nose down when parked. This may be to reduce the AoA when accelerating for takeoff to reduce the lift induced drag and reduce the take-off length.

Ian

[Staiduk]

I stand corrected.

I've always thought the B747 looked a little too nose-up in flight; I always assumed that's the way it fies at altitude; it's a bloody big airplane.

OK; so what's T404.air?

[Graycat8524]

Heya Staiduk,

All FS 2004 aircrafts (whether they are player controlled or AI) have a *.air file associated with it.

[IanK]

While I mention it CL = lift coeficient in T404.

But is that doc on Herve's site? If not I suggest you send it to him and have it up loaded there as all this info can be in a central location.

http://perso.wanadoo.fr/hsors/FS_Soft/

Thanks
Ian

[Staiduk]

Thanks - I'm familiar with the .air files; I wasn't aware of the T404 bit.

I'll work on it; and see if I can get the angles down a bit.