Simviation Forum - High angle-of-attack in Jetliners

Mar 9^th, 2008 at 9:55am

Kartoffelsalatatatat Offline
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Hey

This is something I've always been wondering. Whenever I'm flying a jetliner I always seem to have a relatively high AoA at lower speeds. For instance, when flying @ 220KTS IAS, -1000 F/min descent I find myself with a 5 to 10^o nose-up attitude. Flaps don't seem to correct this problem.

Anyone know whether this in supposed to happen, or I am such a terrible pilot? Cheesy

Err. This is your captain speaking. There is absolutely no cause for alarm.&&&&The wings are not on fire.

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Reply #1 - Mar 9^th, 2008 at 5:40pm

DaveSims Offline
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May just be the aircraft model you are using. Typically a few notches of flap would get the nose down.

Dave

www.flymcw.com

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Reply #2 - Mar 9^th, 2008 at 9:36pm

beaky Offline
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DaveSims wrote on Mar 9^th, 2008 at 5:40pm:

May just be the aircraft model you are using. Typically a few notches of flap would get the nose down.

Read the OP... there's important info re: flaps.

The bottom line: FS9 is an approximation.

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Reply #3 - Mar 10^th, 2008 at 5:04am

Kartoffelsalatatatat Offline
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Ok, so I did some other experimenting with flap settings, and I found out it actually does make a difference, but I wasn't using enough flap. At around 15^o flap setting, the AoA is about 2.5^o. However, I still can't get the nose to go below the horizon, which one would expect from a descending airliner. The way I'm doing my approach now seems like one long flare.

Err. This is your captain speaking. There is absolutely no cause for alarm.&&&&The wings are not on fire.

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Reply #4 - Mar 10^th, 2008 at 10:32am

Brett_Henderson Offline
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Kartoffelsalatatatat wrote on Mar 9^th, 2008 at 9:55am:

Hey

This is something I've always been wondering. Whenever I'm flying a jetliner I always seem to have a relatively high AoA at lower speeds. For instance, when flying @ 220KTS IAS, -1000 F/min descent I find myself with a 5 to 10^o nose-up attitude. Flaps don't seem to correct this problem.

Anyone know whether this in supposed to happen, or I am such a terrible pilot? Cheesy

I don't fly the tubes very often.. so I just took the default 737 up for a test. First, we have to differentiate between pitch angle and AoA.. they aren't interchangable, even if the wing's angle of incidence is zero. Assuming that the wing has no incidence (wing's pitch = fuselage pitch), a wing with zero pitch, while desecnding, actually has a positive AoA.

That aside... I just set up a no-flap, 220kias/1000fps descent (starting at aprox 15000msl).. that gave me a pitch angle of zero (maybe 1 degree positive now and then). That seems about right.. or pretty close, anyway. To a 737, that might as well be gliding. And I checked the 737's cfg file... it has a +1 degree angle of incidence.. so in theory, the wing itself had about a +2 degree pitch. Considereing it was descending, without doing the math, that would be about a +7 degree AoA. Which again seems about right. A 737 isn't a glider.. so once it gets near zero AoA, it's on the edge of diving, not a glide-like descent.

Someone much more "in the know" regarding tube flying will probably post soon. We've got a real world jet pilot around here somewhere Cool

All I can think of, is that maybe you still had too much fuel on board for a regular descent ? The difference between 20% and 60% fuel is substantial.

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Reply #5 - Mar 12^th, 2008 at 12:01pm

C Offline
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Just come back from a trip where I was going to have a look. Sadly, as one normally does when it actually came to the approach, other things were on my mind! What I can tell you is that during the whole stage between 250kts and down the approach, the highest the nose ever went was 4 to 5 degrees above the horizon, just before the final approach, level with gear down and t/o (20*) flap.