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Any Commercial Airliners With A Steep AOA?  
User currently offlineKimon From , joined Dec 1969, posts, RR:
Posted (4 years 7 months 1 week 6 days 10 hours ago) and read 3276 times:

The C-17 and C-130 have steep AOA.
Can any commerical liner do the same?

19 replies: All unread, jump to last
 
User currently offlineSwiftski From Australia, joined Dec 2006, 2701 posts, RR: 2
Reply 1, posted (4 years 7 months 1 week 6 days 9 hours ago) and read 3261 times:



Quoting Kimon (Thread starter):
The C-17 and C-130 have steep AOA.
Can any commerical liner do the same?

Angle of Attack (AoA) is controlled by pitch up/pitch down.

I presume you mean the wing design?


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 2, posted (4 years 7 months 1 week 6 days 7 hours ago) and read 3247 times:

I think Kimon means the ground angle, meaning they climb steeply.

Definitions:
- Angle of attack is the angle of the wing relative to airflow.
- Ground angle (or whatever it is called) is the angle of the wing relative to the ground.

While they may climb steeply, this doesn't mean they have exceptional angles of attack. The angle of the airflow may not be so great. Steep climbs mostly due to (lack of) weight, (excess of) thrust and lift.

High feasible angles of attack, on the other hand, depends mainly on the aerodynamics of the wing and also on whether thrust can be vectored. The intakes also need to be positioned so that they can still suck air at high AoA. This is apparent in the Eurofighter Typhoon, for example.

If you want to see some spectacular angles of attack, look no further than the X-31 program:

View Large View Medium
Click here for bigger photo!

Photo © Thomas Merkl



Here's an in-flight pic. I believe that plane is flying horizontally at that point. The record AoA achieved was 70 degrees.
.

[Edited 2010-01-20 02:57:48]

[Edited 2010-01-20 02:59:30]

[Edited 2010-01-20 03:01:00]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSwiftski From Australia, joined Dec 2006, 2701 posts, RR: 2
Reply 3, posted (4 years 7 months 1 week 6 days 7 hours ago) and read 3243 times:



Quoting Starlionblue (Reply 2):
(excess of) thrust and lift

Thrust really. There is more lift generated in straight and level flight than in a climb.


User currently offlineKeta From Germany, joined Mar 2005, 448 posts, RR: 0
Reply 4, posted (4 years 7 months 1 week 6 days 3 hours ago) and read 3209 times:



Quoting Starlionblue (Reply 2):
I think Kimon means the ground angle, meaning they climb steeply.

Yes, sounds like he either misinterpreted the meaning or wasn't referring to the angle of attack. Maybe "Angle of Ascent" or "Angle of Approach"?



Where there's a will, there's a way
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 5, posted (4 years 7 months 1 week 6 days 3 hours ago) and read 3194 times:



Quoting Keta (Reply 4):
Yes, sounds like he either misinterpreted the meaning or wasn't referring to the angle of attack. Maybe "Angle of Ascent" or "Angle of Approach"?

I think what he is is referring to is the "pitch angle on approach". For the average airliner is approximately 8 degrees nose up. However, the C-130 and C-17 being high wing cargo aircraft their "pitch angle on approach" is approximately 4 degrees nose down.


User currently offlineKimon From , joined Dec 1969, posts, RR:
Reply 6, posted (4 years 7 months 1 week 6 days 1 hour ago) and read 3169 times:

47218:Yes,you are right.
That is what I had in mind.
Newbie's error!
Many thanks


User currently offlineVikkyvik From United States of America, joined Jul 2003, 9945 posts, RR: 26
Reply 7, posted (4 years 7 months 1 week 6 days ago) and read 3151 times:
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Quoting Swiftski (Reply 3):
Thrust really. There is more lift generated in straight and level flight than in a climb.

If I remember correctly, lift is defined as being perpendicular to the relative wind. So if you're at the same speed and AOA in a climb, then you're producing the same lift.

But yes, rate of climb is dependent on excess thrust.

Quoting 474218 (Reply 5):
I think what he is is referring to is the "pitch angle on approach". For the average airliner is approximately 8 degrees nose up. However, the C-130 and C-17 being high wing cargo aircraft their "pitch angle on approach" is approximately 4 degrees nose down.

Worth pointing out that that would be the opposite of what he said in the opening post. The airliners with their nose-up approaches have a higher AOA than the C-130 and C-17 with their nose-down approaches.



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 8, posted (4 years 7 months 1 week 5 days 22 hours ago) and read 3114 times:



Quoting Vikkyvik (Reply 7):
Worth pointing out that that would be the opposite of what he said in the opening post. The airliners with their nose-up approaches have a higher AOA than the C-130 and C-17 with their nose-down approaches.

The secret was the word "steep". Even when landing most commercial look like they are trying to climb. However, when the C-130, ans C-17 appear to be in a steep dive when landing.


User currently offlineSwiftski From Australia, joined Dec 2006, 2701 posts, RR: 2
Reply 9, posted (4 years 7 months 1 week 5 days 22 hours ago) and read 3114 times:



Quoting Vikkyvik (Reply 7):
If I remember correctly, lift is defined as being perpendicular to the relative wind. So if you're at the same speed and AOA in a climb, then you're producing the same lift.

Relative airflow, not wind. Sounds picky of me, I know, but it's true.

I have drawn a diagram to explain how lift is less in a climb that S&L and will upload as soon as I get to a scanner.


User currently offlineA346Dude From Canada, joined Nov 2004, 1283 posts, RR: 7
Reply 10, posted (4 years 7 months 1 week 5 days 22 hours ago) and read 3108 times:



Quoting Swiftski (Reply 9):
Relative airflow, not wind. Sounds picky of me, I know, but it's true.

Relative wind is a commonly used, if not entirely technical term.



You know the gear is up and locked when it takes full throttle to taxi to the terminal.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 11, posted (4 years 7 months 1 week 5 days 21 hours ago) and read 3097 times:



Quoting Vikkyvik (Reply 7):
So if you're at the same speed and AOA in a climb, then you're producing the same lift.

Go to the extreme. It's often a useful exercise. In a straight vertical climb, how much lift is produced by the wing?

Then draw the vector diagram. Or find it on the net, along with an explanation.



Cheers,
/Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 12, posted (4 years 7 months 1 week 5 days 21 hours ago) and read 3094 times:



Quoting A346Dude (Reply 10):
Relative wind is a commonly used, if not entirely technical term.

But... relative to what? The wing? The fuselage? "Perpendicular to the freestream velocity vector" would cover all bases... Big grin



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineSwiftski From Australia, joined Dec 2006, 2701 posts, RR: 2
Reply 13, posted (4 years 7 months 1 week 5 days 13 hours ago) and read 3044 times:



Quoting A346Dude (Reply 10):
Relative wind is a commonly used, if not entirely technical term.

Not by anyone I know or fly with - it's not at all correct. In fact, when I was taught basic aerodynamics it was tripple underlined not to use the term.

The air can be completely still but if you fly through it, you still have relative airflow. No relative wind. Same, if you apply a 100kt tailwind.. the wind is actually coming from up your arse.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 14, posted (4 years 7 months 1 week 5 days 13 hours ago) and read 3041 times:



Quoting Swiftski (Reply 13):
Quoting A346Dude (Reply 10):
Relative wind is a commonly used, if not entirely technical term.

Not by anyone I know or fly with - it's not at all correct.

This may be a regional thing...I've heard (and used) the term often, from two different aero engineering schools here in the US.

Quoting FredT (Reply 12):
Quoting A346Dude (Reply 10):
Relative wind is a commonly used, if not entirely technical term.

But... relative to what? The wing? The fuselage?

Relative to the undisturbed flow...if you run in circles that use "relative wind" as a normal term, nobody's ambiguous about what you're talking about.

Tom.


User currently offlineSwiftski From Australia, joined Dec 2006, 2701 posts, RR: 2
Reply 15, posted (4 years 7 months 1 week 5 days 12 hours ago) and read 3038 times:



Quoting Tdscanuck (Reply 14):
This may be a regional thing...I've heard (and used) the term often, from two different aero engineering schools here in the US.

Fair enough. In this case I guess I would just respectfully disagree.


User currently offlineVikkyvik From United States of America, joined Jul 2003, 9945 posts, RR: 26
Reply 16, posted (4 years 7 months 1 week 5 days 12 hours ago) and read 3035 times:
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Quoting FredT (Reply 11):
Go to the extreme. It's often a useful exercise. In a straight vertical climb, how much lift is produced by the wing?

Then draw the vector diagram. Or find it on the net, along with an explanation.

Understood and thanks for the correction.

However, would this actually be in contradiction to what I said - that with the same AOA and speed in a climb, you're producing the same lift? I would think that, in a typical climb, you'd produce less and less lift as the climb angle increased by the AOA being reduced.

Just trying to figure this out - it's been awhile.



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 17, posted (4 years 7 months 1 week 5 days ago) and read 2976 times:



Quoting Vikkyvik (Reply 16):
However, would this actually be in contradiction to what I said - that with the same AOA and speed in a climb, you're producing the same lift? I would think that, in a typical climb, you'd produce less and less lift as the climb angle increased by the AOA being reduced.

Spot on. Either AoA or airspeed would have to be reduced, and when vertical, i e no lift generated, airspeed would have to be zero or the AoA reduced to the zero-lift AoA. It's hard to determine whether you were in fact right or wrong...  Smile



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineVikkyvik From United States of America, joined Jul 2003, 9945 posts, RR: 26
Reply 18, posted (4 years 7 months 1 week 4 days 20 hours ago) and read 2921 times:
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Quoting FredT (Reply 17):
Spot on. Either AoA or airspeed would have to be reduced, and when vertical, i e no lift generated, airspeed would have to be zero or the AoA reduced to the zero-lift AoA. It's hard to determine whether you were in fact right or wrong...

Haha, no worries - I readily admit I was wrong when it comes to most practical flying situations.

Theory is fun, though. Sort of like how no one is probably going to attempt taking off on a treadmill anytime soon....

Quoting Swiftski (Reply 15):
Fair enough. In this case I guess I would just respectfully disagree.

As others have stated, it seems to be a relatively common term in the US, at least. It's certainly been drilled into my head, apparently, as I used it without even thinking about it  Smile



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineSwiftski From Australia, joined Dec 2006, 2701 posts, RR: 2
Reply 19, posted (4 years 7 months 1 week 4 days 19 hours ago) and read 2916 times:



Quoting Vikkyvik (Reply 18):
As others have stated, it seems to be a relatively common term in the US, at least.

That's fine. Like I said, I just respectfully disagree with the use of the term.


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