The title says it all. Why do we measure wing sweep angle at 25% MAC instead of leading edge? Where's the rationale behind it?
Thank you very much
Moderators: richierich, ua900, PanAm_DC10, hOMSaR
Wing sweep at 25% MAC, why?
Apology if this has been asked before.
The title says it all. Why do we measure wing sweep angle at 25% MAC instead of leading edge? Where's the rationale behind it?
Thank you very much
The title says it all. Why do we measure wing sweep angle at 25% MAC instead of leading edge? Where's the rationale behind it?
Thank you very much
-
- Starlionblue
- Posts: 21730
- Joined:
Re: Wing sweep at 25% MAC, why?
Probably to make a standard for comparison.
-
- trijetsonly
- Posts: 757
- Joined:
Re: Wing sweep at 25% MAC, why?
It is standard assumption that the center of lift is located at or near 25% MAC.
To quote Wikipedia: [For symmetric airfoils in subsonic flight the aerodynamic center is located approximately 25% of the chord from the leading edge of the airfoil. This point is described as the quarter-chord point]
With that in mind, the wing sweep angle is mostly used for aerodynamic considerations. It is logical, that the wing sweep angle at the aerodynamic center is used for that, ergo at 25% MAC.
To quote Wikipedia: [For symmetric airfoils in subsonic flight the aerodynamic center is located approximately 25% of the chord from the leading edge of the airfoil. This point is described as the quarter-chord point]
With that in mind, the wing sweep angle is mostly used for aerodynamic considerations. It is logical, that the wing sweep angle at the aerodynamic center is used for that, ergo at 25% MAC.
-
- WIederling
- Posts: 10043
- Joined:
Re: Wing sweep at 25% MAC, why?
trijetsonly wrote:It is standard assumption that the center of lift is located at or near 25% MAC.
To quote Wikipedia: [For symmetric airfoils in subsonic flight the aerodynamic center is located approximately 25% of the chord from the leading edge of the airfoil. This point is described as the quarter-chord point]
With that in mind, the wing sweep angle is mostly used for aerodynamic considerations. It is logical, that the wing sweep angle at the aerodynamic center is used for that, ergo at 25% MAC.
Does that actually stil apply for the rearloaded ( actually more evenly loaded ) supercritical profiles?
Just asking.
-
- OldAeroGuy
- Posts: 3928
- Joined:
Re: Wing sweep at 25% MAC, why?
Still close enough that there is no need to give up on the 25% standard as a basis for comparison.
Re: Wing sweep at 25% MAC, why?
Thanks guys!
So it's basically just because in average, wing lift is centered around 25%, so it is simple to compare one wings and other
So it's basically just because in average, wing lift is centered around 25%, so it is simple to compare one wings and other
Re: Wing sweep at 25% MAC, why?
The 747 has significantly higher wing sweep (well over 40 degrees) between 25% MAC and the wing root, so that one is skewed a bit. Not sure if any other current aircraft wings have a non-constant sweep angle.
Re: Wing sweep at 25% MAC, why?
SCAT15F wrote:The 747 has significantly higher wing sweep (well over 40 degrees) between 25% MAC and the wing root, so that one is skewed a bit. Not sure if any other current aircraft wings have a non-constant sweep angle.
How do you figure? If anything, the kink and the reduced trailing edge sweep would reduce the sweep there, no?
-
- WIederling
- Posts: 10043
- Joined:
Re: Wing sweep at 25% MAC, why?
LH707330 wrote:SCAT15F wrote:The 747 has significantly higher wing sweep (well over 40 degrees) between 25% MAC and the wing root, so that one is skewed a bit. Not sure if any other current aircraft wings have a non-constant sweep angle.
How do you figure? If anything, the kink and the reduced trailing edge sweep would reduce the sweep there, no?
Given as 37.5° for all 747 models : -100 to -8
The jehudi is not counted ?
Re: Wing sweep at 25% MAC, why?
WIederling wrote:LH707330 wrote:SCAT15F wrote:The 747 has significantly higher wing sweep (well over 40 degrees) between 25% MAC and the wing root, so that one is skewed a bit. Not sure if any other current aircraft wings have a non-constant sweep angle.
How do you figure? If anything, the kink and the reduced trailing edge sweep would reduce the sweep there, no?
Given as 37.5° for all 747 models : -100 to -8
The jehudi is not counted ?
I guess not, nor apparently the reduction in leading edge sweep at the outside pylon:
This also raises the question: where on the wing spanwise is the 25% MAC measured? Think about an A330/340 wing that has three trailing edge kinks: one between the aileron panels, one at the middle flaptrack canoe, and another one inboard. Add to that the wing-glove like inner slat that adds a subtle kink at the inboard pylon....
-
- trijetsonly
- Posts: 757
- Joined:
Re: Wing sweep at 25% MAC, why?
LH707330 wrote:This also raises the question: where on the wing spanwise is the 25% MAC measured?
It is measured at a calculated average wing chord. The wing root length, wing tip length and wing taper ratio go into that equation. The result is an extract of the wing with average chord length.
The basics behind this will look like this:
The result at a complex wing will look like this:
Re: Wing sweep at 25% MAC, why?
That's pretty cool, thanks for that explanation!
Who is online
Users browsing this forum: No registered users and 30 guests