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Wingspan Vs. Wing Area  
User currently offlinetsugambler From United States of America, joined Jul 2010, 302 posts, RR: 0
Posted (4 years 2 months 1 week 5 days 18 hours ago) and read 8350 times:

I have a bunch of (probably stupid) questions regarding wingspan vs. wing area. I know that an increased wingspan will result in increased lift (but also presumably increased drag)... is it the same for a general increase in wing area?

The reason I'm asking is because I'm wondering about the relationship between wingspan, wing sweep, and wing area... If I'm not mistaken, a plane with a wingspan of 200 feet and a sweep of 30 degrees will likely have a smaller overall wing area than a plane with a wingspan of 200 feet and a sweep of 35 degrees--is this correct? How would the difference in wing area affect the overall amounts of lift and drag? Am I correct in assuming the wing with the 35-degree sweep will probably have a longer chord than the wing with the 30-degree sweep? What advantages/disadvantages would this possess? Assuming a 200-foot wingspan, would it be better to have the 30-degree sweep or the 35-degree sweep?

Thanks in advance!

16 replies: All unread, jump to last
 
User currently onlineSEPilot From United States of America, joined Dec 2006, 7106 posts, RR: 46
Reply 1, posted (4 years 2 months 1 week 5 days 17 hours ago) and read 8330 times:

Wing design is concerned with span, area, sweep, and aspect ratio, which is the average ratio of the span to the width of the wing. In general, the higher the aspect ratio the lower the induced drag (which on a wing is much more significant than wetted area drag), which is why sailplanes have very long, narrow wings. A long, narrow wing, however, is structurally much more difficult than a short, wide one, so most aircraft (especially large ones) must make a compromise on drag to be structurally efficient (as well as having the problem that too long wings create a lot of problems at airports.) In general, wing sweep affects speed; the more sweep the higher speed the wing can achieve before encountering mach problems. Aerodynamic advances in recent years have lessened this effect, so that higher speeds can be achieved with less sweep than before. Too much sweep also has the negative effect of reducing low speed lift, and so with high sweep you need much more effective (read complex and heavy) high lift systems.


The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlinetsugambler From United States of America, joined Jul 2010, 302 posts, RR: 0
Reply 2, posted (4 years 2 months 1 week 5 days 17 hours ago) and read 8324 times:

Would the low-speed lift difficulties of highly swept wings be much of a problem anymore, considering the high-lift devices most modern aircraft employ? Or would a higher-sweep wing still result in, say, a higher landing speed, despite the use of slats and flaps?

User currently offlineBMI727 From United States of America, joined Feb 2009, 15830 posts, RR: 27
Reply 3, posted (4 years 2 months 1 week 5 days 16 hours ago) and read 8299 times:

Quoting tsugambler (Thread starter):
How would the difference in wing area affect the overall amounts of lift and drag?

It directly effects it. More area means more drag and more lift.

Quoting SEPilot (Reply 1):
Aerodynamic advances in recent years have lessened this effect, so that higher speeds can be achieved with less sweep than before.

   Supercritical wings are pretty helpful. Plus they have good lift characteristics at low speeds.

Quoting tsugambler (Thread starter):
Assuming a 200-foot wingspan, would it be better to have the 30-degree sweep or the 35-degree sweep?

That depends entirely on what you want your plane to do.

Quoting tsugambler (Reply 2):
Would the low-speed lift difficulties of highly swept wings be much of a problem anymore, considering the high-lift devices most modern aircraft employ?

In absolute terms, probably not. But all of the tricks that one one has to employ to get rid of the problem have a weight and a cost. The ultimate solution to this issue might be variable geometry, but that is almost never employed these days because it is just too much weight, cost, and complexity.

Quoting tsugambler (Reply 2):
Or would a higher-sweep wing still result in, say, a higher landing speed, despite the use of slats and flaps?

Depends on the slats and flaps involved. On the 747 Pan Am wanted 40 degrees of sweep for a higher top speed but Boeing was leaning towards 35 for field performance. In the end they went with 37.5 degrees.



Why do Aerospace Engineering students have to turn things in on time?
User currently onlineSEPilot From United States of America, joined Dec 2006, 7106 posts, RR: 46
Reply 4, posted (4 years 2 months 1 week 5 days 16 hours ago) and read 8299 times:

Quoting tsugambler (Reply 2):
Would the low-speed lift difficulties of highly swept wings be much of a problem anymore, considering the high-lift devices most modern aircraft employ? Or would a higher-sweep wing still result in, say, a higher landing speed, despite the use of slats and flaps?

There is still a trade-off; flaps and slats improve low speed performance but the more performance gain you desire the more the flaps and slats are going to weigh. One of the marvels of the 727 was its triple slotted flaps and leading edge slats; this was a first, and enabled the 727 to have high cruise speed and exceptional short field performance. The original 747 was equally innovative, and had equally impressive performance. Aerodynamic advances have enabled higher speed with less sweep, as I mentioned before, which has made the job of high lift devices easier. Also, aerodynamic advances have enabled mechanically simpler high lift devices to be built; for example, the 747 used to have triple slotted flaps, but the 748 gets by with double slotted flaps. All swept wing aircraft to my knowledge have had high lift devices; they have improved as have all other aircraft components, but the fundamentals have not changed. Wing sweep also has structural penalties, and so anything that can be done to improve high speed performance without increasing sweep usually improves overall performance. Ultimately, every design is a compromise, and a designer has target goals of high speed and low speed performance as well as weight carrying capacity and range. There is no magic solution that gives you everything you want.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlinetsugambler From United States of America, joined Jul 2010, 302 posts, RR: 0
Reply 5, posted (4 years 2 months 1 week 5 days 12 hours ago) and read 8208 times:

Throughout this discussion, I've had two wings/aircraft in mind: the DC-10, which has a 35-degree swept wing, and the A330, which has a 30-degree swept wing. I've always found the 35-degree sweep of the DC-10/MD-11 wing to be very beautiful, but I was just wondering about the compromises it necessitates. If, in some fantasy world, McDonnell Douglas had survived as an independent manufacturer of civilian aircraft, and had produced a twin-engine derivation of the DC-10, I wonder if they would have kept the 35-degree sweep with a greater span, or if they would have moved to a lesser sweep similar to the A330?

User currently onlineSEPilot From United States of America, joined Dec 2006, 7106 posts, RR: 46
Reply 6, posted (4 years 2 months 1 week 5 days 11 hours ago) and read 8179 times:

Quoting tsugambler (Reply 5):
Throughout this discussion, I've had two wings/aircraft in mind: the DC-10, which has a 35-degree swept wing, and the A330, which has a 30-degree swept wing. I've always found the 35-degree sweep of the DC-10/MD-11 wing to be very beautiful, but I was just wondering about the compromises it necessitates. If, in some fantasy world, McDonnell Douglas had survived as an independent manufacturer of civilian aircraft, and had produced a twin-engine derivation of the DC-10, I wonder if they would have kept the 35-degree sweep with a greater span, or if they would have moved to a lesser sweep similar to the A330?

Don't forget that the A330 is a much newer design than the DC-10, and hence had the benefit of more advanced aerodynamic knowledge. That being said, I believe that the DC-10 cruises faster than the A330, which is the advantage of more sweep. The 747 is the airliner that has the greatest sweep, I believe, and it is still the fastest airliner in the sky. As BMI727 points out, supercritical wings do help get more speed with less sweep, but sweep is still important. As to your fantasy, unfortunately that is all it is, as McDonnell was unwilling to put the money into any new designs, and was only interested in making derivatives of existing designs. That's primarily why the MD-11 was such a disappointment. With that in mind, if they had made a two engined derivative it undoubtedly would have had the same sweep; if they had been willing to do the job right then everything would have been on the table.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlinetimz From United States of America, joined Sep 1999, 6902 posts, RR: 7
Reply 7, posted (4 years 2 months 1 week 5 days 10 hours ago) and read 8158 times:

Quoting tsugambler (Thread starter):
a plane with a wingspan of 200 feet and a sweep of 30 degrees will likely have a smaller overall wing area than a plane with a wingspan of 200 feet and a sweep of 35 degrees--is this correct?

"Wingspan" is the straight-line distance between the wingtips, so more sweep means a longer wing, for a given span-- so, any reason to think more sweep means less area?


User currently onlineSEPilot From United States of America, joined Dec 2006, 7106 posts, RR: 46
Reply 8, posted (4 years 2 months 1 week 5 days 9 hours ago) and read 8146 times:

Quoting timz (Reply 7):
"Wingspan" is the straight-line distance between the wingtips, so more sweep means a longer wing, for a given span-- so, any reason to think more sweep means less area?

Sweep, span, and area are all totally independent. Throw in aspect ratio and that links span and area, but sweep is still independent.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (4 years 2 months 1 week 5 days 6 hours ago) and read 8121 times:

Quoting tsugambler (Thread starter):
I know that an increased wingspan will result in increased lift (but also presumably increased drag)... is it the same for a general increase in wing area?

Area is usually an input, not an output, so if you increase span you usually reduce chord to keep area approximately constant. If you increase wingspan while holding area constant you get the same lift but less drag.

Quoting tsugambler (Thread starter):
If I'm not mistaken, a plane with a wingspan of 200 feet and a sweep of 30 degrees will likely have a smaller overall wing area than a plane with a wingspan of 200 feet and a sweep of 35 degrees--is this correct?

Not really. If it's the same plane, it will have about the same area (chord will change).

Quoting tsugambler (Thread starter):
How would the difference in wing area affect the overall amounts of lift and drag?

A key thing is that you're neglecting a free variable...angle of attack. Two very different area wings can provide the same lift by flying at different angles of attack (and hence different lift coefficients). This is a big reason why aerodynamicists tend to work in coefficients rather than absolute forces.

Quoting BMI727 (Reply 3):
More area means more drag and more lift.

Since weight is usually an input, the lift is constant. So more area means less lift coefficient (same lift), and lower drag.

Quoting SEPilot (Reply 8):
Sweep, span, and area are all totally independent.

In the sense that you can move one without moving the others, yes. But you don't generally design the wing first and then fit the airplane around it, you pick the major stuff (GW, wing loading, cruise speed) and the rest falls out of that.

Tom.


User currently offlineBMI727 From United States of America, joined Feb 2009, 15830 posts, RR: 27
Reply 10, posted (4 years 2 months 1 week 5 days 4 hours ago) and read 8090 times:

Quoting tdscanuck (Reply 9):
Since weight is usually an input, the lift is constant. So more area means less lift coefficient (same lift), and lower drag.

I should have added the caveat of having everything else equal. And of course aspect ratio figures into drag as well, so like everything else, it is a balance.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineDocLightning From United States of America, joined Nov 2005, 20334 posts, RR: 59
Reply 11, posted (4 years 2 months 1 week 5 days 3 hours ago) and read 8074 times:

Quoting SEPilot (Reply 6):

Don't forget that the A330 is a much newer design than the DC-10, and hence had the benefit of more advanced aerodynamic knowledge. That being said, I believe that the DC-10 cruises faster than the A330, which is the advantage of more sweep.

A330 has 464kt economical cruise speed. Max is 475
DC-10 has 490kt economical cruise speed. Max is 530.

I think that Airbus reasoned that the difference in flight time would be less than 10% of the total flight time, so at the longest range (~11-12 hours), a 1 hour increase in duration. And that justified a slower cruise.


User currently offlinetsugambler From United States of America, joined Jul 2010, 302 posts, RR: 0
Reply 12, posted (4 years 2 months 1 week 4 days 16 hours ago) and read 7930 times:

Thanks for all the great information... I'm a musician by training, not an engineer, so a lot of these concepts are new to me.

 


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 13, posted (4 years 2 months 1 week 4 days 16 hours ago) and read 7915 times:

I fail to see the relation of wing sweep angle and the wing area. Wing chord has a lot more to do with wing area than wing sweep. Delta wing aircraft can have a 45 degree sweep and still have more wing area than a wing with 35 degree sweep?

User currently onlineSEPilot From United States of America, joined Dec 2006, 7106 posts, RR: 46
Reply 14, posted (4 years 2 months 1 week 4 days 14 hours ago) and read 7882 times:

Quoting 474218 (Reply 13):
I fail to see the relation of wing sweep angle and the wing area. Wing chord has a lot more to do with wing area than wing sweep. Delta wing aircraft can have a 45 degree sweep and still have more wing area than a wing with 35 degree sweep?

You fail to see it because it doesn't exist. Sweep and area are totally independent; chord and span determine area.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 15, posted (4 years 2 months 1 week 4 days 13 hours ago) and read 7865 times:

Quoting SEPilot (Reply 14):
You fail to see it because it doesn't exist. Sweep and area are totally independent; chord and span determine area.


I was trying to be subtle!


User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 16, posted (3 years 11 months 2 weeks 2 days 1 hour ago) and read 6962 times:

Just to explain why modern wings can have less sweep and still keep the speed:

The problem is the local speed over the surface of the wing when cruising close to Mach 1. At about 1/3 of the chord of the wing the speed of air is at its highest in a classical wing. When an airliner flies > Mach 0,8 the local speed of air at that 1/3 chord is close to Mach 1. Drag increases abruptly at air speeds close to Mach1 (transonic drag) so you like to keep your entire wing below say M0,98 for efficiency reasons.

One way to decrease the local Mach number at the critical places is to sweep the wing (747), another way is to make the wing profile less fat at 1/3 chord and to push the max thickness further back and make more of a "whaly" profile instead of the classical drop shaped one, this is called an "aftloaded" wing profile or "supercritical" one. As pointed out a "whaly" profile also helps with lowspeed lift and also gives a more efficient structure as it's fatter over a longer part of the chord.

Modern airliner aerodynamics is much about how to shape this "whaly" profile for lower increase in local Mach numbers=low additional transonic drag at cruise speed and to gain that added benefit of higher low speed lift.



Non French in France
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