hypersonic
Posts: 55
Joined: Tue Oct 04, 2005 12:36 am

Winglets Versus Raked Versus Fence

Wed Apr 02, 2008 2:53 pm

Hi,
Have been curious about this for a while.
Whilst we're seeing a flurry of older aircraft being retro fitted with winglets (757 etc), as well as current designs both large & small getting winglets factored in, ( wing fences (A380).

With claimed fuel savings over a single long haul flight or accumulatively over a period of time between 2% -7%.
How do Winglets, & fences stack up compared to Raked wings, like on the 777-300er, 787 & so on?
- I've read that raked tips create even greater savings that winglets etc? - due to being simply a newer design philosophy in engineering evolution.

Are there any comparative studies between these methods of wingtip vortex /drag reduction (which is what they do?), that shows whether raked is a better method than winglets or fences or visa versa?

Just Curious
Hyper
 
tdscanuck
Posts: 8572
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RE: Winglets Versus Raked Versus Fence

Thu Apr 03, 2008 2:00 am



Quoting Hypersonic (Thread starter):
How do Winglets, & fences stack up compared to Raked wings, like on the 777-300er, 787 & so on?
- I've read that raked tips create even greater savings that winglets etc? - due to being simply a newer design philosophy in engineering evolution.

If you're going cleansheet and you have no span constraint, a raked wingtip is best. Winglet is next, fence is worst.

If you're span constrained, winglet then fence.

If you're retrofitting, you have to work within whatever structural margin the wing has left. A raked wingtip has the highest load, then a winglet, then a fence. You can only use as large as your wing will take before you have to do structural reenforcement (which will hurt the economics and performance).

Quoting Hypersonic (Thread starter):
Are there any comparative studies between these methods of wingtip vortex /drag reduction (which is what they do?),

I don't know of one document that sums it all up, although I've seen many studies on this general topic. The primary purpose of the devices is to reduce drag...vortex reduction is a product of reduced drag (since the main vortex's don't actually form until downstream of the aircraft).

Tom.
 
2H4
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Joined: Tue Oct 19, 2004 11:11 pm

RE: Winglets Versus Raked Versus Fence

Thu Apr 03, 2008 2:08 am



Quoting Hypersonic (Thread starter):
Are there any comparative studies between these methods of wingtip vortex /drag reduction (which is what they do?), that shows whether raked is a better method than winglets or fences or visa versa?

Aeroweanie covered this very question in the past:

Quoting Aeroweanie:
For a first-order analysis of the benefit from a winglet, lay it down flat as if it was a span extension. Hence, taller is better. Then, look at whether the winglet joins the wing in a sharp break or a smooth flow. Smooth is better.

Using this criteria, I'll rank the winglets (and raked tip):

1) The A3100/310/318/319/320/321/380 "winglets" are the least effective, but also increase wing bending moments the least. I have never seen a published number for how much they reduce drag (even Jupp's patent US4,714,215 says little), but I'd guess they are worth 1-1.5% drag improvement.

2) The MD-11 winglets come next. They are a direct outgrowth of Whitcomb's original designs. I have some NASA reports on the flight testing of a similar winglet on a DC-10. According to CR-3704, these winglets are produce a 2-2.5% drag reduction in cruise.

3) The Valsan/Quietwing 727 winglets are a latter Whitcomb influenced design. Coupled with a flap droop on the 727, they are reputed to be worth about 5%. The flap droop reduces wing bending moments and helps reduce wave drag, so the 5% is a mixture of effects. The winglet by itself is probably worth about 3%.

4) The 747-400 and A330/340 winglets are rather similar. They fall on the wing span extension line. I've read that the 747-400 winglets produce about a 3.5% drag reduction.

5) The 776-400ER/777-300ER/777-200LR raked tips also fall on the span extension line. They produce varying amounts of drag reduction, depending on their span. They also increase wing bending moments quite a bit.

6) The API/APB blended winglets produce better results than the span extension line indicates. The 737NG winglets are first generation and I've read that they produce about a 4.5% drag reduction. Later API/APB winglets improve on this.

2H4
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tristanhnl
Posts: 125
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RE: Winglets Versus Raked Versus Fence

Thu Apr 03, 2008 8:16 am

I have a question regarding raked wingtips on the 764ER vs 773ER / 772LR. The size of the 777 wing is significantly larger than the 764ER's and yet both have similarly sized wingtips, about 6-7 feet each. This makes the wingtips on the 764ER to comprise more of the wingspan. So does size of the raked wingtip bear any significance to its function with regard to the size of the wing itself that the wingtip is attached to?
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tdscanuck
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Joined: Wed Jan 11, 2006 7:25 am

RE: Winglets Versus Raked Versus Fence

Fri Apr 04, 2008 1:17 am



Quoting TristanHNL (Reply 3):
I have a question regarding raked wingtips on the 764ER vs 773ER / 772LR. The size of the 777 wing is significantly larger than the 764ER's and yet both have similarly sized wingtips, about 6-7 feet each. This makes the wingtips on the 764ER to comprise more of the wingspan. So does size of the raked wingtip bear any significance to its function with regard to the size of the wing itself that the wingtip is attached to?

From an aerodynamics point of view, the raked tip is basically the same as the wing itself...it's only different from a structural point of view. So, for whatever reason, the 767 and 777 teams made different decisions about where to end the wing and start the wingtip. That was likely a structural decision, not an aerodynamic one. If the lofting and planform are the same, an 80' wing with 10' tips is exactly the same aerodynamically as a 90' wing with 5' tips.

Tom.
 
tristanhnl
Posts: 125
Joined: Thu Apr 13, 2006 2:47 pm

RE: Winglets Versus Raked Versus Fence

Fri Apr 04, 2008 5:34 am

Thanks, Tom!

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