happy-flier From Canada, joined Dec 1999, 290 posts, RR: 0 Posted (3 months 2 weeks 5 days ago) and read 4555 times:
The 707 and all its variants, and the DC-8, did not have external flap fairings like we see on most jets developed from the 747 onward (with the notable exception of the 747SP). The DC-9, DC-10, MD80 and ATR (just to give a few examples) all have under-slung fairings that are of a different design. But all the later Boeings and all Airbuses retain the long, rearward protruding flap fairings. They're totally ubiquitous!
What advantage do the fairings produce? Wouldn't it be aerodynamically advantageous to have a clean underside to the wing, as the 707 has?
Answers would be most appreciated.
May the wind be always at your back . . . except during takeoff & landing.
tdscanuck From Canada, joined Jan 2006, 11032 posts, RR: 72 Reply 1, posted (3 months 2 weeks 4 days 23 hours ago) and read 4525 times:
Quoting happy-flier (Thread starter): The 707 and all its variants, and the DC-8, did not have external flap fairings like we see on most jets developed from the 747 onward
The 707 and DC-8 also had atrocious takeoff performance, partly due to the engines and partly due to poor high-lift systems.
Quoting happy-flier (Thread starter): The DC-9, DC-10, MD80 and ATR (just to give a few examples) all have under-slung fairings that are of a different design.
The DC-9/MD-80/ATR all use offset hinge flap mechanisms, which take up a lot less space, hence the different fairing. I can't speak for the DC-10.
They hide the flap tracks and carriages. Large high lift systems, which came in with the second generation of jets in North America (post 707/DC-8) to provide jet service to shorter runways, require big tracks, carriages, and actuators. You need to provide aerodynamic cover for all that stuff. As a side benefit, done properly, the fairings help smooth out the area dropp off at the wing trailing edge which helps with transsonic drag...they're sort of double-duty Kuchemon carrots.
Quoting happy-flier (Thread starter): Wouldn't it be aerodynamically advantageous to have a clean underside to the wing, as the 707 has?
Yes, if you can get away with it. If you can design a suitably effective high lift system that doesn't need drop hinges or tracks hanging from the underside of the wing the OEM's will beat a path to your door.
MD11Engineer From Germany, joined Oct 2003, 12568 posts, RR: 68 Reply 2, posted (3 months 2 weeks 4 days 21 hours ago) and read 4425 times:
Quoting tdscanuck (Reply 1):
The DC-9/MD-80/ATR all use offset hinge flap mechanisms, which take up a lot less space, hence the different fairing. I can't speak for the DC-10.
Viscount724 From Switzerland, joined Oct 2006, 18467 posts, RR: 17 Reply 3, posted (3 months 2 weeks 4 days 17 hours ago) and read 4277 times:
Quoting tdscanuck (Reply 1): Quoting happy-flier (Thread starter):
The 707 and all its variants, and the DC-8, did not have external flap fairings like we see on most jets developed from the 747 onward
The 707 and DC-8 also had atrocious takeoff performance, partly due to the engines and partly due to poor high-lift systems.
The VC-10 has fairly large flap fairings for a narrowbody, and very good short runway performance. I think the runway being used in the first photo in the last row below (long-closed RAF Gatow in Berlin) was only 6,000 ft.
1. They provide a smooth aerodynamic surface for the flap mechanisms. If a fairings is not present there is a drag penalty.
2. They protect the flap mechanisms from FOD and dirt.
3. They do double duty as area ruling devices as tdscanuck mentions. This is particularly apparent in modern aircraft like the 380. This helps with drag by smoothing out the drop in cross-sectional area around the trailing edge.
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
prebennorholm From Denmark, joined Mar 2000, 5810 posts, RR: 56 Reply 6, posted (3 months 2 weeks 4 days 16 hours ago) and read 4229 times:
Quoting 2H4 (Reply 5): That's one thing I've always admired about Gulfstream - their wing has no flap track fairings at all:
Then you may also admire the Caravelle. And the DC-6. They have the same simple hinged flaps. That was the norm in those distant days 50 years after the Wright Brothers.
There is, however, a good reason why the Gulfstream has those simple flaps. It has a very generous wing area, making it able to cruise comfortably well above most other traffic. That wing area comes in handy for take-off and landing performance, but it would be a disadvantage for efficient high speed cruise at medium altitude.
Always keep your number of landings equal to your number of take-offs, Preben Norholm
737tdi From United States of America, joined Sep 2007, 317 posts, RR: 0 Reply 8, posted (3 months 2 weeks 4 days 11 hours ago) and read 4101 times:
Alot of good inputs here. Remember though that Douglas flaps were hydraulically driven at each flap station. Boeing decided it was better to run the flaps off of one flap actuator/motor using tracks and torque tubes for a more efficient high lift flap system. Douglas and other manufacturers did not use this system. On the DC8/DC9/MD80 it's about putting boards into the airflow to slow/lift, Boeing discovered decades ago that you could do this with alot less weight and components via the single drive system.
They are relatively easy to work on and oh so reliable. I love MC/D but Boeing got it right with their system. JMO.
PapaChuck From United States of America, joined Aug 2010, 112 posts, RR: 0 Reply 10, posted (3 months 2 weeks 4 days 1 hour ago) and read 3858 times:
It all boils down to the function and complexity of the flap system. With a simple hinge/fowler flap, the actuators are typically small enough to be contained in the wing structure itself. It's a mechanically simple system that does need any bulky equipment.
In the case of an offset hinge like the DC-9/10, the pivot point is at the bottom of the fairing. This allows the flap to move aft as it deploys in a fowler-type movement. It's a rather simple mechanical action that requires the hinge to be below the wing, hence the tall, narrow flap fairings.
Boeing, beginning with the 727, and continuing on with the 737 and 747, introduced the mechanical wonder/nightmare of a triple-slotted flap system. There are three separate flap panels, all of which move independently of each other. To further complicate things, the flap panels first move aft with little deflection to increase wing area. Then, all three panels deflect down to increase drag. A rather bulky mechanism is required to move these three panels in a complex motion, hence the need for a large aerodynamic fairing to cover it.
Quoting happy-flier (Thread starter): did not have external flap fairings like we see on most jets developed from the 747 onward (with the notable exception of the 747SP).
vikkyvik From United States of America, joined Jul 2003, 6514 posts, RR: 29 Reply 12, posted (3 months 2 weeks 3 days 20 hours ago) and read 3684 times:
Quoting PapaChuck (Reply 10): Then, all three panels deflect down to increase drag.
Although they do increase drag, particularly at higher deflections, they're also increasing the camber of the wing, thereby increasing lift.
The spirit of Massachusetts is the spirit of America!
faro From Egypt, joined Aug 2007, 1327 posts, RR: 0 Reply 13, posted (3 months 2 weeks 3 days 9 hours ago) and read 3559 times:
Quoting tdscanuck (Reply 1): As a side benefit, done properly, the fairings help smooth out the area dropp off at the wing trailing edge which helps with transsonic drag...they're sort of double-duty Kuchemon carrots.
This is the one I have always had trouble with: look at the size of the 767 or 777's flap track fairings with respect to the A330/A380's. Airbus tends to have numerous and *huge* fairings compared to Boeing. I have always wondered why the glaring differences between the two manufacturers (probably the only significant design difference between them).
Something in that trans-sonic drag arguement is not adding up between A and B...I once heard that in the 767's case there was a very compact and proprietary Boeing flap track mechanism patent that was not available to Airbus. Any substance to that?
tdscanuck From Canada, joined Jan 2006, 11032 posts, RR: 72 Reply 14, posted (3 months 2 weeks 3 days 5 hours ago) and read 3503 times:
Quoting faro (Reply 13): look at the size of the 767 or 777's flap track fairings with respect to the A330/A380's. Airbus tends to have numerous and *huge* fairings compared to Boeing.
There is indeed a difference. Airbus uses a different actuation mechanism on some aircraft (e.g. the 737 uses ballscrews while the A320 uses rotary arms) so that may be a contributor. Airbus also tends to go single-slot where Boeing goes multiple, which is going to change the mechanicals and the loading...I'm not sure how that translates to flap fairing size but I suspect it's more than a coincidence.
Quoting faro (Reply 13): I once heard that in the 767's case there was a very compact and proprietary Boeing flap track mechanism patent that was not available to Airbus. Any substance to that?
News to me but it's certainly possible. However, Airbus have done an excellent job of getting sufficient performance out of a considerably simpler flap mechanism so I really have no idea what's taking up all the space inside those fairings.
It may be an aerodynamic trade and Boeing and Airbus are just pursuing the same goal from opposite design directions; Airbus wing-to-body fairings are noticeably different than Boeing fairings as well. That may play a role in the flap fairing area.
bikerthai From United States of America, joined Apr 2010, 1088 posts, RR: 3 Reply 15, posted (3 months 2 weeks 2 days 22 hours ago) and read 3396 times:
Quoting tdscanuck (Reply 1):
Yes, if you can get away with it. If you can design a suitably effective high lift system that doesn't need drop hinges or tracks hanging from the underside of the wing the OEM's will beat a path to your door.
It's called morphing wings . . . but we are not there yet . . .
Quoting Starlionblue (Reply 7):
Having the engines in that position means they can serve for area ruling aft of the wing, an advantage airliners with underwing engines do not have.
So if they get the morphing wing perfected, then how would they solve the area rule? With composites, you can now have variable diameter fuselage tube!
nonfirm From United States of America, joined Sep 2005, 434 posts, RR: 0 Reply 16, posted (3 months 2 weeks 2 days 20 hours ago) and read 3357 times:
Quoting 737tdi (Reply 8): Boeing discovered decades ago that you could do this with a lot less weight and components via the single drive system.
I would say that the Boeing System is a bit heavier compared to the MD-80 Flap system.The Boeing system has Drive Tracks,Jackscrews,Transmissions,Torque Tubes, 3 Fairings per side (737-400) , A Drive Motor and a 3 pieces Flap that is in 2 pieces.The worst flap I have ever worked on are 737 classic flaps that triple slotted flap system is quite a project plus it has problem with the spindles that can crack out.The MD-80 System had just a few components out on the wing a couple of Hyd Actuators but it did have a large pulley system in the cargo pit.
Starlionblue From Greenland, joined Feb 2004, 15102 posts, RR: 69 Reply 17, posted (3 months 2 weeks 2 days 19 hours ago) and read 3331 times:
Quoting bikerthai (Reply 15): So if they get the morphing wing perfected, then how would they solve the area rule? With composites, you can now have variable diameter fuselage tube!
Well, ideally the fuselage should be have varying diameter like on the Constellation. However the aerodynamic advantages for an airliner are obliterated by the increase in design and manufacturing cost, especially if you consider airliners with different lengths for different versions.
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
dh106 From United Kingdom, joined Jun 2005, 621 posts, RR: 2 Reply 19, posted (3 months 2 weeks 2 days 8 hours ago) and read 3208 times:
Quoting Max Q (Reply 18): The 747 SP is different, it 'only' has double slotted trailing edge flaps, avoiding the complexity and bulk of a triple system.
I believe they're just single slotted, as they use the '4 bar' mechanism rather than tracks or offset pivots.
...I watched c-beams glitter in the dark near the Tanhauser Gate....
daviation From United States of America, joined Sep 2008, 318 posts, RR: 0 Reply 20, posted (3 months 2 weeks 1 day 23 hours ago) and read 3090 times:
I flew as a passenger fairly recently on a few 747-400s. I had forgotten how the wing appears to come undone during approach and landing.
One of the comments above reminded me of the days when I was on many DC-10s. When those flaps were actuated, the hydraulics were so loud it made everyone's heart stop. That's how I recall it anyway.
One question: I noticed on the 747 that the ailerons are on the mid-section of the wing, perhaps even closer than that to the fuselage. But I was on an A-321 a few weeks ago and the ailerons were way outboard. What is the reason for locating them so differently? I was under the (obviously misguided) impression that if the ailerons are way out on the wing, it contributes to bending.
bikerthai From United States of America, joined Apr 2010, 1088 posts, RR: 3 Reply 21, posted (3 months 2 weeks 1 day 22 hours ago) and read 3079 times:
Quoting Starlionblue (Reply 17): obliterated by the increase in design and manufacturing cost,
This was true with sheet metal skin. But with fiberplaced fuselage barrel, most of the additional cost would be Engineering cost. The fiber placed mandrel would be only slightly more complicated. The curvature would not be significant enough to impact tooling.
Different lengths for different version? That's where the Engineering cost comes in. More work for us Design Monkey
KAUSpilot From United States of America, joined Jan 2002, 1934 posts, RR: 43 Reply 22, posted (3 months 2 weeks 1 day 22 hours ago) and read 3070 times:
Quoting daviation (Reply 20): One question: I noticed on the 747 that the ailerons are on the mid-section of the wing, perhaps even closer than that to the fuselage. But I was on an A-321 a few weeks ago and the ailerons were way outboard. What is the reason for locating them so differently? I was under the (obviously misguided) impression that if the ailerons are way out on the wing, it contributes to bending.
The 744 has two sets of ailerons on each wing, a pair outbourd at the more conventional location and a pair of smaller ailerons inboard. The outboard ailerons are locked out at high speed and serve to improve low speed handling while the lockout functions prevents over controlling at high speed. If I recall correctly, the outboard ailerons are locked out when all the flaps are retracted and the speed is greater than 238 Knots indicated airspeed/.53 mach. The reason is that the 747 is a much heavier aircraft than the A320 (thus the extra set of ailerons) and needs to displace more air to achieve acceptable roll rates. The size of the 747's flaps probably also makes it difficult to make one set of ailerons big enough for all flight regimes. These would be better questions for an engineer to answer, however.
geezer From United States of America, joined Aug 2010, 715 posts, RR: 1 Reply 24, posted (3 months 2 weeks 1 day 12 hours ago) and read 2920 times:
All this talk about different types of flaps and ailerons has reminded me of something I have wondered about for many years; engine placement on wings of 4 engine aircraft; I suppose I had better start another thread.
Charley
A home without a cat is just a house
25 Starlionblue: Hehe yeah. Please do though. It's an interesting subject!
26 western727: Intriguing. Sorry to go OT but why does the 310 have only inboard ailerons? Seems counterintuitive for low-speed flight. And how does the B-52 "turn"
27 Starlionblue: The 310 uses spoilers to augment roll control at low speed. the B-52 uses spoilers exclusively. Since its wings are so bendy ailerons would simply le
28 soon7x7: Was working on a G-lV the other day and took these...The pix demonstrate the medicinal design in the flap drive mechanism, all actions are in the win
29 western727: Thanks for the bit on the B-52; such makes sense. I wonder about the "why" on the 310's lack of outboard ailerons. Searching the photo database and s
30 musang: The A300-600 has no outboard ailerons, the roll being augmented by the spoilers, but earlier A300s had outboards. A reason why the outboards are locke
31 western727: In regards to the A306 doing away with the outboard ailerons vs. the original A300 - thank you for that tidbit. Now, WHY did Airbus do away with them
32 2H4: Wow, that's great. I've never seen those mechanisms up close. Thanks for taking the time to post those shots.
33 737tdi: Looks alot like a Boeing jackscrew, of course does not have the segmented flap mechanisms on the track (carriages and toggles) but very similar in de
34 keta: There are many examples where actuators don't fit into the wings, and not only for flaps. For example, here's the rudder actuator for the Concorde: Vi
35 nonfirm: That is not the actuator for the rudder it is the tail bumper.
36 Starlionblue: keta is referring to the rudder actuator on the side of the fin. It is in the middle of the diagonal stripes. Since it didn't fit in the fin they put
37 nonfirm: Sorry I should have looked at the pic.Here is another pic of the pfcu for the lower rudder. [Edited 2012-02-22 15:40:29]
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