BAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0 Reply 1, posted (6 years 4 months ago) and read 16353 times:
The shape created by slotted flaps deploying maintains the boundary layer longer and are less prone to stalling.
::EDIT:: To expand on this, the air passing under the wing passes through the slot and OVER the flap, increasing lift at lower airspeeds. You can therefore operate a heavy aircraft much slower. I didn't know this before, but that's what's meant by "blown flaps".
As far as I know, "blown flaps" are flaps that are in the path of engine driven air, for example in prop wash.
The advantage of slotted flaps (folwer flaps are flaps with multiple slots) is a higher lift coeficient (due to a better attached boundary layer, as BAe146QT mentioned). The disadvantage is that the mechanism is complex and heavy.
There is really no reason to use a completely unslotted "barn door" flap, as the mechanism for a single slotted flap is not signifiacntly more complex. Fowler flaps, however (such as the double slot flaps on the E170 or the triple slot flaps on the 737 (only some versions?)) are a trade-off.
Blackbird From , joined Dec 1969, posts, RR: Reply 3, posted (6 years 3 months 4 weeks 1 day 22 hours ago) and read 16253 times:
Well I meant -- what are the advantages and disadvantages in a DC-8/DC-9 style flap (droops, extends a little, droops, extends a little etc) and what are the advantages and disadvantages an A-310/L-1011/B-727/B-737/B-747 style flap (which slides out a LOT with little deflection FIRST, then droops and extends, then droops and extends).
N231YE From , joined Dec 1969, posts, RR: Reply 4, posted (6 years 3 months 4 weeks 1 day 21 hours ago) and read 16241 times:
Simple/plain flaps are less complex, requiring less maintenance and weight, at a cost of efficiency.
Fowler flaps in operation are better, in that they increase the wing area and as mentioned above, and the creation of a slot allows for air to flow above the airfoil, thus improving lift. However, they are heavier and more complex. In fact, the 747's triple-slotted Fowler flaps added nearly 12,000lbs of weight, which Boeing deleted in favor of a Barn Door flap for the -SP.
By the way, I believe barn door flaps are still a single slotted Fowler flap. I know the 707 and DC-8 had them, and it looks as if there is a slot. I'll double check this.
Tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81 Reply 6, posted (6 years 3 months 4 weeks 1 day 10 hours ago) and read 16135 times:
Quoting Blackbird (Reply 3): what are the advantages and disadvantages in a DC-8/DC-9 style flap (droops, extends a little, droops, extends a little etc) and what are the advantages and disadvantages an A-310/L-1011/B-727/B-737/B-747 style flap (which slides out a LOT with little deflection FIRST, then droops and extends, then droops and extends).
Sliding aft a lot first without dropping increases your wing area significantly (and hence total lift) without much increase in drag...this is great for improving your takeoff roll.
Drooping increases lift even more but your drag goes up significantly as well...this is great for landing but not so good for takeoff.
DC-8/DC-9/707 all had low bypass engines with lousy acceleration, so their takeoff rolls aren't that good anyway...that might be why they didn't bother with flaps that have a lower drag configuration. Also, on a DC-9 (or any other low-wing airplane) you've got less room to fit in the flap mechanisms and fairing so simplicity is definitely in you favour there.
Quoting Blackbird (Reply 5): How much extra weight would a "slideback" flap design (it slides back a lot before drooping adding lots of area even before any major increase in camber is added) add on a DC-8 or 707-style design.
The profile that the flap goes through for any Fowler flap is defined by the flap track and carriage...the actuator just pushes the flap aft and the track/carriage kinematics determine the profile it takes as it moves. So, if you already have a Fowler installation, changing the flap deployment profile just means a different flap track (and maybe carriage), which shoudn't change weight much.
However, if you've got a simple hinged flap, going to a Fowler flap would add significant weight because you need to add the drive system, tracks, carriages, etc., etc.
Jetlagged From United Kingdom, joined Jan 2005, 2508 posts, RR: 24 Reply 7, posted (6 years 3 months 4 weeks 1 day 8 hours ago) and read 16120 times:
Quoting Mrocktor (Reply 2): As far as I know, "blown flaps" are flaps that are in the path of engine driven air, for example in prop wash.
Normally a blown flap is where engine bleed air is fed into the flap slot and blown over the flap upper surface to further increase lift. Great until the engine quits. The F-104 had this system, as did the Buccaneer, amongst others. Where the engine exhaust blows over the flaps the effect is similar, if more localised.
Quoting Blackbird (Reply 3): Well I meant -- what are the advantages and disadvantages in a DC-8/DC-9 style flap (droops, extends a little, droops, extends a little etc) and what are the advantages and disadvantages an A-310/L-1011/B-727/B-737/B-747 style flap (which slides out a LOT with little deflection FIRST, then droops and extends, then droops and extends).
They are all Fowler flaps. The Douglas design is lighter because it uses a simple offset hinge, rather than complex flap tracks, but is less effective because the area increase is smaller. The Douglas flaps on the DC-9, DC-10, MD-80 and MD-11 aren't really "barn doors", unlike the 707 and DC-8 which are slide and pivot designs.
It's a very hard question to answer because there's a lot going into the weight other than just the basic design. Choice of materials, flap size (load), aerodynamics, etc. Probably the only way to do it would be to weight the mechanisms for a similar sized flap of each configuration. That type of data typically isn't in anything but the most detailed engineering drawing and most of us probably don't have access to that for a 707 or DC-8. I actually do have access to those drawings and I'm not sure that I could find it.
Tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81 Reply 12, posted (6 years 3 months 3 weeks 5 days 23 hours ago) and read 15826 times:
Quoting Blackbird (Reply 11): So, it's not an easy yes or no answer -- not even guesstimates?
Complete wild-ass guess...a track/carriage system is 2-8x heavier than the equivalent offset hinge. I haven't been up close with an offset hinge design but, in concept, it's pretty simple. I have been up close and personal with the track/carriage systems and they have some very stout pieces of metal associated with them. Not particularly large components, but heavy (there are very large cantilever loads associated with that design and there's no really light way to take that).
This is right at the edge (okay, beyond the edge) of my ability and engineering knowledge for this particular system so take all of the above with a huge grain of salt.
411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 17, posted (6 years 3 months 3 weeks 5 days 4 hours ago) and read 15711 times:
If we look back in time, and look at the design of the flaps on the DC-4 versus DC-6, we find the following...
DC-4 used a rather basic design flap, and altho it served its purpose, it was not very complicated...you could, for example, compare it to the single slotted 'barn door' variety.
DC-6 however, was another animal alltogether.
Altho the wing on the DC-6 was the same basic airfoil section (DC-7 too, oddly enough) with additional strength built in for the heavier acft and higher cruise speeds (90 mph) expected, the flaps were of a semi-Fowler design and were also double slotted.
This design added (approximately) 745 pounds (1.4%) to the DC-6 structure weight, but provided superb airflow for landing and takeoff.
Blackbird From , joined Dec 1969, posts, RR: Reply 18, posted (6 years 3 months 3 weeks 4 days 23 hours ago) and read 15665 times:
Would the DC-8 have worked better if it had a VC-10 style track and pivot type design (double-slotted) with the thrust-gate (like how the DC-8 had)? Would the increase in weight (any ideas how much) badly offset the performance gain?
Because I remember hearing the DC-8's low speed performance was expected to be drastically lower than it turned out
BTW: How much more expensive is a track and pivot versus a offset-hinge? (Any guesses)
411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 19, posted (6 years 3 months 3 weeks 4 days 16 hours ago) and read 15623 times:
The VC-10 was specifically designed (generally) to a BOAC specification, in order to operate from shorter runways, some hot and high.
It was thought at the time by Vickers that runways at some of these airports would not be extended to allow for the B707 to be used...but of course, they were extended, so the specific performance requirements of the VC-10 could not be fully utilized by other operators.
Hence, not all that many were sold.
The same could be said of the Trident, except that it had a superb triplex autoland system, very useful for BEA.
Blackbird From , joined Dec 1969, posts, RR: Reply 21, posted (6 years 3 months 3 weeks 3 days 19 hours ago) and read 15515 times:
Quote: Was it due to the Boeing 707 AND DC-8 that the runways were extended, or was it primarily one aircraft over another?
And were the VC-10's flaps single or double-slotted, I actually looked and I'm not sure (looks single actually)
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