Blackbird
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Fowler Flaps Vs "Barn-Door Flaps"

Fri Aug 17, 2007 2:14 am

I got a question. What are the advantages and disadvantages of Slotted Fowler-flaps (which slide aft a lot first before drooping), and regular slotted barn-door flaps?

Andrea Kent
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Fri Aug 17, 2007 2:21 am

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".

A useful link;

http://216.239.59.104/search?q=cache...dvantages&hl=en&ct=clnk&cd=4&gl=uk

[Edited 2007-08-16 19:28:13]
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mrocktor
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Fri Aug 17, 2007 3:58 am

Quoting BAe146QT (Reply 1):
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
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Fri Aug 17, 2007 4:55 am

Oh...

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).


Andrea Kent
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Fri Aug 17, 2007 5:29 am

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.
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Fri Aug 17, 2007 6:42 am

The DC-8 and 707 were double-slotted flaps btw,

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.

It may have added a lot to the 747, but the 727 and 737 weren't particularly heavy designs and mounted them fine. Were the B-52's flaps particularly heavy?

Andrea Kent
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Fri Aug 17, 2007 4:26 pm

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.

Tom.
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Fri Aug 17, 2007 6:57 pm

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.

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Boeing used a much simpler single slotted flap design for the 747SP, still a Fowler flap but more like the 707 arrangement. It saved weight as double slotted flaps were not required.

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Blackbird
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Sat Aug 18, 2007 2:47 am

How much extra weight goes into a "slide and pivot" desigh versus an offset hinge?

Andrea
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Sun Aug 19, 2007 10:26 am

Nobody?

Andrea Kent
 
tdscanuck
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Sun Aug 19, 2007 6:52 pm

Quoting Blackbird (Reply 8):
How much extra weight goes into a "slide and pivot" desigh versus an offset hinge?



Quoting Blackbird (Reply 8):
Nobody?

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.

Tom.
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Mon Aug 20, 2007 2:30 am

So, it's not an easy yes or no answer -- not even guesstimates?

Andrea K
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Mon Aug 20, 2007 3:49 am

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.

Tom.
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Mon Aug 20, 2007 4:04 am

Understood...

Just out of curiousity... how did the VC-10 end up just slightly heavier than the DC-8 with a longer fuselage, slats, four/three spars and those huge flaps?
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Mon Aug 20, 2007 5:10 am

Quoting Blackbird (Reply 13):
Just out of curiousity... how did the VC-10 end up just slightly heavier than the DC-8 with a longer fuselage, slats, four/three spars and those huge flaps?

British engineering excellence of course!  duck 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Mon Aug 20, 2007 9:19 am

Jetlagged,

Can you describe how the British accomplished this engineering excellence?

Andrea Kent
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Mon Aug 20, 2007 8:17 pm

Hi Andrea,

Re British engineering excellence: tongue was firmly inserted in cheek.  Wink I guess the downside to this may have been cost of manufacture.

We've been here before with the VC10 structure and why it is lighter for a given strength (i.e. the milled from solid skin). I suppose that is your answer.

Jetlagged
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Mon Aug 20, 2007 10:34 pm

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.
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Tue Aug 21, 2007 3:36 am

Dear 411A,

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)

Andrea Kent
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Tue Aug 21, 2007 10:39 am

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.

DC-8?
Can't say, never flew one.
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Tue Aug 21, 2007 8:01 pm

Was it due to the Boeing 707 AND DC-8 that the runways were extended, or was it primarily one aircraft over another?

Andrea Kent
 
Blackbird
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Wed Aug 22, 2007 8:08 am

*I* wrote:

Quote:
Was it due to the Boeing 707 AND DC-8 that the runways were extended, or was it primarily one aircraft over another?

Nobody?


And were the VC-10's flaps single or double-slotted, I actually looked and I'm not sure (looks single actually)


Andrea V. Kent
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411A
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Wed Aug 22, 2007 12:30 pm

Quoting Blackbird (Reply 20):
Was it due to the Boeing 707 AND DC-8 that the runways were extended, or was it primarily one aircraft over another?

Both.
 
tdscanuck
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Wed Aug 22, 2007 7:04 pm

Quoting Blackbird (Reply 21):
And were the VC-10's flaps single or double-slotted, I actually looked and I'm not sure (looks single actually)

Definitely looks single to me:

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Tom.
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Thu Aug 23, 2007 4:16 am

Tdscanuck,

What are the VC-10's typical takeoff and landing speeds under average loads?


Andrea Kent
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Thu Aug 23, 2007 6:10 pm

Quoting Blackbird (Reply 24):
What are the VC-10's typical takeoff and landing speeds under average loads?

Not really sure. I poked around the web some and couldn't come up with a number. Anyone out there with any old performance manuals?

Tom.
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Fri Aug 24, 2007 9:30 am

Quoting 411A (Reply 17):
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.

I noticed that the C-124 Globemaster II had offset flap hinges that looked like those on the DC-10, including the fairing shape. Presumably, the C-74 Globemaster was the same. Do you know if the DC-6 had that same kind of hinge?
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Sat Aug 25, 2007 4:18 am

To 411A,

So you're saying if the DC-8's takeoff run was acceptable and the B-707's was the same (or vice versa) they wouldn't have shortened the runways? Or would they have done it anyway?

When did they decide to start stretching the runways out (like what year about)... because I'm wondering if it was *before* the DC-8 first flew. Douglas had some pretty impressive performance expectations out of the DC-8, including stall speeds that would allegedly be below that of the DC-7 at flaps 50 (90 kts) and such (once the DC-8 actually flew though it's performance to my knowledge was now nowhere near that)

Andrea Kent
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Sun Aug 26, 2007 5:52 am

Nobody knows what year they started stretching the runways out?

Andrea Kent
 
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Sun Aug 26, 2007 7:20 am

OK, sorry to interrupt, but:

Quoting Blackbird (Reply 9):
Nobody?



Quoting Blackbird (Reply 21):
Nobody?



Quoting Blackbird (Reply 28):
Nobody knows what year they started stretching the runways out?

Will you PLEASE stop doing that? Forum rule #19:

"Do not 'bump' threads back to the top to elicit a response. Where this occurs the thread will be deleted."

If someone knew the answer, they'd post it. The answer is not going to suddenly come to them because you asked "nobody?". Not to mention, it just makes you sound impatient. This is Tech/Ops - your thread isn't going to disappear off the radar anytime soon.

Thank you, and sorry for the off-topic post.
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RE: Fowler Flaps Vs "Barn-Door Flaps"

Sun Aug 26, 2007 8:30 am

I wasn't trying to just "bump it" to the top, I was just looking for an answer.

Andrea Kent

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