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747-8F Flap Buffet Problems - Delays?  
User currently offlinejreuschl From United States of America, joined Jul 2009, 549 posts, RR: 0
Posted (4 years 7 months 2 days 5 hours ago) and read 27443 times:

Flightblogger: 747-8F flap buffet could force landing gear door redesign

http://www.flightglobal.com/blogs/fl...47-8f-flap-buffet-could-force.html

I know there is a flight test thread, but this may be significant enough to warrant its own discussion.

71 replies: All unread, showing first 25:
 
User currently offlineairtran737 From United States of America, joined Apr 2004, 3705 posts, RR: 12
Reply 1, posted (4 years 7 months 2 days 5 hours ago) and read 27257 times:
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I am sure Boeing will find a quick solution to this problem and retrofit the planes as soon as possible.


Nice Trip Report!!! Great Pics, thanks for posting!!!! B747Forever
User currently offlinekl911 From Czech Republic, joined Jul 2003, 5201 posts, RR: 15
Reply 2, posted (4 years 7 months 2 days 5 hours ago) and read 27182 times:

Quoting jreuschl (Thread starter):
could force landing gear door redesign
Quoting airtran737 (Reply 1):
I am sure Boeing will find a quick solution to this problem and retrofit the planes as soon as possible

I'm sure redesigning will not be quick.....


User currently offlineLaddie From United States of America, joined Jan 2010, 610 posts, RR: 8
Reply 3, posted (4 years 7 months 2 days 5 hours ago) and read 26949 times:

Quoting airtran737 (Reply 1):
I'm sure redesigning will not be quick.....

The clock is ticking! The 747-8F is supposed to deliver by the end of the year.

Does anyone know if the 748F can get its Type Certificate with this Flaps 30 issue unresolved?


User currently offlineBMI727 From United States of America, joined Feb 2009, 15780 posts, RR: 27
Reply 4, posted (4 years 7 months 2 days 5 hours ago) and read 26873 times:

Quoting Laddie (Reply 3):

Does anyone know if the 748F can get its Type Certificate with this Flaps 30 issue unresolved?

I don't know any technicalities, but I don't see why not. Certify it without Flaps 30 and then issue an AD later.

Quoting kl911 (Reply 2):
I'm sure redesigning will not be quick....

What sort of delays did the issue with the 777 mentioned cause?



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineLaddie From United States of America, joined Jan 2010, 610 posts, RR: 8
Reply 5, posted (4 years 7 months 2 days 5 hours ago) and read 26791 times:

Quoting BMI727 (Reply 4):
What sort of delays did the issue with the 777 mentioned cause?

None that I am aware of. The 777 delivered to United right on time.


User currently offlineepa001 From Netherlands, joined Sep 2006, 4800 posts, RR: 40
Reply 6, posted (4 years 7 months 2 days 5 hours ago) and read 26797 times:
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Quoting kl911 (Reply 2):
Quoting airtran737 (Reply 1):
I am sure Boeing will find a quick solution to this problem and retrofit the planes as soon as possible

I'm sure redesigning will not be quick.....

Both statements are a bit speculative imho. We have to be a little patient and let the engineers work out a solution that will do what it is supposed to the first. That is most important. After that, we can worry about the possible consequences of this possible redesign. We should take such issues "one step at the time". I am sure the engineers will go at it this way.  


User currently onlinekanban From United States of America, joined Jan 2008, 3621 posts, RR: 27
Reply 7, posted (4 years 7 months 2 days 4 hours ago) and read 26749 times:
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Quoting Laddie (Reply 3):
Does anyone know if the 748F can get its Type Certificate with this Flaps 30 issue unresolved?

the article implies that at Flaps27 the problem doesn't exist... only the landing speed is slightly higher (and the noise envelope during reverser use larger). If the FAA determines that is acceptable while a fix is developed and retrofitted, there would be no impediment to getting the Type Certificate


User currently offlineslz396 From , joined Dec 1969, posts, RR:
Reply 8, posted (4 years 7 months 2 days 4 hours ago) and read 26696 times:

What is surprising to see is that this relatively elementary problem pops up on a derivate of a plane in service for over 40 years...

If it would have shown up on the 787, then okay, it's a new plane and you can't predict everything in wind tunnel tests, but the 747's characteristics should be fairly well known...


User currently offlineLaddie From United States of America, joined Jan 2010, 610 posts, RR: 8
Reply 9, posted (4 years 7 months 2 days 4 hours ago) and read 26652 times:

Quoting slz396 (Reply 8):
What is surprising to see is that this relatively elementary problem pops up on a derivate of a plane in service for over 40 years...

I respectuflly disagree. This airplane has not been in service for 40 years. Yes, the landing gear & doors are the same as the 744, but the wing and flaps on the 748F are all-new.

Aerodynamics is still a wild & unpredictable beast, so I am not completely surprised that this problem surfaced on the 748F. For all we know (because we aren't privy to Boeing's inside info), they may have been aware of this problem because of their CFD and wind tunnel work, but were waiting to see if the problem surfaced during flight test.


User currently offlineBMI727 From United States of America, joined Feb 2009, 15780 posts, RR: 27
Reply 10, posted (4 years 7 months 2 days 4 hours ago) and read 26289 times:

Quoting slz396 (Reply 8):
What is surprising to see is that this relatively elementary problem pops up on a derivate of a plane in service for over 40 years...

CFD still has kinks sometimes, and probably even more so when we are talking about turbulent flow around intricate parts like landing gear and landing gear doors.



Why do Aerospace Engineering students have to turn things in on time?
User currently onlineastuteman From United Kingdom, joined Jan 2005, 10106 posts, RR: 97
Reply 11, posted (4 years 7 months 2 days 3 hours ago) and read 26092 times:
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Quoting jreuschl (Thread starter):
Flightblogger: 747-8F flap buffet could force landing gear door redesign

Well, for what its worth, the A380 didn't escape unscathed in flutter testing, although (curiously, given the attention it generally got) this went largely unnoticed to the wider world. Worth a watch...

http://www.youtube.com/watch?v=ImSuZjvkATw

Quoting kl911 (Reply 2):
I'm sure redesigning will not be quick.....

Again, I'm not aware that it made any material difference to the testing programme. The inference from the above video is that they re-designed the A380 wing/body fairing pretty d qand got on with it.

Rgds


User currently offlineLaddie From United States of America, joined Jan 2010, 610 posts, RR: 8
Reply 12, posted (4 years 7 months 2 days 3 hours ago) and read 25939 times:

Quoting astuteman (Reply 11):
Again, I'm not aware that it made any material difference to the testing programme. The inference from the above video is that they re-designed the A380 wing/body fairing pretty d qand got on with it.

Good point. We should keep our perspective about the Flaps 30 issue on the 748F. Boeing has been solving issues like this for longer decades, so I trust and hope they can solve this one in time to make EIS by the end of 2010.


User currently offlineikramerica From United States of America, joined May 2005, 21544 posts, RR: 59
Reply 13, posted (4 years 7 months 2 days 3 hours ago) and read 25863 times:

I highly doubt it will take long to redesign. Also assume it's only an issue on landing.


Of all the things to worry about... the Wookie has no pants.
User currently offlineBMI727 From United States of America, joined Feb 2009, 15780 posts, RR: 27
Reply 14, posted (4 years 7 months 2 days 3 hours ago) and read 25848 times:

Quoting ikramerica (Reply 13):
Also assume it's only an issue on landing.

Unless you want to do a flaps 30 takeoff.  



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineearlyNFF From Germany, joined Sep 2007, 233 posts, RR: 0
Reply 15, posted (4 years 7 months 2 days 3 hours ago) and read 25750 times:

Quoting kanban (Reply 7):
(and the noise envelope during reverser use larger).

haha, good one! Difference in landing speeds flaps 25 vs. 30 is 5-6 kts, really not that you use more reverse for that! Main job is done by the carbon autobrakes anyway, in night ops or noise critical places you even use idle reverse!


User currently offlinepnwtraveler From Canada, joined Jun 2007, 2248 posts, RR: 12
Reply 16, posted (4 years 7 months 2 days 3 hours ago) and read 25720 times:

Jon thanks for the thorough explanation and information on the 748 turbulence problem.

I think it is very funny when you see Anetters reaction to the information and they are surprized when issues come up during flight testing. Computers can't model everything perfectly. Scale models in wind tunnels can only do so much. Mock ups are just that. People seem to think an airliner should be perfect and the whole "testing" thing is just for fun or to keep the FAA happy. While yes certification obviously is paramount and a lot of the FAA requirements have been reduced by some computer modeling, nothing replaces actual in the air and ground testing. The reactions people have can be excused if the individual is very young, or knows nothing about testing of any product or service or machine.

Food service people, often after weeks and months of laboratory and test kitchen work, roll out to a single geographic location to test if a food tastes different when produced in volume, besides testing the general public's reaction. Frequently adjustments have to be made prior to general release. Recently I was at a steakhouse that moved one block away to a new building. They went through 3 nights of dry runs before opening to the public despite 100% of the staff being trained at the old location, and all the individual areas of the new restaurant had been tested. This is food people and not a very expensive and complicated piece of technology, and testing is still required.

I think rather, if a program has no snags, then that should be the source of shock and surprize. The wingbox issue with the 787, the landing gear doors on the A380 that wouldn't deploy, and now the turbulence at the one flap setting with the landing gear door for the 748 are just some examples of tests that show up issues. These are normal! No individual component or computer testing can anticipate everything hence the need for an actual flying program.


User currently offlineearlyNFF From Germany, joined Sep 2007, 233 posts, RR: 0
Reply 17, posted (4 years 7 months 2 days 3 hours ago) and read 25719 times:

Quoting ikramerica (Reply 13):
Also assume it's only an issue on landing.

Certainly. No take off with flaps 30!


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 18, posted (4 years 7 months 2 days 3 hours ago) and read 25697 times:

Quoting BMI727 (Reply 4):
I don't know any technicalities, but I don't see why not. Certify it without Flaps 30 and then issue an AD later.

Why would an airworthiness directive (AD) be issued? AD's are issued to correct safety problems. If the 747-8F is certified without 30 degree flap setting there can be no safety implications!

Boeing could issue a service bulletin (SB) after certification that corrects the problem that allows for the use of 30 degree flaps. But the FAA would not issue an AD.


User currently onlineStitch From United States of America, joined Jul 2005, 31098 posts, RR: 85
Reply 19, posted (4 years 7 months 2 days 3 hours ago) and read 25696 times:
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Quoting earlyNFF (Reply 15):
Difference in landing speeds flaps 25 vs. 30 is 5-6 kts, really not that you use more reverse for that!

So pretty much a non-issue, then, in terms of customer operations?

Would Boeing even have to reach the 30 degree goal, then? Or could they just certify the plane for 25 degrees and adjust the FCOM accordingly?


User currently offlineKaiarahi From Canada, joined Jul 2009, 3033 posts, RR: 28
Reply 20, posted (4 years 7 months 2 days 3 hours ago) and read 25684 times:

Quoting BMI727 (Reply 14):
Unless you want to do a flaps 30 takeoff.

Tried it once on a soft-field take-off in a C172 - flap indicator was defective. Thought afterwards about entering the plane in the Olympics - long-jump.



Empty vessels make the most noise.
User currently offlineBMI727 From United States of America, joined Feb 2009, 15780 posts, RR: 27
Reply 21, posted (4 years 7 months 2 days 3 hours ago) and read 25662 times:

Quoting 474218 (Reply 18):
Boeing could issue a service bulletin (SB) after certification that corrects the problem that allows for the use of 30 degree flaps. But the FAA would not issue an AD.

You are right, it would be an SB and not an AD. I had the wrong long boring document.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineikramerica From United States of America, joined May 2005, 21544 posts, RR: 59
Reply 22, posted (4 years 7 months 2 days 3 hours ago) and read 25659 times:

Quoting pnwtraveler (Reply 16):
These are normal! No individual component or computer testing can anticipate everything hence the need for an actual flying program.

Exactly. This is why testing is needed in the first place. In this era of advanced aircraft design, it's not a matter of whether the planes will fly at all (despite what some silly A380 and 787 detractors believed), but if they will perform exactly as specified close to their limits.



Of all the things to worry about... the Wookie has no pants.
User currently offlineSEPilot From United States of America, joined Dec 2006, 6952 posts, RR: 46
Reply 23, posted (4 years 7 months 2 days 2 hours ago) and read 25583 times:

Quoting slz396 (Reply 8):
What is surprising to see is that this relatively elementary problem pops up on a derivate of a plane in service for over 40 years...

This is why they do flight testing. As BMI727 points out CFD is not perfect, especially with turbulent flow, which this will be. With a new flap design this is not surprising at all, but as others have said, Boeing has a great deal of experience in solving problems like this. I do not expect them to cut any corners; they will fix it and fix it right, and if it involves a delay, so be it. They will not certify it with 27 deg flaps and fix it later; they will fix it now.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlineearlyNFF From Germany, joined Sep 2007, 233 posts, RR: 0
Reply 24, posted (4 years 7 months 2 days 2 hours ago) and read 25513 times:

Quoting Stitch (Reply 19):
So pretty much a non-issue, then, in terms of customer operations?

I don´t know what the predicted landing speeds will be for the new wing/flap design, for comparable weights. As the max weights for the 748 are higher, the speeds will be higher anyway. At max landing weights, which is quite normal especially for cargo ops, it might become an issue. Under certain conditions, every knot counts.


25 Laddie : Noise is critical for any freighter because they need to operate at night out of noise sensitive airports (such as LHR). I suspect the 748F would nee
26 earlyNFF : It would not be an issue for arrivals, as flaps 25 landings are less noise critical during approach (less drag=less power) After landing during rollo
27 Post contains images lightsaber : This is the only part of your post I disagree with. If 27 deg flaps puts the 748F into service on time, Boeing will do it. The delta certification to
28 Post contains links and images Stitch : Looking at the September 2008 ACAP for the 747-8F, the difference between Flaps 25 and Flaps 30 is about 500 feet with a landing weight of 757,000 po
29 earlyNFF : Theory and practise (experience?) I know both sides, and sometimes they differ!
30 Stitch : Fair enough, but even as someone with zero experience in landing a 747, I'm not seeing any data points that suggest a five degree difference in flap
31 Post contains images BMI727 : So much so that I think that some 737-200s had flaps 40 deactivated for noise compliance, even though flaps 30 landings are standard. If it might cau
32 prebennorholm : I would bet that they don't want to touch the flaps at all. Most likely they will play with altered hinge lines on the gear door. And/or some strakes
33 tdscanuck : I don't understand why "Delays?" is in the thread title...this is why you do flight testing. OEM's are very very bad at predicting what will show up
34 KC135TopBoom : I don't see this as a major issue. The difference in the landing flap setting is minimal and will have a minimal effect of the landing roll out. This
35 flyingAY : The opener of the thread was referring to Jon's article in FlightGlobal. He was implying that it is at least possible putting significant pressure on
36 Stitch : Since the difference is only three degrees, I can't see how this would seriously derail the testing and certification program. Since the ACAP talks ab
37 lightsaber : Interesting option. Since they tested with and without the gear doors (I'm assuming, I haven't followed the flight testing in that detail), then Boei
38 Laddie : All new doors are not required. A simple mod to the doors is in work. I can't say exactly what it is (hint: sharp-eyed spotters will want to use a go
39 kanban : modified maybe... new design, new /revised tooling (remember there are honeycomb/composite structures) normal lead time is around 200 manufacturing d
40 Stitch : Boeing's ACAP for the 747-8 show both a Flaps 25 and Flaps 30 configuration for landing, so it must be an option. The advantage of Flaps 30 is it les
41 Post contains images lightsaber : That is my assumption. While I have every belief Boeing can find the issue and design the solution quickly... there are certain realities in manufact
42 Post contains images Rheinbote : Why does the lower half of the OB wing landing gear fold diagonally at this weird 30 deg (or so) angle to begin with?
43 Post contains images kanban : won't disagree that it can be done... suggest that something this size would fall more into a modification than a total redesign. Having been a proce
44 474218 : Buffeting causes fatigue, fatigue leads failures, failures cause delays, delays cost money. The buffeting has to be corrected.
45 kanban : agreed, and a/c are designed to take a fair share of it... I'm not saying don't worry about it, I'm saying if it is outside the normal flight envelop
46 Stitch : I would think it wouldn't be a problem on any runway at a field that routinely sees operations with 747-400 family aircraft, to be honest. Even with
47 Rheinbote : That goes without saying. But why is the lower half hinged diagonally across the door resulting in a negative angle of attack for that piece of struc
48 474218 : Did anyone report on how the flight tests went sans door?
49 Post contains images Stitch : There was no buffeting.
50 Post contains images 474218 : Simple cheap fix then, leave the door off.
51 tdscanuck : Very few. Landing distance calculations are based off a particular autobrake setting...although it's an economic factor on brake life, bumping up one
52 Post contains images lightsaber : And the cruise range penalty would be. Very well written post. Lightsaber
53 kanban : I second that...nice to get a clear concise answer..
54 Laddie : To get out of the way of water & debris kicked up by the wing landing gear during takeoff and landing? The angled door is a red herring, so don't
55 747classic : Being away for three weeks (no internet, that's a real holiday), I just read about the 747 buffet problems at flaps 30. I wondered that nobody mention
56 kanban : good catch, I'm so used to posters using generic terms and unidentified acronyms, I let it pass. Perfect.. find and treat the cause not the symptom..
57 Laddie : I'm hearing rumors today that this week's issue is cracking found on a bunch of stringers on the upper half of the fuselage just aft of the hump. Some
58 ikramerica : Would assume those could be reinforced while a permanent fix is made. Not exactly a hard place to reach on this plane. The stretch on the 748F is beh
59 Laddie : That is correct. The 160" stretch on the 747-8 Freighter is just aft of the hump (the supposed problem area). The 160" stretch on the 747-8 Intercont
60 ikramerica : That's what I thought. Another screw up between Boeing and supplier of not designing enough strength into a critical area.
61 Laddie : Don't jump to that conclusion. I'm hearing that the drawings are fine, but the stringers were not manufactured correctly, and no one in Quality Contr
62 Stitch : I saw two 747-8F's parked to the side of the Boeing Flight Test Center at BFI about 60 minutes ago, but there was no work being done around them - ju
63 Laddie : OK. Thanks for the info. I heard RC501's stringers were inspected at MWH on April 5. That and what I posted earlier are all I know on this subject. I
64 AA777223 : That's interesting. I've seen diagrams of the stretches with plugs both fore and aft of the wings, However, if the back of the hump has now been move
65 Post contains links 747classic : Laddy, pls. post this rumors on : Official 747-8 Flight Tracking Thread (by moderators Feb 19 2010 in Civil Aviation) to keep all the issues discover
66 Post contains images Stitch : The 747-8 freighter, like the 747-400 freighter, has a much smaller hump than the passenger version. Both the 747-8 and 747-8 freighter have a 4.1m f
67 Laddie : That is correct. My previous post was incorrect. The back of the hump ends at the same spot over the wing. The 160" stretch makes the hump and the fu
68 AA777223 : OK, I see what you were saying I know. I know the freighter has the smaller hump. I thought you were implying that the 747-8I's hump would extend fur
69 Laddie : In spite of the 220" stretch to the fuselage, most folks have a hard time telling the difference between the 747-400F and 747-8F at a casual glance. T
70 tdscanuck : Giant chevrons on the engines are something of a giveaway. Tom.
71 Post contains images Laddie : For you, me, and most A.net-ers, that is true. But, alas, the vast majority of the airline-traveling public are lucky if they are cognizant of how ma
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