smartt1982
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Questions On 737

Fri Apr 01, 2011 11:27 pm

Hello,

Hope some knowledgeable people can help me out with a few things on the 737 (particularly NGS with winglets) and some general points too. Goes on a bit but get there in the end, any info would be greatly appreciated. Thanks

1. Regarding the eyebrows on the 737 (and other types as well like MD80), what is the definite answer for the reason they were there in the first place. I have looked quite far and wide and come back with a number of different reasons for the them being there in the first place such as military design use of the 707/-80 and that the 737 inherited this from 707 fuselage (what explains reason for MD80s then?), initial certification for enough light being in cockpit (is that needed anymore?) to being useful for visual approaches (is that a coincidence or were they put in for that reason). I am aware that some companies are blocking them up to save on maintenance but why now?, has something changed?

2. ’1666537>
 
Fly2HMO
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RE: Questions On 737

Sat Apr 02, 2011 12:26 am

Quoting smartt1982 (Thread starter):
has something changed?

Gas prices. Thick glass is much heavier than the relatively thin and light sheet metal that would cover them up otherwise. The fleet wise savings in fuel and MX made by covering those things up certainly add up.
 
474218
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RE: Questions On 737

Sat Apr 02, 2011 2:26 am

Quoting Fly2HMO (Reply 1):
Gas prices. Thick glass is much heavier than the relatively thin and light sheet metal that would cover them up otherwise. The fleet wise savings in fuel and MX made by covering those things up certainly add up.


I agree with every thing you said ... except ... the eyebrow windows are not glass!
 
soon7x7
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RE: Questions On 737

Sat Apr 02, 2011 4:15 am

Quoting Fly2HMO (Reply 1):
Gas prices. Thick glass is much heavier than the relatively thin and light sheet metal that would cover them up otherwise. The fleet wise savings in fuel and MX made by covering those things up certainly add up.

Strange answer...not saying your wrong but just hazarding a guess here, I would have thought the absence of them would help keep the flight deck cooler resulting in...well a cooler flight deck requiring less energy...in addition the old style see and be seen is not as much a factor anymore as ATC structure works well.
 
boeing767mech
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RE: Questions On 737

Sat Apr 02, 2011 7:35 am

Quoting 474218 (Reply 2):
I agree with every thing you said ... except ... the eyebrow windows are not glass!

The following was taken out of the 737-800 AMM 56-11-00-010

General The left No. 4 window is the pilot's eyebrow window. The right No. 4 window is the co-pilot's eyebrow window. The left and right windows are opposite assemblies and installations. The windows install internal to the airplane. The windows have laminated transparent layers, a phenolic edge material, and weigh approximately 7 pounds. The windows use bolts to attach to the fuselage structure through the phenolic edge material.

Window Construction Each window is a laminated assembly of layers of glass, acrylic, vinyl and urethane. The structural inner glass pane to carry pressure loads. The vinyl interlayers are structural for bird impact resistance and fail-safe pressure loads. The current window manufactured by PPG has these layers: an non-structural outer glass pane, a non-structural urethane interlayer, a structural vinyl (polyvinyl butyral or PVB) interlayer, an structural inner glass pane, a structural vinyl interlayer and a non-structural cast acrylic ane (crew shield).
Never under-estimate the predictably of stupidty
 
Chamonix
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RE: Questions On 737

Sat Apr 02, 2011 12:37 pm

As from 03-Feb-2005:737-700 N201LV L/N 1650 was the first 737 without eyebrows i.e .window #s 4 and 5.
The reduction in weight is 9KG (20LBS) and reduces 300 hours of periodic inspections per airplane.
 
roseflyer
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RE: Questions On 737

Sat Apr 02, 2011 5:07 pm

I've heard a lot of reasons why they were there, but never got a good reason even from the engineers that work on windows. I have heard that back in the 1940s, eyebrow windows were useful in navigation by the moon and stars. I have also heard that they were useful for collision avoidance.

Quoting Fly2HMO (Reply 1):

Gas prices. Thick glass is much heavier than the relatively thin and light sheet metal that would cover them up otherwise. The fleet wise savings in fuel and MX made by covering those things up certainly add up.

The plug is not necessarily lighter than the original window, but it removes any maintenance requirements and saves costs that way.
If you have never designed an airplane part before, let the real designers do the work!
 
474218
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RE: Questions On 737

Sat Apr 02, 2011 5:31 pm

Quoting boeing767mech (Reply 4):
Window Construction Each window is a laminated assembly of layers of glass, acrylic, vinyl and urethane.

Your original statement:

Quoting Fly2HMO (Reply 1):
Thick glass is much heavier than the relatively thin and light sheet metal ...

Glass is the thinnest layers. With the thick part being the acrylic!
 
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HAWK21M
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RE: Questions On 737

Sun Apr 03, 2011 9:06 pm

The Eyebrow windows were there in the old days for Visual reasons to assist in Navigating during turns & avoiding collisions.

There were removed as Weight saved was Important,no need to keep the Windows #4 & 5 on both sides at a risk of needing to be replaced in case of cracking or overheat, reduce noise & unwanted sunlight from them.

regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
474218
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RE: Questions On 737

Sun Apr 03, 2011 11:50 pm

Quoting HAWK21M (Reply 8):
There were removed as Weight saved was Important,no need to keep the Windows #4 & 5 on both sides at a risk of needing to be replaced in case of cracking or overheat, reduce noise & unwanted sunlight from them.

Windows 4 & 5 are heated?
 
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HAWK21M
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RE: Questions On 737

Mon Apr 04, 2011 10:03 am

Quoting 474218 (Reply 9):

Windows 4 & 5 are heated?

Except # 3, The rest are Heated on B737s.
regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
musang
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RE: Questions On 737

Mon Apr 04, 2011 11:02 am

Quoting RoseFlyer (Reply 6):
navigation by the moon and stars. I have also heard that they were useful for collision avoidance.

I don't claim to know the reasons for the original fit, but having used 737s with and without, I believe they would be inefficient for astral navigation because of the bad optical purity/distortion, and as regards collision avoidance in airline operations, they're not in one's normal field of vision. So if a collision risk appeared in an eyebrow window, it would probably be the sudden shadow that got your attention, therefore perhaps a little late!

However given that its a throwback to the C-135 etc., it might have been useful to observe the boom when taking on fuel.

Having earlier heard the theory about improved visibility when maneouvring on visual approaches etc., I tried it. I think they're useless for that purpose. The resulting field of view (through the eyebrow) is like looking through a large tube. The pilot on the side you're turning toward (for the non-aviators amongst us) should be flying the turn, and if the other is landing it, he takes over when he can see the runway.

Our eyebrows used to spend much of their time covered up with pieces of paper to keep the sun out.

Quoting HAWK21M (Reply 10):
Except # 3, The rest are Heated on B737s.

Heated no. 3 window was an option. We had some on lease, the original operators being from the Arctic circle. Normally the No. 3 is perspex or some other plastic I know not precisely, and the heated ones are the usual complex heated window construction although they don't need to be as beefy as the front ones 1 and 2. The relevant pages are now removed from the manual so I can't look them up. They were like sitting next to radiators.

Regards - musang
 
MD11Engineer
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RE: Questions On 737

Mon Apr 04, 2011 11:13 am

Quoting musang (Reply 11):

Having earlier heard the theory about improved visibility when maneouvring on visual approaches etc., I tried it. I think they're useless for that purpose. The resulting field of view (through the eyebrow) is like looking through a large tube. The pilot on the side you're turning toward (for the non-aviators amongst us) should be flying the turn, and if the other is landing it, he takes over when he can see the runway.

Our eyebrows used to spend much of their time covered up with pieces of paper to keep the sun out.

And we had lots of problems with those windows delaminating, which meant that they had to be replaced all the time.
They then got replaced by aluminium blanks.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
JA8119
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RE: Questions On 737

Mon Apr 04, 2011 11:22 am

But I think the 737 looks nuch more beautiful with the eye brow windows!
 
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HAWK21M
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RE: Questions On 737

Mon Apr 04, 2011 9:00 pm

Quoting musang (Reply 11):

Heated no. 3 window was an option

Interesting.....Where was the Source from #1 or #2/4/5 Heat controllers?.
regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
yeelep
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RE: Questions On 737

Mon Apr 04, 2011 9:25 pm

Quoting JA8119 (Reply 13):
But I think the 737 looks nuch more beautiful with the eye brow windows!

I think they look much better without. Though I may be biased, since I've had to replace numerous delaminated ones.
 
musang
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RE: Questions On 737

Tue Apr 05, 2011 11:01 am

Quoting HAWK21M (Reply 14):
Where was the Source from #1 or #2/4/5 Heat controllers?.

Found the old pages - the source was the 2/4/5, i.e. through the "SIDE" switches.

While the UNheated no. 3 is "...two acrylic panes seperated by an air space" * , the heated version is "...glass panes laminated to each side of a vinyl core." (from the flying manual).

* - on the schematic there's a note on the R3 window "Vented to Cabin". The air gap looks about 1/4 inch.

Like the eyebrows, no. 3 has a thermal switch to maintain correct temperature, while "..temperature controllers maintain 1 and 2 at the correct temperature to ensure maximum strength of the windows in the event of bird impact. Power to 1 and 2 is automatically removed if an overheat condition is detected." (again, from the manual).

These manuals are "need-to-know" as far as we pilots are concerned but every now and again they're not deep enough - can someone tell me the diff. between a thermal switch and a temp controller in this context? I assume the former is just on and off, the latter is variable current, with an o/heat off function?

Pilots and Engineers will know that we sometimes get o'heat trips on the ground in hot weather.

Regards - musang
 
boeingfixer
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RE: Questions On 737

Tue Apr 05, 2011 2:29 pm

Quoting 474218 (Reply 2):
I agree with every thing you said ... except ... the eyebrow windows are not glass!

Your reply to boeing767mech(Reply 4):

Quoting 474218 (Reply 7):
Glass is the thinnest layers. With the thick part being the acrylic!

Your comments are contradictory.

The main structural component of the #4 and #5 windows is the inner glass layer which takes all the pressurization loads. The acrylic center layer is a fail safe component with an outer glass layer bonded to it. By weight glass is the primary component of the eyebrow windows.

Cheers,

John
Cheers, John YYC
 
yeelep
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RE: Questions On 737

Tue Apr 05, 2011 4:18 pm

Quoting Chamonix (Reply 5):

As from 03-Feb-2005:737-700 N201LV L/N 1650 was the first 737 without eyebrows i.e .window #s 4 and 5.
The reduction in weight is 9KG (20LBS) and reduces 300 hours of periodic inspections per airplane

The S/B that incorporates the change states the reasons as reduction of maintenance and weight. The total weight reduction is 6.5lbs for the complete conversion, not 20lbs. Makes me believe the primary reason was maintenance. The change was made at the request of numerous operators.
 
474218
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RE: Questions On 737

Tue Apr 05, 2011 6:56 pm

Quoting boeingfixer (Reply 17):
The main structural component of the #4 and #5 windows is the inner glass layer which takes all the pressurization loads. The acrylic center layer is a fail safe component with an outer glass layer bonded to it. By weight glass is the primary component of the eyebrow windows.

Cheers,


Not contradictory at all: Cabin windows (which are much larger than the 737 eyebrow windows) withstand full pressure loads and they contain no glass, just stretched acrylic. In fact the thin (1/4" thick) inner pane will withstand full cabin pressure.

Flight station windows normally have only a thin layer of glass (0.090" thick or less) bonded to the outer face to prevent erosion and scratching by the wipers. For some reason Boeing as added glass to the inner surface.
 
smartt1982
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RE: Questions On 737

Wed Apr 06, 2011 9:28 am

Just realised that in my first post half of it did not post, The other questions should have been,

2. Why is that aircraft with winglets have their optimum altitude much closer to their max or so I have been told on the 737NG and have seen on the FMC that is quite close, or is this normal?

3.
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Photo © JPC van Heijst - AirTeamImages

what is that tube you can see in the top right hand corner, there is on oppisite side also as well as behind standby compass, I have been told it is for drainage when aircraft has been cold soaked.

4. Not unique to 737 but what is situation with N1 at cruise etc when it goes over 100%, how does that work.

5. Again not unique to 737 but more general stuff that I should know, if your high on profile or need to lose a lot of altitude can someone just confirm that the speedbrake works because it destroys lift and creates drag and speeding up also creates drag as in 2 x speed = 4x Drag, its just that what I though the reason was that we speed up but have also been told that you speed up to catch the profile again, is that true as well or is it the same thing?

does anyone know how to delete photos from your profile, the one that you use to upload pics onto forum, mine is full and I cannot get rid of any of them to add different ones.

Many Thanks
 
musang
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RE: Questions On 737

Wed Apr 06, 2011 11:08 am

Quoting smartt1982 (Reply 20):
aircraft with winglets have their optimum altitude much closer to their max

I would think winglet aircraft have their optimum closer to the max for given conditions/load, but weight is the main determinant. On our Classics we can get an optimum equal to the max at up to medium weights.

Quoting smartt1982 (Reply 20):
what is that tube

Condensation drain from the overhead panels. Moisture would form on the inside of the outer skin in extreme cold, and drip trays channel it to one of three tubes. In all my 8 years on 737s I've never seen any water in the tubes, but then I'm in England so no extreme weather.

Quoting smartt1982 (Reply 20):
N1 at cruise etc when it goes over 100%

It might reach about 102% at high weight when its struggling to reach its max Flight Level, but when level it will be back below 90% N1. Typically mid 80s in the cruise.

Quoting smartt1982 (Reply 20):
speedbrake works because it destroys lift and creates drag and speeding up also creates drag as in 2 x speed = 4x Drag

Think of the speed brake as a means of increasing descent rate while keeping the speed under control. Sure the descent rate will increase if you speed up, and yes the drag increases as you say (making the speed brake even more effective), but you might leave yourself with the problem of having to lose the extra speed you aquired in the dive. En route, descending to meet a restriction, no problem as you can slow down in the subsequent level flight. However if you get a short cut in the terminal area, the "dirty dive" simply swaps one problem (too high) for another (too fast with no distance to slow down).

Must dash - I have to go for my 6 - monthly self-humiliation in the sim!

Regards - musang
 
smartt1982
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RE: Questions On 737

Thu Apr 07, 2011 10:56 am

Quoting musang (Reply 21):
I would think winglet aircraft have their optimum closer to the max for given conditions/load, but weight is the main determinant. On our Classics we can get an optimum equal to the max at up to medium weights.

Any help on why this is the case or any where in particular I can find out more about it?

Quoting musang (Reply 21):
It might reach about 102% at high weight when its struggling to reach its max Flight Level, but when level it will be back below 90% N1. Typically mid 80s in the cruise.

What confuses me with this is how anything can go over 100%, does it mean at ISA sea level at 100% you will get full thurst but as altitude increases it has to increase.

Many Thanks for the info, hope sim went well

Cheers
Steve
 
PITingres
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RE: Questions On 737

Thu Apr 07, 2011 12:10 pm

Quoting smartt1982 (Reply 22):
What confuses me with this is how anything can go over 100% ...

It's measured against a standard rated 100%, not a max-this-particular-engine-can-do 100%. A percent of absolute max woudn't be useful, since every engine is going to have a slightly different max-100%. So you pick a standard level that is rated as 100% across the entire fleet, and that 100% level will typically be slightly less than the absolute max you can get out of the engine.

For another example, the Space Shuttle Main Engines regularly throttle up to 104% thrust during parts of the ascent. All that means is that they are running a bit stronger than the originally designed max rated thrust. Fairly early on, the SSME's were improved to put out a wee bit more thrust than the original design, and rather than recalibrate a zillion bits of hardware and software to a new 100% scale, they are simply said to be running at 104%.
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