747400sp
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Why There Not More Airliners With Curve Windshield

Thu Jun 14, 2007 12:18 pm

In the last 30 years, there has been only a small number of airliners that have curve windshield. The A/C are the B 747, L 1011 and regional planes, the rest has strait windshield. The curves windshield look better and would have less drag, so why it took until the 787, for A/C makers to put curve windshield on large airliners?
 
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Starlionblue
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RE: Why There Not More Airliners With Curve Windshield

Thu Jun 14, 2007 12:27 pm

Does the 747 really have a curve? I think the panes are flat.

I can think of a few reasons:
- Ease of pane replacement.
- Stronger design. It does have to pass the chicken test.
- Braces are not that intrusive anyway.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
aeroweanie
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RE: Why There Not More Airliners With Curve Windshield

Thu Jun 14, 2007 1:38 pm

Flat transparencies = cheap
Curved transparencies = expensive

The 747 windshield is curved:

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Photo © Vasco Garcia



The L-1011's windshield is also curved:

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Photo © Rafal Szczypek - DC Aviation Photography



The DC-10/MD-11 windshield is flat:

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Photo © Fabrice Sanchez - Brussels Aviation Photography



The DC-9 windshield is flat:

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Photo © Rafael Cordero - AeroImagenes de Mexico



The DC-8 windshield is flat:

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Photo © Ellis M. Chernoff



The 707/727/737 windshield is flat:

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Photo © Yuxiaobin



The 757 windshield is flat:

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Photo © Tony Marlow [Airplane-Pictures]



The 767/777 windshield is flat:

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Photo © Darren Wilson



I think the 787 windshield is flat:


The A300/310/330/340 windshield is flat:

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Photo © Piotr Marek (EPGD Spotters)



The A320 windshield is flat:

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Photo © Toni Marimon



The A380 windshield is flat:

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Photo © Steven May

 
flyf15
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RE: Why There Not More Airliners With Curve Windshield

Thu Jun 14, 2007 3:51 pm

All 4 panels on the CRJ are curved...


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Legs
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RE: Why There Not More Airliners With Curve Windshield

Thu Jun 14, 2007 4:35 pm

Quoting Starlionblue (Reply 1):
I can think of a few reasons:

Can I also add to that list that Id imagine it would be much harder to keep optical distortion down to acceptable levels in a curved transparency.

Legs
 
Pihero
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RE: Why There Not More Airliners With Curve Windshield

Thu Jun 14, 2007 5:27 pm

Quoting Legs (Reply 4):
Can I also add to that list that Id imagine it would be much harder to keep optical distortion down to acceptable levels in a curved transparency.

 checkmark  ! Bingo !
Contrail designer
 
airfoilsguy
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RE: Why There Not More Airliners With Curve Windshield

Thu Jun 14, 2007 6:37 pm

Quoting AeroWeanie (Reply 2):

I think the 787 windshield is flat:

I would hazard a guess that the side windows are curved. They seem to wrap around the side.
It's not a near miss it's a near hit!!
 
747400sp
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RE: Why There Not More Airliners With Curve Windshield

Fri Jun 15, 2007 3:33 am

Quoting Flyf15 (Reply 3):
All 4 panels on the CRJ are curved...

Same for the E-170-195 model.
 
PGNCS
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RE: Why There Not More Airliners With Curve Windshield

Fri Jun 15, 2007 7:38 am

Quoting Pihero (Reply 5):
Quoting Legs (Reply 4):
Can I also add to that list that Id imagine it would be much harder to keep optical distortion down to acceptable levels in a curved transparency.

! Bingo !

Agreed. The L-1011 wins the visibility contest, hands down. (No surprise.)
 
411A
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RE: Why There Not More Airliners With Curve Windshield

Fri Jun 15, 2007 10:30 am

The visibility out of the L1011 windshield is unsurpassed...but not without some cost.
I seem to remember that a new windshield cost (left or right pane) was $72,000....over twenty years ago.
Older windshields can be re-conditioned, I believe, so the cost of these is a bit lower.

In addition, there are NO pressurization or speed restrictions with an L1011 windshield that is cracked.

TriStar, clearly a superior design.
 
XT6Wagon
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RE: Why There Not More Airliners With Curve Windshield

Fri Jun 15, 2007 11:13 am

Depends, a "2d" curve is fairly easy, and its clear from the photo that the 787 windows are atleast 2d curved.

A 3d curve can be hell given optical effects from dealing very complex curves and stretching the materials to those shapes.


That said I bet with modern computers and 20-30years more glass/plastic casting technology its getting to the point where flat isn't that much cheaper.
 
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jetmech
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RE: Why There Not More Airliners With Curve Windshield

Fri Jun 15, 2007 12:38 pm

Quoting XT6Wagon (Reply 10):
Depends, a "2d" curve is fairly easy, and its clear from the photo that the 787 windows are atleast 2d curved.
A 3d curve can be hell given optical effects from dealing very complex curves and stretching the materials to those shapes.

Out of curiosity, is it actually possible for an essentially 2d object - such as a wind shield - to be curved in 3 dimensions . I know for sure that the 747 windshield is curved in one dimension only, and it looks as if the L1011 windshield is similar. Even the 787 windshields appear to me to be curved in one dimension only. These windshields all appear to be curved across their width only. The Edgley Optica is a good example of a wind shield that is curved in 2 dimensions. What would a 3 dimensionally curved wind shield look like?


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It looks as though the 747, L1011 and 787 windshields are sections form the surface of a cone, which has curvature in 1 dimension only. The Optica windshield appears to be e section for a spherical object that is curved in 2 dimensions.



Regards, JetMech

[Edited 2007-06-15 06:03:56] Spelling and content

[Edited 2007-06-15 06:05:53]
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
747400sp
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RE: Why There Not More Airliners With Curve Windshield

Fri Jun 15, 2007 5:13 pm

Quoting AeroWeanie (Reply 2):
I think the 787 windshield is flat

Take a good look at the B787 windshild, they are curve also.  Wink
 
airfoilsguy
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RE: Why There Not More Airliners With Curve Windshield

Fri Jun 15, 2007 5:55 pm

Quoting JetMech (Reply 11):
What would a 3 dimensionally curved wind shield look like?


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It's not a near miss it's a near hit!!
 
David L
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RE: Why There Not More Airliners With Curve Windshield

Fri Jun 15, 2007 7:12 pm

Quoting JetMech (Reply 11):
Out of curiosity, is it actually possible for an essentially 2d object - such as a wind shield - to be curved in 3

As I see it, if you take a flat sheet of glass (not curved, i.e. curved in zero dimensions), you can curve both sides down (dimension 1 - cylindrical profile), then you can curve the front and rear edges down (dimension 2 - spherical profile).

To bend it in a third dimension, you could take the result from above and curve the front and rear edges in the same direction sideways to get a shape that resembles a section of the surface of a banana. Whether ot not that's ever applied to aircraft windshields, I do not know.
 
liedetectors
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RE: Why There Not More Airliners With Curve Windshield

Sat Jun 16, 2007 4:39 am

The front cockpit windows of all Gulfstreams made after the GII are curved.

http://us.airliners.net/photos/photos/4/1/1/1193114.jpg
If it was said by us, then it must be true.
 
IFEMaster
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RE: Why There Not More Airliners With Curve Windshield

Sat Jun 16, 2007 7:14 am

Three immediate reasons spring to mind:

1. Creating a curve in a piece of glass (or any translucent/transparent material for that matter) causes it to have a lens quality to a certain degree. Given the criticality of a clear and accurate field of vision, this must be a no-no. The curves, if there are any, on a 744 are minimal.

2. Curving glass weakens it as it creates natural points of pressure dispersion that are smaller and more focused than a flat pane of glass.

3. It's harder to uniformly defrost a curved piece of glass. The heating elements in the cockpit windows would have to be designed so as to ensure a uniform spread of heat from the element; something that's tough to do over convex or concave surface.
Delivering Anecdotes of Dubious Relevance Since 1978
 
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jetmech
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RE: Why There Not More Airliners With Curve Windshield

Sat Jun 16, 2007 10:21 am

Quoting Airfoilsguy (Reply 13):



Quoting David L (Reply 14):

Airfoilsguy / David L,

Excellent point you both make, the F-16 canopy is probably a good example of two "banana" shapes mounted back to back. With respect to curvature in 3 mutually perpendicular planes, the F-16 canopy is again an excellent example, and I did neglect to consider this interpretation of 3-dimensional (the most obvious one).

What I was actually thinking of at the time was 3-dimensional curvature with respect to an essentially 2-dimensional object; such as a pane of glass or perspex. I was thinking of curvature across each of the 3 dimensions of the pane, ie curvature across the width, breadth and thickness of the sheet. I was having trouble getting my mind around curvature across the thickness of an essentially 2-dimensional object, which by definition has no thickness.

I was definitely getting a bit ahead of myself here  blush .

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
atct
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RE: Why There Not More Airliners With Curve Windshield

Sat Jun 16, 2007 11:08 am

I wonder if this curvature plays into cockpit noise levels at all?

My friend an ERJ captain says their cockpits are noisy, Ive also heard of the old Hawkers are really bad. (Wind Noise).

Whereas there are planes that dont have much wind noise...

ATCT
Trikes are for kids!
 
Viscount724
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RE: Why There Not More Airliners With Curve Windshield

Sat Jun 16, 2007 11:37 am

Quoting PGNCS (Reply 8):
Agreed. The L-1011 wins the visibility contest, hands down. (No surprise.)

There was one slightly earlier Boeing type that probably gave the L1011 some serious competition in the visibility contest. 19 separate cockpit windshield panels.


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roseflyer
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RE: Why There Not More Airliners With Curve Windshield

Sat Jun 16, 2007 2:35 pm

Quoting IFEMaster (Reply 16):
1. Creating a curve in a piece of glass (or any translucent/transparent material for that matter) causes it to have a lens quality to a certain degree. Given the criticality of a clear and accurate field of vision, this must be a no-no. The curves, if there are any, on a 744 are minimal.

2. Curving glass weakens it as it creates natural points of pressure dispersion that are smaller and more focused than a flat pane of glass.

3. It's harder to uniformly defrost a curved piece of glass. The heating elements in the cockpit windows would have to be designed so as to ensure a uniform spread of heat from the element; something that's tough to do over convex or concave surface.

I think all of those are good reasons, but they can be overcome. I think the biggest reason is probably cost. It's probably more expensive. Furthermore a curved window may be heavier, which is always bad. I don't work on windows, but I do know that cost and weight are always avoided when possible and that might control the selection of the window design.
If you have never designed an airplane part before, let the real designers do the work!
 
David L
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RE: Why There Not More Airliners With Curve Windshield

Sat Jun 16, 2007 11:06 pm

Quoting JetMech (Reply 17):
Excellent point you both make

Actually, Jetmech, I was trying to agree with you.  Smile

I think some are seeing a spherical section as needing to be curved in three "dimensions" when it only needs to be curved in two. That's all I was getting at.
 
411A
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RE: Why There Not More Airliners With Curve Windshield

Sun Jun 17, 2007 2:59 am

You are quite correct, Viscount724, the Boeing Stratocruiser (which, oddly enough, I flew for a brief time) had windows galore.
A true greenhouse, which, in the summertime, flying into the sun, was HOT as heck.
Not to mention...cold in the wintertime, due to rather poor FD heating, unless of course, one was lucky enough to be flying into the sun.

In addition, the Stratocruiser was a faster cruiser than the DC-7...by 10 knots.

A truly nice airplane to fly, from the pilots point of view.
Why?
The Flight Engineer did nearly everything except land and takeoff.
Plenty of time for yours truly to enjoy a fine cigar...enroute.
10 hours enroute was not unusual.

Ahhh, the good 'ole days!
 
n710ps
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RE: Why There Not More Airliners With Curve Windshield

Sun Jun 17, 2007 5:42 am

Beleive it or not the CRJ is fairly and I say fairly quiet for the most part. A little noise but not much. In terms of a fine cigar up front ahhh how I wish I was even 25 years older sometimes.
There is plenty of room for Gods animals, right next to the mashed potatoes!
 
jetstar
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RE: Why There Not More Airliners With Curve Windshield

Sun Jun 17, 2007 11:32 am

The Gulfstream 2 and its predecessor the G1 had flat windshields while the Lockheed JetStar had a combination of flat and curved.

Changing windshields in the G1 or G2 was easy. The windshields were mounted externally to the fuselage. There are fairings that cover the outer edges of the windshield that are held on with numerous screws that go through the windshield into the airframe.


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After removing the screws the plates can be removed and the windshield lifted off. The one important item to do was on a large piece of cardboard draw an outline of the windshield so you can place the screws according to their location on the windshield because many are different lengths. Supplied with the replacement windshield was a roll of zinc chromate tape, this tape is about 1 ½ inches wide and has the consistency of putty. After all the old chromate tape is removed from the fairings the new tape is applied and once the windshield is in place the fairings are reinstalled using the screws from the cardboard. 2 mechanics can change a windshield in about 4 to 6 hours.


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On the Lockheed JetStar the main pilot and co-pilots windshields were flat while the center window was curved, and also more expensive.

Changing a windshield in the JetStar was much more difficult. The windshield is mounted internally so to get to the windshield nuts requires removing the glare shield and a lot of plastic or fiberglass interior panels. Hopefully once the window retaining screws are removed the windshield can be easily be pried out of the frame. Hopefully because you hope the person who installed it previously applied DC-4 silicon compound between the sealant on the windshield and the airframe. The sealant is Pro Seal PRC1422 and if anybody has ever used this sealant knows how strong it adheres and if no DC-4 compound was applied before that you have to bring out the heavy artillery like large blocks of wood to pound on the windshield. I saw another company’s mechanic change the center windshield on the JetStar and had to get a sledge hammer to get the windshield out because the previous mechanic did not use the silicone.

Once the windshield was installed then the sealant had to cure and it could take 12 or more hours if it was in the winter even using the fast cure sealant. Putting a heat lamp and a thermometer on the windshield to watch the temperature helped. Changing a windshield was a 2 day job.

On the DV window, which was always being opened there was no factory replacement seal on the window. On the airframe after cleaning off the old sealant, we would smear on PRC1422 sealant, place a piece of waxed paper between the sealant and the DV window and close it for a day. Then when the sealant cured, the window was opened and the wax paper removed and you were ready to go.

I loved working on the JetStar, but changing windshields and fuel boost pumps were very difficult and time consuming. Considering the Lockheed had been designing and building airplanes for almost 50 years, some engineers had the heads up their a$$es when they designed some things on the JetStar.
 
Viscount724
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RE: Why There Not More Airliners With Curve Windshield

Sun Jun 17, 2007 1:02 pm

Quoting 411A (Reply 22):
You are quite correct, Viscount724, the Boeing Stratocruiser (which, oddly enough, I flew for a brief time) had windows galore. A true greenhouse.

Thanks for the Stratocruiser memories. Very interesting. That's one type I've always wished I was able to fly on at least once. I did make it onto a few Super Connies and DC-6Bs. If you haven't seen the following site it will probably be of interest, especially the "Articles: and "Brochures" links at the bottom. Many articles from Boeing's internal PR magazines and airline brochures etc., including a few photos of the "greenhouse".
http://www.ovi.ch/b377/
 
Strathpeffer
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RE: Why There Not More Airliners With Curve Windshield

Thu Jun 21, 2007 9:45 pm

Quoting IFEMaster (Reply 16):
1. Creating a curve in a piece of glass (or any translucent/transparent material for that matter) causes it to have a lens quality to a certain degree. Given the criticality of a clear and accurate field of vision, this must be a no-no. The curves, if there are any, on a 744 are minimal.

2. Curving glass weakens it as it creates natural points of pressure dispersion that are smaller and more focused than a flat pane of glass.

3. It's harder to uniformly defrost a curved piece of glass. The heating elements in the cockpit windows would have to be designed so as to ensure a uniform spread of heat from the element; something that's tough to do over convex or concave surface.

Bingo. Also add that achieving adequate quality control in manufacturing/maintaining complex curved laminates is difficult and very costly. Mind you, it has probably been made a lot easier with high res computer designs and cumpotuer control of the manufacturing equipment.

By the way, only the central panes of the windsheilds on 757s, 767s, 777s and DC-10s are flat - which would add weight to idea 1.

PJ
Another Technical Problem?
 
aeroweanie
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RE: Why There Not More Airliners With Curve Windshield

Fri Jun 22, 2007 8:45 am

I take back what I said. All of the 787 cockpit windows are curved:
 
pizzaandplanes
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RE: Why There Not More Airliners With Curve Windshield

Sat Jun 23, 2007 12:23 pm

Maybe the curved windows don't reduce as much glare from the sun as the flat windows?
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