New trend in Design of Nose of Aircraft

[Airmann]

Hoping someone with experience in Aircraft design might be able to answer this question.

I have noticed a trend in aircraft design that is witnessed on three new cleansheet deigns of the past decade, the 787, A350, C-Series. And its a design feature that we haven't seen since the Commet or Caravelle. I'm specifically talking about the nose of the aircraft which continues downward from the cockpit windows rather than changing angle and jutting out.

Here are pictures of the Commet and the Caravelle
Commet (http://www.flickr.com/photos/zanatany2b/7230276704/)
Caravelle (http://upload.wikimedia.org/wikipedia/commons/thumb/3/3b/Finnair_Caravelle_Basle_Airport_-_April_1976.jpg/800px-Finnair_Caravelle_Basle_Airport_-_April_1976.jpg)

And here are pictures of the conventianal design of the 20th Century
B777 (http://www.flickr.com/photos/alexhorus/5809981817/)
A330 (http://www.flickr.com/photos/jimmylwh/6932821291/)

Here are the new aircraft
B787 (http://www.nycaviation.com/newspage//wp-content/gallery/boeing-787-osh11/787-nose-1.jpg)
A350 (http://airchive.com/blog/wp-content/uploads/2013/06/A350-FLAG-21.jpg)
C-series (http://img802.imageshack.us/img802/3696/dvqg.jpg)

So what is the deal? Why the sudden change back to this design for all three manufacturers? Obviously its what they have found aerodynamically most efficient, but then what on earth happened between the commet/caravelle and these newer designs? Why the switch away from this type of design and then back?

[rudderrudderrat]

Hi Airmann,

Count the windows.

Commet and Caravelle had 4 windows each side visible (I think the centre window is visible in your Commet picture), but they were all flat plates and quite small.

As the window design improved, they get bigger (hence fewer) and more curved. In order to improve the forward visibility, they are angled inwards at the bottom. Until B787 design where the windows are so huge (only two each side) and curved they can fit the nose profile perfectly.

[speedrestriction]

Embraer 170-190 was the first of recent designs to market with windshields conforming to overall nose design.

Photos: Embraer ERJ-190-200LR 195LR Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/Flybe---British/Embraer-ERJ-190-200LR-195LR/2248570/M/)

[tdracer]

Rudderrat pretty much nailed it - it's improvement in the window technology. Flight deck windows have to meet pretty demanding bird strike criteria - 35 years ago about the only way to do that with large windows was to make them flat plates. The flight deck structure and windows (what Boeing calls "Section 41) is very expensive to design and certify - as a result the 757, 767, and 777 all use the same Section 41. The design was pretty much optimized for the 767, then adapted to the 757 (that's why there is a step down onto the 757 flight deck). When the 777 came along 15 years later it was again adapted to the larger fuselage (the nose of the 777 has always had a bit of a funny profile as a result).

I wouldn't be surprised if the Airbus equivalent uses pretty much the same structure on the A330 as is used on the A300, A310, and A340 - so once again 1970's design.

For the 787, advances in technology allow big, curved, strong, windows that permitted the nose shape to be better optimized.

BTW, a little trivia - during the bird strike testing of the 767 flight deck windows, one of the birds wasn't properly aimed and 'missed high' - and went right through the aluminum skin :eek:. Given there are some pretty important electronics it that area, a doubler plate was quickly implemented into production aircraft :ok:

[clevlandHD]

Might be an urbin myth, but...

They were using the same test for the French TGV. The front windscreen just kept failing! So they called in some expert to surpervise the test (which failed yet again!). The expert's one and only recommendation was to use fresh chickens, not frozen ones. Next test was fine.

[Wizofoz]

Yes, it's a myth.

snopes.com: Chicken Cannon (http://www.snopes.com/science/cannon.asp)

[ChristiaanJ]

When Sud designed and built the Caravelle, they saved themselves a lot of time, effort and trouble by simply buying a complete Comet nose (and presumably the drawings, and a license) from De Havilland.

Hence they don't just look similar ... they are the same.

[tdracer]

Might be an urbin myth, but...

The TV show Mythbusters did an episode on this particular myth a few years back. If I recall correctly, they didn't see a meaningful difference in damage between frozen and thawed chicken.....

[Airmann]

Thanks all for the input

Yes the A300/310/330/340 Nose is one and the same. In fact I think the entire fuselage is the same design

So would it be right to summarize with these points:

--The "flat-nose" shape is aerodynamically more efficient and this has been known by designers since at least the construction of the Commet if not before

--In the past, in order to meet the required strength window panels had to be more or less flat due to limitations in glass technology. Therefore, in order to achieve the "flat nose" shape a greater number of smaller panels had to be installed, which resulted in a compromise in pilot visibility

--Designers of the era and subsequent eras decided that overall visibility was a higher priority than aerodynamic advantages achieved through the "flat nose", and hence the conventional pointed/stub noise design dominated aviation

--Recent advances in glass technology, has allowed manufacturers to design new aircraft with "Flat" noses while maintaining if not improving visibility vs. the conventional aircraft design

BTW, if you notice Airbus still opted with the 6 pane configuration while Boeing opted for 4. As a result the 787 needs an escape hatch as the cockpit windows cannot be opened. Airbus opted for 6 because of customer concerns that it would be too costly if a larger side pane needs replacement, although their initial design like Boeing was for 4.

[CallmeJB]

Don't forget the 747. Every version has had windshields that don't affect the curve of the nose. There is a slight change to the curvature at the top of the cargo door (or where it would be on a/c without a cargo door), but that is not due to windshield limitations.

And the front windshields ARE large, curved, and heavy. 280kg each, compared to 20 and 27kg for the next two windows on each side.

And even though there are six windows, none are able to open, so there is still a crew escape hatch.

[barit1]

Do not forget 411A's favorite, the Lockheed TriStar, cert ca.1970. BIG curved windscreens. :eek:

[CallmeJB]

The L1011 has a noticeable 'bump' right below the windscreen. It is not streamlined from the nose structure through the windshield.

[stilton]

RIP 411A, hope you're looking through a big curved windshield somewhere :)

[stilton]

280KG EACH for the 747 front windows ?


Amazing :eek:

[Groundloop]

Designers of the era and subsequent eras decided that overall visibility was a higher priority than aerodynamic advantages achieved through the "flat nose", and hence the conventional pointed/stub noise design dominated aviation

A lot of the requirement for improved visibilty resulted from the Grand Canyon collision where a TWA Super Constellation climbed up into the underside of a United DC-7 in good weather.

The Caravelle and Viscount required a redesign of the cockpit windows to meet the new American certification requirements.

Advances in technology such as TCAS has relaxed these rules a little - hence the deletion of "eyebrow" windows from the 737 and 717.

[flyboyike]

This is the first I hear of TCAS affecting window design....

[Chris Scott]

Hi ChristiaanJ,
Bien-sur, Sud-Est used the Comet 1 nose section for the early Carravelles. (Round about that time, the Comet 1s were permanently grounded, so perhaps there were plenty of them going cheap?) But the later Caravelles had a modified version, as can be seen in Airmann's link. I think the Comet Mk 3/4 may also have had deeper windshields than the Comet 1/2.

Considering the stunning price of the flat windshields (ignoring the side windows) on large airliners - with anti-misting elements inside the inner lamination, and anti-icing/anti-bird gold film inside the outer lamination - these large curved windshields must cost an absolute fortune. Perhaps the convex shape improves bird resistance?

I wonder how they avoid optical distortion, particularly if they are mounted less vertically than traditional designs. Any B787 pilots out there to comment?

[flarepilot]

ultimate nose, see X3 Stilleto.

I heard that the eyebrow windows were deleted on 737 because (get this) no need since no one does celestial nav anymore.

I like the eyebrow windows...they aid in many things.

[Denti]

Celestial nav in a 737? Whoever did that? Doubt it has been even used in a jurassic, much less in a classic or NG. It is simply not needed anymore as apparently it is deemed sufficient to have the much reduced viewing area and TCAS.

To be honest, i quite liked the eyebrow windows myself, especially when flying visual or circling approaches.

[haughtney1]

Celestial nav in a 737? Whoever did that? Doubt it has been even used in a jurassic, much less in a classic or NG. It is simply not needed anymore as apparently it is deemed sufficient to have the much reduced viewing area and TCAS.

They were in place as the 737, in common with the 727 shared to nose section of the original 707, I'm not sure they took star shots from the 707 that often, but I know it was used.

[Denti]

As far as i know the original 707 had a periscopic sextant through a hole in the crown of the fuselage. The eyebrow windows were there to increase the field of view as pilots were used to larger windows from pre-jet aircraft.

[Groundloop]

The eyebrow windows were there to increase the field of view as pilots were used to larger windows from pre-jet aircraft.

Are you sure. Have you looked at the size of windows on the Constellation series?

The eyebrow windows were brought in to provide a better view up - after the TWA Super Constellation climbed up into the underside of the United DC-7 over the Grand Canyon. Similarly side windows began to have that distinctive downward V so that crews had a better view down.

The advent of TCAS WAS the reason for deletion of eyebrow windows - which also resulted in quite a significant reduction in mass (an alumunium panel is a lot lighter than a window and frame) which is why retrofitting became very popular.

[inducedrag]

Wiper Blades position are also changed from horizontal to vertical

[Spanner Turner]

280KG EACH for the 747 front windows ?


No, they don't weigh THAT much !! About 150lbs (68kgs)
I'm not that strong and I've moved plenty of 'em over the years, -200's, -300's, SP's and -400's. (Mostly with a helping hand though)
Personally, one of my favourite components of the 747. Beautifully designed, constructed and very reliable. Of course originally designed and built in the '60's by draftsman without CAD or any computers- fantastic curved glass !
Below is copied from the Maintenance Manual.


FLIGHT COMPARTMENT WINDOWS - DESCRIPTION AND OPERATION

1. General
A. Six windows are symmetrically located around the forward end of the flight compartment. The windows are designated right side and left side windows No. 1, 2, and 3, as shown on Fig. 1. The corresponding left and right windows are identically opposite assemblies.
B. All flight compartment windows are of laminated construction. The No. 1 windows, which are the pilots' windshields, consist of a greater number of laminations to withstand bird impact.
C. Pressure sealing is accomplished with a gasket or rubber-beaded seal molded to the windshield frame and the No. 2 and 3 window step cuts. An aerodynamic seal is accomplished by filling the gap between window edge and fuselage skin flush with aerodynamic smoother. This also serves as a weather seal for keeping out moisture.

2. No. 1 Windows
A. The left No. 1 window is the captain's windshield. The right No. 1 window is the first officer's windshield. The left and right windshields are opposite assemblies and installations.
B. Each windshield weighs approximately 150 pounds and consists of transparent layers secured between a Z-frame and mounting ring. The layer construction allows for thermal differentials and prevent crack propagation between the structural layers. The Z-frame and mounting ring attach to the fuselage structure surrounding the windshields.
C. Two types of No. 1 windows can be installed: a five-layer soda-lime glass laminate or a five-layer tempered glass and soda-lime glass laminate. Windows with a P prefix serial number are constructed of five basic layers: a glass outer layer, an interlayer, a glass structural ply, an interlayer and a glass crew shield. Windows with a T prefix serial number are constructed of five basic layers: an outer tempered glass layer, an interlayer, a glass structural ply, an interlayer and a glass crew shield, which is a structural ply. New and replacement T prefix No. 1 windows have outer glass ply with greater thickness for added strength.
D. The inner face of the face ply is covered with a conductive coating, which is part of the antifogging and anti-icing systems. Bus bars, embedded in the windshield layers, contact the conductive surface near the top and bottom of the windshield. Two temperature control sensors are laminated into the windshield adjacent to the conductive coating. Only one control sensor is used; one is a spare that is used only if the other fails. Wires from the bus bars and sensors extend through the windshield laminations to the terminals on the inner face.


Confusion can occur when the wrong part of the manual is referenced - my job is to make sure that this doesn't happen!! 2 quotes below from the removal/installation task.
One relates to the equipment required (generic in nature), the other to the window itself.

" Equipment and Materials Required
A. Crane equipped with 40-foot boom and capable of lifting 500 pounds or equivalent
B. Mobil mechanical lift (capable of extending to a height of 35 feet) or overhead crane capable of lifting 500 pounds (i.e 227kgs) "


" CAUTION: USE CARE WHEN HANDLING THE WINDSHIELD ASSEMBLY. IT WEIGHS APPROXIMATELY 150 POUNDS AND IS A HIGH COST ITEM. "

[stilton]

Yes, I can see you wouldn't want to drop one.


Apart from birdstrike damage etc would these front windshields ever need to be replaced or would they last the life of the Airframe ?

[Volume]

they last the life of the Airframe ? That is the dream of all maintenance staff...
No. They do not last very long, on some reginal jets you may have to replace them as frequent as every 2 years. They consist of several bonded layers of glass and/or trasparent plastics, as they are subjected to UV and huge temperature changes, the adhesive ages and you get delaminations. The seals do also age and you get water ingress (no good idea if you freeze it or have an electric heating as part of thze design...). Additionally they sometimes crack, if they are installed with build in stress due to typical tolerances not accounted for in the design.
Industry is still waiting for a company which designs long lasting cockpit windows.

[CallmeJB]

Huh, I stand corrected. I checked and our AMM says the same (obviously).

I was referencing the Weight and Balance Control and Loading Manual, which has a diagram and the below table on one of the later pages:


ITEM WEIGHT B.A.
NO. BODY COMPONENTS LB/EA KG/EA IN.

1 Door 5 Main Entry Door (Left) 440 200 2261

2 Side Cargo Door 1952 885 1850

3 Door 1 Main Entry Door (Left) 452 205 464

4 Upper Deck Door 211 96 405

5 Emergency Exit Left Side (Not Shown) 22 10 370

6 No. 3 Windshield (Left & Right) 60 27 326

7 No. 2 Windshield (Left & Right) 45 20 306

8 No. 1 Windshield (Left & Right) 620 281 299

9 APU Exhaust Cone 100 45 2760

10 APU Access Door (2) 80 36 2699

11 Bulk Cargo Door 147 67 2006

12 Aft Cargo Door 742 337 1865

13 Aft Outbd Main Body Gear Doors (2) 18 8 1465

14 Aft Inbd Main Body Gear Doors (2) 103 47 1441




That's "No. 1 Windshield (Left & Right) 620 LB/each 281 KG/each 299 inches CG"

Perhaps I misread it and it's 281 KG for both the Left and Right together, but that's still a significant difference from the AMM. I wonder why.

Sorry for the formatting. I don't have enough posts yet to be able to post pictures from an album.