Why, until recently, were smooth nose sections not popular?

Question

Why, until recently, were smooth nose sections not popular? By smooth I mean without a break between the nose and windshield. (The question focuses on airliners.)

Seeing the Starliner (left) and DC-7 (middle), which were vying for the transatlantic market, with their almost perpendicular windshields, I wonder if they were more slanted and followed the nose -- like the Commando (right), for example, which proves it was possible -- enough drag reduction would have helped their payloads on windy days.

The Commando style windshields only made a comeback with the 787 and A350 -- the 747 gets close, but like the 75/76/777, there is still a break.

Manufacturing difficulty:
I don't think that's the reason (unless proven otherwise), because the noses are already smooth. The nose could start from the top surface of the fuselage, and cut-outs to be made where the windshield panels would go.

Windshield materials:
Plexiglas was used early on and on wartime aircraft with compound curvatures.

---

^{Image sources:}

• https://i.sstatic.net/PCZge.jpg
• https://airandspace.si.edu/multimedia-gallery/dc-7jpg
• http://www.historynet.com/going-commando.htm

Answer 1

Because it's bloody difficult to make the curved shapes out of the materials used until recently, with the technology available at the time.

The few aircraft that had it in the past generally were very expensive and labour intensive to build, compared to competitors, and therefore not economically successful. Now, with improved manufacturing techniques and materials, plus the rising cost of fuel, it's becoming ever more viable and more such are appearing.

Answer 2

First, the Commando wasn't unique in having a 'stepless' cockpit design- the Boeing 307 Stratoliner, for example had them. Other military aircraft too had them, due to a few reasons like pressurization and the excellent visibility (He 111, Ju 388, B-29 Superfortress, the list goes on... etc) they offered.

While it's true that having this design improves the aerodynamics of the aircraft, there are other things to consider.

• More complex a shape, more difficult is it to manufacture usually (which increases cost). Aircraft design, then as is now is a trade-off. The designer has to select a nose design based on trade-offs between various factors like aerodynamics, ease of manufacture, location of LRUs etc.

In fact, during original design of Lockheed constellation, multiple nose configurations were considered, which included completely faired nose (along with 'bug-eye' types). That the conventional arrangement was finally selected indicates that the designers decided that the drag reduction offered wasn't worthwhile.

• Another problem with curved windshields is that presence of relective and refractive errors. While I'm not sure if this problem was encountered in C-46, the assertion by Willis L Wells, Chief Engineer, Airplane Division, St. Louis Plant, Curtiss-Wright Corp that,

In order to achieve ideal visibility characteristics for the pilot, the entire nose and cockpit of the CW-20E was redesigned to incorporate a flat glass windshield with negligible refractive and reflective errors. At the same time, the field of vision was increased.

indicates that this was definitely a consideration.

The present scenario is different- better materials and manufacturing techniques are available- not only for the windshields reducing errors and quality issues but also the fuselage shell, enabling optimizing structures for better aerodynamics.

I believe the Commando erred on the side of the aerodynamics- it had fairings between the top and bottom fuselage halves, which were later deleted, as flight tests showed they provided no improvement in performance. According to George A Page, Chief Engineer St Louis Airplane Division of Curtiss-Wright Corporation, the C-46 had not only stepless cockpit, but also 'tunnel type' cowlings to reduce drag.

Answer 3

Blow-molded canopies (like the acrylic one on the P-51D) were relatively expensive in the late WWII and early post-War periods when the early-modern airliners were designed. Cost is an important factor in airliner design, and was even in 1950.

Additional cost factors (contributing to the high cost of deeply or compound curved windshields) are that the materials (acrylic, aka Plexiglas or, by preference for its impact resistance, polycarbonate aka Lexan) were new, cutting edge materials in the early 1950s. Further, molding these materials in compound curves had a high drop-out rate due to distortions forming in the sheet material during heat forming.

Add to the above the need for very large panes to achieve required levels of visibility when the pilot is looking through at a sharp angle, and the difficulty of controlling reflections with strong sunlight falling on the (otherwise useless) panel area under the extended windscreen area, and you have a serious practicality issue with the sharply angles windscreens required for a Commando style.

Answer 4

Part of the reason for the nose shape was a radar dish being installed there.

A new Bendix or RCA weather radar could be installed in the nose, which changed the nosecone shape.

Answer 5

Aircraft windshields usually need to be serviced more often than other parts of the nose, because any debris (hail, birds etc) might cause scratch marks or fractures that obstruct the view and might cause a decompression. 'Bulky' windshields are easier to operate than curved ones.

Also, as pointed out in the blog post below [1], airliner front windows were also used for emergency escape purposes, as on China Airlines flight 120 incident [2]. A350, that has curved windshield, includes an additional escape hatch for pilots. The windshield itself is too small to be used as an escape route. Small surface area is preferred to mitigate damage to the windshield.

[1] http://bloga350.blogspot.com/2012/12/a350-xwb-first-curved-windows-airbus-is.html

[2] https://en.wikipedia.org/wiki/China_Airlines_Flight_120