The front end of Jumbos

[Flapping_Madly]

Sorry for this stupid question as I'm sure Boeing know what they are doing but why is the front of a Jumbo so blunt? Would a sharp pointy end be better at slicing through the air and save fuel. (You've spotted this is a Pub discussion have'nt you )

[Load Toad]

I have no technical knowledge on these matters but IIRC:
- The 747 was originally going to have some role as a [military] transport with a nose which could be swung open
- For some reason the shape of the 747 anyway allows it to fly faster.

By all means try sharpening one if you find a willing partner.

[BladePilot]

The classic B747 'Jumbo' shape is cleverly designed to allow the aircraft to fulfill a number of roles. The pilots were positioned way up high to allow 'front loading' of the cargo carrying variant of the series (as LoadToad suggests there was originally a military heavy lift role envisaged for the B747) Putting the flightdeck up high allowed the addition of a fairly simple hinged nose arrangement (hinged at the top) as all the control cables, wiring looms etc ran from the flightdeck along the spine of the aircraft and therefore allowed for a very cavernous cargo area which could be accessed very easily through the huge hinged nose you'll find that the diameter of the door space was such that it allowed maximum use of the cargo space behind it. In the passenger carrying variants (Built without a hinging nose!)the airlines often used the forward cabin for their first class product, the upper deck being very small in the early 747's often wasn't used for passengers. In later variants Boeing recognised the appeal of flying 'up top' so the first (stretched) 'big tops' appeared and were an instant success for airlines.
Believe it or not despite it's shape the good old B747 can actually cruise a wee bit faster than some other modern aircraft on the market these days, the B747/400 will happily sit at .85Mach (nearly 570mph) not bad for a big bird with a blunt nose!

enjoy your pint

[Seat62K]

My understanding (from childhood memory) is that Boeing submitted its design for a military transport and lost to Lockheed, which won the contract. The Lockheed 'plane was the C5A Galaxy.

Boeing then had a design but no customer. Until, that is, it was converted to civilian use, became the 747 and Pan Am signed the first order.

Perhaps I'm wrong e.g., maybe the initial design was for either civilian or military use.

The rest, as they say, is history.

[point8six]

Seat 62K - not quite right; after Lockheed won the military contract with the C5 Galaxy, Boeing were approached by Juan Trippe of PanAm to design a large passenger jet to replace the B707/DC8. Joe Sutter was put in charge of the project and decided from day one that the aircraft would be suitable for both passenger and freight roles - hence the front-hinged freight-door and the elevated cockpit. While much of the technology was used from Boeing's failed military project, the 747 design was new and quite different from the military one, (which was more like the Antonov 124 in looks).
As an aside, the 747-400 likes flying at .86! (unfortunately the beancounters prefer a more sedate speed).
You should get at least 2 pints for this.

[amanoffewwords]

Originally Posted by point8six

the aircraft would be suitable for both passenger and freight roles - hence the front-hinged freight-door and the elevated cockpit.

...always wondered why Concorde has a hinged nose - it all becomes clear now!

[barit1]

While from a side view the Jumbo nose appears blunt, it's also quite narrow and thus low drag. Boeing published cruise control tables up to M.88 on the 747-200 - I cannot verify if later models go that high.

And the reason the cockpit is so high? It's so (in the early days...) the Captain could sit on his wallet!

[BladePilot]

barit1
Ssssshhh you're giving away trade secrets (Pilots don't need big wallets now because they pack plastic not cash!)

[Seat62K]

Ah, that explains why the flight deck is not so high up on more modern designs!

[Flapping_Madly]

Thank you folks--very interesting.
I can't help wondering however why someone has not had the brain-wave of a pointy end to save fuel. Someone must have had a brain-wave over winglets for example. Or with such a big thing would any fuel saving be marginal?
By the way am I right in thinking Jumbos don't fly very high. On trips to New Zealand I have never seen a height greater than 11277 metres. Is there a technical reason for this?
Please/thanks

[BelArgUSA]

An amazing fact about the 747-100/200s, compared to the 747-300s...
Despite the "blunt" appearance of the 300, that aircraft has better Cx than the regular shape 100/200s, and the economy cruise is generally Mach .005 higher in the 300s as compared to the 100/200... "Coke bottle aerodynamics".
xxx

Happy contrails

[Pax Vobiscum]

Flapping_Madly - 37,000 feet is a fairly typical cruising altitude for large passenger jets, chosen for optimal economic performance. The 747SP (a shortened, long range variant of the 'classic' jumbo) liked to cruise at 41,000 feet. There's not too many 747SPs left, but you'll sometimes find the 737-800 at that height today.

[barit1]

When the 767-200 was introduced on US domestic routes (1983-84) it often was shot right up to 41,000 not because of theoretical cruise efficiency, but because they had the sky to themselves up there and encountered minimum ATC delays. That factor outweighed any "book" fuel advantage.

[ProM]

In general the most aero-dynamic (or hydro-dynamic shape) is a rounded front and a tapered rear (this is not true when close to speed of sound).

If you look carefully a lot of objects are like this, right down to fish which have round fronts and taper off to a thin tail. Also not only are wings like this, so are keels and rudders on yachts etc.

Race cars are not because downforce is more important, but low speed high efficiency vehicles (pedal driven endurance tests, minimum energy vehicles etc) are the same shape

[Load Toad]

In general the most aero-dynamic (or hydro-dynamic shape) is a rounded front and a tapered rear

Yeah - I knew a girl like that.

[barit1]

You mean - like THIS?

[SLF3b]

Same principle as the bulbous bow on a ship? The drag along the fuselage is determined by where the displaced air re-attaches to the fuselage. With a point the airflow follows the fuselage all the way along. With a curve the airflow re-attaches further back. So a curve has lower weight than a point and no appreciable affect on drag.

Says he, feeling less confident by the second......

[ProM]

SLF

The bulbous bow of a ship is another example. in fact i believe that the flow over a bulbous front end is actually more likely to stay "attached" than with a sharp point. Thus whilst a sharp point provides very slightly lower drag in perfect conditions, in the real world where gusts of wind, downdrafts, steering inputs etc can all cause small chnages in the flow direction, the bulbous shape is more efficient

[Flapping_Madly]

I recall reading that fish were blunt at the front but tapered to the tail because this shape presents more surface to receive the water pressure behind the widest point than the surface in front of the widest point so the water pressure squeezes the fish forwards.

If you see what I mean. But this can't work in the upper atmosphere can it? There is little pressure.

I'm off to lie down now.

[ProM]

Best do flapping wildly, because that explanation is I am afraid boll*cks. It ignores the fact that though there may be more surface behind teh widest points, the pressure is more lateral in direction. Overall they pressure all cancels out if you consider vectors - until the fish starts swimming of course

p.s. if you do not believe me, put something fish shaped (or triangular) in still water. Does it move in the direction of the widest end?
(The answer will be no)