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 ):rolleyes:

[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:ok:

[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.:ok:

[amanoffewwords]

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! :ok:

http://www.planetsmilies.com/smilies/party/party0005.gif

[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! :p

[BladePilot]

barit1
Ssssshhh you're giving away trade secrets:eek: (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:ok:

[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
:D
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. :ok:

[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 (http://www.youtube.com/watch?v=DwqYh995YhU)?

[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)

[Flapping_Madly]

You might at least get my bloody name right before being rude to me.
Anyway --if you are thinking of a Goldfish at a depth of 4 inches of course it would be difficult to see any forward motion but how can you be so certain that there is none? Eh? Eh? Go on Eh?:rolleyes:

[PAXboy]

Back to the point about what speed that the venerable lady can get to and she really can move ... a friend of mine spoke about when he was a 'boy pilot' (No.3) on the 744 and I quote almost verbatim but no clues as to when and where this event took place!

During a quiet period, one long night when the Cpt was sleeping, the No.2 decided to see what they could get and started to wind her up. My friend said that by increasing slowly (and taking advantage of a tailwind of around 135kts) they got the 400 to M 0.896. He said that the auto on the GE donkeys was lazy and the A/C would overspeed slightly. They had .88 selected and it started rumbling slightly and the speed was touching .90, so they wound her back for fear that the unusual feedback from the airframe might wake up the 'old man' who was in the bunk and he would not be quite so amused by it!

I understand that the co-pilot was an ex-fast jet boy (the little ones with the really point noses!) and that they achieved a ground speed of about 675kts. Not bad for 400 tons with a blunt nose. :ok:

[ProM]

Apologies, i intended to be rude to the theory you had heard, not to you. And I apologise for getting your nam ewrong.

it's still boll*cks though ;)

The reason I know is because i can disprove the theory mathematically.

[TightSlot]

Go on then, we're waiting...


:E

[Rainboe]

Paxboy, the wind only affects the groundspeed. It makes no difference to your Mach number. It a 747 cruising at M.86 and a jetstream tailwind across the Atlantic of over 200kts, we regularly would exceed 700kts groundspeed by a large margin. Back in the old days on VC10 conversions when we used to do training flights out of Shannon, some of the details were high speed runs. We would get the old girl up to M.93 with high speed buffet. Apparently watching the fin and tailplane through the periscope was a bizarre and frightening experience, moreso when watching Dutch Rolls with the aeroplane swinging into 90 degree banks either side. I have also done stalling stick push checks on a VC10. I'd had enough when the airspeed was 95 kts and angle of attack over 15 degrees. I do not enjoy that sort of thing. With years of 747 operating experience, my sense was the 747 envelope would easily match the VC10.

[arkmark]

This is all so simple.

If it were slim and visually streamlined, the ground wouldn't repel it so much just because it's ugly, and therefore it's rate of climb would be less, and hence the aircraft over all would be slower.

The repulsion effect due to ugliness is of course countered on descent by the aircraft's desire to descend because it is after all rather heavy and would prefer to sit in a single place on the ground and do nothing at all.

This is well demonstrated by the relatively more attractive airbus that is of course nowhere near as fast.

:rolleyes::rolleyes::rolleyes:

[PAXboy]

Indeed Rainboe, just me mixing in my words with those of my friend so not the best result. However, it was the info about the M.89/.90 that I wanted to add to the thread, given where it started.

Your stories of the VC10 are staggering and am very glad not to have been onboard! My first flight was on a VC10 and I think that she has the finest of lines, which were so beautifully set off by the classic BOAC paint scheme.

[ssflyer]

Thank goodness it is blunt up front - gives so much more room between 1A(me) and 1K(her indoors) so at least I get some sleep without being elbowed on a long haul overnight flight.

[PAXboy]

ssflyer, sounds like - in fact - you are up the sharp end ... :E

[ProM]

I will try Tightslot, but this forum is very short of mathmatical symbology - I blame the mods


Let us say that a between 0 and amax represents every point on the boundary of the shape.

then fx(a) represents its x coordinate and fy(a) represents its y coordinate. Then the angle of the shape at that point is

(dfx/dfa)/(dfy/dfa)

Now the presssue on each point is the same, let us say that the pressure is P. therefore the a force of PdA (should be a delta sign but we don't have one) is applied at that point, orthogonally to the contour, i.e.
(dfx/dfa)/(dfy/dfa) + pi/2 (we don't have pi symbol either and I am assuming radians and that I have chosen x and y orinettaions correctly so that it is a + not a - in that last bit)

Do you really want me to continue? :8

[barit1]

My head hertz. Think I'll go ohm. :ooh:

[TightSlot]

Impressive - and I completely agree with you - about all of that stuff you've written

[Flapping_Madly]

TightSlot

Do you really ?:eek: