Re: An-124 and wing dihedral

Date:         16 Jun 98 02:15:25 
From: (MechB747)
Organization: AOL
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>MechB747 wrote:
>> The wings on a 747 flex  A LOT on take-off...
>> I think the 747 wings may be less stiff because of the additional  weight of
>> the engines  help to "pull" the wing down against the lifting force.
>> Aircraft that have engines mounted on the fuselage and not on the wings,
>> like 727s and DC-9s, actually have to have stronger wings because of this.
>During take off, with tanks filled to the brim, are there any general
>guidelines as to the percentages of weight each of the following
>represents ?
>			-fuel
>			-engines
>			-aircraft itself.
>			-passengers/cargo

Guidelines for loading the aircraft or engineering/design guidelines? I
don't know of any guidelines as to the percentages of weight for the
above, but I am not an engineer, either.

The engines and the airframe both are included in the Operating Empty
Weight.  There is the operating empty  weight, then  fuel, passengers
and cargo can be added to this while keeping  within the Max Take-off
weight, and weight and balance parameters, of course.   In terms of the
percentages of weight....  there are weight limitations for the
passenger floor, but this shouldn't be a problem with a passenger
aircraft... it is a factor with a freighter.

>Would these vary significantly between different aircraft types from the
>bae-146 up to an AN-124 or B747 ?

I don't know because I've never heard of these weight percentage guidlines.

>If engines are a lot lighther than the fuel, then once at cruise, the
>wings would have a lot of available strength to support the engines once
>much of the fuel has been burned since the wings would have to be
>designed to lift a whole lot more at take off.  Correct ?

I'm not exactly sure what you mean, but the wing is designed with the
strength to support the engines, full fuel, and the airframe with  max
payload plus extra strength designed into the wing for safety.  There's
no question that a having a lot of fuel in the wings will exert a
downward force to help counteract the upward pressure on the wing, just
like the engines do, but the wing is designed to have the structural
strength to take-off and cruise at the MTOW without fuel in the wings...
Technically, I don't know if you could load the aircraft to MTOW without
filling the wing tanks because the floor beams probably couldn't handle
all the weight that would be loaded onto them to get to MTOW, but the
point is that I don't think any fuel is required in the wings to help
counteract the lifting force on the wings.

The Center wing section where all of the upward pressure acting on the
wings is concentrated is VERY strong and is designed that way to keep
the wings where they belong... even without fuel in them, I think.

>Also, am I right in assuming that lift is not evenly produced along the
>length of the wing ? (eg: less lift generated near wing-tip ?).

Yes there is less lift generated at the wingtip(on a swept wing plane... I'm
referring to the 747 throughout)...because there is less surface area of the
wing farther outboard, there is less area for the airflow to "push" against.

>Would that also not contribute to the placement of engines ? You'd want the
>heavier stuff nearest to the area where the greatest lift is being
>produced, right ? Or aerodynamic considerations much more important in
>selecting placement of engines ?

That sounds very logical to me, and yes, aerodynamics probably are a more
important consideration, but I'm just an assembler, not an Engineer.

.....Any engineers out there?

Student Pilot  4.5PIC "Airline Pilot in Training", 747-400 Assembler. of Airliner Info at  /mechb747/cjt1