Wings and cargo

from what i know

during the flight as fuel is used up, the wings become lighter as the fuel inside them is used up. perhaps wings that are lighter are better on landing? not sure…

i think its advantageous if weight distribution can be altered across the aircraft, for whatever reason. fuel can be transfered across the aircraft from tank to tank to improve performance/weight distribution/flight load relief/trim change/in flight safety etc during flight – although transfer possiblities are limited to the crew. weight in the form of fuel is taken from the wing and put elsewhere.

if there was baggage and cargo in the wing, and changes to performance/weight distribution/flight load relief/trim change/in flight safety needed to be made by moving weight from the wings, it wouldn’t be possible – you can’t move baggage and cargo in flight.

the wing is designed to bend as lift is created, but if the wing is filled or partly filled with solid items like baggage and cargo, it might affect how flexible the wing is – the fuel, being a liquid allows the wing to bend without so much restriction.

also, for lots of types of cargo, you need a pressurised space. whilst fuel is also pressurised, the pressurisation for the fuel isn’t the same for cargo. the fuel is stored at very cold temperatures, and the contents of the wing gets very cold – if cargo was stored in the wing, it would have to be heated to stop your clothes in your baggage from freezing. you would need space wasting heating systems and pressurisation systems in the wing to store baggage and cargo.

also the shape and structure of the wing probably isn’t suitable for baggage and cargo. there really isn’t much space in a wing for anyhting other than fuel – being a liquid it can get into lots of spaces – you can’t shove a solid suitcase into a tight space. there are lots of ribs and stringers forming the wing, taking up lots of the large, open spaces, so you end up with lots of smaller spaces which i should think could only be filled efficiently with fuel.

access also probably isn’t the best. how would the cargo be put into the wing? from the bottom or top? new equipment would have to be designed.

you mention engines being put on the fuselage. if the engines remain on the wing, and fuel is put elsewhere on the aircraft, i.e. not the wing, more complex fuel feed systems would be needed to take the fuel further across the aircraft to the engines. with much of the fuel on the wing, next to the engines, the fuel has to travel shorter distances so a less complex fuel feed and fuel transfer system is needed.

safety is another reason. if all the fuel is located in the fuselage, there is perhaps a greater fire hazard and danger to the passengers as the fuel is closer.

i write too much…
if im wrong on any of that, someone feel free to correct me.

thanks

I agree with all your points. Especially the pressurization didn’t come to my mind.
The best would be if the wing always keeps its weight. In some situations a loaded wing is better than an unloaden. Problems occur especially for flutter and gust loads.

Cargo pallets – most long haul aircraft are designed to take a form of standardised aircraft pallet in their lower deck. This makes loading of larger aircraft faster as baggage can be pre packaged into a set block.

Smaller aircraft, the short haul ones will not be designed to take pallets. This is because for smaller aircraft it is easier and faster to just have people throwing bags into the hold (I mean no offence to baggage handlers). Also, special equipment in needed to unload the cargo pallets… which may be in short supply, and it would probably take longer than a couple of guys unloading manually.

http://www.qantas.com.au/freight/dyn/capacity/loading

This link is for qantas freight… it’s got pics and dimensions of some standard freight pallets… if you’re interested!

The majority of civil aircraft wings have 2 main spars, one towards the front, and another towards the rear (in the outboard of the wing). Inboard, there is usually another spar which travels towards the tip at the rear of the wing which meets the rear main spar somewhere in the middle of the wing (but closer to the fuselage than the tip), this spar is used to hang the flap mechanisms and other associated things like spoilers etc. Now, the engine mounting will be attached somewhere near where the rear main spar and the spar at the rear of the inboard section of the wing meet. This is a structural strong point so on aircraft with wings mounted under the wing, the landing gear is mounted here.

For tail mounter engine aircraft, the same spars will exist in a simlar layout, the point where the rear main spar and the rear spar on the inboard section is still a structural strong point so the landing gear will be mounted there.

Do those bulky pieces fit in a belly?

Looking at just how big the useful cargo spaces in a belly are… like Boeing 717 rear cargo compartment… the height of belly is at most 99 cm from ceiling to flat floor at most 84 cm wide, in the front belly… in rear belly, there is not supposed to be a flat floor… the rear belly compartment is a total of 540 cm long… the cargo door opens inwards, and needs a clearance that extends across the aircraft centerline…

Pretty awkward place to insert big bulky pieces, isn´t it?

On the 767, 777 and 747 that we handle the standard Cargo Pallet is 125 inches long, 96 inches wide and you can go to 63 Inches high. So if you have one piece of freight that big on a pallet then i would call that fairly bulky !
You can fairly comfortably fit a Formula One type car on a pallet, and on a 767-300 you can have a long piece (Such as a Yacht Mast) up to around 146 inches long as the Pallets are loaded lengthways down the Aircraft from nose to tail, they have to be turned as they go in the door.

Do those bulky pieces fit in a belly?

Looking at just how big the useful cargo spaces in a belly are… like Boeing 717 rear cargo compartment… the height of belly is at most 99 cm from ceiling to flat floor at most 84 cm wide, in the front belly… in rear belly, there is not supposed to be a flat floor… the rear belly compartment is a total of 540 cm long… the cargo door opens inwards, and needs a clearance that extends across the aircraft centerline…

Pretty awkward place to insert big bulky pieces, isn´t it?

Yes, but you don’t catch many 717’s flying across the Atlantic!

I work in one of the Cargo sheds at Heathrow, there isnt much Cargo out there that would fit in the wings, most of the stuff we ship (mainly to the USA) is big bulky awkward pieces.

Do those bulky pieces fit in a belly?

Looking at just how big the useful cargo spaces in a belly are… like Boeing 717 rear cargo compartment… the height of belly is at most 99 cm from ceiling to flat floor at most 84 cm wide, in the front belly… in rear belly, there is not supposed to be a flat floor… the rear belly compartment is a total of 540 cm long… the cargo door opens inwards, and needs a clearance that extends across the aircraft centerline…

Pretty awkward place to insert big bulky pieces, isn´t it?

I work in one of the Cargo sheds at Heathrow, there isnt much Cargo out there that would fit in the wings, most of the stuff we ship (mainly to the USA) is big bulky awkward pieces.

Landing gear – This is located where it is on low wing, wing mounted engine type aircraft because the landing gear has to be mounted on something solid, with plenty of strong structural members. On civil airliners, the strongest part of a wing is the point where the main spars meet with the structure for mounting the engines. Here, there will be some hefty structure… so, landing gear is mounted there.

There are also guidelines as to where landing gear should be mounted. Aircraft can not have landing gear with too narrow track, as the aircraft would tip over on turns on the ground. Also, landing gear has to be placed somewhere where the angle between the ground under the centre of the main landing gear wheel (rear wheel if on a bogey) and the swept up rear fuselage is 15 degrees. The ideal point for these criteria to be met is somewhere under the wings.

Another factor is centre of gravity, the main wheels need to be behind the CoG to ensure the aircraft doesnt tip back on its tail. And, main landing gear units typicallty take 85% of the weight of the aircraft, so it makes sense to have them under the wings as then, you dont need extra structure to pass the weight to the landing gear… as the spars are already doing that for you!

Indeed. The gear needs to be just the right distance behind the centre of lift and gravity – too close and the plane can tip back on tail, too far and the plane is hard to rotate. That leaves the rear part of wing.

But I observe that the aircraft with low wing and rear engines also often have the usual tricycle landing gear. They won´t have engine mounting hardpoints on wing… how do they support the landing gear?

Landing gear – This is located where it is on low wing, wing mounted engine type aircraft because the landing gear has to be mounted on something solid, with plenty of strong structural members. On civil airliners, the strongest part of a wing is the point where the main spars meet with the structure for mounting the engines. Here, there will be some hefty structure… so, landing gear is mounted there.

There are also guidelines as to where landing gear should be mounted. Aircraft can not have landing gear with too narrow track, as the aircraft would tip over on turns on the ground. Also, landing gear has to be placed somewhere where the angle between the ground under the centre of the main landing gear wheel (rear wheel if on a bogey) and the swept up rear fuselage is 15 degrees. The ideal point for these criteria to be met is somewhere under the wings.

Another factor is centre of gravity, the main wheels need to be behind the CoG to ensure the aircraft doesnt tip back on its tail. And, main landing gear units typicallty take 85% of the weight of the aircraft, so it makes sense to have them under the wings as then, you dont need extra structure to pass the weight to the landing gear… as the spars are already doing that for you!

from what i know

during the flight as fuel is used up, the wings become lighter as the fuel inside them is used up. perhaps wings that are lighter are better on landing? not sure…

i think its advantageous if weight distribution can be altered across the aircraft, for whatever reason. fuel can be transfered across the aircraft from tank to tank to improve performance/weight distribution/flight load relief/trim change/in flight safety etc during flight – although transfer possiblities are limited to the crew. weight in the form of fuel is taken from the wing and put elsewhere.

if there was baggage and cargo in the wing, and changes to performance/weight distribution/flight load relief/trim change/in flight safety needed to be made by moving weight from the wings, it wouldn’t be possible – you can’t move baggage and cargo in flight.

the wing is designed to bend as lift is created, but if the wing is filled or partly filled with solid items like baggage and cargo, it might affect how flexible the wing is – the fuel, being a liquid allows the wing to bend without so much restriction.

also, for lots of types of cargo, you need a pressurised space. whilst fuel is also pressurised, the pressurisation for the fuel isn’t the same for cargo. the fuel is stored at very cold temperatures, and the contents of the wing gets very cold – if cargo was stored in the wing, it would have to be heated to stop your clothes in your baggage from freezing. you would need space wasting heating systems and pressurisation systems in the wing to store baggage and cargo.

also the shape and structure of the wing probably isn’t suitable for baggage and cargo. there really isn’t much space in a wing for anyhting other than fuel – being a liquid it can get into lots of spaces – you can’t shove a solid suitcase into a tight space. there are lots of ribs and stringers forming the wing, taking up lots of the large, open spaces, so you end up with lots of smaller spaces which i should think could only be filled efficiently with fuel.

access also probably isn’t the best. how would the cargo be put into the wing? from the bottom or top? new equipment would have to be designed.

you mention engines being put on the fuselage. if the engines remain on the wing, and fuel is put elsewhere on the aircraft, i.e. not the wing, more complex fuel feed systems would be needed to take the fuel further across the aircraft to the engines. with much of the fuel on the wing, next to the engines, the fuel has to travel shorter distances so a less complex fuel feed and fuel transfer system is needed.

safety is another reason. if all the fuel is located in the fuselage, there is perhaps a greater fire hazard and danger to the passengers as the fuel is closer.

i write too much…
if im wrong on any of that, someone feel free to correct me.

thanks

Additionally is it very critical to have large rooms in the wing or anything like doors. Fuel doesn’t care if its room is full with spares and ribs, but luggage does.

What about landing gear, though – do the landing gear accommodations do much harm to structural integrity of wing?

There are obvious advantages to having much of the aircraft in wing. Less bending loads by distributing the weight along the lifting surface, less parasite drag.

Airplanes have their fuel in wing tanks if they can and only have fuselage tanks if they have not enough wing volume. The engines are often mounted on wing rather than on fuselage – again, less structural bending loads. The main landing gear is accommodated in bays inside the wing if possible – having it all in fuselage is difficult.

People, however, like fuselage with windows and evacuation exits.

What about luggage? Is there any strong structural reason why cargo bays for checked luggage and other cargo cannot be made inside the wing?

Fuselage is circular, so their is lots of space unused in the fuselage. Luggage normally has low density. There is no point for storing it in the wing, especially the oprational disadvatage could not be offset by any gain in performance. Additionally is it very critical to have large rooms in the wing or anything like doors. Fuel doesn’t care if its room is full with spares and ribs, but luggage does.