Commercial aircraft versus military freight planes

Why is it that modern Airforce cargo planes, like the C5 and C17, cannot fly further than commercial long-haul aircraft like the Boeing 747?

 

why would they need to?

Plus for every 1lb of fuel carried to get you that bit further reduces the carrying capacity.

As such it's easier to optimise the range vs capacity based upon the distribution of your air bases.

FNG

 

Just spank up a tanker alongside the cargo plane and range problems are solved.

 

So the more fuel you carry the less payload you carry, and military cargo planes are aiming for payload.

 

no, they are aiming for a balance based on capacity and range.

Like all designs a comremise has to be made as weight affects performance and as such you have to cap the wieght at the design stage to ensure that what you make is practical and useful.

FNG

 

Maybe because of long-range deliveries to foreign USAF bases?

 

The engines and the aerodynamics are essentially the same, which then makes it a question of how much fuel you can (or want) to carry. Which in turn brings it back to the range-fuel-payload tradeoff. With world wide bases and aerial refueling, USAF seems to value payload more than base range. Note that the 747 started life as the Boeing entry in the C-5 competition anyway.

 

To further the weight debate, a C-17 would be carrying more weight than even a fully loaded 747, right? (one C-17 hauls about 4 times as much as the Herc....and twice as fast....W00t, we got 4 of 'em.)

 

A C-17 is also capable of dropping M1 Abrams tanks in mid flight, while the B-747 isn't even capable of carrying such a tank.

Unfortunately, when making the C-17 to a more capable tactical transport, the USAF had to sacrifice a bit from the strategic end of the aircraft and the aircraft now suffers from the limited strategic range.

edit: Oh buggers, I was spewing misinformation around. LAPES system for C-17 is rated currently for only 19.000 Kg, thus clearly, a C-17 can not drop Abrams mid flight

 

No it can, it's just actually called a bomb! It could possably need some field repairs as well once they dig it out of it's 30 foot deep crater

FNG

 

Heh, aye, noticed how silly it actually would be. Altough, you should have refreshed before posting and notice the edit part at the end of the post

edit: For some reason, my deluded mind was thing something like this which is shown around 15 seconds in to the film.

 

Actually the B747-400F has a much higher payload than the C-17

Payload - Tons (Metric tonnes)
B747-400F = 154 (140)
C-17 = 85.5 (77.5)
C-130J = 21 (19.1)
C-5B = 135 (122.5)

Speed (Mach)
B747-400F = 0.85M
C-17 = 0.76M
C-130J = 0.59M
C-5B = 0.77M

Range (Nautical Miles)
B747-400F = 4450nm
C-17 = 2400nm
C-130J = 1800nm
C-5B = 6320nm

Cost (US dollars)
B747-400F = $168M
C-17 = $236M
C-130J = $48.5M
C-5B = $179M

 

Yup, higher overall load, but not as concentrated.
C-17 etc have strengthened floors, an M1 for instance couldn't be carried in a stock B747 because the "ground pressure" would punch it through the floor.

 

The C-17 was designed to be a direct replacement for the C-141. It does that job very well. It has a much stronger airframe and better lift capability.

One of the roles that the C-141 had to do was that of carrying paratroopers. I don't think a 747 would be as well suited for this.

 

Unless Boeing makes some modifications including a back hatch for the paratroopers to jump out.

But seriously, a B-747 400ER can fly 7,670 nm nonstop, the new B-747-8 can fly 8,000 nm, and an extended-range B-777 can fly over 9,000 nm. Why do passenger haulers fly farther than freighters?

 

Presumably because passengers take up less room. And because they only need a 7 foot-high ceiling, whereas frieght planes need a nice tall hold.

 

If anything probably the other way around. I'd imagine passengers and luggage on the whole weigh less per cubic metre of space required (Including leg-room, aisle space, luggage) than cargo which can be palletted quite densely, so I'd imagine a full passenger plane will typically be carrying less weight than a full cargo hauler of equal size.

 

Sorry - I'll make myself clearer...

Passengers & luggage do weigh less, which is a big bonus.

also, some cargos (like vehicles) need to have a big tall/wide space inside the plane to fit into, whereas an area to hold passengers can be subdivided up however you want, allowing more room to add useful things like fuel in your plane. Saying that, I doubt they'd put the fuel tanks terribly close to the passengers...

 

Air transport isn't an efficient way to transport MBT's like the Abrams.
The C-5 can only carry one at a time. Presumably the C-17 could also carry one. Nobody is going to airdrop them though. That much is for sure.

 

Apparently there is no tank-sized parachutes available. But are you sure the huge C5 Galaxy can only carry one Abrams?