How practical is mid-air cargo transfer?

Question

Mid-air refueling is now commonplace and I have even heard that passenger transfer in mid-air has been possible for stunts. What is the practicality of mid-air cargo transfer?

Answer 1

It's technically feasible to do this, there are mid-air capture systems already, developed to snag payloads returning from space (film, samples, etc) which are descending by parachute. There are fixed wing and helicopter versions of the technology. So, you could drop a cargo out of the back of one airplane, and another could catch it, winch it in and fly it somewhere else. In fact, technically this has been done numerous time as the testing of these systems and training of the pilots involved pushing the test article out of the back of another airplane.

The reasons it's impractical to use this are:

1. It's expensive: The hardware costs money and adds weight to the aircraft, the aircraft have to be unpressurized if the cargo is to be winched in, which some cargo won't tolerate, the aircraft will have much less capacity due to the equipment involved, and other reasons
2. It's dangerous: Flying an aircraft into a parachute or other drop system is inherently hazardous, it's only done when there's no other alternative
3. It's weather intolerant: whatever solution is used, the transfer would need decent weather conditions, and probably need to be done during the day, which would limit it's utility
4. It has no practical benefit: transferring cargo from one perfectly good airplane to another one doesn't get the cargo there faster, safer, or cheaper. If the cargo needs to go where an airplane can't land then it can be transferred to another one, or to a helicopter at a field. If time is of the essence then the cargo can be air-dropped. There's no problem that mid-air cargo transfer solves

Answer 2

Grossly impractical, and manifestly unsafe as well. Here are a few reasons why.

To transfer cargo from one plane to another requires mechanized material handling systems which can be extended hundreds of feet through the air from one plane to the other and retracted again when the job is done, while the plane is flying at perhaps 200MPH or more. Every pound of material handling machinery built into a plane represents a pound of lost payload, in a business where a fuel cost increase of order ~pennies per pound is enough to ground an entire fleet of cargo planes.

Now imagine the size of the cargo conduit itself. It will have to pass objects the size of a preloaded cargo bin, perhaps 6 feet on a side, so the conduit will be about 8 feet across and let's say 100 feet long.

That tube will be extending through the slipstream of one plane and into the oncoming flow field of the other plane at very high Reynolds numbers; the flow fields surrounding both planes will be significantly upset by the presence of that tube and that disturbance will grow from nothing to its full extent as the tube gets extended on a timescale of ~100 seconds.

Both planes need to be fully controllable before, during, and after the transfer process which will involve the exchange of one plane's full useful cargo load to the other, leaving one empty plane at max gross and one plane at max gross empty.

And during that process, the two planes will be physically connected together and flying at the same speed, which will require both of them to be actively trimming and modulating their power settings the whole time.

And the whole shebang must be resistant to perturbations from the environment.

...and for what purpose, exactly?

Answer 3

It's probably not what you mean, but this could be practical when one craft is so large (and slow) it can wholly contain another, such as a cargo or "aircraft carrier" rigid airship.

However, these crafts themselves are considered to be impractical (CargoLifter, DARPA Walrus/HULA), I believe largely due to the impracticality of acquiring and maintaining storage of helium (which is hugely safer than hydrogen, but still sneaks out of everything because it's so small)

Answer 4

While mid-air cargo transfer is technically feasible, its practicality is limited in most cargo transportation scenarios. The complexities of coordinating multiple aircraft, ensuring safe cargo attachment and detachment, and maintaining stability during the transfer make it challenging. Additionally, the cost-effectiveness and efficiency of mid-air cargo transfer compared to ground-based methods raise concerns. Although it may have niche applications, mid-air cargo transfer is not widely employed in real-world cargo logistics operations.

Answer 5

Certainly using a long tube to transfer cargo would be insane, and as others have said it's generally impractical. But, let's assume that for some reason it really needs to be done, and the importance of this outweighs the complications and inefficiencies.

Transferring fuel from one plane to another is already possible. Flight control surfaces are installed on the nozzle to allow an operator to accurately control its position relative to the receiving plane. Why don't we learn from that?

Scenario 1:

Transfer of cargo by zip line: The receiving plane is equipped with loading doors on the top. A zip line emerges from the back of the first plane, and is steered using control surfaces down into the cargo bay of the receiving plane. When it arrives, an operator attaches it to a fixture so that it's secure.

Next, cargo boxes are sent to slide down the zip line, using some device to slow their motion. The operators in the receiving plane receive them detach them from the line, and pack them onto the cargo hold.

Scenario 2:

Transfer of cargo by aerodynamic body: What if the cargo could be 'flown' from one plane to the next? The cargo is packed into an aerodynamic container which emerges from the back of the first plane, attached by three tethers.

The cargo can be steered by controlling the lengths of these three tethers. This gives 3 degrees of freedom in the control, allowing the cargo to be steered relative to the second plane, which is following the first plane at a slightly lower altitude. Again there are cargo doors on the top of the plane to accept the cargo. Alternatively, the cargo simply attaches to the top of the receiving plane, like the space shuttle.