Forum: aviation.stackexchange.com
Tags: <taxiing>
Title: Would a chain strip built in the airport taxiways, help airlines in saving money and time during taxi?
Question: I am referring to the mechanism used in aircraft carriers, which help in catapulting fighter aircraft. What I had in mind is a milder version of the same concept. It would massively save cost, due to it being operated by electric power, save energy and time of the pilots, less exertion.  Would such a system be feasible?

Answers:
sents: text: Airports already have several ways to move aircraft along taxiways Aircraft engines (least economical but always available) Tugs (often used for pushback from terminals)
text: Aircraft wheel-motors (some makers are at least planning for electric taxi) A system of fixed chains along a complex network of intersecting taxiways would be expensive to install and maintain and might be unreliable (e.g. icing up in cold weather).
text: See also Does it make sense towing airplanes to the head of airstrip by external means?
answer_details: author: aviation.stackexchange.com/users/1289/RedGrittyBrick
score: 12
sents: text: An airport has taxiways that cross other taxiways and runways, so any chain system would require breaks in the chains at these points.
text: Airplanes would need some sort of motive power to cross these breaks, it's impractical and slow for an airplane to spin up its engines for 20 seconds to cross a break in the chain.
text: A chain system would also be very expensive to install and run, probably more expensive than the fuel it takes to taxi the airplanes.
answer_details: author: aviation.stackexchange.com/users/1791/GdD
score: 8
sents: text: They don't do it for roughly the same reasons that they don't install such systems in roads.
text: Expensive modifications would be required to every aircraft of a vast array of aircraft types.
text: This alone would probably mean that you'd never recover the costs over the entire expected life of the system.
text: And getting modifications approved by the relevant regulatory agencies for airworthy aircraft designs is even more of a pain than getting them approved for road-worthy car designs.
text: The systems themselves would be quite expensive for initial install, especially if they were designed to operate in all weather conditions in which airports can currently operate.
text: Being able to drive where you want is much more flexible (which is somewhat less of a concern at an airport than on roads, but still a concern.)
text: Stopping or turning suddenly to avoid a collision (like when you're cleared to taxi across a runway and suddenly realize that there's a Learjet taking off on it ) might not be possible or would at least be slower.
text: In short, there are already cheaper alternatives that don't suffer these drawbacks, such as tugs (manual or automated,) electric motors on the gear, and, of course, aircraft engines, as mentioned in RedGrittyBrick's answer .
answer_details: author: aviation.stackexchange.com/users/755/reirab
score: 3
sents: text: One point has been missed in the other fine answers.
text: On an aircraft carrier, the nose gear of each aircraft has a pull bar installed that links with the catapult sled.
text: This pull bar is manually engaged by a deck crew member for each aircraft that is to launch.
text: In order to do this at an airport, there would need to be a ground handler stationed at each runway turn-off point to engage the pull bar to get the aircraft moving.
text: I pity the poor souls who would have to stand next to a runway at KBOS or KJFK in the wonderful weather they are expecting this weekend.
text: It's possible that this system could be automated, but that's another very expensive design element that has to be brought into play, tested, and receive CAA certification.
answer_details: author: aviation.stackexchange.com/users/5517/FreeMan
score: 3
sents: text: In addition to all the 'minor' drawbacks already discussed, there is one huge, basic problem with this idea.
text: What has to be moved is an airplane, weighing less than about 600 tonnes, designed to move, with a manageable rolling resistance.
text: A chain or cable system extensive enough to take its payload everywhere
text: it should go adds many tonnes of metal to move with a lot of friction, that will only grow as water and dirt enter the trench.
text: The whole thing will need enormous horsepower just to get moving even without an aircraft attached.
text: Compared to a tug, or even compared to an aircraft taxiing under its own power, this will simply need too much energy to be feasible.
text: The only place where this system can make money is in some streets in San Francisco.
answer_details: author: aviation.stackexchange.com/users/3353/Rob Vermeulen
score: 3
sents: text: Also, note that the modifications to fighter planes (Air Force vs Navy) are fairly significant, as the forces on the plane (and humans inside) are significant when using the arrestor (sp?)
text: cables on aircraft carriers.
text: And yes, reducing the force is possible, but reducing it so that all existing planes flying could use it may (mostly) eliminate its benefit.
answer_details: author: aviation.stackexchange.com/users/13087/Jake Peters
score: 2

Summary of the answers:
A chain system would be quite expensive to install and run. Moreover, it would require breaks where taxiways cross other taxiways or the runways. Stopping or turning suddenly to avoid a collision might not be possible or would be slower.
Several potential disadvantages are cited. Such a system would be very expensive. In addition, a chain system would need breaks in the chains where taxiways cross one another. Moreover, it would be much harder, or potentially impossible, to stop or turn in order to avoid a collision.