[HNaTTY]

One thing that always bothered me about airplanes is the energy used to take off. On aircraft carriers, they use a launch device, allowing the airplane to "push off" against the carrier. Compare this to airplanes taking off on land, they just nail the throttle and take off by pushing air...

A land-based launch system would have a lot of advantages; lower peak power would be needed from the motor and batteries, the engines could be made smaller, the energy used to take off doesn't have to be stored on the plane, everything gets lighter and more efficient.

[mikeash]

I'm not sure that it would let you lower the peak power. Most takeoffs aren't limited by runway length. You use full power just because it's safer to get off the ground earlier. Max power requirements come from the maximum altitude the plane is expected to reach, or for multi-engine aircraft the need to be able to climb out after an engine failure.

Aircraft carriers (some of them) use catapults because that's a case where runway length is, by far, the limiting factor.

[ndespres]

This is addressed in the article:

"We designed and built a pneumatic rail launcher so that the plane does not have to take off under its own power."

In the spirit of everything old being new again, the Wright Brothers' original 1908 flyer also used a catapult to launch the planes. https://simanaitissays.com/2012/08/13/vintage-aero-wilber-wo...

[larkeith]

Note that this quote was in reference to the autonomous drone they produce, not the manned trainer that was the subject of the article. I would presume there are more challenges in building a launch assist catapult for a crewed flight.

[zerebubuth]

From the data on the Wikipedia page for the Boeing 747, it looks like the empty weight is around half the maximum take-off weight. Passenger and cargo aircraft seem to usually turn around quite quickly and spend only a small amount of time on the ground. In which case around half of the energy required on take off is just to lift the airframe back to the same altitude it landed from.

Perhaps if aircraft could use some sort of funicular system so that one aircraft taking off could get a "boost" from one slowing down to land?

Or planes could land on giant inflatable runways at 30,000ft, with the passengers and cargo taking a lift down to ground level?

[sokoloff]

I would think that most of that energy is used to transport the 747 1/3 of the way around the earth, overcoming induced and parasitic drag for 8+ hours.

From a straight lifting standpoint, lifting 910K pounds to 37K feet takes about 45 billion joules, which is the energy content in about 320 gallons (~2200 pounds) of jet fuel (if consumed perfectly efficiently).

A 747 burns about 1 gallon of fuel per second, meaning the straight lifting fuel consumed represents about 5 minutes or 1% of the fuel consumption on the flight.

[avn2109]

>> "... lower peak power would be needed..."

While it is true that you "nail the throttle" during takeoff in a little general aviation Cessna, the same is not true of jet-powered heavy metal. The big planes that account for most passenger miles are limited by engine noise regulations and scaring passengers, and run the engines at a fraction of peak power during takeoff.

You can find implausible-looking-but-true videos of big ungainly airplanes taking off near the edge of the flight envelope in ways that look very surprising.

[justadeveloper2]

Catapults don't save energy--they shorten runway. The jet is at full throttle on takeoff and military aircraft are not exactly fuel misers.

[ndespres]

Sure, they don't save energy in the sense that the laws of physics must still be obeyed- but by using the power of the catapult to increase the plane's velocity at takeoff, the motor can be optimized for flight rather than takeoff and less battery weight needs to be carried.

[nkoren]

That's because catapults are used in places where space is at a premium. Catapult + full throttle will minimize takeoff length. But if space wasn't at a premium, then surely throttles could be reduced, no?

[nradov]

This has been proposed many times but doesn't seem to be practical or cost effective. The airport infrastructure investment would be huge. And aircraft would have to be redesigned so that the nose wheel (catapult attachment point) could handle a much higher sheer force. Making those parts stronger adds weight, which wastes energy during the rest of the flight.

[stevep001]

1. Aircraft use 100% power in situations other than takeoff, so it's hard to see how you could lower peak power/use smaller engines just by eliminating takeoff.

2. Typical aircraft takeoff roll is under 30 seconds, and most aircraft have 3hours+ endurance, so you'd be extending the range of the aircraft by < 1/360th.

[subway]

That's a lot of infrastructure to maintain, and significantly increases the costs of airports.