Everyone is talking about making the global greener, but few come up with concrete suggestions that could not only be immediately implemented, but would also be profitable. Flying is a very special case in this regard as there is only little that can be done except for reinventing the plane as a whole. It‘s an endeavor that still is decades in the future… or is it?
Getting A Plane To Take-Off Needs A Lot Of Fuel
If you think of a big passenger plane, they usually come in weight classes between 50 tons an 100 tons and in order to lift off, they have to be around 400kph fast. These numbers can be used to estimate the fuel consumption just alone to get the plane‘s tires off the ground.
At 50 tons and 400 kph a plane needs at least 1 Giga Joule of energy plus the energy to overcome the drag of its huge construction, which increases the energy needed by perhaps another 30%. This results in 360 KWh which the engines have to get out of the kerosene. Engines usually can transform around 3 KWh of the kerosene into motion. This means, that lifting such a plane off the ground requires 1,000 liters of kerosene.
It‘s hard to imagine that such a plane loses 2% of its weight even before it leaves the ground. This fact makes it easy to imagine ways of externalizing the energy input and have the plane take-off lighter while there are less emissions – and also less noise – during the take-off.
Using Catapults Like On Aircraft Carriers
Luckily, there is an apparent solution for this already on the market since many years. Of course, I‘m talking about the catapults used on aircraft carriers and which are strong enough to get planes to the necessary speed for a take-off within 200 or less meters.
A civilian version would not need this kind of short distance take-off capability, conventional airstrips are usually at least one kilometer long. Civilian planes have time, which means the experience for passengers would not be different than normally. There would also be no safety issue as catapults can be detached or stopped during the starting phase.
Pilots would need a special training and both planes and airports would need to be retrofitted. But overall, there is no real reason why this would not work just as well (or likely even better) for civilian planes on land.
What Would It Cost
Ideally, the catapults would be installed in pairs to make sure that planes which go back and forth between two fixed airports. The total costs per catapult may be at 10 million USD, which you have to take by two. Written off over ten years, the annual capital costs are 2 million USD.
For the daily operation, you need a total crew of around ten at every given time to handle the catapult of a runway. In case the two airports are open 24/7, there are 40 personnel needed to run the entire operation. If you assume costs per head of 250,000 USD, you have total costs of 10 million USD.
Beyond that you have insurance, maintenance, energy costs etc. These will amount to perhaps 3 million USD, which brings the operation of both catapults to a total annual cost of 15 million USD.
What Money Could You Make?
On the revenue side, it is important to know the maximal number of flights per runway. Normally, one start every two minutes is possible. If you assume the planes always land on a runway without a catapult, while only planes start from the catapult runway that will use it, the theoretic maximum is at 8,760 planes per year. This would be one plane every two minutes, but on two airports simultaneously.
Most of the income would come from the pushing service for the planes. They save around 1,000 liters of kerosene and on top, they can sell ten more seats on each plane for the lost weight from the kerosene. The kerosene is worth around 20 Cents per liter while every passenger added brings in 20 USD. Every take-off is therefore worth 400 USD.
The maximum revenue per year for the two catapult system is 3.5 million USD. Unfortunately, that is only 20-25% of the annual costs for the system. But there are several other ways in which the system can improve on its revenue.
Making Planes Faster And More Silent
Right now, planes have to take off at one point. After that they run out of runway and crash like a car. There is no reason though that speaks against sloped circular runways with a diameter of 5km. Equipped with catapults, the planes could be made much faster before their take-off, which would reduce the need for carrying and burning kerosene further.
With every meter in altitude, a big passenger plane burns another 100 liters of kerosene. If the ground speed from the catapult is enough for 10 meters in altitude, then the plane could save another 1,000 liters. This in return would double the revenue per plane to 800 USD. With the given specifications, the break-even for the catapult system would be reached if the ground speed was enough for the plane to gain 40 meters in altitude.
But even if that may not be feasible in its entirety, there are other advantages which may play a significant role in the implementation of catapults. The biggest argument might be the lowering of the noise coming from the engines on full trottle during the start. Airports could remain open much longer in the evening and on the weekends, for which passengers, airlines and freight haulers may be willing to pay extra for.
I may not reach break-even for catapults used on civilian planes in this post. But the concept may be closer to feasibility than one might expect.
What do you think about this idea, would you fly with a plane using a catapult?