In 2010, I proposed the idea of planes with no landing gear which land on robotic platforms. The spring loaded platforms are pulled by cables and so can accelerate and turn with multiple gees, so that almost no matter what the plane does, it can’t miss the platform, and it can even hit hard with safety.
Today I learned there is a European research project called Gabriel with very similar ideas. In their plan, the plane has landing pillars which insert into the platform, rather than wheels. This requires retractable pillars but not the weight of the wheels. The platform runs on a maglev track but can tilt and rotate slightly to match the plane as it lands or takes off.
Overall I still prefer my plan — and I have added some refinements in the intervening years.
- I am not quite sure of the value of maglev, which is quite expensive. Cables can provide high acceleration quite well.
- The pillars still need a complex mechanism (which can fail) though they make a very solid connection — if you can place them just right.
- Their platform tilts up — this may mean it can provide power longer which could be useful. It also allows easier release of pillars.
- My approach allowed, in theory the ability to land in any direction, eliminating crosswinds. Gabriel uses a linear track.
- I don’t think there is much need for communications between the aircraft and the platform. Can’t see much the platform can’t figure out — it can easily track the aircraft with its cameras and position itself. There are a few things that could be communicated, but why not have it work fine even if the communications are out — which could happen.
- My goal was to have a super short runway, taking off and landing with high acceleration.
- My aim was to handle small aircraft, Gabriel seems aimed at larger ones. Admittedly larger ones may be more tolerant of landing only at prepared airports.
One refinement I have added involves the hard question of what to do if you lose power at takeoff. This is the scariest thing in flying, and you must be able to recover. You could have a longer takeoff runway, so that there is enough space to slow down again if the aircraft loses power just before being released.
An alternative, as suggested by Gregg Maryniak is to have a “catch” airfield downrange from the main airfield. In this case, if you lost power, the system could keep accelerating you and even release you, with enough power that you can climb over the intervening space and then glide to a landing on an emergency catch platform — which would grab you no matter what, and let you land hard. The intervening land could be farmland or any sort of land use willing to be at the end of an airport, but it need not be airstrip. The downside of this is you must take off along a vector which lets you get, with no power, to the catch robot, so you may have to deal with crosswinds. You could have more than one catch robot allowing different takeoff vectors, but it’s still vastly less land than a typical airport would require, with most of the land finding other uses. Indeed it might be possible to have a small set of catch robots arrayed around the takeoff airstrip and allow takeoff in almost any direction.
The emergency catch robots, being only for emergencies, might stop you faster than an ordinary landing, and thus require less land. For example, if you can take 20m/s/s of deceleration (2gs) you can stop from 40m/s in just 40 meters, meaning the emergency catch strip could be very small, an insignificant amount of land. At such a small size, it’s easy to imagine an array of pads around the main takeoff-zone. Admittedly it’s a hard landing, but it would be a rare exception. Better be belted in on takeoff and everything stowed in the back.
It seems concluded for now, but it will be interested to see if anything develops further.