Robotic landing pad gets more serious

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.

Short take off and landing

When I was a grad student (before there was an Internet) in Physics, Professor Wynans at U. Wisc. had a plane, which he outfitted so that he could tether one wing
to a pivot in the middle of a field. He took off by taxying and then climbing while still tethered, hence an infinite circular runway. I flew with him doing this
once. If power failed before you cast off the tether wire you just glided round and round till you landed. Worked fine for a small craft.

How fast

Must have made you dizzy. So how many circuits did you do before getting into the air? I presume once you are off the ground you don’t need the tether other than, as suggested, to deal with a power failure. One could imagine paying out the tether as you climb to make it less tight a circle, so long as you could safely pull it back in on power failure. Don’t know if that would work.

Of course you can also do takeoff with a tether just pulling you at high acceleration as long as you can be sure you will maintain power and will release.

It would be interesting to

It would be interesting to have Elon finally give his design for vertical takeoff and landing supersonic electric jet. Apparently, outside of the electric car, rockets, the hyperloop, and his replaceable intersection, this is the only design he has that he hasn't revealed.

Supersonic jet

It is a cool design. He’s described it to me — are the main elements of it not public? I mean, he pretends to want to tell Tony Stark about it in the Iron Man movie. Not that I know a lot. I don’t know how you build an electric supersonic engine, for example.

Reduces number of usable runways in an emergency

In an emergency, an airplane must be able to land at the nearest airport.

A plane with no wheels will be restricted to a tiny subset of airfields / runways equipped with this system.

As is often the case, we are stuck in a local optimum, unable to cross the gap to the next optima.

No wheels

My actual proposal has some small wheels at the touch points on the fuselage, for use in both emergency landings and moving aircraft on and off landing platforms. You can land on your belly — though of course that comes with more risk, and damage to your plane, and to your prop — clearly not what you want to do. You might try to find a balance of minimal aerodynamic fixed gear with the least weight and drag which can still help you survive an emergency without too much damage.

And you might favour designs with higher props that would not hit the ground in such landings.

There are plenty of

There are plenty of airplanes without wheels. They are called seaplanes. If your primary goal is no landing gear, this seems like the best option. If your primary goal is short takeoff and landing, an aircraft carrier style cable catapult and cable arrestor would be much simpler than a robotic platform, especially for landing: no power or intelligence required, relatively easy to deploy at existing airfields, could be used by both wheeled and non-wheeled aircraft. As for acceleration/deceleration, there might be limits based on passenger comfort. I've never been in an arrested carrier landing, but I'm told it's a lot like being in a car crash.

The goals

The goals of the idea were both reduced weight and drag (ie. definitely not float planes) and STOL.

Landing on a carrier and catching a tailhook are challenging and require lots of training. The goal with the robot is you can’t miss it because it finds you. You could overshoot it, and if you saw yourself doing that, you would need to know to pull up. If you didn’t it would probably try to launch you again because it can’t stop you in time.

Stopping at 1g is harsh but manageable. 2gs would be quite something, for emergencies only. The acceleration depends on how much runway you have. If airstrips need only be 100m long, you can put them in vastly more places for far less cost.

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His name is Brad Templeton. You figure it out.
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