Fixed-wing landing

Many people assume that a scale plane should land and take off just like the full-scale counterparts, on wheels on a runway dozens of body-lengths long. However, scale counts. Even when it's still plausible to fly a plane at 1/10 full size, the wheels becoming that much smaller make it very difficult to deal with any surface roughness in the runway. Retracting landing gear (among scale RC enthusiasts, 'retracts') is very complex, expensive, and heavy for the aerodynamic benefit it provides, and there may not be that much space inside the plane in the first place. In most cases, the RC flyer doesn't even have access to a piece of flat pavement with a guarantee of no automobile traffic; Grass and dirt lots runways render most landing gear useless.

All these factors conspire to create a situation where RC pilots' most common method of landing is on their belly, or on strengthened landing gear that deflects impact, rather than making a smooth reverse-thrust roll to a stop. All of the materials in question have a surface toughness that is proportionately a hell of a lot stronger than full-size planes, and damage is a lot less important consideration. 99% of RC landings would kill people if a passenger jet performed them, but for many model planes damage is only sustained in extreme nose-on collisions.

Materials matter a lot to the landing method. Balsa planes in particular are very fragile things, and the class has earned the nickname "Crunchies". "Foamies" made from EPS or EPO are more resilient, with the capacity to bend and crush in an impact rather than shattering. Foamies are still often toughened with tape ("covered") or fiberglass ("glassed") / carbon fiber on the fuselage designed to take the brunt of the landing, in the hopes that bending grass and shrubs will absorb the impact without damaging the fuselage. Fiberglass, carbon fiber, and nylon fuselages have to worry less about non-catastrophic landings, because anything they hit is likely to yield some to their solid skin, dissipating energy.

Techniques

Wind

Pilots have always and will always try to land into the wind, and this is even more important for the low speeds of RC pilots. Full-size airplane runways are often built at angles to each other, and used in different orientations for landing and takeoff depending on the prevailing wind conditions of the day. This might offer an advantage of putting down at 140 knots instead of 190 knots, and save five hundred meters of landing strip length.

An RC pilot may attempt to land at 20 knots airspeed, so landing into a 10 knot wind will give 10 knots groundspeed. Landing in the same direction as a 10 knot wind, on the other hand, might be 30 knots ground speed: in terms of kinetic energy, 9 times as much needs to be dissipated rapidly.

Crosswind

Fullsize

A full-sized plane at minimum landing speed may move at several times their acceptable landing-strip positional error per second. Landing strips are fixed and despite adjustments for wind, limited in number: sometimes pilots must attempt to land with significant wind blowing (10% of airspeed or more) perpendicular to the direction of landing. This necessitates one of the most difficult things a commercial pilot ever does: a crosswind landing.

Landing in a crosswind falls on one of three techniques to avoid drifting

• De-crab landings yaw into the wind with a level roll angle (something that takes a lot of aileron feedback), and the pilot approaches the runway moving in the correct line of approach, but pointing off-axis, and then corrects at the last moment before touchdown.
• Crab landings are precisely like de-crab landings, without the last-minute correction. Landing is achieved with the wheels pointed off-axis, and heavy rudder and aileron are used to maintain heading while the wheels slip into the proper orientation. This is best done on a smooth, slippery/wet runway.
• Sideslip landings start out with yaw, but shift over to a roll-upwind bank, and rely on their horizontal 'slipping' into the wind to hold the right course, with the yaw and direction of motion aligned. The plane is controlled very carefully as one side's wheels hit the ground before the other side's. In the most difficult landings, crab and sideslip must be combined.

Scale

Crosswind landing techniques are difficult in a full-size plane, but in an RC plane the chances of making the landing worse are so high as to make them impractical. Most importantly, the relative windspeed of a crosswind is proportionately much higher, and RC planes tend to largely eschew fixed runways in the first place. The reaction times necessary to correct problems are much smaller, and the pilot rarely has a very accurate grasp of yaw or roll, which may be oscillating rapidly. Lastly, the control surfaces that are functional at cruising speed in prop backwash may not be viable for precise control in a landing situation. Wheels for RC planes don't pivot, are proportionately high-friction, and may not be as controllable as they are in a full-size plane. After the plane has touched the ground, except for on the smoothest runways the pilot has little control.

If at all possible, land into the wind. If not possible, just try to land in a way that doesn't depend on smooth transition from gliding flight to wheel traction for its safety.

Tail-Down Stall

The ideal method of landing is:

• Make one final pass of the pilot's position, going downwind one mistake above treetop level, going past the landing zone
• Make a 180 degree banked turn
• Come in straight and into the wind
• Cut throttle
• Dive to near the ground at the beginning of the landing zone, far from the pilot
• Bleed off speed by gliding the length of the landing zone, until just about to stall
• Pull up slightly, gaining a touch of altitude but inducing a mild stall
• Touch down, while still moving forward, with the rear of the plane

Touching down with the rear end of the plane, at minimal forward speed, breaks the fall with the whole of the fuselage, and it does it slowly as the plane bounced on the grass for the next ten meters (~1 second).

Touching down with the nose down, like an arrow, digs the plane into the grass where it can no longer move forward, and then confronts the whole airframe with the solid soil, which may absorb the entire kinetic energy of the landing in 1/100 second. If the soil is soft and the nose is rigid, this might not cause damage, or it might crack the whole of the fuselage. If the nose is foam, or poorly reinforced, it may absorb the whole of the impact energy and sacrifice itself for the rest of the plane.

Slope

Landing downhill can be more difficult than landing downwind: every meter is constantly adding speed to the plane, and the only way to bleed off that speed is by plunging into the ground at a sharper angle than the grade of the ground. Landing uphill, conversely, takes some attention to detail but can be a lot easier than landing on level ground, because for every meter the plane moves parallel to the ground it's bleeding off speed, and this rapidly creates an opportunity for a controlled tail-down stalled landing.

One aspect of pilot experience that distinguishes an expert from a novice is what combination of 'upwind' and 'uphill' and 'obstacle-free' makes for the most achievable landing.

Flaps and Weight

Double an airframe's weight with additional batteries or a camera system, and you significantly increase the speed that it has to maintain to keep up altitude. When you do that, you dramatically increase the speed at which the plane has to land, on top of increasing the kinetic energy that the plane has to dissipate in a collision. For a given airframe, this is an unavoidable problem, except for one optional control surface that is available on some types of planes.

Flaps make a plane's wing "liftier", extending the airfoil downwards to increase both lift and induced drag. This will tend to reduce the sustainable cruise speed, at the expense of a significantly poorer glide ratio. This is one reason it might not always be helpful to reinforce a plane's landing strength at the expense of increased weight.

Sailplane pilots use flaps as an alternative to (and sometimes alongside) spoilers to bleed off forward velocity without sending the plane into a stall. Most large plane pilots use them during a gliding landing. Because they can be retracted in forward flight, they offer a "free" boost to the security of landing, without the increase in weight that usually comes with such efforts.

Prop Backwash

On some planes, the prop is positioned directly forward of the elevator and rudder. Some of the cone of air moving back from the propeller hits these and is deflected, so the plane has a significantly increased ability to maneuver while the prop is spinning. This is a problem in landing, since if the prop is spinning the plane is speeding up. The low-hanging fruit way to mitigate this is to have a separate mode set for landing which gives greater control throw per stick input. This isn't always sufficient, though, and in some planes with undersized control surfaces, it's better to try and land with the prop speeding up the plane but keeping it maneuverable, than to try and land without controls. Mitigating this in hardware usually involves extending control surfaces so that they will deflect more air.

Types

Belly Landing

Most commonly, the RC pilot can locate a grass, scrub, or dirt field to land on, but with some well-build models with a skid plate this is even done on a hard surface. The belly may be reinforced with a skid plate covering only the impact zone to protect against gritty obstacles, or it may be designed to absorb the impact slowly by bending to protect against overall impact.

It is very common, even if the rest of the plane is unmodified, to tape up or even fiberglass the belly of a foam plane to protect against scratches & grit. Without some protective covering, the cosmetic appearance of an unwashed foam plane doing belly landings rapidly deteriorates.

Wheeled Landing

Wheeled landings should ideally be directly into the wind, for a whole host of reasons mentioned above. A large spring effect is ideal, either from a spring shock absorber or bending legs, to reduce the shock of touching down. Scale wheels are extremely small for an average road surface, and so selection of an overly smooth patch is wise.

Barrier Landing

A wheeled landing on a surface with a limited runway, for example a roof or a parking garage, may use a soft target to roll into nose-first and drag behind. This is an emergency technique used on aircraft carriers, and may help reduce the spinning that often occurs when the wheels touch down improperly or aren't very functional at rolling.

Parachute Landing

• Main article at Parachute landing

One option that both reduces necessary pilot skill and eliminates the need to balance landing speed against cruise speed & payload is to use a parachute to come down. Some experience is necessary to pack most parachutes, but the amateur rocketry community has produced a significant knowledge and product compendium in this area. There are calculators available to determine parachute size versus weight versus sink rate, and the ground will still be a significant impact, but on a grass surface this can make for a reliable retrieval damage-free mechanism. A large parachute may be used for normal retrieval, or a smaller, lighter parachute might be used for emergency landings.

A parachute landing can be performed without any human input necessary, enabling 'fire and forget' functionality, an extremely valuable option in a drone.

Steered Parachute Landing

Instead of a simple parachute, deploying a paraglider allows some measure of control in descent, and may be a better option for people who don't need fire-and-forget, and who are working with a significant wind. It may even be desirable to convert to a paramotor, and fly for the last few minutes and land in a high drag, but otherwise normal fashion.

Skid Landing

Due to the propensity towards belly landing, a hard skid with a large angled tip is more than a niche product used for snow landings. A narrow (aerodynamic) skid that bends a bit can take the impact for the belly, protecting it and any payload from impact with the ground.

Water Landing

• Main article at Amphibious planes

Flying boats and waterplanes, even scale ones, are able to take off and land safely on flat water. Because of the geographic consistency of bodies of flat water under a certain wind regime, this may even be an automatable behavior.

Net Recovery

Several military-style UAVs fly at cruise speed into large nets for retrieval, which can give a soft landing for rigid-body planes on any terrain, at the expense of somewhat unpredictable pressure sources. A net landing where all joints are attached by wing savers and prop savers can be a very reliable system.

• Aerosonde ship recovery

Hook Landing

Full-scale planes have used arrestor hooks to land on aircraft carriers, and 'sky hooks' for in-flight cargo pickup. With proportionately stronger airframes, no pilot to protect, and the security with which a ground anchor can be attached, a more sophisticated landing system using a towed hook and elastic arrestor cables can 'pluck' a UAV out of the sky, and rely on bending loads for shock absorption.

VTOL Landing

• Main article at hybrid tilting aircraft

VTOL fixed-wing craft each have their own unique characteristics for a hovering landing, some even going so far as to require a vertical climb to stall/hover above the landing site. When descending rapidly, an airfoil designed to glide *will* try to glide forward, even if its propellers are simply lowering it in hover, and this makes VTOL craft a lot more difficult to land than simple multirotors, even when the principle of hover is the same. Wind also has an outsize effect on VTOL fixed-wings, with tilt-wing planes being functionally equivalent to a sail mounted on a hovering craft.