1. Wire mount

Simplicity at Century 21

Typically model aircraft  in visual effects shots have been hung on wires.  Perhaps an example of the simplest method is that which was employed on the classic puppet television series Thunderbirds which consisted of an effects technician, usually Peter Wragg,  balancing on a raised plank over the miniature set  holding a marionette style control stick to which the flying model was attached via thin tungsten wires. The elevated operator would manipulate the stick to make the model do whatever action was required in the shot while the camera ran at high speed (meaning an increased frame rate over the normal 24 frames per second).

Peter Wragg on the plank manipulating Thunderbird 2.

Notice in the picture above that the plank is actually doubled up with a clamp at the end. This was to help reduce the diving board like bounce that a single plank had. Below you can see that he is up in the studio ceiling where all the heat from the lamps gathered with not much to hang on to making it a very uncomfortable, precarious and hence unpopular job. It also took some skill to manipulate the model smoothly with the right sort of pitch and yaw and reach the start and end positions in the timing required for the shot all without falling off the plank.

Tungsten wire has the property of high tensile strength in an extremely small cross section (thin) allowing it to support the weight of a model and hopefully not show up on camera. One other important feature is that it effectively does not stretch so any movement of the control stick is directly imparted to the model. Fishing line is not a good substitute as it stretches like crazy and has no where near the tensile strength in a comparable cross section.
Unfortunately tungsten wire is particularly susceptible to kinking which will result in a break and therefore you can't tie a knot, it has to be carefully wrapped around a fixing pin with many passes and itself to secure the end and stop it unraveling.
When I worked on a series of Ultraman in Australia in 1989 all the flying models had shortened dressmakers pins glued into the models at the support points and the tungsten wire was wrapped around the exposed shaft of the pin, under the pin head, several times and secured with a drop of superglue.

The following link goes to a source of Tungsten wire.

Another property of tungsten wire that was employed in Thunderbirds was that it is an electrical conductor so current could be fed down the wires to ignite the rocket jet effects. Sometimes the electrical current and resistance in the long lengths of thin tungsten would cause the wire to heat up  to red heat and then instantly break. That and the forces the models were subjected to during high speed shooting would mean many a model had to be sent back to the model shop for repairs after a wire or two would snap suddenly.

The Thunderbirds visual effects team under Derek Meddings developed a method of hiding the wires so they were not seen by the camera. They would first spray them with dulling spray which is a temporary matte surface coating used to get rid of unwanted highlights in photography. It has the property of remaining greasy to touch, so they would then puff poster paint, generally in the shade of the sky backing, onto the wires which would then stick to the greasy dulling spray. The wires would thus be a very matte surface the same colour as the background effectively making them invisible.
The efficacy of this technique was born out throughout the series, while you do occasionally see the puppet wires which were the same tungsten material, you virtually never see any flying model wires.

Harry Oakes the D.P. puffing a sky blue powder paint onto the wires for a Thunderbird 3 launch. He has a dark colour powder paint puffer bottle in his left hand

Another very simple method of flying models employed at Century 21 was using a greased steel cable and a brass tube. A Steel cable was stretched across the studio and tensioned by a rope and pulleys with a heavy weight. Onto the cable was threaded a brass tube that the model was attached to with the usual tungsten wire. The brass tube could then be pulled along the lubricated cable across the background or miniature set. This technique was used where the model had to travel across the frame in a straight line.

Ian Wingrove next to the rope used for tensioning the flying cable on UFO. Brian Smithies next to the sky backing accompanying him on the Hammond organ (actually its a dry ice machine used to produce the cloud layer).

Lydecker Rig

Howard and Thoedore Lydecker (after which the technique is named) developed a simple wire rig for flying model aircraft, employed in the many Republic serials and feature films they contributed to. It consists of two support wires that are threaded through small tubes in the wings of the model aircraft. These wires are securely attached at both ends usually mounted to a tower at one end which is higher.  A third wire is attached to the model and pulls it along the two support wires, against gravity, either to make the aircraft climb or allow it to dive. The support wires can also be horizontal and the third wire just pulls it along. The two wires may also be attached to a pivoting bar at both ends so that an operator or two can rotate and impart a barrel roll to the aircraft model.

Sky One launch being set up at Century 21. You can clearly see a derivation of the Lydecker rig in use, two support wires and a third wire to pull the model up out of the sea. Here they are wiring up the Schermuly rockets for ignition.

Sky One in the tank at Century 21. You can see the post that the other end of the wires are attached to.

These days hiding the wires is not as critical as it was, being relatively easy to remove during digital compositing. This means that very heavy models can be supported by very strong cables without fear of impending breakage. Quite a number of modern miniature aircraft have been filmed this way.

Die Hard 2 "Windsor" crash setup. Note large eyelets in wings, and thick cables. This is an adaption of the Lydecker Rig.

Boom Arm wire mount.

Another way to support a flying model was to hang it from the end of a boom arm of some sort. This is good for a model on a curved trajectory such as when it makes a turn.
On "Ultraman: Into the future" we re-purposed an old television studio microphone boom and hung flying models from from it, sometimes arranged in a formation.

TV Microphone Boom similar to that used for Ultraman: Into the Future.
The use of a boom is a common technique used in many Japanese aircraft miniature effects shots. It is more noticeable as the aircraft don't usually bank in the turns.
A more sophisticated and elaborate boom apparatus for flying miniatures was developed by Gordon Jennings at Paramount Studios for "The Forest Rangers" in 1942. It consisted of a wheeled trolley with a 50 foot (15m) boom. There was an arc shaped platform for a boom swinging, raising and lowering operator and two seats for another two operators, one of whom could control the attitude of the model hung at the end of a rotating head mechanism. The other operator controlled the rotation of the head which could be used for tighter turns than the boom was capable of. The head could support more than one model. There were also electrical controls for releasing bombs, igniting smoke and other miscellaneous devices. The whole unit could also be towed by a tractor to impart linear motion as well as the arcing motion of the boom.

Gordon Jennings' flying model boom device from 1942, large sky backing behind miniature forest.

The rotatable head. Control wires lead from the operators seat controls to the model over pulleys for diving and banking.

Krzanowski rig

More elaborate methods for wire hanging from a boom arm have been developed over the years. One of the problems with wire support systems has been the model's propensity to swing due to the pendulum nature of a weight on the end of a string. To reduce and even remove this effect a system using multiple wires to each mounting point on the model has been employed thus setting up a form of cross bracing. The ultimate expression of this idea was developed for "Batteries not Included" (1987) by Tad Krzanowski. His system used a series of  nine wires that in groups of three attached to three points on the model. Having each mounting point secured by three wires from separate overhead and therefore triangulated positions made for a very stable model mount. The wires ran over a series of pulleys back to a swatch plate that could effect pitch and yaw movement that was precisely repeatable.

This technique proved so precisely repeatable that it has been employed for in-camera shots filmed outdoors as well as motion control shots filmed in a studio. It has been adapted and modified to fly submersibles in "The Abyss" (1989), the smaller submarines in "The Hunt For Red October" (1990) and in a similar manner, a large model 747 Aircraft in "Turbulence"(1997).

Krzanowski rig on "Batteries not Included" (1987).

Krzanowski rig on "The Abyss" (1989).

Miniature 747 in "Turbulence"(1997). Note triangulated wires.

2. Rigid Mount

In Camera shots

The alternative to hanging from wires is some form of rigid mounting, either a pole or sometimes mounted to glass. This method was mostly used when the model was filmed against a coloured (for example blue) backing screen for compositing into the background at a later date. In this case any visible mounting pole can be removed as part of the compositing process. When front projection was a popular technique of combining a foreground subject with a pre-filmed background, the model could be mounted on a pole that extended out through a hole in the scotchlite screen, the model itself hiding the support pole.
Depending on the action required of the shot a matte painted background could be filmed with a small foreground model mounted on glass and animated or motorised to move.

One of the most effective uses of a rigid mount is when a large model is shot outdoors in sunlight with the model mounted from the tail on a boom attached to a camera vehicle moving along at speed. The framing of the shot excludes the end of the tail where the boom would be visible. The model can be raised and lowered through frame and a real sky moves in the background. The bumps and vibration of the vehicle add to the realism of the mock aerial photography. This is obviously suited to closer shots looking up at the model and can work very well for telephoto shots. For a higher vantage point mountain roads and coastal roads for an over the ocean shot can provide a more downward looking shot.
Examples of this technique can be found in Memphis Belle supervised by Richard Conway and Iron Eagles III supervised by John Richardson.

Sixteen foot (4.9m) wingspan Memphis Belle model on the end of a scaffold pipe boom mounted to a moving truck. Real B17 flying in background.

Boom arm mount just sneaking into frame.

Boom arm truck with mounted model in background left.

Smaller simpler boom arm with Zero model for Iron Eagles III. Note pulley for effecting a banking maneuver.

Motion Control

The other main use for rigid mounting is for motion control shots where the background will be shot separately and combined later. The model is usually built with a number of alternate mounting points so the least visible one is chosen depending position of the computer controlled camera and the dictates of the shot.
The 747 Model in "Executive Decision" (1996) had a pretty elaborate rigid mount to allow for banking, climbing, diving and turning motion with a tail mounted model.

Model 747 on its elaborate rigid motion control model mount.

3. Radio Control

Perhaps the method with the most verisimilitude is to actually film a model outside that is actually flying under radio control. While there have been a number of examples of the use of this method in the past, it has been generally considered unreliable and a risky process to tackle. Radio control units in the past were prone to interference from other radio control sets on the same frequency or sparking motors and other electrical  discharges that produce radio waves. This can lead to an out of control model ending in an expensive crash.
Recent technology has almost totally eliminated the possibility of radio interference with digital signal discrimination and frequency hopping algorithms. Radio control is now a reliable and robust control system. Battery technology and electric motors are more reliable and multi engine setups simpler than ever was the case with RC aircraft using combustion engines.

It is possible to achieve shots from the ground as well as shooting large radio control models using a helicopter as an aerial platform with the radio pilot on board.

The most recent film to use this technique was "Dunkirk" (2017) which had flying shots using large radio controlled models that were indistinguishable from the real thing. I might add that one of the Me 109s models did crash.

Large scale radio controlled flying Heinkel 111 from "Dunkirk" (2017). Note practical but non-scale landing gear, not visible in the movie.
Model Stuka in flight.

Racks of Stuka and Spitfire models ready for deployment.

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